-@c Copyright (C) 1988-2015 Free Software Foundation, Inc.
+@c Copyright (C) 1988-2016 Free Software Foundation, Inc.
@c This is part of the GCC manual.
@c For copying conditions, see the file gcc.texi.
@c man end
@c man begin COPYRIGHT
-Copyright @copyright{} 1988-2015 Free Software Foundation, Inc.
+Copyright @copyright{} 1988-2016 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
process at an intermediate stage. For example, the @option{-c} option
says not to run the linker. Then the output consists of object files
output by the assembler.
+@xref{Overall Options,,Options Controlling the Kind of Output}.
-Other options are passed on to one stage of processing. Some options
+Other options are passed on to one or more stages of processing. Some options
control the preprocessor and others the compiler itself. Yet other
options control the assembler and linker; most of these are not
documented here, since you rarely need to use any of them.
for a particular option does not mention a source language, you can use
that option with all supported languages.
-@cindex C++ compilation options
-@xref{Invoking G++,,Compiling C++ Programs}, for a summary of special
-options for compiling C++ programs.
+@cindex cross compiling
+@cindex specifying machine version
+@cindex specifying compiler version and target machine
+@cindex compiler version, specifying
+@cindex target machine, specifying
+The usual way to run GCC is to run the executable called @command{gcc}, or
+@command{@var{machine}-gcc} when cross-compiling, or
+@command{@var{machine}-gcc-@var{version}} to run a specific version of GCC.
+When you compile C++ programs, you should invoke GCC as @command{g++}
+instead. @xref{Invoking G++,,Compiling C++ Programs},
+for information about the differences in behavior between @command{gcc}
+and @code{g++} when compiling C++ programs.
@cindex grouping options
@cindex options, grouping
* Diagnostic Message Formatting Options:: Controlling how diagnostics should
be formatted.
* Warning Options:: How picky should the compiler be?
-* Debugging Options:: Symbol tables, measurements, and debugging dumps.
+* Debugging Options:: Producing debuggable code.
* Optimize Options:: How much optimization?
+* Instrumentation Options:: Enabling profiling and extra run-time error checking.
* Preprocessor Options:: Controlling header files and macro definitions.
Also, getting dependency information for Make.
* Assembler Options:: Passing options to the assembler.
* Link Options:: Specifying libraries and so on.
* Directory Options:: Where to find header files and libraries.
Where to find the compiler executable files.
-* Spec Files:: How to pass switches to sub-processes.
-* Target Options:: Running a cross-compiler, or an old version of GCC.
-* Submodel Options:: Specifying minor hardware or convention variations,
- such as 68010 vs 68020.
* Code Gen Options:: Specifying conventions for function calls, data layout
and register usage.
+* Developer Options:: Printing GCC configuration info, statistics, and
+ debugging dumps.
+* Submodel Options:: Target-specific options, such as compiling for a
+ specific processor variant.
+* Spec Files:: How to pass switches to sub-processes.
* Environment Variables:: Env vars that affect GCC.
* Precompiled Headers:: Compiling a header once, and using it many times.
@end menu
@table @emph
@item Overall Options
@xref{Overall Options,,Options Controlling the Kind of Output}.
-@gccoptlist{-c -S -E -o @var{file} -no-canonical-prefixes @gol
--pipe -pass-exit-codes @gol
--x @var{language} -v -### --help@r{[}=@var{class}@r{[},@dots{}@r{]]} --target-help @gol
---version -wrapper @@@var{file} -fplugin=@var{file} -fplugin-arg-@var{name}=@var{arg} @gol
+@gccoptlist{-c -S -E -o @var{file} -x @var{language} @gol
+-v -### --help@r{[}=@var{class}@r{[},@dots{}@r{]]} --target-help --version @gol
+-pass-exit-codes -pipe -specs=@var{file} -wrapper @gol
+@@@var{file} -fplugin=@var{file} -fplugin-arg-@var{name}=@var{arg} @gol
-fdump-ada-spec@r{[}-slim@r{]} -fada-spec-parent=@var{unit} -fdump-go-spec=@var{file}}
@item C Language Options
-aux-info @var{filename} -fallow-parameterless-variadic-functions @gol
-fno-asm -fno-builtin -fno-builtin-@var{function} @gol
-fhosted -ffreestanding -fopenacc -fopenmp -fopenmp-simd @gol
--fms-extensions -fplan9-extensions -trigraphs -traditional -traditional-cpp @gol
+-fms-extensions -fplan9-extensions -fsso-struct=@var{endianness}
-fallow-single-precision -fcond-mismatch -flax-vector-conversions @gol
-fsigned-bitfields -fsigned-char @gol
--funsigned-bitfields -funsigned-char}
+-funsigned-bitfields -funsigned-char @gol
+-trigraphs -traditional -traditional-cpp}
@item C++ Language Options
@xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
-fno-optional-diags -fpermissive @gol
-fno-pretty-templates @gol
-frepo -fno-rtti -fsized-deallocation @gol
--fstats -ftemplate-backtrace-limit=@var{n} @gol
+-ftemplate-backtrace-limit=@var{n} @gol
-ftemplate-depth=@var{n} @gol
-fno-threadsafe-statics -fuse-cxa-atexit @gol
-fno-weak -nostdinc++ @gol
-fvisibility-inlines-hidden @gol
--fvtable-verify=@r{[}std@r{|}preinit@r{|}none@r{]} @gol
--fvtv-counts -fvtv-debug @gol
-fvisibility-ms-compat @gol
-fext-numeric-literals @gol
-Wabi=@var{n} -Wabi-tag -Wconversion-null -Wctor-dtor-privacy @gol
@gccoptlist{-fsyntax-only -fmax-errors=@var{n} -Wpedantic @gol
-pedantic-errors @gol
-w -Wextra -Wall -Waddress -Waggregate-return @gol
--Waggressive-loop-optimizations -Warray-bounds -Warray-bounds=@var{n} @gol
--Wbool-compare -Wduplicated-cond -Wframe-address @gol
--Wno-attributes -Wno-builtin-macro-redefined @gol
+-Wno-aggressive-loop-optimizations -Warray-bounds -Warray-bounds=@var{n} @gol
+-Wno-attributes -Wbool-compare -Wno-builtin-macro-redefined @gol
-Wc90-c99-compat -Wc99-c11-compat @gol
-Wc++-compat -Wc++11-compat -Wc++14-compat -Wcast-align -Wcast-qual @gol
-Wchar-subscripts -Wclobbered -Wcomment -Wconditionally-supported @gol
--Wconversion -Wcoverage-mismatch -Wdate-time -Wdelete-incomplete -Wno-cpp @gol
+-Wconversion -Wcoverage-mismatch -Wno-cpp -Wdate-time -Wdelete-incomplete @gol
-Wno-deprecated -Wno-deprecated-declarations -Wno-designated-init @gol
-Wdisabled-optimization @gol
-Wno-discarded-qualifiers -Wno-discarded-array-qualifiers @gol
--Wno-div-by-zero -Wdouble-promotion -Wempty-body -Wenum-compare @gol
--Wno-endif-labels -Werror -Werror=* @gol
--Wfatal-errors -Wfloat-equal -Wformat -Wformat=2 @gol
+-Wno-div-by-zero -Wdouble-promotion -Wduplicated-cond @gol
+-Wempty-body -Wenum-compare -Wno-endif-labels @gol
+-Werror -Werror=* -Wfatal-errors -Wfloat-equal -Wformat -Wformat=2 @gol
-Wno-format-contains-nul -Wno-format-extra-args -Wformat-nonliteral @gol
--Wformat-security -Wformat-signedness -Wformat-y2k @gol
+-Wformat-security -Wformat-signedness -Wformat-y2k -Wframe-address @gol
-Wframe-larger-than=@var{len} -Wno-free-nonheap-object -Wjump-misses-init @gol
--Wignored-qualifiers -Wincompatible-pointer-types @gol
+-Wignored-qualifiers -Wignored-attributes -Wincompatible-pointer-types @gol
-Wimplicit -Wimplicit-function-declaration -Wimplicit-int @gol
-Winit-self -Winline -Wno-int-conversion @gol
--Wno-int-to-pointer-cast -Wno-invalid-offsetof @gol
--Wnull-dereference @gol
--Winvalid-pch -Wlarger-than=@var{len} -Wunsafe-loop-optimizations @gol
+-Wno-int-to-pointer-cast -Winvalid-memory-model -Wno-invalid-offsetof @gol
+-Winvalid-pch -Wlarger-than=@var{len} @gol
-Wlogical-op -Wlogical-not-parentheses -Wlong-long @gol
-Wmain -Wmaybe-uninitialized -Wmemset-transposed-args @gol
-Wmisleading-indentation -Wmissing-braces @gol
-Wmissing-field-initializers -Wmissing-include-dirs @gol
--Wno-multichar -Wnonnull -Wnormalized=@r{[}none@r{|}id@r{|}nfc@r{|}nfkc@r{]} @gol
--Wodr -Wno-overflow -Wopenmp-simd @gol
--Woverride-init-side-effects @gol
--Woverlength-strings -Wpacked -Wpacked-bitfield-compat -Wpadded @gol
--Wparentheses -Wpedantic-ms-format -Wno-pedantic-ms-format @gol
+-Wno-multichar -Wnonnull -Wnonnull-compare @gol
+-Wnormalized=@r{[}none@r{|}id@r{|}nfc@r{|}nfkc@r{]} @gol
+-Wnull-dereference -Wodr -Wno-overflow -Wopenmp-simd @gol
+-Woverride-init-side-effects -Woverlength-strings @gol
+-Wpacked -Wpacked-bitfield-compat -Wpadded @gol
+-Wparentheses -Wno-pedantic-ms-format @gol
+-Wplacement-new -Wplacement-new=@var{n} @gol
-Wpointer-arith -Wno-pointer-to-int-cast @gol
--Wredundant-decls -Wno-return-local-addr @gol
+-Wno-pragmas -Wredundant-decls -Wno-return-local-addr @gol
-Wreturn-type -Wsequence-point -Wshadow -Wno-shadow-ivar @gol
-Wshift-overflow -Wshift-overflow=@var{n} @gol
-Wshift-count-negative -Wshift-count-overflow -Wshift-negative-value @gol
-Wsign-compare -Wsign-conversion -Wfloat-conversion @gol
+-Wno-scalar-storage-order @gol
-Wsizeof-pointer-memaccess -Wsizeof-array-argument @gol
-Wstack-protector -Wstack-usage=@var{len} -Wstrict-aliasing @gol
--Wstrict-aliasing=n @gol -Wstrict-overflow -Wstrict-overflow=@var{n} @gol
+-Wstrict-aliasing=n -Wstrict-overflow -Wstrict-overflow=@var{n} @gol
-Wsuggest-attribute=@r{[}pure@r{|}const@r{|}noreturn@r{|}format@r{]} @gol
-Wsuggest-final-types @gol -Wsuggest-final-methods -Wsuggest-override @gol
-Wmissing-format-attribute -Wsubobject-linkage @gol
-Wswitch -Wswitch-default -Wswitch-enum -Wswitch-bool -Wsync-nand @gol
-Wsystem-headers -Wtautological-compare -Wtrampolines -Wtrigraphs @gol
-Wtype-limits -Wundef @gol
--Wuninitialized -Wunknown-pragmas -Wno-pragmas @gol
+-Wuninitialized -Wunknown-pragmas -Wunsafe-loop-optimizations @gol
-Wunsuffixed-float-constants -Wunused -Wunused-function @gol
-Wunused-label -Wunused-local-typedefs -Wunused-parameter @gol
-Wno-unused-result -Wunused-value @gol -Wunused-variable @gol
--Wunused-const-variable @gol
+-Wunused-const-variable -Wunused-const-variable=@var{n} @gol
-Wunused-but-set-parameter -Wunused-but-set-variable @gol
-Wuseless-cast -Wvariadic-macros -Wvector-operation-performance @gol
-Wvla -Wvolatile-register-var -Wwrite-strings @gol
--Wzero-as-null-pointer-constant}
+-Wzero-as-null-pointer-constant -Whsa}
@item C and Objective-C-only Warning Options
@gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol
-Wdeclaration-after-statement -Wpointer-sign}
@item Debugging Options
-@xref{Debugging Options,,Options for Debugging Your Program or GCC}.
-@gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
--fsanitize=@var{style} -fsanitize-recover -fsanitize-recover=@var{style} @gol
--fasan-shadow-offset=@var{number} -fsanitize-sections=@var{s1},@var{s2},... @gol
--fsanitize-undefined-trap-on-error @gol
--fcheck-pointer-bounds -fchkp-check-incomplete-type @gol
--fchkp-first-field-has-own-bounds -fchkp-narrow-bounds @gol
--fchkp-narrow-to-innermost-array -fchkp-optimize @gol
--fchkp-use-fast-string-functions -fchkp-use-nochk-string-functions @gol
--fchkp-use-static-bounds -fchkp-use-static-const-bounds @gol
--fchkp-treat-zero-dynamic-size-as-infinite -fchkp-check-read @gol
--fchkp-check-read -fchkp-check-write -fchkp-store-bounds @gol
--fchkp-instrument-calls -fchkp-instrument-marked-only @gol
--fchkp-use-wrappers @gol
--fdbg-cnt-list -fdbg-cnt=@var{counter-value-list} @gol
--fdisable-ipa-@var{pass_name} @gol
--fdisable-rtl-@var{pass_name} @gol
--fdisable-rtl-@var{pass-name}=@var{range-list} @gol
--fdisable-tree-@var{pass_name} @gol
--fdisable-tree-@var{pass-name}=@var{range-list} @gol
--fdump-noaddr -fdump-unnumbered -fdump-unnumbered-links @gol
--fdump-translation-unit@r{[}-@var{n}@r{]} @gol
--fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
--fdump-ipa-all -fdump-ipa-cgraph -fdump-ipa-inline @gol
--fdump-passes @gol
--fdump-statistics @gol
--fdump-tree-all @gol
--fdump-tree-original@r{[}-@var{n}@r{]} @gol
--fdump-tree-optimized@r{[}-@var{n}@r{]} @gol
--fdump-tree-cfg -fdump-tree-alias @gol
--fdump-tree-ch @gol
--fdump-tree-ssa@r{[}-@var{n}@r{]} -fdump-tree-pre@r{[}-@var{n}@r{]} @gol
--fdump-tree-ccp@r{[}-@var{n}@r{]} -fdump-tree-dce@r{[}-@var{n}@r{]} @gol
--fdump-tree-gimple@r{[}-raw@r{]} @gol
--fdump-tree-dom@r{[}-@var{n}@r{]} @gol
--fdump-tree-dse@r{[}-@var{n}@r{]} @gol
--fdump-tree-phiprop@r{[}-@var{n}@r{]} @gol
--fdump-tree-phiopt@r{[}-@var{n}@r{]} @gol
--fdump-tree-backprop@r{[}-@var{n}@r{]} @gol
--fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol
--fdump-tree-nrv -fdump-tree-vect @gol
--fdump-tree-sink @gol
--fdump-tree-sra@r{[}-@var{n}@r{]} @gol
--fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol
--fdump-tree-fre@r{[}-@var{n}@r{]} @gol
--fdump-tree-vtable-verify @gol
--fdump-tree-vrp@r{[}-@var{n}@r{]} @gol
--fdump-tree-storeccp@r{[}-@var{n}@r{]} @gol
--fdump-final-insns=@var{file} @gol
--fcompare-debug@r{[}=@var{opts}@r{]} -fcompare-debug-second @gol
--feliminate-dwarf2-dups -fno-eliminate-unused-debug-types @gol
--feliminate-unused-debug-symbols -femit-class-debug-always @gol
--fenable-@var{kind}-@var{pass} @gol
--fenable-@var{kind}-@var{pass}=@var{range-list} @gol
--fdebug-types-section -fmem-report-wpa @gol
--fmem-report -fpre-ipa-mem-report -fpost-ipa-mem-report -fprofile-arcs @gol
--fopt-info @gol
--fopt-info-@var{options}@r{[}=@var{file}@r{]} @gol
--frandom-seed=@var{number} -fsched-verbose=@var{n} @gol
--fsel-sched-verbose -fsel-sched-dump-cfg -fsel-sched-pipelining-verbose @gol
--fstack-usage -ftest-coverage -ftime-report -fvar-tracking @gol
--fvar-tracking-assignments -fvar-tracking-assignments-toggle @gol
--g -g@var{level} -gtoggle -gcoff -gdwarf-@var{version} @gol
+@xref{Debugging Options,,Options for Debugging Your Program}.
+@gccoptlist{-g -g@var{level} -gcoff -gdwarf -gdwarf-@var{version} @gol
-ggdb -grecord-gcc-switches -gno-record-gcc-switches @gol
-gstabs -gstabs+ -gstrict-dwarf -gno-strict-dwarf @gol
-gvms -gxcoff -gxcoff+ -gz@r{[}=@var{type}@r{]} @gol
--fno-merge-debug-strings -fno-dwarf2-cfi-asm @gol
--fdebug-prefix-map=@var{old}=@var{new} @gol
+-fdebug-prefix-map=@var{old}=@var{new} -fdebug-types-section @gol
+-feliminate-dwarf2-dups -fno-eliminate-unused-debug-types @gol
-femit-struct-debug-baseonly -femit-struct-debug-reduced @gol
-femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]} @gol
--p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol
--print-multi-directory -print-multi-lib -print-multi-os-directory @gol
--print-prog-name=@var{program} -print-search-dirs -Q @gol
--print-sysroot -print-sysroot-headers-suffix @gol
--save-temps -save-temps=cwd -save-temps=obj -time@r{[}=@var{file}@r{]}}
+-feliminate-unused-debug-symbols -femit-class-debug-always @gol
+-fno-merge-debug-strings -fno-dwarf2-cfi-asm @gol
+-fvar-tracking -fvar-tracking-assignments}
@item Optimization Options
@xref{Optimize Options,,Options that Control Optimization}.
-fira-algorithm=@var{algorithm} @gol
-fira-region=@var{region} -fira-hoist-pressure @gol
-fira-loop-pressure -fno-ira-share-save-slots @gol
--fno-ira-share-spill-slots -fira-verbose=@var{n} @gol
+-fno-ira-share-spill-slots @gol
-fisolate-erroneous-paths-dereference -fisolate-erroneous-paths-attribute @gol
-fivopts -fkeep-inline-functions -fkeep-static-functions @gol
-fkeep-static-consts -flive-range-shrinkage @gol
-floop-block -floop-interchange -floop-strip-mine @gol
-floop-unroll-and-jam -floop-nest-optimize @gol
-floop-parallelize-all -flra-remat -flto -flto-compression-level @gol
--flto-partition=@var{alg} -flto-report -flto-report-wpa -fmerge-all-constants @gol
+-flto-partition=@var{alg} -fmerge-all-constants @gol
-fmerge-constants -fmodulo-sched -fmodulo-sched-allow-regmoves @gol
-fmove-loop-invariants -fno-branch-count-reg @gol
-fno-defer-pop -fno-function-cse -fno-guess-branch-probability @gol
-fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss @gol
-fomit-frame-pointer -foptimize-sibling-calls @gol
-fpartial-inlining -fpeel-loops -fpredictive-commoning @gol
--fprefetch-loop-arrays -fprofile-report @gol
--fprofile-correction -fprofile-dir=@var{path} -fprofile-generate @gol
--fprofile-generate=@var{path} @gol
+-fprefetch-loop-arrays @gol
+-fprofile-correction @gol
-fprofile-use -fprofile-use=@var{path} -fprofile-values @gol
-fprofile-reorder-functions @gol
-freciprocal-math -free -frename-registers -freorder-blocks @gol
-fsel-sched-pipelining -fsel-sched-pipelining-outer-loops @gol
-fsemantic-interposition -fshrink-wrap -fsignaling-nans @gol
-fsingle-precision-constant -fsplit-ivs-in-unroller @gol
+-fsplit-paths @gol
-fsplit-wide-types -fssa-backprop -fssa-phiopt @gol
--fstack-protector -fstack-protector-all -fstack-protector-strong @gol
--fstack-protector-explicit -fstdarg-opt -fstrict-aliasing @gol
+-fstdarg-opt -fstrict-aliasing @gol
-fstrict-overflow -fthread-jumps -ftracer -ftree-bit-ccp @gol
-ftree-builtin-call-dce -ftree-ccp -ftree-ch @gol
-ftree-coalesce-vars -ftree-copy-prop -ftree-dce -ftree-dominator-opts @gol
-ftree-parallelize-loops=@var{n} -ftree-pre -ftree-partial-pre -ftree-pta @gol
-ftree-reassoc -ftree-sink -ftree-slsr -ftree-sra @gol
-ftree-switch-conversion -ftree-tail-merge -ftree-ter @gol
--ftree-vectorize -ftree-vrp @gol
+-ftree-vectorize -ftree-vrp -funconstrained-commons @gol
-funit-at-a-time -funroll-all-loops -funroll-loops @gol
-funsafe-loop-optimizations -funsafe-math-optimizations -funswitch-loops @gol
-fipa-ra -fvariable-expansion-in-unroller -fvect-cost-model -fvpt @gol
--param @var{name}=@var{value}
-O -O0 -O1 -O2 -O3 -Os -Ofast -Og}
+@item Program Instrumentation Options
+@xref{Instrumentation Options,,Program Instrumentation Options}.
+@gccoptlist{-p -pg -fprofile-arcs --coverage -ftest-coverage @gol
+-fprofile-dir=@var{path} -fprofile-generate -fprofile-generate=@var{path} @gol
+-fsanitize=@var{style} -fsanitize-recover -fsanitize-recover=@var{style} @gol
+-fasan-shadow-offset=@var{number} -fsanitize-sections=@var{s1},@var{s2},... @gol
+-fsanitize-undefined-trap-on-error -fbounds-check @gol
+-fcheck-pointer-bounds -fchkp-check-incomplete-type @gol
+-fchkp-first-field-has-own-bounds -fchkp-narrow-bounds @gol
+-fchkp-narrow-to-innermost-array -fchkp-optimize @gol
+-fchkp-use-fast-string-functions -fchkp-use-nochk-string-functions @gol
+-fchkp-use-static-bounds -fchkp-use-static-const-bounds @gol
+-fchkp-treat-zero-dynamic-size-as-infinite -fchkp-check-read @gol
+-fchkp-check-read -fchkp-check-write -fchkp-store-bounds @gol
+-fchkp-instrument-calls -fchkp-instrument-marked-only @gol
+-fchkp-use-wrappers @gol
+-fstack-protector -fstack-protector-all -fstack-protector-strong @gol
+-fstack-protector-explicit -fstack-check @gol
+-fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
+-fno-stack-limit -fsplit-stack @gol
+-fvtable-verify=@r{[}std@r{|}preinit@r{|}none@r{]} @gol
+-fvtv-counts -fvtv-debug @gol
+-finstrument-functions @gol
+-finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{} @gol
+-finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{}}
+
@item Preprocessor Options
@xref{Preprocessor Options,,Options Controlling the Preprocessor}.
@gccoptlist{-A@var{question}=@var{answer} @gol
@item Directory Options
@xref{Directory Options,,Options for Directory Search}.
@gccoptlist{-B@var{prefix} -I@var{dir} -iplugindir=@var{dir} @gol
--iquote@var{dir} -L@var{dir} -specs=@var{file} -I- @gol
+-iquote@var{dir} -L@var{dir} -no-canonical-prefixes -I- @gol
--sysroot=@var{dir} --no-sysroot-suffix}
-@item Machine Dependent Options
-@xref{Submodel Options,,Hardware Models and Configurations}.
+@item Code Generation Options
+@xref{Code Gen Options,,Options for Code Generation Conventions}.
+@gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
+-ffixed-@var{reg} -fexceptions @gol
+-fnon-call-exceptions -fdelete-dead-exceptions -funwind-tables @gol
+-fasynchronous-unwind-tables @gol
+-fno-gnu-unique @gol
+-finhibit-size-directive -fno-common -fno-ident @gol
+-fpcc-struct-return -fpic -fPIC -fpie -fPIE -fno-plt @gol
+-fno-jump-tables @gol
+-frecord-gcc-switches @gol
+-freg-struct-return -fshort-enums -fshort-wchar @gol
+-fverbose-asm -fpack-struct[=@var{n}] @gol
+-fleading-underscore -ftls-model=@var{model} @gol
+-fstack-reuse=@var{reuse_level} @gol
+-ftrapv -fwrapv @gol
+-fvisibility=@r{[}default@r{|}internal@r{|}hidden@r{|}protected@r{]} @gol
+-fstrict-volatile-bitfields -fsync-libcalls}
+
+@item Developer Options
+@xref{Developer Options,,GCC Developer Options}.
+@gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
+-fchecking -fchecking=@var{n} -fdbg-cnt-list @gol
+-fdbg-cnt=@var{counter-value-list} @gol
+-fdisable-ipa-@var{pass_name} @gol
+-fdisable-rtl-@var{pass_name} @gol
+-fdisable-rtl-@var{pass-name}=@var{range-list} @gol
+-fdisable-tree-@var{pass_name} @gol
+-fdisable-tree-@var{pass-name}=@var{range-list} @gol
+-fdump-noaddr -fdump-unnumbered -fdump-unnumbered-links @gol
+-fdump-translation-unit@r{[}-@var{n}@r{]} @gol
+-fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
+-fdump-ipa-all -fdump-ipa-cgraph -fdump-ipa-inline @gol
+-fdump-passes @gol
+-fdump-rtl-@var{pass} -fdump-rtl-@var{pass}=@var{filename} @gol
+-fdump-statistics @gol
+-fdump-tree-all @gol
+-fdump-tree-original@r{[}-@var{n}@r{]} @gol
+-fdump-tree-optimized@r{[}-@var{n}@r{]} @gol
+-fdump-tree-cfg -fdump-tree-alias @gol
+-fdump-tree-ch @gol
+-fdump-tree-ssa@r{[}-@var{n}@r{]} -fdump-tree-pre@r{[}-@var{n}@r{]} @gol
+-fdump-tree-ccp@r{[}-@var{n}@r{]} -fdump-tree-dce@r{[}-@var{n}@r{]} @gol
+-fdump-tree-gimple@r{[}-raw@r{]} @gol
+-fdump-tree-dom@r{[}-@var{n}@r{]} @gol
+-fdump-tree-dse@r{[}-@var{n}@r{]} @gol
+-fdump-tree-phiprop@r{[}-@var{n}@r{]} @gol
+-fdump-tree-phiopt@r{[}-@var{n}@r{]} @gol
+-fdump-tree-backprop@r{[}-@var{n}@r{]} @gol
+-fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol
+-fdump-tree-nrv -fdump-tree-vect @gol
+-fdump-tree-sink @gol
+-fdump-tree-sra@r{[}-@var{n}@r{]} @gol
+-fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol
+-fdump-tree-fre@r{[}-@var{n}@r{]} @gol
+-fdump-tree-vtable-verify @gol
+-fdump-tree-vrp@r{[}-@var{n}@r{]} @gol
+-fdump-tree-split-paths@r{[}-@var{n}@r{]} @gol
+-fdump-tree-storeccp@r{[}-@var{n}@r{]} @gol
+-fdump-final-insns=@var{file} @gol
+-fcompare-debug@r{[}=@var{opts}@r{]} -fcompare-debug-second @gol
+-fenable-@var{kind}-@var{pass} @gol
+-fenable-@var{kind}-@var{pass}=@var{range-list} @gol
+-fira-verbose=@var{n} @gol
+-flto-report -flto-report-wpa -fmem-report-wpa @gol
+-fmem-report -fpre-ipa-mem-report -fpost-ipa-mem-report @gol
+-fopt-info -fopt-info-@var{options}@r{[}=@var{file}@r{]} @gol
+-fprofile-report @gol
+-frandom-seed=@var{string} -fsched-verbose=@var{n} @gol
+-fsel-sched-verbose -fsel-sched-dump-cfg -fsel-sched-pipelining-verbose @gol
+-fstats -fstack-usage -ftime-report @gol
+-fvar-tracking-assignments-toggle -gtoggle @gol
+-print-file-name=@var{library} -print-libgcc-file-name @gol
+-print-multi-directory -print-multi-lib -print-multi-os-directory @gol
+-print-prog-name=@var{program} -print-search-dirs -Q @gol
+-print-sysroot -print-sysroot-headers-suffix @gol
+-save-temps -save-temps=cwd -save-temps=obj -time@r{[}=@var{file}@r{]}}
+
+@item Machine-Dependent Options
+@xref{Submodel Options,,Machine-Dependent Options}.
@c This list is ordered alphanumerically by subsection name.
@c Try and put the significant identifier (CPU or system) first,
@c so users have a clue at guessing where the ones they want will be.
-mtls-size=@var{size} @gol
-mfix-cortex-a53-835769 -mno-fix-cortex-a53-835769 @gol
-mfix-cortex-a53-843419 -mno-fix-cortex-a53-843419 @gol
+-mlow-precision-recip-sqrt -mno-low-precision-recip-sqrt@gol
-march=@var{name} -mcpu=@var{name} -mtune=@var{name}}
@emph{Adapteva Epiphany Options}
@gccoptlist{-mbarrel-shifter @gol
-mcpu=@var{cpu} -mA6 -mARC600 -mA7 -mARC700 @gol
-mdpfp -mdpfp-compact -mdpfp-fast -mno-dpfp-lrsr @gol
--mea -mno-mpy -mmul32x16 -mmul64 @gol
+-mea -mno-mpy -mmul32x16 -mmul64 -matomic @gol
-mnorm -mspfp -mspfp-compact -mspfp-fast -msimd -msoft-float -mswap @gol
-mcrc -mdsp-packa -mdvbf -mlock -mmac-d16 -mmac-24 -mrtsc -mswape @gol
-mtelephony -mxy -misize -mannotate-align -marclinux -marclinux_prof @gol
--mepilogue-cfi -mlong-calls -mmedium-calls -msdata @gol
+-mlong-calls -mmedium-calls -msdata @gol
-mucb-mcount -mvolatile-cache @gol
-malign-call -mauto-modify-reg -mbbit-peephole -mno-brcc @gol
-mcase-vector-pcrel -mcompact-casesi -mno-cond-exec -mearly-cbranchsi @gol
-mexpand-adddi -mindexed-loads -mlra -mlra-priority-none @gol
-mlra-priority-compact mlra-priority-noncompact -mno-millicode @gol
-mmixed-code -mq-class -mRcq -mRcw -msize-level=@var{level} @gol
--mtune=@var{cpu} -mmultcost=@var{num} -munalign-prob-threshold=@var{probability}}
+-mtune=@var{cpu} -mmultcost=@var{num} @gol
+-munalign-prob-threshold=@var{probability} -mmpy-option=@var{multo} @gol
+-mdiv-rem -mcode-density -mll64 -mfpu=@var{fpu}}
@emph{ARM Options}
@gccoptlist{-mapcs-frame -mno-apcs-frame @gol
@gccoptlist{-msmall-model -mno-lsim}
@emph{FT32 Options}
-@gccoptlist{-msim -mlra}
+@gccoptlist{-msim -mlra -mnodiv}
@emph{FRV Options}
@gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol
-mgp32 -mgp64 -mfp32 -mfpxx -mfp64 -mhard-float -msoft-float @gol
-mno-float -msingle-float -mdouble-float @gol
-modd-spreg -mno-odd-spreg @gol
--mcompact-branches=@var{policy} @gol
-mabs=@var{mode} -mnan=@var{encoding} @gol
-mdsp -mno-dsp -mdspr2 -mno-dspr2 @gol
-mmcu -mmno-mcu @gol
-mfix-vr4130 -mno-fix-vr4130 -mfix-sb1 -mno-fix-sb1 @gol
-mflush-func=@var{func} -mno-flush-func @gol
-mbranch-cost=@var{num} -mbranch-likely -mno-branch-likely @gol
+-mcompact-branches=@var{policy} @gol
-mfp-exceptions -mno-fp-exceptions @gol
-mvr4130-align -mno-vr4130-align -msynci -mno-synci @gol
-mrelax-pic-calls -mno-relax-pic-calls -mmcount-ra-address @gol
@emph{MSP430 Options}
@gccoptlist{-msim -masm-hex -mmcu= -mcpu= -mlarge -msmall -mrelax @gol
+-mwarn-mcu @gol
-mcode-region= -mdata-region= @gol
-msilicon-errata= -msilicon-errata-warn= @gol
-mhwmult= -minrt}
-march=@var{arch} -mbmx -mno-bmx -mcdx -mno-cdx}
@emph{Nvidia PTX Options}
-@gccoptlist{-m32 -m64 -mmainkernel}
+@gccoptlist{-m32 -m64 -mmainkernel -moptimize}
@emph{PDP-11 Options}
@gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol
-mquad-memory-atomic -mno-quad-memory-atomic @gol
-mcompat-align-parm -mno-compat-align-parm @gol
-mupper-regs-df -mno-upper-regs-df -mupper-regs-sf -mno-upper-regs-sf @gol
--mupper-regs -mno-upper-regs}
+-mupper-regs -mno-upper-regs -mmodulo -mno-modulo @gol
+-mfloat128 -mno-float128 -mfloat128-hardware -mno-float128-hardware @gol
+-mpower9-fusion -mno-mpower9-fusion -mpower9-vector -mno-power9-vector}
@emph{RX Options}
@gccoptlist{-m64bit-doubles -m32bit-doubles -fpu -nofpu@gol
-mint-register=@gol
-mpid@gol
-mallow-string-insns -mno-allow-string-insns@gol
+-mjsr@gol
-mno-warn-multiple-fast-interrupts@gol
-msave-acc-in-interrupts}
-mfpu -mno-fpu -mhard-float -msoft-float @gol
-mhard-quad-float -msoft-quad-float @gol
-mstack-bias -mno-stack-bias @gol
+-mstd-struct-return -mno-std-struct-return @gol
-munaligned-doubles -mno-unaligned-doubles @gol
-muser-mode -mno-user-mode @gol
-mv8plus -mno-v8plus -mvis -mno-vis @gol
-mpclmul -mfsgsbase -mrdrnd -mf16c -mfma @gol
-mprefetchwt1 -mclflushopt -mxsavec -mxsaves @gol
-msse4a -m3dnow -mpopcnt -mabm -mbmi -mtbm -mfma4 -mxop -mlzcnt @gol
--mbmi2 -mfxsr -mxsave -mxsaveopt -mrtm -mlwp -mmpx -mmwaitx -mthreads @gol
--mno-align-stringops -minline-all-stringops @gol
+-mbmi2 -mfxsr -mxsave -mxsaveopt -mrtm -mlwp -mmpx -mmwaitx -mclzero
+-mpku -mthreads @gol
+-mms-bitfields -mno-align-stringops -minline-all-stringops @gol
-minline-stringops-dynamically -mstringop-strategy=@var{alg} @gol
-mmemcpy-strategy=@var{strategy} -mmemset-strategy=@var{strategy} @gol
-mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
-m32 -m64 -mx32 -m16 -miamcu -mlarge-data-threshold=@var{num} @gol
-msse2avx -mfentry -mrecord-mcount -mnop-mcount -m8bit-idiv @gol
-mavx256-split-unaligned-load -mavx256-split-unaligned-store @gol
--malign-data=@var{type} -mstack-protector-guard=@var{guard}}
+-malign-data=@var{type} -mstack-protector-guard=@var{guard} @gol
+-mmitigate-rop}
@emph{x86 Windows Options}
@gccoptlist{-mconsole -mcygwin -mno-cygwin -mdll @gol
@emph{zSeries Options}
See S/390 and zSeries Options.
-
-@item Code Generation Options
-@xref{Code Gen Options,,Options for Code Generation Conventions}.
-@gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
--ffixed-@var{reg} -fexceptions @gol
--fnon-call-exceptions -fdelete-dead-exceptions -funwind-tables @gol
--fasynchronous-unwind-tables @gol
--fno-gnu-unique @gol
--finhibit-size-directive -finstrument-functions @gol
--finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{} @gol
--finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{} @gol
--fno-common -fno-ident @gol
--fpcc-struct-return -fpic -fPIC -fpie -fPIE -fno-plt @gol
--fno-jump-tables @gol
--frecord-gcc-switches @gol
--freg-struct-return -fshort-enums @gol
--fshort-double -fshort-wchar @gol
--fverbose-asm -fpack-struct[=@var{n}] -fstack-check @gol
--fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
--fno-stack-limit -fsplit-stack @gol
--fleading-underscore -ftls-model=@var{model} @gol
--fstack-reuse=@var{reuse_level} @gol
--ftrapv -fwrapv -fbounds-check @gol
--fvisibility=@r{[}default@r{|}internal@r{|}hidden@r{|}protected@r{]} @gol
--fstrict-volatile-bitfields -fsync-libcalls}
@end table
Turn off any specification of a language, so that subsequent files are
handled according to their file name suffixes (as they are if @option{-x}
has not been used at all).
-
-@item -pass-exit-codes
-@opindex pass-exit-codes
-Normally the @command{gcc} program exits with the code of 1 if any
-phase of the compiler returns a non-success return code. If you specify
-@option{-pass-exit-codes}, the @command{gcc} program instead returns with
-the numerically highest error produced by any phase returning an error
-indication. The C, C++, and Fortran front ends return 4 if an internal
-compiler error is encountered.
@end table
If you only want some of the stages of compilation, you can use
are quoted unless they contain only alphanumeric characters or @code{./-_}.
This is useful for shell scripts to capture the driver-generated command lines.
-@item -pipe
-@opindex pipe
-Use pipes rather than temporary files for communication between the
-various stages of compilation. This fails to work on some systems where
-the assembler is unable to read from a pipe; but the GNU assembler has
-no trouble.
-
@item --help
@opindex help
Print (on the standard output) a description of the command-line options
diff /tmp/O2-opts /tmp/O3-opts | grep enabled
@end smallexample
-@item -no-canonical-prefixes
-@opindex no-canonical-prefixes
-Do not expand any symbolic links, resolve references to @samp{/../}
-or @samp{/./}, or make the path absolute when generating a relative
-prefix.
-
@item --version
@opindex version
Display the version number and copyrights of the invoked GCC@.
+@item -pass-exit-codes
+@opindex pass-exit-codes
+Normally the @command{gcc} program exits with the code of 1 if any
+phase of the compiler returns a non-success return code. If you specify
+@option{-pass-exit-codes}, the @command{gcc} program instead returns with
+the numerically highest error produced by any phase returning an error
+indication. The C, C++, and Fortran front ends return 4 if an internal
+compiler error is encountered.
+
+@item -pipe
+@opindex pipe
+Use pipes rather than temporary files for communication between the
+various stages of compilation. This fails to work on some systems where
+the assembler is unable to read from a pipe; but the GNU assembler has
+no trouble.
+
+@item -specs=@var{file}
+@opindex specs
+Process @var{file} after the compiler reads in the standard @file{specs}
+file, in order to override the defaults which the @command{gcc} driver
+program uses when determining what switches to pass to @command{cc1},
+@command{cc1plus}, @command{as}, @command{ld}, etc. More than one
+@option{-specs=@var{file}} can be specified on the command line, and they
+are processed in order, from left to right. @xref{Spec Files}, for
+information about the format of the @var{file}.
+
@item -wrapper
@opindex wrapper
Invoke all subcommands under a wrapper program. The name of the
@item gnu++98
@itemx gnu++03
-GNU dialect of @option{-std=c++98}. This is the default for
-C++ code.
+GNU dialect of @option{-std=c++98}.
@item c++11
@itemx c++0x
@item gnu++14
@itemx gnu++1y
GNU dialect of @option{-std=c++14}.
+This is the default for C++ code.
The name @samp{gnu++1y} is deprecated.
@item c++1z
implies @option{-pthread}, and thus is only supported on targets that
have support for @option{-pthread}.
-Note that this is an experimental feature, incomplete, and subject to
-change in future versions of GCC. See
-@w{@uref{https://gcc.gnu.org/wiki/OpenACC}} for more information.
+@item -fopenacc-dim=@var{geom}
+@opindex fopenacc-dim
+@cindex OpenACC accelerator programming
+Specify default compute dimensions for parallel offload regions that do
+not explicitly specify. The @var{geom} value is a triple of
+':'-separated sizes, in order 'gang', 'worker' and, 'vector'. A size
+can be omitted, to use a target-specific default value.
@item -fopenmp
@opindex fopenmp
declaration does not use either @code{signed} or @code{unsigned}. By
default, such a bit-field is signed, because this is consistent: the
basic integer types such as @code{int} are signed types.
+
+@item -fsso-struct=@var{endianness}
+@opindex fsso-struct
+Set the default scalar storage order of structures and unions to the
+specified endianness. The accepted values are @samp{big-endian} and
+@samp{little-endian}. If the option is not passed, the compiler uses
+the native endianness of the target. This option is not supported for C++.
+
+@strong{Warning:} the @option{-fsso-struct} switch causes GCC to generate
+code that is not binary compatible with code generated without it if the
+specified endianness is not the native endianness of the target.
@end table
@node C++ Dialect Options
only for C++ programs; you can use the other options with any
language supported by GCC@.
+Some options for compiling C programs, such as @option{-std}, are also
+relevant for C++ programs.
+@xref{C Dialect Options,,Options Controlling C Dialect}.
+
Here is a list of options that are @emph{only} for compiling C++ programs:
@table @gcctabopt
exhaustion is signalled by throwing @code{std::bad_alloc}. See also
@samp{new (nothrow)}.
+@item -fconcepts
+@opindex fconcepts
+Enable support for the C++ Extensions for Concepts Technical
+Specification, ISO 19217 (2015), which allows code like
+
+@smallexample
+template <class T> concept bool Addable = requires (T t) @{ t + t; @};
+template <Addable T> T add (T a, T b) @{ return a + b; @}
+@end smallexample
+
@item -fconstexpr-depth=@var{n}
@opindex fconstexpr-depth
Set the maximum nested evaluation depth for C++11 constexpr functions
@opindex fno-gnu-keywords
Do not recognize @code{typeof} as a keyword, so that code can use this
word as an identifier. You can use the keyword @code{__typeof__} instead.
-@option{-ansi} implies @option{-fno-gnu-keywords}.
+This option is implied by the strict ISO C++ dialects: @option{-ansi},
+@option{-std=c++98}, @option{-std=c++11}, etc.
@item -fno-implicit-templates
@opindex fno-implicit-templates
@option{-std=c++14} and above. The flag @option{-Wsized-deallocation}
warns about places that might want to add a definition.
-@item -fstats
-@opindex fstats
-Emit statistics about front-end processing at the end of the compilation.
-This information is generally only useful to the G++ development team.
-
@item -fstrict-enums
@opindex fstrict-enums
Allow the compiler to optimize using the assumption that a value of
objects may not compare equal. When this flag is given, it is a
violation of the ODR to define types with the same name differently.
-@item -fvtable-verify=@r{[}std@r{|}preinit@r{|}none@r{]}
-@opindex fvtable-verify
-Turn on (or off, if using @option{-fvtable-verify=none}) the security
-feature that verifies at run time, for every virtual call, that
-the vtable pointer through which the call is made is valid for the type of
-the object, and has not been corrupted or overwritten. If an invalid vtable
-pointer is detected at run time, an error is reported and execution of the
-program is immediately halted.
-
-This option causes run-time data structures to be built at program startup,
-which are used for verifying the vtable pointers.
-The options @samp{std} and @samp{preinit}
-control the timing of when these data structures are built. In both cases the
-data structures are built before execution reaches @code{main}. Using
-@option{-fvtable-verify=std} causes the data structures to be built after
-shared libraries have been loaded and initialized.
-@option{-fvtable-verify=preinit} causes them to be built before shared
-libraries have been loaded and initialized.
-
-If this option appears multiple times in the command line with different
-values specified, @samp{none} takes highest priority over both @samp{std} and
-@samp{preinit}; @samp{preinit} takes priority over @samp{std}.
-
-@item -fvtv-debug
-@opindex fvtv-debug
-When used in conjunction with @option{-fvtable-verify=std} or
-@option{-fvtable-verify=preinit}, causes debug versions of the
-runtime functions for the vtable verification feature to be called.
-This flag also causes the compiler to log information about which
-vtable pointers it finds for each class.
-This information is written to a file named @file{vtv_set_ptr_data.log}
-in the directory named by the environment variable @env{VTV_LOGS_DIR}
-if that is defined or the current working directory otherwise.
-
-Note: This feature @emph{appends} data to the log file. If you want a fresh log
-file, be sure to delete any existing one.
-
-@item -fvtv-counts
-@opindex fvtv-counts
-This is a debugging flag. When used in conjunction with
-@option{-fvtable-verify=std} or @option{-fvtable-verify=preinit}, this
-causes the compiler to keep track of the total number of virtual calls
-it encounters and the number of verifications it inserts. It also
-counts the number of calls to certain run-time library functions
-that it inserts and logs this information for each compilation unit.
-The compiler writes this information to a file named
-@file{vtv_count_data.log} in the directory named by the environment
-variable @env{VTV_LOGS_DIR} if that is defined or the current working
-directory otherwise. It also counts the size of the vtable pointer sets
-for each class, and writes this information to @file{vtv_class_set_sizes.log}
-in the same directory.
-
-Note: This feature @emph{appends} data to the log files. To get fresh log
-files, be sure to delete any existing ones.
-
-@item -fno-weak
-@opindex fno-weak
-Do not use weak symbol support, even if it is provided by the linker.
-By default, G++ uses weak symbols if they are available. This
-option exists only for testing, and should not be used by end-users;
-it results in inferior code and has no benefits. This option may
-be removed in a future release of G++.
+@item -fno-weak
+@opindex fno-weak
+Do not use weak symbol support, even if it is provided by the linker.
+By default, G++ uses weak symbols if they are available. This
+option exists only for testing, and should not be used by end-users;
+it results in inferior code and has no benefits. This option may
+be removed in a future release of G++.
@item -nostdinc++
@opindex nostdinc++
@item -Wlto-type-mismatch
@opindex Wlto-type-mismatch
-@opindex Wno-lto-type-mistmach
+@opindex Wno-lto-type-mismatch
-During the link-time optimization warn about type mismatches in between
+During the link-time optimization warn about type mismatches in
global declarations from different compilation units.
Requires @option{-flto} to be enabled. Enabled by default.
@item -Wnarrowing @r{(C++ and Objective-C++ only)}
@opindex Wnarrowing
@opindex Wno-narrowing
-Warn when a narrowing conversion prohibited by C++11 occurs within
+With @option{-std=gnu++98} or @option{-std=c++98}, warn when a narrowing
+conversion prohibited by C++11 occurs within
@samp{@{ @}}, e.g.
@smallexample
This flag is included in @option{-Wall} and @option{-Wc++11-compat}.
-With @option{-std=c++11}, @option{-Wno-narrowing} suppresses the diagnostic
-required by the standard. Note that this does not affect the meaning
-of well-formed code; narrowing conversions are still considered
-ill-formed in SFINAE context.
+When a later standard is in effect, e.g. when using @option{-std=c++11},
+narrowing conversions are diagnosed by default, as required by the standard.
+A narrowing conversion from a constant produces an error,
+and a narrowing conversion from a non-constant produces a warning,
+but @option{-Wno-narrowing} suppresses the diagnostic.
+Note that this does not affect the meaning of well-formed code;
+narrowing conversions are still considered ill-formed in SFINAE contexts.
@item -Wnoexcept @r{(C++ and Objective-C++ only)}
@opindex Wnoexcept
@item -fdiagnostics-color[=@var{WHEN}]
@itemx -fno-diagnostics-color
@opindex fdiagnostics-color
-@cindex highlight, color, colour
+@cindex highlight, color
@vindex GCC_COLORS @r{environment variable}
Use color in diagnostics. @var{WHEN} is @samp{never}, @samp{always},
or @samp{auto}. The default depends on how the compiler has been configured,
@opindex fno-diagnostics-show-caret
@opindex fdiagnostics-show-caret
By default, each diagnostic emitted includes the original source line
-and a caret '^' indicating the column. This option suppresses this
+and a caret @samp{^} indicating the column. This option suppresses this
information. The source line is truncated to @var{n} characters, if
the @option{-fmessage-length=n} option is given. When the output is done
to the terminal, the width is limited to the width given by the
@gccoptlist{-Waddress @gol
-Warray-bounds=1 @r{(only with} @option{-O2}@r{)} @gol
+-Wbool-compare @gol
-Wc++11-compat -Wc++14-compat@gol
-Wchar-subscripts @gol
+-Wcomment @gol
-Wenum-compare @r{(in C/ObjC; this is on by default in C++)} @gol
+-Wformat @gol
+-Wimplicit @r{(C and Objective-C only)} @gol
-Wimplicit-int @r{(C and Objective-C only)} @gol
-Wimplicit-function-declaration @r{(C and Objective-C only)} @gol
--Wbool-compare @gol
--Wduplicated-cond @gol
--Wcomment @gol
--Wformat @gol
+-Winit-self @r{(only for C++)} @gol
+-Wlogical-not-parentheses
-Wmain @r{(only for C/ObjC and unless} @option{-ffreestanding}@r{)} @gol
-Wmaybe-uninitialized @gol
+-Wmemset-transposed-args @gol
+-Wmisleading-indentation @r{(only for C/C++)} @gol
-Wmissing-braces @r{(only for C/ObjC)} @gol
+-Wnarrowing @r{(only for C++)} @gol
-Wnonnull @gol
+-Wnonnull-compare @gol
-Wopenmp-simd @gol
-Wparentheses @gol
-Wpointer-sign @gol
-Wreturn-type @gol
-Wsequence-point @gol
-Wsign-compare @r{(only in C++)} @gol
+-Wsizeof-pointer-memaccess @gol
-Wstrict-aliasing @gol
-Wstrict-overflow=1 @gol
-Wswitch @gol
-Wmissing-parameter-type @r{(C only)} @gol
-Wold-style-declaration @r{(C only)} @gol
-Woverride-init @gol
--Wsign-compare @gol
+-Wsign-compare @r{(C only)} @gol
-Wtype-limits @gol
-Wuninitialized @gol
--Wshift-negative-value @gol
+-Wshift-negative-value @r{(in C++03 and in C99 and newer)} @gol
-Wunused-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)} @gol
-Wunused-but-set-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)} @gol
}
Warn about passing a null pointer for arguments marked as
requiring a non-null value by the @code{nonnull} function attribute.
-Also warns when comparing an argument marked with the @code{nonnull}
-function attribute against null inside the function.
-
@option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
can be disabled with the @option{-Wno-nonnull} option.
+@item -Wnonnull-compare
+@opindex Wnonnull-compare
+@opindex Wno-nonnull-compare
+Warn when comparing an argument marked with the @code{nonnull}
+function attribute against null inside the function.
+
+@option{-Wnonnull-compare} is included in @option{-Wall}. It
+can be disabled with the @option{-Wno-nonnull-compare} option.
+
@item -Wnull-dereference
@opindex Wnull-dereference
@opindex Wno-null-dereference
This warning is also enabled by @option{-Wextra}.
+@item -Wignored-attributes @r{(C and C++ only)}
+@opindex Wignored-attributes
+@opindex Wno-ignored-attributes
+Warn when an attribute is ignored. This is different from the
+@option{-Wattributes} option in that it warns whenever the compiler decides
+to drop an attribute, not that the attribute is either unknown, used in a
+wrong place, etc. This warning is enabled by default.
+
@item -Wmain
@opindex Wmain
@opindex Wno-main
@code{for} clauses with a guarded statement that does not use braces,
followed by an unguarded statement with the same indentation.
-This warning is disabled by default.
-
In the following example, the call to ``bar'' is misleadingly indented as
if it were guarded by the ``if'' conditional.
typically indicates autogenerated code, and no assumptions can be made
about the layout of the file that the directive references.
+This warning is enabled by @option{-Wall} in C and C++.
+
@item -Wmissing-braces
@opindex Wmissing-braces
@opindex Wno-missing-braces
@opindex Wunused-variable
@opindex Wno-unused-variable
Warn whenever a local or static variable is unused aside from its
-declaration. This option implies @option{-Wunused-const-variable} for C,
+declaration. This option implies @option{-Wunused-const-variable=1} for C,
but not for C++. This warning is enabled by @option{-Wall}.
To suppress this warning use the @code{unused} attribute
(@pxref{Variable Attributes}).
@item -Wunused-const-variable
+@itemx -Wunused-const-variable=@var{n}
@opindex Wunused-const-variable
@opindex Wno-unused-const-variable
Warn whenever a constant static variable is unused aside from its declaration.
-This warning is enabled by @option{-Wunused-variable} for C, but not for C++.
-In C++ this is normally not an error since const variables take the place of
-@code{#define}s in C++.
+@option{-Wunused-const-variable=1} is enabled by @option{-Wunused-variable}
+for C, but not for C++. In C this declares variable storage, but in C++ this
+is not an error since const variables take the place of @code{#define}s.
To suppress this warning use the @code{unused} attribute
(@pxref{Variable Attributes}).
+@table @gcctabopt
+@item -Wunused-const-variable=1
+This is the warning level that is enabled by @option{-Wunused-variable} for
+C. It warns only about unused static const variables defined in the main
+compilation unit, but not about static const variables declared in any
+header included.
+
+@item -Wunused-const-variable=2
+This warning level also warns for unused constant static variables in
+headers (excluding system headers). This is the warning level of
+@option{-Wunused-const-variable} and must be explicitly requested since
+in C++ this isn't an error and in C it might be harder to clean up all
+headers included.
+@end table
+
@item -Wunused-value
@opindex Wunused-value
@opindex Wno-unused-value
computations may be deleted by data flow analysis before the warnings
are printed.
+@item -Winvalid-memory-model
+@opindex Winvalid-memory-model
+@opindex Wno-invalid-memory-model
+Warn for invocations of @ref{__atomic Builtins}, @ref{__sync Builtins},
+and the C11 atomic generic functions with a memory consistency argument
+that is either invalid for the operation or outside the range of values
+of the @code{memory_order} enumeration. For example, since the
+@code{__atomic_store} and @code{__atomic_store_n} built-ins are only
+defined for the relaxed, release, and sequentially consistent memory
+orders the following code is diagnosed:
+
+@smallexample
+void store (int *i)
+@{
+ __atomic_store_n (i, 0, memory_order_consume);
+@}
+@end smallexample
+
+@option{-Winvalid-memory-model} is enabled by default.
+
@item -Wmaybe-uninitialized
@opindex Wmaybe-uninitialized
@opindex Wno-maybe-uninitialized
if (p->q != NULL) @{ @dots{} @}
else if (p->q != NULL) @{ @dots{} @}
@end smallexample
-This warning is enabled by @option{-Wall}.
@item -Wframe-address
@opindex Wno-frame-address
width specifiers @code{I32}, @code{I64}, and @code{I} used on Windows targets,
which depend on the MS runtime.
+@item -Wplacement-new
+@itemx -Wplacement-new=@var{n}
+@opindex Wplacement-new
+@opindex Wno-placement-new
+Warn about placement new expressions with undefined behavior, such as
+constructing an object in a buffer that is smaller than the type of
+the object. For example, the placement new expression below is diagnosed
+because it attempts to construct an array of 64 integers in a buffer only
+64 bytes large.
+@smallexample
+char buf [64];
+new (buf) int[64];
+@end smallexample
+This warning is enabled by default.
+
+@table @gcctabopt
+@item -Wplacement-new=1
+This is the default warning level of @option{-Wplacement-new}. At this
+level the warning is not issued for some strictly undefined constructs that
+GCC allows as extensions for compatibility with legacy code. For example,
+the following @code{new} expression is not diagnosed at this level even
+though it has undefined behavior according to the C++ standard because
+it writes past the end of the one-element array.
+@smallexample
+struct S @{ int n, a[1]; @};
+S *s = (S *)malloc (sizeof *s + 31 * sizeof s->a[0]);
+new (s->a)int [32]();
+@end smallexample
+
+@item -Wplacement-new=2
+At this level, in addition to diagnosing all the same constructs as at level
+1, a diagnostic is also issued for placement new expressions that construct
+an object in the last member of structure whose type is an array of a single
+element and whose size is less than the size of the object being constructed.
+While the previous example would be diagnosed, the following construct makes
+use of the flexible member array extension to avoid the warning at level 2.
+@smallexample
+struct S @{ int n, a[]; @};
+S *s = (S *)malloc (sizeof *s + 32 * sizeof s->a[0]);
+new (s->a)int [32]();
+@end smallexample
+
+@end table
+
@item -Wpointer-arith
@opindex Wpointer-arith
@opindex Wno-pointer-arith
@item -Wzero-as-null-pointer-constant @r{(C++ and Objective-C++ only)}
@opindex Wzero-as-null-pointer-constant
@opindex Wno-zero-as-null-pointer-constant
-Warn when a literal '0' is used as null pointer constant. This can
+Warn when a literal @samp{0} is used as null pointer constant. This can
be useful to facilitate the conversion to @code{nullptr} in C++11.
@item -Wsubobject-linkage @r{(C++ and Objective-C++ only)}
@cindex signed and unsigned values, comparison warning
Warn when a comparison between signed and unsigned values could produce
an incorrect result when the signed value is converted to unsigned.
-This warning is also enabled by @option{-Wextra}; to get the other warnings
-of @option{-Wextra} without this warning, use @option{-Wextra -Wno-sign-compare}.
+In C++, this warning is also enabled by @option{-Wall}. In C, it is
+also enabled by @option{-Wextra}.
@item -Wsign-conversion
@opindex Wsign-conversion
real to lower precision real values. This option is also enabled by
@option{-Wconversion}.
+@item -Wno-scalar-storage-order
+@opindex -Wno-scalar-storage-order
+@opindex -Wscalar-storage-order
+Do not warn on suspicious constructs involving reverse scalar storage order.
+
@item -Wsized-deallocation @r{(C++ and Objective-C++ only)}
@opindex Wsized-deallocation
@opindex Wno-sized-deallocation
a structure that has been marked with the @code{designated_init}
attribute.
+@item -Whsa
+Issue a warning when HSAIL cannot be emitted for the compiled function or
+OpenMP construct.
+
@end table
@node Debugging Options
-@section Options for Debugging Your Program or GCC
+@section Options for Debugging Your Program
@cindex options, debugging
@cindex debugging information options
-GCC has various special options that are used for debugging
-either your program or GCC:
+To tell GCC to emit extra information for use by a debugger, in almost
+all cases you need only to add @option{-g} to your other options.
+
+GCC allows you to use @option{-g} with
+@option{-O}. The shortcuts taken by optimized code may occasionally
+be surprising: some variables you declared may not exist
+at all; flow of control may briefly move where you did not expect it;
+some statements may not be executed because they compute constant
+results or their values are already at hand; some statements may
+execute in different places because they have been moved out of loops.
+Nevertheless it is possible to debug optimized output. This makes
+it reasonable to use the optimizer for programs that might have bugs.
+
+If you are not using some other optimization option, consider
+using @option{-Og} (@pxref{Optimize Options}) with @option{-g}.
+With no @option{-O} option at all, some compiler passes that collect
+information useful for debugging do not run at all, so that
+@option{-Og} may result in a better debugging experience.
@table @gcctabopt
@item -g
@opindex g
Produce debugging information in the operating system's native format
-(stabs, COFF, XCOFF, or DWARF 2)@. GDB can work with this debugging
+(stabs, COFF, XCOFF, or DWARF)@. GDB can work with this debugging
information.
On most systems that use stabs format, @option{-g} enables use of extra
to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
@option{-gxcoff+}, @option{-gxcoff}, or @option{-gvms} (see below).
-GCC allows you to use @option{-g} with
-@option{-O}. The shortcuts taken by optimized code may occasionally
-produce surprising results: some variables you declared may not exist
-at all; flow of control may briefly move where you did not expect it;
-some statements may not be executed because they compute constant
-results or their values are already at hand; some statements may
-execute in different places because they have been moved out of loops.
-
-Nevertheless it proves possible to debug optimized output. This makes
-it reasonable to use the optimizer for programs that might have bugs.
-
-The following options are useful when GCC is generated with the
-capability for more than one debugging format.
-
-@item -gsplit-dwarf
-@opindex gsplit-dwarf
-Separate as much dwarf debugging information as possible into a
-separate output file with the extension .dwo. This option allows
-the build system to avoid linking files with debug information. To
-be useful, this option requires a debugger capable of reading .dwo
-files.
-
@item -ggdb
@opindex ggdb
Produce debugging information for use by GDB@. This means to use the
-most expressive format available (DWARF 2, stabs, or the native format
+most expressive format available (DWARF, stabs, or the native format
if neither of those are supported), including GDB extensions if at all
possible.
-@item -gpubnames
-@opindex gpubnames
-Generate dwarf .debug_pubnames and .debug_pubtypes sections.
+@item -gdwarf
+@itemx -gdwarf-@var{version}
+@opindex gdwarf
+Produce debugging information in DWARF format (if that is supported).
+The value of @var{version} may be either 2, 3, 4 or 5; the default version
+for most targets is 4. DWARF Version 5 is only experimental.
-@item -ggnu-pubnames
-@opindex ggnu-pubnames
-Generate .debug_pubnames and .debug_pubtypes sections in a format
-suitable for conversion into a GDB@ index. This option is only useful
-with a linker that can produce GDB@ index version 7.
+Note that with DWARF Version 2, some ports require and always
+use some non-conflicting DWARF 3 extensions in the unwind tables.
+
+Version 4 may require GDB 7.0 and @option{-fvar-tracking-assignments}
+for maximum benefit.
+
+GCC no longer supports DWARF Version 1, which is substantially
+different than Version 2 and later. For historical reasons, some
+other DWARF-related options (including @option{-feliminate-dwarf2-dups}
+and @option{-fno-dwarf2-cfi-asm}) retain a reference to DWARF Version 2
+in their names, but apply to all currently-supported versions of DWARF.
@item -gstabs
@opindex gstabs
produces stabs debugging output that is not understood by DBX or SDB@.
On System V Release 4 systems this option requires the GNU assembler.
-@item -feliminate-unused-debug-symbols
-@opindex feliminate-unused-debug-symbols
-Produce debugging information in stabs format (if that is supported),
-for only symbols that are actually used.
-
-@item -femit-class-debug-always
-@opindex femit-class-debug-always
-Instead of emitting debugging information for a C++ class in only one
-object file, emit it in all object files using the class. This option
-should be used only with debuggers that are unable to handle the way GCC
-normally emits debugging information for classes because using this
-option increases the size of debugging information by as much as a
-factor of two.
-
-@item -fdebug-types-section
-@opindex fdebug-types-section
-@opindex fno-debug-types-section
-When using DWARF Version 4 or higher, type DIEs can be put into
-their own @code{.debug_types} section instead of making them part of the
-@code{.debug_info} section. It is more efficient to put them in a separate
-comdat sections since the linker can then remove duplicates.
-But not all DWARF consumers support @code{.debug_types} sections yet
-and on some objects @code{.debug_types} produces larger instead of smaller
-debugging information.
-
@item -gstabs+
@opindex gstabs+
Produce debugging information in stabs format (if that is supported),
refuse to read the program, and may cause assemblers other than the GNU
assembler (GAS) to fail with an error.
-@item -gdwarf-@var{version}
-@opindex gdwarf-@var{version}
-Produce debugging information in DWARF format (if that is supported).
-The value of @var{version} may be either 2, 3, 4 or 5; the default version
-for most targets is 4. DWARF Version 5 is only experimental.
-
-Note that with DWARF Version 2, some ports require and always
-use some non-conflicting DWARF 3 extensions in the unwind tables.
-
-Version 4 may require GDB 7.0 and @option{-fvar-tracking-assignments}
-for maximum benefit.
-
-@item -grecord-gcc-switches
-@opindex grecord-gcc-switches
-This switch causes the command-line options used to invoke the
-compiler that may affect code generation to be appended to the
-DW_AT_producer attribute in DWARF debugging information. The options
-are concatenated with spaces separating them from each other and from
-the compiler version. See also @option{-frecord-gcc-switches} for another
-way of storing compiler options into the object file. This is the default.
-
-@item -gno-record-gcc-switches
-@opindex gno-record-gcc-switches
-Disallow appending command-line options to the DW_AT_producer attribute
-in DWARF debugging information.
-
-@item -gstrict-dwarf
-@opindex gstrict-dwarf
-Disallow using extensions of later DWARF standard version than selected
-with @option{-gdwarf-@var{version}}. On most targets using non-conflicting
-DWARF extensions from later standard versions is allowed.
-
-@item -gno-strict-dwarf
-@opindex gno-strict-dwarf
-Allow using extensions of later DWARF standard version than selected with
-@option{-gdwarf-@var{version}}.
-
-@item -gz@r{[}=@var{type}@r{]}
-@opindex gz
-Produce compressed debug sections in DWARF format, if that is supported.
-If @var{type} is not given, the default type depends on the capabilities
-of the assembler and linker used. @var{type} may be one of
-@samp{none} (don't compress debug sections), @samp{zlib} (use zlib
-compression in ELF gABI format), or @samp{zlib-gnu} (use zlib
-compression in traditional GNU format). If the linker doesn't support
-writing compressed debug sections, the option is rejected. Otherwise,
-if the assembler does not support them, @option{-gz} is silently ignored
-when producing object files.
-
@item -gvms
@opindex gvms
Produce debugging information in Alpha/VMS debug format (if that is
present in the program. Some debuggers support macro expansion when
you use @option{-g3}.
-@option{-gdwarf-2} does not accept a concatenated debug level, because
-GCC used to support an option @option{-gdwarf} that meant to generate
-debug information in version 1 of the DWARF format (which is very
-different from version 2), and it would have been too confusing. That
-debug format is long obsolete, but the option cannot be changed now.
+@option{-gdwarf} does not accept a concatenated debug level, to avoid
+confusion with @option{-gdwarf-@var{level}}.
Instead use an additional @option{-g@var{level}} option to change the
debug level for DWARF.
-@item -gtoggle
-@opindex gtoggle
-Turn off generation of debug info, if leaving out this option
-generates it, or turn it on at level 2 otherwise. The position of this
-argument in the command line does not matter; it takes effect after all
-other options are processed, and it does so only once, no matter how
-many times it is given. This is mainly intended to be used with
-@option{-fcompare-debug}.
-
-@item -fsanitize=address
-@opindex fsanitize=address
-Enable AddressSanitizer, a fast memory error detector.
-Memory access instructions are instrumented to detect
-out-of-bounds and use-after-free bugs.
-See @uref{https://github.com/google/sanitizers/wiki/AddressSanitizer} for
-more details. The run-time behavior can be influenced using the
-@env{ASAN_OPTIONS} environment variable. When set to @code{help=1},
-the available options are shown at startup of the instrumended program. See
-@url{https://github.com/google/sanitizers/wiki/AddressSanitizerFlags#run-time-flags}
-for a list of supported options.
+@item -feliminate-unused-debug-symbols
+@opindex feliminate-unused-debug-symbols
+Produce debugging information in stabs format (if that is supported),
+for only symbols that are actually used.
-@item -fsanitize=kernel-address
-@opindex fsanitize=kernel-address
-Enable AddressSanitizer for Linux kernel.
-See @uref{https://github.com/google/kasan/wiki} for more details.
+@item -femit-class-debug-always
+@opindex femit-class-debug-always
+Instead of emitting debugging information for a C++ class in only one
+object file, emit it in all object files using the class. This option
+should be used only with debuggers that are unable to handle the way GCC
+normally emits debugging information for classes because using this
+option increases the size of debugging information by as much as a
+factor of two.
-@item -fsanitize=thread
-@opindex fsanitize=thread
-Enable ThreadSanitizer, a fast data race detector.
-Memory access instructions are instrumented to detect
-data race bugs. See @uref{https://github.com/google/sanitizers/wiki#threadsanitizer} for more
-details. The run-time behavior can be influenced using the @env{TSAN_OPTIONS}
-environment variable; see
-@url{https://github.com/google/sanitizers/wiki/ThreadSanitizerFlags} for a list of
-supported options.
+@item -fno-merge-debug-strings
+@opindex fmerge-debug-strings
+@opindex fno-merge-debug-strings
+Direct the linker to not merge together strings in the debugging
+information that are identical in different object files. Merging is
+not supported by all assemblers or linkers. Merging decreases the size
+of the debug information in the output file at the cost of increasing
+link processing time. Merging is enabled by default.
-@item -fsanitize=leak
-@opindex fsanitize=leak
-Enable LeakSanitizer, a memory leak detector.
-This option only matters for linking of executables and if neither
-@option{-fsanitize=address} nor @option{-fsanitize=thread} is used. In that
-case the executable is linked against a library that overrides @code{malloc}
-and other allocator functions. See
-@uref{https://github.com/google/sanitizers/wiki/AddressSanitizerLeakSanitizer} for more
-details. The run-time behavior can be influenced using the
-@env{LSAN_OPTIONS} environment variable.
+@item -fdebug-prefix-map=@var{old}=@var{new}
+@opindex fdebug-prefix-map
+When compiling files in directory @file{@var{old}}, record debugging
+information describing them as in @file{@var{new}} instead.
-@item -fsanitize=undefined
-@opindex fsanitize=undefined
-Enable UndefinedBehaviorSanitizer, a fast undefined behavior detector.
-Various computations are instrumented to detect undefined behavior
-at runtime. Current suboptions are:
+@item -fvar-tracking
+@opindex fvar-tracking
+Run variable tracking pass. It computes where variables are stored at each
+position in code. Better debugging information is then generated
+(if the debugging information format supports this information).
-@table @gcctabopt
+It is enabled by default when compiling with optimization (@option{-Os},
+@option{-O}, @option{-O2}, @dots{}), debugging information (@option{-g}) and
+the debug info format supports it.
-@item -fsanitize=shift
-@opindex fsanitize=shift
-This option enables checking that the result of a shift operation is
-not undefined. Note that what exactly is considered undefined differs
-slightly between C and C++, as well as between ISO C90 and C99, etc.
+@item -fvar-tracking-assignments
+@opindex fvar-tracking-assignments
+@opindex fno-var-tracking-assignments
+Annotate assignments to user variables early in the compilation and
+attempt to carry the annotations over throughout the compilation all the
+way to the end, in an attempt to improve debug information while
+optimizing. Use of @option{-gdwarf-4} is recommended along with it.
-@item -fsanitize=integer-divide-by-zero
-@opindex fsanitize=integer-divide-by-zero
-Detect integer division by zero as well as @code{INT_MIN / -1} division.
+It can be enabled even if var-tracking is disabled, in which case
+annotations are created and maintained, but discarded at the end.
+By default, this flag is enabled together with @option{-fvar-tracking},
+except when selective scheduling is enabled.
-@item -fsanitize=unreachable
-@opindex fsanitize=unreachable
-With this option, the compiler turns the @code{__builtin_unreachable}
-call into a diagnostics message call instead. When reaching the
-@code{__builtin_unreachable} call, the behavior is undefined.
+@item -gsplit-dwarf
+@opindex gsplit-dwarf
+Separate as much DWARF debugging information as possible into a
+separate output file with the extension @file{.dwo}. This option allows
+the build system to avoid linking files with debug information. To
+be useful, this option requires a debugger capable of reading @file{.dwo}
+files.
-@item -fsanitize=vla-bound
-@opindex fsanitize=vla-bound
-This option instructs the compiler to check that the size of a variable
-length array is positive.
+@item -gpubnames
+@opindex gpubnames
+Generate DWARF @code{.debug_pubnames} and @code{.debug_pubtypes} sections.
-@item -fsanitize=null
-@opindex fsanitize=null
-This option enables pointer checking. Particularly, the application
-built with this option turned on will issue an error message when it
-tries to dereference a NULL pointer, or if a reference (possibly an
-rvalue reference) is bound to a NULL pointer, or if a method is invoked
-on an object pointed by a NULL pointer.
+@item -ggnu-pubnames
+@opindex ggnu-pubnames
+Generate @code{.debug_pubnames} and @code{.debug_pubtypes} sections in a format
+suitable for conversion into a GDB@ index. This option is only useful
+with a linker that can produce GDB@ index version 7.
-@item -fsanitize=return
-@opindex fsanitize=return
-This option enables return statement checking. Programs
-built with this option turned on will issue an error message
-when the end of a non-void function is reached without actually
-returning a value. This option works in C++ only.
+@item -fdebug-types-section
+@opindex fdebug-types-section
+@opindex fno-debug-types-section
+When using DWARF Version 4 or higher, type DIEs can be put into
+their own @code{.debug_types} section instead of making them part of the
+@code{.debug_info} section. It is more efficient to put them in a separate
+comdat sections since the linker can then remove duplicates.
+But not all DWARF consumers support @code{.debug_types} sections yet
+and on some objects @code{.debug_types} produces larger instead of smaller
+debugging information.
-@item -fsanitize=signed-integer-overflow
-@opindex fsanitize=signed-integer-overflow
-This option enables signed integer overflow checking. We check that
-the result of @code{+}, @code{*}, and both unary and binary @code{-}
-does not overflow in the signed arithmetics. Note, integer promotion
-rules must be taken into account. That is, the following is not an
-overflow:
-@smallexample
-signed char a = SCHAR_MAX;
-a++;
-@end smallexample
+@item -grecord-gcc-switches
+@item -gno-record-gcc-switches
+@opindex grecord-gcc-switches
+@opindex gno-record-gcc-switches
+This switch causes the command-line options used to invoke the
+compiler that may affect code generation to be appended to the
+DW_AT_producer attribute in DWARF debugging information. The options
+are concatenated with spaces separating them from each other and from
+the compiler version.
+It is enabled by default.
+See also @option{-frecord-gcc-switches} for another
+way of storing compiler options into the object file.
-@item -fsanitize=bounds
-@opindex fsanitize=bounds
-This option enables instrumentation of array bounds. Various out of bounds
-accesses are detected. Flexible array members, flexible array member-like
-arrays, and initializers of variables with static storage are not instrumented.
+@item -gstrict-dwarf
+@opindex gstrict-dwarf
+Disallow using extensions of later DWARF standard version than selected
+with @option{-gdwarf-@var{version}}. On most targets using non-conflicting
+DWARF extensions from later standard versions is allowed.
-@item -fsanitize=bounds-strict
-@opindex fsanitize=bounds-strict
-This option enables strict instrumentation of array bounds. Most out of bounds
-accesses are detected, including flexible array members and flexible array
-member-like arrays. Initializers of variables with static storage are not
-instrumented.
+@item -gno-strict-dwarf
+@opindex gno-strict-dwarf
+Allow using extensions of later DWARF standard version than selected with
+@option{-gdwarf-@var{version}}.
-@item -fsanitize=alignment
-@opindex fsanitize=alignment
+@item -gz@r{[}=@var{type}@r{]}
+@opindex gz
+Produce compressed debug sections in DWARF format, if that is supported.
+If @var{type} is not given, the default type depends on the capabilities
+of the assembler and linker used. @var{type} may be one of
+@samp{none} (don't compress debug sections), @samp{zlib} (use zlib
+compression in ELF gABI format), or @samp{zlib-gnu} (use zlib
+compression in traditional GNU format). If the linker doesn't support
+writing compressed debug sections, the option is rejected. Otherwise,
+if the assembler does not support them, @option{-gz} is silently ignored
+when producing object files.
-This option enables checking of alignment of pointers when they are
-dereferenced, or when a reference is bound to insufficiently aligned target,
-or when a method or constructor is invoked on insufficiently aligned object.
+@item -feliminate-dwarf2-dups
+@opindex feliminate-dwarf2-dups
+Compress DWARF debugging information by eliminating duplicated
+information about each symbol. This option only makes sense when
+generating DWARF debugging information.
-@item -fsanitize=object-size
-@opindex fsanitize=object-size
-This option enables instrumentation of memory references using the
-@code{__builtin_object_size} function. Various out of bounds pointer
-accesses are detected.
+@item -femit-struct-debug-baseonly
+@opindex femit-struct-debug-baseonly
+Emit debug information for struct-like types
+only when the base name of the compilation source file
+matches the base name of file in which the struct is defined.
-@item -fsanitize=float-divide-by-zero
-@opindex fsanitize=float-divide-by-zero
-Detect floating-point division by zero. Unlike other similar options,
-@option{-fsanitize=float-divide-by-zero} is not enabled by
-@option{-fsanitize=undefined}, since floating-point division by zero can
-be a legitimate way of obtaining infinities and NaNs.
+This option substantially reduces the size of debugging information,
+but at significant potential loss in type information to the debugger.
+See @option{-femit-struct-debug-reduced} for a less aggressive option.
+See @option{-femit-struct-debug-detailed} for more detailed control.
-@item -fsanitize=float-cast-overflow
-@opindex fsanitize=float-cast-overflow
-This option enables floating-point type to integer conversion checking.
-We check that the result of the conversion does not overflow.
-Unlike other similar options, @option{-fsanitize=float-cast-overflow} is
-not enabled by @option{-fsanitize=undefined}.
-This option does not work well with @code{FE_INVALID} exceptions enabled.
+This option works only with DWARF debug output.
-@item -fsanitize=nonnull-attribute
-@opindex fsanitize=nonnull-attribute
+@item -femit-struct-debug-reduced
+@opindex femit-struct-debug-reduced
+Emit debug information for struct-like types
+only when the base name of the compilation source file
+matches the base name of file in which the type is defined,
+unless the struct is a template or defined in a system header.
-This option enables instrumentation of calls, checking whether null values
-are not passed to arguments marked as requiring a non-null value by the
-@code{nonnull} function attribute.
+This option significantly reduces the size of debugging information,
+with some potential loss in type information to the debugger.
+See @option{-femit-struct-debug-baseonly} for a more aggressive option.
+See @option{-femit-struct-debug-detailed} for more detailed control.
-@item -fsanitize=returns-nonnull-attribute
-@opindex fsanitize=returns-nonnull-attribute
+This option works only with DWARF debug output.
-This option enables instrumentation of return statements in functions
-marked with @code{returns_nonnull} function attribute, to detect returning
-of null values from such functions.
+@item -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]}
+@opindex femit-struct-debug-detailed
+Specify the struct-like types
+for which the compiler generates debug information.
+The intent is to reduce duplicate struct debug information
+between different object files within the same program.
-@item -fsanitize=bool
-@opindex fsanitize=bool
+This option is a detailed version of
+@option{-femit-struct-debug-reduced} and @option{-femit-struct-debug-baseonly},
+which serves for most needs.
-This option enables instrumentation of loads from bool. If a value other
-than 0/1 is loaded, a run-time error is issued.
+A specification has the syntax@*
+[@samp{dir:}|@samp{ind:}][@samp{ord:}|@samp{gen:}](@samp{any}|@samp{sys}|@samp{base}|@samp{none})
-@item -fsanitize=enum
-@opindex fsanitize=enum
+The optional first word limits the specification to
+structs that are used directly (@samp{dir:}) or used indirectly (@samp{ind:}).
+A struct type is used directly when it is the type of a variable, member.
+Indirect uses arise through pointers to structs.
+That is, when use of an incomplete struct is valid, the use is indirect.
+An example is
+@samp{struct one direct; struct two * indirect;}.
-This option enables instrumentation of loads from an enum type. If
-a value outside the range of values for the enum type is loaded,
-a run-time error is issued.
+The optional second word limits the specification to
+ordinary structs (@samp{ord:}) or generic structs (@samp{gen:}).
+Generic structs are a bit complicated to explain.
+For C++, these are non-explicit specializations of template classes,
+or non-template classes within the above.
+Other programming languages have generics,
+but @option{-femit-struct-debug-detailed} does not yet implement them.
-@item -fsanitize=vptr
-@opindex fsanitize=vptr
+The third word specifies the source files for those
+structs for which the compiler should emit debug information.
+The values @samp{none} and @samp{any} have the normal meaning.
+The value @samp{base} means that
+the base of name of the file in which the type declaration appears
+must match the base of the name of the main compilation file.
+In practice, this means that when compiling @file{foo.c}, debug information
+is generated for types declared in that file and @file{foo.h},
+but not other header files.
+The value @samp{sys} means those types satisfying @samp{base}
+or declared in system or compiler headers.
-This option enables instrumentation of C++ member function calls, member
-accesses and some conversions between pointers to base and derived classes,
-to verify the referenced object has the correct dynamic type.
+You may need to experiment to determine the best settings for your application.
-@end table
+The default is @option{-femit-struct-debug-detailed=all}.
-While @option{-ftrapv} causes traps for signed overflows to be emitted,
-@option{-fsanitize=undefined} gives a diagnostic message.
-This currently works only for the C family of languages.
+This option works only with DWARF debug output.
-@item -fno-sanitize=all
-@opindex fno-sanitize=all
+@item -fno-dwarf2-cfi-asm
+@opindex fdwarf2-cfi-asm
+@opindex fno-dwarf2-cfi-asm
+Emit DWARF unwind info as compiler generated @code{.eh_frame} section
+instead of using GAS @code{.cfi_*} directives.
-This option disables all previously enabled sanitizers.
-@option{-fsanitize=all} is not allowed, as some sanitizers cannot be used
-together.
+@item -fno-eliminate-unused-debug-types
+@opindex feliminate-unused-debug-types
+@opindex fno-eliminate-unused-debug-types
+Normally, when producing DWARF output, GCC avoids producing debug symbol
+output for types that are nowhere used in the source file being compiled.
+Sometimes it is useful to have GCC emit debugging
+information for all types declared in a compilation
+unit, regardless of whether or not they are actually used
+in that compilation unit, for example
+if, in the debugger, you want to cast a value to a type that is
+not actually used in your program (but is declared). More often,
+however, this results in a significant amount of wasted space.
+@end table
-@item -fasan-shadow-offset=@var{number}
-@opindex fasan-shadow-offset
-This option forces GCC to use custom shadow offset in AddressSanitizer checks.
-It is useful for experimenting with different shadow memory layouts in
-Kernel AddressSanitizer.
+@node Optimize Options
+@section Options That Control Optimization
+@cindex optimize options
+@cindex options, optimization
-@item -fsanitize-sections=@var{s1},@var{s2},...
-@opindex fsanitize-sections
-Sanitize global variables in selected user-defined sections. @var{si} may
-contain wildcards.
+These options control various sorts of optimizations.
-@item -fsanitize-recover@r{[}=@var{opts}@r{]}
-@opindex fsanitize-recover
-@opindex fno-sanitize-recover
-@option{-fsanitize-recover=} controls error recovery mode for sanitizers
-mentioned in comma-separated list of @var{opts}. Enabling this option
-for a sanitizer component causes it to attempt to continue
-running the program as if no error happened. This means multiple
-runtime errors can be reported in a single program run, and the exit
-code of the program may indicate success even when errors
-have been reported. The @option{-fno-sanitize-recover=} option
-can be used to alter
-this behavior: only the first detected error is reported
-and program then exits with a non-zero exit code.
+Without any optimization option, the compiler's goal is to reduce the
+cost of compilation and to make debugging produce the expected
+results. Statements are independent: if you stop the program with a
+breakpoint between statements, you can then assign a new value to any
+variable or change the program counter to any other statement in the
+function and get exactly the results you expect from the source
+code.
-Currently this feature only works for @option{-fsanitize=undefined} (and its suboptions
-except for @option{-fsanitize=unreachable} and @option{-fsanitize=return}),
-@option{-fsanitize=float-cast-overflow}, @option{-fsanitize=float-divide-by-zero} and
-@option{-fsanitize=kernel-address}. For these sanitizers error recovery is turned on by default.
-@option{-fsanitize-recover=all} and @option{-fno-sanitize-recover=all} is also
-accepted, the former enables recovery for all sanitizers that support it,
-the latter disables recovery for all sanitizers that support it.
+Turning on optimization flags makes the compiler attempt to improve
+the performance and/or code size at the expense of compilation time
+and possibly the ability to debug the program.
-Syntax without explicit @var{opts} parameter is deprecated. It is equivalent to
-@smallexample
--fsanitize-recover=undefined,float-cast-overflow,float-divide-by-zero
-@end smallexample
-@noindent
-Similarly @option{-fno-sanitize-recover} is equivalent to
-@smallexample
--fno-sanitize-recover=undefined,float-cast-overflow,float-divide-by-zero
-@end smallexample
+The compiler performs optimization based on the knowledge it has of the
+program. Compiling multiple files at once to a single output file mode allows
+the compiler to use information gained from all of the files when compiling
+each of them.
-@item -fsanitize-undefined-trap-on-error
-@opindex fsanitize-undefined-trap-on-error
-The @option{-fsanitize-undefined-trap-on-error} option instructs the compiler to
-report undefined behavior using @code{__builtin_trap} rather than
-a @code{libubsan} library routine. The advantage of this is that the
-@code{libubsan} library is not needed and is not linked in, so this
-is usable even in freestanding environments.
+Not all optimizations are controlled directly by a flag. Only
+optimizations that have a flag are listed in this section.
-@item -fcheck-pointer-bounds
-@opindex fcheck-pointer-bounds
-@opindex fno-check-pointer-bounds
-@cindex Pointer Bounds Checker options
-Enable Pointer Bounds Checker instrumentation. Each memory reference
-is instrumented with checks of the pointer used for memory access against
-bounds associated with that pointer.
+Most optimizations are only enabled if an @option{-O} level is set on
+the command line. Otherwise they are disabled, even if individual
+optimization flags are specified.
-Currently there
-is only an implementation for Intel MPX available, thus x86 target
-and @option{-mmpx} are required to enable this feature.
-MPX-based instrumentation requires
-a runtime library to enable MPX in hardware and handle bounds
-violation signals. By default when @option{-fcheck-pointer-bounds}
-and @option{-mmpx} options are used to link a program, the GCC driver
-links against the @file{libmpx} runtime library and @file{libmpxwrappers}
-library. It also passes '-z bndplt' to a linker in case it supports this
-option (which is checked on libmpx configuration). Note that old versions
-of linker may ignore option. Gold linker doesn't support '-z bndplt'
-option. With no '-z bndplt' support in linker all calls to dynamic libraries
-lose passed bounds reducing overall protection level. It's highly
-recommended to use linker with '-z bndplt' support. In case such linker
-is not available it is adviced to always use @option{-static-libmpxwrappers}
-for better protection level or use @option{-static} to completely avoid
-external calls to dynamic libraries. MPX-based instrumentation
-may be used for debugging and also may be included in production code
-to increase program security. Depending on usage, you may
-have different requirements for the runtime library. The current version
-of the MPX runtime library is more oriented for use as a debugging
-tool. MPX runtime library usage implies @option{-lpthread}. See
-also @option{-static-libmpx}. The runtime library behavior can be
-influenced using various @env{CHKP_RT_*} environment variables. See
-@uref{https://gcc.gnu.org/wiki/Intel%20MPX%20support%20in%20the%20GCC%20compiler}
-for more details.
+Depending on the target and how GCC was configured, a slightly different
+set of optimizations may be enabled at each @option{-O} level than
+those listed here. You can invoke GCC with @option{-Q --help=optimizers}
+to find out the exact set of optimizations that are enabled at each level.
+@xref{Overall Options}, for examples.
-Generated instrumentation may be controlled by various
-@option{-fchkp-*} options and by the @code{bnd_variable_size}
-structure field attribute (@pxref{Type Attributes}) and
-@code{bnd_legacy}, and @code{bnd_instrument} function attributes
-(@pxref{Function Attributes}). GCC also provides a number of built-in
-functions for controlling the Pointer Bounds Checker. @xref{Pointer
-Bounds Checker builtins}, for more information.
+@table @gcctabopt
+@item -O
+@itemx -O1
+@opindex O
+@opindex O1
+Optimize. Optimizing compilation takes somewhat more time, and a lot
+more memory for a large function.
-@item -fchkp-check-incomplete-type
-@opindex fchkp-check-incomplete-type
-@opindex fno-chkp-check-incomplete-type
-Generate pointer bounds checks for variables with incomplete type.
-Enabled by default.
+With @option{-O}, the compiler tries to reduce code size and execution
+time, without performing any optimizations that take a great deal of
+compilation time.
-@item -fchkp-narrow-bounds
-@opindex fchkp-narrow-bounds
-@opindex fno-chkp-narrow-bounds
-Controls bounds used by Pointer Bounds Checker for pointers to object
-fields. If narrowing is enabled then field bounds are used. Otherwise
-object bounds are used. See also @option{-fchkp-narrow-to-innermost-array}
-and @option{-fchkp-first-field-has-own-bounds}. Enabled by default.
+@option{-O} turns on the following optimization flags:
+@gccoptlist{
+-fauto-inc-dec @gol
+-fbranch-count-reg @gol
+-fcombine-stack-adjustments @gol
+-fcompare-elim @gol
+-fcprop-registers @gol
+-fdce @gol
+-fdefer-pop @gol
+-fdelayed-branch @gol
+-fdse @gol
+-fforward-propagate @gol
+-fguess-branch-probability @gol
+-fif-conversion2 @gol
+-fif-conversion @gol
+-finline-functions-called-once @gol
+-fipa-pure-const @gol
+-fipa-profile @gol
+-fipa-reference @gol
+-fmerge-constants @gol
+-fmove-loop-invariants @gol
+-freorder-blocks @gol
+-fshrink-wrap @gol
+-fsplit-wide-types @gol
+-fssa-backprop @gol
+-fssa-phiopt @gol
+-ftree-bit-ccp @gol
+-ftree-ccp @gol
+-ftree-ch @gol
+-ftree-coalesce-vars @gol
+-ftree-copy-prop @gol
+-ftree-dce @gol
+-ftree-dominator-opts @gol
+-ftree-dse @gol
+-ftree-forwprop @gol
+-ftree-fre @gol
+-ftree-phiprop @gol
+-ftree-sink @gol
+-ftree-slsr @gol
+-ftree-sra @gol
+-ftree-pta @gol
+-ftree-ter @gol
+-funit-at-a-time}
-@item -fchkp-first-field-has-own-bounds
-@opindex fchkp-first-field-has-own-bounds
-@opindex fno-chkp-first-field-has-own-bounds
-Forces Pointer Bounds Checker to use narrowed bounds for the address of the
-first field in the structure. By default a pointer to the first field has
-the same bounds as a pointer to the whole structure.
+@option{-O} also turns on @option{-fomit-frame-pointer} on machines
+where doing so does not interfere with debugging.
-@item -fchkp-narrow-to-innermost-array
-@opindex fchkp-narrow-to-innermost-array
-@opindex fno-chkp-narrow-to-innermost-array
-Forces Pointer Bounds Checker to use bounds of the innermost arrays in
-case of nested static array access. By default this option is disabled and
-bounds of the outermost array are used.
+@item -O2
+@opindex O2
+Optimize even more. GCC performs nearly all supported optimizations
+that do not involve a space-speed tradeoff.
+As compared to @option{-O}, this option increases both compilation time
+and the performance of the generated code.
-@item -fchkp-optimize
-@opindex fchkp-optimize
-@opindex fno-chkp-optimize
-Enables Pointer Bounds Checker optimizations. Enabled by default at
-optimization levels @option{-O}, @option{-O2}, @option{-O3}.
+@option{-O2} turns on all optimization flags specified by @option{-O}. It
+also turns on the following optimization flags:
+@gccoptlist{-fthread-jumps @gol
+-falign-functions -falign-jumps @gol
+-falign-loops -falign-labels @gol
+-fcaller-saves @gol
+-fcrossjumping @gol
+-fcse-follow-jumps -fcse-skip-blocks @gol
+-fdelete-null-pointer-checks @gol
+-fdevirtualize -fdevirtualize-speculatively @gol
+-fexpensive-optimizations @gol
+-fgcse -fgcse-lm @gol
+-fhoist-adjacent-loads @gol
+-finline-small-functions @gol
+-findirect-inlining @gol
+-fipa-cp @gol
+-fipa-cp-alignment @gol
+-fipa-sra @gol
+-fipa-icf @gol
+-fisolate-erroneous-paths-dereference @gol
+-flra-remat @gol
+-foptimize-sibling-calls @gol
+-foptimize-strlen @gol
+-fpartial-inlining @gol
+-fpeephole2 @gol
+-frename-registers @gol
+-freorder-blocks-algorithm=stc @gol
+-freorder-blocks-and-partition -freorder-functions @gol
+-frerun-cse-after-loop @gol
+-fsched-interblock -fsched-spec @gol
+-fschedule-insns -fschedule-insns2 @gol
+-fstrict-aliasing -fstrict-overflow @gol
+-ftree-builtin-call-dce @gol
+-ftree-switch-conversion -ftree-tail-merge @gol
+-ftree-pre @gol
+-ftree-vrp @gol
+-fipa-ra}
-@item -fchkp-use-fast-string-functions
-@opindex fchkp-use-fast-string-functions
-@opindex fno-chkp-use-fast-string-functions
-Enables use of @code{*_nobnd} versions of string functions (not copying bounds)
-by Pointer Bounds Checker. Disabled by default.
+Please note the warning under @option{-fgcse} about
+invoking @option{-O2} on programs that use computed gotos.
-@item -fchkp-use-nochk-string-functions
-@opindex fchkp-use-nochk-string-functions
-@opindex fno-chkp-use-nochk-string-functions
-Enables use of @code{*_nochk} versions of string functions (not checking bounds)
-by Pointer Bounds Checker. Disabled by default.
+@item -O3
+@opindex O3
+Optimize yet more. @option{-O3} turns on all optimizations specified
+by @option{-O2} and also turns on the @option{-finline-functions},
+@option{-funswitch-loops}, @option{-fpredictive-commoning},
+@option{-fgcse-after-reload}, @option{-ftree-loop-vectorize},
+@option{-ftree-loop-distribute-patterns}, @option{-fsplit-paths}
+@option{-ftree-slp-vectorize}, @option{-fvect-cost-model},
+@option{-ftree-partial-pre} and @option{-fipa-cp-clone} options.
-@item -fchkp-use-static-bounds
-@opindex fchkp-use-static-bounds
-@opindex fno-chkp-use-static-bounds
-Allow Pointer Bounds Checker to generate static bounds holding
-bounds of static variables. Enabled by default.
+@item -O0
+@opindex O0
+Reduce compilation time and make debugging produce the expected
+results. This is the default.
-@item -fchkp-use-static-const-bounds
-@opindex fchkp-use-static-const-bounds
-@opindex fno-chkp-use-static-const-bounds
-Use statically-initialized bounds for constant bounds instead of
-generating them each time they are required. By default enabled when
-@option{-fchkp-use-static-bounds} is enabled.
+@item -Os
+@opindex Os
+Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
+do not typically increase code size. It also performs further
+optimizations designed to reduce code size.
-@item -fchkp-treat-zero-dynamic-size-as-infinite
-@opindex fchkp-treat-zero-dynamic-size-as-infinite
-@opindex fno-chkp-treat-zero-dynamic-size-as-infinite
-With this option, objects with incomplete type whose
-dynamically-obtained size is zero are treated as having infinite size
-instead by Pointer Bounds
-Checker. This option may be helpful if a program is linked with a library
-missing size information for some symbols. Disabled by default.
+@option{-Os} disables the following optimization flags:
+@gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
+-falign-labels -freorder-blocks -freorder-blocks-algorithm=stc @gol
+-freorder-blocks-and-partition -fprefetch-loop-arrays}
-@item -fchkp-check-read
-@opindex fchkp-check-read
-@opindex fno-chkp-check-read
-Instructs Pointer Bounds Checker to generate checks for all read
-accesses to memory. Enabled by default.
+@item -Ofast
+@opindex Ofast
+Disregard strict standards compliance. @option{-Ofast} enables all
+@option{-O3} optimizations. It also enables optimizations that are not
+valid for all standard-compliant programs.
+It turns on @option{-ffast-math} and the Fortran-specific
+@option{-fno-protect-parens} and @option{-fstack-arrays}.
-@item -fchkp-check-write
-@opindex fchkp-check-write
-@opindex fno-chkp-check-write
-Instructs Pointer Bounds Checker to generate checks for all write
-accesses to memory. Enabled by default.
+@item -Og
+@opindex Og
+Optimize debugging experience. @option{-Og} enables optimizations
+that do not interfere with debugging. It should be the optimization
+level of choice for the standard edit-compile-debug cycle, offering
+a reasonable level of optimization while maintaining fast compilation
+and a good debugging experience.
+@end table
-@item -fchkp-store-bounds
-@opindex fchkp-store-bounds
-@opindex fno-chkp-store-bounds
-Instructs Pointer Bounds Checker to generate bounds stores for
-pointer writes. Enabled by default.
+If you use multiple @option{-O} options, with or without level numbers,
+the last such option is the one that is effective.
-@item -fchkp-instrument-calls
-@opindex fchkp-instrument-calls
-@opindex fno-chkp-instrument-calls
-Instructs Pointer Bounds Checker to pass pointer bounds to calls.
-Enabled by default.
+Options of the form @option{-f@var{flag}} specify machine-independent
+flags. Most flags have both positive and negative forms; the negative
+form of @option{-ffoo} is @option{-fno-foo}. In the table
+below, only one of the forms is listed---the one you typically
+use. You can figure out the other form by either removing @samp{no-}
+or adding it.
-@item -fchkp-instrument-marked-only
-@opindex fchkp-instrument-marked-only
-@opindex fno-chkp-instrument-marked-only
-Instructs Pointer Bounds Checker to instrument only functions
-marked with the @code{bnd_instrument} attribute
-(@pxref{Function Attributes}). Disabled by default.
+The following options control specific optimizations. They are either
+activated by @option{-O} options or are related to ones that are. You
+can use the following flags in the rare cases when ``fine-tuning'' of
+optimizations to be performed is desired.
-@item -fchkp-use-wrappers
-@opindex fchkp-use-wrappers
-@opindex fno-chkp-use-wrappers
-Allows Pointer Bounds Checker to replace calls to built-in functions
-with calls to wrapper functions. When @option{-fchkp-use-wrappers}
-is used to link a program, the GCC driver automatically links
-against @file{libmpxwrappers}. See also @option{-static-libmpxwrappers}.
-Enabled by default.
+@table @gcctabopt
+@item -fno-defer-pop
+@opindex fno-defer-pop
+Always pop the arguments to each function call as soon as that function
+returns. For machines that must pop arguments after a function call,
+the compiler normally lets arguments accumulate on the stack for several
+function calls and pops them all at once.
-@item -fdump-final-insns@r{[}=@var{file}@r{]}
-@opindex fdump-final-insns
-Dump the final internal representation (RTL) to @var{file}. If the
-optional argument is omitted (or if @var{file} is @code{.}), the name
-of the dump file is determined by appending @code{.gkd} to the
-compilation output file name.
+Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
-@item -fcompare-debug@r{[}=@var{opts}@r{]}
-@opindex fcompare-debug
-@opindex fno-compare-debug
-If no error occurs during compilation, run the compiler a second time,
-adding @var{opts} and @option{-fcompare-debug-second} to the arguments
-passed to the second compilation. Dump the final internal
-representation in both compilations, and print an error if they differ.
+@item -fforward-propagate
+@opindex fforward-propagate
+Perform a forward propagation pass on RTL@. The pass tries to combine two
+instructions and checks if the result can be simplified. If loop unrolling
+is active, two passes are performed and the second is scheduled after
+loop unrolling.
-If the equal sign is omitted, the default @option{-gtoggle} is used.
+This option is enabled by default at optimization levels @option{-O},
+@option{-O2}, @option{-O3}, @option{-Os}.
-The environment variable @env{GCC_COMPARE_DEBUG}, if defined, non-empty
-and nonzero, implicitly enables @option{-fcompare-debug}. If
-@env{GCC_COMPARE_DEBUG} is defined to a string starting with a dash,
-then it is used for @var{opts}, otherwise the default @option{-gtoggle}
-is used.
+@item -ffp-contract=@var{style}
+@opindex ffp-contract
+@option{-ffp-contract=off} disables floating-point expression contraction.
+@option{-ffp-contract=fast} enables floating-point expression contraction
+such as forming of fused multiply-add operations if the target has
+native support for them.
+@option{-ffp-contract=on} enables floating-point expression contraction
+if allowed by the language standard. This is currently not implemented
+and treated equal to @option{-ffp-contract=off}.
-@option{-fcompare-debug=}, with the equal sign but without @var{opts},
-is equivalent to @option{-fno-compare-debug}, which disables the dumping
-of the final representation and the second compilation, preventing even
-@env{GCC_COMPARE_DEBUG} from taking effect.
+The default is @option{-ffp-contract=fast}.
-To verify full coverage during @option{-fcompare-debug} testing, set
-@env{GCC_COMPARE_DEBUG} to say @option{-fcompare-debug-not-overridden},
-which GCC rejects as an invalid option in any actual compilation
-(rather than preprocessing, assembly or linking). To get just a
-warning, setting @env{GCC_COMPARE_DEBUG} to @samp{-w%n-fcompare-debug
-not overridden} will do.
+@item -fomit-frame-pointer
+@opindex fomit-frame-pointer
+Don't keep the frame pointer in a register for functions that
+don't need one. This avoids the instructions to save, set up and
+restore frame pointers; it also makes an extra register available
+in many functions. @strong{It also makes debugging impossible on
+some machines.}
-@item -fcompare-debug-second
-@opindex fcompare-debug-second
-This option is implicitly passed to the compiler for the second
-compilation requested by @option{-fcompare-debug}, along with options to
-silence warnings, and omitting other options that would cause
-side-effect compiler outputs to files or to the standard output. Dump
-files and preserved temporary files are renamed so as to contain the
-@code{.gk} additional extension during the second compilation, to avoid
-overwriting those generated by the first.
+On some machines, such as the VAX, this flag has no effect, because
+the standard calling sequence automatically handles the frame pointer
+and nothing is saved by pretending it doesn't exist. The
+machine-description macro @code{FRAME_POINTER_REQUIRED} controls
+whether a target machine supports this flag. @xref{Registers,,Register
+Usage, gccint, GNU Compiler Collection (GCC) Internals}.
-When this option is passed to the compiler driver, it causes the
-@emph{first} compilation to be skipped, which makes it useful for little
-other than debugging the compiler proper.
+The default setting (when not optimizing for
+size) for 32-bit GNU/Linux x86 and 32-bit Darwin x86 targets is
+@option{-fomit-frame-pointer}. You can configure GCC with the
+@option{--enable-frame-pointer} configure option to change the default.
-@item -feliminate-dwarf2-dups
-@opindex feliminate-dwarf2-dups
-Compress DWARF 2 debugging information by eliminating duplicated
-information about each symbol. This option only makes sense when
-generating DWARF 2 debugging information with @option{-gdwarf-2}.
+Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
-@item -femit-struct-debug-baseonly
-@opindex femit-struct-debug-baseonly
-Emit debug information for struct-like types
-only when the base name of the compilation source file
-matches the base name of file in which the struct is defined.
+@item -foptimize-sibling-calls
+@opindex foptimize-sibling-calls
+Optimize sibling and tail recursive calls.
-This option substantially reduces the size of debugging information,
-but at significant potential loss in type information to the debugger.
-See @option{-femit-struct-debug-reduced} for a less aggressive option.
-See @option{-femit-struct-debug-detailed} for more detailed control.
+Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
-This option works only with DWARF 2.
+@item -foptimize-strlen
+@opindex foptimize-strlen
+Optimize various standard C string functions (e.g. @code{strlen},
+@code{strchr} or @code{strcpy}) and
+their @code{_FORTIFY_SOURCE} counterparts into faster alternatives.
-@item -femit-struct-debug-reduced
-@opindex femit-struct-debug-reduced
-Emit debug information for struct-like types
-only when the base name of the compilation source file
-matches the base name of file in which the type is defined,
-unless the struct is a template or defined in a system header.
+Enabled at levels @option{-O2}, @option{-O3}.
-This option significantly reduces the size of debugging information,
-with some potential loss in type information to the debugger.
-See @option{-femit-struct-debug-baseonly} for a more aggressive option.
-See @option{-femit-struct-debug-detailed} for more detailed control.
+@item -fno-inline
+@opindex fno-inline
+Do not expand any functions inline apart from those marked with
+the @code{always_inline} attribute. This is the default when not
+optimizing.
-This option works only with DWARF 2.
+Single functions can be exempted from inlining by marking them
+with the @code{noinline} attribute.
-@item -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]}
-@opindex femit-struct-debug-detailed
-Specify the struct-like types
-for which the compiler generates debug information.
-The intent is to reduce duplicate struct debug information
-between different object files within the same program.
+@item -finline-small-functions
+@opindex finline-small-functions
+Integrate functions into their callers when their body is smaller than expected
+function call code (so overall size of program gets smaller). The compiler
+heuristically decides which functions are simple enough to be worth integrating
+in this way. This inlining applies to all functions, even those not declared
+inline.
-This option is a detailed version of
-@option{-femit-struct-debug-reduced} and @option{-femit-struct-debug-baseonly},
-which serves for most needs.
+Enabled at level @option{-O2}.
-A specification has the syntax@*
-[@samp{dir:}|@samp{ind:}][@samp{ord:}|@samp{gen:}](@samp{any}|@samp{sys}|@samp{base}|@samp{none})
+@item -findirect-inlining
+@opindex findirect-inlining
+Inline also indirect calls that are discovered to be known at compile
+time thanks to previous inlining. This option has any effect only
+when inlining itself is turned on by the @option{-finline-functions}
+or @option{-finline-small-functions} options.
-The optional first word limits the specification to
-structs that are used directly (@samp{dir:}) or used indirectly (@samp{ind:}).
-A struct type is used directly when it is the type of a variable, member.
-Indirect uses arise through pointers to structs.
-That is, when use of an incomplete struct is valid, the use is indirect.
-An example is
-@samp{struct one direct; struct two * indirect;}.
+Enabled at level @option{-O2}.
-The optional second word limits the specification to
-ordinary structs (@samp{ord:}) or generic structs (@samp{gen:}).
-Generic structs are a bit complicated to explain.
-For C++, these are non-explicit specializations of template classes,
-or non-template classes within the above.
-Other programming languages have generics,
-but @option{-femit-struct-debug-detailed} does not yet implement them.
+@item -finline-functions
+@opindex finline-functions
+Consider all functions for inlining, even if they are not declared inline.
+The compiler heuristically decides which functions are worth integrating
+in this way.
-The third word specifies the source files for those
-structs for which the compiler should emit debug information.
-The values @samp{none} and @samp{any} have the normal meaning.
-The value @samp{base} means that
-the base of name of the file in which the type declaration appears
-must match the base of the name of the main compilation file.
-In practice, this means that when compiling @file{foo.c}, debug information
-is generated for types declared in that file and @file{foo.h},
-but not other header files.
-The value @samp{sys} means those types satisfying @samp{base}
-or declared in system or compiler headers.
-
-You may need to experiment to determine the best settings for your application.
+If all calls to a given function are integrated, and the function is
+declared @code{static}, then the function is normally not output as
+assembler code in its own right.
-The default is @option{-femit-struct-debug-detailed=all}.
+Enabled at level @option{-O3}.
-This option works only with DWARF 2.
+@item -finline-functions-called-once
+@opindex finline-functions-called-once
+Consider all @code{static} functions called once for inlining into their
+caller even if they are not marked @code{inline}. If a call to a given
+function is integrated, then the function is not output as assembler code
+in its own right.
-@item -fno-merge-debug-strings
-@opindex fmerge-debug-strings
-@opindex fno-merge-debug-strings
-Direct the linker to not merge together strings in the debugging
-information that are identical in different object files. Merging is
-not supported by all assemblers or linkers. Merging decreases the size
-of the debug information in the output file at the cost of increasing
-link processing time. Merging is enabled by default.
+Enabled at levels @option{-O1}, @option{-O2}, @option{-O3} and @option{-Os}.
-@item -fdebug-prefix-map=@var{old}=@var{new}
-@opindex fdebug-prefix-map
-When compiling files in directory @file{@var{old}}, record debugging
-information describing them as in @file{@var{new}} instead.
+@item -fearly-inlining
+@opindex fearly-inlining
+Inline functions marked by @code{always_inline} and functions whose body seems
+smaller than the function call overhead early before doing
+@option{-fprofile-generate} instrumentation and real inlining pass. Doing so
+makes profiling significantly cheaper and usually inlining faster on programs
+having large chains of nested wrapper functions.
-@item -fno-dwarf2-cfi-asm
-@opindex fdwarf2-cfi-asm
-@opindex fno-dwarf2-cfi-asm
-Emit DWARF 2 unwind info as compiler generated @code{.eh_frame} section
-instead of using GAS @code{.cfi_*} directives.
+Enabled by default.
-@cindex @command{prof}
-@item -p
-@opindex p
-Generate extra code to write profile information suitable for the
-analysis program @command{prof}. You must use this option when compiling
-the source files you want data about, and you must also use it when
-linking.
+@item -fipa-sra
+@opindex fipa-sra
+Perform interprocedural scalar replacement of aggregates, removal of
+unused parameters and replacement of parameters passed by reference
+by parameters passed by value.
-@cindex @command{gprof}
-@item -pg
-@opindex pg
-Generate extra code to write profile information suitable for the
-analysis program @command{gprof}. You must use this option when compiling
-the source files you want data about, and you must also use it when
-linking.
+Enabled at levels @option{-O2}, @option{-O3} and @option{-Os}.
-@item -Q
-@opindex Q
-Makes the compiler print out each function name as it is compiled, and
-print some statistics about each pass when it finishes.
+@item -finline-limit=@var{n}
+@opindex finline-limit
+By default, GCC limits the size of functions that can be inlined. This flag
+allows coarse control of this limit. @var{n} is the size of functions that
+can be inlined in number of pseudo instructions.
-@item -ftime-report
-@opindex ftime-report
-Makes the compiler print some statistics about the time consumed by each
-pass when it finishes.
+Inlining is actually controlled by a number of parameters, which may be
+specified individually by using @option{--param @var{name}=@var{value}}.
+The @option{-finline-limit=@var{n}} option sets some of these parameters
+as follows:
-@item -fmem-report
-@opindex fmem-report
-Makes the compiler print some statistics about permanent memory
-allocation when it finishes.
+@table @gcctabopt
+@item max-inline-insns-single
+is set to @var{n}/2.
+@item max-inline-insns-auto
+is set to @var{n}/2.
+@end table
-@item -fmem-report-wpa
-@opindex fmem-report-wpa
-Makes the compiler print some statistics about permanent memory
-allocation for the WPA phase only.
+See below for a documentation of the individual
+parameters controlling inlining and for the defaults of these parameters.
-@item -fpre-ipa-mem-report
-@opindex fpre-ipa-mem-report
-@item -fpost-ipa-mem-report
-@opindex fpost-ipa-mem-report
-Makes the compiler print some statistics about permanent memory
-allocation before or after interprocedural optimization.
+@emph{Note:} there may be no value to @option{-finline-limit} that results
+in default behavior.
-@item -fprofile-report
-@opindex fprofile-report
-Makes the compiler print some statistics about consistency of the
-(estimated) profile and effect of individual passes.
+@emph{Note:} pseudo instruction represents, in this particular context, an
+abstract measurement of function's size. In no way does it represent a count
+of assembly instructions and as such its exact meaning might change from one
+release to an another.
-@item -fstack-usage
-@opindex fstack-usage
-Makes the compiler output stack usage information for the program, on a
-per-function basis. The filename for the dump is made by appending
-@file{.su} to the @var{auxname}. @var{auxname} is generated from the name of
-the output file, if explicitly specified and it is not an executable,
-otherwise it is the basename of the source file. An entry is made up
-of three fields:
+@item -fno-keep-inline-dllexport
+@opindex fno-keep-inline-dllexport
+This is a more fine-grained version of @option{-fkeep-inline-functions},
+which applies only to functions that are declared using the @code{dllexport}
+attribute or declspec (@xref{Function Attributes,,Declaring Attributes of
+Functions}.)
-@itemize
-@item
-The name of the function.
-@item
-A number of bytes.
-@item
-One or more qualifiers: @code{static}, @code{dynamic}, @code{bounded}.
-@end itemize
+@item -fkeep-inline-functions
+@opindex fkeep-inline-functions
+In C, emit @code{static} functions that are declared @code{inline}
+into the object file, even if the function has been inlined into all
+of its callers. This switch does not affect functions using the
+@code{extern inline} extension in GNU C90@. In C++, emit any and all
+inline functions into the object file.
-The qualifier @code{static} means that the function manipulates the stack
-statically: a fixed number of bytes are allocated for the frame on function
-entry and released on function exit; no stack adjustments are otherwise made
-in the function. The second field is this fixed number of bytes.
+@item -fkeep-static-functions
+@opindex fkeep-static-functions
+Emit @code{static} functions into the object file, even if the function
+is never used.
-The qualifier @code{dynamic} means that the function manipulates the stack
-dynamically: in addition to the static allocation described above, stack
-adjustments are made in the body of the function, for example to push/pop
-arguments around function calls. If the qualifier @code{bounded} is also
-present, the amount of these adjustments is bounded at compile time and
-the second field is an upper bound of the total amount of stack used by
-the function. If it is not present, the amount of these adjustments is
-not bounded at compile time and the second field only represents the
-bounded part.
+@item -fkeep-static-consts
+@opindex fkeep-static-consts
+Emit variables declared @code{static const} when optimization isn't turned
+on, even if the variables aren't referenced.
-@item -fprofile-arcs
-@opindex fprofile-arcs
-Add code so that program flow @dfn{arcs} are instrumented. During
-execution the program records how many times each branch and call is
-executed and how many times it is taken or returns. When the compiled
-program exits it saves this data to a file called
-@file{@var{auxname}.gcda} for each source file. The data may be used for
-profile-directed optimizations (@option{-fbranch-probabilities}), or for
-test coverage analysis (@option{-ftest-coverage}). Each object file's
-@var{auxname} is generated from the name of the output file, if
-explicitly specified and it is not the final executable, otherwise it is
-the basename of the source file. In both cases any suffix is removed
-(e.g.@: @file{foo.gcda} for input file @file{dir/foo.c}, or
-@file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}).
-@xref{Cross-profiling}.
+GCC enables this option by default. If you want to force the compiler to
+check if a variable is referenced, regardless of whether or not
+optimization is turned on, use the @option{-fno-keep-static-consts} option.
-@cindex @command{gcov}
-@item --coverage
-@opindex coverage
+@item -fmerge-constants
+@opindex fmerge-constants
+Attempt to merge identical constants (string constants and floating-point
+constants) across compilation units.
-This option is used to compile and link code instrumented for coverage
-analysis. The option is a synonym for @option{-fprofile-arcs}
-@option{-ftest-coverage} (when compiling) and @option{-lgcov} (when
-linking). See the documentation for those options for more details.
+This option is the default for optimized compilation if the assembler and
+linker support it. Use @option{-fno-merge-constants} to inhibit this
+behavior.
-@itemize
+Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
-@item
-Compile the source files with @option{-fprofile-arcs} plus optimization
-and code generation options. For test coverage analysis, use the
-additional @option{-ftest-coverage} option. You do not need to profile
-every source file in a program.
+@item -fmerge-all-constants
+@opindex fmerge-all-constants
+Attempt to merge identical constants and identical variables.
-@item
-Link your object files with @option{-lgcov} or @option{-fprofile-arcs}
-(the latter implies the former).
+This option implies @option{-fmerge-constants}. In addition to
+@option{-fmerge-constants} this considers e.g.@: even constant initialized
+arrays or initialized constant variables with integral or floating-point
+types. Languages like C or C++ require each variable, including multiple
+instances of the same variable in recursive calls, to have distinct locations,
+so using this option results in non-conforming
+behavior.
-@item
-Run the program on a representative workload to generate the arc profile
-information. This may be repeated any number of times. You can run
-concurrent instances of your program, and provided that the file system
-supports locking, the data files will be correctly updated. Also
-@code{fork} calls are detected and correctly handled (double counting
-will not happen).
+@item -fmodulo-sched
+@opindex fmodulo-sched
+Perform swing modulo scheduling immediately before the first scheduling
+pass. This pass looks at innermost loops and reorders their
+instructions by overlapping different iterations.
-@item
-For profile-directed optimizations, compile the source files again with
-the same optimization and code generation options plus
-@option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
-Control Optimization}).
+@item -fmodulo-sched-allow-regmoves
+@opindex fmodulo-sched-allow-regmoves
+Perform more aggressive SMS-based modulo scheduling with register moves
+allowed. By setting this flag certain anti-dependences edges are
+deleted, which triggers the generation of reg-moves based on the
+life-range analysis. This option is effective only with
+@option{-fmodulo-sched} enabled.
-@item
-For test coverage analysis, use @command{gcov} to produce human readable
-information from the @file{.gcno} and @file{.gcda} files. Refer to the
-@command{gcov} documentation for further information.
+@item -fno-branch-count-reg
+@opindex fno-branch-count-reg
+Avoid running a pass scanning for opportunities to use ``decrement and
+branch'' instructions on a count register instead of generating sequences
+of instructions that decrement a register, compare it against zero, and
+then branch based upon the result. This option is only meaningful on
+architectures that support such instructions, which include x86, PowerPC,
+IA-64 and S/390. Note that the @option{-fno-branch-count-reg} option
+doesn't remove the decrement and branch instructions from the generated
+instruction stream introduced by other optimization passes.
-@end itemize
+Enabled by default at @option{-O1} and higher.
-With @option{-fprofile-arcs}, for each function of your program GCC
-creates a program flow graph, then finds a spanning tree for the graph.
-Only arcs that are not on the spanning tree have to be instrumented: the
-compiler adds code to count the number of times that these arcs are
-executed. When an arc is the only exit or only entrance to a block, the
-instrumentation code can be added to the block; otherwise, a new basic
-block must be created to hold the instrumentation code.
+The default is @option{-fbranch-count-reg}.
-@need 2000
-@item -ftest-coverage
-@opindex ftest-coverage
-Produce a notes file that the @command{gcov} code-coverage utility
-(@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to
-show program coverage. Each source file's note file is called
-@file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option
-above for a description of @var{auxname} and instructions on how to
-generate test coverage data. Coverage data matches the source files
-more closely if you do not optimize.
-
-@item -fdbg-cnt-list
-@opindex fdbg-cnt-list
-Print the name and the counter upper bound for all debug counters.
+@item -fno-function-cse
+@opindex fno-function-cse
+Do not put function addresses in registers; make each instruction that
+calls a constant function contain the function's address explicitly.
+This option results in less efficient code, but some strange hacks
+that alter the assembler output may be confused by the optimizations
+performed when this option is not used.
-@item -fdbg-cnt=@var{counter-value-list}
-@opindex fdbg-cnt
-Set the internal debug counter upper bound. @var{counter-value-list}
-is a comma-separated list of @var{name}:@var{value} pairs
-which sets the upper bound of each debug counter @var{name} to @var{value}.
-All debug counters have the initial upper bound of @code{UINT_MAX};
-thus @code{dbg_cnt} returns true always unless the upper bound
-is set by this option.
-For example, with @option{-fdbg-cnt=dce:10,tail_call:0},
-@code{dbg_cnt(dce)} returns true only for first 10 invocations.
+The default is @option{-ffunction-cse}
-@item -fenable-@var{kind}-@var{pass}
-@itemx -fdisable-@var{kind}-@var{pass}=@var{range-list}
-@opindex fdisable-
-@opindex fenable-
+@item -fno-zero-initialized-in-bss
+@opindex fno-zero-initialized-in-bss
+If the target supports a BSS section, GCC by default puts variables that
+are initialized to zero into BSS@. This can save space in the resulting
+code.
-This is a set of options that are used to explicitly disable/enable
-optimization passes. These options are intended for use for debugging GCC.
-Compiler users should use regular options for enabling/disabling
-passes instead.
+This option turns off this behavior because some programs explicitly
+rely on variables going to the data section---e.g., so that the
+resulting executable can find the beginning of that section and/or make
+assumptions based on that.
-@table @gcctabopt
+The default is @option{-fzero-initialized-in-bss}.
-@item -fdisable-ipa-@var{pass}
-Disable IPA pass @var{pass}. @var{pass} is the pass name. If the same pass is
-statically invoked in the compiler multiple times, the pass name should be
-appended with a sequential number starting from 1.
+@item -fthread-jumps
+@opindex fthread-jumps
+Perform optimizations that check to see if a jump branches to a
+location where another comparison subsumed by the first is found. If
+so, the first branch is redirected to either the destination of the
+second branch or a point immediately following it, depending on whether
+the condition is known to be true or false.
-@item -fdisable-rtl-@var{pass}
-@itemx -fdisable-rtl-@var{pass}=@var{range-list}
-Disable RTL pass @var{pass}. @var{pass} is the pass name. If the same pass is
-statically invoked in the compiler multiple times, the pass name should be
-appended with a sequential number starting from 1. @var{range-list} is a
-comma-separated list of function ranges or assembler names. Each range is a number
-pair separated by a colon. The range is inclusive in both ends. If the range
-is trivial, the number pair can be simplified as a single number. If the
-function's call graph node's @var{uid} falls within one of the specified ranges,
-the @var{pass} is disabled for that function. The @var{uid} is shown in the
-function header of a dump file, and the pass names can be dumped by using
-option @option{-fdump-passes}.
+Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
-@item -fdisable-tree-@var{pass}
-@itemx -fdisable-tree-@var{pass}=@var{range-list}
-Disable tree pass @var{pass}. See @option{-fdisable-rtl} for the description of
-option arguments.
+@item -fsplit-wide-types
+@opindex fsplit-wide-types
+When using a type that occupies multiple registers, such as @code{long
+long} on a 32-bit system, split the registers apart and allocate them
+independently. This normally generates better code for those types,
+but may make debugging more difficult.
-@item -fenable-ipa-@var{pass}
-Enable IPA pass @var{pass}. @var{pass} is the pass name. If the same pass is
-statically invoked in the compiler multiple times, the pass name should be
-appended with a sequential number starting from 1.
+Enabled at levels @option{-O}, @option{-O2}, @option{-O3},
+@option{-Os}.
-@item -fenable-rtl-@var{pass}
-@itemx -fenable-rtl-@var{pass}=@var{range-list}
-Enable RTL pass @var{pass}. See @option{-fdisable-rtl} for option argument
-description and examples.
+@item -fcse-follow-jumps
+@opindex fcse-follow-jumps
+In common subexpression elimination (CSE), scan through jump instructions
+when the target of the jump is not reached by any other path. For
+example, when CSE encounters an @code{if} statement with an
+@code{else} clause, CSE follows the jump when the condition
+tested is false.
-@item -fenable-tree-@var{pass}
-@itemx -fenable-tree-@var{pass}=@var{range-list}
-Enable tree pass @var{pass}. See @option{-fdisable-rtl} for the description
-of option arguments.
+Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
-@end table
+@item -fcse-skip-blocks
+@opindex fcse-skip-blocks
+This is similar to @option{-fcse-follow-jumps}, but causes CSE to
+follow jumps that conditionally skip over blocks. When CSE
+encounters a simple @code{if} statement with no else clause,
+@option{-fcse-skip-blocks} causes CSE to follow the jump around the
+body of the @code{if}.
-Here are some examples showing uses of these options.
+Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
-@smallexample
+@item -frerun-cse-after-loop
+@opindex frerun-cse-after-loop
+Re-run common subexpression elimination after loop optimizations are
+performed.
-# disable ccp1 for all functions
- -fdisable-tree-ccp1
-# disable complete unroll for function whose cgraph node uid is 1
- -fenable-tree-cunroll=1
-# disable gcse2 for functions at the following ranges [1,1],
-# [300,400], and [400,1000]
-# disable gcse2 for functions foo and foo2
- -fdisable-rtl-gcse2=foo,foo2
-# disable early inlining
- -fdisable-tree-einline
-# disable ipa inlining
- -fdisable-ipa-inline
-# enable tree full unroll
- -fenable-tree-unroll
+Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
-@end smallexample
+@item -fgcse
+@opindex fgcse
+Perform a global common subexpression elimination pass.
+This pass also performs global constant and copy propagation.
-@item -d@var{letters}
-@itemx -fdump-rtl-@var{pass}
-@itemx -fdump-rtl-@var{pass}=@var{filename}
-@opindex d
-@opindex fdump-rtl-@var{pass}
-Says to make debugging dumps during compilation at times specified by
-@var{letters}. This is used for debugging the RTL-based passes of the
-compiler. The file names for most of the dumps are made by appending
-a pass number and a word to the @var{dumpname}, and the files are
-created in the directory of the output file. In case of
-@option{=@var{filename}} option, the dump is output on the given file
-instead of the pass numbered dump files. Note that the pass number is
-computed statically as passes get registered into the pass manager.
-Thus the numbering is not related to the dynamic order of execution of
-passes. In particular, a pass installed by a plugin could have a
-number over 200 even if it executed quite early. @var{dumpname} is
-generated from the name of the output file, if explicitly specified
-and it is not an executable, otherwise it is the basename of the
-source file. These switches may have different effects when
-@option{-E} is used for preprocessing.
+@emph{Note:} When compiling a program using computed gotos, a GCC
+extension, you may get better run-time performance if you disable
+the global common subexpression elimination pass by adding
+@option{-fno-gcse} to the command line.
-Debug dumps can be enabled with a @option{-fdump-rtl} switch or some
-@option{-d} option @var{letters}. Here are the possible
-letters for use in @var{pass} and @var{letters}, and their meanings:
+Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
-@table @gcctabopt
+@item -fgcse-lm
+@opindex fgcse-lm
+When @option{-fgcse-lm} is enabled, global common subexpression elimination
+attempts to move loads that are only killed by stores into themselves. This
+allows a loop containing a load/store sequence to be changed to a load outside
+the loop, and a copy/store within the loop.
-@item -fdump-rtl-alignments
-@opindex fdump-rtl-alignments
-Dump after branch alignments have been computed.
+Enabled by default when @option{-fgcse} is enabled.
-@item -fdump-rtl-asmcons
-@opindex fdump-rtl-asmcons
-Dump after fixing rtl statements that have unsatisfied in/out constraints.
+@item -fgcse-sm
+@opindex fgcse-sm
+When @option{-fgcse-sm} is enabled, a store motion pass is run after
+global common subexpression elimination. This pass attempts to move
+stores out of loops. When used in conjunction with @option{-fgcse-lm},
+loops containing a load/store sequence can be changed to a load before
+the loop and a store after the loop.
-@item -fdump-rtl-auto_inc_dec
-@opindex fdump-rtl-auto_inc_dec
-Dump after auto-inc-dec discovery. This pass is only run on
-architectures that have auto inc or auto dec instructions.
+Not enabled at any optimization level.
-@item -fdump-rtl-barriers
-@opindex fdump-rtl-barriers
-Dump after cleaning up the barrier instructions.
+@item -fgcse-las
+@opindex fgcse-las
+When @option{-fgcse-las} is enabled, the global common subexpression
+elimination pass eliminates redundant loads that come after stores to the
+same memory location (both partial and full redundancies).
-@item -fdump-rtl-bbpart
-@opindex fdump-rtl-bbpart
-Dump after partitioning hot and cold basic blocks.
+Not enabled at any optimization level.
-@item -fdump-rtl-bbro
-@opindex fdump-rtl-bbro
-Dump after block reordering.
+@item -fgcse-after-reload
+@opindex fgcse-after-reload
+When @option{-fgcse-after-reload} is enabled, a redundant load elimination
+pass is performed after reload. The purpose of this pass is to clean up
+redundant spilling.
-@item -fdump-rtl-btl1
-@itemx -fdump-rtl-btl2
-@opindex fdump-rtl-btl2
-@opindex fdump-rtl-btl2
-@option{-fdump-rtl-btl1} and @option{-fdump-rtl-btl2} enable dumping
-after the two branch
-target load optimization passes.
+@item -faggressive-loop-optimizations
+@opindex faggressive-loop-optimizations
+This option tells the loop optimizer to use language constraints to
+derive bounds for the number of iterations of a loop. This assumes that
+loop code does not invoke undefined behavior by for example causing signed
+integer overflows or out-of-bound array accesses. The bounds for the
+number of iterations of a loop are used to guide loop unrolling and peeling
+and loop exit test optimizations.
+This option is enabled by default.
-@item -fdump-rtl-bypass
-@opindex fdump-rtl-bypass
-Dump after jump bypassing and control flow optimizations.
+@item -funsafe-loop-optimizations
+@opindex funsafe-loop-optimizations
+This option tells the loop optimizer to assume that loop indices do not
+overflow, and that loops with nontrivial exit condition are not
+infinite. This enables a wider range of loop optimizations even if
+the loop optimizer itself cannot prove that these assumptions are valid.
+If you use @option{-Wunsafe-loop-optimizations}, the compiler warns you
+if it finds this kind of loop.
-@item -fdump-rtl-combine
-@opindex fdump-rtl-combine
-Dump after the RTL instruction combination pass.
+@item -funconstrained-commons
+@opindex funconstrained-commons
+This option tells the compiler that variables declared in common blocks
+(e.g. Fortran) may later be overridden with longer trailing arrays. This
+prevents certain optimizations that depend on knowing the array bounds.
-@item -fdump-rtl-compgotos
-@opindex fdump-rtl-compgotos
-Dump after duplicating the computed gotos.
+@item -fcrossjumping
+@opindex fcrossjumping
+Perform cross-jumping transformation.
+This transformation unifies equivalent code and saves code size. The
+resulting code may or may not perform better than without cross-jumping.
-@item -fdump-rtl-ce1
-@itemx -fdump-rtl-ce2
-@itemx -fdump-rtl-ce3
-@opindex fdump-rtl-ce1
-@opindex fdump-rtl-ce2
-@opindex fdump-rtl-ce3
-@option{-fdump-rtl-ce1}, @option{-fdump-rtl-ce2}, and
-@option{-fdump-rtl-ce3} enable dumping after the three
-if conversion passes.
+Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
-@item -fdump-rtl-cprop_hardreg
-@opindex fdump-rtl-cprop_hardreg
-Dump after hard register copy propagation.
+@item -fauto-inc-dec
+@opindex fauto-inc-dec
+Combine increments or decrements of addresses with memory accesses.
+This pass is always skipped on architectures that do not have
+instructions to support this. Enabled by default at @option{-O} and
+higher on architectures that support this.
-@item -fdump-rtl-csa
-@opindex fdump-rtl-csa
-Dump after combining stack adjustments.
+@item -fdce
+@opindex fdce
+Perform dead code elimination (DCE) on RTL@.
+Enabled by default at @option{-O} and higher.
-@item -fdump-rtl-cse1
-@itemx -fdump-rtl-cse2
-@opindex fdump-rtl-cse1
-@opindex fdump-rtl-cse2
-@option{-fdump-rtl-cse1} and @option{-fdump-rtl-cse2} enable dumping after
-the two common subexpression elimination passes.
+@item -fdse
+@opindex fdse
+Perform dead store elimination (DSE) on RTL@.
+Enabled by default at @option{-O} and higher.
-@item -fdump-rtl-dce
-@opindex fdump-rtl-dce
-Dump after the standalone dead code elimination passes.
+@item -fif-conversion
+@opindex fif-conversion
+Attempt to transform conditional jumps into branch-less equivalents. This
+includes use of conditional moves, min, max, set flags and abs instructions, and
+some tricks doable by standard arithmetics. The use of conditional execution
+on chips where it is available is controlled by @option{-fif-conversion2}.
-@item -fdump-rtl-dbr
-@opindex fdump-rtl-dbr
-Dump after delayed branch scheduling.
+Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
-@item -fdump-rtl-dce1
-@itemx -fdump-rtl-dce2
-@opindex fdump-rtl-dce1
-@opindex fdump-rtl-dce2
-@option{-fdump-rtl-dce1} and @option{-fdump-rtl-dce2} enable dumping after
-the two dead store elimination passes.
+@item -fif-conversion2
+@opindex fif-conversion2
+Use conditional execution (where available) to transform conditional jumps into
+branch-less equivalents.
-@item -fdump-rtl-eh
-@opindex fdump-rtl-eh
-Dump after finalization of EH handling code.
+Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
-@item -fdump-rtl-eh_ranges
-@opindex fdump-rtl-eh_ranges
-Dump after conversion of EH handling range regions.
+@item -fdeclone-ctor-dtor
+@opindex fdeclone-ctor-dtor
+The C++ ABI requires multiple entry points for constructors and
+destructors: one for a base subobject, one for a complete object, and
+one for a virtual destructor that calls operator delete afterwards.
+For a hierarchy with virtual bases, the base and complete variants are
+clones, which means two copies of the function. With this option, the
+base and complete variants are changed to be thunks that call a common
+implementation.
-@item -fdump-rtl-expand
-@opindex fdump-rtl-expand
-Dump after RTL generation.
+Enabled by @option{-Os}.
-@item -fdump-rtl-fwprop1
-@itemx -fdump-rtl-fwprop2
-@opindex fdump-rtl-fwprop1
-@opindex fdump-rtl-fwprop2
-@option{-fdump-rtl-fwprop1} and @option{-fdump-rtl-fwprop2} enable
-dumping after the two forward propagation passes.
+@item -fdelete-null-pointer-checks
+@opindex fdelete-null-pointer-checks
+Assume that programs cannot safely dereference null pointers, and that
+no code or data element resides at address zero.
+This option enables simple constant
+folding optimizations at all optimization levels. In addition, other
+optimization passes in GCC use this flag to control global dataflow
+analyses that eliminate useless checks for null pointers; these assume
+that a memory access to address zero always results in a trap, so
+that if a pointer is checked after it has already been dereferenced,
+it cannot be null.
-@item -fdump-rtl-gcse1
-@itemx -fdump-rtl-gcse2
-@opindex fdump-rtl-gcse1
-@opindex fdump-rtl-gcse2
-@option{-fdump-rtl-gcse1} and @option{-fdump-rtl-gcse2} enable dumping
-after global common subexpression elimination.
+Note however that in some environments this assumption is not true.
+Use @option{-fno-delete-null-pointer-checks} to disable this optimization
+for programs that depend on that behavior.
-@item -fdump-rtl-init-regs
-@opindex fdump-rtl-init-regs
-Dump after the initialization of the registers.
+This option is enabled by default on most targets. On Nios II ELF, it
+defaults to off. On AVR and CR16, this option is completely disabled.
-@item -fdump-rtl-initvals
-@opindex fdump-rtl-initvals
-Dump after the computation of the initial value sets.
+Passes that use the dataflow information
+are enabled independently at different optimization levels.
-@item -fdump-rtl-into_cfglayout
-@opindex fdump-rtl-into_cfglayout
-Dump after converting to cfglayout mode.
+@item -fdevirtualize
+@opindex fdevirtualize
+Attempt to convert calls to virtual functions to direct calls. This
+is done both within a procedure and interprocedurally as part of
+indirect inlining (@option{-findirect-inlining}) and interprocedural constant
+propagation (@option{-fipa-cp}).
+Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
-@item -fdump-rtl-ira
-@opindex fdump-rtl-ira
-Dump after iterated register allocation.
+@item -fdevirtualize-speculatively
+@opindex fdevirtualize-speculatively
+Attempt to convert calls to virtual functions to speculative direct calls.
+Based on the analysis of the type inheritance graph, determine for a given call
+the set of likely targets. If the set is small, preferably of size 1, change
+the call into a conditional deciding between direct and indirect calls. The
+speculative calls enable more optimizations, such as inlining. When they seem
+useless after further optimization, they are converted back into original form.
-@item -fdump-rtl-jump
-@opindex fdump-rtl-jump
-Dump after the second jump optimization.
+@item -fdevirtualize-at-ltrans
+@opindex fdevirtualize-at-ltrans
+Stream extra information needed for aggressive devirtualization when running
+the link-time optimizer in local transformation mode.
+This option enables more devirtualization but
+significantly increases the size of streamed data. For this reason it is
+disabled by default.
-@item -fdump-rtl-loop2
-@opindex fdump-rtl-loop2
-@option{-fdump-rtl-loop2} enables dumping after the rtl
-loop optimization passes.
+@item -fexpensive-optimizations
+@opindex fexpensive-optimizations
+Perform a number of minor optimizations that are relatively expensive.
-@item -fdump-rtl-mach
-@opindex fdump-rtl-mach
-Dump after performing the machine dependent reorganization pass, if that
-pass exists.
+Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
-@item -fdump-rtl-mode_sw
-@opindex fdump-rtl-mode_sw
-Dump after removing redundant mode switches.
+@item -free
+@opindex free
+Attempt to remove redundant extension instructions. This is especially
+helpful for the x86-64 architecture, which implicitly zero-extends in 64-bit
+registers after writing to their lower 32-bit half.
-@item -fdump-rtl-rnreg
-@opindex fdump-rtl-rnreg
-Dump after register renumbering.
+Enabled for Alpha, AArch64 and x86 at levels @option{-O2},
+@option{-O3}, @option{-Os}.
-@item -fdump-rtl-outof_cfglayout
-@opindex fdump-rtl-outof_cfglayout
-Dump after converting from cfglayout mode.
+@item -fno-lifetime-dse
+@opindex fno-lifetime-dse
+In C++ the value of an object is only affected by changes within its
+lifetime: when the constructor begins, the object has an indeterminate
+value, and any changes during the lifetime of the object are dead when
+the object is destroyed. Normally dead store elimination will take
+advantage of this; if your code relies on the value of the object
+storage persisting beyond the lifetime of the object, you can use this
+flag to disable this optimization. To preserve stores before the
+constructor starts (e.g. because your operator new clears the object
+storage) but still treat the object as dead after the destructor you,
+can use @option{-flifetime-dse=1}. The default behavior can be
+explicitly selected with @option{-flifetime-dse=2}.
+@option{-flifetime-dse=0} is equivalent to @option{-fno-lifetime-dse}.
-@item -fdump-rtl-peephole2
-@opindex fdump-rtl-peephole2
-Dump after the peephole pass.
+@item -flive-range-shrinkage
+@opindex flive-range-shrinkage
+Attempt to decrease register pressure through register live range
+shrinkage. This is helpful for fast processors with small or moderate
+size register sets.
-@item -fdump-rtl-postreload
-@opindex fdump-rtl-postreload
-Dump after post-reload optimizations.
+@item -fira-algorithm=@var{algorithm}
+@opindex fira-algorithm
+Use the specified coloring algorithm for the integrated register
+allocator. The @var{algorithm} argument can be @samp{priority}, which
+specifies Chow's priority coloring, or @samp{CB}, which specifies
+Chaitin-Briggs coloring. Chaitin-Briggs coloring is not implemented
+for all architectures, but for those targets that do support it, it is
+the default because it generates better code.
-@item -fdump-rtl-pro_and_epilogue
-@opindex fdump-rtl-pro_and_epilogue
-Dump after generating the function prologues and epilogues.
+@item -fira-region=@var{region}
+@opindex fira-region
+Use specified regions for the integrated register allocator. The
+@var{region} argument should be one of the following:
-@item -fdump-rtl-sched1
-@itemx -fdump-rtl-sched2
-@opindex fdump-rtl-sched1
-@opindex fdump-rtl-sched2
-@option{-fdump-rtl-sched1} and @option{-fdump-rtl-sched2} enable dumping
-after the basic block scheduling passes.
+@table @samp
-@item -fdump-rtl-ree
-@opindex fdump-rtl-ree
-Dump after sign/zero extension elimination.
+@item all
+Use all loops as register allocation regions.
+This can give the best results for machines with a small and/or
+irregular register set.
-@item -fdump-rtl-seqabstr
-@opindex fdump-rtl-seqabstr
-Dump after common sequence discovery.
+@item mixed
+Use all loops except for loops with small register pressure
+as the regions. This value usually gives
+the best results in most cases and for most architectures,
+and is enabled by default when compiling with optimization for speed
+(@option{-O}, @option{-O2}, @dots{}).
-@item -fdump-rtl-shorten
-@opindex fdump-rtl-shorten
-Dump after shortening branches.
+@item one
+Use all functions as a single region.
+This typically results in the smallest code size, and is enabled by default for
+@option{-Os} or @option{-O0}.
-@item -fdump-rtl-sibling
-@opindex fdump-rtl-sibling
-Dump after sibling call optimizations.
+@end table
-@item -fdump-rtl-split1
-@itemx -fdump-rtl-split2
-@itemx -fdump-rtl-split3
-@itemx -fdump-rtl-split4
-@itemx -fdump-rtl-split5
-@opindex fdump-rtl-split1
-@opindex fdump-rtl-split2
-@opindex fdump-rtl-split3
-@opindex fdump-rtl-split4
-@opindex fdump-rtl-split5
-These options enable dumping after five rounds of
-instruction splitting.
+@item -fira-hoist-pressure
+@opindex fira-hoist-pressure
+Use IRA to evaluate register pressure in the code hoisting pass for
+decisions to hoist expressions. This option usually results in smaller
+code, but it can slow the compiler down.
-@item -fdump-rtl-sms
-@opindex fdump-rtl-sms
-Dump after modulo scheduling. This pass is only run on some
-architectures.
+This option is enabled at level @option{-Os} for all targets.
-@item -fdump-rtl-stack
-@opindex fdump-rtl-stack
-Dump after conversion from GCC's ``flat register file'' registers to the
-x87's stack-like registers. This pass is only run on x86 variants.
+@item -fira-loop-pressure
+@opindex fira-loop-pressure
+Use IRA to evaluate register pressure in loops for decisions to move
+loop invariants. This option usually results in generation
+of faster and smaller code on machines with large register files (>= 32
+registers), but it can slow the compiler down.
-@item -fdump-rtl-subreg1
-@itemx -fdump-rtl-subreg2
-@opindex fdump-rtl-subreg1
-@opindex fdump-rtl-subreg2
-@option{-fdump-rtl-subreg1} and @option{-fdump-rtl-subreg2} enable dumping after
-the two subreg expansion passes.
+This option is enabled at level @option{-O3} for some targets.
-@item -fdump-rtl-unshare
-@opindex fdump-rtl-unshare
-Dump after all rtl has been unshared.
+@item -fno-ira-share-save-slots
+@opindex fno-ira-share-save-slots
+Disable sharing of stack slots used for saving call-used hard
+registers living through a call. Each hard register gets a
+separate stack slot, and as a result function stack frames are
+larger.
-@item -fdump-rtl-vartrack
-@opindex fdump-rtl-vartrack
-Dump after variable tracking.
+@item -fno-ira-share-spill-slots
+@opindex fno-ira-share-spill-slots
+Disable sharing of stack slots allocated for pseudo-registers. Each
+pseudo-register that does not get a hard register gets a separate
+stack slot, and as a result function stack frames are larger.
-@item -fdump-rtl-vregs
-@opindex fdump-rtl-vregs
-Dump after converting virtual registers to hard registers.
+@item -flra-remat
+@opindex flra-remat
+Enable CFG-sensitive rematerialization in LRA. Instead of loading
+values of spilled pseudos, LRA tries to rematerialize (recalculate)
+values if it is profitable.
-@item -fdump-rtl-web
-@opindex fdump-rtl-web
-Dump after live range splitting.
+Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
-@item -fdump-rtl-regclass
-@itemx -fdump-rtl-subregs_of_mode_init
-@itemx -fdump-rtl-subregs_of_mode_finish
-@itemx -fdump-rtl-dfinit
-@itemx -fdump-rtl-dfinish
-@opindex fdump-rtl-regclass
-@opindex fdump-rtl-subregs_of_mode_init
-@opindex fdump-rtl-subregs_of_mode_finish
-@opindex fdump-rtl-dfinit
-@opindex fdump-rtl-dfinish
-These dumps are defined but always produce empty files.
+@item -fdelayed-branch
+@opindex fdelayed-branch
+If supported for the target machine, attempt to reorder instructions
+to exploit instruction slots available after delayed branch
+instructions.
-@item -da
-@itemx -fdump-rtl-all
-@opindex da
-@opindex fdump-rtl-all
-Produce all the dumps listed above.
+Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
-@item -dA
-@opindex dA
-Annotate the assembler output with miscellaneous debugging information.
+@item -fschedule-insns
+@opindex fschedule-insns
+If supported for the target machine, attempt to reorder instructions to
+eliminate execution stalls due to required data being unavailable. This
+helps machines that have slow floating point or memory load instructions
+by allowing other instructions to be issued until the result of the load
+or floating-point instruction is required.
-@item -dD
-@opindex dD
-Dump all macro definitions, at the end of preprocessing, in addition to
-normal output.
+Enabled at levels @option{-O2}, @option{-O3}.
-@item -dH
-@opindex dH
-Produce a core dump whenever an error occurs.
+@item -fschedule-insns2
+@opindex fschedule-insns2
+Similar to @option{-fschedule-insns}, but requests an additional pass of
+instruction scheduling after register allocation has been done. This is
+especially useful on machines with a relatively small number of
+registers and where memory load instructions take more than one cycle.
-@item -dp
-@opindex dp
-Annotate the assembler output with a comment indicating which
-pattern and alternative is used. The length of each instruction is
-also printed.
+Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
-@item -dP
-@opindex dP
-Dump the RTL in the assembler output as a comment before each instruction.
-Also turns on @option{-dp} annotation.
+@item -fno-sched-interblock
+@opindex fno-sched-interblock
+Don't schedule instructions across basic blocks. This is normally
+enabled by default when scheduling before register allocation, i.e.@:
+with @option{-fschedule-insns} or at @option{-O2} or higher.
-@item -dx
-@opindex dx
-Just generate RTL for a function instead of compiling it. Usually used
-with @option{-fdump-rtl-expand}.
-@end table
+@item -fno-sched-spec
+@opindex fno-sched-spec
+Don't allow speculative motion of non-load instructions. This is normally
+enabled by default when scheduling before register allocation, i.e.@:
+with @option{-fschedule-insns} or at @option{-O2} or higher.
-@item -fdump-noaddr
-@opindex fdump-noaddr
-When doing debugging dumps, suppress address output. This makes it more
-feasible to use diff on debugging dumps for compiler invocations with
-different compiler binaries and/or different
-text / bss / data / heap / stack / dso start locations.
+@item -fsched-pressure
+@opindex fsched-pressure
+Enable register pressure sensitive insn scheduling before register
+allocation. This only makes sense when scheduling before register
+allocation is enabled, i.e.@: with @option{-fschedule-insns} or at
+@option{-O2} or higher. Usage of this option can improve the
+generated code and decrease its size by preventing register pressure
+increase above the number of available hard registers and subsequent
+spills in register allocation.
-@item -freport-bug
-@opindex freport-bug
-Collect and dump debug information into temporary file if ICE in C/C++
-compiler occured.
+@item -fsched-spec-load
+@opindex fsched-spec-load
+Allow speculative motion of some load instructions. This only makes
+sense when scheduling before register allocation, i.e.@: with
+@option{-fschedule-insns} or at @option{-O2} or higher.
-@item -fdump-unnumbered
-@opindex fdump-unnumbered
-When doing debugging dumps, suppress instruction numbers and address output.
-This makes it more feasible to use diff on debugging dumps for compiler
-invocations with different options, in particular with and without
-@option{-g}.
+@item -fsched-spec-load-dangerous
+@opindex fsched-spec-load-dangerous
+Allow speculative motion of more load instructions. This only makes
+sense when scheduling before register allocation, i.e.@: with
+@option{-fschedule-insns} or at @option{-O2} or higher.
-@item -fdump-unnumbered-links
-@opindex fdump-unnumbered-links
-When doing debugging dumps (see @option{-d} option above), suppress
-instruction numbers for the links to the previous and next instructions
-in a sequence.
+@item -fsched-stalled-insns
+@itemx -fsched-stalled-insns=@var{n}
+@opindex fsched-stalled-insns
+Define how many insns (if any) can be moved prematurely from the queue
+of stalled insns into the ready list during the second scheduling pass.
+@option{-fno-sched-stalled-insns} means that no insns are moved
+prematurely, @option{-fsched-stalled-insns=0} means there is no limit
+on how many queued insns can be moved prematurely.
+@option{-fsched-stalled-insns} without a value is equivalent to
+@option{-fsched-stalled-insns=1}.
-@item -fdump-translation-unit @r{(C++ only)}
-@itemx -fdump-translation-unit-@var{options} @r{(C++ only)}
-@opindex fdump-translation-unit
-Dump a representation of the tree structure for the entire translation
-unit to a file. The file name is made by appending @file{.tu} to the
-source file name, and the file is created in the same directory as the
-output file. If the @samp{-@var{options}} form is used, @var{options}
-controls the details of the dump as described for the
-@option{-fdump-tree} options.
+@item -fsched-stalled-insns-dep
+@itemx -fsched-stalled-insns-dep=@var{n}
+@opindex fsched-stalled-insns-dep
+Define how many insn groups (cycles) are examined for a dependency
+on a stalled insn that is a candidate for premature removal from the queue
+of stalled insns. This has an effect only during the second scheduling pass,
+and only if @option{-fsched-stalled-insns} is used.
+@option{-fno-sched-stalled-insns-dep} is equivalent to
+@option{-fsched-stalled-insns-dep=0}.
+@option{-fsched-stalled-insns-dep} without a value is equivalent to
+@option{-fsched-stalled-insns-dep=1}.
-@item -fdump-class-hierarchy @r{(C++ only)}
-@itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
-@opindex fdump-class-hierarchy
-Dump a representation of each class's hierarchy and virtual function
-table layout to a file. The file name is made by appending
-@file{.class} to the source file name, and the file is created in the
-same directory as the output file. If the @samp{-@var{options}} form
-is used, @var{options} controls the details of the dump as described
-for the @option{-fdump-tree} options.
+@item -fsched2-use-superblocks
+@opindex fsched2-use-superblocks
+When scheduling after register allocation, use superblock scheduling.
+This allows motion across basic block boundaries,
+resulting in faster schedules. This option is experimental, as not all machine
+descriptions used by GCC model the CPU closely enough to avoid unreliable
+results from the algorithm.
-@item -fdump-ipa-@var{switch}
-@opindex fdump-ipa
-Control the dumping at various stages of inter-procedural analysis
-language tree to a file. The file name is generated by appending a
-switch specific suffix to the source file name, and the file is created
-in the same directory as the output file. The following dumps are
-possible:
+This only makes sense when scheduling after register allocation, i.e.@: with
+@option{-fschedule-insns2} or at @option{-O2} or higher.
-@table @samp
-@item all
-Enables all inter-procedural analysis dumps.
+@item -fsched-group-heuristic
+@opindex fsched-group-heuristic
+Enable the group heuristic in the scheduler. This heuristic favors
+the instruction that belongs to a schedule group. This is enabled
+by default when scheduling is enabled, i.e.@: with @option{-fschedule-insns}
+or @option{-fschedule-insns2} or at @option{-O2} or higher.
-@item cgraph
-Dumps information about call-graph optimization, unused function removal,
-and inlining decisions.
+@item -fsched-critical-path-heuristic
+@opindex fsched-critical-path-heuristic
+Enable the critical-path heuristic in the scheduler. This heuristic favors
+instructions on the critical path. This is enabled by default when
+scheduling is enabled, i.e.@: with @option{-fschedule-insns}
+or @option{-fschedule-insns2} or at @option{-O2} or higher.
-@item inline
-Dump after function inlining.
+@item -fsched-spec-insn-heuristic
+@opindex fsched-spec-insn-heuristic
+Enable the speculative instruction heuristic in the scheduler. This
+heuristic favors speculative instructions with greater dependency weakness.
+This is enabled by default when scheduling is enabled, i.e.@:
+with @option{-fschedule-insns} or @option{-fschedule-insns2}
+or at @option{-O2} or higher.
-@end table
+@item -fsched-rank-heuristic
+@opindex fsched-rank-heuristic
+Enable the rank heuristic in the scheduler. This heuristic favors
+the instruction belonging to a basic block with greater size or frequency.
+This is enabled by default when scheduling is enabled, i.e.@:
+with @option{-fschedule-insns} or @option{-fschedule-insns2} or
+at @option{-O2} or higher.
-@item -fdump-passes
-@opindex fdump-passes
-Dump the list of optimization passes that are turned on and off by
-the current command-line options.
+@item -fsched-last-insn-heuristic
+@opindex fsched-last-insn-heuristic
+Enable the last-instruction heuristic in the scheduler. This heuristic
+favors the instruction that is less dependent on the last instruction
+scheduled. This is enabled by default when scheduling is enabled,
+i.e.@: with @option{-fschedule-insns} or @option{-fschedule-insns2} or
+at @option{-O2} or higher.
-@item -fdump-statistics-@var{option}
-@opindex fdump-statistics
-Enable and control dumping of pass statistics in a separate file. The
-file name is generated by appending a suffix ending in
-@samp{.statistics} to the source file name, and the file is created in
-the same directory as the output file. If the @samp{-@var{option}}
-form is used, @samp{-stats} causes counters to be summed over the
-whole compilation unit while @samp{-details} dumps every event as
-the passes generate them. The default with no option is to sum
-counters for each function compiled.
-
-@item -fdump-tree-@var{switch}
-@itemx -fdump-tree-@var{switch}-@var{options}
-@itemx -fdump-tree-@var{switch}-@var{options}=@var{filename}
-@opindex fdump-tree
-Control the dumping at various stages of processing the intermediate
-language tree to a file. The file name is generated by appending a
-switch-specific suffix to the source file name, and the file is
-created in the same directory as the output file. In case of
-@option{=@var{filename}} option, the dump is output on the given file
-instead of the auto named dump files. If the @samp{-@var{options}}
-form is used, @var{options} is a list of @samp{-} separated options
-which control the details of the dump. Not all options are applicable
-to all dumps; those that are not meaningful are ignored. The
-following options are available
+@item -fsched-dep-count-heuristic
+@opindex fsched-dep-count-heuristic
+Enable the dependent-count heuristic in the scheduler. This heuristic
+favors the instruction that has more instructions depending on it.
+This is enabled by default when scheduling is enabled, i.e.@:
+with @option{-fschedule-insns} or @option{-fschedule-insns2} or
+at @option{-O2} or higher.
-@table @samp
-@item address
-Print the address of each node. Usually this is not meaningful as it
-changes according to the environment and source file. Its primary use
-is for tying up a dump file with a debug environment.
-@item asmname
-If @code{DECL_ASSEMBLER_NAME} has been set for a given decl, use that
-in the dump instead of @code{DECL_NAME}. Its primary use is ease of
-use working backward from mangled names in the assembly file.
-@item slim
-When dumping front-end intermediate representations, inhibit dumping
-of members of a scope or body of a function merely because that scope
-has been reached. Only dump such items when they are directly reachable
-by some other path.
+@item -freschedule-modulo-scheduled-loops
+@opindex freschedule-modulo-scheduled-loops
+Modulo scheduling is performed before traditional scheduling. If a loop
+is modulo scheduled, later scheduling passes may change its schedule.
+Use this option to control that behavior.
-When dumping pretty-printed trees, this option inhibits dumping the
-bodies of control structures.
+@item -fselective-scheduling
+@opindex fselective-scheduling
+Schedule instructions using selective scheduling algorithm. Selective
+scheduling runs instead of the first scheduler pass.
-When dumping RTL, print the RTL in slim (condensed) form instead of
-the default LISP-like representation.
-@item raw
-Print a raw representation of the tree. By default, trees are
-pretty-printed into a C-like representation.
-@item details
-Enable more detailed dumps (not honored by every dump option). Also
-include information from the optimization passes.
-@item stats
-Enable dumping various statistics about the pass (not honored by every dump
-option).
-@item blocks
-Enable showing basic block boundaries (disabled in raw dumps).
-@item graph
-For each of the other indicated dump files (@option{-fdump-rtl-@var{pass}}),
-dump a representation of the control flow graph suitable for viewing with
-GraphViz to @file{@var{file}.@var{passid}.@var{pass}.dot}. Each function in
-the file is pretty-printed as a subgraph, so that GraphViz can render them
-all in a single plot.
+@item -fselective-scheduling2
+@opindex fselective-scheduling2
+Schedule instructions using selective scheduling algorithm. Selective
+scheduling runs instead of the second scheduler pass.
-This option currently only works for RTL dumps, and the RTL is always
-dumped in slim form.
-@item vops
-Enable showing virtual operands for every statement.
-@item lineno
-Enable showing line numbers for statements.
-@item uid
-Enable showing the unique ID (@code{DECL_UID}) for each variable.
-@item verbose
-Enable showing the tree dump for each statement.
-@item eh
-Enable showing the EH region number holding each statement.
-@item scev
-Enable showing scalar evolution analysis details.
-@item optimized
-Enable showing optimization information (only available in certain
-passes).
-@item missed
-Enable showing missed optimization information (only available in certain
-passes).
-@item note
-Enable other detailed optimization information (only available in
-certain passes).
-@item =@var{filename}
-Instead of an auto named dump file, output into the given file
-name. The file names @file{stdout} and @file{stderr} are treated
-specially and are considered already open standard streams. For
-example,
+@item -fsel-sched-pipelining
+@opindex fsel-sched-pipelining
+Enable software pipelining of innermost loops during selective scheduling.
+This option has no effect unless one of @option{-fselective-scheduling} or
+@option{-fselective-scheduling2} is turned on.
-@smallexample
-gcc -O2 -ftree-vectorize -fdump-tree-vect-blocks=foo.dump
- -fdump-tree-pre=stderr file.c
-@end smallexample
+@item -fsel-sched-pipelining-outer-loops
+@opindex fsel-sched-pipelining-outer-loops
+When pipelining loops during selective scheduling, also pipeline outer loops.
+This option has no effect unless @option{-fsel-sched-pipelining} is turned on.
-outputs vectorizer dump into @file{foo.dump}, while the PRE dump is
-output on to @file{stderr}. If two conflicting dump filenames are
-given for the same pass, then the latter option overrides the earlier
-one.
+@item -fsemantic-interposition
+@opindex fsemantic-interposition
+Some object formats, like ELF, allow interposing of symbols by the
+dynamic linker.
+This means that for symbols exported from the DSO, the compiler cannot perform
+interprocedural propagation, inlining and other optimizations in anticipation
+that the function or variable in question may change. While this feature is
+useful, for example, to rewrite memory allocation functions by a debugging
+implementation, it is expensive in the terms of code quality.
+With @option{-fno-semantic-interposition} the compiler assumes that
+if interposition happens for functions the overwriting function will have
+precisely the same semantics (and side effects).
+Similarly if interposition happens
+for variables, the constructor of the variable will be the same. The flag
+has no effect for functions explicitly declared inline
+(where it is never allowed for interposition to change semantics)
+and for symbols explicitly declared weak.
-@item all
-Turn on all options, except @option{raw}, @option{slim}, @option{verbose}
-and @option{lineno}.
+@item -fshrink-wrap
+@opindex fshrink-wrap
+Emit function prologues only before parts of the function that need it,
+rather than at the top of the function. This flag is enabled by default at
+@option{-O} and higher.
-@item optall
-Turn on all optimization options, i.e., @option{optimized},
-@option{missed}, and @option{note}.
-@end table
+@item -fcaller-saves
+@opindex fcaller-saves
+Enable allocation of values to registers that are clobbered by
+function calls, by emitting extra instructions to save and restore the
+registers around such calls. Such allocation is done only when it
+seems to result in better code.
-The following tree dumps are possible:
-@table @samp
+This option is always enabled by default on certain machines, usually
+those which have no call-preserved registers to use instead.
-@item original
-@opindex fdump-tree-original
-Dump before any tree based optimization, to @file{@var{file}.original}.
+Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
-@item optimized
-@opindex fdump-tree-optimized
-Dump after all tree based optimization, to @file{@var{file}.optimized}.
+@item -fcombine-stack-adjustments
+@opindex fcombine-stack-adjustments
+Tracks stack adjustments (pushes and pops) and stack memory references
+and then tries to find ways to combine them.
-@item gimple
-@opindex fdump-tree-gimple
-Dump each function before and after the gimplification pass to a file. The
-file name is made by appending @file{.gimple} to the source file name.
+Enabled by default at @option{-O1} and higher.
-@item cfg
-@opindex fdump-tree-cfg
-Dump the control flow graph of each function to a file. The file name is
-made by appending @file{.cfg} to the source file name.
+@item -fipa-ra
+@opindex fipa-ra
+Use caller save registers for allocation if those registers are not used by
+any called function. In that case it is not necessary to save and restore
+them around calls. This is only possible if called functions are part of
+same compilation unit as current function and they are compiled before it.
-@item ch
-@opindex fdump-tree-ch
-Dump each function after copying loop headers. The file name is made by
-appending @file{.ch} to the source file name.
+Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
-@item ssa
-@opindex fdump-tree-ssa
-Dump SSA related information to a file. The file name is made by appending
-@file{.ssa} to the source file name.
+@item -fconserve-stack
+@opindex fconserve-stack
+Attempt to minimize stack usage. The compiler attempts to use less
+stack space, even if that makes the program slower. This option
+implies setting the @option{large-stack-frame} parameter to 100
+and the @option{large-stack-frame-growth} parameter to 400.
-@item alias
-@opindex fdump-tree-alias
-Dump aliasing information for each function. The file name is made by
-appending @file{.alias} to the source file name.
+@item -ftree-reassoc
+@opindex ftree-reassoc
+Perform reassociation on trees. This flag is enabled by default
+at @option{-O} and higher.
-@item ccp
-@opindex fdump-tree-ccp
-Dump each function after CCP@. The file name is made by appending
-@file{.ccp} to the source file name.
+@item -ftree-pre
+@opindex ftree-pre
+Perform partial redundancy elimination (PRE) on trees. This flag is
+enabled by default at @option{-O2} and @option{-O3}.
-@item storeccp
-@opindex fdump-tree-storeccp
-Dump each function after STORE-CCP@. The file name is made by appending
-@file{.storeccp} to the source file name.
+@item -ftree-partial-pre
+@opindex ftree-partial-pre
+Make partial redundancy elimination (PRE) more aggressive. This flag is
+enabled by default at @option{-O3}.
-@item pre
-@opindex fdump-tree-pre
-Dump trees after partial redundancy elimination. The file name is made
-by appending @file{.pre} to the source file name.
+@item -ftree-forwprop
+@opindex ftree-forwprop
+Perform forward propagation on trees. This flag is enabled by default
+at @option{-O} and higher.
-@item fre
-@opindex fdump-tree-fre
-Dump trees after full redundancy elimination. The file name is made
-by appending @file{.fre} to the source file name.
+@item -ftree-fre
+@opindex ftree-fre
+Perform full redundancy elimination (FRE) on trees. The difference
+between FRE and PRE is that FRE only considers expressions
+that are computed on all paths leading to the redundant computation.
+This analysis is faster than PRE, though it exposes fewer redundancies.
+This flag is enabled by default at @option{-O} and higher.
-@item copyprop
-@opindex fdump-tree-copyprop
-Dump trees after copy propagation. The file name is made
-by appending @file{.copyprop} to the source file name.
+@item -ftree-phiprop
+@opindex ftree-phiprop
+Perform hoisting of loads from conditional pointers on trees. This
+pass is enabled by default at @option{-O} and higher.
-@item store_copyprop
-@opindex fdump-tree-store_copyprop
-Dump trees after store copy-propagation. The file name is made
-by appending @file{.store_copyprop} to the source file name.
+@item -fhoist-adjacent-loads
+@opindex fhoist-adjacent-loads
+Speculatively hoist loads from both branches of an if-then-else if the
+loads are from adjacent locations in the same structure and the target
+architecture has a conditional move instruction. This flag is enabled
+by default at @option{-O2} and higher.
-@item dce
-@opindex fdump-tree-dce
-Dump each function after dead code elimination. The file name is made by
-appending @file{.dce} to the source file name.
+@item -ftree-copy-prop
+@opindex ftree-copy-prop
+Perform copy propagation on trees. This pass eliminates unnecessary
+copy operations. This flag is enabled by default at @option{-O} and
+higher.
-@item sra
-@opindex fdump-tree-sra
-Dump each function after performing scalar replacement of aggregates. The
-file name is made by appending @file{.sra} to the source file name.
+@item -fipa-pure-const
+@opindex fipa-pure-const
+Discover which functions are pure or constant.
+Enabled by default at @option{-O} and higher.
-@item sink
-@opindex fdump-tree-sink
-Dump each function after performing code sinking. The file name is made
-by appending @file{.sink} to the source file name.
+@item -fipa-reference
+@opindex fipa-reference
+Discover which static variables do not escape the
+compilation unit.
+Enabled by default at @option{-O} and higher.
-@item dom
-@opindex fdump-tree-dom
-Dump each function after applying dominator tree optimizations. The file
-name is made by appending @file{.dom} to the source file name.
+@item -fipa-pta
+@opindex fipa-pta
+Perform interprocedural pointer analysis and interprocedural modification
+and reference analysis. This option can cause excessive memory and
+compile-time usage on large compilation units. It is not enabled by
+default at any optimization level.
-@item dse
-@opindex fdump-tree-dse
-Dump each function after applying dead store elimination. The file
-name is made by appending @file{.dse} to the source file name.
+@item -fipa-profile
+@opindex fipa-profile
+Perform interprocedural profile propagation. The functions called only from
+cold functions are marked as cold. Also functions executed once (such as
+@code{cold}, @code{noreturn}, static constructors or destructors) are identified. Cold
+functions and loop less parts of functions executed once are then optimized for
+size.
+Enabled by default at @option{-O} and higher.
-@item phiopt
-@opindex fdump-tree-phiopt
-Dump each function after optimizing PHI nodes into straightline code. The file
-name is made by appending @file{.phiopt} to the source file name.
+@item -fipa-cp
+@opindex fipa-cp
+Perform interprocedural constant propagation.
+This optimization analyzes the program to determine when values passed
+to functions are constants and then optimizes accordingly.
+This optimization can substantially increase performance
+if the application has constants passed to functions.
+This flag is enabled by default at @option{-O2}, @option{-Os} and @option{-O3}.
-@item backprop
-@opindex fdump-tree-backprop
-Dump each function after back-propagating use information up the definition
-chain. The file name is made by appending @file{.backprop} to the
-source file name.
+@item -fipa-cp-clone
+@opindex fipa-cp-clone
+Perform function cloning to make interprocedural constant propagation stronger.
+When enabled, interprocedural constant propagation performs function cloning
+when externally visible function can be called with constant arguments.
+Because this optimization can create multiple copies of functions,
+it may significantly increase code size
+(see @option{--param ipcp-unit-growth=@var{value}}).
+This flag is enabled by default at @option{-O3}.
-@item forwprop
-@opindex fdump-tree-forwprop
-Dump each function after forward propagating single use variables. The file
-name is made by appending @file{.forwprop} to the source file name.
+@item -fipa-cp-alignment
+@opindex -fipa-cp-alignment
+When enabled, this optimization propagates alignment of function
+parameters to support better vectorization and string operations.
-@item nrv
-@opindex fdump-tree-nrv
-Dump each function after applying the named return value optimization on
-generic trees. The file name is made by appending @file{.nrv} to the source
-file name.
+This flag is enabled by default at @option{-O2} and @option{-Os}. It
+requires that @option{-fipa-cp} is enabled.
-@item vect
-@opindex fdump-tree-vect
-Dump each function after applying vectorization of loops. The file name is
-made by appending @file{.vect} to the source file name.
+@item -fipa-icf
+@opindex fipa-icf
+Perform Identical Code Folding for functions and read-only variables.
+The optimization reduces code size and may disturb unwind stacks by replacing
+a function by equivalent one with a different name. The optimization works
+more effectively with link time optimization enabled.
-@item slp
-@opindex fdump-tree-slp
-Dump each function after applying vectorization of basic blocks. The file name
-is made by appending @file{.slp} to the source file name.
+Nevertheless the behavior is similar to Gold Linker ICF optimization, GCC ICF
+works on different levels and thus the optimizations are not same - there are
+equivalences that are found only by GCC and equivalences found only by Gold.
-@item vrp
-@opindex fdump-tree-vrp
-Dump each function after Value Range Propagation (VRP). The file name
-is made by appending @file{.vrp} to the source file name.
+This flag is enabled by default at @option{-O2} and @option{-Os}.
-@item oaccdevlow
-@opindex fdump-tree-oaccdevlow
-Dump each function after applying device-specific OpenACC transformations.
-The file name is made by appending @file{.oaccdevlow} to the source file name.
+@item -fisolate-erroneous-paths-dereference
+@opindex fisolate-erroneous-paths-dereference
+Detect paths that trigger erroneous or undefined behavior due to
+dereferencing a null pointer. Isolate those paths from the main control
+flow and turn the statement with erroneous or undefined behavior into a trap.
+This flag is enabled by default at @option{-O2} and higher and depends on
+@option{-fdelete-null-pointer-checks} also being enabled.
-@item all
-@opindex fdump-tree-all
-Enable all the available tree dumps with the flags provided in this option.
-@end table
+@item -fisolate-erroneous-paths-attribute
+@opindex fisolate-erroneous-paths-attribute
+Detect paths that trigger erroneous or undefined behavior due a null value
+being used in a way forbidden by a @code{returns_nonnull} or @code{nonnull}
+attribute. Isolate those paths from the main control flow and turn the
+statement with erroneous or undefined behavior into a trap. This is not
+currently enabled, but may be enabled by @option{-O2} in the future.
-@item -fopt-info
-@itemx -fopt-info-@var{options}
-@itemx -fopt-info-@var{options}=@var{filename}
-@opindex fopt-info
-Controls optimization dumps from various optimization passes. If the
-@samp{-@var{options}} form is used, @var{options} is a list of
-@samp{-} separated option keywords to select the dump details and
-optimizations.
+@item -ftree-sink
+@opindex ftree-sink
+Perform forward store motion on trees. This flag is
+enabled by default at @option{-O} and higher.
-The @var{options} can be divided into two groups: options describing the
-verbosity of the dump, and options describing which optimizations
-should be included. The options from both the groups can be freely
-mixed as they are non-overlapping. However, in case of any conflicts,
-the later options override the earlier options on the command
-line.
+@item -ftree-bit-ccp
+@opindex ftree-bit-ccp
+Perform sparse conditional bit constant propagation on trees and propagate
+pointer alignment information.
+This pass only operates on local scalar variables and is enabled by default
+at @option{-O} and higher. It requires that @option{-ftree-ccp} is enabled.
-The following options control the dump verbosity:
+@item -ftree-ccp
+@opindex ftree-ccp
+Perform sparse conditional constant propagation (CCP) on trees. This
+pass only operates on local scalar variables and is enabled by default
+at @option{-O} and higher.
-@table @samp
-@item optimized
-Print information when an optimization is successfully applied. It is
-up to a pass to decide which information is relevant. For example, the
-vectorizer passes print the source location of loops which are
-successfully vectorized.
-@item missed
-Print information about missed optimizations. Individual passes
-control which information to include in the output.
-@item note
-Print verbose information about optimizations, such as certain
-transformations, more detailed messages about decisions etc.
-@item all
-Print detailed optimization information. This includes
-@samp{optimized}, @samp{missed}, and @samp{note}.
-@end table
+@item -fssa-backprop
+@opindex fssa-backprop
+Propagate information about uses of a value up the definition chain
+in order to simplify the definitions. For example, this pass strips
+sign operations if the sign of a value never matters. The flag is
+enabled by default at @option{-O} and higher.
-One or more of the following option keywords can be used to describe a
-group of optimizations:
+@item -fssa-phiopt
+@opindex fssa-phiopt
+Perform pattern matching on SSA PHI nodes to optimize conditional
+code. This pass is enabled by default at @option{-O} and higher.
-@table @samp
-@item ipa
-Enable dumps from all interprocedural optimizations.
-@item loop
-Enable dumps from all loop optimizations.
-@item inline
-Enable dumps from all inlining optimizations.
-@item vec
-Enable dumps from all vectorization optimizations.
-@item optall
-Enable dumps from all optimizations. This is a superset of
-the optimization groups listed above.
-@end table
+@item -ftree-switch-conversion
+@opindex ftree-switch-conversion
+Perform conversion of simple initializations in a switch to
+initializations from a scalar array. This flag is enabled by default
+at @option{-O2} and higher.
-If @var{options} is
-omitted, it defaults to @samp{optimized-optall}, which means to dump all
-info about successful optimizations from all the passes.
+@item -ftree-tail-merge
+@opindex ftree-tail-merge
+Look for identical code sequences. When found, replace one with a jump to the
+other. This optimization is known as tail merging or cross jumping. This flag
+is enabled by default at @option{-O2} and higher. The compilation time
+in this pass can
+be limited using @option{max-tail-merge-comparisons} parameter and
+@option{max-tail-merge-iterations} parameter.
-If the @var{filename} is provided, then the dumps from all the
-applicable optimizations are concatenated into the @var{filename}.
-Otherwise the dump is output onto @file{stderr}. Though multiple
-@option{-fopt-info} options are accepted, only one of them can include
-a @var{filename}. If other filenames are provided then all but the
-first such option are ignored.
+@item -ftree-dce
+@opindex ftree-dce
+Perform dead code elimination (DCE) on trees. This flag is enabled by
+default at @option{-O} and higher.
-Note that the output @var{filename} is overwritten
-in case of multiple translation units. If a combined output from
-multiple translation units is desired, @file{stderr} should be used
-instead.
+@item -ftree-builtin-call-dce
+@opindex ftree-builtin-call-dce
+Perform conditional dead code elimination (DCE) for calls to built-in functions
+that may set @code{errno} but are otherwise side-effect free. This flag is
+enabled by default at @option{-O2} and higher if @option{-Os} is not also
+specified.
-In the following example, the optimization info is output to
-@file{stderr}:
+@item -ftree-dominator-opts
+@opindex ftree-dominator-opts
+Perform a variety of simple scalar cleanups (constant/copy
+propagation, redundancy elimination, range propagation and expression
+simplification) based on a dominator tree traversal. This also
+performs jump threading (to reduce jumps to jumps). This flag is
+enabled by default at @option{-O} and higher.
-@smallexample
-gcc -O3 -fopt-info
-@end smallexample
+@item -ftree-dse
+@opindex ftree-dse
+Perform dead store elimination (DSE) on trees. A dead store is a store into
+a memory location that is later overwritten by another store without
+any intervening loads. In this case the earlier store can be deleted. This
+flag is enabled by default at @option{-O} and higher.
-This example:
-@smallexample
-gcc -O3 -fopt-info-missed=missed.all
-@end smallexample
+@item -ftree-ch
+@opindex ftree-ch
+Perform loop header copying on trees. This is beneficial since it increases
+effectiveness of code motion optimizations. It also saves one jump. This flag
+is enabled by default at @option{-O} and higher. It is not enabled
+for @option{-Os}, since it usually increases code size.
-@noindent
-outputs missed optimization report from all the passes into
-@file{missed.all}, and this one:
+@item -ftree-loop-optimize
+@opindex ftree-loop-optimize
+Perform loop optimizations on trees. This flag is enabled by default
+at @option{-O} and higher.
-@smallexample
-gcc -O2 -ftree-vectorize -fopt-info-vec-missed
-@end smallexample
+@item -ftree-loop-linear
+@itemx -floop-interchange
+@itemx -floop-strip-mine
+@itemx -floop-block
+@itemx -floop-unroll-and-jam
+@opindex ftree-loop-linear
+@opindex floop-interchange
+@opindex floop-strip-mine
+@opindex floop-block
+@opindex floop-unroll-and-jam
+Perform loop nest optimizations. Same as
+@option{-floop-nest-optimize}. To use this code transformation, GCC has
+to be configured with @option{--with-isl} to enable the Graphite loop
+transformation infrastructure.
-@noindent
-prints information about missed optimization opportunities from
-vectorization passes on @file{stderr}.
-Note that @option{-fopt-info-vec-missed} is equivalent to
-@option{-fopt-info-missed-vec}.
+@item -fgraphite-identity
+@opindex fgraphite-identity
+Enable the identity transformation for graphite. For every SCoP we generate
+the polyhedral representation and transform it back to gimple. Using
+@option{-fgraphite-identity} we can check the costs or benefits of the
+GIMPLE -> GRAPHITE -> GIMPLE transformation. Some minimal optimizations
+are also performed by the code generator isl, like index splitting and
+dead code elimination in loops.
-As another example,
-@smallexample
-gcc -O3 -fopt-info-inline-optimized-missed=inline.txt
-@end smallexample
+@item -floop-nest-optimize
+@opindex floop-nest-optimize
+Enable the isl based loop nest optimizer. This is a generic loop nest
+optimizer based on the Pluto optimization algorithms. It calculates a loop
+structure optimized for data-locality and parallelism. This option
+is experimental.
-@noindent
-outputs information about missed optimizations as well as
-optimized locations from all the inlining passes into
-@file{inline.txt}.
+@item -floop-parallelize-all
+@opindex floop-parallelize-all
+Use the Graphite data dependence analysis to identify loops that can
+be parallelized. Parallelize all the loops that can be analyzed to
+not contain loop carried dependences without checking that it is
+profitable to parallelize the loops.
-Finally, consider:
+@item -ftree-coalesce-vars
+@opindex ftree-coalesce-vars
+While transforming the program out of the SSA representation, attempt to
+reduce copying by coalescing versions of different user-defined
+variables, instead of just compiler temporaries. This may severely
+limit the ability to debug an optimized program compiled with
+@option{-fno-var-tracking-assignments}. In the negated form, this flag
+prevents SSA coalescing of user variables. This option is enabled by
+default if optimization is enabled, and it does very little otherwise.
+
+@item -ftree-loop-if-convert
+@opindex ftree-loop-if-convert
+Attempt to transform conditional jumps in the innermost loops to
+branch-less equivalents. The intent is to remove control-flow from
+the innermost loops in order to improve the ability of the
+vectorization pass to handle these loops. This is enabled by default
+if vectorization is enabled.
+@item -ftree-loop-if-convert-stores
+@opindex ftree-loop-if-convert-stores
+Attempt to also if-convert conditional jumps containing memory writes.
+This transformation can be unsafe for multi-threaded programs as it
+transforms conditional memory writes into unconditional memory writes.
+For example,
@smallexample
-gcc -fopt-info-vec-missed=vec.miss -fopt-info-loop-optimized=loop.opt
+for (i = 0; i < N; i++)
+ if (cond)
+ A[i] = expr;
@end smallexample
-
-@noindent
-Here the two output filenames @file{vec.miss} and @file{loop.opt} are
-in conflict since only one output file is allowed. In this case, only
-the first option takes effect and the subsequent options are
-ignored. Thus only @file{vec.miss} is produced which contains
-dumps from the vectorizer about missed opportunities.
-
-@item -frandom-seed=@var{number}
-@opindex frandom-seed
-This option provides a seed that GCC uses in place of
-random numbers in generating certain symbol names
-that have to be different in every compiled file. It is also used to
-place unique stamps in coverage data files and the object files that
-produce them. You can use the @option{-frandom-seed} option to produce
-reproducibly identical object files.
-
-The @var{number} should be different for every file you compile.
-
-@item -fsched-verbose=@var{n}
-@opindex fsched-verbose
-On targets that use instruction scheduling, this option controls the
-amount of debugging output the scheduler prints. This information is
-written to standard error, unless @option{-fdump-rtl-sched1} or
-@option{-fdump-rtl-sched2} is specified, in which case it is output
-to the usual dump listing file, @file{.sched1} or @file{.sched2}
-respectively. However for @var{n} greater than nine, the output is
-always printed to standard error.
-
-For @var{n} greater than zero, @option{-fsched-verbose} outputs the
-same information as @option{-fdump-rtl-sched1} and @option{-fdump-rtl-sched2}.
-For @var{n} greater than one, it also output basic block probabilities,
-detailed ready list information and unit/insn info. For @var{n} greater
-than two, it includes RTL at abort point, control-flow and regions info.
-And for @var{n} over four, @option{-fsched-verbose} also includes
-dependence info.
-
-@item -save-temps
-@itemx -save-temps=cwd
-@opindex save-temps
-Store the usual ``temporary'' intermediate files permanently; place them
-in the current directory and name them based on the source file. Thus,
-compiling @file{foo.c} with @option{-c -save-temps} produces files
-@file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
-preprocessed @file{foo.i} output file even though the compiler now
-normally uses an integrated preprocessor.
-
-When used in combination with the @option{-x} command-line option,
-@option{-save-temps} is sensible enough to avoid over writing an
-input source file with the same extension as an intermediate file.
-The corresponding intermediate file may be obtained by renaming the
-source file before using @option{-save-temps}.
-
-If you invoke GCC in parallel, compiling several different source
-files that share a common base name in different subdirectories or the
-same source file compiled for multiple output destinations, it is
-likely that the different parallel compilers will interfere with each
-other, and overwrite the temporary files. For instance:
-
+is transformed to
@smallexample
-gcc -save-temps -o outdir1/foo.o indir1/foo.c&
-gcc -save-temps -o outdir2/foo.o indir2/foo.c&
+for (i = 0; i < N; i++)
+ A[i] = cond ? expr : A[i];
@end smallexample
+potentially producing data races.
-may result in @file{foo.i} and @file{foo.o} being written to
-simultaneously by both compilers.
-
-@item -save-temps=obj
-@opindex save-temps=obj
-Store the usual ``temporary'' intermediate files permanently. If the
-@option{-o} option is used, the temporary files are based on the
-object file. If the @option{-o} option is not used, the
-@option{-save-temps=obj} switch behaves like @option{-save-temps}.
-
-For example:
-
+@item -ftree-loop-distribution
+@opindex ftree-loop-distribution
+Perform loop distribution. This flag can improve cache performance on
+big loop bodies and allow further loop optimizations, like
+parallelization or vectorization, to take place. For example, the loop
@smallexample
-gcc -save-temps=obj -c foo.c
-gcc -save-temps=obj -c bar.c -o dir/xbar.o
-gcc -save-temps=obj foobar.c -o dir2/yfoobar
+DO I = 1, N
+ A(I) = B(I) + C
+ D(I) = E(I) * F
+ENDDO
@end smallexample
-
-@noindent
-creates @file{foo.i}, @file{foo.s}, @file{dir/xbar.i},
-@file{dir/xbar.s}, @file{dir2/yfoobar.i}, @file{dir2/yfoobar.s}, and
-@file{dir2/yfoobar.o}.
-
-@item -time@r{[}=@var{file}@r{]}
-@opindex time
-Report the CPU time taken by each subprocess in the compilation
-sequence. For C source files, this is the compiler proper and assembler
-(plus the linker if linking is done).
-
-Without the specification of an output file, the output looks like this:
-
+is transformed to
@smallexample
-# cc1 0.12 0.01
-# as 0.00 0.01
+DO I = 1, N
+ A(I) = B(I) + C
+ENDDO
+DO I = 1, N
+ D(I) = E(I) * F
+ENDDO
@end smallexample
-The first number on each line is the ``user time'', that is time spent
-executing the program itself. The second number is ``system time'',
-time spent executing operating system routines on behalf of the program.
-Both numbers are in seconds.
-
-With the specification of an output file, the output is appended to the
-named file, and it looks like this:
+@item -ftree-loop-distribute-patterns
+@opindex ftree-loop-distribute-patterns
+Perform loop distribution of patterns that can be code generated with
+calls to a library. This flag is enabled by default at @option{-O3}.
+This pass distributes the initialization loops and generates a call to
+memset zero. For example, the loop
@smallexample
-0.12 0.01 cc1 @var{options}
-0.00 0.01 as @var{options}
+DO I = 1, N
+ A(I) = 0
+ B(I) = A(I) + I
+ENDDO
+@end smallexample
+is transformed to
+@smallexample
+DO I = 1, N
+ A(I) = 0
+ENDDO
+DO I = 1, N
+ B(I) = A(I) + I
+ENDDO
@end smallexample
+and the initialization loop is transformed into a call to memset zero.
-The ``user time'' and the ``system time'' are moved before the program
-name, and the options passed to the program are displayed, so that one
-can later tell what file was being compiled, and with which options.
+@item -ftree-loop-im
+@opindex ftree-loop-im
+Perform loop invariant motion on trees. This pass moves only invariants that
+are hard to handle at RTL level (function calls, operations that expand to
+nontrivial sequences of insns). With @option{-funswitch-loops} it also moves
+operands of conditions that are invariant out of the loop, so that we can use
+just trivial invariantness analysis in loop unswitching. The pass also includes
+store motion.
-@item -fvar-tracking
-@opindex fvar-tracking
-Run variable tracking pass. It computes where variables are stored at each
-position in code. Better debugging information is then generated
-(if the debugging information format supports this information).
+@item -ftree-loop-ivcanon
+@opindex ftree-loop-ivcanon
+Create a canonical counter for number of iterations in loops for which
+determining number of iterations requires complicated analysis. Later
+optimizations then may determine the number easily. Useful especially
+in connection with unrolling.
-It is enabled by default when compiling with optimization (@option{-Os},
-@option{-O}, @option{-O2}, @dots{}), debugging information (@option{-g}) and
-the debug info format supports it.
-
-@item -fvar-tracking-assignments
-@opindex fvar-tracking-assignments
-@opindex fno-var-tracking-assignments
-Annotate assignments to user variables early in the compilation and
-attempt to carry the annotations over throughout the compilation all the
-way to the end, in an attempt to improve debug information while
-optimizing. Use of @option{-gdwarf-4} is recommended along with it.
+@item -fivopts
+@opindex fivopts
+Perform induction variable optimizations (strength reduction, induction
+variable merging and induction variable elimination) on trees.
-It can be enabled even if var-tracking is disabled, in which case
-annotations are created and maintained, but discarded at the end.
-By default, this flag is enabled together with @option{-fvar-tracking},
-except when selective scheduling is enabled.
+@item -ftree-parallelize-loops=n
+@opindex ftree-parallelize-loops
+Parallelize loops, i.e., split their iteration space to run in n threads.
+This is only possible for loops whose iterations are independent
+and can be arbitrarily reordered. The optimization is only
+profitable on multiprocessor machines, for loops that are CPU-intensive,
+rather than constrained e.g.@: by memory bandwidth. This option
+implies @option{-pthread}, and thus is only supported on targets
+that have support for @option{-pthread}.
-@item -fvar-tracking-assignments-toggle
-@opindex fvar-tracking-assignments-toggle
-@opindex fno-var-tracking-assignments-toggle
-Toggle @option{-fvar-tracking-assignments}, in the same way that
-@option{-gtoggle} toggles @option{-g}.
+@item -ftree-pta
+@opindex ftree-pta
+Perform function-local points-to analysis on trees. This flag is
+enabled by default at @option{-O} and higher.
-@item -print-file-name=@var{library}
-@opindex print-file-name
-Print the full absolute name of the library file @var{library} that
-would be used when linking---and don't do anything else. With this
-option, GCC does not compile or link anything; it just prints the
-file name.
+@item -ftree-sra
+@opindex ftree-sra
+Perform scalar replacement of aggregates. This pass replaces structure
+references with scalars to prevent committing structures to memory too
+early. This flag is enabled by default at @option{-O} and higher.
-@item -print-multi-directory
-@opindex print-multi-directory
-Print the directory name corresponding to the multilib selected by any
-other switches present in the command line. This directory is supposed
-to exist in @env{GCC_EXEC_PREFIX}.
+@item -ftree-ter
+@opindex ftree-ter
+Perform temporary expression replacement during the SSA->normal phase. Single
+use/single def temporaries are replaced at their use location with their
+defining expression. This results in non-GIMPLE code, but gives the expanders
+much more complex trees to work on resulting in better RTL generation. This is
+enabled by default at @option{-O} and higher.
-@item -print-multi-lib
-@opindex print-multi-lib
-Print the mapping from multilib directory names to compiler switches
-that enable them. The directory name is separated from the switches by
-@samp{;}, and each switch starts with an @samp{@@} instead of the
-@samp{-}, without spaces between multiple switches. This is supposed to
-ease shell processing.
+@item -ftree-slsr
+@opindex ftree-slsr
+Perform straight-line strength reduction on trees. This recognizes related
+expressions involving multiplications and replaces them by less expensive
+calculations when possible. This is enabled by default at @option{-O} and
+higher.
-@item -print-multi-os-directory
-@opindex print-multi-os-directory
-Print the path to OS libraries for the selected
-multilib, relative to some @file{lib} subdirectory. If OS libraries are
-present in the @file{lib} subdirectory and no multilibs are used, this is
-usually just @file{.}, if OS libraries are present in @file{lib@var{suffix}}
-sibling directories this prints e.g.@: @file{../lib64}, @file{../lib} or
-@file{../lib32}, or if OS libraries are present in @file{lib/@var{subdir}}
-subdirectories it prints e.g.@: @file{amd64}, @file{sparcv9} or @file{ev6}.
+@item -ftree-vectorize
+@opindex ftree-vectorize
+Perform vectorization on trees. This flag enables @option{-ftree-loop-vectorize}
+and @option{-ftree-slp-vectorize} if not explicitly specified.
-@item -print-multiarch
-@opindex print-multiarch
-Print the path to OS libraries for the selected multiarch,
-relative to some @file{lib} subdirectory.
+@item -ftree-loop-vectorize
+@opindex ftree-loop-vectorize
+Perform loop vectorization on trees. This flag is enabled by default at
+@option{-O3} and when @option{-ftree-vectorize} is enabled.
-@item -print-prog-name=@var{program}
-@opindex print-prog-name
-Like @option{-print-file-name}, but searches for a program such as @command{cpp}.
+@item -ftree-slp-vectorize
+@opindex ftree-slp-vectorize
+Perform basic block vectorization on trees. This flag is enabled by default at
+@option{-O3} and when @option{-ftree-vectorize} is enabled.
-@item -print-libgcc-file-name
-@opindex print-libgcc-file-name
-Same as @option{-print-file-name=libgcc.a}.
+@item -fvect-cost-model=@var{model}
+@opindex fvect-cost-model
+Alter the cost model used for vectorization. The @var{model} argument
+should be one of @samp{unlimited}, @samp{dynamic} or @samp{cheap}.
+With the @samp{unlimited} model the vectorized code-path is assumed
+to be profitable while with the @samp{dynamic} model a runtime check
+guards the vectorized code-path to enable it only for iteration
+counts that will likely execute faster than when executing the original
+scalar loop. The @samp{cheap} model disables vectorization of
+loops where doing so would be cost prohibitive for example due to
+required runtime checks for data dependence or alignment but otherwise
+is equal to the @samp{dynamic} model.
+The default cost model depends on other optimization flags and is
+either @samp{dynamic} or @samp{cheap}.
-This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
-but you do want to link with @file{libgcc.a}. You can do:
+@item -fsimd-cost-model=@var{model}
+@opindex fsimd-cost-model
+Alter the cost model used for vectorization of loops marked with the OpenMP
+or Cilk Plus simd directive. The @var{model} argument should be one of
+@samp{unlimited}, @samp{dynamic}, @samp{cheap}. All values of @var{model}
+have the same meaning as described in @option{-fvect-cost-model} and by
+default a cost model defined with @option{-fvect-cost-model} is used.
-@smallexample
-gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
-@end smallexample
+@item -ftree-vrp
+@opindex ftree-vrp
+Perform Value Range Propagation on trees. This is similar to the
+constant propagation pass, but instead of values, ranges of values are
+propagated. This allows the optimizers to remove unnecessary range
+checks like array bound checks and null pointer checks. This is
+enabled by default at @option{-O2} and higher. Null pointer check
+elimination is only done if @option{-fdelete-null-pointer-checks} is
+enabled.
-@item -print-search-dirs
-@opindex print-search-dirs
-Print the name of the configured installation directory and a list of
-program and library directories @command{gcc} searches---and don't do anything else.
+@item -fsplit-paths
+@opindex fsplit-paths
+Split paths leading to loop backedges. This can improve dead code
+elimination and common subexpression elimination. This is enabled by
+default at @option{-O2} and above.
-This is useful when @command{gcc} prints the error message
-@samp{installation problem, cannot exec cpp0: No such file or directory}.
-To resolve this you either need to put @file{cpp0} and the other compiler
-components where @command{gcc} expects to find them, or you can set the environment
-variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
-Don't forget the trailing @samp{/}.
-@xref{Environment Variables}.
+@item -fsplit-ivs-in-unroller
+@opindex fsplit-ivs-in-unroller
+Enables expression of values of induction variables in later iterations
+of the unrolled loop using the value in the first iteration. This breaks
+long dependency chains, thus improving efficiency of the scheduling passes.
-@item -print-sysroot
-@opindex print-sysroot
-Print the target sysroot directory that is used during
-compilation. This is the target sysroot specified either at configure
-time or using the @option{--sysroot} option, possibly with an extra
-suffix that depends on compilation options. If no target sysroot is
-specified, the option prints nothing.
+A combination of @option{-fweb} and CSE is often sufficient to obtain the
+same effect. However, that is not reliable in cases where the loop body
+is more complicated than a single basic block. It also does not work at all
+on some architectures due to restrictions in the CSE pass.
-@item -print-sysroot-headers-suffix
-@opindex print-sysroot-headers-suffix
-Print the suffix added to the target sysroot when searching for
-headers, or give an error if the compiler is not configured with such
-a suffix---and don't do anything else.
+This optimization is enabled by default.
-@item -dumpmachine
-@opindex dumpmachine
-Print the compiler's target machine (for example,
-@samp{i686-pc-linux-gnu})---and don't do anything else.
+@item -fvariable-expansion-in-unroller
+@opindex fvariable-expansion-in-unroller
+With this option, the compiler creates multiple copies of some
+local variables when unrolling a loop, which can result in superior code.
-@item -dumpversion
-@opindex dumpversion
-Print the compiler version (for example, @code{3.0})---and don't do
-anything else.
+@item -fpartial-inlining
+@opindex fpartial-inlining
+Inline parts of functions. This option has any effect only
+when inlining itself is turned on by the @option{-finline-functions}
+or @option{-finline-small-functions} options.
-@item -dumpspecs
-@opindex dumpspecs
-Print the compiler's built-in specs---and don't do anything else. (This
-is used when GCC itself is being built.) @xref{Spec Files}.
+Enabled at level @option{-O2}.
-@item -fno-eliminate-unused-debug-types
-@opindex feliminate-unused-debug-types
-@opindex fno-eliminate-unused-debug-types
-Normally, when producing DWARF 2 output, GCC avoids producing debug symbol
-output for types that are nowhere used in the source file being compiled.
-Sometimes it is useful to have GCC emit debugging
-information for all types declared in a compilation
-unit, regardless of whether or not they are actually used
-in that compilation unit, for example
-if, in the debugger, you want to cast a value to a type that is
-not actually used in your program (but is declared). More often,
-however, this results in a significant amount of wasted space.
-@end table
+@item -fpredictive-commoning
+@opindex fpredictive-commoning
+Perform predictive commoning optimization, i.e., reusing computations
+(especially memory loads and stores) performed in previous
+iterations of loops.
-@node Optimize Options
-@section Options That Control Optimization
-@cindex optimize options
-@cindex options, optimization
+This option is enabled at level @option{-O3}.
-These options control various sorts of optimizations.
+@item -fprefetch-loop-arrays
+@opindex fprefetch-loop-arrays
+If supported by the target machine, generate instructions to prefetch
+memory to improve the performance of loops that access large arrays.
-Without any optimization option, the compiler's goal is to reduce the
-cost of compilation and to make debugging produce the expected
-results. Statements are independent: if you stop the program with a
-breakpoint between statements, you can then assign a new value to any
-variable or change the program counter to any other statement in the
-function and get exactly the results you expect from the source
-code.
+This option may generate better or worse code; results are highly
+dependent on the structure of loops within the source code.
-Turning on optimization flags makes the compiler attempt to improve
-the performance and/or code size at the expense of compilation time
-and possibly the ability to debug the program.
+Disabled at level @option{-Os}.
-The compiler performs optimization based on the knowledge it has of the
-program. Compiling multiple files at once to a single output file mode allows
-the compiler to use information gained from all of the files when compiling
-each of them.
+@item -fno-peephole
+@itemx -fno-peephole2
+@opindex fno-peephole
+@opindex fno-peephole2
+Disable any machine-specific peephole optimizations. The difference
+between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
+are implemented in the compiler; some targets use one, some use the
+other, a few use both.
-Not all optimizations are controlled directly by a flag. Only
-optimizations that have a flag are listed in this section.
+@option{-fpeephole} is enabled by default.
+@option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
-Most optimizations are only enabled if an @option{-O} level is set on
-the command line. Otherwise they are disabled, even if individual
-optimization flags are specified.
+@item -fno-guess-branch-probability
+@opindex fno-guess-branch-probability
+Do not guess branch probabilities using heuristics.
-Depending on the target and how GCC was configured, a slightly different
-set of optimizations may be enabled at each @option{-O} level than
-those listed here. You can invoke GCC with @option{-Q --help=optimizers}
-to find out the exact set of optimizations that are enabled at each level.
-@xref{Overall Options}, for examples.
+GCC uses heuristics to guess branch probabilities if they are
+not provided by profiling feedback (@option{-fprofile-arcs}). These
+heuristics are based on the control flow graph. If some branch probabilities
+are specified by @code{__builtin_expect}, then the heuristics are
+used to guess branch probabilities for the rest of the control flow graph,
+taking the @code{__builtin_expect} info into account. The interactions
+between the heuristics and @code{__builtin_expect} can be complex, and in
+some cases, it may be useful to disable the heuristics so that the effects
+of @code{__builtin_expect} are easier to understand.
-@table @gcctabopt
-@item -O
-@itemx -O1
-@opindex O
-@opindex O1
-Optimize. Optimizing compilation takes somewhat more time, and a lot
-more memory for a large function.
+The default is @option{-fguess-branch-probability} at levels
+@option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
-With @option{-O}, the compiler tries to reduce code size and execution
-time, without performing any optimizations that take a great deal of
-compilation time.
+@item -freorder-blocks
+@opindex freorder-blocks
+Reorder basic blocks in the compiled function in order to reduce number of
+taken branches and improve code locality.
-@option{-O} turns on the following optimization flags:
-@gccoptlist{
--fauto-inc-dec @gol
--fbranch-count-reg @gol
--fcombine-stack-adjustments @gol
--fcompare-elim @gol
--fcprop-registers @gol
--fdce @gol
--fdefer-pop @gol
--fdelayed-branch @gol
--fdse @gol
--fforward-propagate @gol
--fguess-branch-probability @gol
--fif-conversion2 @gol
--fif-conversion @gol
--finline-functions-called-once @gol
--fipa-pure-const @gol
--fipa-profile @gol
--fipa-reference @gol
--fmerge-constants @gol
--fmove-loop-invariants @gol
--freorder-blocks @gol
--fshrink-wrap @gol
--fsplit-wide-types @gol
--fssa-backprop @gol
--fssa-phiopt @gol
--ftree-bit-ccp @gol
--ftree-ccp @gol
--ftree-ch @gol
--ftree-coalesce-vars @gol
--ftree-copy-prop @gol
--ftree-dce @gol
--ftree-dominator-opts @gol
--ftree-dse @gol
--ftree-forwprop @gol
--ftree-fre @gol
--ftree-phiprop @gol
--ftree-sink @gol
--ftree-slsr @gol
--ftree-sra @gol
--ftree-pta @gol
--ftree-ter @gol
--funit-at-a-time}
+Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
-@option{-O} also turns on @option{-fomit-frame-pointer} on machines
-where doing so does not interfere with debugging.
+@item -freorder-blocks-algorithm=@var{algorithm}
+@opindex freorder-blocks-algorithm
+Use the specified algorithm for basic block reordering. The
+@var{algorithm} argument can be @samp{simple}, which does not increase
+code size (except sometimes due to secondary effects like alignment),
+or @samp{stc}, the ``software trace cache'' algorithm, which tries to
+put all often executed code together, minimizing the number of branches
+executed by making extra copies of code.
-@item -O2
-@opindex O2
-Optimize even more. GCC performs nearly all supported optimizations
-that do not involve a space-speed tradeoff.
-As compared to @option{-O}, this option increases both compilation time
-and the performance of the generated code.
+The default is @samp{simple} at levels @option{-O}, @option{-Os}, and
+@samp{stc} at levels @option{-O2}, @option{-O3}.
-@option{-O2} turns on all optimization flags specified by @option{-O}. It
-also turns on the following optimization flags:
-@gccoptlist{-fthread-jumps @gol
--falign-functions -falign-jumps @gol
--falign-loops -falign-labels @gol
--fcaller-saves @gol
--fcrossjumping @gol
--fcse-follow-jumps -fcse-skip-blocks @gol
--fdelete-null-pointer-checks @gol
--fdevirtualize -fdevirtualize-speculatively @gol
--fexpensive-optimizations @gol
--fgcse -fgcse-lm @gol
--fhoist-adjacent-loads @gol
--finline-small-functions @gol
--findirect-inlining @gol
--fipa-cp @gol
--fipa-cp-alignment @gol
--fipa-sra @gol
--fipa-icf @gol
--fisolate-erroneous-paths-dereference @gol
--flra-remat @gol
--foptimize-sibling-calls @gol
--foptimize-strlen @gol
--fpartial-inlining @gol
--fpeephole2 @gol
--freorder-blocks-algorithm=stc @gol
--freorder-blocks-and-partition -freorder-functions @gol
--frerun-cse-after-loop @gol
--fsched-interblock -fsched-spec @gol
--fschedule-insns -fschedule-insns2 @gol
--fstrict-aliasing -fstrict-overflow @gol
--ftree-builtin-call-dce @gol
--ftree-switch-conversion -ftree-tail-merge @gol
--ftree-pre @gol
--ftree-vrp @gol
--fipa-ra}
+@item -freorder-blocks-and-partition
+@opindex freorder-blocks-and-partition
+In addition to reordering basic blocks in the compiled function, in order
+to reduce number of taken branches, partitions hot and cold basic blocks
+into separate sections of the assembly and @file{.o} files, to improve
+paging and cache locality performance.
-Please note the warning under @option{-fgcse} about
-invoking @option{-O2} on programs that use computed gotos.
+This optimization is automatically turned off in the presence of
+exception handling, for linkonce sections, for functions with a user-defined
+section attribute and on any architecture that does not support named
+sections.
-@item -O3
-@opindex O3
-Optimize yet more. @option{-O3} turns on all optimizations specified
-by @option{-O2} and also turns on the @option{-finline-functions},
-@option{-funswitch-loops}, @option{-fpredictive-commoning},
-@option{-fgcse-after-reload}, @option{-ftree-loop-vectorize},
-@option{-ftree-loop-distribute-patterns},
-@option{-ftree-slp-vectorize}, @option{-fvect-cost-model},
-@option{-ftree-partial-pre} and @option{-fipa-cp-clone} options.
+Enabled for x86 at levels @option{-O2}, @option{-O3}.
-@item -O0
-@opindex O0
-Reduce compilation time and make debugging produce the expected
-results. This is the default.
+@item -freorder-functions
+@opindex freorder-functions
+Reorder functions in the object file in order to
+improve code locality. This is implemented by using special
+subsections @code{.text.hot} for most frequently executed functions and
+@code{.text.unlikely} for unlikely executed functions. Reordering is done by
+the linker so object file format must support named sections and linker must
+place them in a reasonable way.
-@item -Os
-@opindex Os
-Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
-do not typically increase code size. It also performs further
-optimizations designed to reduce code size.
+Also profile feedback must be available to make this option effective. See
+@option{-fprofile-arcs} for details.
-@option{-Os} disables the following optimization flags:
-@gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
--falign-labels -freorder-blocks -freorder-blocks-algorithm=stc @gol
--freorder-blocks-and-partition -fprefetch-loop-arrays}
+Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
-@item -Ofast
-@opindex Ofast
-Disregard strict standards compliance. @option{-Ofast} enables all
-@option{-O3} optimizations. It also enables optimizations that are not
-valid for all standard-compliant programs.
-It turns on @option{-ffast-math} and the Fortran-specific
-@option{-fno-protect-parens} and @option{-fstack-arrays}.
+@item -fstrict-aliasing
+@opindex fstrict-aliasing
+Allow the compiler to assume the strictest aliasing rules applicable to
+the language being compiled. For C (and C++), this activates
+optimizations based on the type of expressions. In particular, an
+object of one type is assumed never to reside at the same address as an
+object of a different type, unless the types are almost the same. For
+example, an @code{unsigned int} can alias an @code{int}, but not a
+@code{void*} or a @code{double}. A character type may alias any other
+type.
-@item -Og
-@opindex Og
-Optimize debugging experience. @option{-Og} enables optimizations
-that do not interfere with debugging. It should be the optimization
-level of choice for the standard edit-compile-debug cycle, offering
-a reasonable level of optimization while maintaining fast compilation
-and a good debugging experience.
+@anchor{Type-punning}Pay special attention to code like this:
+@smallexample
+union a_union @{
+ int i;
+ double d;
+@};
-If you use multiple @option{-O} options, with or without level numbers,
-the last such option is the one that is effective.
-@end table
+int f() @{
+ union a_union t;
+ t.d = 3.0;
+ return t.i;
+@}
+@end smallexample
+The practice of reading from a different union member than the one most
+recently written to (called ``type-punning'') is common. Even with
+@option{-fstrict-aliasing}, type-punning is allowed, provided the memory
+is accessed through the union type. So, the code above works as
+expected. @xref{Structures unions enumerations and bit-fields
+implementation}. However, this code might not:
+@smallexample
+int f() @{
+ union a_union t;
+ int* ip;
+ t.d = 3.0;
+ ip = &t.i;
+ return *ip;
+@}
+@end smallexample
-Options of the form @option{-f@var{flag}} specify machine-independent
-flags. Most flags have both positive and negative forms; the negative
-form of @option{-ffoo} is @option{-fno-foo}. In the table
-below, only one of the forms is listed---the one you typically
-use. You can figure out the other form by either removing @samp{no-}
-or adding it.
+Similarly, access by taking the address, casting the resulting pointer
+and dereferencing the result has undefined behavior, even if the cast
+uses a union type, e.g.:
+@smallexample
+int f() @{
+ double d = 3.0;
+ return ((union a_union *) &d)->i;
+@}
+@end smallexample
-The following options control specific optimizations. They are either
-activated by @option{-O} options or are related to ones that are. You
-can use the following flags in the rare cases when ``fine-tuning'' of
-optimizations to be performed is desired.
+The @option{-fstrict-aliasing} option is enabled at levels
+@option{-O2}, @option{-O3}, @option{-Os}.
-@table @gcctabopt
-@item -fno-defer-pop
-@opindex fno-defer-pop
-Always pop the arguments to each function call as soon as that function
-returns. For machines that must pop arguments after a function call,
-the compiler normally lets arguments accumulate on the stack for several
-function calls and pops them all at once.
+@item -fstrict-overflow
+@opindex fstrict-overflow
+Allow the compiler to assume strict signed overflow rules, depending
+on the language being compiled. For C (and C++) this means that
+overflow when doing arithmetic with signed numbers is undefined, which
+means that the compiler may assume that it does not happen. This
+permits various optimizations. For example, the compiler assumes
+that an expression like @code{i + 10 > i} is always true for
+signed @code{i}. This assumption is only valid if signed overflow is
+undefined, as the expression is false if @code{i + 10} overflows when
+using twos complement arithmetic. When this option is in effect any
+attempt to determine whether an operation on signed numbers
+overflows must be written carefully to not actually involve overflow.
+
+This option also allows the compiler to assume strict pointer
+semantics: given a pointer to an object, if adding an offset to that
+pointer does not produce a pointer to the same object, the addition is
+undefined. This permits the compiler to conclude that @code{p + u >
+p} is always true for a pointer @code{p} and unsigned integer
+@code{u}. This assumption is only valid because pointer wraparound is
+undefined, as the expression is false if @code{p + u} overflows using
+twos complement arithmetic.
+
+See also the @option{-fwrapv} option. Using @option{-fwrapv} means
+that integer signed overflow is fully defined: it wraps. When
+@option{-fwrapv} is used, there is no difference between
+@option{-fstrict-overflow} and @option{-fno-strict-overflow} for
+integers. With @option{-fwrapv} certain types of overflow are
+permitted. For example, if the compiler gets an overflow when doing
+arithmetic on constants, the overflowed value can still be used with
+@option{-fwrapv}, but not otherwise.
+
+The @option{-fstrict-overflow} option is enabled at levels
+@option{-O2}, @option{-O3}, @option{-Os}.
+
+@item -falign-functions
+@itemx -falign-functions=@var{n}
+@opindex falign-functions
+Align the start of functions to the next power-of-two greater than
+@var{n}, skipping up to @var{n} bytes. For instance,
+@option{-falign-functions=32} aligns functions to the next 32-byte
+boundary, but @option{-falign-functions=24} aligns to the next
+32-byte boundary only if this can be done by skipping 23 bytes or less.
-Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
+@option{-fno-align-functions} and @option{-falign-functions=1} are
+equivalent and mean that functions are not aligned.
-@item -fforward-propagate
-@opindex fforward-propagate
-Perform a forward propagation pass on RTL@. The pass tries to combine two
-instructions and checks if the result can be simplified. If loop unrolling
-is active, two passes are performed and the second is scheduled after
-loop unrolling.
+Some assemblers only support this flag when @var{n} is a power of two;
+in that case, it is rounded up.
-This option is enabled by default at optimization levels @option{-O},
-@option{-O2}, @option{-O3}, @option{-Os}.
+If @var{n} is not specified or is zero, use a machine-dependent default.
-@item -ffp-contract=@var{style}
-@opindex ffp-contract
-@option{-ffp-contract=off} disables floating-point expression contraction.
-@option{-ffp-contract=fast} enables floating-point expression contraction
-such as forming of fused multiply-add operations if the target has
-native support for them.
-@option{-ffp-contract=on} enables floating-point expression contraction
-if allowed by the language standard. This is currently not implemented
-and treated equal to @option{-ffp-contract=off}.
+Enabled at levels @option{-O2}, @option{-O3}.
-The default is @option{-ffp-contract=fast}.
+@item -falign-labels
+@itemx -falign-labels=@var{n}
+@opindex falign-labels
+Align all branch targets to a power-of-two boundary, skipping up to
+@var{n} bytes like @option{-falign-functions}. This option can easily
+make code slower, because it must insert dummy operations for when the
+branch target is reached in the usual flow of the code.
-@item -fomit-frame-pointer
-@opindex fomit-frame-pointer
-Don't keep the frame pointer in a register for functions that
-don't need one. This avoids the instructions to save, set up and
-restore frame pointers; it also makes an extra register available
-in many functions. @strong{It also makes debugging impossible on
-some machines.}
+@option{-fno-align-labels} and @option{-falign-labels=1} are
+equivalent and mean that labels are not aligned.
-On some machines, such as the VAX, this flag has no effect, because
-the standard calling sequence automatically handles the frame pointer
-and nothing is saved by pretending it doesn't exist. The
-machine-description macro @code{FRAME_POINTER_REQUIRED} controls
-whether a target machine supports this flag. @xref{Registers,,Register
-Usage, gccint, GNU Compiler Collection (GCC) Internals}.
+If @option{-falign-loops} or @option{-falign-jumps} are applicable and
+are greater than this value, then their values are used instead.
-The default setting (when not optimizing for
-size) for 32-bit GNU/Linux x86 and 32-bit Darwin x86 targets is
-@option{-fomit-frame-pointer}. You can configure GCC with the
-@option{--enable-frame-pointer} configure option to change the default.
+If @var{n} is not specified or is zero, use a machine-dependent default
+which is very likely to be @samp{1}, meaning no alignment.
-Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
+Enabled at levels @option{-O2}, @option{-O3}.
-@item -foptimize-sibling-calls
-@opindex foptimize-sibling-calls
-Optimize sibling and tail recursive calls.
+@item -falign-loops
+@itemx -falign-loops=@var{n}
+@opindex falign-loops
+Align loops to a power-of-two boundary, skipping up to @var{n} bytes
+like @option{-falign-functions}. If the loops are
+executed many times, this makes up for any execution of the dummy
+operations.
-Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
+@option{-fno-align-loops} and @option{-falign-loops=1} are
+equivalent and mean that loops are not aligned.
-@item -foptimize-strlen
-@opindex foptimize-strlen
-Optimize various standard C string functions (e.g. @code{strlen},
-@code{strchr} or @code{strcpy}) and
-their @code{_FORTIFY_SOURCE} counterparts into faster alternatives.
+If @var{n} is not specified or is zero, use a machine-dependent default.
Enabled at levels @option{-O2}, @option{-O3}.
-@item -fno-inline
-@opindex fno-inline
-Do not expand any functions inline apart from those marked with
-the @code{always_inline} attribute. This is the default when not
-optimizing.
+@item -falign-jumps
+@itemx -falign-jumps=@var{n}
+@opindex falign-jumps
+Align branch targets to a power-of-two boundary, for branch targets
+where the targets can only be reached by jumping, skipping up to @var{n}
+bytes like @option{-falign-functions}. In this case, no dummy operations
+need be executed.
-Single functions can be exempted from inlining by marking them
-with the @code{noinline} attribute.
+@option{-fno-align-jumps} and @option{-falign-jumps=1} are
+equivalent and mean that loops are not aligned.
-@item -finline-small-functions
-@opindex finline-small-functions
-Integrate functions into their callers when their body is smaller than expected
-function call code (so overall size of program gets smaller). The compiler
-heuristically decides which functions are simple enough to be worth integrating
-in this way. This inlining applies to all functions, even those not declared
-inline.
+If @var{n} is not specified or is zero, use a machine-dependent default.
-Enabled at level @option{-O2}.
+Enabled at levels @option{-O2}, @option{-O3}.
-@item -findirect-inlining
-@opindex findirect-inlining
-Inline also indirect calls that are discovered to be known at compile
-time thanks to previous inlining. This option has any effect only
-when inlining itself is turned on by the @option{-finline-functions}
-or @option{-finline-small-functions} options.
+@item -funit-at-a-time
+@opindex funit-at-a-time
+This option is left for compatibility reasons. @option{-funit-at-a-time}
+has no effect, while @option{-fno-unit-at-a-time} implies
+@option{-fno-toplevel-reorder} and @option{-fno-section-anchors}.
-Enabled at level @option{-O2}.
+Enabled by default.
-@item -finline-functions
-@opindex finline-functions
-Consider all functions for inlining, even if they are not declared inline.
-The compiler heuristically decides which functions are worth integrating
-in this way.
+@item -fno-toplevel-reorder
+@opindex fno-toplevel-reorder
+Do not reorder top-level functions, variables, and @code{asm}
+statements. Output them in the same order that they appear in the
+input file. When this option is used, unreferenced static variables
+are not removed. This option is intended to support existing code
+that relies on a particular ordering. For new code, it is better to
+use attributes when possible.
-If all calls to a given function are integrated, and the function is
-declared @code{static}, then the function is normally not output as
-assembler code in its own right.
+Enabled at level @option{-O0}. When disabled explicitly, it also implies
+@option{-fno-section-anchors}, which is otherwise enabled at @option{-O0} on some
+targets.
-Enabled at level @option{-O3}.
+@item -fweb
+@opindex fweb
+Constructs webs as commonly used for register allocation purposes and assign
+each web individual pseudo register. This allows the register allocation pass
+to operate on pseudos directly, but also strengthens several other optimization
+passes, such as CSE, loop optimizer and trivial dead code remover. It can,
+however, make debugging impossible, since variables no longer stay in a
+``home register''.
-@item -finline-functions-called-once
-@opindex finline-functions-called-once
-Consider all @code{static} functions called once for inlining into their
-caller even if they are not marked @code{inline}. If a call to a given
-function is integrated, then the function is not output as assembler code
-in its own right.
+Enabled by default with @option{-funroll-loops}.
-Enabled at levels @option{-O1}, @option{-O2}, @option{-O3} and @option{-Os}.
+@item -fwhole-program
+@opindex fwhole-program
+Assume that the current compilation unit represents the whole program being
+compiled. All public functions and variables with the exception of @code{main}
+and those merged by attribute @code{externally_visible} become static functions
+and in effect are optimized more aggressively by interprocedural optimizers.
-@item -fearly-inlining
-@opindex fearly-inlining
-Inline functions marked by @code{always_inline} and functions whose body seems
-smaller than the function call overhead early before doing
-@option{-fprofile-generate} instrumentation and real inlining pass. Doing so
-makes profiling significantly cheaper and usually inlining faster on programs
-having large chains of nested wrapper functions.
+This option should not be used in combination with @option{-flto}.
+Instead relying on a linker plugin should provide safer and more precise
+information.
-Enabled by default.
+@item -flto[=@var{n}]
+@opindex flto
+This option runs the standard link-time optimizer. When invoked
+with source code, it generates GIMPLE (one of GCC's internal
+representations) and writes it to special ELF sections in the object
+file. When the object files are linked together, all the function
+bodies are read from these ELF sections and instantiated as if they
+had been part of the same translation unit.
-@item -fipa-sra
-@opindex fipa-sra
-Perform interprocedural scalar replacement of aggregates, removal of
-unused parameters and replacement of parameters passed by reference
-by parameters passed by value.
+To use the link-time optimizer, @option{-flto} and optimization
+options should be specified at compile time and during the final link.
+It is recommended that you compile all the files participating in the
+same link with the same options and also specify those options at
+link time.
+For example:
-Enabled at levels @option{-O2}, @option{-O3} and @option{-Os}.
+@smallexample
+gcc -c -O2 -flto foo.c
+gcc -c -O2 -flto bar.c
+gcc -o myprog -flto -O2 foo.o bar.o
+@end smallexample
-@item -finline-limit=@var{n}
-@opindex finline-limit
-By default, GCC limits the size of functions that can be inlined. This flag
-allows coarse control of this limit. @var{n} is the size of functions that
-can be inlined in number of pseudo instructions.
+The first two invocations to GCC save a bytecode representation
+of GIMPLE into special ELF sections inside @file{foo.o} and
+@file{bar.o}. The final invocation reads the GIMPLE bytecode from
+@file{foo.o} and @file{bar.o}, merges the two files into a single
+internal image, and compiles the result as usual. Since both
+@file{foo.o} and @file{bar.o} are merged into a single image, this
+causes all the interprocedural analyses and optimizations in GCC to
+work across the two files as if they were a single one. This means,
+for example, that the inliner is able to inline functions in
+@file{bar.o} into functions in @file{foo.o} and vice-versa.
-Inlining is actually controlled by a number of parameters, which may be
-specified individually by using @option{--param @var{name}=@var{value}}.
-The @option{-finline-limit=@var{n}} option sets some of these parameters
-as follows:
+Another (simpler) way to enable link-time optimization is:
-@table @gcctabopt
-@item max-inline-insns-single
-is set to @var{n}/2.
-@item max-inline-insns-auto
-is set to @var{n}/2.
-@end table
+@smallexample
+gcc -o myprog -flto -O2 foo.c bar.c
+@end smallexample
-See below for a documentation of the individual
-parameters controlling inlining and for the defaults of these parameters.
+The above generates bytecode for @file{foo.c} and @file{bar.c},
+merges them together into a single GIMPLE representation and optimizes
+them as usual to produce @file{myprog}.
-@emph{Note:} there may be no value to @option{-finline-limit} that results
-in default behavior.
+The only important thing to keep in mind is that to enable link-time
+optimizations you need to use the GCC driver to perform the link step.
+GCC then automatically performs link-time optimization if any of the
+objects involved were compiled with the @option{-flto} command-line option.
+You generally
+should specify the optimization options to be used for link-time
+optimization though GCC tries to be clever at guessing an
+optimization level to use from the options used at compile time
+if you fail to specify one at link time. You can always override
+the automatic decision to do link-time optimization at link time
+by passing @option{-fno-lto} to the link command.
+
+To make whole program optimization effective, it is necessary to make
+certain whole program assumptions. The compiler needs to know
+what functions and variables can be accessed by libraries and runtime
+outside of the link-time optimized unit. When supported by the linker,
+the linker plugin (see @option{-fuse-linker-plugin}) passes information
+to the compiler about used and externally visible symbols. When
+the linker plugin is not available, @option{-fwhole-program} should be
+used to allow the compiler to make these assumptions, which leads
+to more aggressive optimization decisions.
+
+When @option{-fuse-linker-plugin} is not enabled, when a file is
+compiled with @option{-flto}, the generated object file is larger than
+a regular object file because it contains GIMPLE bytecodes and the usual
+final code (see @option{-ffat-lto-objects}. This means that
+object files with LTO information can be linked as normal object
+files; if @option{-fno-lto} is passed to the linker, no
+interprocedural optimizations are applied. Note that when
+@option{-fno-fat-lto-objects} is enabled the compile stage is faster
+but you cannot perform a regular, non-LTO link on them.
+
+Additionally, the optimization flags used to compile individual files
+are not necessarily related to those used at link time. For instance,
-@emph{Note:} pseudo instruction represents, in this particular context, an
-abstract measurement of function's size. In no way does it represent a count
-of assembly instructions and as such its exact meaning might change from one
-release to an another.
+@smallexample
+gcc -c -O0 -ffat-lto-objects -flto foo.c
+gcc -c -O0 -ffat-lto-objects -flto bar.c
+gcc -o myprog -O3 foo.o bar.o
+@end smallexample
-@item -fno-keep-inline-dllexport
-@opindex fno-keep-inline-dllexport
-This is a more fine-grained version of @option{-fkeep-inline-functions},
-which applies only to functions that are declared using the @code{dllexport}
-attribute or declspec (@xref{Function Attributes,,Declaring Attributes of
-Functions}.)
+This produces individual object files with unoptimized assembler
+code, but the resulting binary @file{myprog} is optimized at
+@option{-O3}. If, instead, the final binary is generated with
+@option{-fno-lto}, then @file{myprog} is not optimized.
-@item -fkeep-inline-functions
-@opindex fkeep-inline-functions
-In C, emit @code{static} functions that are declared @code{inline}
-into the object file, even if the function has been inlined into all
-of its callers. This switch does not affect functions using the
-@code{extern inline} extension in GNU C90@. In C++, emit any and all
-inline functions into the object file.
+When producing the final binary, GCC only
+applies link-time optimizations to those files that contain bytecode.
+Therefore, you can mix and match object files and libraries with
+GIMPLE bytecodes and final object code. GCC automatically selects
+which files to optimize in LTO mode and which files to link without
+further processing.
-@item -fkeep-static-functions
-@opindex fkeep-static-functions
-Emit @code{static} functions into the object file, even if the function
-is never used.
+There are some code generation flags preserved by GCC when
+generating bytecodes, as they need to be used during the final link
+stage. Generally options specified at link time override those
+specified at compile time.
-@item -fkeep-static-consts
-@opindex fkeep-static-consts
-Emit variables declared @code{static const} when optimization isn't turned
-on, even if the variables aren't referenced.
+If you do not specify an optimization level option @option{-O} at
+link time, then GCC uses the highest optimization level
+used when compiling the object files.
-GCC enables this option by default. If you want to force the compiler to
-check if a variable is referenced, regardless of whether or not
-optimization is turned on, use the @option{-fno-keep-static-consts} option.
+Currently, the following options and their settings are taken from
+the first object file that explicitly specifies them:
+@option{-fPIC}, @option{-fpic}, @option{-fpie}, @option{-fcommon},
+@option{-fexceptions}, @option{-fnon-call-exceptions}, @option{-fgnu-tm}
+and all the @option{-m} target flags.
-@item -fmerge-constants
-@opindex fmerge-constants
-Attempt to merge identical constants (string constants and floating-point
-constants) across compilation units.
+Certain ABI-changing flags are required to match in all compilation units,
+and trying to override this at link time with a conflicting value
+is ignored. This includes options such as @option{-freg-struct-return}
+and @option{-fpcc-struct-return}.
-This option is the default for optimized compilation if the assembler and
-linker support it. Use @option{-fno-merge-constants} to inhibit this
-behavior.
+Other options such as @option{-ffp-contract}, @option{-fno-strict-overflow},
+@option{-fwrapv}, @option{-fno-trapv} or @option{-fno-strict-aliasing}
+are passed through to the link stage and merged conservatively for
+conflicting translation units. Specifically
+@option{-fno-strict-overflow}, @option{-fwrapv} and @option{-fno-trapv} take
+precedence; and for example @option{-ffp-contract=off} takes precedence
+over @option{-ffp-contract=fast}. You can override them at link time.
-Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
+If LTO encounters objects with C linkage declared with incompatible
+types in separate translation units to be linked together (undefined
+behavior according to ISO C99 6.2.7), a non-fatal diagnostic may be
+issued. The behavior is still undefined at run time. Similar
+diagnostics may be raised for other languages.
-@item -fmerge-all-constants
-@opindex fmerge-all-constants
-Attempt to merge identical constants and identical variables.
+Another feature of LTO is that it is possible to apply interprocedural
+optimizations on files written in different languages:
-This option implies @option{-fmerge-constants}. In addition to
-@option{-fmerge-constants} this considers e.g.@: even constant initialized
-arrays or initialized constant variables with integral or floating-point
-types. Languages like C or C++ require each variable, including multiple
-instances of the same variable in recursive calls, to have distinct locations,
-so using this option results in non-conforming
-behavior.
+@smallexample
+gcc -c -flto foo.c
+g++ -c -flto bar.cc
+gfortran -c -flto baz.f90
+g++ -o myprog -flto -O3 foo.o bar.o baz.o -lgfortran
+@end smallexample
-@item -fmodulo-sched
-@opindex fmodulo-sched
-Perform swing modulo scheduling immediately before the first scheduling
-pass. This pass looks at innermost loops and reorders their
-instructions by overlapping different iterations.
+Notice that the final link is done with @command{g++} to get the C++
+runtime libraries and @option{-lgfortran} is added to get the Fortran
+runtime libraries. In general, when mixing languages in LTO mode, you
+should use the same link command options as when mixing languages in a
+regular (non-LTO) compilation.
-@item -fmodulo-sched-allow-regmoves
-@opindex fmodulo-sched-allow-regmoves
-Perform more aggressive SMS-based modulo scheduling with register moves
-allowed. By setting this flag certain anti-dependences edges are
-deleted, which triggers the generation of reg-moves based on the
-life-range analysis. This option is effective only with
-@option{-fmodulo-sched} enabled.
+If object files containing GIMPLE bytecode are stored in a library archive, say
+@file{libfoo.a}, it is possible to extract and use them in an LTO link if you
+are using a linker with plugin support. To create static libraries suitable
+for LTO, use @command{gcc-ar} and @command{gcc-ranlib} instead of @command{ar}
+and @command{ranlib};
+to show the symbols of object files with GIMPLE bytecode, use
+@command{gcc-nm}. Those commands require that @command{ar}, @command{ranlib}
+and @command{nm} have been compiled with plugin support. At link time, use the the
+flag @option{-fuse-linker-plugin} to ensure that the library participates in
+the LTO optimization process:
-@item -fno-branch-count-reg
-@opindex fno-branch-count-reg
-Do not use ``decrement and branch'' instructions on a count register,
-but instead generate a sequence of instructions that decrement a
-register, compare it against zero, then branch based upon the result.
-This option is only meaningful on architectures that support such
-instructions, which include x86, PowerPC, IA-64 and S/390.
+@smallexample
+gcc -o myprog -O2 -flto -fuse-linker-plugin a.o b.o -lfoo
+@end smallexample
-Enabled by default at @option{-O1} and higher.
+With the linker plugin enabled, the linker extracts the needed
+GIMPLE files from @file{libfoo.a} and passes them on to the running GCC
+to make them part of the aggregated GIMPLE image to be optimized.
-The default is @option{-fbranch-count-reg}.
+If you are not using a linker with plugin support and/or do not
+enable the linker plugin, then the objects inside @file{libfoo.a}
+are extracted and linked as usual, but they do not participate
+in the LTO optimization process. In order to make a static library suitable
+for both LTO optimization and usual linkage, compile its object files with
+@option{-flto} @option{-ffat-lto-objects}.
-@item -fno-function-cse
-@opindex fno-function-cse
-Do not put function addresses in registers; make each instruction that
-calls a constant function contain the function's address explicitly.
+Link-time optimizations do not require the presence of the whole program to
+operate. If the program does not require any symbols to be exported, it is
+possible to combine @option{-flto} and @option{-fwhole-program} to allow
+the interprocedural optimizers to use more aggressive assumptions which may
+lead to improved optimization opportunities.
+Use of @option{-fwhole-program} is not needed when linker plugin is
+active (see @option{-fuse-linker-plugin}).
-This option results in less efficient code, but some strange hacks
-that alter the assembler output may be confused by the optimizations
-performed when this option is not used.
+The current implementation of LTO makes no
+attempt to generate bytecode that is portable between different
+types of hosts. The bytecode files are versioned and there is a
+strict version check, so bytecode files generated in one version of
+GCC do not work with an older or newer version of GCC.
-The default is @option{-ffunction-cse}
+Link-time optimization does not work well with generation of debugging
+information. Combining @option{-flto} with
+@option{-g} is currently experimental and expected to produce unexpected
+results.
-@item -fno-zero-initialized-in-bss
-@opindex fno-zero-initialized-in-bss
-If the target supports a BSS section, GCC by default puts variables that
-are initialized to zero into BSS@. This can save space in the resulting
-code.
+If you specify the optional @var{n}, the optimization and code
+generation done at link time is executed in parallel using @var{n}
+parallel jobs by utilizing an installed @command{make} program. The
+environment variable @env{MAKE} may be used to override the program
+used. The default value for @var{n} is 1.
-This option turns off this behavior because some programs explicitly
-rely on variables going to the data section---e.g., so that the
-resulting executable can find the beginning of that section and/or make
-assumptions based on that.
+You can also specify @option{-flto=jobserver} to use GNU make's
+job server mode to determine the number of parallel jobs. This
+is useful when the Makefile calling GCC is already executing in parallel.
+You must prepend a @samp{+} to the command recipe in the parent Makefile
+for this to work. This option likely only works if @env{MAKE} is
+GNU make.
-The default is @option{-fzero-initialized-in-bss}.
+@item -flto-partition=@var{alg}
+@opindex flto-partition
+Specify the partitioning algorithm used by the link-time optimizer.
+The value is either @samp{1to1} to specify a partitioning mirroring
+the original source files or @samp{balanced} to specify partitioning
+into equally sized chunks (whenever possible) or @samp{max} to create
+new partition for every symbol where possible. Specifying @samp{none}
+as an algorithm disables partitioning and streaming completely.
+The default value is @samp{balanced}. While @samp{1to1} can be used
+as an workaround for various code ordering issues, the @samp{max}
+partitioning is intended for internal testing only.
+The value @samp{one} specifies that exactly one partition should be
+used while the value @samp{none} bypasses partitioning and executes
+the link-time optimization step directly from the WPA phase.
-@item -fthread-jumps
-@opindex fthread-jumps
-Perform optimizations that check to see if a jump branches to a
-location where another comparison subsumed by the first is found. If
-so, the first branch is redirected to either the destination of the
-second branch or a point immediately following it, depending on whether
-the condition is known to be true or false.
+@item -flto-odr-type-merging
+@opindex flto-odr-type-merging
+Enable streaming of mangled types names of C++ types and their unification
+at link time. This increases size of LTO object files, but enables
+diagnostics about One Definition Rule violations.
-Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
+@item -flto-compression-level=@var{n}
+@opindex flto-compression-level
+This option specifies the level of compression used for intermediate
+language written to LTO object files, and is only meaningful in
+conjunction with LTO mode (@option{-flto}). Valid
+values are 0 (no compression) to 9 (maximum compression). Values
+outside this range are clamped to either 0 or 9. If the option is not
+given, a default balanced compression setting is used.
-@item -fsplit-wide-types
-@opindex fsplit-wide-types
-When using a type that occupies multiple registers, such as @code{long
-long} on a 32-bit system, split the registers apart and allocate them
-independently. This normally generates better code for those types,
-but may make debugging more difficult.
+@item -fuse-linker-plugin
+@opindex fuse-linker-plugin
+Enables the use of a linker plugin during link-time optimization. This
+option relies on plugin support in the linker, which is available in gold
+or in GNU ld 2.21 or newer.
-Enabled at levels @option{-O}, @option{-O2}, @option{-O3},
-@option{-Os}.
+This option enables the extraction of object files with GIMPLE bytecode out
+of library archives. This improves the quality of optimization by exposing
+more code to the link-time optimizer. This information specifies what
+symbols can be accessed externally (by non-LTO object or during dynamic
+linking). Resulting code quality improvements on binaries (and shared
+libraries that use hidden visibility) are similar to @option{-fwhole-program}.
+See @option{-flto} for a description of the effect of this flag and how to
+use it.
-@item -fcse-follow-jumps
-@opindex fcse-follow-jumps
-In common subexpression elimination (CSE), scan through jump instructions
-when the target of the jump is not reached by any other path. For
-example, when CSE encounters an @code{if} statement with an
-@code{else} clause, CSE follows the jump when the condition
-tested is false.
+This option is enabled by default when LTO support in GCC is enabled
+and GCC was configured for use with
+a linker supporting plugins (GNU ld 2.21 or newer or gold).
-Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
+@item -ffat-lto-objects
+@opindex ffat-lto-objects
+Fat LTO objects are object files that contain both the intermediate language
+and the object code. This makes them usable for both LTO linking and normal
+linking. This option is effective only when compiling with @option{-flto}
+and is ignored at link time.
+
+@option{-fno-fat-lto-objects} improves compilation time over plain LTO, but
+requires the complete toolchain to be aware of LTO. It requires a linker with
+linker plugin support for basic functionality. Additionally,
+@command{nm}, @command{ar} and @command{ranlib}
+need to support linker plugins to allow a full-featured build environment
+(capable of building static libraries etc). GCC provides the @command{gcc-ar},
+@command{gcc-nm}, @command{gcc-ranlib} wrappers to pass the right options
+to these tools. With non fat LTO makefiles need to be modified to use them.
-@item -fcse-skip-blocks
-@opindex fcse-skip-blocks
-This is similar to @option{-fcse-follow-jumps}, but causes CSE to
-follow jumps that conditionally skip over blocks. When CSE
-encounters a simple @code{if} statement with no else clause,
-@option{-fcse-skip-blocks} causes CSE to follow the jump around the
-body of the @code{if}.
+The default is @option{-fno-fat-lto-objects} on targets with linker plugin
+support.
-Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
+@item -fcompare-elim
+@opindex fcompare-elim
+After register allocation and post-register allocation instruction splitting,
+identify arithmetic instructions that compute processor flags similar to a
+comparison operation based on that arithmetic. If possible, eliminate the
+explicit comparison operation.
-@item -frerun-cse-after-loop
-@opindex frerun-cse-after-loop
-Re-run common subexpression elimination after loop optimizations are
-performed.
+This pass only applies to certain targets that cannot explicitly represent
+the comparison operation before register allocation is complete.
-Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
+Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
-@item -fgcse
-@opindex fgcse
-Perform a global common subexpression elimination pass.
-This pass also performs global constant and copy propagation.
+@item -fcprop-registers
+@opindex fcprop-registers
+After register allocation and post-register allocation instruction splitting,
+perform a copy-propagation pass to try to reduce scheduling dependencies
+and occasionally eliminate the copy.
-@emph{Note:} When compiling a program using computed gotos, a GCC
-extension, you may get better run-time performance if you disable
-the global common subexpression elimination pass by adding
-@option{-fno-gcse} to the command line.
+Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
-Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
+@item -fprofile-correction
+@opindex fprofile-correction
+Profiles collected using an instrumented binary for multi-threaded programs may
+be inconsistent due to missed counter updates. When this option is specified,
+GCC uses heuristics to correct or smooth out such inconsistencies. By
+default, GCC emits an error message when an inconsistent profile is detected.
-@item -fgcse-lm
-@opindex fgcse-lm
-When @option{-fgcse-lm} is enabled, global common subexpression elimination
-attempts to move loads that are only killed by stores into themselves. This
-allows a loop containing a load/store sequence to be changed to a load outside
-the loop, and a copy/store within the loop.
+@item -fprofile-use
+@itemx -fprofile-use=@var{path}
+@opindex fprofile-use
+Enable profile feedback-directed optimizations,
+and the following optimizations
+which are generally profitable only with profile feedback available:
+@option{-fbranch-probabilities}, @option{-fvpt},
+@option{-funroll-loops}, @option{-fpeel-loops}, @option{-ftracer},
+@option{-ftree-vectorize}, and @option{ftree-loop-distribute-patterns}.
-Enabled by default when @option{-fgcse} is enabled.
+Before you can use this option, you must first generate profiling information.
+@xref{Optimize Options}, for information about the @option{-fprofile-generate}
+option.
-@item -fgcse-sm
-@opindex fgcse-sm
-When @option{-fgcse-sm} is enabled, a store motion pass is run after
-global common subexpression elimination. This pass attempts to move
-stores out of loops. When used in conjunction with @option{-fgcse-lm},
-loops containing a load/store sequence can be changed to a load before
-the loop and a store after the loop.
+By default, GCC emits an error message if the feedback profiles do not
+match the source code. This error can be turned into a warning by using
+@option{-Wcoverage-mismatch}. Note this may result in poorly optimized
+code.
-Not enabled at any optimization level.
+If @var{path} is specified, GCC looks at the @var{path} to find
+the profile feedback data files. See @option{-fprofile-dir}.
-@item -fgcse-las
-@opindex fgcse-las
-When @option{-fgcse-las} is enabled, the global common subexpression
-elimination pass eliminates redundant loads that come after stores to the
-same memory location (both partial and full redundancies).
+@item -fauto-profile
+@itemx -fauto-profile=@var{path}
+@opindex fauto-profile
+Enable sampling-based feedback-directed optimizations,
+and the following optimizations
+which are generally profitable only with profile feedback available:
+@option{-fbranch-probabilities}, @option{-fvpt},
+@option{-funroll-loops}, @option{-fpeel-loops}, @option{-ftracer},
+@option{-ftree-vectorize},
+@option{-finline-functions}, @option{-fipa-cp}, @option{-fipa-cp-clone},
+@option{-fpredictive-commoning}, @option{-funswitch-loops},
+@option{-fgcse-after-reload}, and @option{-ftree-loop-distribute-patterns}.
-Not enabled at any optimization level.
+@var{path} is the name of a file containing AutoFDO profile information.
+If omitted, it defaults to @file{fbdata.afdo} in the current directory.
-@item -fgcse-after-reload
-@opindex fgcse-after-reload
-When @option{-fgcse-after-reload} is enabled, a redundant load elimination
-pass is performed after reload. The purpose of this pass is to clean up
-redundant spilling.
+Producing an AutoFDO profile data file requires running your program
+with the @command{perf} utility on a supported GNU/Linux target system.
+For more information, see @uref{https://perf.wiki.kernel.org/}.
-@item -faggressive-loop-optimizations
-@opindex faggressive-loop-optimizations
-This option tells the loop optimizer to use language constraints to
-derive bounds for the number of iterations of a loop. This assumes that
-loop code does not invoke undefined behavior by for example causing signed
-integer overflows or out-of-bound array accesses. The bounds for the
-number of iterations of a loop are used to guide loop unrolling and peeling
-and loop exit test optimizations.
-This option is enabled by default.
+E.g.
+@smallexample
+perf record -e br_inst_retired:near_taken -b -o perf.data \
+ -- your_program
+@end smallexample
-@item -funsafe-loop-optimizations
-@opindex funsafe-loop-optimizations
-This option tells the loop optimizer to assume that loop indices do not
-overflow, and that loops with nontrivial exit condition are not
-infinite. This enables a wider range of loop optimizations even if
-the loop optimizer itself cannot prove that these assumptions are valid.
-If you use @option{-Wunsafe-loop-optimizations}, the compiler warns you
-if it finds this kind of loop.
+Then use the @command{create_gcov} tool to convert the raw profile data
+to a format that can be used by GCC.@ You must also supply the
+unstripped binary for your program to this tool.
+See @uref{https://github.com/google/autofdo}.
-@item -fcrossjumping
-@opindex fcrossjumping
-Perform cross-jumping transformation.
-This transformation unifies equivalent code and saves code size. The
-resulting code may or may not perform better than without cross-jumping.
+E.g.
+@smallexample
+create_gcov --binary=your_program.unstripped --profile=perf.data \
+ --gcov=profile.afdo
+@end smallexample
+@end table
-Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
+The following options control compiler behavior regarding floating-point
+arithmetic. These options trade off between speed and
+correctness. All must be specifically enabled.
-@item -fauto-inc-dec
-@opindex fauto-inc-dec
-Combine increments or decrements of addresses with memory accesses.
-This pass is always skipped on architectures that do not have
-instructions to support this. Enabled by default at @option{-O} and
-higher on architectures that support this.
+@table @gcctabopt
+@item -ffloat-store
+@opindex ffloat-store
+Do not store floating-point variables in registers, and inhibit other
+options that might change whether a floating-point value is taken from a
+register or memory.
-@item -fdce
-@opindex fdce
-Perform dead code elimination (DCE) on RTL@.
-Enabled by default at @option{-O} and higher.
+@cindex floating-point precision
+This option prevents undesirable excess precision on machines such as
+the 68000 where the floating registers (of the 68881) keep more
+precision than a @code{double} is supposed to have. Similarly for the
+x86 architecture. For most programs, the excess precision does only
+good, but a few programs rely on the precise definition of IEEE floating
+point. Use @option{-ffloat-store} for such programs, after modifying
+them to store all pertinent intermediate computations into variables.
-@item -fdse
-@opindex fdse
-Perform dead store elimination (DSE) on RTL@.
-Enabled by default at @option{-O} and higher.
+@item -fexcess-precision=@var{style}
+@opindex fexcess-precision
+This option allows further control over excess precision on machines
+where floating-point registers have more precision than the IEEE
+@code{float} and @code{double} types and the processor does not
+support operations rounding to those types. By default,
+@option{-fexcess-precision=fast} is in effect; this means that
+operations are carried out in the precision of the registers and that
+it is unpredictable when rounding to the types specified in the source
+code takes place. When compiling C, if
+@option{-fexcess-precision=standard} is specified then excess
+precision follows the rules specified in ISO C99; in particular,
+both casts and assignments cause values to be rounded to their
+semantic types (whereas @option{-ffloat-store} only affects
+assignments). This option is enabled by default for C if a strict
+conformance option such as @option{-std=c99} is used.
-@item -fif-conversion
-@opindex fif-conversion
-Attempt to transform conditional jumps into branch-less equivalents. This
-includes use of conditional moves, min, max, set flags and abs instructions, and
-some tricks doable by standard arithmetics. The use of conditional execution
-on chips where it is available is controlled by @option{-fif-conversion2}.
+@opindex mfpmath
+@option{-fexcess-precision=standard} is not implemented for languages
+other than C, and has no effect if
+@option{-funsafe-math-optimizations} or @option{-ffast-math} is
+specified. On the x86, it also has no effect if @option{-mfpmath=sse}
+or @option{-mfpmath=sse+387} is specified; in the former case, IEEE
+semantics apply without excess precision, and in the latter, rounding
+is unpredictable.
-Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
+@item -ffast-math
+@opindex ffast-math
+Sets the options @option{-fno-math-errno}, @option{-funsafe-math-optimizations},
+@option{-ffinite-math-only}, @option{-fno-rounding-math},
+@option{-fno-signaling-nans} and @option{-fcx-limited-range}.
-@item -fif-conversion2
-@opindex fif-conversion2
-Use conditional execution (where available) to transform conditional jumps into
-branch-less equivalents.
+This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
-Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
+This option is not turned on by any @option{-O} option besides
+@option{-Ofast} since it can result in incorrect output for programs
+that depend on an exact implementation of IEEE or ISO rules/specifications
+for math functions. It may, however, yield faster code for programs
+that do not require the guarantees of these specifications.
-@item -fdeclone-ctor-dtor
-@opindex fdeclone-ctor-dtor
-The C++ ABI requires multiple entry points for constructors and
-destructors: one for a base subobject, one for a complete object, and
-one for a virtual destructor that calls operator delete afterwards.
-For a hierarchy with virtual bases, the base and complete variants are
-clones, which means two copies of the function. With this option, the
-base and complete variants are changed to be thunks that call a common
-implementation.
+@item -fno-math-errno
+@opindex fno-math-errno
+Do not set @code{errno} after calling math functions that are executed
+with a single instruction, e.g., @code{sqrt}. A program that relies on
+IEEE exceptions for math error handling may want to use this flag
+for speed while maintaining IEEE arithmetic compatibility.
-Enabled by @option{-Os}.
+This option is not turned on by any @option{-O} option since
+it can result in incorrect output for programs that depend on
+an exact implementation of IEEE or ISO rules/specifications for
+math functions. It may, however, yield faster code for programs
+that do not require the guarantees of these specifications.
-@item -fdelete-null-pointer-checks
-@opindex fdelete-null-pointer-checks
-Assume that programs cannot safely dereference null pointers, and that
-no code or data element resides at address zero.
-This option enables simple constant
-folding optimizations at all optimization levels. In addition, other
-optimization passes in GCC use this flag to control global dataflow
-analyses that eliminate useless checks for null pointers; these assume
-that a memory access to address zero always results in a trap, so
-that if a pointer is checked after it has already been dereferenced,
-it cannot be null.
+The default is @option{-fmath-errno}.
-Note however that in some environments this assumption is not true.
-Use @option{-fno-delete-null-pointer-checks} to disable this optimization
-for programs that depend on that behavior.
+On Darwin systems, the math library never sets @code{errno}. There is
+therefore no reason for the compiler to consider the possibility that
+it might, and @option{-fno-math-errno} is the default.
-This option is enabled by default on most targets. On Nios II ELF, it
-defaults to off. On AVR and CR16, this option is completely disabled.
+@item -funsafe-math-optimizations
+@opindex funsafe-math-optimizations
-Passes that use the dataflow information
-are enabled independently at different optimization levels.
+Allow optimizations for floating-point arithmetic that (a) assume
+that arguments and results are valid and (b) may violate IEEE or
+ANSI standards. When used at link time, it may include libraries
+or startup files that change the default FPU control word or other
+similar optimizations.
-@item -fdevirtualize
-@opindex fdevirtualize
-Attempt to convert calls to virtual functions to direct calls. This
-is done both within a procedure and interprocedurally as part of
-indirect inlining (@option{-findirect-inlining}) and interprocedural constant
-propagation (@option{-fipa-cp}).
-Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
+This option is not turned on by any @option{-O} option since
+it can result in incorrect output for programs that depend on
+an exact implementation of IEEE or ISO rules/specifications for
+math functions. It may, however, yield faster code for programs
+that do not require the guarantees of these specifications.
+Enables @option{-fno-signed-zeros}, @option{-fno-trapping-math},
+@option{-fassociative-math} and @option{-freciprocal-math}.
-@item -fdevirtualize-speculatively
-@opindex fdevirtualize-speculatively
-Attempt to convert calls to virtual functions to speculative direct calls.
-Based on the analysis of the type inheritance graph, determine for a given call
-the set of likely targets. If the set is small, preferably of size 1, change
-the call into a conditional deciding between direct and indirect calls. The
-speculative calls enable more optimizations, such as inlining. When they seem
-useless after further optimization, they are converted back into original form.
+The default is @option{-fno-unsafe-math-optimizations}.
-@item -fdevirtualize-at-ltrans
-@opindex fdevirtualize-at-ltrans
-Stream extra information needed for aggressive devirtualization when running
-the link-time optimizer in local transformation mode.
-This option enables more devirtualization but
-significantly increases the size of streamed data. For this reason it is
-disabled by default.
+@item -fassociative-math
+@opindex fassociative-math
-@item -fexpensive-optimizations
-@opindex fexpensive-optimizations
-Perform a number of minor optimizations that are relatively expensive.
+Allow re-association of operands in series of floating-point operations.
+This violates the ISO C and C++ language standard by possibly changing
+computation result. NOTE: re-ordering may change the sign of zero as
+well as ignore NaNs and inhibit or create underflow or overflow (and
+thus cannot be used on code that relies on rounding behavior like
+@code{(x + 2**52) - 2**52}. May also reorder floating-point comparisons
+and thus may not be used when ordered comparisons are required.
+This option requires that both @option{-fno-signed-zeros} and
+@option{-fno-trapping-math} be in effect. Moreover, it doesn't make
+much sense with @option{-frounding-math}. For Fortran the option
+is automatically enabled when both @option{-fno-signed-zeros} and
+@option{-fno-trapping-math} are in effect.
-Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
+The default is @option{-fno-associative-math}.
-@item -free
-@opindex free
-Attempt to remove redundant extension instructions. This is especially
-helpful for the x86-64 architecture, which implicitly zero-extends in 64-bit
-registers after writing to their lower 32-bit half.
+@item -freciprocal-math
+@opindex freciprocal-math
-Enabled for Alpha, AArch64 and x86 at levels @option{-O2},
-@option{-O3}, @option{-Os}.
+Allow the reciprocal of a value to be used instead of dividing by
+the value if this enables optimizations. For example @code{x / y}
+can be replaced with @code{x * (1/y)}, which is useful if @code{(1/y)}
+is subject to common subexpression elimination. Note that this loses
+precision and increases the number of flops operating on the value.
-@item -fno-lifetime-dse
-@opindex fno-lifetime-dse
-In C++ the value of an object is only affected by changes within its
-lifetime: when the constructor begins, the object has an indeterminate
-value, and any changes during the lifetime of the object are dead when
-the object is destroyed. Normally dead store elimination will take
-advantage of this; if your code relies on the value of the object
-storage persisting beyond the lifetime of the object, you can use this
-flag to disable this optimization.
+The default is @option{-fno-reciprocal-math}.
-@item -flive-range-shrinkage
-@opindex flive-range-shrinkage
-Attempt to decrease register pressure through register live range
-shrinkage. This is helpful for fast processors with small or moderate
-size register sets.
+@item -ffinite-math-only
+@opindex ffinite-math-only
+Allow optimizations for floating-point arithmetic that assume
+that arguments and results are not NaNs or +-Infs.
-@item -fira-algorithm=@var{algorithm}
-@opindex fira-algorithm
-Use the specified coloring algorithm for the integrated register
-allocator. The @var{algorithm} argument can be @samp{priority}, which
-specifies Chow's priority coloring, or @samp{CB}, which specifies
-Chaitin-Briggs coloring. Chaitin-Briggs coloring is not implemented
-for all architectures, but for those targets that do support it, it is
-the default because it generates better code.
+This option is not turned on by any @option{-O} option since
+it can result in incorrect output for programs that depend on
+an exact implementation of IEEE or ISO rules/specifications for
+math functions. It may, however, yield faster code for programs
+that do not require the guarantees of these specifications.
-@item -fira-region=@var{region}
-@opindex fira-region
-Use specified regions for the integrated register allocator. The
-@var{region} argument should be one of the following:
+The default is @option{-fno-finite-math-only}.
-@table @samp
+@item -fno-signed-zeros
+@opindex fno-signed-zeros
+Allow optimizations for floating-point arithmetic that ignore the
+signedness of zero. IEEE arithmetic specifies the behavior of
+distinct +0.0 and @minus{}0.0 values, which then prohibits simplification
+of expressions such as x+0.0 or 0.0*x (even with @option{-ffinite-math-only}).
+This option implies that the sign of a zero result isn't significant.
-@item all
-Use all loops as register allocation regions.
-This can give the best results for machines with a small and/or
-irregular register set.
+The default is @option{-fsigned-zeros}.
-@item mixed
-Use all loops except for loops with small register pressure
-as the regions. This value usually gives
-the best results in most cases and for most architectures,
-and is enabled by default when compiling with optimization for speed
-(@option{-O}, @option{-O2}, @dots{}).
+@item -fno-trapping-math
+@opindex fno-trapping-math
+Compile code assuming that floating-point operations cannot generate
+user-visible traps. These traps include division by zero, overflow,
+underflow, inexact result and invalid operation. This option requires
+that @option{-fno-signaling-nans} be in effect. Setting this option may
+allow faster code if one relies on ``non-stop'' IEEE arithmetic, for example.
-@item one
-Use all functions as a single region.
-This typically results in the smallest code size, and is enabled by default for
-@option{-Os} or @option{-O0}.
+This option should never be turned on by any @option{-O} option since
+it can result in incorrect output for programs that depend on
+an exact implementation of IEEE or ISO rules/specifications for
+math functions.
-@end table
+The default is @option{-ftrapping-math}.
-@item -fira-hoist-pressure
-@opindex fira-hoist-pressure
-Use IRA to evaluate register pressure in the code hoisting pass for
-decisions to hoist expressions. This option usually results in smaller
-code, but it can slow the compiler down.
+@item -frounding-math
+@opindex frounding-math
+Disable transformations and optimizations that assume default floating-point
+rounding behavior. This is round-to-zero for all floating point
+to integer conversions, and round-to-nearest for all other arithmetic
+truncations. This option should be specified for programs that change
+the FP rounding mode dynamically, or that may be executed with a
+non-default rounding mode. This option disables constant folding of
+floating-point expressions at compile time (which may be affected by
+rounding mode) and arithmetic transformations that are unsafe in the
+presence of sign-dependent rounding modes.
-This option is enabled at level @option{-Os} for all targets.
+The default is @option{-fno-rounding-math}.
-@item -fira-loop-pressure
-@opindex fira-loop-pressure
-Use IRA to evaluate register pressure in loops for decisions to move
-loop invariants. This option usually results in generation
-of faster and smaller code on machines with large register files (>= 32
-registers), but it can slow the compiler down.
+This option is experimental and does not currently guarantee to
+disable all GCC optimizations that are affected by rounding mode.
+Future versions of GCC may provide finer control of this setting
+using C99's @code{FENV_ACCESS} pragma. This command-line option
+will be used to specify the default state for @code{FENV_ACCESS}.
-This option is enabled at level @option{-O3} for some targets.
+@item -fsignaling-nans
+@opindex fsignaling-nans
+Compile code assuming that IEEE signaling NaNs may generate user-visible
+traps during floating-point operations. Setting this option disables
+optimizations that may change the number of exceptions visible with
+signaling NaNs. This option implies @option{-ftrapping-math}.
-@item -fno-ira-share-save-slots
-@opindex fno-ira-share-save-slots
-Disable sharing of stack slots used for saving call-used hard
-registers living through a call. Each hard register gets a
-separate stack slot, and as a result function stack frames are
-larger.
+This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
+be defined.
-@item -fno-ira-share-spill-slots
-@opindex fno-ira-share-spill-slots
-Disable sharing of stack slots allocated for pseudo-registers. Each
-pseudo-register that does not get a hard register gets a separate
-stack slot, and as a result function stack frames are larger.
+The default is @option{-fno-signaling-nans}.
-@item -fira-verbose=@var{n}
-@opindex fira-verbose
-Control the verbosity of the dump file for the integrated register allocator.
-The default value is 5. If the value @var{n} is greater or equal to 10,
-the dump output is sent to stderr using the same format as @var{n} minus 10.
+This option is experimental and does not currently guarantee to
+disable all GCC optimizations that affect signaling NaN behavior.
-@item -flra-remat
-@opindex flra-remat
-Enable CFG-sensitive rematerialization in LRA. Instead of loading
-values of spilled pseudos, LRA tries to rematerialize (recalculate)
-values if it is profitable.
+@item -fsingle-precision-constant
+@opindex fsingle-precision-constant
+Treat floating-point constants as single precision instead of
+implicitly converting them to double-precision constants.
-Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
+@item -fcx-limited-range
+@opindex fcx-limited-range
+When enabled, this option states that a range reduction step is not
+needed when performing complex division. Also, there is no checking
+whether the result of a complex multiplication or division is @code{NaN
++ I*NaN}, with an attempt to rescue the situation in that case. The
+default is @option{-fno-cx-limited-range}, but is enabled by
+@option{-ffast-math}.
-@item -fdelayed-branch
-@opindex fdelayed-branch
-If supported for the target machine, attempt to reorder instructions
-to exploit instruction slots available after delayed branch
-instructions.
+This option controls the default setting of the ISO C99
+@code{CX_LIMITED_RANGE} pragma. Nevertheless, the option applies to
+all languages.
-Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
+@item -fcx-fortran-rules
+@opindex fcx-fortran-rules
+Complex multiplication and division follow Fortran rules. Range
+reduction is done as part of complex division, but there is no checking
+whether the result of a complex multiplication or division is @code{NaN
++ I*NaN}, with an attempt to rescue the situation in that case.
-@item -fschedule-insns
-@opindex fschedule-insns
-If supported for the target machine, attempt to reorder instructions to
-eliminate execution stalls due to required data being unavailable. This
-helps machines that have slow floating point or memory load instructions
-by allowing other instructions to be issued until the result of the load
-or floating-point instruction is required.
+The default is @option{-fno-cx-fortran-rules}.
-Enabled at levels @option{-O2}, @option{-O3}.
+@end table
-@item -fschedule-insns2
-@opindex fschedule-insns2
-Similar to @option{-fschedule-insns}, but requests an additional pass of
-instruction scheduling after register allocation has been done. This is
-especially useful on machines with a relatively small number of
-registers and where memory load instructions take more than one cycle.
+The following options control optimizations that may improve
+performance, but are not enabled by any @option{-O} options. This
+section includes experimental options that may produce broken code.
-Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
+@table @gcctabopt
+@item -fbranch-probabilities
+@opindex fbranch-probabilities
+After running a program compiled with @option{-fprofile-arcs}
+(@pxref{Instrumentation Options}),
+you can compile it a second time using
+@option{-fbranch-probabilities}, to improve optimizations based on
+the number of times each branch was taken. When a program
+compiled with @option{-fprofile-arcs} exits, it saves arc execution
+counts to a file called @file{@var{sourcename}.gcda} for each source
+file. The information in this data file is very dependent on the
+structure of the generated code, so you must use the same source code
+and the same optimization options for both compilations.
-@item -fno-sched-interblock
-@opindex fno-sched-interblock
-Don't schedule instructions across basic blocks. This is normally
-enabled by default when scheduling before register allocation, i.e.@:
-with @option{-fschedule-insns} or at @option{-O2} or higher.
+With @option{-fbranch-probabilities}, GCC puts a
+@samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
+These can be used to improve optimization. Currently, they are only
+used in one place: in @file{reorg.c}, instead of guessing which path a
+branch is most likely to take, the @samp{REG_BR_PROB} values are used to
+exactly determine which path is taken more often.
-@item -fno-sched-spec
-@opindex fno-sched-spec
-Don't allow speculative motion of non-load instructions. This is normally
-enabled by default when scheduling before register allocation, i.e.@:
-with @option{-fschedule-insns} or at @option{-O2} or higher.
+@item -fprofile-values
+@opindex fprofile-values
+If combined with @option{-fprofile-arcs}, it adds code so that some
+data about values of expressions in the program is gathered.
-@item -fsched-pressure
-@opindex fsched-pressure
-Enable register pressure sensitive insn scheduling before register
-allocation. This only makes sense when scheduling before register
-allocation is enabled, i.e.@: with @option{-fschedule-insns} or at
-@option{-O2} or higher. Usage of this option can improve the
-generated code and decrease its size by preventing register pressure
-increase above the number of available hard registers and subsequent
-spills in register allocation.
+With @option{-fbranch-probabilities}, it reads back the data gathered
+from profiling values of expressions for usage in optimizations.
-@item -fsched-spec-load
-@opindex fsched-spec-load
-Allow speculative motion of some load instructions. This only makes
-sense when scheduling before register allocation, i.e.@: with
-@option{-fschedule-insns} or at @option{-O2} or higher.
+Enabled with @option{-fprofile-generate} and @option{-fprofile-use}.
-@item -fsched-spec-load-dangerous
-@opindex fsched-spec-load-dangerous
-Allow speculative motion of more load instructions. This only makes
-sense when scheduling before register allocation, i.e.@: with
-@option{-fschedule-insns} or at @option{-O2} or higher.
+@item -fprofile-reorder-functions
+@opindex fprofile-reorder-functions
+Function reordering based on profile instrumentation collects
+first time of execution of a function and orders these functions
+in ascending order.
-@item -fsched-stalled-insns
-@itemx -fsched-stalled-insns=@var{n}
-@opindex fsched-stalled-insns
-Define how many insns (if any) can be moved prematurely from the queue
-of stalled insns into the ready list during the second scheduling pass.
-@option{-fno-sched-stalled-insns} means that no insns are moved
-prematurely, @option{-fsched-stalled-insns=0} means there is no limit
-on how many queued insns can be moved prematurely.
-@option{-fsched-stalled-insns} without a value is equivalent to
-@option{-fsched-stalled-insns=1}.
+Enabled with @option{-fprofile-use}.
-@item -fsched-stalled-insns-dep
-@itemx -fsched-stalled-insns-dep=@var{n}
-@opindex fsched-stalled-insns-dep
-Define how many insn groups (cycles) are examined for a dependency
-on a stalled insn that is a candidate for premature removal from the queue
-of stalled insns. This has an effect only during the second scheduling pass,
-and only if @option{-fsched-stalled-insns} is used.
-@option{-fno-sched-stalled-insns-dep} is equivalent to
-@option{-fsched-stalled-insns-dep=0}.
-@option{-fsched-stalled-insns-dep} without a value is equivalent to
-@option{-fsched-stalled-insns-dep=1}.
+@item -fvpt
+@opindex fvpt
+If combined with @option{-fprofile-arcs}, this option instructs the compiler
+to add code to gather information about values of expressions.
-@item -fsched2-use-superblocks
-@opindex fsched2-use-superblocks
-When scheduling after register allocation, use superblock scheduling.
-This allows motion across basic block boundaries,
-resulting in faster schedules. This option is experimental, as not all machine
-descriptions used by GCC model the CPU closely enough to avoid unreliable
-results from the algorithm.
+With @option{-fbranch-probabilities}, it reads back the data gathered
+and actually performs the optimizations based on them.
+Currently the optimizations include specialization of division operations
+using the knowledge about the value of the denominator.
-This only makes sense when scheduling after register allocation, i.e.@: with
-@option{-fschedule-insns2} or at @option{-O2} or higher.
+@item -frename-registers
+@opindex frename-registers
+Attempt to avoid false dependencies in scheduled code by making use
+of registers left over after register allocation. This optimization
+most benefits processors with lots of registers. Depending on the
+debug information format adopted by the target, however, it can
+make debugging impossible, since variables no longer stay in
+a ``home register''.
-@item -fsched-group-heuristic
-@opindex fsched-group-heuristic
-Enable the group heuristic in the scheduler. This heuristic favors
-the instruction that belongs to a schedule group. This is enabled
-by default when scheduling is enabled, i.e.@: with @option{-fschedule-insns}
-or @option{-fschedule-insns2} or at @option{-O2} or higher.
+Enabled by default with @option{-funroll-loops} and @option{-fpeel-loops},
+and also enabled at levels @option{-O2} and @option{-O3}.
-@item -fsched-critical-path-heuristic
-@opindex fsched-critical-path-heuristic
-Enable the critical-path heuristic in the scheduler. This heuristic favors
-instructions on the critical path. This is enabled by default when
-scheduling is enabled, i.e.@: with @option{-fschedule-insns}
-or @option{-fschedule-insns2} or at @option{-O2} or higher.
+@item -fschedule-fusion
+@opindex fschedule-fusion
+Performs a target dependent pass over the instruction stream to schedule
+instructions of same type together because target machine can execute them
+more efficiently if they are adjacent to each other in the instruction flow.
-@item -fsched-spec-insn-heuristic
-@opindex fsched-spec-insn-heuristic
-Enable the speculative instruction heuristic in the scheduler. This
-heuristic favors speculative instructions with greater dependency weakness.
-This is enabled by default when scheduling is enabled, i.e.@:
-with @option{-fschedule-insns} or @option{-fschedule-insns2}
-or at @option{-O2} or higher.
+Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
-@item -fsched-rank-heuristic
-@opindex fsched-rank-heuristic
-Enable the rank heuristic in the scheduler. This heuristic favors
-the instruction belonging to a basic block with greater size or frequency.
-This is enabled by default when scheduling is enabled, i.e.@:
-with @option{-fschedule-insns} or @option{-fschedule-insns2} or
-at @option{-O2} or higher.
+@item -ftracer
+@opindex ftracer
+Perform tail duplication to enlarge superblock size. This transformation
+simplifies the control flow of the function allowing other optimizations to do
+a better job.
-@item -fsched-last-insn-heuristic
-@opindex fsched-last-insn-heuristic
-Enable the last-instruction heuristic in the scheduler. This heuristic
-favors the instruction that is less dependent on the last instruction
-scheduled. This is enabled by default when scheduling is enabled,
-i.e.@: with @option{-fschedule-insns} or @option{-fschedule-insns2} or
-at @option{-O2} or higher.
+Enabled with @option{-fprofile-use}.
-@item -fsched-dep-count-heuristic
-@opindex fsched-dep-count-heuristic
-Enable the dependent-count heuristic in the scheduler. This heuristic
-favors the instruction that has more instructions depending on it.
-This is enabled by default when scheduling is enabled, i.e.@:
-with @option{-fschedule-insns} or @option{-fschedule-insns2} or
-at @option{-O2} or higher.
+@item -funroll-loops
+@opindex funroll-loops
+Unroll loops whose number of iterations can be determined at compile time or
+upon entry to the loop. @option{-funroll-loops} implies
+@option{-frerun-cse-after-loop}, @option{-fweb} and @option{-frename-registers}.
+It also turns on complete loop peeling (i.e.@: complete removal of loops with
+a small constant number of iterations). This option makes code larger, and may
+or may not make it run faster.
-@item -freschedule-modulo-scheduled-loops
-@opindex freschedule-modulo-scheduled-loops
-Modulo scheduling is performed before traditional scheduling. If a loop
-is modulo scheduled, later scheduling passes may change its schedule.
-Use this option to control that behavior.
+Enabled with @option{-fprofile-use}.
-@item -fselective-scheduling
-@opindex fselective-scheduling
-Schedule instructions using selective scheduling algorithm. Selective
-scheduling runs instead of the first scheduler pass.
+@item -funroll-all-loops
+@opindex funroll-all-loops
+Unroll all loops, even if their number of iterations is uncertain when
+the loop is entered. This usually makes programs run more slowly.
+@option{-funroll-all-loops} implies the same options as
+@option{-funroll-loops}.
-@item -fselective-scheduling2
-@opindex fselective-scheduling2
-Schedule instructions using selective scheduling algorithm. Selective
-scheduling runs instead of the second scheduler pass.
+@item -fpeel-loops
+@opindex fpeel-loops
+Peels loops for which there is enough information that they do not
+roll much (from profile feedback). It also turns on complete loop peeling
+(i.e.@: complete removal of loops with small constant number of iterations).
-@item -fsel-sched-pipelining
-@opindex fsel-sched-pipelining
-Enable software pipelining of innermost loops during selective scheduling.
-This option has no effect unless one of @option{-fselective-scheduling} or
-@option{-fselective-scheduling2} is turned on.
+Enabled with @option{-fprofile-use}.
-@item -fsel-sched-pipelining-outer-loops
-@opindex fsel-sched-pipelining-outer-loops
-When pipelining loops during selective scheduling, also pipeline outer loops.
-This option has no effect unless @option{-fsel-sched-pipelining} is turned on.
+@item -fmove-loop-invariants
+@opindex fmove-loop-invariants
+Enables the loop invariant motion pass in the RTL loop optimizer. Enabled
+at level @option{-O1}
-@item -fsemantic-interposition
-@opindex fsemantic-interposition
-Some object formats, like ELF, allow interposing of symbols by the
-dynamic linker.
-This means that for symbols exported from the DSO, the compiler cannot perform
-interprocedural propagation, inlining and other optimizations in anticipation
-that the function or variable in question may change. While this feature is
-useful, for example, to rewrite memory allocation functions by a debugging
-implementation, it is expensive in the terms of code quality.
-With @option{-fno-semantic-interposition} the compiler assumes that
-if interposition happens for functions the overwriting function will have
-precisely the same semantics (and side effects).
-Similarly if interposition happens
-for variables, the constructor of the variable will be the same. The flag
-has no effect for functions explicitly declared inline
-(where it is never allowed for interposition to change semantics)
-and for symbols explicitly declared weak.
+@item -funswitch-loops
+@opindex funswitch-loops
+Move branches with loop invariant conditions out of the loop, with duplicates
+of the loop on both branches (modified according to result of the condition).
-@item -fshrink-wrap
-@opindex fshrink-wrap
-Emit function prologues only before parts of the function that need it,
-rather than at the top of the function. This flag is enabled by default at
-@option{-O} and higher.
+@item -ffunction-sections
+@itemx -fdata-sections
+@opindex ffunction-sections
+@opindex fdata-sections
+Place each function or data item into its own section in the output
+file if the target supports arbitrary sections. The name of the
+function or the name of the data item determines the section's name
+in the output file.
-@item -fcaller-saves
-@opindex fcaller-saves
-Enable allocation of values to registers that are clobbered by
-function calls, by emitting extra instructions to save and restore the
-registers around such calls. Such allocation is done only when it
-seems to result in better code.
+Use these options on systems where the linker can perform optimizations
+to improve locality of reference in the instruction space. Most systems
+using the ELF object format and SPARC processors running Solaris 2 have
+linkers with such optimizations. AIX may have these optimizations in
+the future.
+
+Only use these options when there are significant benefits from doing
+so. When you specify these options, the assembler and linker
+create larger object and executable files and are also slower.
+You cannot use @command{gprof} on all systems if you
+specify this option, and you may have problems with debugging if
+you specify both this option and @option{-g}.
-This option is always enabled by default on certain machines, usually
-those which have no call-preserved registers to use instead.
+@item -fbranch-target-load-optimize
+@opindex fbranch-target-load-optimize
+Perform branch target register load optimization before prologue / epilogue
+threading.
+The use of target registers can typically be exposed only during reload,
+thus hoisting loads out of loops and doing inter-block scheduling needs
+a separate optimization pass.
-Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
+@item -fbranch-target-load-optimize2
+@opindex fbranch-target-load-optimize2
+Perform branch target register load optimization after prologue / epilogue
+threading.
-@item -fcombine-stack-adjustments
-@opindex fcombine-stack-adjustments
-Tracks stack adjustments (pushes and pops) and stack memory references
-and then tries to find ways to combine them.
+@item -fbtr-bb-exclusive
+@opindex fbtr-bb-exclusive
+When performing branch target register load optimization, don't reuse
+branch target registers within any basic block.
-Enabled by default at @option{-O1} and higher.
+@item -fstdarg-opt
+@opindex fstdarg-opt
+Optimize the prologue of variadic argument functions with respect to usage of
+those arguments.
-@item -fipa-ra
-@opindex fipa-ra
-Use caller save registers for allocation if those registers are not used by
-any called function. In that case it is not necessary to save and restore
-them around calls. This is only possible if called functions are part of
-same compilation unit as current function and they are compiled before it.
+@item -fsection-anchors
+@opindex fsection-anchors
+Try to reduce the number of symbolic address calculations by using
+shared ``anchor'' symbols to address nearby objects. This transformation
+can help to reduce the number of GOT entries and GOT accesses on some
+targets.
-Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
+For example, the implementation of the following function @code{foo}:
-@item -fconserve-stack
-@opindex fconserve-stack
-Attempt to minimize stack usage. The compiler attempts to use less
-stack space, even if that makes the program slower. This option
-implies setting the @option{large-stack-frame} parameter to 100
-and the @option{large-stack-frame-growth} parameter to 400.
+@smallexample
+static int a, b, c;
+int foo (void) @{ return a + b + c; @}
+@end smallexample
-@item -ftree-reassoc
-@opindex ftree-reassoc
-Perform reassociation on trees. This flag is enabled by default
-at @option{-O} and higher.
+@noindent
+usually calculates the addresses of all three variables, but if you
+compile it with @option{-fsection-anchors}, it accesses the variables
+from a common anchor point instead. The effect is similar to the
+following pseudocode (which isn't valid C):
-@item -ftree-pre
-@opindex ftree-pre
-Perform partial redundancy elimination (PRE) on trees. This flag is
-enabled by default at @option{-O2} and @option{-O3}.
+@smallexample
+int foo (void)
+@{
+ register int *xr = &x;
+ return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
+@}
+@end smallexample
-@item -ftree-partial-pre
-@opindex ftree-partial-pre
-Make partial redundancy elimination (PRE) more aggressive. This flag is
-enabled by default at @option{-O3}.
+Not all targets support this option.
-@item -ftree-forwprop
-@opindex ftree-forwprop
-Perform forward propagation on trees. This flag is enabled by default
-at @option{-O} and higher.
+@item --param @var{name}=@var{value}
+@opindex param
+In some places, GCC uses various constants to control the amount of
+optimization that is done. For example, GCC does not inline functions
+that contain more than a certain number of instructions. You can
+control some of these constants on the command line using the
+@option{--param} option.
-@item -ftree-fre
-@opindex ftree-fre
-Perform full redundancy elimination (FRE) on trees. The difference
-between FRE and PRE is that FRE only considers expressions
-that are computed on all paths leading to the redundant computation.
-This analysis is faster than PRE, though it exposes fewer redundancies.
-This flag is enabled by default at @option{-O} and higher.
+The names of specific parameters, and the meaning of the values, are
+tied to the internals of the compiler, and are subject to change
+without notice in future releases.
-@item -ftree-phiprop
-@opindex ftree-phiprop
-Perform hoisting of loads from conditional pointers on trees. This
-pass is enabled by default at @option{-O} and higher.
+In each case, the @var{value} is an integer. The allowable choices for
+@var{name} are:
-@item -fhoist-adjacent-loads
-@opindex fhoist-adjacent-loads
-Speculatively hoist loads from both branches of an if-then-else if the
-loads are from adjacent locations in the same structure and the target
-architecture has a conditional move instruction. This flag is enabled
-by default at @option{-O2} and higher.
+@table @gcctabopt
+@item predictable-branch-outcome
+When branch is predicted to be taken with probability lower than this threshold
+(in percent), then it is considered well predictable. The default is 10.
-@item -ftree-copy-prop
-@opindex ftree-copy-prop
-Perform copy propagation on trees. This pass eliminates unnecessary
-copy operations. This flag is enabled by default at @option{-O} and
-higher.
+@item max-rtl-if-conversion-insns
+RTL if-conversion tries to remove conditional branches around a block and
+replace them with conditionally executed instructions. This parameter
+gives the maximum number of instructions in a block which should be
+considered for if-conversion. The default is 10, though the compiler will
+also use other heuristics to decide whether if-conversion is likely to be
+profitable.
-@item -fipa-pure-const
-@opindex fipa-pure-const
-Discover which functions are pure or constant.
-Enabled by default at @option{-O} and higher.
+@item max-crossjump-edges
+The maximum number of incoming edges to consider for cross-jumping.
+The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in
+the number of edges incoming to each block. Increasing values mean
+more aggressive optimization, making the compilation time increase with
+probably small improvement in executable size.
-@item -fipa-reference
-@opindex fipa-reference
-Discover which static variables do not escape the
-compilation unit.
-Enabled by default at @option{-O} and higher.
+@item min-crossjump-insns
+The minimum number of instructions that must be matched at the end
+of two blocks before cross-jumping is performed on them. This
+value is ignored in the case where all instructions in the block being
+cross-jumped from are matched. The default value is 5.
-@item -fipa-pta
-@opindex fipa-pta
-Perform interprocedural pointer analysis and interprocedural modification
-and reference analysis. This option can cause excessive memory and
-compile-time usage on large compilation units. It is not enabled by
-default at any optimization level.
+@item max-grow-copy-bb-insns
+The maximum code size expansion factor when copying basic blocks
+instead of jumping. The expansion is relative to a jump instruction.
+The default value is 8.
-@item -fipa-profile
-@opindex fipa-profile
-Perform interprocedural profile propagation. The functions called only from
-cold functions are marked as cold. Also functions executed once (such as
-@code{cold}, @code{noreturn}, static constructors or destructors) are identified. Cold
-functions and loop less parts of functions executed once are then optimized for
-size.
-Enabled by default at @option{-O} and higher.
+@item max-goto-duplication-insns
+The maximum number of instructions to duplicate to a block that jumps
+to a computed goto. To avoid @math{O(N^2)} behavior in a number of
+passes, GCC factors computed gotos early in the compilation process,
+and unfactors them as late as possible. Only computed jumps at the
+end of a basic blocks with no more than max-goto-duplication-insns are
+unfactored. The default value is 8.
-@item -fipa-cp
-@opindex fipa-cp
-Perform interprocedural constant propagation.
-This optimization analyzes the program to determine when values passed
-to functions are constants and then optimizes accordingly.
-This optimization can substantially increase performance
-if the application has constants passed to functions.
-This flag is enabled by default at @option{-O2}, @option{-Os} and @option{-O3}.
+@item max-delay-slot-insn-search
+The maximum number of instructions to consider when looking for an
+instruction to fill a delay slot. If more than this arbitrary number of
+instructions are searched, the time savings from filling the delay slot
+are minimal, so stop searching. Increasing values mean more
+aggressive optimization, making the compilation time increase with probably
+small improvement in execution time.
-@item -fipa-cp-clone
-@opindex fipa-cp-clone
-Perform function cloning to make interprocedural constant propagation stronger.
-When enabled, interprocedural constant propagation performs function cloning
-when externally visible function can be called with constant arguments.
-Because this optimization can create multiple copies of functions,
-it may significantly increase code size
-(see @option{--param ipcp-unit-growth=@var{value}}).
-This flag is enabled by default at @option{-O3}.
+@item max-delay-slot-live-search
+When trying to fill delay slots, the maximum number of instructions to
+consider when searching for a block with valid live register
+information. Increasing this arbitrarily chosen value means more
+aggressive optimization, increasing the compilation time. This parameter
+should be removed when the delay slot code is rewritten to maintain the
+control-flow graph.
-@item -fipa-cp-alignment
-@opindex -fipa-cp-alignment
-When enabled, this optimization propagates alignment of function
-parameters to support better vectorization and string operations.
+@item max-gcse-memory
+The approximate maximum amount of memory that can be allocated in
+order to perform the global common subexpression elimination
+optimization. If more memory than specified is required, the
+optimization is not done.
-This flag is enabled by default at @option{-O2} and @option{-Os}. It
-requires that @option{-fipa-cp} is enabled.
+@item max-gcse-insertion-ratio
+If the ratio of expression insertions to deletions is larger than this value
+for any expression, then RTL PRE inserts or removes the expression and thus
+leaves partially redundant computations in the instruction stream. The default value is 20.
-@item -fipa-icf
-@opindex fipa-icf
-Perform Identical Code Folding for functions and read-only variables.
-The optimization reduces code size and may disturb unwind stacks by replacing
-a function by equivalent one with a different name. The optimization works
-more effectively with link time optimization enabled.
+@item max-pending-list-length
+The maximum number of pending dependencies scheduling allows
+before flushing the current state and starting over. Large functions
+with few branches or calls can create excessively large lists which
+needlessly consume memory and resources.
-Nevertheless the behavior is similar to Gold Linker ICF optimization, GCC ICF
-works on different levels and thus the optimizations are not same - there are
-equivalences that are found only by GCC and equivalences found only by Gold.
+@item max-modulo-backtrack-attempts
+The maximum number of backtrack attempts the scheduler should make
+when modulo scheduling a loop. Larger values can exponentially increase
+compilation time.
-This flag is enabled by default at @option{-O2} and @option{-Os}.
+@item max-inline-insns-single
+Several parameters control the tree inliner used in GCC@.
+This number sets the maximum number of instructions (counted in GCC's
+internal representation) in a single function that the tree inliner
+considers for inlining. This only affects functions declared
+inline and methods implemented in a class declaration (C++).
+The default value is 400.
-@item -fisolate-erroneous-paths-dereference
-@opindex fisolate-erroneous-paths-dereference
-Detect paths that trigger erroneous or undefined behavior due to
-dereferencing a null pointer. Isolate those paths from the main control
-flow and turn the statement with erroneous or undefined behavior into a trap.
-This flag is enabled by default at @option{-O2} and higher and depends on
-@option{-fdelete-null-pointer-checks} also being enabled.
+@item max-inline-insns-auto
+When you use @option{-finline-functions} (included in @option{-O3}),
+a lot of functions that would otherwise not be considered for inlining
+by the compiler are investigated. To those functions, a different
+(more restrictive) limit compared to functions declared inline can
+be applied.
+The default value is 40.
+
+@item inline-min-speedup
+When estimated performance improvement of caller + callee runtime exceeds this
+threshold (in precent), the function can be inlined regardless the limit on
+@option{--param max-inline-insns-single} and @option{--param
+max-inline-insns-auto}.
-@item -fisolate-erroneous-paths-attribute
-@opindex fisolate-erroneous-paths-attribute
-Detect paths that trigger erroneous or undefined behavior due a null value
-being used in a way forbidden by a @code{returns_nonnull} or @code{nonnull}
-attribute. Isolate those paths from the main control flow and turn the
-statement with erroneous or undefined behavior into a trap. This is not
-currently enabled, but may be enabled by @option{-O2} in the future.
+@item large-function-insns
+The limit specifying really large functions. For functions larger than this
+limit after inlining, inlining is constrained by
+@option{--param large-function-growth}. This parameter is useful primarily
+to avoid extreme compilation time caused by non-linear algorithms used by the
+back end.
+The default value is 2700.
-@item -ftree-sink
-@opindex ftree-sink
-Perform forward store motion on trees. This flag is
-enabled by default at @option{-O} and higher.
+@item large-function-growth
+Specifies maximal growth of large function caused by inlining in percents.
+The default value is 100 which limits large function growth to 2.0 times
+the original size.
-@item -ftree-bit-ccp
-@opindex ftree-bit-ccp
-Perform sparse conditional bit constant propagation on trees and propagate
-pointer alignment information.
-This pass only operates on local scalar variables and is enabled by default
-at @option{-O} and higher. It requires that @option{-ftree-ccp} is enabled.
+@item large-unit-insns
+The limit specifying large translation unit. Growth caused by inlining of
+units larger than this limit is limited by @option{--param inline-unit-growth}.
+For small units this might be too tight.
+For example, consider a unit consisting of function A
+that is inline and B that just calls A three times. If B is small relative to
+A, the growth of unit is 300\% and yet such inlining is very sane. For very
+large units consisting of small inlineable functions, however, the overall unit
+growth limit is needed to avoid exponential explosion of code size. Thus for
+smaller units, the size is increased to @option{--param large-unit-insns}
+before applying @option{--param inline-unit-growth}. The default is 10000.
-@item -ftree-ccp
-@opindex ftree-ccp
-Perform sparse conditional constant propagation (CCP) on trees. This
-pass only operates on local scalar variables and is enabled by default
-at @option{-O} and higher.
+@item inline-unit-growth
+Specifies maximal overall growth of the compilation unit caused by inlining.
+The default value is 20 which limits unit growth to 1.2 times the original
+size. Cold functions (either marked cold via an attribute or by profile
+feedback) are not accounted into the unit size.
-@item -fssa-backprop
-@opindex fssa-backprop
-Propagate information about uses of a value up the definition chain
-in order to simplify the definitions. For example, this pass strips
-sign operations if the sign of a value never matters. The flag is
-enabled by default at @option{-O} and higher.
+@item ipcp-unit-growth
+Specifies maximal overall growth of the compilation unit caused by
+interprocedural constant propagation. The default value is 10 which limits
+unit growth to 1.1 times the original size.
-@item -fssa-phiopt
-@opindex fssa-phiopt
-Perform pattern matching on SSA PHI nodes to optimize conditional
-code. This pass is enabled by default at @option{-O} and higher.
+@item large-stack-frame
+The limit specifying large stack frames. While inlining the algorithm is trying
+to not grow past this limit too much. The default value is 256 bytes.
-@item -ftree-switch-conversion
-@opindex ftree-switch-conversion
-Perform conversion of simple initializations in a switch to
-initializations from a scalar array. This flag is enabled by default
-at @option{-O2} and higher.
+@item large-stack-frame-growth
+Specifies maximal growth of large stack frames caused by inlining in percents.
+The default value is 1000 which limits large stack frame growth to 11 times
+the original size.
-@item -ftree-tail-merge
-@opindex ftree-tail-merge
-Look for identical code sequences. When found, replace one with a jump to the
-other. This optimization is known as tail merging or cross jumping. This flag
-is enabled by default at @option{-O2} and higher. The compilation time
-in this pass can
-be limited using @option{max-tail-merge-comparisons} parameter and
-@option{max-tail-merge-iterations} parameter.
+@item max-inline-insns-recursive
+@itemx max-inline-insns-recursive-auto
+Specifies the maximum number of instructions an out-of-line copy of a
+self-recursive inline
+function can grow into by performing recursive inlining.
-@item -ftree-dce
-@opindex ftree-dce
-Perform dead code elimination (DCE) on trees. This flag is enabled by
-default at @option{-O} and higher.
+@option{--param max-inline-insns-recursive} applies to functions
+declared inline.
+For functions not declared inline, recursive inlining
+happens only when @option{-finline-functions} (included in @option{-O3}) is
+enabled; @option{--param max-inline-insns-recursive-auto} applies instead. The
+default value is 450.
-@item -ftree-builtin-call-dce
-@opindex ftree-builtin-call-dce
-Perform conditional dead code elimination (DCE) for calls to built-in functions
-that may set @code{errno} but are otherwise side-effect free. This flag is
-enabled by default at @option{-O2} and higher if @option{-Os} is not also
-specified.
+@item max-inline-recursive-depth
+@itemx max-inline-recursive-depth-auto
+Specifies the maximum recursion depth used for recursive inlining.
-@item -ftree-dominator-opts
-@opindex ftree-dominator-opts
-Perform a variety of simple scalar cleanups (constant/copy
-propagation, redundancy elimination, range propagation and expression
-simplification) based on a dominator tree traversal. This also
-performs jump threading (to reduce jumps to jumps). This flag is
-enabled by default at @option{-O} and higher.
+@option{--param max-inline-recursive-depth} applies to functions
+declared inline. For functions not declared inline, recursive inlining
+happens only when @option{-finline-functions} (included in @option{-O3}) is
+enabled; @option{--param max-inline-recursive-depth-auto} applies instead. The
+default value is 8.
-@item -ftree-dse
-@opindex ftree-dse
-Perform dead store elimination (DSE) on trees. A dead store is a store into
-a memory location that is later overwritten by another store without
-any intervening loads. In this case the earlier store can be deleted. This
-flag is enabled by default at @option{-O} and higher.
+@item min-inline-recursive-probability
+Recursive inlining is profitable only for function having deep recursion
+in average and can hurt for function having little recursion depth by
+increasing the prologue size or complexity of function body to other
+optimizers.
-@item -ftree-ch
-@opindex ftree-ch
-Perform loop header copying on trees. This is beneficial since it increases
-effectiveness of code motion optimizations. It also saves one jump. This flag
-is enabled by default at @option{-O} and higher. It is not enabled
-for @option{-Os}, since it usually increases code size.
+When profile feedback is available (see @option{-fprofile-generate}) the actual
+recursion depth can be guessed from probability that function recurses via a
+given call expression. This parameter limits inlining only to call expressions
+whose probability exceeds the given threshold (in percents).
+The default value is 10.
-@item -ftree-loop-optimize
-@opindex ftree-loop-optimize
-Perform loop optimizations on trees. This flag is enabled by default
-at @option{-O} and higher.
+@item early-inlining-insns
+Specify growth that the early inliner can make. In effect it increases
+the amount of inlining for code having a large abstraction penalty.
+The default value is 14.
-@item -ftree-loop-linear
-@itemx -floop-interchange
-@itemx -floop-strip-mine
-@itemx -floop-block
-@itemx -floop-unroll-and-jam
-@opindex ftree-loop-linear
-@opindex floop-interchange
-@opindex floop-strip-mine
-@opindex floop-block
-@opindex floop-unroll-and-jam
-Perform loop nest optimizations. Same as
-@option{-floop-nest-optimize}. To use this code transformation, GCC has
-to be configured with @option{--with-isl} to enable the Graphite loop
-transformation infrastructure.
+@item max-early-inliner-iterations
+Limit of iterations of the early inliner. This basically bounds
+the number of nested indirect calls the early inliner can resolve.
+Deeper chains are still handled by late inlining.
-@item -fgraphite-identity
-@opindex fgraphite-identity
-Enable the identity transformation for graphite. For every SCoP we generate
-the polyhedral representation and transform it back to gimple. Using
-@option{-fgraphite-identity} we can check the costs or benefits of the
-GIMPLE -> GRAPHITE -> GIMPLE transformation. Some minimal optimizations
-are also performed by the code generator ISL, like index splitting and
-dead code elimination in loops.
+@item comdat-sharing-probability
+Probability (in percent) that C++ inline function with comdat visibility
+are shared across multiple compilation units. The default value is 20.
-@item -floop-nest-optimize
-@opindex floop-nest-optimize
-Enable the ISL based loop nest optimizer. This is a generic loop nest
-optimizer based on the Pluto optimization algorithms. It calculates a loop
-structure optimized for data-locality and parallelism. This option
-is experimental.
+@item profile-func-internal-id
+A parameter to control whether to use function internal id in profile
+database lookup. If the value is 0, the compiler uses an id that
+is based on function assembler name and filename, which makes old profile
+data more tolerant to source changes such as function reordering etc.
+The default value is 0.
-@item -floop-parallelize-all
-@opindex floop-parallelize-all
-Use the Graphite data dependence analysis to identify loops that can
-be parallelized. Parallelize all the loops that can be analyzed to
-not contain loop carried dependences without checking that it is
-profitable to parallelize the loops.
+@item min-vect-loop-bound
+The minimum number of iterations under which loops are not vectorized
+when @option{-ftree-vectorize} is used. The number of iterations after
+vectorization needs to be greater than the value specified by this option
+to allow vectorization. The default value is 0.
-@item -ftree-coalesce-vars
-@opindex ftree-coalesce-vars
-While transforming the program out of the SSA representation, attempt to
-reduce copying by coalescing versions of different user-defined
-variables, instead of just compiler temporaries. This may severely
-limit the ability to debug an optimized program compiled with
-@option{-fno-var-tracking-assignments}. In the negated form, this flag
-prevents SSA coalescing of user variables. This option is enabled by
-default if optimization is enabled, and it does very little otherwise.
+@item gcse-cost-distance-ratio
+Scaling factor in calculation of maximum distance an expression
+can be moved by GCSE optimizations. This is currently supported only in the
+code hoisting pass. The bigger the ratio, the more aggressive code hoisting
+is with simple expressions, i.e., the expressions that have cost
+less than @option{gcse-unrestricted-cost}. Specifying 0 disables
+hoisting of simple expressions. The default value is 10.
-@item -ftree-loop-if-convert
-@opindex ftree-loop-if-convert
-Attempt to transform conditional jumps in the innermost loops to
-branch-less equivalents. The intent is to remove control-flow from
-the innermost loops in order to improve the ability of the
-vectorization pass to handle these loops. This is enabled by default
-if vectorization is enabled.
+@item gcse-unrestricted-cost
+Cost, roughly measured as the cost of a single typical machine
+instruction, at which GCSE optimizations do not constrain
+the distance an expression can travel. This is currently
+supported only in the code hoisting pass. The lesser the cost,
+the more aggressive code hoisting is. Specifying 0
+allows all expressions to travel unrestricted distances.
+The default value is 3.
-@item -ftree-loop-if-convert-stores
-@opindex ftree-loop-if-convert-stores
-Attempt to also if-convert conditional jumps containing memory writes.
-This transformation can be unsafe for multi-threaded programs as it
-transforms conditional memory writes into unconditional memory writes.
-For example,
-@smallexample
-for (i = 0; i < N; i++)
- if (cond)
- A[i] = expr;
-@end smallexample
-is transformed to
-@smallexample
-for (i = 0; i < N; i++)
- A[i] = cond ? expr : A[i];
-@end smallexample
-potentially producing data races.
+@item max-hoist-depth
+The depth of search in the dominator tree for expressions to hoist.
+This is used to avoid quadratic behavior in hoisting algorithm.
+The value of 0 does not limit on the search, but may slow down compilation
+of huge functions. The default value is 30.
+
+@item max-tail-merge-comparisons
+The maximum amount of similar bbs to compare a bb with. This is used to
+avoid quadratic behavior in tree tail merging. The default value is 10.
-@item -ftree-loop-distribution
-@opindex ftree-loop-distribution
-Perform loop distribution. This flag can improve cache performance on
-big loop bodies and allow further loop optimizations, like
-parallelization or vectorization, to take place. For example, the loop
-@smallexample
-DO I = 1, N
- A(I) = B(I) + C
- D(I) = E(I) * F
-ENDDO
-@end smallexample
-is transformed to
-@smallexample
-DO I = 1, N
- A(I) = B(I) + C
-ENDDO
-DO I = 1, N
- D(I) = E(I) * F
-ENDDO
-@end smallexample
+@item max-tail-merge-iterations
+The maximum amount of iterations of the pass over the function. This is used to
+limit compilation time in tree tail merging. The default value is 2.
-@item -ftree-loop-distribute-patterns
-@opindex ftree-loop-distribute-patterns
-Perform loop distribution of patterns that can be code generated with
-calls to a library. This flag is enabled by default at @option{-O3}.
+@item max-unrolled-insns
+The maximum number of instructions that a loop may have to be unrolled.
+If a loop is unrolled, this parameter also determines how many times
+the loop code is unrolled.
-This pass distributes the initialization loops and generates a call to
-memset zero. For example, the loop
-@smallexample
-DO I = 1, N
- A(I) = 0
- B(I) = A(I) + I
-ENDDO
-@end smallexample
-is transformed to
-@smallexample
-DO I = 1, N
- A(I) = 0
-ENDDO
-DO I = 1, N
- B(I) = A(I) + I
-ENDDO
-@end smallexample
-and the initialization loop is transformed into a call to memset zero.
+@item max-average-unrolled-insns
+The maximum number of instructions biased by probabilities of their execution
+that a loop may have to be unrolled. If a loop is unrolled,
+this parameter also determines how many times the loop code is unrolled.
-@item -ftree-loop-im
-@opindex ftree-loop-im
-Perform loop invariant motion on trees. This pass moves only invariants that
-are hard to handle at RTL level (function calls, operations that expand to
-nontrivial sequences of insns). With @option{-funswitch-loops} it also moves
-operands of conditions that are invariant out of the loop, so that we can use
-just trivial invariantness analysis in loop unswitching. The pass also includes
-store motion.
+@item max-unroll-times
+The maximum number of unrollings of a single loop.
-@item -ftree-loop-ivcanon
-@opindex ftree-loop-ivcanon
-Create a canonical counter for number of iterations in loops for which
-determining number of iterations requires complicated analysis. Later
-optimizations then may determine the number easily. Useful especially
-in connection with unrolling.
+@item max-peeled-insns
+The maximum number of instructions that a loop may have to be peeled.
+If a loop is peeled, this parameter also determines how many times
+the loop code is peeled.
-@item -fivopts
-@opindex fivopts
-Perform induction variable optimizations (strength reduction, induction
-variable merging and induction variable elimination) on trees.
+@item max-peel-times
+The maximum number of peelings of a single loop.
-@item -ftree-parallelize-loops=n
-@opindex ftree-parallelize-loops
-Parallelize loops, i.e., split their iteration space to run in n threads.
-This is only possible for loops whose iterations are independent
-and can be arbitrarily reordered. The optimization is only
-profitable on multiprocessor machines, for loops that are CPU-intensive,
-rather than constrained e.g.@: by memory bandwidth. This option
-implies @option{-pthread}, and thus is only supported on targets
-that have support for @option{-pthread}.
+@item max-peel-branches
+The maximum number of branches on the hot path through the peeled sequence.
-@item -ftree-pta
-@opindex ftree-pta
-Perform function-local points-to analysis on trees. This flag is
-enabled by default at @option{-O} and higher.
+@item max-completely-peeled-insns
+The maximum number of insns of a completely peeled loop.
-@item -ftree-sra
-@opindex ftree-sra
-Perform scalar replacement of aggregates. This pass replaces structure
-references with scalars to prevent committing structures to memory too
-early. This flag is enabled by default at @option{-O} and higher.
+@item max-completely-peel-times
+The maximum number of iterations of a loop to be suitable for complete peeling.
-@item -ftree-ter
-@opindex ftree-ter
-Perform temporary expression replacement during the SSA->normal phase. Single
-use/single def temporaries are replaced at their use location with their
-defining expression. This results in non-GIMPLE code, but gives the expanders
-much more complex trees to work on resulting in better RTL generation. This is
-enabled by default at @option{-O} and higher.
+@item max-completely-peel-loop-nest-depth
+The maximum depth of a loop nest suitable for complete peeling.
-@item -ftree-slsr
-@opindex ftree-slsr
-Perform straight-line strength reduction on trees. This recognizes related
-expressions involving multiplications and replaces them by less expensive
-calculations when possible. This is enabled by default at @option{-O} and
-higher.
+@item max-unswitch-insns
+The maximum number of insns of an unswitched loop.
-@item -ftree-vectorize
-@opindex ftree-vectorize
-Perform vectorization on trees. This flag enables @option{-ftree-loop-vectorize}
-and @option{-ftree-slp-vectorize} if not explicitly specified.
+@item max-unswitch-level
+The maximum number of branches unswitched in a single loop.
-@item -ftree-loop-vectorize
-@opindex ftree-loop-vectorize
-Perform loop vectorization on trees. This flag is enabled by default at
-@option{-O3} and when @option{-ftree-vectorize} is enabled.
+@item lim-expensive
+The minimum cost of an expensive expression in the loop invariant motion.
-@item -ftree-slp-vectorize
-@opindex ftree-slp-vectorize
-Perform basic block vectorization on trees. This flag is enabled by default at
-@option{-O3} and when @option{-ftree-vectorize} is enabled.
+@item iv-consider-all-candidates-bound
+Bound on number of candidates for induction variables, below which
+all candidates are considered for each use in induction variable
+optimizations. If there are more candidates than this,
+only the most relevant ones are considered to avoid quadratic time complexity.
-@item -fvect-cost-model=@var{model}
-@opindex fvect-cost-model
-Alter the cost model used for vectorization. The @var{model} argument
-should be one of @samp{unlimited}, @samp{dynamic} or @samp{cheap}.
-With the @samp{unlimited} model the vectorized code-path is assumed
-to be profitable while with the @samp{dynamic} model a runtime check
-guards the vectorized code-path to enable it only for iteration
-counts that will likely execute faster than when executing the original
-scalar loop. The @samp{cheap} model disables vectorization of
-loops where doing so would be cost prohibitive for example due to
-required runtime checks for data dependence or alignment but otherwise
-is equal to the @samp{dynamic} model.
-The default cost model depends on other optimization flags and is
-either @samp{dynamic} or @samp{cheap}.
+@item iv-max-considered-uses
+The induction variable optimizations give up on loops that contain more
+induction variable uses.
-@item -fsimd-cost-model=@var{model}
-@opindex fsimd-cost-model
-Alter the cost model used for vectorization of loops marked with the OpenMP
-or Cilk Plus simd directive. The @var{model} argument should be one of
-@samp{unlimited}, @samp{dynamic}, @samp{cheap}. All values of @var{model}
-have the same meaning as described in @option{-fvect-cost-model} and by
-default a cost model defined with @option{-fvect-cost-model} is used.
+@item iv-always-prune-cand-set-bound
+If the number of candidates in the set is smaller than this value,
+always try to remove unnecessary ivs from the set
+when adding a new one.
-@item -ftree-vrp
-@opindex ftree-vrp
-Perform Value Range Propagation on trees. This is similar to the
-constant propagation pass, but instead of values, ranges of values are
-propagated. This allows the optimizers to remove unnecessary range
-checks like array bound checks and null pointer checks. This is
-enabled by default at @option{-O2} and higher. Null pointer check
-elimination is only done if @option{-fdelete-null-pointer-checks} is
-enabled.
+@item scev-max-expr-size
+Bound on size of expressions used in the scalar evolutions analyzer.
+Large expressions slow the analyzer.
-@item -fsplit-ivs-in-unroller
-@opindex fsplit-ivs-in-unroller
-Enables expression of values of induction variables in later iterations
-of the unrolled loop using the value in the first iteration. This breaks
-long dependency chains, thus improving efficiency of the scheduling passes.
+@item scev-max-expr-complexity
+Bound on the complexity of the expressions in the scalar evolutions analyzer.
+Complex expressions slow the analyzer.
-A combination of @option{-fweb} and CSE is often sufficient to obtain the
-same effect. However, that is not reliable in cases where the loop body
-is more complicated than a single basic block. It also does not work at all
-on some architectures due to restrictions in the CSE pass.
+@item vect-max-version-for-alignment-checks
+The maximum number of run-time checks that can be performed when
+doing loop versioning for alignment in the vectorizer.
-This optimization is enabled by default.
+@item vect-max-version-for-alias-checks
+The maximum number of run-time checks that can be performed when
+doing loop versioning for alias in the vectorizer.
-@item -fvariable-expansion-in-unroller
-@opindex fvariable-expansion-in-unroller
-With this option, the compiler creates multiple copies of some
-local variables when unrolling a loop, which can result in superior code.
+@item vect-max-peeling-for-alignment
+The maximum number of loop peels to enhance access alignment
+for vectorizer. Value -1 means no limit.
-@item -fpartial-inlining
-@opindex fpartial-inlining
-Inline parts of functions. This option has any effect only
-when inlining itself is turned on by the @option{-finline-functions}
-or @option{-finline-small-functions} options.
+@item max-iterations-to-track
+The maximum number of iterations of a loop the brute-force algorithm
+for analysis of the number of iterations of the loop tries to evaluate.
-Enabled at level @option{-O2}.
+@item hot-bb-count-ws-permille
+A basic block profile count is considered hot if it contributes to
+the given permillage (i.e. 0...1000) of the entire profiled execution.
-@item -fpredictive-commoning
-@opindex fpredictive-commoning
-Perform predictive commoning optimization, i.e., reusing computations
-(especially memory loads and stores) performed in previous
-iterations of loops.
+@item hot-bb-frequency-fraction
+Select fraction of the entry block frequency of executions of basic block in
+function given basic block needs to have to be considered hot.
-This option is enabled at level @option{-O3}.
+@item max-predicted-iterations
+The maximum number of loop iterations we predict statically. This is useful
+in cases where a function contains a single loop with known bound and
+another loop with unknown bound.
+The known number of iterations is predicted correctly, while
+the unknown number of iterations average to roughly 10. This means that the
+loop without bounds appears artificially cold relative to the other one.
-@item -fprefetch-loop-arrays
-@opindex fprefetch-loop-arrays
-If supported by the target machine, generate instructions to prefetch
-memory to improve the performance of loops that access large arrays.
+@item builtin-expect-probability
+Control the probability of the expression having the specified value. This
+parameter takes a percentage (i.e. 0 ... 100) as input.
+The default probability of 90 is obtained empirically.
-This option may generate better or worse code; results are highly
-dependent on the structure of loops within the source code.
+@item align-threshold
-Disabled at level @option{-Os}.
+Select fraction of the maximal frequency of executions of a basic block in
+a function to align the basic block.
-@item -fno-peephole
-@itemx -fno-peephole2
-@opindex fno-peephole
-@opindex fno-peephole2
-Disable any machine-specific peephole optimizations. The difference
-between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
-are implemented in the compiler; some targets use one, some use the
-other, a few use both.
+@item align-loop-iterations
-@option{-fpeephole} is enabled by default.
-@option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
+A loop expected to iterate at least the selected number of iterations is
+aligned.
-@item -fno-guess-branch-probability
-@opindex fno-guess-branch-probability
-Do not guess branch probabilities using heuristics.
+@item tracer-dynamic-coverage
+@itemx tracer-dynamic-coverage-feedback
-GCC uses heuristics to guess branch probabilities if they are
-not provided by profiling feedback (@option{-fprofile-arcs}). These
-heuristics are based on the control flow graph. If some branch probabilities
-are specified by @code{__builtin_expect}, then the heuristics are
-used to guess branch probabilities for the rest of the control flow graph,
-taking the @code{__builtin_expect} info into account. The interactions
-between the heuristics and @code{__builtin_expect} can be complex, and in
-some cases, it may be useful to disable the heuristics so that the effects
-of @code{__builtin_expect} are easier to understand.
+This value is used to limit superblock formation once the given percentage of
+executed instructions is covered. This limits unnecessary code size
+expansion.
-The default is @option{-fguess-branch-probability} at levels
-@option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
+The @option{tracer-dynamic-coverage-feedback} parameter
+is used only when profile
+feedback is available. The real profiles (as opposed to statically estimated
+ones) are much less balanced allowing the threshold to be larger value.
-@item -freorder-blocks
-@opindex freorder-blocks
-Reorder basic blocks in the compiled function in order to reduce number of
-taken branches and improve code locality.
+@item tracer-max-code-growth
+Stop tail duplication once code growth has reached given percentage. This is
+a rather artificial limit, as most of the duplicates are eliminated later in
+cross jumping, so it may be set to much higher values than is the desired code
+growth.
-Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
+@item tracer-min-branch-ratio
-@item -freorder-blocks-algorithm=@var{algorithm}
-@opindex freorder-blocks-algorithm
-Use the specified algorithm for basic block reordering. The
-@var{algorithm} argument can be @samp{simple}, which does not increase
-code size (except sometimes due to secondary effects like alignment),
-or @samp{stc}, the ``software trace cache'' algorithm, which tries to
-put all often executed code together, minimizing the number of branches
-executed by making extra copies of code.
+Stop reverse growth when the reverse probability of best edge is less than this
+threshold (in percent).
-The default is @samp{simple} at levels @option{-O}, @option{-Os}, and
-@samp{stc} at levels @option{-O2}, @option{-O3}.
+@item tracer-min-branch-probability
+@itemx tracer-min-branch-probability-feedback
-@item -freorder-blocks-and-partition
-@opindex freorder-blocks-and-partition
-In addition to reordering basic blocks in the compiled function, in order
-to reduce number of taken branches, partitions hot and cold basic blocks
-into separate sections of the assembly and .o files, to improve
-paging and cache locality performance.
+Stop forward growth if the best edge has probability lower than this
+threshold.
-This optimization is automatically turned off in the presence of
-exception handling, for linkonce sections, for functions with a user-defined
-section attribute and on any architecture that does not support named
-sections.
+Similarly to @option{tracer-dynamic-coverage} two parameters are
+provided. @option{tracer-min-branch-probability-feedback} is used for
+compilation with profile feedback and @option{tracer-min-branch-probability}
+compilation without. The value for compilation with profile feedback
+needs to be more conservative (higher) in order to make tracer
+effective.
-Enabled for x86 at levels @option{-O2}, @option{-O3}.
+@item max-cse-path-length
-@item -freorder-functions
-@opindex freorder-functions
-Reorder functions in the object file in order to
-improve code locality. This is implemented by using special
-subsections @code{.text.hot} for most frequently executed functions and
-@code{.text.unlikely} for unlikely executed functions. Reordering is done by
-the linker so object file format must support named sections and linker must
-place them in a reasonable way.
+The maximum number of basic blocks on path that CSE considers.
+The default is 10.
-Also profile feedback must be available to make this option effective. See
-@option{-fprofile-arcs} for details.
+@item max-cse-insns
+The maximum number of instructions CSE processes before flushing.
+The default is 1000.
-Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
+@item ggc-min-expand
-@item -fstrict-aliasing
-@opindex fstrict-aliasing
-Allow the compiler to assume the strictest aliasing rules applicable to
-the language being compiled. For C (and C++), this activates
-optimizations based on the type of expressions. In particular, an
-object of one type is assumed never to reside at the same address as an
-object of a different type, unless the types are almost the same. For
-example, an @code{unsigned int} can alias an @code{int}, but not a
-@code{void*} or a @code{double}. A character type may alias any other
-type.
+GCC uses a garbage collector to manage its own memory allocation. This
+parameter specifies the minimum percentage by which the garbage
+collector's heap should be allowed to expand between collections.
+Tuning this may improve compilation speed; it has no effect on code
+generation.
-@anchor{Type-punning}Pay special attention to code like this:
-@smallexample
-union a_union @{
- int i;
- double d;
-@};
+The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
+RAM >= 1GB@. If @code{getrlimit} is available, the notion of ``RAM'' is
+the smallest of actual RAM and @code{RLIMIT_DATA} or @code{RLIMIT_AS}. If
+GCC is not able to calculate RAM on a particular platform, the lower
+bound of 30% is used. Setting this parameter and
+@option{ggc-min-heapsize} to zero causes a full collection to occur at
+every opportunity. This is extremely slow, but can be useful for
+debugging.
-int f() @{
- union a_union t;
- t.d = 3.0;
- return t.i;
-@}
-@end smallexample
-The practice of reading from a different union member than the one most
-recently written to (called ``type-punning'') is common. Even with
-@option{-fstrict-aliasing}, type-punning is allowed, provided the memory
-is accessed through the union type. So, the code above works as
-expected. @xref{Structures unions enumerations and bit-fields
-implementation}. However, this code might not:
-@smallexample
-int f() @{
- union a_union t;
- int* ip;
- t.d = 3.0;
- ip = &t.i;
- return *ip;
-@}
-@end smallexample
+@item ggc-min-heapsize
-Similarly, access by taking the address, casting the resulting pointer
-and dereferencing the result has undefined behavior, even if the cast
-uses a union type, e.g.:
-@smallexample
-int f() @{
- double d = 3.0;
- return ((union a_union *) &d)->i;
-@}
-@end smallexample
+Minimum size of the garbage collector's heap before it begins bothering
+to collect garbage. The first collection occurs after the heap expands
+by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again,
+tuning this may improve compilation speed, and has no effect on code
+generation.
-The @option{-fstrict-aliasing} option is enabled at levels
-@option{-O2}, @option{-O3}, @option{-Os}.
+The default is the smaller of RAM/8, RLIMIT_RSS, or a limit that
+tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but
+with a lower bound of 4096 (four megabytes) and an upper bound of
+131072 (128 megabytes). If GCC is not able to calculate RAM on a
+particular platform, the lower bound is used. Setting this parameter
+very large effectively disables garbage collection. Setting this
+parameter and @option{ggc-min-expand} to zero causes a full collection
+to occur at every opportunity.
-@item -fstrict-overflow
-@opindex fstrict-overflow
-Allow the compiler to assume strict signed overflow rules, depending
-on the language being compiled. For C (and C++) this means that
-overflow when doing arithmetic with signed numbers is undefined, which
-means that the compiler may assume that it does not happen. This
-permits various optimizations. For example, the compiler assumes
-that an expression like @code{i + 10 > i} is always true for
-signed @code{i}. This assumption is only valid if signed overflow is
-undefined, as the expression is false if @code{i + 10} overflows when
-using twos complement arithmetic. When this option is in effect any
-attempt to determine whether an operation on signed numbers
-overflows must be written carefully to not actually involve overflow.
+@item max-reload-search-insns
+The maximum number of instruction reload should look backward for equivalent
+register. Increasing values mean more aggressive optimization, making the
+compilation time increase with probably slightly better performance.
+The default value is 100.
-This option also allows the compiler to assume strict pointer
-semantics: given a pointer to an object, if adding an offset to that
-pointer does not produce a pointer to the same object, the addition is
-undefined. This permits the compiler to conclude that @code{p + u >
-p} is always true for a pointer @code{p} and unsigned integer
-@code{u}. This assumption is only valid because pointer wraparound is
-undefined, as the expression is false if @code{p + u} overflows using
-twos complement arithmetic.
+@item max-cselib-memory-locations
+The maximum number of memory locations cselib should take into account.
+Increasing values mean more aggressive optimization, making the compilation time
+increase with probably slightly better performance. The default value is 500.
-See also the @option{-fwrapv} option. Using @option{-fwrapv} means
-that integer signed overflow is fully defined: it wraps. When
-@option{-fwrapv} is used, there is no difference between
-@option{-fstrict-overflow} and @option{-fno-strict-overflow} for
-integers. With @option{-fwrapv} certain types of overflow are
-permitted. For example, if the compiler gets an overflow when doing
-arithmetic on constants, the overflowed value can still be used with
-@option{-fwrapv}, but not otherwise.
+@item max-sched-ready-insns
+The maximum number of instructions ready to be issued the scheduler should
+consider at any given time during the first scheduling pass. Increasing
+values mean more thorough searches, making the compilation time increase
+with probably little benefit. The default value is 100.
-The @option{-fstrict-overflow} option is enabled at levels
-@option{-O2}, @option{-O3}, @option{-Os}.
+@item max-sched-region-blocks
+The maximum number of blocks in a region to be considered for
+interblock scheduling. The default value is 10.
-@item -falign-functions
-@itemx -falign-functions=@var{n}
-@opindex falign-functions
-Align the start of functions to the next power-of-two greater than
-@var{n}, skipping up to @var{n} bytes. For instance,
-@option{-falign-functions=32} aligns functions to the next 32-byte
-boundary, but @option{-falign-functions=24} aligns to the next
-32-byte boundary only if this can be done by skipping 23 bytes or less.
+@item max-pipeline-region-blocks
+The maximum number of blocks in a region to be considered for
+pipelining in the selective scheduler. The default value is 15.
-@option{-fno-align-functions} and @option{-falign-functions=1} are
-equivalent and mean that functions are not aligned.
+@item max-sched-region-insns
+The maximum number of insns in a region to be considered for
+interblock scheduling. The default value is 100.
-Some assemblers only support this flag when @var{n} is a power of two;
-in that case, it is rounded up.
+@item max-pipeline-region-insns
+The maximum number of insns in a region to be considered for
+pipelining in the selective scheduler. The default value is 200.
-If @var{n} is not specified or is zero, use a machine-dependent default.
+@item min-spec-prob
+The minimum probability (in percents) of reaching a source block
+for interblock speculative scheduling. The default value is 40.
-Enabled at levels @option{-O2}, @option{-O3}.
+@item max-sched-extend-regions-iters
+The maximum number of iterations through CFG to extend regions.
+A value of 0 (the default) disables region extensions.
-@item -falign-labels
-@itemx -falign-labels=@var{n}
-@opindex falign-labels
-Align all branch targets to a power-of-two boundary, skipping up to
-@var{n} bytes like @option{-falign-functions}. This option can easily
-make code slower, because it must insert dummy operations for when the
-branch target is reached in the usual flow of the code.
+@item max-sched-insn-conflict-delay
+The maximum conflict delay for an insn to be considered for speculative motion.
+The default value is 3.
-@option{-fno-align-labels} and @option{-falign-labels=1} are
-equivalent and mean that labels are not aligned.
+@item sched-spec-prob-cutoff
+The minimal probability of speculation success (in percents), so that
+speculative insns are scheduled.
+The default value is 40.
-If @option{-falign-loops} or @option{-falign-jumps} are applicable and
-are greater than this value, then their values are used instead.
+@item sched-state-edge-prob-cutoff
+The minimum probability an edge must have for the scheduler to save its
+state across it.
+The default value is 10.
+
+@item sched-mem-true-dep-cost
+Minimal distance (in CPU cycles) between store and load targeting same
+memory locations. The default value is 1.
-If @var{n} is not specified or is zero, use a machine-dependent default
-which is very likely to be @samp{1}, meaning no alignment.
+@item selsched-max-lookahead
+The maximum size of the lookahead window of selective scheduling. It is a
+depth of search for available instructions.
+The default value is 50.
-Enabled at levels @option{-O2}, @option{-O3}.
+@item selsched-max-sched-times
+The maximum number of times that an instruction is scheduled during
+selective scheduling. This is the limit on the number of iterations
+through which the instruction may be pipelined. The default value is 2.
-@item -falign-loops
-@itemx -falign-loops=@var{n}
-@opindex falign-loops
-Align loops to a power-of-two boundary, skipping up to @var{n} bytes
-like @option{-falign-functions}. If the loops are
-executed many times, this makes up for any execution of the dummy
-operations.
+@item selsched-insns-to-rename
+The maximum number of best instructions in the ready list that are considered
+for renaming in the selective scheduler. The default value is 2.
-@option{-fno-align-loops} and @option{-falign-loops=1} are
-equivalent and mean that loops are not aligned.
+@item sms-min-sc
+The minimum value of stage count that swing modulo scheduler
+generates. The default value is 2.
-If @var{n} is not specified or is zero, use a machine-dependent default.
+@item max-last-value-rtl
+The maximum size measured as number of RTLs that can be recorded in an expression
+in combiner for a pseudo register as last known value of that register. The default
+is 10000.
-Enabled at levels @option{-O2}, @option{-O3}.
+@item max-combine-insns
+The maximum number of instructions the RTL combiner tries to combine.
+The default value is 2 at @option{-Og} and 4 otherwise.
-@item -falign-jumps
-@itemx -falign-jumps=@var{n}
-@opindex falign-jumps
-Align branch targets to a power-of-two boundary, for branch targets
-where the targets can only be reached by jumping, skipping up to @var{n}
-bytes like @option{-falign-functions}. In this case, no dummy operations
-need be executed.
+@item integer-share-limit
+Small integer constants can use a shared data structure, reducing the
+compiler's memory usage and increasing its speed. This sets the maximum
+value of a shared integer constant. The default value is 256.
-@option{-fno-align-jumps} and @option{-falign-jumps=1} are
-equivalent and mean that loops are not aligned.
+@item ssp-buffer-size
+The minimum size of buffers (i.e.@: arrays) that receive stack smashing
+protection when @option{-fstack-protection} is used.
-If @var{n} is not specified or is zero, use a machine-dependent default.
+@item min-size-for-stack-sharing
+The minimum size of variables taking part in stack slot sharing when not
+optimizing. The default value is 32.
-Enabled at levels @option{-O2}, @option{-O3}.
+@item max-jump-thread-duplication-stmts
+Maximum number of statements allowed in a block that needs to be
+duplicated when threading jumps.
-@item -funit-at-a-time
-@opindex funit-at-a-time
-This option is left for compatibility reasons. @option{-funit-at-a-time}
-has no effect, while @option{-fno-unit-at-a-time} implies
-@option{-fno-toplevel-reorder} and @option{-fno-section-anchors}.
+@item max-fields-for-field-sensitive
+Maximum number of fields in a structure treated in
+a field sensitive manner during pointer analysis. The default is zero
+for @option{-O0} and @option{-O1},
+and 100 for @option{-Os}, @option{-O2}, and @option{-O3}.
-Enabled by default.
+@item prefetch-latency
+Estimate on average number of instructions that are executed before
+prefetch finishes. The distance prefetched ahead is proportional
+to this constant. Increasing this number may also lead to less
+streams being prefetched (see @option{simultaneous-prefetches}).
-@item -fno-toplevel-reorder
-@opindex fno-toplevel-reorder
-Do not reorder top-level functions, variables, and @code{asm}
-statements. Output them in the same order that they appear in the
-input file. When this option is used, unreferenced static variables
-are not removed. This option is intended to support existing code
-that relies on a particular ordering. For new code, it is better to
-use attributes when possible.
+@item simultaneous-prefetches
+Maximum number of prefetches that can run at the same time.
-Enabled at level @option{-O0}. When disabled explicitly, it also implies
-@option{-fno-section-anchors}, which is otherwise enabled at @option{-O0} on some
-targets.
+@item l1-cache-line-size
+The size of cache line in L1 cache, in bytes.
-@item -fweb
-@opindex fweb
-Constructs webs as commonly used for register allocation purposes and assign
-each web individual pseudo register. This allows the register allocation pass
-to operate on pseudos directly, but also strengthens several other optimization
-passes, such as CSE, loop optimizer and trivial dead code remover. It can,
-however, make debugging impossible, since variables no longer stay in a
-``home register''.
+@item l1-cache-size
+The size of L1 cache, in kilobytes.
-Enabled by default with @option{-funroll-loops}.
+@item l2-cache-size
+The size of L2 cache, in kilobytes.
-@item -fwhole-program
-@opindex fwhole-program
-Assume that the current compilation unit represents the whole program being
-compiled. All public functions and variables with the exception of @code{main}
-and those merged by attribute @code{externally_visible} become static functions
-and in effect are optimized more aggressively by interprocedural optimizers.
+@item min-insn-to-prefetch-ratio
+The minimum ratio between the number of instructions and the
+number of prefetches to enable prefetching in a loop.
-This option should not be used in combination with @option{-flto}.
-Instead relying on a linker plugin should provide safer and more precise
-information.
+@item prefetch-min-insn-to-mem-ratio
+The minimum ratio between the number of instructions and the
+number of memory references to enable prefetching in a loop.
-@item -flto[=@var{n}]
-@opindex flto
-This option runs the standard link-time optimizer. When invoked
-with source code, it generates GIMPLE (one of GCC's internal
-representations) and writes it to special ELF sections in the object
-file. When the object files are linked together, all the function
-bodies are read from these ELF sections and instantiated as if they
-had been part of the same translation unit.
+@item use-canonical-types
+Whether the compiler should use the ``canonical'' type system. By
+default, this should always be 1, which uses a more efficient internal
+mechanism for comparing types in C++ and Objective-C++. However, if
+bugs in the canonical type system are causing compilation failures,
+set this value to 0 to disable canonical types.
-To use the link-time optimizer, @option{-flto} and optimization
-options should be specified at compile time and during the final link.
-For example:
+@item switch-conversion-max-branch-ratio
+Switch initialization conversion refuses to create arrays that are
+bigger than @option{switch-conversion-max-branch-ratio} times the number of
+branches in the switch.
-@smallexample
-gcc -c -O2 -flto foo.c
-gcc -c -O2 -flto bar.c
-gcc -o myprog -flto -O2 foo.o bar.o
-@end smallexample
+@item max-partial-antic-length
+Maximum length of the partial antic set computed during the tree
+partial redundancy elimination optimization (@option{-ftree-pre}) when
+optimizing at @option{-O3} and above. For some sorts of source code
+the enhanced partial redundancy elimination optimization can run away,
+consuming all of the memory available on the host machine. This
+parameter sets a limit on the length of the sets that are computed,
+which prevents the runaway behavior. Setting a value of 0 for
+this parameter allows an unlimited set length.
-The first two invocations to GCC save a bytecode representation
-of GIMPLE into special ELF sections inside @file{foo.o} and
-@file{bar.o}. The final invocation reads the GIMPLE bytecode from
-@file{foo.o} and @file{bar.o}, merges the two files into a single
-internal image, and compiles the result as usual. Since both
-@file{foo.o} and @file{bar.o} are merged into a single image, this
-causes all the interprocedural analyses and optimizations in GCC to
-work across the two files as if they were a single one. This means,
-for example, that the inliner is able to inline functions in
-@file{bar.o} into functions in @file{foo.o} and vice-versa.
+@item sccvn-max-scc-size
+Maximum size of a strongly connected component (SCC) during SCCVN
+processing. If this limit is hit, SCCVN processing for the whole
+function is not done and optimizations depending on it are
+disabled. The default maximum SCC size is 10000.
-Another (simpler) way to enable link-time optimization is:
+@item sccvn-max-alias-queries-per-access
+Maximum number of alias-oracle queries we perform when looking for
+redundancies for loads and stores. If this limit is hit the search
+is aborted and the load or store is not considered redundant. The
+number of queries is algorithmically limited to the number of
+stores on all paths from the load to the function entry.
+The default maximum number of queries is 1000.
-@smallexample
-gcc -o myprog -flto -O2 foo.c bar.c
-@end smallexample
+@item ira-max-loops-num
+IRA uses regional register allocation by default. If a function
+contains more loops than the number given by this parameter, only at most
+the given number of the most frequently-executed loops form regions
+for regional register allocation. The default value of the
+parameter is 100.
-The above generates bytecode for @file{foo.c} and @file{bar.c},
-merges them together into a single GIMPLE representation and optimizes
-them as usual to produce @file{myprog}.
+@item ira-max-conflict-table-size
+Although IRA uses a sophisticated algorithm to compress the conflict
+table, the table can still require excessive amounts of memory for
+huge functions. If the conflict table for a function could be more
+than the size in MB given by this parameter, the register allocator
+instead uses a faster, simpler, and lower-quality
+algorithm that does not require building a pseudo-register conflict table.
+The default value of the parameter is 2000.
-The only important thing to keep in mind is that to enable link-time
-optimizations you need to use the GCC driver to perform the link-step.
-GCC then automatically performs link-time optimization if any of the
-objects involved were compiled with the @option{-flto} command-line option.
-You generally
-should specify the optimization options to be used for link-time
-optimization though GCC tries to be clever at guessing an
-optimization level to use from the options used at compile-time
-if you fail to specify one at link-time. You can always override
-the automatic decision to do link-time optimization at link-time
-by passing @option{-fno-lto} to the link command.
+@item ira-loop-reserved-regs
+IRA can be used to evaluate more accurate register pressure in loops
+for decisions to move loop invariants (see @option{-O3}). The number
+of available registers reserved for some other purposes is given
+by this parameter. The default value of the parameter is 2, which is
+the minimal number of registers needed by typical instructions.
+This value is the best found from numerous experiments.
-To make whole program optimization effective, it is necessary to make
-certain whole program assumptions. The compiler needs to know
-what functions and variables can be accessed by libraries and runtime
-outside of the link-time optimized unit. When supported by the linker,
-the linker plugin (see @option{-fuse-linker-plugin}) passes information
-to the compiler about used and externally visible symbols. When
-the linker plugin is not available, @option{-fwhole-program} should be
-used to allow the compiler to make these assumptions, which leads
-to more aggressive optimization decisions.
+@item lra-inheritance-ebb-probability-cutoff
+LRA tries to reuse values reloaded in registers in subsequent insns.
+This optimization is called inheritance. EBB is used as a region to
+do this optimization. The parameter defines a minimal fall-through
+edge probability in percentage used to add BB to inheritance EBB in
+LRA. The default value of the parameter is 40. The value was chosen
+from numerous runs of SPEC2000 on x86-64.
-When @option{-fuse-linker-plugin} is not enabled then, when a file is
-compiled with @option{-flto}, the generated object file is larger than
-a regular object file because it contains GIMPLE bytecodes and the usual
-final code (see @option{-ffat-lto-objects}. This means that
-object files with LTO information can be linked as normal object
-files; if @option{-fno-lto} is passed to the linker, no
-interprocedural optimizations are applied. Note that when
-@option{-fno-fat-lto-objects} is enabled the compile-stage is faster
-but you cannot perform a regular, non-LTO link on them.
+@item loop-invariant-max-bbs-in-loop
+Loop invariant motion can be very expensive, both in compilation time and
+in amount of needed compile-time memory, with very large loops. Loops
+with more basic blocks than this parameter won't have loop invariant
+motion optimization performed on them. The default value of the
+parameter is 1000 for @option{-O1} and 10000 for @option{-O2} and above.
-Additionally, the optimization flags used to compile individual files
-are not necessarily related to those used at link time. For instance,
+@item loop-max-datarefs-for-datadeps
+Building data dependencies is expensive for very large loops. This
+parameter limits the number of data references in loops that are
+considered for data dependence analysis. These large loops are no
+handled by the optimizations using loop data dependencies.
+The default value is 1000.
-@smallexample
-gcc -c -O0 -ffat-lto-objects -flto foo.c
-gcc -c -O0 -ffat-lto-objects -flto bar.c
-gcc -o myprog -O3 foo.o bar.o
-@end smallexample
+@item max-vartrack-size
+Sets a maximum number of hash table slots to use during variable
+tracking dataflow analysis of any function. If this limit is exceeded
+with variable tracking at assignments enabled, analysis for that
+function is retried without it, after removing all debug insns from
+the function. If the limit is exceeded even without debug insns, var
+tracking analysis is completely disabled for the function. Setting
+the parameter to zero makes it unlimited.
-This produces individual object files with unoptimized assembler
-code, but the resulting binary @file{myprog} is optimized at
-@option{-O3}. If, instead, the final binary is generated with
-@option{-fno-lto}, then @file{myprog} is not optimized.
+@item max-vartrack-expr-depth
+Sets a maximum number of recursion levels when attempting to map
+variable names or debug temporaries to value expressions. This trades
+compilation time for more complete debug information. If this is set too
+low, value expressions that are available and could be represented in
+debug information may end up not being used; setting this higher may
+enable the compiler to find more complex debug expressions, but compile
+time and memory use may grow. The default is 12.
-When producing the final binary, GCC only
-applies link-time optimizations to those files that contain bytecode.
-Therefore, you can mix and match object files and libraries with
-GIMPLE bytecodes and final object code. GCC automatically selects
-which files to optimize in LTO mode and which files to link without
-further processing.
+@item min-nondebug-insn-uid
+Use uids starting at this parameter for nondebug insns. The range below
+the parameter is reserved exclusively for debug insns created by
+@option{-fvar-tracking-assignments}, but debug insns may get
+(non-overlapping) uids above it if the reserved range is exhausted.
-There are some code generation flags preserved by GCC when
-generating bytecodes, as they need to be used during the final link
-stage. Generally options specified at link-time override those
-specified at compile-time.
+@item ipa-sra-ptr-growth-factor
+IPA-SRA replaces a pointer to an aggregate with one or more new
+parameters only when their cumulative size is less or equal to
+@option{ipa-sra-ptr-growth-factor} times the size of the original
+pointer parameter.
-If you do not specify an optimization level option @option{-O} at
-link-time then GCC computes one based on the optimization levels
-used when compiling the object files. The highest optimization
-level wins here.
+@item sra-max-scalarization-size-Ospeed
+@item sra-max-scalarization-size-Osize
+The two Scalar Reduction of Aggregates passes (SRA and IPA-SRA) aim to
+replace scalar parts of aggregates with uses of independent scalar
+variables. These parameters control the maximum size, in storage units,
+of aggregate which is considered for replacement when compiling for
+speed
+(@option{sra-max-scalarization-size-Ospeed}) or size
+(@option{sra-max-scalarization-size-Osize}) respectively.
-Currently, the following options and their setting are take from
-the first object file that explicitely specified it:
-@option{-fPIC}, @option{-fpic}, @option{-fpie}, @option{-fcommon},
-@option{-fexceptions}, @option{-fnon-call-exceptions}, @option{-fgnu-tm}
-and all the @option{-m} target flags.
+@item tm-max-aggregate-size
+When making copies of thread-local variables in a transaction, this
+parameter specifies the size in bytes after which variables are
+saved with the logging functions as opposed to save/restore code
+sequence pairs. This option only applies when using
+@option{-fgnu-tm}.
-Certain ABI changing flags are required to match in all compilation-units
-and trying to override this at link-time with a conflicting value
-is ignored. This includes options such as @option{-freg-struct-return}
-and @option{-fpcc-struct-return}.
+@item graphite-max-nb-scop-params
+To avoid exponential effects in the Graphite loop transforms, the
+number of parameters in a Static Control Part (SCoP) is bounded. The
+default value is 10 parameters. A variable whose value is unknown at
+compilation time and defined outside a SCoP is a parameter of the SCoP.
-Other options such as @option{-ffp-contract}, @option{-fno-strict-overflow},
-@option{-fwrapv}, @option{-fno-trapv} or @option{-fno-strict-aliasing}
-are passed through to the link stage and merged conservatively for
-conflicting translation units. Specifically
-@option{-fno-strict-overflow}, @option{-fwrapv} and @option{-fno-trapv} take
-precedence and for example @option{-ffp-contract=off} takes precedence
-over @option{-ffp-contract=fast}. You can override them at linke-time.
+@item graphite-max-bbs-per-function
+To avoid exponential effects in the detection of SCoPs, the size of
+the functions analyzed by Graphite is bounded. The default value is
+100 basic blocks.
-It is recommended that you compile all the files participating in the
-same link with the same options and also specify those options at
-link time.
+@item loop-block-tile-size
+Loop blocking or strip mining transforms, enabled with
+@option{-floop-block} or @option{-floop-strip-mine}, strip mine each
+loop in the loop nest by a given number of iterations. The strip
+length can be changed using the @option{loop-block-tile-size}
+parameter. The default value is 51 iterations.
-If LTO encounters objects with C linkage declared with incompatible
-types in separate translation units to be linked together (undefined
-behavior according to ISO C99 6.2.7), a non-fatal diagnostic may be
-issued. The behavior is still undefined at run time. Similar
-diagnostics may be raised for other languages.
+@item loop-unroll-jam-size
+Specify the unroll factor for the @option{-floop-unroll-and-jam} option. The
+default value is 4.
-Another feature of LTO is that it is possible to apply interprocedural
-optimizations on files written in different languages:
+@item loop-unroll-jam-depth
+Specify the dimension to be unrolled (counting from the most inner loop)
+for the @option{-floop-unroll-and-jam}. The default value is 2.
-@smallexample
-gcc -c -flto foo.c
-g++ -c -flto bar.cc
-gfortran -c -flto baz.f90
-g++ -o myprog -flto -O3 foo.o bar.o baz.o -lgfortran
-@end smallexample
+@item ipa-cp-value-list-size
+IPA-CP attempts to track all possible values and types passed to a function's
+parameter in order to propagate them and perform devirtualization.
+@option{ipa-cp-value-list-size} is the maximum number of values and types it
+stores per one formal parameter of a function.
-Notice that the final link is done with @command{g++} to get the C++
-runtime libraries and @option{-lgfortran} is added to get the Fortran
-runtime libraries. In general, when mixing languages in LTO mode, you
-should use the same link command options as when mixing languages in a
-regular (non-LTO) compilation.
+@item ipa-cp-eval-threshold
+IPA-CP calculates its own score of cloning profitability heuristics
+and performs those cloning opportunities with scores that exceed
+@option{ipa-cp-eval-threshold}.
-If object files containing GIMPLE bytecode are stored in a library archive, say
-@file{libfoo.a}, it is possible to extract and use them in an LTO link if you
-are using a linker with plugin support. To create static libraries suitable
-for LTO, use @command{gcc-ar} and @command{gcc-ranlib} instead of @command{ar}
-and @command{ranlib};
-to show the symbols of object files with GIMPLE bytecode, use
-@command{gcc-nm}. Those commands require that @command{ar}, @command{ranlib}
-and @command{nm} have been compiled with plugin support. At link time, use the the
-flag @option{-fuse-linker-plugin} to ensure that the library participates in
-the LTO optimization process:
+@item ipa-cp-recursion-penalty
+Percentage penalty the recursive functions will receive when they
+are evaluated for cloning.
-@smallexample
-gcc -o myprog -O2 -flto -fuse-linker-plugin a.o b.o -lfoo
-@end smallexample
+@item ipa-cp-single-call-penalty
+Percentage penalty functions containg a single call to another
+function will receive when they are evaluated for cloning.
-With the linker plugin enabled, the linker extracts the needed
-GIMPLE files from @file{libfoo.a} and passes them on to the running GCC
-to make them part of the aggregated GIMPLE image to be optimized.
-If you are not using a linker with plugin support and/or do not
-enable the linker plugin, then the objects inside @file{libfoo.a}
-are extracted and linked as usual, but they do not participate
-in the LTO optimization process. In order to make a static library suitable
-for both LTO optimization and usual linkage, compile its object files with
-@option{-flto} @option{-ffat-lto-objects}.
+@item ipa-max-agg-items
+IPA-CP is also capable to propagate a number of scalar values passed
+in an aggregate. @option{ipa-max-agg-items} controls the maximum
+number of such values per one parameter.
-Link-time optimizations do not require the presence of the whole program to
-operate. If the program does not require any symbols to be exported, it is
-possible to combine @option{-flto} and @option{-fwhole-program} to allow
-the interprocedural optimizers to use more aggressive assumptions which may
-lead to improved optimization opportunities.
-Use of @option{-fwhole-program} is not needed when linker plugin is
-active (see @option{-fuse-linker-plugin}).
+@item ipa-cp-loop-hint-bonus
+When IPA-CP determines that a cloning candidate would make the number
+of iterations of a loop known, it adds a bonus of
+@option{ipa-cp-loop-hint-bonus} to the profitability score of
+the candidate.
-The current implementation of LTO makes no
-attempt to generate bytecode that is portable between different
-types of hosts. The bytecode files are versioned and there is a
-strict version check, so bytecode files generated in one version of
-GCC do not work with an older or newer version of GCC.
+@item ipa-cp-array-index-hint-bonus
+When IPA-CP determines that a cloning candidate would make the index of
+an array access known, it adds a bonus of
+@option{ipa-cp-array-index-hint-bonus} to the profitability
+score of the candidate.
-Link-time optimization does not work well with generation of debugging
-information. Combining @option{-flto} with
-@option{-g} is currently experimental and expected to produce unexpected
-results.
+@item ipa-max-aa-steps
+During its analysis of function bodies, IPA-CP employs alias analysis
+in order to track values pointed to by function parameters. In order
+not spend too much time analyzing huge functions, it gives up and
+consider all memory clobbered after examining
+@option{ipa-max-aa-steps} statements modifying memory.
-If you specify the optional @var{n}, the optimization and code
-generation done at link time is executed in parallel using @var{n}
-parallel jobs by utilizing an installed @command{make} program. The
-environment variable @env{MAKE} may be used to override the program
-used. The default value for @var{n} is 1.
+@item lto-partitions
+Specify desired number of partitions produced during WHOPR compilation.
+The number of partitions should exceed the number of CPUs used for compilation.
+The default value is 32.
-You can also specify @option{-flto=jobserver} to use GNU make's
-job server mode to determine the number of parallel jobs. This
-is useful when the Makefile calling GCC is already executing in parallel.
-You must prepend a @samp{+} to the command recipe in the parent Makefile
-for this to work. This option likely only works if @env{MAKE} is
-GNU make.
+@item lto-min-partition
+Size of minimal partition for WHOPR (in estimated instructions).
+This prevents expenses of splitting very small programs into too many
+partitions.
-@item -flto-partition=@var{alg}
-@opindex flto-partition
-Specify the partitioning algorithm used by the link-time optimizer.
-The value is either @samp{1to1} to specify a partitioning mirroring
-the original source files or @samp{balanced} to specify partitioning
-into equally sized chunks (whenever possible) or @samp{max} to create
-new partition for every symbol where possible. Specifying @samp{none}
-as an algorithm disables partitioning and streaming completely.
-The default value is @samp{balanced}. While @samp{1to1} can be used
-as an workaround for various code ordering issues, the @samp{max}
-partitioning is intended for internal testing only.
-The value @samp{one} specifies that exactly one partition should be
-used while the value @samp{none} bypasses partitioning and executes
-the link-time optimization step directly from the WPA phase.
+@item cxx-max-namespaces-for-diagnostic-help
+The maximum number of namespaces to consult for suggestions when C++
+name lookup fails for an identifier. The default is 1000.
-@item -flto-odr-type-merging
-@opindex flto-odr-type-merging
-Enable streaming of mangled types names of C++ types and their unification
-at linktime. This increases size of LTO object files, but enable
-diagnostics about One Definition Rule violations.
+@item sink-frequency-threshold
+The maximum relative execution frequency (in percents) of the target block
+relative to a statement's original block to allow statement sinking of a
+statement. Larger numbers result in more aggressive statement sinking.
+The default value is 75. A small positive adjustment is applied for
+statements with memory operands as those are even more profitable so sink.
-@item -flto-compression-level=@var{n}
-@opindex flto-compression-level
-This option specifies the level of compression used for intermediate
-language written to LTO object files, and is only meaningful in
-conjunction with LTO mode (@option{-flto}). Valid
-values are 0 (no compression) to 9 (maximum compression). Values
-outside this range are clamped to either 0 or 9. If the option is not
-given, a default balanced compression setting is used.
+@item max-stores-to-sink
+The maximum number of conditional store pairs that can be sunk. Set to 0
+if either vectorization (@option{-ftree-vectorize}) or if-conversion
+(@option{-ftree-loop-if-convert}) is disabled. The default is 2.
-@item -flto-report
-@opindex flto-report
-Prints a report with internal details on the workings of the link-time
-optimizer. The contents of this report vary from version to version.
-It is meant to be useful to GCC developers when processing object
-files in LTO mode (via @option{-flto}).
+@item allow-store-data-races
+Allow optimizers to introduce new data races on stores.
+Set to 1 to allow, otherwise to 0. This option is enabled by default
+at optimization level @option{-Ofast}.
-Disabled by default.
+@item case-values-threshold
+The smallest number of different values for which it is best to use a
+jump-table instead of a tree of conditional branches. If the value is
+0, use the default for the machine. The default is 0.
-@item -flto-report-wpa
-@opindex flto-report-wpa
-Like @option{-flto-report}, but only print for the WPA phase of Link
-Time Optimization.
+@item tree-reassoc-width
+Set the maximum number of instructions executed in parallel in
+reassociated tree. This parameter overrides target dependent
+heuristics used by default if has non zero value.
+
+@item sched-pressure-algorithm
+Choose between the two available implementations of
+@option{-fsched-pressure}. Algorithm 1 is the original implementation
+and is the more likely to prevent instructions from being reordered.
+Algorithm 2 was designed to be a compromise between the relatively
+conservative approach taken by algorithm 1 and the rather aggressive
+approach taken by the default scheduler. It relies more heavily on
+having a regular register file and accurate register pressure classes.
+See @file{haifa-sched.c} in the GCC sources for more details.
-@item -fuse-linker-plugin
-@opindex fuse-linker-plugin
-Enables the use of a linker plugin during link-time optimization. This
-option relies on plugin support in the linker, which is available in gold
-or in GNU ld 2.21 or newer.
+The default choice depends on the target.
-This option enables the extraction of object files with GIMPLE bytecode out
-of library archives. This improves the quality of optimization by exposing
-more code to the link-time optimizer. This information specifies what
-symbols can be accessed externally (by non-LTO object or during dynamic
-linking). Resulting code quality improvements on binaries (and shared
-libraries that use hidden visibility) are similar to @option{-fwhole-program}.
-See @option{-flto} for a description of the effect of this flag and how to
-use it.
+@item max-slsr-cand-scan
+Set the maximum number of existing candidates that are considered when
+seeking a basis for a new straight-line strength reduction candidate.
-This option is enabled by default when LTO support in GCC is enabled
-and GCC was configured for use with
-a linker supporting plugins (GNU ld 2.21 or newer or gold).
+@item asan-globals
+Enable buffer overflow detection for global objects. This kind
+of protection is enabled by default if you are using
+@option{-fsanitize=address} option.
+To disable global objects protection use @option{--param asan-globals=0}.
-@item -ffat-lto-objects
-@opindex ffat-lto-objects
-Fat LTO objects are object files that contain both the intermediate language
-and the object code. This makes them usable for both LTO linking and normal
-linking. This option is effective only when compiling with @option{-flto}
-and is ignored at link time.
+@item asan-stack
+Enable buffer overflow detection for stack objects. This kind of
+protection is enabled by default when using @option{-fsanitize=address}.
+To disable stack protection use @option{--param asan-stack=0} option.
-@option{-fno-fat-lto-objects} improves compilation time over plain LTO, but
-requires the complete toolchain to be aware of LTO. It requires a linker with
-linker plugin support for basic functionality. Additionally,
-@command{nm}, @command{ar} and @command{ranlib}
-need to support linker plugins to allow a full-featured build environment
-(capable of building static libraries etc). GCC provides the @command{gcc-ar},
-@command{gcc-nm}, @command{gcc-ranlib} wrappers to pass the right options
-to these tools. With non fat LTO makefiles need to be modified to use them.
+@item asan-instrument-reads
+Enable buffer overflow detection for memory reads. This kind of
+protection is enabled by default when using @option{-fsanitize=address}.
+To disable memory reads protection use
+@option{--param asan-instrument-reads=0}.
-The default is @option{-fno-fat-lto-objects} on targets with linker plugin
-support.
+@item asan-instrument-writes
+Enable buffer overflow detection for memory writes. This kind of
+protection is enabled by default when using @option{-fsanitize=address}.
+To disable memory writes protection use
+@option{--param asan-instrument-writes=0} option.
-@item -fcompare-elim
-@opindex fcompare-elim
-After register allocation and post-register allocation instruction splitting,
-identify arithmetic instructions that compute processor flags similar to a
-comparison operation based on that arithmetic. If possible, eliminate the
-explicit comparison operation.
+@item asan-memintrin
+Enable detection for built-in functions. This kind of protection
+is enabled by default when using @option{-fsanitize=address}.
+To disable built-in functions protection use
+@option{--param asan-memintrin=0}.
-This pass only applies to certain targets that cannot explicitly represent
-the comparison operation before register allocation is complete.
+@item asan-use-after-return
+Enable detection of use-after-return. This kind of protection
+is enabled by default when using @option{-fsanitize=address} option.
+To disable use-after-return detection use
+@option{--param asan-use-after-return=0}.
-Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
+@item asan-instrumentation-with-call-threshold
+If number of memory accesses in function being instrumented
+is greater or equal to this number, use callbacks instead of inline checks.
+E.g. to disable inline code use
+@option{--param asan-instrumentation-with-call-threshold=0}.
-@item -fcprop-registers
-@opindex fcprop-registers
-After register allocation and post-register allocation instruction splitting,
-perform a copy-propagation pass to try to reduce scheduling dependencies
-and occasionally eliminate the copy.
+@item chkp-max-ctor-size
+Static constructors generated by Pointer Bounds Checker may become very
+large and significantly increase compile time at optimization level
+@option{-O1} and higher. This parameter is a maximum nubmer of statements
+in a single generated constructor. Default value is 5000.
-Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
+@item max-fsm-thread-path-insns
+Maximum number of instructions to copy when duplicating blocks on a
+finite state automaton jump thread path. The default is 100.
-@item -fprofile-correction
-@opindex fprofile-correction
-Profiles collected using an instrumented binary for multi-threaded programs may
-be inconsistent due to missed counter updates. When this option is specified,
-GCC uses heuristics to correct or smooth out such inconsistencies. By
-default, GCC emits an error message when an inconsistent profile is detected.
+@item max-fsm-thread-length
+Maximum number of basic blocks on a finite state automaton jump thread
+path. The default is 10.
-@item -fprofile-dir=@var{path}
-@opindex fprofile-dir
+@item max-fsm-thread-paths
+Maximum number of new jump thread paths to create for a finite state
+automaton. The default is 50.
-Set the directory to search for the profile data files in to @var{path}.
-This option affects only the profile data generated by
-@option{-fprofile-generate}, @option{-ftest-coverage}, @option{-fprofile-arcs}
-and used by @option{-fprofile-use} and @option{-fbranch-probabilities}
-and its related options. Both absolute and relative paths can be used.
-By default, GCC uses the current directory as @var{path}, thus the
-profile data file appears in the same directory as the object file.
+@item parloops-chunk-size
+Chunk size of omp schedule for loops parallelized by parloops. The default
+is 0.
-@item -fprofile-generate
-@itemx -fprofile-generate=@var{path}
-@opindex fprofile-generate
+@item parloops-schedule
+Schedule type of omp schedule for loops parallelized by parloops (static,
+dynamic, guided, auto, runtime). The default is static.
-Enable options usually used for instrumenting application to produce
-profile useful for later recompilation with profile feedback based
-optimization. You must use @option{-fprofile-generate} both when
-compiling and when linking your program.
+@item max-ssa-name-query-depth
+Maximum depth of recursion when querying properties of SSA names in things
+like fold routines. One level of recursion corresponds to following a
+use-def chain.
-The following options are enabled: @option{-fprofile-arcs}, @option{-fprofile-values}, @option{-fvpt}.
+@item hsa-gen-debug-stores
+Enable emission of special debug stores within HSA kernels which are
+then read and reported by libgomp plugin. Generation of these stores
+is disabled by default, use @option{--param hsa-gen-debug-stores=1} to
+enable it.
-If @var{path} is specified, GCC looks at the @var{path} to find
-the profile feedback data files. See @option{-fprofile-dir}.
+@item max-speculative-devirt-maydefs
+The maximum number of may-defs we analyze when looking for a must-def
+specifying the dynamic type of an object that invokes a virtual call
+we may be able to devirtualize speculatively.
+@end table
+@end table
-@item -fprofile-use
-@itemx -fprofile-use=@var{path}
-@opindex fprofile-use
-Enable profile feedback-directed optimizations,
-and the following optimizations
-which are generally profitable only with profile feedback available:
-@option{-fbranch-probabilities}, @option{-fvpt},
-@option{-funroll-loops}, @option{-fpeel-loops}, @option{-ftracer},
-@option{-ftree-vectorize}, and @option{ftree-loop-distribute-patterns}.
+@node Instrumentation Options
+@section Program Instrumentation Options
+@cindex instrumentation options
+@cindex program instrumentation options
+@cindex run-time error checking options
+@cindex profiling options
+@cindex options, program instrumentation
+@cindex options, run-time error checking
+@cindex options, profiling
+
+GCC supports a number of command-line options that control adding
+run-time instrumentation to the code it normally generates.
+For example, one purpose of instrumentation is collect profiling
+statistics for use in finding program hot spots, code coverage
+analysis, or profile-guided optimizations.
+Another class of program instrumentation is adding run-time checking
+to detect programming errors like invalid pointer
+dereferences or out-of-bounds array accesses, as well as deliberately
+hostile attacks such as stack smashing or C++ vtable hijacking.
+There is also a general hook which can be used to implement other
+forms of tracing or function-level instrumentation for debug or
+program analysis purposes.
-By default, GCC emits an error message if the feedback profiles do not
-match the source code. This error can be turned into a warning by using
-@option{-Wcoverage-mismatch}. Note this may result in poorly optimized
-code.
+@table @gcctabopt
+@cindex @command{prof}
+@item -p
+@opindex p
+Generate extra code to write profile information suitable for the
+analysis program @command{prof}. You must use this option when compiling
+the source files you want data about, and you must also use it when
+linking.
-If @var{path} is specified, GCC looks at the @var{path} to find
-the profile feedback data files. See @option{-fprofile-dir}.
+@cindex @command{gprof}
+@item -pg
+@opindex pg
+Generate extra code to write profile information suitable for the
+analysis program @command{gprof}. You must use this option when compiling
+the source files you want data about, and you must also use it when
+linking.
-@item -fauto-profile
-@itemx -fauto-profile=@var{path}
-@opindex fauto-profile
-Enable sampling-based feedback-directed optimizations,
-and the following optimizations
-which are generally profitable only with profile feedback available:
-@option{-fbranch-probabilities}, @option{-fvpt},
-@option{-funroll-loops}, @option{-fpeel-loops}, @option{-ftracer},
-@option{-ftree-vectorize},
-@option{-finline-functions}, @option{-fipa-cp}, @option{-fipa-cp-clone},
-@option{-fpredictive-commoning}, @option{-funswitch-loops},
-@option{-fgcse-after-reload}, and @option{-ftree-loop-distribute-patterns}.
+@item -fprofile-arcs
+@opindex fprofile-arcs
+Add code so that program flow @dfn{arcs} are instrumented. During
+execution the program records how many times each branch and call is
+executed and how many times it is taken or returns. When the compiled
+program exits it saves this data to a file called
+@file{@var{auxname}.gcda} for each source file. The data may be used for
+profile-directed optimizations (@option{-fbranch-probabilities}), or for
+test coverage analysis (@option{-ftest-coverage}). Each object file's
+@var{auxname} is generated from the name of the output file, if
+explicitly specified and it is not the final executable, otherwise it is
+the basename of the source file. In both cases any suffix is removed
+(e.g.@: @file{foo.gcda} for input file @file{dir/foo.c}, or
+@file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}).
+@xref{Cross-profiling}.
-@var{path} is the name of a file containing AutoFDO profile information.
-If omitted, it defaults to @file{fbdata.afdo} in the current directory.
+@cindex @command{gcov}
+@item --coverage
+@opindex coverage
-Producing an AutoFDO profile data file requires running your program
-with the @command{perf} utility on a supported GNU/Linux target system.
-For more information, see @uref{https://perf.wiki.kernel.org/}.
+This option is used to compile and link code instrumented for coverage
+analysis. The option is a synonym for @option{-fprofile-arcs}
+@option{-ftest-coverage} (when compiling) and @option{-lgcov} (when
+linking). See the documentation for those options for more details.
-E.g.
-@smallexample
-perf record -e br_inst_retired:near_taken -b -o perf.data \
- -- your_program
-@end smallexample
+@itemize
-Then use the @command{create_gcov} tool to convert the raw profile data
-to a format that can be used by GCC.@ You must also supply the
-unstripped binary for your program to this tool.
-See @uref{https://github.com/google/autofdo}.
+@item
+Compile the source files with @option{-fprofile-arcs} plus optimization
+and code generation options. For test coverage analysis, use the
+additional @option{-ftest-coverage} option. You do not need to profile
+every source file in a program.
-E.g.
-@smallexample
-create_gcov --binary=your_program.unstripped --profile=perf.data \
- --gcov=profile.afdo
-@end smallexample
-@end table
+@item
+Link your object files with @option{-lgcov} or @option{-fprofile-arcs}
+(the latter implies the former).
-The following options control compiler behavior regarding floating-point
-arithmetic. These options trade off between speed and
-correctness. All must be specifically enabled.
+@item
+Run the program on a representative workload to generate the arc profile
+information. This may be repeated any number of times. You can run
+concurrent instances of your program, and provided that the file system
+supports locking, the data files will be correctly updated. Also
+@code{fork} calls are detected and correctly handled (double counting
+will not happen).
-@table @gcctabopt
-@item -ffloat-store
-@opindex ffloat-store
-Do not store floating-point variables in registers, and inhibit other
-options that might change whether a floating-point value is taken from a
-register or memory.
+@item
+For profile-directed optimizations, compile the source files again with
+the same optimization and code generation options plus
+@option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
+Control Optimization}).
-@cindex floating-point precision
-This option prevents undesirable excess precision on machines such as
-the 68000 where the floating registers (of the 68881) keep more
-precision than a @code{double} is supposed to have. Similarly for the
-x86 architecture. For most programs, the excess precision does only
-good, but a few programs rely on the precise definition of IEEE floating
-point. Use @option{-ffloat-store} for such programs, after modifying
-them to store all pertinent intermediate computations into variables.
+@item
+For test coverage analysis, use @command{gcov} to produce human readable
+information from the @file{.gcno} and @file{.gcda} files. Refer to the
+@command{gcov} documentation for further information.
-@item -fexcess-precision=@var{style}
-@opindex fexcess-precision
-This option allows further control over excess precision on machines
-where floating-point registers have more precision than the IEEE
-@code{float} and @code{double} types and the processor does not
-support operations rounding to those types. By default,
-@option{-fexcess-precision=fast} is in effect; this means that
-operations are carried out in the precision of the registers and that
-it is unpredictable when rounding to the types specified in the source
-code takes place. When compiling C, if
-@option{-fexcess-precision=standard} is specified then excess
-precision follows the rules specified in ISO C99; in particular,
-both casts and assignments cause values to be rounded to their
-semantic types (whereas @option{-ffloat-store} only affects
-assignments). This option is enabled by default for C if a strict
-conformance option such as @option{-std=c99} is used.
+@end itemize
-@opindex mfpmath
-@option{-fexcess-precision=standard} is not implemented for languages
-other than C, and has no effect if
-@option{-funsafe-math-optimizations} or @option{-ffast-math} is
-specified. On the x86, it also has no effect if @option{-mfpmath=sse}
-or @option{-mfpmath=sse+387} is specified; in the former case, IEEE
-semantics apply without excess precision, and in the latter, rounding
-is unpredictable.
+With @option{-fprofile-arcs}, for each function of your program GCC
+creates a program flow graph, then finds a spanning tree for the graph.
+Only arcs that are not on the spanning tree have to be instrumented: the
+compiler adds code to count the number of times that these arcs are
+executed. When an arc is the only exit or only entrance to a block, the
+instrumentation code can be added to the block; otherwise, a new basic
+block must be created to hold the instrumentation code.
-@item -ffast-math
-@opindex ffast-math
-Sets the options @option{-fno-math-errno}, @option{-funsafe-math-optimizations},
-@option{-ffinite-math-only}, @option{-fno-rounding-math},
-@option{-fno-signaling-nans} and @option{-fcx-limited-range}.
+@need 2000
+@item -ftest-coverage
+@opindex ftest-coverage
+Produce a notes file that the @command{gcov} code-coverage utility
+(@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to
+show program coverage. Each source file's note file is called
+@file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option
+above for a description of @var{auxname} and instructions on how to
+generate test coverage data. Coverage data matches the source files
+more closely if you do not optimize.
-This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
+@item -fprofile-dir=@var{path}
+@opindex fprofile-dir
-This option is not turned on by any @option{-O} option besides
-@option{-Ofast} since it can result in incorrect output for programs
-that depend on an exact implementation of IEEE or ISO rules/specifications
-for math functions. It may, however, yield faster code for programs
-that do not require the guarantees of these specifications.
+Set the directory to search for the profile data files in to @var{path}.
+This option affects only the profile data generated by
+@option{-fprofile-generate}, @option{-ftest-coverage}, @option{-fprofile-arcs}
+and used by @option{-fprofile-use} and @option{-fbranch-probabilities}
+and its related options. Both absolute and relative paths can be used.
+By default, GCC uses the current directory as @var{path}, thus the
+profile data file appears in the same directory as the object file.
-@item -fno-math-errno
-@opindex fno-math-errno
-Do not set @code{errno} after calling math functions that are executed
-with a single instruction, e.g., @code{sqrt}. A program that relies on
-IEEE exceptions for math error handling may want to use this flag
-for speed while maintaining IEEE arithmetic compatibility.
+@item -fprofile-generate
+@itemx -fprofile-generate=@var{path}
+@opindex fprofile-generate
-This option is not turned on by any @option{-O} option since
-it can result in incorrect output for programs that depend on
-an exact implementation of IEEE or ISO rules/specifications for
-math functions. It may, however, yield faster code for programs
-that do not require the guarantees of these specifications.
+Enable options usually used for instrumenting application to produce
+profile useful for later recompilation with profile feedback based
+optimization. You must use @option{-fprofile-generate} both when
+compiling and when linking your program.
-The default is @option{-fmath-errno}.
+The following options are enabled: @option{-fprofile-arcs}, @option{-fprofile-values}, @option{-fvpt}.
-On Darwin systems, the math library never sets @code{errno}. There is
-therefore no reason for the compiler to consider the possibility that
-it might, and @option{-fno-math-errno} is the default.
+If @var{path} is specified, GCC looks at the @var{path} to find
+the profile feedback data files. See @option{-fprofile-dir}.
-@item -funsafe-math-optimizations
-@opindex funsafe-math-optimizations
+To optimize the program based on the collected profile information, use
+@option{-fprofile-use}. @xref{Optimize Options}, for more information.
-Allow optimizations for floating-point arithmetic that (a) assume
-that arguments and results are valid and (b) may violate IEEE or
-ANSI standards. When used at link-time, it may include libraries
-or startup files that change the default FPU control word or other
-similar optimizations.
+@item -fsanitize=address
+@opindex fsanitize=address
+Enable AddressSanitizer, a fast memory error detector.
+Memory access instructions are instrumented to detect
+out-of-bounds and use-after-free bugs.
+See @uref{https://github.com/google/sanitizers/wiki/AddressSanitizer} for
+more details. The run-time behavior can be influenced using the
+@env{ASAN_OPTIONS} environment variable. When set to @code{help=1},
+the available options are shown at startup of the instrumented program. See
+@url{https://github.com/google/sanitizers/wiki/AddressSanitizerFlags#run-time-flags}
+for a list of supported options.
-This option is not turned on by any @option{-O} option since
-it can result in incorrect output for programs that depend on
-an exact implementation of IEEE or ISO rules/specifications for
-math functions. It may, however, yield faster code for programs
-that do not require the guarantees of these specifications.
-Enables @option{-fno-signed-zeros}, @option{-fno-trapping-math},
-@option{-fassociative-math} and @option{-freciprocal-math}.
+@item -fsanitize=kernel-address
+@opindex fsanitize=kernel-address
+Enable AddressSanitizer for Linux kernel.
+See @uref{https://github.com/google/kasan/wiki} for more details.
-The default is @option{-fno-unsafe-math-optimizations}.
+@item -fsanitize=thread
+@opindex fsanitize=thread
+Enable ThreadSanitizer, a fast data race detector.
+Memory access instructions are instrumented to detect
+data race bugs. See @uref{https://github.com/google/sanitizers/wiki#threadsanitizer} for more
+details. The run-time behavior can be influenced using the @env{TSAN_OPTIONS}
+environment variable; see
+@url{https://github.com/google/sanitizers/wiki/ThreadSanitizerFlags} for a list of
+supported options.
-@item -fassociative-math
-@opindex fassociative-math
+@item -fsanitize=leak
+@opindex fsanitize=leak
+Enable LeakSanitizer, a memory leak detector.
+This option only matters for linking of executables and if neither
+@option{-fsanitize=address} nor @option{-fsanitize=thread} is used. In that
+case the executable is linked against a library that overrides @code{malloc}
+and other allocator functions. See
+@uref{https://github.com/google/sanitizers/wiki/AddressSanitizerLeakSanitizer} for more
+details. The run-time behavior can be influenced using the
+@env{LSAN_OPTIONS} environment variable.
-Allow re-association of operands in series of floating-point operations.
-This violates the ISO C and C++ language standard by possibly changing
-computation result. NOTE: re-ordering may change the sign of zero as
-well as ignore NaNs and inhibit or create underflow or overflow (and
-thus cannot be used on code that relies on rounding behavior like
-@code{(x + 2**52) - 2**52}. May also reorder floating-point comparisons
-and thus may not be used when ordered comparisons are required.
-This option requires that both @option{-fno-signed-zeros} and
-@option{-fno-trapping-math} be in effect. Moreover, it doesn't make
-much sense with @option{-frounding-math}. For Fortran the option
-is automatically enabled when both @option{-fno-signed-zeros} and
-@option{-fno-trapping-math} are in effect.
+@item -fsanitize=undefined
+@opindex fsanitize=undefined
+Enable UndefinedBehaviorSanitizer, a fast undefined behavior detector.
+Various computations are instrumented to detect undefined behavior
+at runtime. Current suboptions are:
-The default is @option{-fno-associative-math}.
+@table @gcctabopt
-@item -freciprocal-math
-@opindex freciprocal-math
+@item -fsanitize=shift
+@opindex fsanitize=shift
+This option enables checking that the result of a shift operation is
+not undefined. Note that what exactly is considered undefined differs
+slightly between C and C++, as well as between ISO C90 and C99, etc.
-Allow the reciprocal of a value to be used instead of dividing by
-the value if this enables optimizations. For example @code{x / y}
-can be replaced with @code{x * (1/y)}, which is useful if @code{(1/y)}
-is subject to common subexpression elimination. Note that this loses
-precision and increases the number of flops operating on the value.
+@item -fsanitize=integer-divide-by-zero
+@opindex fsanitize=integer-divide-by-zero
+Detect integer division by zero as well as @code{INT_MIN / -1} division.
-The default is @option{-fno-reciprocal-math}.
+@item -fsanitize=unreachable
+@opindex fsanitize=unreachable
+With this option, the compiler turns the @code{__builtin_unreachable}
+call into a diagnostics message call instead. When reaching the
+@code{__builtin_unreachable} call, the behavior is undefined.
-@item -ffinite-math-only
-@opindex ffinite-math-only
-Allow optimizations for floating-point arithmetic that assume
-that arguments and results are not NaNs or +-Infs.
+@item -fsanitize=vla-bound
+@opindex fsanitize=vla-bound
+This option instructs the compiler to check that the size of a variable
+length array is positive.
-This option is not turned on by any @option{-O} option since
-it can result in incorrect output for programs that depend on
-an exact implementation of IEEE or ISO rules/specifications for
-math functions. It may, however, yield faster code for programs
-that do not require the guarantees of these specifications.
+@item -fsanitize=null
+@opindex fsanitize=null
+This option enables pointer checking. Particularly, the application
+built with this option turned on will issue an error message when it
+tries to dereference a NULL pointer, or if a reference (possibly an
+rvalue reference) is bound to a NULL pointer, or if a method is invoked
+on an object pointed by a NULL pointer.
-The default is @option{-fno-finite-math-only}.
+@item -fsanitize=return
+@opindex fsanitize=return
+This option enables return statement checking. Programs
+built with this option turned on will issue an error message
+when the end of a non-void function is reached without actually
+returning a value. This option works in C++ only.
-@item -fno-signed-zeros
-@opindex fno-signed-zeros
-Allow optimizations for floating-point arithmetic that ignore the
-signedness of zero. IEEE arithmetic specifies the behavior of
-distinct +0.0 and @minus{}0.0 values, which then prohibits simplification
-of expressions such as x+0.0 or 0.0*x (even with @option{-ffinite-math-only}).
-This option implies that the sign of a zero result isn't significant.
+@item -fsanitize=signed-integer-overflow
+@opindex fsanitize=signed-integer-overflow
+This option enables signed integer overflow checking. We check that
+the result of @code{+}, @code{*}, and both unary and binary @code{-}
+does not overflow in the signed arithmetics. Note, integer promotion
+rules must be taken into account. That is, the following is not an
+overflow:
+@smallexample
+signed char a = SCHAR_MAX;
+a++;
+@end smallexample
-The default is @option{-fsigned-zeros}.
+@item -fsanitize=bounds
+@opindex fsanitize=bounds
+This option enables instrumentation of array bounds. Various out of bounds
+accesses are detected. Flexible array members, flexible array member-like
+arrays, and initializers of variables with static storage are not instrumented.
-@item -fno-trapping-math
-@opindex fno-trapping-math
-Compile code assuming that floating-point operations cannot generate
-user-visible traps. These traps include division by zero, overflow,
-underflow, inexact result and invalid operation. This option requires
-that @option{-fno-signaling-nans} be in effect. Setting this option may
-allow faster code if one relies on ``non-stop'' IEEE arithmetic, for example.
+@item -fsanitize=bounds-strict
+@opindex fsanitize=bounds-strict
+This option enables strict instrumentation of array bounds. Most out of bounds
+accesses are detected, including flexible array members and flexible array
+member-like arrays. Initializers of variables with static storage are not
+instrumented.
-This option should never be turned on by any @option{-O} option since
-it can result in incorrect output for programs that depend on
-an exact implementation of IEEE or ISO rules/specifications for
-math functions.
+@item -fsanitize=alignment
+@opindex fsanitize=alignment
-The default is @option{-ftrapping-math}.
+This option enables checking of alignment of pointers when they are
+dereferenced, or when a reference is bound to insufficiently aligned target,
+or when a method or constructor is invoked on insufficiently aligned object.
-@item -frounding-math
-@opindex frounding-math
-Disable transformations and optimizations that assume default floating-point
-rounding behavior. This is round-to-zero for all floating point
-to integer conversions, and round-to-nearest for all other arithmetic
-truncations. This option should be specified for programs that change
-the FP rounding mode dynamically, or that may be executed with a
-non-default rounding mode. This option disables constant folding of
-floating-point expressions at compile time (which may be affected by
-rounding mode) and arithmetic transformations that are unsafe in the
-presence of sign-dependent rounding modes.
+@item -fsanitize=object-size
+@opindex fsanitize=object-size
+This option enables instrumentation of memory references using the
+@code{__builtin_object_size} function. Various out of bounds pointer
+accesses are detected.
-The default is @option{-fno-rounding-math}.
+@item -fsanitize=float-divide-by-zero
+@opindex fsanitize=float-divide-by-zero
+Detect floating-point division by zero. Unlike other similar options,
+@option{-fsanitize=float-divide-by-zero} is not enabled by
+@option{-fsanitize=undefined}, since floating-point division by zero can
+be a legitimate way of obtaining infinities and NaNs.
-This option is experimental and does not currently guarantee to
-disable all GCC optimizations that are affected by rounding mode.
-Future versions of GCC may provide finer control of this setting
-using C99's @code{FENV_ACCESS} pragma. This command-line option
-will be used to specify the default state for @code{FENV_ACCESS}.
+@item -fsanitize=float-cast-overflow
+@opindex fsanitize=float-cast-overflow
+This option enables floating-point type to integer conversion checking.
+We check that the result of the conversion does not overflow.
+Unlike other similar options, @option{-fsanitize=float-cast-overflow} is
+not enabled by @option{-fsanitize=undefined}.
+This option does not work well with @code{FE_INVALID} exceptions enabled.
-@item -fsignaling-nans
-@opindex fsignaling-nans
-Compile code assuming that IEEE signaling NaNs may generate user-visible
-traps during floating-point operations. Setting this option disables
-optimizations that may change the number of exceptions visible with
-signaling NaNs. This option implies @option{-ftrapping-math}.
+@item -fsanitize=nonnull-attribute
+@opindex fsanitize=nonnull-attribute
-This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
-be defined.
+This option enables instrumentation of calls, checking whether null values
+are not passed to arguments marked as requiring a non-null value by the
+@code{nonnull} function attribute.
-The default is @option{-fno-signaling-nans}.
+@item -fsanitize=returns-nonnull-attribute
+@opindex fsanitize=returns-nonnull-attribute
-This option is experimental and does not currently guarantee to
-disable all GCC optimizations that affect signaling NaN behavior.
+This option enables instrumentation of return statements in functions
+marked with @code{returns_nonnull} function attribute, to detect returning
+of null values from such functions.
-@item -fsingle-precision-constant
-@opindex fsingle-precision-constant
-Treat floating-point constants as single precision instead of
-implicitly converting them to double-precision constants.
+@item -fsanitize=bool
+@opindex fsanitize=bool
-@item -fcx-limited-range
-@opindex fcx-limited-range
-When enabled, this option states that a range reduction step is not
-needed when performing complex division. Also, there is no checking
-whether the result of a complex multiplication or division is @code{NaN
-+ I*NaN}, with an attempt to rescue the situation in that case. The
-default is @option{-fno-cx-limited-range}, but is enabled by
-@option{-ffast-math}.
+This option enables instrumentation of loads from bool. If a value other
+than 0/1 is loaded, a run-time error is issued.
-This option controls the default setting of the ISO C99
-@code{CX_LIMITED_RANGE} pragma. Nevertheless, the option applies to
-all languages.
+@item -fsanitize=enum
+@opindex fsanitize=enum
-@item -fcx-fortran-rules
-@opindex fcx-fortran-rules
-Complex multiplication and division follow Fortran rules. Range
-reduction is done as part of complex division, but there is no checking
-whether the result of a complex multiplication or division is @code{NaN
-+ I*NaN}, with an attempt to rescue the situation in that case.
+This option enables instrumentation of loads from an enum type. If
+a value outside the range of values for the enum type is loaded,
+a run-time error is issued.
-The default is @option{-fno-cx-fortran-rules}.
+@item -fsanitize=vptr
+@opindex fsanitize=vptr
+
+This option enables instrumentation of C++ member function calls, member
+accesses and some conversions between pointers to base and derived classes,
+to verify the referenced object has the correct dynamic type.
@end table
-The following options control optimizations that may improve
-performance, but are not enabled by any @option{-O} options. This
-section includes experimental options that may produce broken code.
+While @option{-ftrapv} causes traps for signed overflows to be emitted,
+@option{-fsanitize=undefined} gives a diagnostic message.
+This currently works only for the C family of languages.
-@table @gcctabopt
-@item -fbranch-probabilities
-@opindex fbranch-probabilities
-After running a program compiled with @option{-fprofile-arcs}
-(@pxref{Debugging Options,, Options for Debugging Your Program or
-@command{gcc}}), you can compile it a second time using
-@option{-fbranch-probabilities}, to improve optimizations based on
-the number of times each branch was taken. When a program
-compiled with @option{-fprofile-arcs} exits, it saves arc execution
-counts to a file called @file{@var{sourcename}.gcda} for each source
-file. The information in this data file is very dependent on the
-structure of the generated code, so you must use the same source code
-and the same optimization options for both compilations.
+@item -fno-sanitize=all
+@opindex fno-sanitize=all
-With @option{-fbranch-probabilities}, GCC puts a
-@samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
-These can be used to improve optimization. Currently, they are only
-used in one place: in @file{reorg.c}, instead of guessing which path a
-branch is most likely to take, the @samp{REG_BR_PROB} values are used to
-exactly determine which path is taken more often.
+This option disables all previously enabled sanitizers.
+@option{-fsanitize=all} is not allowed, as some sanitizers cannot be used
+together.
-@item -fprofile-values
-@opindex fprofile-values
-If combined with @option{-fprofile-arcs}, it adds code so that some
-data about values of expressions in the program is gathered.
+@item -fasan-shadow-offset=@var{number}
+@opindex fasan-shadow-offset
+This option forces GCC to use custom shadow offset in AddressSanitizer checks.
+It is useful for experimenting with different shadow memory layouts in
+Kernel AddressSanitizer.
-With @option{-fbranch-probabilities}, it reads back the data gathered
-from profiling values of expressions for usage in optimizations.
+@item -fsanitize-sections=@var{s1},@var{s2},...
+@opindex fsanitize-sections
+Sanitize global variables in selected user-defined sections. @var{si} may
+contain wildcards.
-Enabled with @option{-fprofile-generate} and @option{-fprofile-use}.
+@item -fsanitize-recover@r{[}=@var{opts}@r{]}
+@opindex fsanitize-recover
+@opindex fno-sanitize-recover
+@option{-fsanitize-recover=} controls error recovery mode for sanitizers
+mentioned in comma-separated list of @var{opts}. Enabling this option
+for a sanitizer component causes it to attempt to continue
+running the program as if no error happened. This means multiple
+runtime errors can be reported in a single program run, and the exit
+code of the program may indicate success even when errors
+have been reported. The @option{-fno-sanitize-recover=} option
+can be used to alter
+this behavior: only the first detected error is reported
+and program then exits with a non-zero exit code.
-@item -fprofile-reorder-functions
-@opindex fprofile-reorder-functions
-Function reordering based on profile instrumentation collects
-first time of execution of a function and orders these functions
-in ascending order.
+Currently this feature only works for @option{-fsanitize=undefined} (and its suboptions
+except for @option{-fsanitize=unreachable} and @option{-fsanitize=return}),
+@option{-fsanitize=float-cast-overflow}, @option{-fsanitize=float-divide-by-zero},
+@option{-fsanitize=kernel-address} and @option{-fsanitize=address}.
+For these sanitizers error recovery is turned on by default, except @option{-fsanitize=address},
+for which this feature is experimental.
+@option{-fsanitize-recover=all} and @option{-fno-sanitize-recover=all} is also
+accepted, the former enables recovery for all sanitizers that support it,
+the latter disables recovery for all sanitizers that support it.
-Enabled with @option{-fprofile-use}.
+Syntax without explicit @var{opts} parameter is deprecated. It is equivalent to
+@smallexample
+-fsanitize-recover=undefined,float-cast-overflow,float-divide-by-zero
+@end smallexample
+@noindent
+Similarly @option{-fno-sanitize-recover} is equivalent to
+@smallexample
+-fno-sanitize-recover=undefined,float-cast-overflow,float-divide-by-zero
+@end smallexample
-@item -fvpt
-@opindex fvpt
-If combined with @option{-fprofile-arcs}, this option instructs the compiler
-to add code to gather information about values of expressions.
+@item -fsanitize-undefined-trap-on-error
+@opindex fsanitize-undefined-trap-on-error
+The @option{-fsanitize-undefined-trap-on-error} option instructs the compiler to
+report undefined behavior using @code{__builtin_trap} rather than
+a @code{libubsan} library routine. The advantage of this is that the
+@code{libubsan} library is not needed and is not linked in, so this
+is usable even in freestanding environments.
-With @option{-fbranch-probabilities}, it reads back the data gathered
-and actually performs the optimizations based on them.
-Currently the optimizations include specialization of division operations
-using the knowledge about the value of the denominator.
+@item -fsanitize-coverage=trace-pc
+@opindex fsanitize-coverage=trace-pc
+Enable coverage-guided fuzzing code instrumentation.
+Inserts a call to @code{__sanitizer_cov_trace_pc} into every basic block.
-@item -frename-registers
-@opindex frename-registers
-Attempt to avoid false dependencies in scheduled code by making use
-of registers left over after register allocation. This optimization
-most benefits processors with lots of registers. Depending on the
-debug information format adopted by the target, however, it can
-make debugging impossible, since variables no longer stay in
-a ``home register''.
+@item -fbounds-check
+@opindex fbounds-check
+For front ends that support it, generate additional code to check that
+indices used to access arrays are within the declared range. This is
+currently only supported by the Java and Fortran front ends, where
+this option defaults to true and false respectively.
-Enabled by default with @option{-funroll-loops} and @option{-fpeel-loops}.
+@item -fcheck-pointer-bounds
+@opindex fcheck-pointer-bounds
+@opindex fno-check-pointer-bounds
+@cindex Pointer Bounds Checker options
+Enable Pointer Bounds Checker instrumentation. Each memory reference
+is instrumented with checks of the pointer used for memory access against
+bounds associated with that pointer.
-@item -fschedule-fusion
-@opindex fschedule-fusion
-Performs a target dependent pass over the instruction stream to schedule
-instructions of same type together because target machine can execute them
-more efficiently if they are adjacent to each other in the instruction flow.
+Currently there
+is only an implementation for Intel MPX available, thus x86 GNU/Linux target
+and @option{-mmpx} are required to enable this feature.
+MPX-based instrumentation requires
+a runtime library to enable MPX in hardware and handle bounds
+violation signals. By default when @option{-fcheck-pointer-bounds}
+and @option{-mmpx} options are used to link a program, the GCC driver
+links against the @file{libmpx} and @file{libmpxwrappers} libraries.
+Bounds checking on calls to dynamic libraries requires a linker
+with @option{-z bndplt} support; if GCC was configured with a linker
+without support for this option (including the Gold linker and older
+versions of ld), a warning is given if you link with @option{-mmpx}
+without also specifying @option{-static}, since the overall effectiveness
+of the bounds checking protection is reduced.
+See also @option{-static-libmpxwrappers}.
+
+MPX-based instrumentation
+may be used for debugging and also may be included in production code
+to increase program security. Depending on usage, you may
+have different requirements for the runtime library. The current version
+of the MPX runtime library is more oriented for use as a debugging
+tool. MPX runtime library usage implies @option{-lpthread}. See
+also @option{-static-libmpx}. The runtime library behavior can be
+influenced using various @env{CHKP_RT_*} environment variables. See
+@uref{https://gcc.gnu.org/wiki/Intel%20MPX%20support%20in%20the%20GCC%20compiler}
+for more details.
-Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
+Generated instrumentation may be controlled by various
+@option{-fchkp-*} options and by the @code{bnd_variable_size}
+structure field attribute (@pxref{Type Attributes}) and
+@code{bnd_legacy}, and @code{bnd_instrument} function attributes
+(@pxref{Function Attributes}). GCC also provides a number of built-in
+functions for controlling the Pointer Bounds Checker. @xref{Pointer
+Bounds Checker builtins}, for more information.
-@item -ftracer
-@opindex ftracer
-Perform tail duplication to enlarge superblock size. This transformation
-simplifies the control flow of the function allowing other optimizations to do
-a better job.
+@item -fchkp-check-incomplete-type
+@opindex fchkp-check-incomplete-type
+@opindex fno-chkp-check-incomplete-type
+Generate pointer bounds checks for variables with incomplete type.
+Enabled by default.
+
+@item -fchkp-narrow-bounds
+@opindex fchkp-narrow-bounds
+@opindex fno-chkp-narrow-bounds
+Controls bounds used by Pointer Bounds Checker for pointers to object
+fields. If narrowing is enabled then field bounds are used. Otherwise
+object bounds are used. See also @option{-fchkp-narrow-to-innermost-array}
+and @option{-fchkp-first-field-has-own-bounds}. Enabled by default.
-Enabled with @option{-fprofile-use}.
+@item -fchkp-first-field-has-own-bounds
+@opindex fchkp-first-field-has-own-bounds
+@opindex fno-chkp-first-field-has-own-bounds
+Forces Pointer Bounds Checker to use narrowed bounds for the address of the
+first field in the structure. By default a pointer to the first field has
+the same bounds as a pointer to the whole structure.
-@item -funroll-loops
-@opindex funroll-loops
-Unroll loops whose number of iterations can be determined at compile time or
-upon entry to the loop. @option{-funroll-loops} implies
-@option{-frerun-cse-after-loop}, @option{-fweb} and @option{-frename-registers}.
-It also turns on complete loop peeling (i.e.@: complete removal of loops with
-a small constant number of iterations). This option makes code larger, and may
-or may not make it run faster.
+@item -fchkp-narrow-to-innermost-array
+@opindex fchkp-narrow-to-innermost-array
+@opindex fno-chkp-narrow-to-innermost-array
+Forces Pointer Bounds Checker to use bounds of the innermost arrays in
+case of nested static array access. By default this option is disabled and
+bounds of the outermost array are used.
-Enabled with @option{-fprofile-use}.
+@item -fchkp-optimize
+@opindex fchkp-optimize
+@opindex fno-chkp-optimize
+Enables Pointer Bounds Checker optimizations. Enabled by default at
+optimization levels @option{-O}, @option{-O2}, @option{-O3}.
-@item -funroll-all-loops
-@opindex funroll-all-loops
-Unroll all loops, even if their number of iterations is uncertain when
-the loop is entered. This usually makes programs run more slowly.
-@option{-funroll-all-loops} implies the same options as
-@option{-funroll-loops}.
+@item -fchkp-use-fast-string-functions
+@opindex fchkp-use-fast-string-functions
+@opindex fno-chkp-use-fast-string-functions
+Enables use of @code{*_nobnd} versions of string functions (not copying bounds)
+by Pointer Bounds Checker. Disabled by default.
-@item -fpeel-loops
-@opindex fpeel-loops
-Peels loops for which there is enough information that they do not
-roll much (from profile feedback). It also turns on complete loop peeling
-(i.e.@: complete removal of loops with small constant number of iterations).
+@item -fchkp-use-nochk-string-functions
+@opindex fchkp-use-nochk-string-functions
+@opindex fno-chkp-use-nochk-string-functions
+Enables use of @code{*_nochk} versions of string functions (not checking bounds)
+by Pointer Bounds Checker. Disabled by default.
-Enabled with @option{-fprofile-use}.
+@item -fchkp-use-static-bounds
+@opindex fchkp-use-static-bounds
+@opindex fno-chkp-use-static-bounds
+Allow Pointer Bounds Checker to generate static bounds holding
+bounds of static variables. Enabled by default.
-@item -fmove-loop-invariants
-@opindex fmove-loop-invariants
-Enables the loop invariant motion pass in the RTL loop optimizer. Enabled
-at level @option{-O1}
+@item -fchkp-use-static-const-bounds
+@opindex fchkp-use-static-const-bounds
+@opindex fno-chkp-use-static-const-bounds
+Use statically-initialized bounds for constant bounds instead of
+generating them each time they are required. By default enabled when
+@option{-fchkp-use-static-bounds} is enabled.
-@item -funswitch-loops
-@opindex funswitch-loops
-Move branches with loop invariant conditions out of the loop, with duplicates
-of the loop on both branches (modified according to result of the condition).
+@item -fchkp-treat-zero-dynamic-size-as-infinite
+@opindex fchkp-treat-zero-dynamic-size-as-infinite
+@opindex fno-chkp-treat-zero-dynamic-size-as-infinite
+With this option, objects with incomplete type whose
+dynamically-obtained size is zero are treated as having infinite size
+instead by Pointer Bounds
+Checker. This option may be helpful if a program is linked with a library
+missing size information for some symbols. Disabled by default.
-@item -ffunction-sections
-@itemx -fdata-sections
-@opindex ffunction-sections
-@opindex fdata-sections
-Place each function or data item into its own section in the output
-file if the target supports arbitrary sections. The name of the
-function or the name of the data item determines the section's name
-in the output file.
+@item -fchkp-check-read
+@opindex fchkp-check-read
+@opindex fno-chkp-check-read
+Instructs Pointer Bounds Checker to generate checks for all read
+accesses to memory. Enabled by default.
-Use these options on systems where the linker can perform optimizations
-to improve locality of reference in the instruction space. Most systems
-using the ELF object format and SPARC processors running Solaris 2 have
-linkers with such optimizations. AIX may have these optimizations in
-the future.
+@item -fchkp-check-write
+@opindex fchkp-check-write
+@opindex fno-chkp-check-write
+Instructs Pointer Bounds Checker to generate checks for all write
+accesses to memory. Enabled by default.
-Only use these options when there are significant benefits from doing
-so. When you specify these options, the assembler and linker
-create larger object and executable files and are also slower.
-You cannot use @command{gprof} on all systems if you
-specify this option, and you may have problems with debugging if
-you specify both this option and @option{-g}.
+@item -fchkp-store-bounds
+@opindex fchkp-store-bounds
+@opindex fno-chkp-store-bounds
+Instructs Pointer Bounds Checker to generate bounds stores for
+pointer writes. Enabled by default.
-@item -fbranch-target-load-optimize
-@opindex fbranch-target-load-optimize
-Perform branch target register load optimization before prologue / epilogue
-threading.
-The use of target registers can typically be exposed only during reload,
-thus hoisting loads out of loops and doing inter-block scheduling needs
-a separate optimization pass.
+@item -fchkp-instrument-calls
+@opindex fchkp-instrument-calls
+@opindex fno-chkp-instrument-calls
+Instructs Pointer Bounds Checker to pass pointer bounds to calls.
+Enabled by default.
-@item -fbranch-target-load-optimize2
-@opindex fbranch-target-load-optimize2
-Perform branch target register load optimization after prologue / epilogue
-threading.
+@item -fchkp-instrument-marked-only
+@opindex fchkp-instrument-marked-only
+@opindex fno-chkp-instrument-marked-only
+Instructs Pointer Bounds Checker to instrument only functions
+marked with the @code{bnd_instrument} attribute
+(@pxref{Function Attributes}). Disabled by default.
-@item -fbtr-bb-exclusive
-@opindex fbtr-bb-exclusive
-When performing branch target register load optimization, don't reuse
-branch target registers within any basic block.
+@item -fchkp-use-wrappers
+@opindex fchkp-use-wrappers
+@opindex fno-chkp-use-wrappers
+Allows Pointer Bounds Checker to replace calls to built-in functions
+with calls to wrapper functions. When @option{-fchkp-use-wrappers}
+is used to link a program, the GCC driver automatically links
+against @file{libmpxwrappers}. See also @option{-static-libmpxwrappers}.
+Enabled by default.
@item -fstack-protector
@opindex fstack-protector
@item -fstack-protector-explicit
@opindex fstack-protector-explicit
Like @option{-fstack-protector} but only protects those functions which
-have the @code{stack_protect} attribute
+have the @code{stack_protect} attribute.
-@item -fstdarg-opt
-@opindex fstdarg-opt
-Optimize the prologue of variadic argument functions with respect to usage of
-those arguments.
+@item -fstack-check
+@opindex fstack-check
+Generate code to verify that you do not go beyond the boundary of the
+stack. You should specify this flag if you are running in an
+environment with multiple threads, but you only rarely need to specify it in
+a single-threaded environment since stack overflow is automatically
+detected on nearly all systems if there is only one stack.
+
+Note that this switch does not actually cause checking to be done; the
+operating system or the language runtime must do that. The switch causes
+generation of code to ensure that they see the stack being extended.
+
+You can additionally specify a string parameter: @samp{no} means no
+checking, @samp{generic} means force the use of old-style checking,
+@samp{specific} means use the best checking method and is equivalent
+to bare @option{-fstack-check}.
+
+Old-style checking is a generic mechanism that requires no specific
+target support in the compiler but comes with the following drawbacks:
+
+@enumerate
+@item
+Modified allocation strategy for large objects: they are always
+allocated dynamically if their size exceeds a fixed threshold.
+
+@item
+Fixed limit on the size of the static frame of functions: when it is
+topped by a particular function, stack checking is not reliable and
+a warning is issued by the compiler.
+
+@item
+Inefficiency: because of both the modified allocation strategy and the
+generic implementation, code performance is hampered.
+@end enumerate
+
+Note that old-style stack checking is also the fallback method for
+@samp{specific} if no target support has been added in the compiler.
+
+@item -fstack-limit-register=@var{reg}
+@itemx -fstack-limit-symbol=@var{sym}
+@itemx -fno-stack-limit
+@opindex fstack-limit-register
+@opindex fstack-limit-symbol
+@opindex fno-stack-limit
+Generate code to ensure that the stack does not grow beyond a certain value,
+either the value of a register or the address of a symbol. If a larger
+stack is required, a signal is raised at run time. For most targets,
+the signal is raised before the stack overruns the boundary, so
+it is possible to catch the signal without taking special precautions.
+
+For instance, if the stack starts at absolute address @samp{0x80000000}
+and grows downwards, you can use the flags
+@option{-fstack-limit-symbol=__stack_limit} and
+@option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
+of 128KB@. Note that this may only work with the GNU linker.
+
+You can locally override stack limit checking by using the
+@code{no_stack_limit} function attribute (@pxref{Function Attributes}).
+
+@item -fsplit-stack
+@opindex fsplit-stack
+Generate code to automatically split the stack before it overflows.
+The resulting program has a discontiguous stack which can only
+overflow if the program is unable to allocate any more memory. This
+is most useful when running threaded programs, as it is no longer
+necessary to calculate a good stack size to use for each thread. This
+is currently only implemented for the x86 targets running
+GNU/Linux.
+
+When code compiled with @option{-fsplit-stack} calls code compiled
+without @option{-fsplit-stack}, there may not be much stack space
+available for the latter code to run. If compiling all code,
+including library code, with @option{-fsplit-stack} is not an option,
+then the linker can fix up these calls so that the code compiled
+without @option{-fsplit-stack} always has a large stack. Support for
+this is implemented in the gold linker in GNU binutils release 2.21
+and later.
+
+@item -fvtable-verify=@r{[}std@r{|}preinit@r{|}none@r{]}
+@opindex fvtable-verify
+This option is only available when compiling C++ code.
+It turns on (or off, if using @option{-fvtable-verify=none}) the security
+feature that verifies at run time, for every virtual call, that
+the vtable pointer through which the call is made is valid for the type of
+the object, and has not been corrupted or overwritten. If an invalid vtable
+pointer is detected at run time, an error is reported and execution of the
+program is immediately halted.
+
+This option causes run-time data structures to be built at program startup,
+which are used for verifying the vtable pointers.
+The options @samp{std} and @samp{preinit}
+control the timing of when these data structures are built. In both cases the
+data structures are built before execution reaches @code{main}. Using
+@option{-fvtable-verify=std} causes the data structures to be built after
+shared libraries have been loaded and initialized.
+@option{-fvtable-verify=preinit} causes them to be built before shared
+libraries have been loaded and initialized.
+
+If this option appears multiple times in the command line with different
+values specified, @samp{none} takes highest priority over both @samp{std} and
+@samp{preinit}; @samp{preinit} takes priority over @samp{std}.
+
+@item -fvtv-debug
+@opindex fvtv-debug
+When used in conjunction with @option{-fvtable-verify=std} or
+@option{-fvtable-verify=preinit}, causes debug versions of the
+runtime functions for the vtable verification feature to be called.
+This flag also causes the compiler to log information about which
+vtable pointers it finds for each class.
+This information is written to a file named @file{vtv_set_ptr_data.log}
+in the directory named by the environment variable @env{VTV_LOGS_DIR}
+if that is defined or the current working directory otherwise.
-@item -fsection-anchors
-@opindex fsection-anchors
-Try to reduce the number of symbolic address calculations by using
-shared ``anchor'' symbols to address nearby objects. This transformation
-can help to reduce the number of GOT entries and GOT accesses on some
-targets.
+Note: This feature @emph{appends} data to the log file. If you want a fresh log
+file, be sure to delete any existing one.
-For example, the implementation of the following function @code{foo}:
+@item -fvtv-counts
+@opindex fvtv-counts
+This is a debugging flag. When used in conjunction with
+@option{-fvtable-verify=std} or @option{-fvtable-verify=preinit}, this
+causes the compiler to keep track of the total number of virtual calls
+it encounters and the number of verifications it inserts. It also
+counts the number of calls to certain run-time library functions
+that it inserts and logs this information for each compilation unit.
+The compiler writes this information to a file named
+@file{vtv_count_data.log} in the directory named by the environment
+variable @env{VTV_LOGS_DIR} if that is defined or the current working
+directory otherwise. It also counts the size of the vtable pointer sets
+for each class, and writes this information to @file{vtv_class_set_sizes.log}
+in the same directory.
-@smallexample
-static int a, b, c;
-int foo (void) @{ return a + b + c; @}
-@end smallexample
+Note: This feature @emph{appends} data to the log files. To get fresh log
+files, be sure to delete any existing ones.
-@noindent
-usually calculates the addresses of all three variables, but if you
-compile it with @option{-fsection-anchors}, it accesses the variables
-from a common anchor point instead. The effect is similar to the
-following pseudocode (which isn't valid C):
+@item -finstrument-functions
+@opindex finstrument-functions
+Generate instrumentation calls for entry and exit to functions. Just
+after function entry and just before function exit, the following
+profiling functions are called with the address of the current
+function and its call site. (On some platforms,
+@code{__builtin_return_address} does not work beyond the current
+function, so the call site information may not be available to the
+profiling functions otherwise.)
@smallexample
-int foo (void)
-@{
- register int *xr = &x;
- return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
-@}
+void __cyg_profile_func_enter (void *this_fn,
+ void *call_site);
+void __cyg_profile_func_exit (void *this_fn,
+ void *call_site);
@end smallexample
-Not all targets support this option.
-
-@item --param @var{name}=@var{value}
-@opindex param
-In some places, GCC uses various constants to control the amount of
-optimization that is done. For example, GCC does not inline functions
-that contain more than a certain number of instructions. You can
-control some of these constants on the command line using the
-@option{--param} option.
+The first argument is the address of the start of the current function,
+which may be looked up exactly in the symbol table.
-The names of specific parameters, and the meaning of the values, are
-tied to the internals of the compiler, and are subject to change
-without notice in future releases.
+This instrumentation is also done for functions expanded inline in other
+functions. The profiling calls indicate where, conceptually, the
+inline function is entered and exited. This means that addressable
+versions of such functions must be available. If all your uses of a
+function are expanded inline, this may mean an additional expansion of
+code size. If you use @code{extern inline} in your C code, an
+addressable version of such functions must be provided. (This is
+normally the case anyway, but if you get lucky and the optimizer always
+expands the functions inline, you might have gotten away without
+providing static copies.)
-In each case, the @var{value} is an integer. The allowable choices for
-@var{name} are:
+A function may be given the attribute @code{no_instrument_function}, in
+which case this instrumentation is not done. This can be used, for
+example, for the profiling functions listed above, high-priority
+interrupt routines, and any functions from which the profiling functions
+cannot safely be called (perhaps signal handlers, if the profiling
+routines generate output or allocate memory).
-@table @gcctabopt
-@item predictable-branch-outcome
-When branch is predicted to be taken with probability lower than this threshold
-(in percent), then it is considered well predictable. The default is 10.
+@item -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{}
+@opindex finstrument-functions-exclude-file-list
-@item max-crossjump-edges
-The maximum number of incoming edges to consider for cross-jumping.
-The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in
-the number of edges incoming to each block. Increasing values mean
-more aggressive optimization, making the compilation time increase with
-probably small improvement in executable size.
+Set the list of functions that are excluded from instrumentation (see
+the description of @option{-finstrument-functions}). If the file that
+contains a function definition matches with one of @var{file}, then
+that function is not instrumented. The match is done on substrings:
+if the @var{file} parameter is a substring of the file name, it is
+considered to be a match.
-@item min-crossjump-insns
-The minimum number of instructions that must be matched at the end
-of two blocks before cross-jumping is performed on them. This
-value is ignored in the case where all instructions in the block being
-cross-jumped from are matched. The default value is 5.
+For example:
-@item max-grow-copy-bb-insns
-The maximum code size expansion factor when copying basic blocks
-instead of jumping. The expansion is relative to a jump instruction.
-The default value is 8.
+@smallexample
+-finstrument-functions-exclude-file-list=/bits/stl,include/sys
+@end smallexample
-@item max-goto-duplication-insns
-The maximum number of instructions to duplicate to a block that jumps
-to a computed goto. To avoid @math{O(N^2)} behavior in a number of
-passes, GCC factors computed gotos early in the compilation process,
-and unfactors them as late as possible. Only computed jumps at the
-end of a basic blocks with no more than max-goto-duplication-insns are
-unfactored. The default value is 8.
+@noindent
+excludes any inline function defined in files whose pathnames
+contain @file{/bits/stl} or @file{include/sys}.
-@item max-delay-slot-insn-search
-The maximum number of instructions to consider when looking for an
-instruction to fill a delay slot. If more than this arbitrary number of
-instructions are searched, the time savings from filling the delay slot
-are minimal, so stop searching. Increasing values mean more
-aggressive optimization, making the compilation time increase with probably
-small improvement in execution time.
+If, for some reason, you want to include letter @samp{,} in one of
+@var{sym}, write @samp{\,}. For example,
+@option{-finstrument-functions-exclude-file-list='\,\,tmp'}
+(note the single quote surrounding the option).
-@item max-delay-slot-live-search
-When trying to fill delay slots, the maximum number of instructions to
-consider when searching for a block with valid live register
-information. Increasing this arbitrarily chosen value means more
-aggressive optimization, increasing the compilation time. This parameter
-should be removed when the delay slot code is rewritten to maintain the
-control-flow graph.
+@item -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{}
+@opindex finstrument-functions-exclude-function-list
-@item max-gcse-memory
-The approximate maximum amount of memory that can be allocated in
-order to perform the global common subexpression elimination
-optimization. If more memory than specified is required, the
-optimization is not done.
+This is similar to @option{-finstrument-functions-exclude-file-list},
+but this option sets the list of function names to be excluded from
+instrumentation. The function name to be matched is its user-visible
+name, such as @code{vector<int> blah(const vector<int> &)}, not the
+internal mangled name (e.g., @code{_Z4blahRSt6vectorIiSaIiEE}). The
+match is done on substrings: if the @var{sym} parameter is a substring
+of the function name, it is considered to be a match. For C99 and C++
+extended identifiers, the function name must be given in UTF-8, not
+using universal character names.
-@item max-gcse-insertion-ratio
-If the ratio of expression insertions to deletions is larger than this value
-for any expression, then RTL PRE inserts or removes the expression and thus
-leaves partially redundant computations in the instruction stream. The default value is 20.
+@end table
-@item max-pending-list-length
-The maximum number of pending dependencies scheduling allows
-before flushing the current state and starting over. Large functions
-with few branches or calls can create excessively large lists which
-needlessly consume memory and resources.
-@item max-modulo-backtrack-attempts
-The maximum number of backtrack attempts the scheduler should make
-when modulo scheduling a loop. Larger values can exponentially increase
-compilation time.
+@node Preprocessor Options
+@section Options Controlling the Preprocessor
+@cindex preprocessor options
+@cindex options, preprocessor
-@item max-inline-insns-single
-Several parameters control the tree inliner used in GCC@.
-This number sets the maximum number of instructions (counted in GCC's
-internal representation) in a single function that the tree inliner
-considers for inlining. This only affects functions declared
-inline and methods implemented in a class declaration (C++).
-The default value is 400.
+These options control the C preprocessor, which is run on each C source
+file before actual compilation.
-@item max-inline-insns-auto
-When you use @option{-finline-functions} (included in @option{-O3}),
-a lot of functions that would otherwise not be considered for inlining
-by the compiler are investigated. To those functions, a different
-(more restrictive) limit compared to functions declared inline can
-be applied.
-The default value is 40.
+If you use the @option{-E} option, nothing is done except preprocessing.
+Some of these options make sense only together with @option{-E} because
+they cause the preprocessor output to be unsuitable for actual
+compilation.
-@item inline-min-speedup
-When estimated performance improvement of caller + callee runtime exceeds this
-threshold (in precent), the function can be inlined regardless the limit on
-@option{--param max-inline-insns-single} and @option{--param
-max-inline-insns-auto}.
+@table @gcctabopt
+@item -Wp,@var{option}
+@opindex Wp
+You can use @option{-Wp,@var{option}} to bypass the compiler driver
+and pass @var{option} directly through to the preprocessor. If
+@var{option} contains commas, it is split into multiple options at the
+commas. However, many options are modified, translated or interpreted
+by the compiler driver before being passed to the preprocessor, and
+@option{-Wp} forcibly bypasses this phase. The preprocessor's direct
+interface is undocumented and subject to change, so whenever possible
+you should avoid using @option{-Wp} and let the driver handle the
+options instead.
-@item large-function-insns
-The limit specifying really large functions. For functions larger than this
-limit after inlining, inlining is constrained by
-@option{--param large-function-growth}. This parameter is useful primarily
-to avoid extreme compilation time caused by non-linear algorithms used by the
-back end.
-The default value is 2700.
+@item -Xpreprocessor @var{option}
+@opindex Xpreprocessor
+Pass @var{option} as an option to the preprocessor. You can use this to
+supply system-specific preprocessor options that GCC does not
+recognize.
-@item large-function-growth
-Specifies maximal growth of large function caused by inlining in percents.
-The default value is 100 which limits large function growth to 2.0 times
-the original size.
+If you want to pass an option that takes an argument, you must use
+@option{-Xpreprocessor} twice, once for the option and once for the argument.
-@item large-unit-insns
-The limit specifying large translation unit. Growth caused by inlining of
-units larger than this limit is limited by @option{--param inline-unit-growth}.
-For small units this might be too tight.
-For example, consider a unit consisting of function A
-that is inline and B that just calls A three times. If B is small relative to
-A, the growth of unit is 300\% and yet such inlining is very sane. For very
-large units consisting of small inlineable functions, however, the overall unit
-growth limit is needed to avoid exponential explosion of code size. Thus for
-smaller units, the size is increased to @option{--param large-unit-insns}
-before applying @option{--param inline-unit-growth}. The default is 10000.
+@item -no-integrated-cpp
+@opindex no-integrated-cpp
+Perform preprocessing as a separate pass before compilation.
+By default, GCC performs preprocessing as an integrated part of
+input tokenization and parsing.
+If this option is provided, the appropriate language front end
+(@command{cc1}, @command{cc1plus}, or @command{cc1obj} for C, C++,
+and Objective-C, respectively) is instead invoked twice,
+once for preprocessing only and once for actual compilation
+of the preprocessed input.
+This option may be useful in conjunction with the @option{-B} or
+@option{-wrapper} options to specify an alternate preprocessor or
+perform additional processing of the program source between
+normal preprocessing and compilation.
+@end table
-@item inline-unit-growth
-Specifies maximal overall growth of the compilation unit caused by inlining.
-The default value is 20 which limits unit growth to 1.2 times the original
-size. Cold functions (either marked cold via an attribute or by profile
-feedback) are not accounted into the unit size.
+@include cppopts.texi
-@item ipcp-unit-growth
-Specifies maximal overall growth of the compilation unit caused by
-interprocedural constant propagation. The default value is 10 which limits
-unit growth to 1.1 times the original size.
+@node Assembler Options
+@section Passing Options to the Assembler
-@item large-stack-frame
-The limit specifying large stack frames. While inlining the algorithm is trying
-to not grow past this limit too much. The default value is 256 bytes.
+@c prevent bad page break with this line
+You can pass options to the assembler.
-@item large-stack-frame-growth
-Specifies maximal growth of large stack frames caused by inlining in percents.
-The default value is 1000 which limits large stack frame growth to 11 times
-the original size.
+@table @gcctabopt
+@item -Wa,@var{option}
+@opindex Wa
+Pass @var{option} as an option to the assembler. If @var{option}
+contains commas, it is split into multiple options at the commas.
-@item max-inline-insns-recursive
-@itemx max-inline-insns-recursive-auto
-Specifies the maximum number of instructions an out-of-line copy of a
-self-recursive inline
-function can grow into by performing recursive inlining.
+@item -Xassembler @var{option}
+@opindex Xassembler
+Pass @var{option} as an option to the assembler. You can use this to
+supply system-specific assembler options that GCC does not
+recognize.
-@option{--param max-inline-insns-recursive} applies to functions
-declared inline.
-For functions not declared inline, recursive inlining
-happens only when @option{-finline-functions} (included in @option{-O3}) is
-enabled; @option{--param max-inline-insns-recursive-auto} applies instead. The
-default value is 450.
+If you want to pass an option that takes an argument, you must use
+@option{-Xassembler} twice, once for the option and once for the argument.
-@item max-inline-recursive-depth
-@itemx max-inline-recursive-depth-auto
-Specifies the maximum recursion depth used for recursive inlining.
+@end table
-@option{--param max-inline-recursive-depth} applies to functions
-declared inline. For functions not declared inline, recursive inlining
-happens only when @option{-finline-functions} (included in @option{-O3}) is
-enabled; @option{--param max-inline-recursive-depth-auto} applies instead. The
-default value is 8.
+@node Link Options
+@section Options for Linking
+@cindex link options
+@cindex options, linking
-@item min-inline-recursive-probability
-Recursive inlining is profitable only for function having deep recursion
-in average and can hurt for function having little recursion depth by
-increasing the prologue size or complexity of function body to other
-optimizers.
+These options come into play when the compiler links object files into
+an executable output file. They are meaningless if the compiler is
+not doing a link step.
-When profile feedback is available (see @option{-fprofile-generate}) the actual
-recursion depth can be guessed from probability that function recurses via a
-given call expression. This parameter limits inlining only to call expressions
-whose probability exceeds the given threshold (in percents).
-The default value is 10.
+@table @gcctabopt
+@cindex file names
+@item @var{object-file-name}
+A file name that does not end in a special recognized suffix is
+considered to name an object file or library. (Object files are
+distinguished from libraries by the linker according to the file
+contents.) If linking is done, these object files are used as input
+to the linker.
-@item early-inlining-insns
-Specify growth that the early inliner can make. In effect it increases
-the amount of inlining for code having a large abstraction penalty.
-The default value is 14.
+@item -c
+@itemx -S
+@itemx -E
+@opindex c
+@opindex S
+@opindex E
+If any of these options is used, then the linker is not run, and
+object file names should not be used as arguments. @xref{Overall
+Options}.
-@item max-early-inliner-iterations
-Limit of iterations of the early inliner. This basically bounds
-the number of nested indirect calls the early inliner can resolve.
-Deeper chains are still handled by late inlining.
+@item -fuse-ld=bfd
+@opindex fuse-ld=bfd
+Use the @command{bfd} linker instead of the default linker.
-@item comdat-sharing-probability
-Probability (in percent) that C++ inline function with comdat visibility
-are shared across multiple compilation units. The default value is 20.
+@item -fuse-ld=gold
+@opindex fuse-ld=gold
+Use the @command{gold} linker instead of the default linker.
-@item profile-func-internal-id
-A parameter to control whether to use function internal id in profile
-database lookup. If the value is 0, the compiler uses an id that
-is based on function assembler name and filename, which makes old profile
-data more tolerant to source changes such as function reordering etc.
-The default value is 0.
+@cindex Libraries
+@item -l@var{library}
+@itemx -l @var{library}
+@opindex l
+Search the library named @var{library} when linking. (The second
+alternative with the library as a separate argument is only for
+POSIX compliance and is not recommended.)
-@item min-vect-loop-bound
-The minimum number of iterations under which loops are not vectorized
-when @option{-ftree-vectorize} is used. The number of iterations after
-vectorization needs to be greater than the value specified by this option
-to allow vectorization. The default value is 0.
+It makes a difference where in the command you write this option; the
+linker searches and processes libraries and object files in the order they
+are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
+after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
+to functions in @samp{z}, those functions may not be loaded.
-@item gcse-cost-distance-ratio
-Scaling factor in calculation of maximum distance an expression
-can be moved by GCSE optimizations. This is currently supported only in the
-code hoisting pass. The bigger the ratio, the more aggressive code hoisting
-is with simple expressions, i.e., the expressions that have cost
-less than @option{gcse-unrestricted-cost}. Specifying 0 disables
-hoisting of simple expressions. The default value is 10.
+The linker searches a standard list of directories for the library,
+which is actually a file named @file{lib@var{library}.a}. The linker
+then uses this file as if it had been specified precisely by name.
-@item gcse-unrestricted-cost
-Cost, roughly measured as the cost of a single typical machine
-instruction, at which GCSE optimizations do not constrain
-the distance an expression can travel. This is currently
-supported only in the code hoisting pass. The lesser the cost,
-the more aggressive code hoisting is. Specifying 0
-allows all expressions to travel unrestricted distances.
-The default value is 3.
+The directories searched include several standard system directories
+plus any that you specify with @option{-L}.
-@item max-hoist-depth
-The depth of search in the dominator tree for expressions to hoist.
-This is used to avoid quadratic behavior in hoisting algorithm.
-The value of 0 does not limit on the search, but may slow down compilation
-of huge functions. The default value is 30.
+Normally the files found this way are library files---archive files
+whose members are object files. The linker handles an archive file by
+scanning through it for members which define symbols that have so far
+been referenced but not defined. But if the file that is found is an
+ordinary object file, it is linked in the usual fashion. The only
+difference between using an @option{-l} option and specifying a file name
+is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
+and searches several directories.
-@item max-tail-merge-comparisons
-The maximum amount of similar bbs to compare a bb with. This is used to
-avoid quadratic behavior in tree tail merging. The default value is 10.
+@item -lobjc
+@opindex lobjc
+You need this special case of the @option{-l} option in order to
+link an Objective-C or Objective-C++ program.
-@item max-tail-merge-iterations
-The maximum amount of iterations of the pass over the function. This is used to
-limit compilation time in tree tail merging. The default value is 2.
+@item -nostartfiles
+@opindex nostartfiles
+Do not use the standard system startup files when linking.
+The standard system libraries are used normally, unless @option{-nostdlib}
+or @option{-nodefaultlibs} is used.
-@item max-unrolled-insns
-The maximum number of instructions that a loop may have to be unrolled.
-If a loop is unrolled, this parameter also determines how many times
-the loop code is unrolled.
+@item -nodefaultlibs
+@opindex nodefaultlibs
+Do not use the standard system libraries when linking.
+Only the libraries you specify are passed to the linker, and options
+specifying linkage of the system libraries, such as @option{-static-libgcc}
+or @option{-shared-libgcc}, are ignored.
+The standard startup files are used normally, unless @option{-nostartfiles}
+is used.
-@item max-average-unrolled-insns
-The maximum number of instructions biased by probabilities of their execution
-that a loop may have to be unrolled. If a loop is unrolled,
-this parameter also determines how many times the loop code is unrolled.
+The compiler may generate calls to @code{memcmp},
+@code{memset}, @code{memcpy} and @code{memmove}.
+These entries are usually resolved by entries in
+libc. These entry points should be supplied through some other
+mechanism when this option is specified.
-@item max-unroll-times
-The maximum number of unrollings of a single loop.
+@item -nostdlib
+@opindex nostdlib
+Do not use the standard system startup files or libraries when linking.
+No startup files and only the libraries you specify are passed to
+the linker, and options specifying linkage of the system libraries, such as
+@option{-static-libgcc} or @option{-shared-libgcc}, are ignored.
-@item max-peeled-insns
-The maximum number of instructions that a loop may have to be peeled.
-If a loop is peeled, this parameter also determines how many times
-the loop code is peeled.
+The compiler may generate calls to @code{memcmp}, @code{memset},
+@code{memcpy} and @code{memmove}.
+These entries are usually resolved by entries in
+libc. These entry points should be supplied through some other
+mechanism when this option is specified.
-@item max-peel-times
-The maximum number of peelings of a single loop.
+@cindex @option{-lgcc}, use with @option{-nostdlib}
+@cindex @option{-nostdlib} and unresolved references
+@cindex unresolved references and @option{-nostdlib}
+@cindex @option{-lgcc}, use with @option{-nodefaultlibs}
+@cindex @option{-nodefaultlibs} and unresolved references
+@cindex unresolved references and @option{-nodefaultlibs}
+One of the standard libraries bypassed by @option{-nostdlib} and
+@option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
+which GCC uses to overcome shortcomings of particular machines, or special
+needs for some languages.
+(@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
+Collection (GCC) Internals},
+for more discussion of @file{libgcc.a}.)
+In most cases, you need @file{libgcc.a} even when you want to avoid
+other standard libraries. In other words, when you specify @option{-nostdlib}
+or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
+This ensures that you have no unresolved references to internal GCC
+library subroutines.
+(An example of such an internal subroutine is @code{__main}, used to ensure C++
+constructors are called; @pxref{Collect2,,@code{collect2}, gccint,
+GNU Compiler Collection (GCC) Internals}.)
+
+@item -pie
+@opindex pie
+Produce a position independent executable on targets that support it.
+For predictable results, you must also specify the same set of options
+used for compilation (@option{-fpie}, @option{-fPIE},
+or model suboptions) when you specify this linker option.
+
+@item -no-pie
+@opindex no-pie
+Don't produce a position independent executable.
+
+@item -rdynamic
+@opindex rdynamic
+Pass the flag @option{-export-dynamic} to the ELF linker, on targets
+that support it. This instructs the linker to add all symbols, not
+only used ones, to the dynamic symbol table. This option is needed
+for some uses of @code{dlopen} or to allow obtaining backtraces
+from within a program.
-@item max-peel-branches
-The maximum number of branches on the hot path through the peeled sequence.
+@item -s
+@opindex s
+Remove all symbol table and relocation information from the executable.
-@item max-completely-peeled-insns
-The maximum number of insns of a completely peeled loop.
+@item -static
+@opindex static
+On systems that support dynamic linking, this prevents linking with the shared
+libraries. On other systems, this option has no effect.
-@item max-completely-peel-times
-The maximum number of iterations of a loop to be suitable for complete peeling.
+@item -shared
+@opindex shared
+Produce a shared object which can then be linked with other objects to
+form an executable. Not all systems support this option. For predictable
+results, you must also specify the same set of options used for compilation
+(@option{-fpic}, @option{-fPIC}, or model suboptions) when
+you specify this linker option.@footnote{On some systems, @samp{gcc -shared}
+needs to build supplementary stub code for constructors to work. On
+multi-libbed systems, @samp{gcc -shared} must select the correct support
+libraries to link against. Failing to supply the correct flags may lead
+to subtle defects. Supplying them in cases where they are not necessary
+is innocuous.}
-@item max-completely-peel-loop-nest-depth
-The maximum depth of a loop nest suitable for complete peeling.
+@item -shared-libgcc
+@itemx -static-libgcc
+@opindex shared-libgcc
+@opindex static-libgcc
+On systems that provide @file{libgcc} as a shared library, these options
+force the use of either the shared or static version, respectively.
+If no shared version of @file{libgcc} was built when the compiler was
+configured, these options have no effect.
-@item max-unswitch-insns
-The maximum number of insns of an unswitched loop.
+There are several situations in which an application should use the
+shared @file{libgcc} instead of the static version. The most common
+of these is when the application wishes to throw and catch exceptions
+across different shared libraries. In that case, each of the libraries
+as well as the application itself should use the shared @file{libgcc}.
-@item max-unswitch-level
-The maximum number of branches unswitched in a single loop.
+Therefore, the G++ and GCJ drivers automatically add
+@option{-shared-libgcc} whenever you build a shared library or a main
+executable, because C++ and Java programs typically use exceptions, so
+this is the right thing to do.
-@item lim-expensive
-The minimum cost of an expensive expression in the loop invariant motion.
+If, instead, you use the GCC driver to create shared libraries, you may
+find that they are not always linked with the shared @file{libgcc}.
+If GCC finds, at its configuration time, that you have a non-GNU linker
+or a GNU linker that does not support option @option{--eh-frame-hdr},
+it links the shared version of @file{libgcc} into shared libraries
+by default. Otherwise, it takes advantage of the linker and optimizes
+away the linking with the shared version of @file{libgcc}, linking with
+the static version of libgcc by default. This allows exceptions to
+propagate through such shared libraries, without incurring relocation
+costs at library load time.
-@item iv-consider-all-candidates-bound
-Bound on number of candidates for induction variables, below which
-all candidates are considered for each use in induction variable
-optimizations. If there are more candidates than this,
-only the most relevant ones are considered to avoid quadratic time complexity.
+However, if a library or main executable is supposed to throw or catch
+exceptions, you must link it using the G++ or GCJ driver, as appropriate
+for the languages used in the program, or using the option
+@option{-shared-libgcc}, such that it is linked with the shared
+@file{libgcc}.
-@item iv-max-considered-uses
-The induction variable optimizations give up on loops that contain more
-induction variable uses.
+@item -static-libasan
+@opindex static-libasan
+When the @option{-fsanitize=address} option is used to link a program,
+the GCC driver automatically links against @option{libasan}. If
+@file{libasan} is available as a shared library, and the @option{-static}
+option is not used, then this links against the shared version of
+@file{libasan}. The @option{-static-libasan} option directs the GCC
+driver to link @file{libasan} statically, without necessarily linking
+other libraries statically.
-@item iv-always-prune-cand-set-bound
-If the number of candidates in the set is smaller than this value,
-always try to remove unnecessary ivs from the set
-when adding a new one.
+@item -static-libtsan
+@opindex static-libtsan
+When the @option{-fsanitize=thread} option is used to link a program,
+the GCC driver automatically links against @option{libtsan}. If
+@file{libtsan} is available as a shared library, and the @option{-static}
+option is not used, then this links against the shared version of
+@file{libtsan}. The @option{-static-libtsan} option directs the GCC
+driver to link @file{libtsan} statically, without necessarily linking
+other libraries statically.
-@item scev-max-expr-size
-Bound on size of expressions used in the scalar evolutions analyzer.
-Large expressions slow the analyzer.
+@item -static-liblsan
+@opindex static-liblsan
+When the @option{-fsanitize=leak} option is used to link a program,
+the GCC driver automatically links against @option{liblsan}. If
+@file{liblsan} is available as a shared library, and the @option{-static}
+option is not used, then this links against the shared version of
+@file{liblsan}. The @option{-static-liblsan} option directs the GCC
+driver to link @file{liblsan} statically, without necessarily linking
+other libraries statically.
-@item scev-max-expr-complexity
-Bound on the complexity of the expressions in the scalar evolutions analyzer.
-Complex expressions slow the analyzer.
+@item -static-libubsan
+@opindex static-libubsan
+When the @option{-fsanitize=undefined} option is used to link a program,
+the GCC driver automatically links against @option{libubsan}. If
+@file{libubsan} is available as a shared library, and the @option{-static}
+option is not used, then this links against the shared version of
+@file{libubsan}. The @option{-static-libubsan} option directs the GCC
+driver to link @file{libubsan} statically, without necessarily linking
+other libraries statically.
-@item vect-max-version-for-alignment-checks
-The maximum number of run-time checks that can be performed when
-doing loop versioning for alignment in the vectorizer.
+@item -static-libmpx
+@opindex static-libmpx
+When the @option{-fcheck-pointer bounds} and @option{-mmpx} options are
+used to link a program, the GCC driver automatically links against
+@file{libmpx}. If @file{libmpx} is available as a shared library,
+and the @option{-static} option is not used, then this links against
+the shared version of @file{libmpx}. The @option{-static-libmpx}
+option directs the GCC driver to link @file{libmpx} statically,
+without necessarily linking other libraries statically.
-@item vect-max-version-for-alias-checks
-The maximum number of run-time checks that can be performed when
-doing loop versioning for alias in the vectorizer.
+@item -static-libmpxwrappers
+@opindex static-libmpxwrappers
+When the @option{-fcheck-pointer bounds} and @option{-mmpx} options are used
+to link a program without also using @option{-fno-chkp-use-wrappers}, the
+GCC driver automatically links against @file{libmpxwrappers}. If
+@file{libmpxwrappers} is available as a shared library, and the
+@option{-static} option is not used, then this links against the shared
+version of @file{libmpxwrappers}. The @option{-static-libmpxwrappers}
+option directs the GCC driver to link @file{libmpxwrappers} statically,
+without necessarily linking other libraries statically.
-@item vect-max-peeling-for-alignment
-The maximum number of loop peels to enhance access alignment
-for vectorizer. Value -1 means 'no limit'.
+@item -static-libstdc++
+@opindex static-libstdc++
+When the @command{g++} program is used to link a C++ program, it
+normally automatically links against @option{libstdc++}. If
+@file{libstdc++} is available as a shared library, and the
+@option{-static} option is not used, then this links against the
+shared version of @file{libstdc++}. That is normally fine. However, it
+is sometimes useful to freeze the version of @file{libstdc++} used by
+the program without going all the way to a fully static link. The
+@option{-static-libstdc++} option directs the @command{g++} driver to
+link @file{libstdc++} statically, without necessarily linking other
+libraries statically.
-@item max-iterations-to-track
-The maximum number of iterations of a loop the brute-force algorithm
-for analysis of the number of iterations of the loop tries to evaluate.
+@item -symbolic
+@opindex symbolic
+Bind references to global symbols when building a shared object. Warn
+about any unresolved references (unless overridden by the link editor
+option @option{-Xlinker -z -Xlinker defs}). Only a few systems support
+this option.
-@item hot-bb-count-ws-permille
-A basic block profile count is considered hot if it contributes to
-the given permillage (i.e. 0...1000) of the entire profiled execution.
+@item -T @var{script}
+@opindex T
+@cindex linker script
+Use @var{script} as the linker script. This option is supported by most
+systems using the GNU linker. On some targets, such as bare-board
+targets without an operating system, the @option{-T} option may be required
+when linking to avoid references to undefined symbols.
-@item hot-bb-frequency-fraction
-Select fraction of the entry block frequency of executions of basic block in
-function given basic block needs to have to be considered hot.
+@item -Xlinker @var{option}
+@opindex Xlinker
+Pass @var{option} as an option to the linker. You can use this to
+supply system-specific linker options that GCC does not recognize.
-@item max-predicted-iterations
-The maximum number of loop iterations we predict statically. This is useful
-in cases where a function contains a single loop with known bound and
-another loop with unknown bound.
-The known number of iterations is predicted correctly, while
-the unknown number of iterations average to roughly 10. This means that the
-loop without bounds appears artificially cold relative to the other one.
+If you want to pass an option that takes a separate argument, you must use
+@option{-Xlinker} twice, once for the option and once for the argument.
+For example, to pass @option{-assert definitions}, you must write
+@option{-Xlinker -assert -Xlinker definitions}. It does not work to write
+@option{-Xlinker "-assert definitions"}, because this passes the entire
+string as a single argument, which is not what the linker expects.
-@item builtin-expect-probability
-Control the probability of the expression having the specified value. This
-parameter takes a percentage (i.e. 0 ... 100) as input.
-The default probability of 90 is obtained empirically.
+When using the GNU linker, it is usually more convenient to pass
+arguments to linker options using the @option{@var{option}=@var{value}}
+syntax than as separate arguments. For example, you can specify
+@option{-Xlinker -Map=output.map} rather than
+@option{-Xlinker -Map -Xlinker output.map}. Other linkers may not support
+this syntax for command-line options.
-@item align-threshold
+@item -Wl,@var{option}
+@opindex Wl
+Pass @var{option} as an option to the linker. If @var{option} contains
+commas, it is split into multiple options at the commas. You can use this
+syntax to pass an argument to the option.
+For example, @option{-Wl,-Map,output.map} passes @option{-Map output.map} to the
+linker. When using the GNU linker, you can also get the same effect with
+@option{-Wl,-Map=output.map}.
-Select fraction of the maximal frequency of executions of a basic block in
-a function to align the basic block.
+@item -u @var{symbol}
+@opindex u
+Pretend the symbol @var{symbol} is undefined, to force linking of
+library modules to define it. You can use @option{-u} multiple times with
+different symbols to force loading of additional library modules.
-@item align-loop-iterations
+@item -z @var{keyword}
+@opindex z
+@option{-z} is passed directly on to the linker along with the keyword
+@var{keyword}. See the section in the documentation of your linker for
+permitted values and their meanings.
+@end table
-A loop expected to iterate at least the selected number of iterations is
-aligned.
+@node Directory Options
+@section Options for Directory Search
+@cindex directory options
+@cindex options, directory search
+@cindex search path
-@item tracer-dynamic-coverage
-@itemx tracer-dynamic-coverage-feedback
+These options specify directories to search for header files, for
+libraries and for parts of the compiler:
-This value is used to limit superblock formation once the given percentage of
-executed instructions is covered. This limits unnecessary code size
-expansion.
+@table @gcctabopt
+@item -I@var{dir}
+@opindex I
+Add the directory @var{dir} to the head of the list of directories to be
+searched for header files. This can be used to override a system header
+file, substituting your own version, since these directories are
+searched before the system header file directories. However, you should
+not use this option to add directories that contain vendor-supplied
+system header files (use @option{-isystem} for that). If you use more than
+one @option{-I} option, the directories are scanned in left-to-right
+order; the standard system directories come after.
-The @option{tracer-dynamic-coverage-feedback} parameter
-is used only when profile
-feedback is available. The real profiles (as opposed to statically estimated
-ones) are much less balanced allowing the threshold to be larger value.
+If a standard system include directory, or a directory specified with
+@option{-isystem}, is also specified with @option{-I}, the @option{-I}
+option is ignored. The directory is still searched but as a
+system directory at its normal position in the system include chain.
+This is to ensure that GCC's procedure to fix buggy system headers and
+the ordering for the @code{include_next} directive are not inadvertently changed.
+If you really need to change the search order for system directories,
+use the @option{-nostdinc} and/or @option{-isystem} options.
-@item tracer-max-code-growth
-Stop tail duplication once code growth has reached given percentage. This is
-a rather artificial limit, as most of the duplicates are eliminated later in
-cross jumping, so it may be set to much higher values than is the desired code
-growth.
+@item -iplugindir=@var{dir}
+@opindex iplugindir=
+Set the directory to search for plugins that are passed
+by @option{-fplugin=@var{name}} instead of
+@option{-fplugin=@var{path}/@var{name}.so}. This option is not meant
+to be used by the user, but only passed by the driver.
-@item tracer-min-branch-ratio
+@item -iquote@var{dir}
+@opindex iquote
+Add the directory @var{dir} to the head of the list of directories to
+be searched for header files only for the case of @code{#include
+"@var{file}"}; they are not searched for @code{#include <@var{file}>},
+otherwise just like @option{-I}.
-Stop reverse growth when the reverse probability of best edge is less than this
-threshold (in percent).
+@item -L@var{dir}
+@opindex L
+Add directory @var{dir} to the list of directories to be searched
+for @option{-l}.
-@item tracer-min-branch-ratio
-@itemx tracer-min-branch-ratio-feedback
+@item -B@var{prefix}
+@opindex B
+This option specifies where to find the executables, libraries,
+include files, and data files of the compiler itself.
-Stop forward growth if the best edge has probability lower than this
-threshold.
+The compiler driver program runs one or more of the subprograms
+@command{cpp}, @command{cc1}, @command{as} and @command{ld}. It tries
+@var{prefix} as a prefix for each program it tries to run, both with and
+without @samp{@var{machine}/@var{version}/} for the corresponding target
+machine and compiler version.
-Similarly to @option{tracer-dynamic-coverage} two values are present, one for
-compilation for profile feedback and one for compilation without. The value
-for compilation with profile feedback needs to be more conservative (higher) in
-order to make tracer effective.
+For each subprogram to be run, the compiler driver first tries the
+@option{-B} prefix, if any. If that name is not found, or if @option{-B}
+is not specified, the driver tries two standard prefixes,
+@file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of
+those results in a file name that is found, the unmodified program
+name is searched for using the directories specified in your
+@env{PATH} environment variable.
-@item max-cse-path-length
+The compiler checks to see if the path provided by @option{-B}
+refers to a directory, and if necessary it adds a directory
+separator character at the end of the path.
-The maximum number of basic blocks on path that CSE considers.
-The default is 10.
+@option{-B} prefixes that effectively specify directory names also apply
+to libraries in the linker, because the compiler translates these
+options into @option{-L} options for the linker. They also apply to
+include files in the preprocessor, because the compiler translates these
+options into @option{-isystem} options for the preprocessor. In this case,
+the compiler appends @samp{include} to the prefix.
-@item max-cse-insns
-The maximum number of instructions CSE processes before flushing.
-The default is 1000.
+The runtime support file @file{libgcc.a} can also be searched for using
+the @option{-B} prefix, if needed. If it is not found there, the two
+standard prefixes above are tried, and that is all. The file is left
+out of the link if it is not found by those means.
-@item ggc-min-expand
+Another way to specify a prefix much like the @option{-B} prefix is to use
+the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
+Variables}.
-GCC uses a garbage collector to manage its own memory allocation. This
-parameter specifies the minimum percentage by which the garbage
-collector's heap should be allowed to expand between collections.
-Tuning this may improve compilation speed; it has no effect on code
-generation.
+As a special kludge, if the path provided by @option{-B} is
+@file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
+9, then it is replaced by @file{[dir/]include}. This is to help
+with boot-strapping the compiler.
-The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
-RAM >= 1GB@. If @code{getrlimit} is available, the notion of ``RAM'' is
-the smallest of actual RAM and @code{RLIMIT_DATA} or @code{RLIMIT_AS}. If
-GCC is not able to calculate RAM on a particular platform, the lower
-bound of 30% is used. Setting this parameter and
-@option{ggc-min-heapsize} to zero causes a full collection to occur at
-every opportunity. This is extremely slow, but can be useful for
-debugging.
+@item -no-canonical-prefixes
+@opindex no-canonical-prefixes
+Do not expand any symbolic links, resolve references to @samp{/../}
+or @samp{/./}, or make the path absolute when generating a relative
+prefix.
-@item ggc-min-heapsize
+@item --sysroot=@var{dir}
+@opindex sysroot
+Use @var{dir} as the logical root directory for headers and libraries.
+For example, if the compiler normally searches for headers in
+@file{/usr/include} and libraries in @file{/usr/lib}, it instead
+searches @file{@var{dir}/usr/include} and @file{@var{dir}/usr/lib}.
-Minimum size of the garbage collector's heap before it begins bothering
-to collect garbage. The first collection occurs after the heap expands
-by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again,
-tuning this may improve compilation speed, and has no effect on code
-generation.
+If you use both this option and the @option{-isysroot} option, then
+the @option{--sysroot} option applies to libraries, but the
+@option{-isysroot} option applies to header files.
-The default is the smaller of RAM/8, RLIMIT_RSS, or a limit that
-tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but
-with a lower bound of 4096 (four megabytes) and an upper bound of
-131072 (128 megabytes). If GCC is not able to calculate RAM on a
-particular platform, the lower bound is used. Setting this parameter
-very large effectively disables garbage collection. Setting this
-parameter and @option{ggc-min-expand} to zero causes a full collection
-to occur at every opportunity.
+The GNU linker (beginning with version 2.16) has the necessary support
+for this option. If your linker does not support this option, the
+header file aspect of @option{--sysroot} still works, but the
+library aspect does not.
-@item max-reload-search-insns
-The maximum number of instruction reload should look backward for equivalent
-register. Increasing values mean more aggressive optimization, making the
-compilation time increase with probably slightly better performance.
-The default value is 100.
+@item --no-sysroot-suffix
+@opindex no-sysroot-suffix
+For some targets, a suffix is added to the root directory specified
+with @option{--sysroot}, depending on the other options used, so that
+headers may for example be found in
+@file{@var{dir}/@var{suffix}/usr/include} instead of
+@file{@var{dir}/usr/include}. This option disables the addition of
+such a suffix.
-@item max-cselib-memory-locations
-The maximum number of memory locations cselib should take into account.
-Increasing values mean more aggressive optimization, making the compilation time
-increase with probably slightly better performance. The default value is 500.
+@item -I-
+@opindex I-
+This option has been deprecated. Please use @option{-iquote} instead for
+@option{-I} directories before the @option{-I-} and remove the @option{-I-}
+option.
+Any directories you specify with @option{-I} options before the @option{-I-}
+option are searched only for the case of @code{#include "@var{file}"};
+they are not searched for @code{#include <@var{file}>}.
-@item reorder-blocks-duplicate
-@itemx reorder-blocks-duplicate-feedback
+If additional directories are specified with @option{-I} options after
+the @option{-I-} option, these directories are searched for all @code{#include}
+directives. (Ordinarily @emph{all} @option{-I} directories are used
+this way.)
-Used by the basic block reordering pass to decide whether to use unconditional
-branch or duplicate the code on its destination. Code is duplicated when its
-estimated size is smaller than this value multiplied by the estimated size of
-unconditional jump in the hot spots of the program.
+In addition, the @option{-I-} option inhibits the use of the current
+directory (where the current input file came from) as the first search
+directory for @code{#include "@var{file}"}. There is no way to
+override this effect of @option{-I-}. With @option{-I.} you can specify
+searching the directory that is current when the compiler is
+invoked. That is not exactly the same as what the preprocessor does
+by default, but it is often satisfactory.
-The @option{reorder-block-duplicate-feedback} parameter
-is used only when profile
-feedback is available. It may be set to higher values than
-@option{reorder-block-duplicate} since information about the hot spots is more
-accurate.
+@option{-I-} does not inhibit the use of the standard system directories
+for header files. Thus, @option{-I-} and @option{-nostdinc} are
+independent.
+@end table
-@item max-sched-ready-insns
-The maximum number of instructions ready to be issued the scheduler should
-consider at any given time during the first scheduling pass. Increasing
-values mean more thorough searches, making the compilation time increase
-with probably little benefit. The default value is 100.
+@node Code Gen Options
+@section Options for Code Generation Conventions
+@cindex code generation conventions
+@cindex options, code generation
+@cindex run-time options
-@item max-sched-region-blocks
-The maximum number of blocks in a region to be considered for
-interblock scheduling. The default value is 10.
+These machine-independent options control the interface conventions
+used in code generation.
-@item max-pipeline-region-blocks
-The maximum number of blocks in a region to be considered for
-pipelining in the selective scheduler. The default value is 15.
+Most of them have both positive and negative forms; the negative form
+of @option{-ffoo} is @option{-fno-foo}. In the table below, only
+one of the forms is listed---the one that is not the default. You
+can figure out the other form by either removing @samp{no-} or adding
+it.
-@item max-sched-region-insns
-The maximum number of insns in a region to be considered for
-interblock scheduling. The default value is 100.
+@table @gcctabopt
+@item -fstack-reuse=@var{reuse-level}
+@opindex fstack_reuse
+This option controls stack space reuse for user declared local/auto variables
+and compiler generated temporaries. @var{reuse_level} can be @samp{all},
+@samp{named_vars}, or @samp{none}. @samp{all} enables stack reuse for all
+local variables and temporaries, @samp{named_vars} enables the reuse only for
+user defined local variables with names, and @samp{none} disables stack reuse
+completely. The default value is @samp{all}. The option is needed when the
+program extends the lifetime of a scoped local variable or a compiler generated
+temporary beyond the end point defined by the language. When a lifetime of
+a variable ends, and if the variable lives in memory, the optimizing compiler
+has the freedom to reuse its stack space with other temporaries or scoped
+local variables whose live range does not overlap with it. Legacy code extending
+local lifetime is likely to break with the stack reuse optimization.
-@item max-pipeline-region-insns
-The maximum number of insns in a region to be considered for
-pipelining in the selective scheduler. The default value is 200.
+For example,
-@item min-spec-prob
-The minimum probability (in percents) of reaching a source block
-for interblock speculative scheduling. The default value is 40.
+@smallexample
+ int *p;
+ @{
+ int local1;
-@item max-sched-extend-regions-iters
-The maximum number of iterations through CFG to extend regions.
-A value of 0 (the default) disables region extensions.
+ p = &local1;
+ local1 = 10;
+ ....
+ @}
+ @{
+ int local2;
+ local2 = 20;
+ ...
+ @}
-@item max-sched-insn-conflict-delay
-The maximum conflict delay for an insn to be considered for speculative motion.
-The default value is 3.
+ if (*p == 10) // out of scope use of local1
+ @{
-@item sched-spec-prob-cutoff
-The minimal probability of speculation success (in percents), so that
-speculative insns are scheduled.
-The default value is 40.
+ @}
+@end smallexample
-@item sched-spec-state-edge-prob-cutoff
-The minimum probability an edge must have for the scheduler to save its
-state across it.
-The default value is 10.
+Another example:
+@smallexample
-@item sched-mem-true-dep-cost
-Minimal distance (in CPU cycles) between store and load targeting same
-memory locations. The default value is 1.
+ struct A
+ @{
+ A(int k) : i(k), j(k) @{ @}
+ int i;
+ int j;
+ @};
-@item selsched-max-lookahead
-The maximum size of the lookahead window of selective scheduling. It is a
-depth of search for available instructions.
-The default value is 50.
+ A *ap;
-@item selsched-max-sched-times
-The maximum number of times that an instruction is scheduled during
-selective scheduling. This is the limit on the number of iterations
-through which the instruction may be pipelined. The default value is 2.
+ void foo(const A& ar)
+ @{
+ ap = &ar;
+ @}
-@item selsched-max-insns-to-rename
-The maximum number of best instructions in the ready list that are considered
-for renaming in the selective scheduler. The default value is 2.
+ void bar()
+ @{
+ foo(A(10)); // temp object's lifetime ends when foo returns
-@item sms-min-sc
-The minimum value of stage count that swing modulo scheduler
-generates. The default value is 2.
+ @{
+ A a(20);
+ ....
+ @}
+ ap->i+= 10; // ap references out of scope temp whose space
+ // is reused with a. What is the value of ap->i?
+ @}
-@item max-last-value-rtl
-The maximum size measured as number of RTLs that can be recorded in an expression
-in combiner for a pseudo register as last known value of that register. The default
-is 10000.
+@end smallexample
-@item max-combine-insns
-The maximum number of instructions the RTL combiner tries to combine.
-The default value is 2 at @option{-Og} and 4 otherwise.
+The lifetime of a compiler generated temporary is well defined by the C++
+standard. When a lifetime of a temporary ends, and if the temporary lives
+in memory, the optimizing compiler has the freedom to reuse its stack
+space with other temporaries or scoped local variables whose live range
+does not overlap with it. However some of the legacy code relies on
+the behavior of older compilers in which temporaries' stack space is
+not reused, the aggressive stack reuse can lead to runtime errors. This
+option is used to control the temporary stack reuse optimization.
-@item integer-share-limit
-Small integer constants can use a shared data structure, reducing the
-compiler's memory usage and increasing its speed. This sets the maximum
-value of a shared integer constant. The default value is 256.
+@item -ftrapv
+@opindex ftrapv
+This option generates traps for signed overflow on addition, subtraction,
+multiplication operations.
+The options @option{-ftrapv} and @option{-fwrapv} override each other, so using
+@option{-ftrapv} @option{-fwrapv} on the command-line results in
+@option{-fwrapv} being effective. Note that only active options override, so
+using @option{-ftrapv} @option{-fwrapv} @option{-fno-wrapv} on the command-line
+results in @option{-ftrapv} being effective.
-@item ssp-buffer-size
-The minimum size of buffers (i.e.@: arrays) that receive stack smashing
-protection when @option{-fstack-protection} is used.
+@item -fwrapv
+@opindex fwrapv
+This option instructs the compiler to assume that signed arithmetic
+overflow of addition, subtraction and multiplication wraps around
+using twos-complement representation. This flag enables some optimizations
+and disables others. This option is enabled by default for the Java
+front end, as required by the Java language specification.
+The options @option{-ftrapv} and @option{-fwrapv} override each other, so using
+@option{-ftrapv} @option{-fwrapv} on the command-line results in
+@option{-fwrapv} being effective. Note that only active options override, so
+using @option{-ftrapv} @option{-fwrapv} @option{-fno-wrapv} on the command-line
+results in @option{-ftrapv} being effective.
-@item min-size-for-stack-sharing
-The minimum size of variables taking part in stack slot sharing when not
-optimizing. The default value is 32.
+@item -fexceptions
+@opindex fexceptions
+Enable exception handling. Generates extra code needed to propagate
+exceptions. For some targets, this implies GCC generates frame
+unwind information for all functions, which can produce significant data
+size overhead, although it does not affect execution. If you do not
+specify this option, GCC enables it by default for languages like
+C++ that normally require exception handling, and disables it for
+languages like C that do not normally require it. However, you may need
+to enable this option when compiling C code that needs to interoperate
+properly with exception handlers written in C++. You may also wish to
+disable this option if you are compiling older C++ programs that don't
+use exception handling.
-@item max-jump-thread-duplication-stmts
-Maximum number of statements allowed in a block that needs to be
-duplicated when threading jumps.
+@item -fnon-call-exceptions
+@opindex fnon-call-exceptions
+Generate code that allows trapping instructions to throw exceptions.
+Note that this requires platform-specific runtime support that does
+not exist everywhere. Moreover, it only allows @emph{trapping}
+instructions to throw exceptions, i.e.@: memory references or floating-point
+instructions. It does not allow exceptions to be thrown from
+arbitrary signal handlers such as @code{SIGALRM}.
-@item max-fields-for-field-sensitive
-Maximum number of fields in a structure treated in
-a field sensitive manner during pointer analysis. The default is zero
-for @option{-O0} and @option{-O1},
-and 100 for @option{-Os}, @option{-O2}, and @option{-O3}.
+@item -fdelete-dead-exceptions
+@opindex fdelete-dead-exceptions
+Consider that instructions that may throw exceptions but don't otherwise
+contribute to the execution of the program can be optimized away.
+This option is enabled by default for the Ada front end, as permitted by
+the Ada language specification.
+Optimization passes that cause dead exceptions to be removed are enabled independently at different optimization levels.
-@item prefetch-latency
-Estimate on average number of instructions that are executed before
-prefetch finishes. The distance prefetched ahead is proportional
-to this constant. Increasing this number may also lead to less
-streams being prefetched (see @option{simultaneous-prefetches}).
+@item -funwind-tables
+@opindex funwind-tables
+Similar to @option{-fexceptions}, except that it just generates any needed
+static data, but does not affect the generated code in any other way.
+You normally do not need to enable this option; instead, a language processor
+that needs this handling enables it on your behalf.
-@item simultaneous-prefetches
-Maximum number of prefetches that can run at the same time.
+@item -fasynchronous-unwind-tables
+@opindex fasynchronous-unwind-tables
+Generate unwind table in DWARF format, if supported by target machine. The
+table is exact at each instruction boundary, so it can be used for stack
+unwinding from asynchronous events (such as debugger or garbage collector).
-@item l1-cache-line-size
-The size of cache line in L1 cache, in bytes.
+@item -fno-gnu-unique
+@opindex fno-gnu-unique
+On systems with recent GNU assembler and C library, the C++ compiler
+uses the @code{STB_GNU_UNIQUE} binding to make sure that definitions
+of template static data members and static local variables in inline
+functions are unique even in the presence of @code{RTLD_LOCAL}; this
+is necessary to avoid problems with a library used by two different
+@code{RTLD_LOCAL} plugins depending on a definition in one of them and
+therefore disagreeing with the other one about the binding of the
+symbol. But this causes @code{dlclose} to be ignored for affected
+DSOs; if your program relies on reinitialization of a DSO via
+@code{dlclose} and @code{dlopen}, you can use
+@option{-fno-gnu-unique}.
-@item l1-cache-size
-The size of L1 cache, in kilobytes.
+@item -fpcc-struct-return
+@opindex fpcc-struct-return
+Return ``short'' @code{struct} and @code{union} values in memory like
+longer ones, rather than in registers. This convention is less
+efficient, but it has the advantage of allowing intercallability between
+GCC-compiled files and files compiled with other compilers, particularly
+the Portable C Compiler (pcc).
-@item l2-cache-size
-The size of L2 cache, in kilobytes.
+The precise convention for returning structures in memory depends
+on the target configuration macros.
-@item min-insn-to-prefetch-ratio
-The minimum ratio between the number of instructions and the
-number of prefetches to enable prefetching in a loop.
+Short structures and unions are those whose size and alignment match
+that of some integer type.
-@item prefetch-min-insn-to-mem-ratio
-The minimum ratio between the number of instructions and the
-number of memory references to enable prefetching in a loop.
+@strong{Warning:} code compiled with the @option{-fpcc-struct-return}
+switch is not binary compatible with code compiled with the
+@option{-freg-struct-return} switch.
+Use it to conform to a non-default application binary interface.
-@item use-canonical-types
-Whether the compiler should use the ``canonical'' type system. By
-default, this should always be 1, which uses a more efficient internal
-mechanism for comparing types in C++ and Objective-C++. However, if
-bugs in the canonical type system are causing compilation failures,
-set this value to 0 to disable canonical types.
+@item -freg-struct-return
+@opindex freg-struct-return
+Return @code{struct} and @code{union} values in registers when possible.
+This is more efficient for small structures than
+@option{-fpcc-struct-return}.
-@item switch-conversion-max-branch-ratio
-Switch initialization conversion refuses to create arrays that are
-bigger than @option{switch-conversion-max-branch-ratio} times the number of
-branches in the switch.
+If you specify neither @option{-fpcc-struct-return} nor
+@option{-freg-struct-return}, GCC defaults to whichever convention is
+standard for the target. If there is no standard convention, GCC
+defaults to @option{-fpcc-struct-return}, except on targets where GCC is
+the principal compiler. In those cases, we can choose the standard, and
+we chose the more efficient register return alternative.
-@item max-partial-antic-length
-Maximum length of the partial antic set computed during the tree
-partial redundancy elimination optimization (@option{-ftree-pre}) when
-optimizing at @option{-O3} and above. For some sorts of source code
-the enhanced partial redundancy elimination optimization can run away,
-consuming all of the memory available on the host machine. This
-parameter sets a limit on the length of the sets that are computed,
-which prevents the runaway behavior. Setting a value of 0 for
-this parameter allows an unlimited set length.
+@strong{Warning:} code compiled with the @option{-freg-struct-return}
+switch is not binary compatible with code compiled with the
+@option{-fpcc-struct-return} switch.
+Use it to conform to a non-default application binary interface.
-@item sccvn-max-scc-size
-Maximum size of a strongly connected component (SCC) during SCCVN
-processing. If this limit is hit, SCCVN processing for the whole
-function is not done and optimizations depending on it are
-disabled. The default maximum SCC size is 10000.
+@item -fshort-enums
+@opindex fshort-enums
+Allocate to an @code{enum} type only as many bytes as it needs for the
+declared range of possible values. Specifically, the @code{enum} type
+is equivalent to the smallest integer type that has enough room.
-@item sccvn-max-alias-queries-per-access
-Maximum number of alias-oracle queries we perform when looking for
-redundancies for loads and stores. If this limit is hit the search
-is aborted and the load or store is not considered redundant. The
-number of queries is algorithmically limited to the number of
-stores on all paths from the load to the function entry.
-The default maxmimum number of queries is 1000.
+@strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
+code that is not binary compatible with code generated without that switch.
+Use it to conform to a non-default application binary interface.
-@item ira-max-loops-num
-IRA uses regional register allocation by default. If a function
-contains more loops than the number given by this parameter, only at most
-the given number of the most frequently-executed loops form regions
-for regional register allocation. The default value of the
-parameter is 100.
+@item -fshort-wchar
+@opindex fshort-wchar
+Override the underlying type for @code{wchar_t} to be @code{short
+unsigned int} instead of the default for the target. This option is
+useful for building programs to run under WINE@.
-@item ira-max-conflict-table-size
-Although IRA uses a sophisticated algorithm to compress the conflict
-table, the table can still require excessive amounts of memory for
-huge functions. If the conflict table for a function could be more
-than the size in MB given by this parameter, the register allocator
-instead uses a faster, simpler, and lower-quality
-algorithm that does not require building a pseudo-register conflict table.
-The default value of the parameter is 2000.
+@strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
+code that is not binary compatible with code generated without that switch.
+Use it to conform to a non-default application binary interface.
+
+@item -fno-common
+@opindex fno-common
+In C code, controls the placement of uninitialized global variables.
+Unix C compilers have traditionally permitted multiple definitions of
+such variables in different compilation units by placing the variables
+in a common block.
+This is the behavior specified by @option{-fcommon}, and is the default
+for GCC on most targets.
+On the other hand, this behavior is not required by ISO C, and on some
+targets may carry a speed or code size penalty on variable references.
+The @option{-fno-common} option specifies that the compiler should place
+uninitialized global variables in the data section of the object file,
+rather than generating them as common blocks.
+This has the effect that if the same variable is declared
+(without @code{extern}) in two different compilations,
+you get a multiple-definition error when you link them.
+In this case, you must compile with @option{-fcommon} instead.
+Compiling with @option{-fno-common} is useful on targets for which
+it provides better performance, or if you wish to verify that the
+program will work on other systems that always treat uninitialized
+variable declarations this way.
-@item ira-loop-reserved-regs
-IRA can be used to evaluate more accurate register pressure in loops
-for decisions to move loop invariants (see @option{-O3}). The number
-of available registers reserved for some other purposes is given
-by this parameter. The default value of the parameter is 2, which is
-the minimal number of registers needed by typical instructions.
-This value is the best found from numerous experiments.
+@item -fno-ident
+@opindex fno-ident
+Ignore the @code{#ident} directive.
-@item lra-inheritance-ebb-probability-cutoff
-LRA tries to reuse values reloaded in registers in subsequent insns.
-This optimization is called inheritance. EBB is used as a region to
-do this optimization. The parameter defines a minimal fall-through
-edge probability in percentage used to add BB to inheritance EBB in
-LRA. The default value of the parameter is 40. The value was chosen
-from numerous runs of SPEC2000 on x86-64.
+@item -finhibit-size-directive
+@opindex finhibit-size-directive
+Don't output a @code{.size} assembler directive, or anything else that
+would cause trouble if the function is split in the middle, and the
+two halves are placed at locations far apart in memory. This option is
+used when compiling @file{crtstuff.c}; you should not need to use it
+for anything else.
-@item loop-invariant-max-bbs-in-loop
-Loop invariant motion can be very expensive, both in compilation time and
-in amount of needed compile-time memory, with very large loops. Loops
-with more basic blocks than this parameter won't have loop invariant
-motion optimization performed on them. The default value of the
-parameter is 1000 for @option{-O1} and 10000 for @option{-O2} and above.
+@item -fverbose-asm
+@opindex fverbose-asm
+Put extra commentary information in the generated assembly code to
+make it more readable. This option is generally only of use to those
+who actually need to read the generated assembly code (perhaps while
+debugging the compiler itself).
-@item loop-max-datarefs-for-datadeps
-Building data dapendencies is expensive for very large loops. This
-parameter limits the number of data references in loops that are
-considered for data dependence analysis. These large loops are no
-handled by the optimizations using loop data dependencies.
-The default value is 1000.
+@option{-fno-verbose-asm}, the default, causes the
+extra information to be omitted and is useful when comparing two assembler
+files.
-@item max-vartrack-size
-Sets a maximum number of hash table slots to use during variable
-tracking dataflow analysis of any function. If this limit is exceeded
-with variable tracking at assignments enabled, analysis for that
-function is retried without it, after removing all debug insns from
-the function. If the limit is exceeded even without debug insns, var
-tracking analysis is completely disabled for the function. Setting
-the parameter to zero makes it unlimited.
+@item -frecord-gcc-switches
+@opindex frecord-gcc-switches
+This switch causes the command line used to invoke the
+compiler to be recorded into the object file that is being created.
+This switch is only implemented on some targets and the exact format
+of the recording is target and binary file format dependent, but it
+usually takes the form of a section containing ASCII text. This
+switch is related to the @option{-fverbose-asm} switch, but that
+switch only records information in the assembler output file as
+comments, so it never reaches the object file.
+See also @option{-grecord-gcc-switches} for another
+way of storing compiler options into the object file.
-@item max-vartrack-expr-depth
-Sets a maximum number of recursion levels when attempting to map
-variable names or debug temporaries to value expressions. This trades
-compilation time for more complete debug information. If this is set too
-low, value expressions that are available and could be represented in
-debug information may end up not being used; setting this higher may
-enable the compiler to find more complex debug expressions, but compile
-time and memory use may grow. The default is 12.
+@item -fpic
+@opindex fpic
+@cindex global offset table
+@cindex PIC
+Generate position-independent code (PIC) suitable for use in a shared
+library, if supported for the target machine. Such code accesses all
+constant addresses through a global offset table (GOT)@. The dynamic
+loader resolves the GOT entries when the program starts (the dynamic
+loader is not part of GCC; it is part of the operating system). If
+the GOT size for the linked executable exceeds a machine-specific
+maximum size, you get an error message from the linker indicating that
+@option{-fpic} does not work; in that case, recompile with @option{-fPIC}
+instead. (These maximums are 8k on the SPARC, 28k on AArch64 and 32k
+on the m68k and RS/6000. The x86 has no such limit.)
-@item min-nondebug-insn-uid
-Use uids starting at this parameter for nondebug insns. The range below
-the parameter is reserved exclusively for debug insns created by
-@option{-fvar-tracking-assignments}, but debug insns may get
-(non-overlapping) uids above it if the reserved range is exhausted.
+Position-independent code requires special support, and therefore works
+only on certain machines. For the x86, GCC supports PIC for System V
+but not for the Sun 386i. Code generated for the IBM RS/6000 is always
+position-independent.
-@item ipa-sra-ptr-growth-factor
-IPA-SRA replaces a pointer to an aggregate with one or more new
-parameters only when their cumulative size is less or equal to
-@option{ipa-sra-ptr-growth-factor} times the size of the original
-pointer parameter.
+When this flag is set, the macros @code{__pic__} and @code{__PIC__}
+are defined to 1.
-@item sra-max-scalarization-size-Ospeed
-@item sra-max-scalarization-size-Osize
-The two Scalar Reduction of Aggregates passes (SRA and IPA-SRA) aim to
-replace scalar parts of aggregates with uses of independent scalar
-variables. These parameters control the maximum size, in storage units,
-of aggregate which is considered for replacement when compiling for
-speed
-(@option{sra-max-scalarization-size-Ospeed}) or size
-(@option{sra-max-scalarization-size-Osize}) respectively.
+@item -fPIC
+@opindex fPIC
+If supported for the target machine, emit position-independent code,
+suitable for dynamic linking and avoiding any limit on the size of the
+global offset table. This option makes a difference on AArch64, m68k,
+PowerPC and SPARC@.
-@item tm-max-aggregate-size
-When making copies of thread-local variables in a transaction, this
-parameter specifies the size in bytes after which variables are
-saved with the logging functions as opposed to save/restore code
-sequence pairs. This option only applies when using
-@option{-fgnu-tm}.
+Position-independent code requires special support, and therefore works
+only on certain machines.
-@item graphite-max-nb-scop-params
-To avoid exponential effects in the Graphite loop transforms, the
-number of parameters in a Static Control Part (SCoP) is bounded. The
-default value is 10 parameters. A variable whose value is unknown at
-compilation time and defined outside a SCoP is a parameter of the SCoP.
+When this flag is set, the macros @code{__pic__} and @code{__PIC__}
+are defined to 2.
-@item graphite-max-bbs-per-function
-To avoid exponential effects in the detection of SCoPs, the size of
-the functions analyzed by Graphite is bounded. The default value is
-100 basic blocks.
+@item -fpie
+@itemx -fPIE
+@opindex fpie
+@opindex fPIE
+These options are similar to @option{-fpic} and @option{-fPIC}, but
+generated position independent code can be only linked into executables.
+Usually these options are used when @option{-pie} GCC option is
+used during linking.
-@item loop-block-tile-size
-Loop blocking or strip mining transforms, enabled with
-@option{-floop-block} or @option{-floop-strip-mine}, strip mine each
-loop in the loop nest by a given number of iterations. The strip
-length can be changed using the @option{loop-block-tile-size}
-parameter. The default value is 51 iterations.
+@option{-fpie} and @option{-fPIE} both define the macros
+@code{__pie__} and @code{__PIE__}. The macros have the value 1
+for @option{-fpie} and 2 for @option{-fPIE}.
-@item loop-unroll-jam-size
-Specify the unroll factor for the @option{-floop-unroll-and-jam} option. The
-default value is 4.
+@item -fno-plt
+@opindex fno-plt
+Do not use the PLT for external function calls in position-independent code.
+Instead, load the callee address at call sites from the GOT and branch to it.
+This leads to more efficient code by eliminating PLT stubs and exposing
+GOT loads to optimizations. On architectures such as 32-bit x86 where
+PLT stubs expect the GOT pointer in a specific register, this gives more
+register allocation freedom to the compiler.
+Lazy binding requires use of the PLT;
+with @option{-fno-plt} all external symbols are resolved at load time.
-@item loop-unroll-jam-depth
-Specify the dimension to be unrolled (counting from the most inner loop)
-for the @option{-floop-unroll-and-jam}. The default value is 2.
+Alternatively, the function attribute @code{noplt} can be used to avoid calls
+through the PLT for specific external functions.
-@item ipa-cp-value-list-size
-IPA-CP attempts to track all possible values and types passed to a function's
-parameter in order to propagate them and perform devirtualization.
-@option{ipa-cp-value-list-size} is the maximum number of values and types it
-stores per one formal parameter of a function.
+In position-dependent code, a few targets also convert calls to
+functions that are marked to not use the PLT to use the GOT instead.
-@item ipa-cp-eval-threshold
-IPA-CP calculates its own score of cloning profitability heuristics
-and performs those cloning opportunities with scores that exceed
-@option{ipa-cp-eval-threshold}.
+@item -fno-jump-tables
+@opindex fno-jump-tables
+Do not use jump tables for switch statements even where it would be
+more efficient than other code generation strategies. This option is
+of use in conjunction with @option{-fpic} or @option{-fPIC} for
+building code that forms part of a dynamic linker and cannot
+reference the address of a jump table. On some targets, jump tables
+do not require a GOT and this option is not needed.
-@item ipa-cp-recursion-penalty
-Percentage penalty the recursive functions will receive when they
-are evaluated for cloning.
+@item -ffixed-@var{reg}
+@opindex ffixed
+Treat the register named @var{reg} as a fixed register; generated code
+should never refer to it (except perhaps as a stack pointer, frame
+pointer or in some other fixed role).
-@item ipa-cp-single-call-penalty
-Percentage penalty functions containg a single call to another
-function will receive when they are evaluated for cloning.
+@var{reg} must be the name of a register. The register names accepted
+are machine-specific and are defined in the @code{REGISTER_NAMES}
+macro in the machine description macro file.
+This flag does not have a negative form, because it specifies a
+three-way choice.
-@item ipa-max-agg-items
-IPA-CP is also capable to propagate a number of scalar values passed
-in an aggregate. @option{ipa-max-agg-items} controls the maximum
-number of such values per one parameter.
+@item -fcall-used-@var{reg}
+@opindex fcall-used
+Treat the register named @var{reg} as an allocable register that is
+clobbered by function calls. It may be allocated for temporaries or
+variables that do not live across a call. Functions compiled this way
+do not save and restore the register @var{reg}.
-@item ipa-cp-loop-hint-bonus
-When IPA-CP determines that a cloning candidate would make the number
-of iterations of a loop known, it adds a bonus of
-@option{ipa-cp-loop-hint-bonus} to the profitability score of
-the candidate.
+It is an error to use this flag with the frame pointer or stack pointer.
+Use of this flag for other registers that have fixed pervasive roles in
+the machine's execution model produces disastrous results.
-@item ipa-cp-array-index-hint-bonus
-When IPA-CP determines that a cloning candidate would make the index of
-an array access known, it adds a bonus of
-@option{ipa-cp-array-index-hint-bonus} to the profitability
-score of the candidate.
+This flag does not have a negative form, because it specifies a
+three-way choice.
-@item ipa-max-aa-steps
-During its analysis of function bodies, IPA-CP employs alias analysis
-in order to track values pointed to by function parameters. In order
-not spend too much time analyzing huge functions, it gives up and
-consider all memory clobbered after examining
-@option{ipa-max-aa-steps} statements modifying memory.
+@item -fcall-saved-@var{reg}
+@opindex fcall-saved
+Treat the register named @var{reg} as an allocable register saved by
+functions. It may be allocated even for temporaries or variables that
+live across a call. Functions compiled this way save and restore
+the register @var{reg} if they use it.
-@item lto-partitions
-Specify desired number of partitions produced during WHOPR compilation.
-The number of partitions should exceed the number of CPUs used for compilation.
-The default value is 32.
+It is an error to use this flag with the frame pointer or stack pointer.
+Use of this flag for other registers that have fixed pervasive roles in
+the machine's execution model produces disastrous results.
-@item lto-minpartition
-Size of minimal partition for WHOPR (in estimated instructions).
-This prevents expenses of splitting very small programs into too many
-partitions.
+A different sort of disaster results from the use of this flag for
+a register in which function values may be returned.
-@item cxx-max-namespaces-for-diagnostic-help
-The maximum number of namespaces to consult for suggestions when C++
-name lookup fails for an identifier. The default is 1000.
+This flag does not have a negative form, because it specifies a
+three-way choice.
-@item sink-frequency-threshold
-The maximum relative execution frequency (in percents) of the target block
-relative to a statement's original block to allow statement sinking of a
-statement. Larger numbers result in more aggressive statement sinking.
-The default value is 75. A small positive adjustment is applied for
-statements with memory operands as those are even more profitable so sink.
+@item -fpack-struct[=@var{n}]
+@opindex fpack-struct
+Without a value specified, pack all structure members together without
+holes. When a value is specified (which must be a small power of two), pack
+structure members according to this value, representing the maximum
+alignment (that is, objects with default alignment requirements larger than
+this are output potentially unaligned at the next fitting location.
-@item max-stores-to-sink
-The maximum number of conditional stores paires that can be sunk. Set to 0
-if either vectorization (@option{-ftree-vectorize}) or if-conversion
-(@option{-ftree-loop-if-convert}) is disabled. The default is 2.
+@strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
+code that is not binary compatible with code generated without that switch.
+Additionally, it makes the code suboptimal.
+Use it to conform to a non-default application binary interface.
-@item allow-store-data-races
-Allow optimizers to introduce new data races on stores.
-Set to 1 to allow, otherwise to 0. This option is enabled by default
-at optimization level @option{-Ofast}.
+@item -fleading-underscore
+@opindex fleading-underscore
+This option and its counterpart, @option{-fno-leading-underscore}, forcibly
+change the way C symbols are represented in the object file. One use
+is to help link with legacy assembly code.
-@item case-values-threshold
-The smallest number of different values for which it is best to use a
-jump-table instead of a tree of conditional branches. If the value is
-0, use the default for the machine. The default is 0.
+@strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
+generate code that is not binary compatible with code generated without that
+switch. Use it to conform to a non-default application binary interface.
+Not all targets provide complete support for this switch.
-@item tree-reassoc-width
-Set the maximum number of instructions executed in parallel in
-reassociated tree. This parameter overrides target dependent
-heuristics used by default if has non zero value.
+@item -ftls-model=@var{model}
+@opindex ftls-model
+Alter the thread-local storage model to be used (@pxref{Thread-Local}).
+The @var{model} argument should be one of @samp{global-dynamic},
+@samp{local-dynamic}, @samp{initial-exec} or @samp{local-exec}.
+Note that the choice is subject to optimization: the compiler may use
+a more efficient model for symbols not visible outside of the translation
+unit, or if @option{-fpic} is not given on the command line.
-@item sched-pressure-algorithm
-Choose between the two available implementations of
-@option{-fsched-pressure}. Algorithm 1 is the original implementation
-and is the more likely to prevent instructions from being reordered.
-Algorithm 2 was designed to be a compromise between the relatively
-conservative approach taken by algorithm 1 and the rather aggressive
-approach taken by the default scheduler. It relies more heavily on
-having a regular register file and accurate register pressure classes.
-See @file{haifa-sched.c} in the GCC sources for more details.
+The default without @option{-fpic} is @samp{initial-exec}; with
+@option{-fpic} the default is @samp{global-dynamic}.
-The default choice depends on the target.
+@item -fvisibility=@r{[}default@r{|}internal@r{|}hidden@r{|}protected@r{]}
+@opindex fvisibility
+Set the default ELF image symbol visibility to the specified option---all
+symbols are marked with this unless overridden within the code.
+Using this feature can very substantially improve linking and
+load times of shared object libraries, produce more optimized
+code, provide near-perfect API export and prevent symbol clashes.
+It is @strong{strongly} recommended that you use this in any shared objects
+you distribute.
-@item max-slsr-cand-scan
-Set the maximum number of existing candidates that are considered when
-seeking a basis for a new straight-line strength reduction candidate.
+Despite the nomenclature, @samp{default} always means public; i.e.,
+available to be linked against from outside the shared object.
+@samp{protected} and @samp{internal} are pretty useless in real-world
+usage so the only other commonly used option is @samp{hidden}.
+The default if @option{-fvisibility} isn't specified is
+@samp{default}, i.e., make every symbol public.
-@item asan-globals
-Enable buffer overflow detection for global objects. This kind
-of protection is enabled by default if you are using
-@option{-fsanitize=address} option.
-To disable global objects protection use @option{--param asan-globals=0}.
+A good explanation of the benefits offered by ensuring ELF
+symbols have the correct visibility is given by ``How To Write
+Shared Libraries'' by Ulrich Drepper (which can be found at
+@w{@uref{http://www.akkadia.org/drepper/}})---however a superior
+solution made possible by this option to marking things hidden when
+the default is public is to make the default hidden and mark things
+public. This is the norm with DLLs on Windows and with @option{-fvisibility=hidden}
+and @code{__attribute__ ((visibility("default")))} instead of
+@code{__declspec(dllexport)} you get almost identical semantics with
+identical syntax. This is a great boon to those working with
+cross-platform projects.
-@item asan-stack
-Enable buffer overflow detection for stack objects. This kind of
-protection is enabled by default when using @option{-fsanitize=address}.
-To disable stack protection use @option{--param asan-stack=0} option.
+For those adding visibility support to existing code, you may find
+@code{#pragma GCC visibility} of use. This works by you enclosing
+the declarations you wish to set visibility for with (for example)
+@code{#pragma GCC visibility push(hidden)} and
+@code{#pragma GCC visibility pop}.
+Bear in mind that symbol visibility should be viewed @strong{as
+part of the API interface contract} and thus all new code should
+always specify visibility when it is not the default; i.e., declarations
+only for use within the local DSO should @strong{always} be marked explicitly
+as hidden as so to avoid PLT indirection overheads---making this
+abundantly clear also aids readability and self-documentation of the code.
+Note that due to ISO C++ specification requirements, @code{operator new} and
+@code{operator delete} must always be of default visibility.
-@item asan-instrument-reads
-Enable buffer overflow detection for memory reads. This kind of
-protection is enabled by default when using @option{-fsanitize=address}.
-To disable memory reads protection use
-@option{--param asan-instrument-reads=0}.
+Be aware that headers from outside your project, in particular system
+headers and headers from any other library you use, may not be
+expecting to be compiled with visibility other than the default. You
+may need to explicitly say @code{#pragma GCC visibility push(default)}
+before including any such headers.
-@item asan-instrument-writes
-Enable buffer overflow detection for memory writes. This kind of
-protection is enabled by default when using @option{-fsanitize=address}.
-To disable memory writes protection use
-@option{--param asan-instrument-writes=0} option.
+@code{extern} declarations are not affected by @option{-fvisibility}, so
+a lot of code can be recompiled with @option{-fvisibility=hidden} with
+no modifications. However, this means that calls to @code{extern}
+functions with no explicit visibility use the PLT, so it is more
+effective to use @code{__attribute ((visibility))} and/or
+@code{#pragma GCC visibility} to tell the compiler which @code{extern}
+declarations should be treated as hidden.
-@item asan-memintrin
-Enable detection for built-in functions. This kind of protection
-is enabled by default when using @option{-fsanitize=address}.
-To disable built-in functions protection use
-@option{--param asan-memintrin=0}.
+Note that @option{-fvisibility} does affect C++ vague linkage
+entities. This means that, for instance, an exception class that is
+be thrown between DSOs must be explicitly marked with default
+visibility so that the @samp{type_info} nodes are unified between
+the DSOs.
-@item asan-use-after-return
-Enable detection of use-after-return. This kind of protection
-is enabled by default when using @option{-fsanitize=address} option.
-To disable use-after-return detection use
-@option{--param asan-use-after-return=0}.
+An overview of these techniques, their benefits and how to use them
+is at @uref{http://gcc.gnu.org/@/wiki/@/Visibility}.
-@item asan-instrumentation-with-call-threshold
-If number of memory accesses in function being instrumented
-is greater or equal to this number, use callbacks instead of inline checks.
-E.g. to disable inline code use
-@option{--param asan-instrumentation-with-call-threshold=0}.
+@item -fstrict-volatile-bitfields
+@opindex fstrict-volatile-bitfields
+This option should be used if accesses to volatile bit-fields (or other
+structure fields, although the compiler usually honors those types
+anyway) should use a single access of the width of the
+field's type, aligned to a natural alignment if possible. For
+example, targets with memory-mapped peripheral registers might require
+all such accesses to be 16 bits wide; with this flag you can
+declare all peripheral bit-fields as @code{unsigned short} (assuming short
+is 16 bits on these targets) to force GCC to use 16-bit accesses
+instead of, perhaps, a more efficient 32-bit access.
-@item chkp-max-ctor-size
-Static constructors generated by Pointer Bounds Checker may become very
-large and significantly increase compile time at optimization level
-@option{-O1} and higher. This parameter is a maximum nubmer of statements
-in a single generated constructor. Default value is 5000.
+If this option is disabled, the compiler uses the most efficient
+instruction. In the previous example, that might be a 32-bit load
+instruction, even though that accesses bytes that do not contain
+any portion of the bit-field, or memory-mapped registers unrelated to
+the one being updated.
-@item max-fsm-thread-path-insns
-Maximum number of instructions to copy when duplicating blocks on a
-finite state automaton jump thread path. The default is 100.
+In some cases, such as when the @code{packed} attribute is applied to a
+structure field, it may not be possible to access the field with a single
+read or write that is correctly aligned for the target machine. In this
+case GCC falls back to generating multiple accesses rather than code that
+will fault or truncate the result at run time.
-@item max-fsm-thread-length
-Maximum number of basic blocks on a finite state automaton jump thread
-path. The default is 10.
+Note: Due to restrictions of the C/C++11 memory model, write accesses are
+not allowed to touch non bit-field members. It is therefore recommended
+to define all bits of the field's type as bit-field members.
-@item max-fsm-thread-paths
-Maximum number of new jump thread paths to create for a finite state
-automaton. The default is 50.
+The default value of this option is determined by the application binary
+interface for the target processor.
-@item parloops-chunk-size
-Chunk size of omp schedule for loops parallelized by parloops. The default
-is 0.
+@item -fsync-libcalls
+@opindex fsync-libcalls
+This option controls whether any out-of-line instance of the @code{__sync}
+family of functions may be used to implement the C++11 @code{__atomic}
+family of functions.
-@item parloops-schedule
-Schedule type of omp schedule for loops parallelized by parloops (static,
-dynamic, guided, auto, runtime). The default is static.
+The default value of this option is enabled, thus the only useful form
+of the option is @option{-fno-sync-libcalls}. This option is used in
+the implementation of the @file{libatomic} runtime library.
-@item max-ssa-name-query-depth
-Maximum depth of recursion when querying properties of SSA names in things
-like fold routines. One level of recursion corresponds to following a
-use-def chain.
-@end table
@end table
-@node Preprocessor Options
-@section Options Controlling the Preprocessor
-@cindex preprocessor options
-@cindex options, preprocessor
+@node Developer Options
+@section GCC Developer Options
+@cindex developer options
+@cindex debugging GCC
+@cindex debug dump options
+@cindex dump options
+@cindex compilation statistics
+
+This section describes command-line options that are primarily of
+interest to GCC developers, including options to support compiler
+testing and investigation of compiler bugs and compile-time
+performance problems. This includes options that produce debug dumps
+at various points in the compilation; that print statistics such as
+memory use and execution time; and that print information about GCC's
+configuration, such as where it searches for libraries. You should
+rarely need to use any of these options for ordinary compilation and
+linking tasks.
-These options control the C preprocessor, which is run on each C source
-file before actual compilation.
+@table @gcctabopt
-If you use the @option{-E} option, nothing is done except preprocessing.
-Some of these options make sense only together with @option{-E} because
-they cause the preprocessor output to be unsuitable for actual
-compilation.
+@item -d@var{letters}
+@itemx -fdump-rtl-@var{pass}
+@itemx -fdump-rtl-@var{pass}=@var{filename}
+@opindex d
+@opindex fdump-rtl-@var{pass}
+Says to make debugging dumps during compilation at times specified by
+@var{letters}. This is used for debugging the RTL-based passes of the
+compiler. The file names for most of the dumps are made by appending
+a pass number and a word to the @var{dumpname}, and the files are
+created in the directory of the output file. In case of
+@option{=@var{filename}} option, the dump is output on the given file
+instead of the pass numbered dump files. Note that the pass number is
+assigned as passes are registered into the pass manager. Most passes
+are registered in the order that they will execute and for these passes
+the number corresponds to the pass execution order. However, passes
+registered by plugins, passes specific to compilation targets, or
+passes that are otherwise registered after all the other passes are
+numbered higher than a pass named "final", even if they are executed
+earlier. @var{dumpname} is generated from the name of the output
+file if explicitly specified and not an executable, otherwise it is
+the basename of the source file. These switches may have different
+effects when @option{-E} is used for preprocessing.
+
+Debug dumps can be enabled with a @option{-fdump-rtl} switch or some
+@option{-d} option @var{letters}. Here are the possible
+letters for use in @var{pass} and @var{letters}, and their meanings:
@table @gcctabopt
-@item -Wp,@var{option}
-@opindex Wp
-You can use @option{-Wp,@var{option}} to bypass the compiler driver
-and pass @var{option} directly through to the preprocessor. If
-@var{option} contains commas, it is split into multiple options at the
-commas. However, many options are modified, translated or interpreted
-by the compiler driver before being passed to the preprocessor, and
-@option{-Wp} forcibly bypasses this phase. The preprocessor's direct
-interface is undocumented and subject to change, so whenever possible
-you should avoid using @option{-Wp} and let the driver handle the
-options instead.
-@item -Xpreprocessor @var{option}
-@opindex Xpreprocessor
-Pass @var{option} as an option to the preprocessor. You can use this to
-supply system-specific preprocessor options that GCC does not
-recognize.
+@item -fdump-rtl-alignments
+@opindex fdump-rtl-alignments
+Dump after branch alignments have been computed.
+
+@item -fdump-rtl-asmcons
+@opindex fdump-rtl-asmcons
+Dump after fixing rtl statements that have unsatisfied in/out constraints.
-If you want to pass an option that takes an argument, you must use
-@option{-Xpreprocessor} twice, once for the option and once for the argument.
+@item -fdump-rtl-auto_inc_dec
+@opindex fdump-rtl-auto_inc_dec
+Dump after auto-inc-dec discovery. This pass is only run on
+architectures that have auto inc or auto dec instructions.
-@item -no-integrated-cpp
-@opindex no-integrated-cpp
-Perform preprocessing as a separate pass before compilation.
-By default, GCC performs preprocessing as an integrated part of
-input tokenization and parsing.
-If this option is provided, the appropriate language front end
-(@command{cc1}, @command{cc1plus}, or @command{cc1obj} for C, C++,
-and Objective-C, respectively) is instead invoked twice,
-once for preprocessing only and once for actual compilation
-of the preprocessed input.
-This option may be useful in conjunction with the @option{-B} or
-@option{-wrapper} options to specify an alternate preprocessor or
-perform additional processing of the program source between
-normal preprocessing and compilation.
-@end table
+@item -fdump-rtl-barriers
+@opindex fdump-rtl-barriers
+Dump after cleaning up the barrier instructions.
-@include cppopts.texi
+@item -fdump-rtl-bbpart
+@opindex fdump-rtl-bbpart
+Dump after partitioning hot and cold basic blocks.
-@node Assembler Options
-@section Passing Options to the Assembler
+@item -fdump-rtl-bbro
+@opindex fdump-rtl-bbro
+Dump after block reordering.
-@c prevent bad page break with this line
-You can pass options to the assembler.
+@item -fdump-rtl-btl1
+@itemx -fdump-rtl-btl2
+@opindex fdump-rtl-btl2
+@opindex fdump-rtl-btl2
+@option{-fdump-rtl-btl1} and @option{-fdump-rtl-btl2} enable dumping
+after the two branch
+target load optimization passes.
-@table @gcctabopt
-@item -Wa,@var{option}
-@opindex Wa
-Pass @var{option} as an option to the assembler. If @var{option}
-contains commas, it is split into multiple options at the commas.
+@item -fdump-rtl-bypass
+@opindex fdump-rtl-bypass
+Dump after jump bypassing and control flow optimizations.
-@item -Xassembler @var{option}
-@opindex Xassembler
-Pass @var{option} as an option to the assembler. You can use this to
-supply system-specific assembler options that GCC does not
-recognize.
+@item -fdump-rtl-combine
+@opindex fdump-rtl-combine
+Dump after the RTL instruction combination pass.
-If you want to pass an option that takes an argument, you must use
-@option{-Xassembler} twice, once for the option and once for the argument.
+@item -fdump-rtl-compgotos
+@opindex fdump-rtl-compgotos
+Dump after duplicating the computed gotos.
-@end table
+@item -fdump-rtl-ce1
+@itemx -fdump-rtl-ce2
+@itemx -fdump-rtl-ce3
+@opindex fdump-rtl-ce1
+@opindex fdump-rtl-ce2
+@opindex fdump-rtl-ce3
+@option{-fdump-rtl-ce1}, @option{-fdump-rtl-ce2}, and
+@option{-fdump-rtl-ce3} enable dumping after the three
+if conversion passes.
-@node Link Options
-@section Options for Linking
-@cindex link options
-@cindex options, linking
+@item -fdump-rtl-cprop_hardreg
+@opindex fdump-rtl-cprop_hardreg
+Dump after hard register copy propagation.
-These options come into play when the compiler links object files into
-an executable output file. They are meaningless if the compiler is
-not doing a link step.
+@item -fdump-rtl-csa
+@opindex fdump-rtl-csa
+Dump after combining stack adjustments.
-@table @gcctabopt
-@cindex file names
-@item @var{object-file-name}
-A file name that does not end in a special recognized suffix is
-considered to name an object file or library. (Object files are
-distinguished from libraries by the linker according to the file
-contents.) If linking is done, these object files are used as input
-to the linker.
+@item -fdump-rtl-cse1
+@itemx -fdump-rtl-cse2
+@opindex fdump-rtl-cse1
+@opindex fdump-rtl-cse2
+@option{-fdump-rtl-cse1} and @option{-fdump-rtl-cse2} enable dumping after
+the two common subexpression elimination passes.
-@item -c
-@itemx -S
-@itemx -E
-@opindex c
-@opindex S
-@opindex E
-If any of these options is used, then the linker is not run, and
-object file names should not be used as arguments. @xref{Overall
-Options}.
+@item -fdump-rtl-dce
+@opindex fdump-rtl-dce
+Dump after the standalone dead code elimination passes.
-@item -fuse-ld=bfd
-@opindex fuse-ld=bfd
-Use the @command{bfd} linker instead of the default linker.
+@item -fdump-rtl-dbr
+@opindex fdump-rtl-dbr
+Dump after delayed branch scheduling.
-@item -fuse-ld=gold
-@opindex fuse-ld=gold
-Use the @command{gold} linker instead of the default linker.
+@item -fdump-rtl-dce1
+@itemx -fdump-rtl-dce2
+@opindex fdump-rtl-dce1
+@opindex fdump-rtl-dce2
+@option{-fdump-rtl-dce1} and @option{-fdump-rtl-dce2} enable dumping after
+the two dead store elimination passes.
-@cindex Libraries
-@item -l@var{library}
-@itemx -l @var{library}
-@opindex l
-Search the library named @var{library} when linking. (The second
-alternative with the library as a separate argument is only for
-POSIX compliance and is not recommended.)
+@item -fdump-rtl-eh
+@opindex fdump-rtl-eh
+Dump after finalization of EH handling code.
-It makes a difference where in the command you write this option; the
-linker searches and processes libraries and object files in the order they
-are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
-after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
-to functions in @samp{z}, those functions may not be loaded.
+@item -fdump-rtl-eh_ranges
+@opindex fdump-rtl-eh_ranges
+Dump after conversion of EH handling range regions.
-The linker searches a standard list of directories for the library,
-which is actually a file named @file{lib@var{library}.a}. The linker
-then uses this file as if it had been specified precisely by name.
+@item -fdump-rtl-expand
+@opindex fdump-rtl-expand
+Dump after RTL generation.
-The directories searched include several standard system directories
-plus any that you specify with @option{-L}.
+@item -fdump-rtl-fwprop1
+@itemx -fdump-rtl-fwprop2
+@opindex fdump-rtl-fwprop1
+@opindex fdump-rtl-fwprop2
+@option{-fdump-rtl-fwprop1} and @option{-fdump-rtl-fwprop2} enable
+dumping after the two forward propagation passes.
-Normally the files found this way are library files---archive files
-whose members are object files. The linker handles an archive file by
-scanning through it for members which define symbols that have so far
-been referenced but not defined. But if the file that is found is an
-ordinary object file, it is linked in the usual fashion. The only
-difference between using an @option{-l} option and specifying a file name
-is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
-and searches several directories.
+@item -fdump-rtl-gcse1
+@itemx -fdump-rtl-gcse2
+@opindex fdump-rtl-gcse1
+@opindex fdump-rtl-gcse2
+@option{-fdump-rtl-gcse1} and @option{-fdump-rtl-gcse2} enable dumping
+after global common subexpression elimination.
-@item -lobjc
-@opindex lobjc
-You need this special case of the @option{-l} option in order to
-link an Objective-C or Objective-C++ program.
+@item -fdump-rtl-init-regs
+@opindex fdump-rtl-init-regs
+Dump after the initialization of the registers.
-@item -nostartfiles
-@opindex nostartfiles
-Do not use the standard system startup files when linking.
-The standard system libraries are used normally, unless @option{-nostdlib}
-or @option{-nodefaultlibs} is used.
+@item -fdump-rtl-initvals
+@opindex fdump-rtl-initvals
+Dump after the computation of the initial value sets.
-@item -nodefaultlibs
-@opindex nodefaultlibs
-Do not use the standard system libraries when linking.
-Only the libraries you specify are passed to the linker, and options
-specifying linkage of the system libraries, such as @option{-static-libgcc}
-or @option{-shared-libgcc}, are ignored.
-The standard startup files are used normally, unless @option{-nostartfiles}
-is used.
+@item -fdump-rtl-into_cfglayout
+@opindex fdump-rtl-into_cfglayout
+Dump after converting to cfglayout mode.
-The compiler may generate calls to @code{memcmp},
-@code{memset}, @code{memcpy} and @code{memmove}.
-These entries are usually resolved by entries in
-libc. These entry points should be supplied through some other
-mechanism when this option is specified.
+@item -fdump-rtl-ira
+@opindex fdump-rtl-ira
+Dump after iterated register allocation.
-@item -nostdlib
-@opindex nostdlib
-Do not use the standard system startup files or libraries when linking.
-No startup files and only the libraries you specify are passed to
-the linker, and options specifying linkage of the system libraries, such as
-@option{-static-libgcc} or @option{-shared-libgcc}, are ignored.
+@item -fdump-rtl-jump
+@opindex fdump-rtl-jump
+Dump after the second jump optimization.
-The compiler may generate calls to @code{memcmp}, @code{memset},
-@code{memcpy} and @code{memmove}.
-These entries are usually resolved by entries in
-libc. These entry points should be supplied through some other
-mechanism when this option is specified.
+@item -fdump-rtl-loop2
+@opindex fdump-rtl-loop2
+@option{-fdump-rtl-loop2} enables dumping after the rtl
+loop optimization passes.
-@cindex @option{-lgcc}, use with @option{-nostdlib}
-@cindex @option{-nostdlib} and unresolved references
-@cindex unresolved references and @option{-nostdlib}
-@cindex @option{-lgcc}, use with @option{-nodefaultlibs}
-@cindex @option{-nodefaultlibs} and unresolved references
-@cindex unresolved references and @option{-nodefaultlibs}
-One of the standard libraries bypassed by @option{-nostdlib} and
-@option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
-which GCC uses to overcome shortcomings of particular machines, or special
-needs for some languages.
-(@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
-Collection (GCC) Internals},
-for more discussion of @file{libgcc.a}.)
-In most cases, you need @file{libgcc.a} even when you want to avoid
-other standard libraries. In other words, when you specify @option{-nostdlib}
-or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
-This ensures that you have no unresolved references to internal GCC
-library subroutines.
-(An example of such an internal subroutine is @code{__main}, used to ensure C++
-constructors are called; @pxref{Collect2,,@code{collect2}, gccint,
-GNU Compiler Collection (GCC) Internals}.)
+@item -fdump-rtl-mach
+@opindex fdump-rtl-mach
+Dump after performing the machine dependent reorganization pass, if that
+pass exists.
-@item -pie
-@opindex pie
-Produce a position independent executable on targets that support it.
-For predictable results, you must also specify the same set of options
-used for compilation (@option{-fpie}, @option{-fPIE},
-or model suboptions) when you specify this linker option.
+@item -fdump-rtl-mode_sw
+@opindex fdump-rtl-mode_sw
+Dump after removing redundant mode switches.
-@item -no-pie
-@opindex no-pie
-Don't produce a position independent executable.
+@item -fdump-rtl-rnreg
+@opindex fdump-rtl-rnreg
+Dump after register renumbering.
-@item -rdynamic
-@opindex rdynamic
-Pass the flag @option{-export-dynamic} to the ELF linker, on targets
-that support it. This instructs the linker to add all symbols, not
-only used ones, to the dynamic symbol table. This option is needed
-for some uses of @code{dlopen} or to allow obtaining backtraces
-from within a program.
+@item -fdump-rtl-outof_cfglayout
+@opindex fdump-rtl-outof_cfglayout
+Dump after converting from cfglayout mode.
-@item -s
-@opindex s
-Remove all symbol table and relocation information from the executable.
+@item -fdump-rtl-peephole2
+@opindex fdump-rtl-peephole2
+Dump after the peephole pass.
-@item -static
-@opindex static
-On systems that support dynamic linking, this prevents linking with the shared
-libraries. On other systems, this option has no effect.
+@item -fdump-rtl-postreload
+@opindex fdump-rtl-postreload
+Dump after post-reload optimizations.
-@item -shared
-@opindex shared
-Produce a shared object which can then be linked with other objects to
-form an executable. Not all systems support this option. For predictable
-results, you must also specify the same set of options used for compilation
-(@option{-fpic}, @option{-fPIC}, or model suboptions) when
-you specify this linker option.@footnote{On some systems, @samp{gcc -shared}
-needs to build supplementary stub code for constructors to work. On
-multi-libbed systems, @samp{gcc -shared} must select the correct support
-libraries to link against. Failing to supply the correct flags may lead
-to subtle defects. Supplying them in cases where they are not necessary
-is innocuous.}
+@item -fdump-rtl-pro_and_epilogue
+@opindex fdump-rtl-pro_and_epilogue
+Dump after generating the function prologues and epilogues.
-@item -shared-libgcc
-@itemx -static-libgcc
-@opindex shared-libgcc
-@opindex static-libgcc
-On systems that provide @file{libgcc} as a shared library, these options
-force the use of either the shared or static version, respectively.
-If no shared version of @file{libgcc} was built when the compiler was
-configured, these options have no effect.
+@item -fdump-rtl-sched1
+@itemx -fdump-rtl-sched2
+@opindex fdump-rtl-sched1
+@opindex fdump-rtl-sched2
+@option{-fdump-rtl-sched1} and @option{-fdump-rtl-sched2} enable dumping
+after the basic block scheduling passes.
-There are several situations in which an application should use the
-shared @file{libgcc} instead of the static version. The most common
-of these is when the application wishes to throw and catch exceptions
-across different shared libraries. In that case, each of the libraries
-as well as the application itself should use the shared @file{libgcc}.
+@item -fdump-rtl-ree
+@opindex fdump-rtl-ree
+Dump after sign/zero extension elimination.
-Therefore, the G++ and GCJ drivers automatically add
-@option{-shared-libgcc} whenever you build a shared library or a main
-executable, because C++ and Java programs typically use exceptions, so
-this is the right thing to do.
+@item -fdump-rtl-seqabstr
+@opindex fdump-rtl-seqabstr
+Dump after common sequence discovery.
-If, instead, you use the GCC driver to create shared libraries, you may
-find that they are not always linked with the shared @file{libgcc}.
-If GCC finds, at its configuration time, that you have a non-GNU linker
-or a GNU linker that does not support option @option{--eh-frame-hdr},
-it links the shared version of @file{libgcc} into shared libraries
-by default. Otherwise, it takes advantage of the linker and optimizes
-away the linking with the shared version of @file{libgcc}, linking with
-the static version of libgcc by default. This allows exceptions to
-propagate through such shared libraries, without incurring relocation
-costs at library load time.
+@item -fdump-rtl-shorten
+@opindex fdump-rtl-shorten
+Dump after shortening branches.
-However, if a library or main executable is supposed to throw or catch
-exceptions, you must link it using the G++ or GCJ driver, as appropriate
-for the languages used in the program, or using the option
-@option{-shared-libgcc}, such that it is linked with the shared
-@file{libgcc}.
+@item -fdump-rtl-sibling
+@opindex fdump-rtl-sibling
+Dump after sibling call optimizations.
-@item -static-libasan
-@opindex static-libasan
-When the @option{-fsanitize=address} option is used to link a program,
-the GCC driver automatically links against @option{libasan}. If
-@file{libasan} is available as a shared library, and the @option{-static}
-option is not used, then this links against the shared version of
-@file{libasan}. The @option{-static-libasan} option directs the GCC
-driver to link @file{libasan} statically, without necessarily linking
-other libraries statically.
+@item -fdump-rtl-split1
+@itemx -fdump-rtl-split2
+@itemx -fdump-rtl-split3
+@itemx -fdump-rtl-split4
+@itemx -fdump-rtl-split5
+@opindex fdump-rtl-split1
+@opindex fdump-rtl-split2
+@opindex fdump-rtl-split3
+@opindex fdump-rtl-split4
+@opindex fdump-rtl-split5
+These options enable dumping after five rounds of
+instruction splitting.
-@item -static-libtsan
-@opindex static-libtsan
-When the @option{-fsanitize=thread} option is used to link a program,
-the GCC driver automatically links against @option{libtsan}. If
-@file{libtsan} is available as a shared library, and the @option{-static}
-option is not used, then this links against the shared version of
-@file{libtsan}. The @option{-static-libtsan} option directs the GCC
-driver to link @file{libtsan} statically, without necessarily linking
-other libraries statically.
+@item -fdump-rtl-sms
+@opindex fdump-rtl-sms
+Dump after modulo scheduling. This pass is only run on some
+architectures.
-@item -static-liblsan
-@opindex static-liblsan
-When the @option{-fsanitize=leak} option is used to link a program,
-the GCC driver automatically links against @option{liblsan}. If
-@file{liblsan} is available as a shared library, and the @option{-static}
-option is not used, then this links against the shared version of
-@file{liblsan}. The @option{-static-liblsan} option directs the GCC
-driver to link @file{liblsan} statically, without necessarily linking
-other libraries statically.
+@item -fdump-rtl-stack
+@opindex fdump-rtl-stack
+Dump after conversion from GCC's ``flat register file'' registers to the
+x87's stack-like registers. This pass is only run on x86 variants.
-@item -static-libubsan
-@opindex static-libubsan
-When the @option{-fsanitize=undefined} option is used to link a program,
-the GCC driver automatically links against @option{libubsan}. If
-@file{libubsan} is available as a shared library, and the @option{-static}
-option is not used, then this links against the shared version of
-@file{libubsan}. The @option{-static-libubsan} option directs the GCC
-driver to link @file{libubsan} statically, without necessarily linking
-other libraries statically.
+@item -fdump-rtl-subreg1
+@itemx -fdump-rtl-subreg2
+@opindex fdump-rtl-subreg1
+@opindex fdump-rtl-subreg2
+@option{-fdump-rtl-subreg1} and @option{-fdump-rtl-subreg2} enable dumping after
+the two subreg expansion passes.
-@item -static-libmpx
-@opindex static-libmpx
-When the @option{-fcheck-pointer bounds} and @option{-mmpx} options are
-used to link a program, the GCC driver automatically links against
-@file{libmpx}. If @file{libmpx} is available as a shared library,
-and the @option{-static} option is not used, then this links against
-the shared version of @file{libmpx}. The @option{-static-libmpx}
-option directs the GCC driver to link @file{libmpx} statically,
-without necessarily linking other libraries statically.
+@item -fdump-rtl-unshare
+@opindex fdump-rtl-unshare
+Dump after all rtl has been unshared.
-@item -static-libmpxwrappers
-@opindex static-libmpxwrappers
-When the @option{-fcheck-pointer bounds} and @option{-mmpx} options are used
-to link a program without also using @option{-fno-chkp-use-wrappers}, the
-GCC driver automatically links against @file{libmpxwrappers}. If
-@file{libmpxwrappers} is available as a shared library, and the
-@option{-static} option is not used, then this links against the shared
-version of @file{libmpxwrappers}. The @option{-static-libmpxwrappers}
-option directs the GCC driver to link @file{libmpxwrappers} statically,
-without necessarily linking other libraries statically.
+@item -fdump-rtl-vartrack
+@opindex fdump-rtl-vartrack
+Dump after variable tracking.
-@item -static-libstdc++
-@opindex static-libstdc++
-When the @command{g++} program is used to link a C++ program, it
-normally automatically links against @option{libstdc++}. If
-@file{libstdc++} is available as a shared library, and the
-@option{-static} option is not used, then this links against the
-shared version of @file{libstdc++}. That is normally fine. However, it
-is sometimes useful to freeze the version of @file{libstdc++} used by
-the program without going all the way to a fully static link. The
-@option{-static-libstdc++} option directs the @command{g++} driver to
-link @file{libstdc++} statically, without necessarily linking other
-libraries statically.
+@item -fdump-rtl-vregs
+@opindex fdump-rtl-vregs
+Dump after converting virtual registers to hard registers.
-@item -symbolic
-@opindex symbolic
-Bind references to global symbols when building a shared object. Warn
-about any unresolved references (unless overridden by the link editor
-option @option{-Xlinker -z -Xlinker defs}). Only a few systems support
-this option.
+@item -fdump-rtl-web
+@opindex fdump-rtl-web
+Dump after live range splitting.
-@item -T @var{script}
-@opindex T
-@cindex linker script
-Use @var{script} as the linker script. This option is supported by most
-systems using the GNU linker. On some targets, such as bare-board
-targets without an operating system, the @option{-T} option may be required
-when linking to avoid references to undefined symbols.
+@item -fdump-rtl-regclass
+@itemx -fdump-rtl-subregs_of_mode_init
+@itemx -fdump-rtl-subregs_of_mode_finish
+@itemx -fdump-rtl-dfinit
+@itemx -fdump-rtl-dfinish
+@opindex fdump-rtl-regclass
+@opindex fdump-rtl-subregs_of_mode_init
+@opindex fdump-rtl-subregs_of_mode_finish
+@opindex fdump-rtl-dfinit
+@opindex fdump-rtl-dfinish
+These dumps are defined but always produce empty files.
-@item -Xlinker @var{option}
-@opindex Xlinker
-Pass @var{option} as an option to the linker. You can use this to
-supply system-specific linker options that GCC does not recognize.
+@item -da
+@itemx -fdump-rtl-all
+@opindex da
+@opindex fdump-rtl-all
+Produce all the dumps listed above.
-If you want to pass an option that takes a separate argument, you must use
-@option{-Xlinker} twice, once for the option and once for the argument.
-For example, to pass @option{-assert definitions}, you must write
-@option{-Xlinker -assert -Xlinker definitions}. It does not work to write
-@option{-Xlinker "-assert definitions"}, because this passes the entire
-string as a single argument, which is not what the linker expects.
+@item -dA
+@opindex dA
+Annotate the assembler output with miscellaneous debugging information.
+
+@item -dD
+@opindex dD
+Dump all macro definitions, at the end of preprocessing, in addition to
+normal output.
-When using the GNU linker, it is usually more convenient to pass
-arguments to linker options using the @option{@var{option}=@var{value}}
-syntax than as separate arguments. For example, you can specify
-@option{-Xlinker -Map=output.map} rather than
-@option{-Xlinker -Map -Xlinker output.map}. Other linkers may not support
-this syntax for command-line options.
+@item -dH
+@opindex dH
+Produce a core dump whenever an error occurs.
-@item -Wl,@var{option}
-@opindex Wl
-Pass @var{option} as an option to the linker. If @var{option} contains
-commas, it is split into multiple options at the commas. You can use this
-syntax to pass an argument to the option.
-For example, @option{-Wl,-Map,output.map} passes @option{-Map output.map} to the
-linker. When using the GNU linker, you can also get the same effect with
-@option{-Wl,-Map=output.map}.
+@item -dp
+@opindex dp
+Annotate the assembler output with a comment indicating which
+pattern and alternative is used. The length of each instruction is
+also printed.
-@item -u @var{symbol}
-@opindex u
-Pretend the symbol @var{symbol} is undefined, to force linking of
-library modules to define it. You can use @option{-u} multiple times with
-different symbols to force loading of additional library modules.
+@item -dP
+@opindex dP
+Dump the RTL in the assembler output as a comment before each instruction.
+Also turns on @option{-dp} annotation.
-@item -z @var{keyword}
-@opindex z
-@option{-z} is passed directly on to the linker along with the keyword
-@var{keyword}. See the section in the documentation of your linker for
-permitted values and their meanings.
+@item -dx
+@opindex dx
+Just generate RTL for a function instead of compiling it. Usually used
+with @option{-fdump-rtl-expand}.
@end table
-@node Directory Options
-@section Options for Directory Search
-@cindex directory options
-@cindex options, directory search
-@cindex search path
-
-These options specify directories to search for header files, for
-libraries and for parts of the compiler:
+@item -fdump-noaddr
+@opindex fdump-noaddr
+When doing debugging dumps, suppress address output. This makes it more
+feasible to use diff on debugging dumps for compiler invocations with
+different compiler binaries and/or different
+text / bss / data / heap / stack / dso start locations.
-@table @gcctabopt
-@item -I@var{dir}
-@opindex I
-Add the directory @var{dir} to the head of the list of directories to be
-searched for header files. This can be used to override a system header
-file, substituting your own version, since these directories are
-searched before the system header file directories. However, you should
-not use this option to add directories that contain vendor-supplied
-system header files (use @option{-isystem} for that). If you use more than
-one @option{-I} option, the directories are scanned in left-to-right
-order; the standard system directories come after.
+@item -freport-bug
+@opindex freport-bug
+Collect and dump debug information into a temporary file if an
+internal compiler error (ICE) occurs.
-If a standard system include directory, or a directory specified with
-@option{-isystem}, is also specified with @option{-I}, the @option{-I}
-option is ignored. The directory is still searched but as a
-system directory at its normal position in the system include chain.
-This is to ensure that GCC's procedure to fix buggy system headers and
-the ordering for the @code{include_next} directive are not inadvertently changed.
-If you really need to change the search order for system directories,
-use the @option{-nostdinc} and/or @option{-isystem} options.
+@item -fdump-unnumbered
+@opindex fdump-unnumbered
+When doing debugging dumps, suppress instruction numbers and address output.
+This makes it more feasible to use diff on debugging dumps for compiler
+invocations with different options, in particular with and without
+@option{-g}.
-@item -iplugindir=@var{dir}
-@opindex iplugindir=
-Set the directory to search for plugins that are passed
-by @option{-fplugin=@var{name}} instead of
-@option{-fplugin=@var{path}/@var{name}.so}. This option is not meant
-to be used by the user, but only passed by the driver.
+@item -fdump-unnumbered-links
+@opindex fdump-unnumbered-links
+When doing debugging dumps (see @option{-d} option above), suppress
+instruction numbers for the links to the previous and next instructions
+in a sequence.
-@item -iquote@var{dir}
-@opindex iquote
-Add the directory @var{dir} to the head of the list of directories to
-be searched for header files only for the case of @code{#include
-"@var{file}"}; they are not searched for @code{#include <@var{file}>},
-otherwise just like @option{-I}.
+@item -fdump-translation-unit @r{(C++ only)}
+@itemx -fdump-translation-unit-@var{options} @r{(C++ only)}
+@opindex fdump-translation-unit
+Dump a representation of the tree structure for the entire translation
+unit to a file. The file name is made by appending @file{.tu} to the
+source file name, and the file is created in the same directory as the
+output file. If the @samp{-@var{options}} form is used, @var{options}
+controls the details of the dump as described for the
+@option{-fdump-tree} options.
-@item -L@var{dir}
-@opindex L
-Add directory @var{dir} to the list of directories to be searched
-for @option{-l}.
+@item -fdump-class-hierarchy @r{(C++ only)}
+@itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
+@opindex fdump-class-hierarchy
+Dump a representation of each class's hierarchy and virtual function
+table layout to a file. The file name is made by appending
+@file{.class} to the source file name, and the file is created in the
+same directory as the output file. If the @samp{-@var{options}} form
+is used, @var{options} controls the details of the dump as described
+for the @option{-fdump-tree} options.
-@item -B@var{prefix}
-@opindex B
-This option specifies where to find the executables, libraries,
-include files, and data files of the compiler itself.
+@item -fdump-ipa-@var{switch}
+@opindex fdump-ipa
+Control the dumping at various stages of inter-procedural analysis
+language tree to a file. The file name is generated by appending a
+switch specific suffix to the source file name, and the file is created
+in the same directory as the output file. The following dumps are
+possible:
-The compiler driver program runs one or more of the subprograms
-@command{cpp}, @command{cc1}, @command{as} and @command{ld}. It tries
-@var{prefix} as a prefix for each program it tries to run, both with and
-without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
+@table @samp
+@item all
+Enables all inter-procedural analysis dumps.
-For each subprogram to be run, the compiler driver first tries the
-@option{-B} prefix, if any. If that name is not found, or if @option{-B}
-is not specified, the driver tries two standard prefixes,
-@file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of
-those results in a file name that is found, the unmodified program
-name is searched for using the directories specified in your
-@env{PATH} environment variable.
+@item cgraph
+Dumps information about call-graph optimization, unused function removal,
+and inlining decisions.
-The compiler checks to see if the path provided by @option{-B}
-refers to a directory, and if necessary it adds a directory
-separator character at the end of the path.
+@item inline
+Dump after function inlining.
-@option{-B} prefixes that effectively specify directory names also apply
-to libraries in the linker, because the compiler translates these
-options into @option{-L} options for the linker. They also apply to
-include files in the preprocessor, because the compiler translates these
-options into @option{-isystem} options for the preprocessor. In this case,
-the compiler appends @samp{include} to the prefix.
+@end table
-The runtime support file @file{libgcc.a} can also be searched for using
-the @option{-B} prefix, if needed. If it is not found there, the two
-standard prefixes above are tried, and that is all. The file is left
-out of the link if it is not found by those means.
+@item -fdump-passes
+@opindex fdump-passes
+Dump the list of optimization passes that are turned on and off by
+the current command-line options.
-Another way to specify a prefix much like the @option{-B} prefix is to use
-the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
-Variables}.
+@item -fdump-statistics-@var{option}
+@opindex fdump-statistics
+Enable and control dumping of pass statistics in a separate file. The
+file name is generated by appending a suffix ending in
+@samp{.statistics} to the source file name, and the file is created in
+the same directory as the output file. If the @samp{-@var{option}}
+form is used, @samp{-stats} causes counters to be summed over the
+whole compilation unit while @samp{-details} dumps every event as
+the passes generate them. The default with no option is to sum
+counters for each function compiled.
-As a special kludge, if the path provided by @option{-B} is
-@file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
-9, then it is replaced by @file{[dir/]include}. This is to help
-with boot-strapping the compiler.
+@item -fdump-tree-@var{switch}
+@itemx -fdump-tree-@var{switch}-@var{options}
+@itemx -fdump-tree-@var{switch}-@var{options}=@var{filename}
+@opindex fdump-tree
+Control the dumping at various stages of processing the intermediate
+language tree to a file. The file name is generated by appending a
+switch-specific suffix to the source file name, and the file is
+created in the same directory as the output file. In case of
+@option{=@var{filename}} option, the dump is output on the given file
+instead of the auto named dump files. If the @samp{-@var{options}}
+form is used, @var{options} is a list of @samp{-} separated options
+which control the details of the dump. Not all options are applicable
+to all dumps; those that are not meaningful are ignored. The
+following options are available
-@item -specs=@var{file}
-@opindex specs
-Process @var{file} after the compiler reads in the standard @file{specs}
-file, in order to override the defaults which the @command{gcc} driver
-program uses when determining what switches to pass to @command{cc1},
-@command{cc1plus}, @command{as}, @command{ld}, etc. More than one
-@option{-specs=@var{file}} can be specified on the command line, and they
-are processed in order, from left to right.
+@table @samp
+@item address
+Print the address of each node. Usually this is not meaningful as it
+changes according to the environment and source file. Its primary use
+is for tying up a dump file with a debug environment.
+@item asmname
+If @code{DECL_ASSEMBLER_NAME} has been set for a given decl, use that
+in the dump instead of @code{DECL_NAME}. Its primary use is ease of
+use working backward from mangled names in the assembly file.
+@item slim
+When dumping front-end intermediate representations, inhibit dumping
+of members of a scope or body of a function merely because that scope
+has been reached. Only dump such items when they are directly reachable
+by some other path.
-@item --sysroot=@var{dir}
-@opindex sysroot
-Use @var{dir} as the logical root directory for headers and libraries.
-For example, if the compiler normally searches for headers in
-@file{/usr/include} and libraries in @file{/usr/lib}, it instead
-searches @file{@var{dir}/usr/include} and @file{@var{dir}/usr/lib}.
+When dumping pretty-printed trees, this option inhibits dumping the
+bodies of control structures.
-If you use both this option and the @option{-isysroot} option, then
-the @option{--sysroot} option applies to libraries, but the
-@option{-isysroot} option applies to header files.
+When dumping RTL, print the RTL in slim (condensed) form instead of
+the default LISP-like representation.
+@item raw
+Print a raw representation of the tree. By default, trees are
+pretty-printed into a C-like representation.
+@item details
+Enable more detailed dumps (not honored by every dump option). Also
+include information from the optimization passes.
+@item stats
+Enable dumping various statistics about the pass (not honored by every dump
+option).
+@item blocks
+Enable showing basic block boundaries (disabled in raw dumps).
+@item graph
+For each of the other indicated dump files (@option{-fdump-rtl-@var{pass}}),
+dump a representation of the control flow graph suitable for viewing with
+GraphViz to @file{@var{file}.@var{passid}.@var{pass}.dot}. Each function in
+the file is pretty-printed as a subgraph, so that GraphViz can render them
+all in a single plot.
-The GNU linker (beginning with version 2.16) has the necessary support
-for this option. If your linker does not support this option, the
-header file aspect of @option{--sysroot} still works, but the
-library aspect does not.
+This option currently only works for RTL dumps, and the RTL is always
+dumped in slim form.
+@item vops
+Enable showing virtual operands for every statement.
+@item lineno
+Enable showing line numbers for statements.
+@item uid
+Enable showing the unique ID (@code{DECL_UID}) for each variable.
+@item verbose
+Enable showing the tree dump for each statement.
+@item eh
+Enable showing the EH region number holding each statement.
+@item scev
+Enable showing scalar evolution analysis details.
+@item optimized
+Enable showing optimization information (only available in certain
+passes).
+@item missed
+Enable showing missed optimization information (only available in certain
+passes).
+@item note
+Enable other detailed optimization information (only available in
+certain passes).
+@item =@var{filename}
+Instead of an auto named dump file, output into the given file
+name. The file names @file{stdout} and @file{stderr} are treated
+specially and are considered already open standard streams. For
+example,
-@item --no-sysroot-suffix
-@opindex no-sysroot-suffix
-For some targets, a suffix is added to the root directory specified
-with @option{--sysroot}, depending on the other options used, so that
-headers may for example be found in
-@file{@var{dir}/@var{suffix}/usr/include} instead of
-@file{@var{dir}/usr/include}. This option disables the addition of
-such a suffix.
+@smallexample
+gcc -O2 -ftree-vectorize -fdump-tree-vect-blocks=foo.dump
+ -fdump-tree-pre=stderr file.c
+@end smallexample
-@item -I-
-@opindex I-
-This option has been deprecated. Please use @option{-iquote} instead for
-@option{-I} directories before the @option{-I-} and remove the @option{-I-}
-option.
-Any directories you specify with @option{-I} options before the @option{-I-}
-option are searched only for the case of @code{#include "@var{file}"};
-they are not searched for @code{#include <@var{file}>}.
+outputs vectorizer dump into @file{foo.dump}, while the PRE dump is
+output on to @file{stderr}. If two conflicting dump filenames are
+given for the same pass, then the latter option overrides the earlier
+one.
-If additional directories are specified with @option{-I} options after
-the @option{-I-} option, these directories are searched for all @code{#include}
-directives. (Ordinarily @emph{all} @option{-I} directories are used
-this way.)
+@item split-paths
+@opindex fdump-tree-split-paths
+Dump each function after splitting paths to loop backedges. The file
+name is made by appending @file{.split-paths} to the source file name.
-In addition, the @option{-I-} option inhibits the use of the current
-directory (where the current input file came from) as the first search
-directory for @code{#include "@var{file}"}. There is no way to
-override this effect of @option{-I-}. With @option{-I.} you can specify
-searching the directory that is current when the compiler is
-invoked. That is not exactly the same as what the preprocessor does
-by default, but it is often satisfactory.
+@item all
+Turn on all options, except @option{raw}, @option{slim}, @option{verbose}
+and @option{lineno}.
-@option{-I-} does not inhibit the use of the standard system directories
-for header files. Thus, @option{-I-} and @option{-nostdinc} are
-independent.
+@item optall
+Turn on all optimization options, i.e., @option{optimized},
+@option{missed}, and @option{note}.
@end table
-@c man end
-
-@node Spec Files
-@section Specifying Subprocesses and the Switches to Pass to Them
-@cindex Spec Files
+The following tree dumps are possible:
+@table @samp
-@command{gcc} is a driver program. It performs its job by invoking a
-sequence of other programs to do the work of compiling, assembling and
-linking. GCC interprets its command-line parameters and uses these to
-deduce which programs it should invoke, and which command-line options
-it ought to place on their command lines. This behavior is controlled
-by @dfn{spec strings}. In most cases there is one spec string for each
-program that GCC can invoke, but a few programs have multiple spec
-strings to control their behavior. The spec strings built into GCC can
-be overridden by using the @option{-specs=} command-line switch to specify
-a spec file.
+@item original
+@opindex fdump-tree-original
+Dump before any tree based optimization, to @file{@var{file}.original}.
-@dfn{Spec files} are plaintext files that are used to construct spec
-strings. They consist of a sequence of directives separated by blank
-lines. The type of directive is determined by the first non-whitespace
-character on the line, which can be one of the following:
+@item optimized
+@opindex fdump-tree-optimized
+Dump after all tree based optimization, to @file{@var{file}.optimized}.
-@table @code
-@item %@var{command}
-Issues a @var{command} to the spec file processor. The commands that can
-appear here are:
+@item gimple
+@opindex fdump-tree-gimple
+Dump each function before and after the gimplification pass to a file. The
+file name is made by appending @file{.gimple} to the source file name.
-@table @code
-@item %include <@var{file}>
-@cindex @code{%include}
-Search for @var{file} and insert its text at the current point in the
-specs file.
+@item cfg
+@opindex fdump-tree-cfg
+Dump the control flow graph of each function to a file. The file name is
+made by appending @file{.cfg} to the source file name.
-@item %include_noerr <@var{file}>
-@cindex @code{%include_noerr}
-Just like @samp{%include}, but do not generate an error message if the include
-file cannot be found.
+@item ch
+@opindex fdump-tree-ch
+Dump each function after copying loop headers. The file name is made by
+appending @file{.ch} to the source file name.
-@item %rename @var{old_name} @var{new_name}
-@cindex @code{%rename}
-Rename the spec string @var{old_name} to @var{new_name}.
+@item ssa
+@opindex fdump-tree-ssa
+Dump SSA related information to a file. The file name is made by appending
+@file{.ssa} to the source file name.
-@end table
+@item alias
+@opindex fdump-tree-alias
+Dump aliasing information for each function. The file name is made by
+appending @file{.alias} to the source file name.
-@item *[@var{spec_name}]:
-This tells the compiler to create, override or delete the named spec
-string. All lines after this directive up to the next directive or
-blank line are considered to be the text for the spec string. If this
-results in an empty string then the spec is deleted. (Or, if the
-spec did not exist, then nothing happens.) Otherwise, if the spec
-does not currently exist a new spec is created. If the spec does
-exist then its contents are overridden by the text of this
-directive, unless the first character of that text is the @samp{+}
-character, in which case the text is appended to the spec.
+@item ccp
+@opindex fdump-tree-ccp
+Dump each function after CCP@. The file name is made by appending
+@file{.ccp} to the source file name.
-@item [@var{suffix}]:
-Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
-and up to the next directive or blank line are considered to make up the
-spec string for the indicated suffix. When the compiler encounters an
-input file with the named suffix, it processes the spec string in
-order to work out how to compile that file. For example:
+@item storeccp
+@opindex fdump-tree-storeccp
+Dump each function after STORE-CCP@. The file name is made by appending
+@file{.storeccp} to the source file name.
-@smallexample
-.ZZ:
-z-compile -input %i
-@end smallexample
+@item pre
+@opindex fdump-tree-pre
+Dump trees after partial redundancy elimination. The file name is made
+by appending @file{.pre} to the source file name.
-This says that any input file whose name ends in @samp{.ZZ} should be
-passed to the program @samp{z-compile}, which should be invoked with the
-command-line switch @option{-input} and with the result of performing the
-@samp{%i} substitution. (See below.)
+@item fre
+@opindex fdump-tree-fre
+Dump trees after full redundancy elimination. The file name is made
+by appending @file{.fre} to the source file name.
-As an alternative to providing a spec string, the text following a
-suffix directive can be one of the following:
+@item copyprop
+@opindex fdump-tree-copyprop
+Dump trees after copy propagation. The file name is made
+by appending @file{.copyprop} to the source file name.
-@table @code
-@item @@@var{language}
-This says that the suffix is an alias for a known @var{language}. This is
-similar to using the @option{-x} command-line switch to GCC to specify a
-language explicitly. For example:
+@item store_copyprop
+@opindex fdump-tree-store_copyprop
+Dump trees after store copy-propagation. The file name is made
+by appending @file{.store_copyprop} to the source file name.
-@smallexample
-.ZZ:
-@@c++
-@end smallexample
+@item dce
+@opindex fdump-tree-dce
+Dump each function after dead code elimination. The file name is made by
+appending @file{.dce} to the source file name.
-Says that .ZZ files are, in fact, C++ source files.
+@item sra
+@opindex fdump-tree-sra
+Dump each function after performing scalar replacement of aggregates. The
+file name is made by appending @file{.sra} to the source file name.
-@item #@var{name}
-This causes an error messages saying:
+@item sink
+@opindex fdump-tree-sink
+Dump each function after performing code sinking. The file name is made
+by appending @file{.sink} to the source file name.
-@smallexample
-@var{name} compiler not installed on this system.
-@end smallexample
-@end table
+@item dom
+@opindex fdump-tree-dom
+Dump each function after applying dominator tree optimizations. The file
+name is made by appending @file{.dom} to the source file name.
-GCC already has an extensive list of suffixes built into it.
-This directive adds an entry to the end of the list of suffixes, but
-since the list is searched from the end backwards, it is effectively
-possible to override earlier entries using this technique.
+@item dse
+@opindex fdump-tree-dse
+Dump each function after applying dead store elimination. The file
+name is made by appending @file{.dse} to the source file name.
-@end table
+@item phiopt
+@opindex fdump-tree-phiopt
+Dump each function after optimizing PHI nodes into straightline code. The file
+name is made by appending @file{.phiopt} to the source file name.
-GCC has the following spec strings built into it. Spec files can
-override these strings or create their own. Note that individual
-targets can also add their own spec strings to this list.
+@item backprop
+@opindex fdump-tree-backprop
+Dump each function after back-propagating use information up the definition
+chain. The file name is made by appending @file{.backprop} to the
+source file name.
-@smallexample
-asm Options to pass to the assembler
-asm_final Options to pass to the assembler post-processor
-cpp Options to pass to the C preprocessor
-cc1 Options to pass to the C compiler
-cc1plus Options to pass to the C++ compiler
-endfile Object files to include at the end of the link
-link Options to pass to the linker
-lib Libraries to include on the command line to the linker
-libgcc Decides which GCC support library to pass to the linker
-linker Sets the name of the linker
-predefines Defines to be passed to the C preprocessor
-signed_char Defines to pass to CPP to say whether @code{char} is signed
- by default
-startfile Object files to include at the start of the link
-@end smallexample
+@item forwprop
+@opindex fdump-tree-forwprop
+Dump each function after forward propagating single use variables. The file
+name is made by appending @file{.forwprop} to the source file name.
-Here is a small example of a spec file:
+@item nrv
+@opindex fdump-tree-nrv
+Dump each function after applying the named return value optimization on
+generic trees. The file name is made by appending @file{.nrv} to the source
+file name.
-@smallexample
-%rename lib old_lib
+@item vect
+@opindex fdump-tree-vect
+Dump each function after applying vectorization of loops. The file name is
+made by appending @file{.vect} to the source file name.
-*lib:
---start-group -lgcc -lc -leval1 --end-group %(old_lib)
-@end smallexample
+@item slp
+@opindex fdump-tree-slp
+Dump each function after applying vectorization of basic blocks. The file name
+is made by appending @file{.slp} to the source file name.
-This example renames the spec called @samp{lib} to @samp{old_lib} and
-then overrides the previous definition of @samp{lib} with a new one.
-The new definition adds in some extra command-line options before
-including the text of the old definition.
+@item vrp
+@opindex fdump-tree-vrp
+Dump each function after Value Range Propagation (VRP). The file name
+is made by appending @file{.vrp} to the source file name.
-@dfn{Spec strings} are a list of command-line options to be passed to their
-corresponding program. In addition, the spec strings can contain
-@samp{%}-prefixed sequences to substitute variable text or to
-conditionally insert text into the command line. Using these constructs
-it is possible to generate quite complex command lines.
+@item oaccdevlow
+@opindex fdump-tree-oaccdevlow
+Dump each function after applying device-specific OpenACC transformations.
+The file name is made by appending @file{.oaccdevlow} to the source file name.
-Here is a table of all defined @samp{%}-sequences for spec
-strings. Note that spaces are not generated automatically around the
-results of expanding these sequences. Therefore you can concatenate them
-together or combine them with constant text in a single argument.
+@item all
+@opindex fdump-tree-all
+Enable all the available tree dumps with the flags provided in this option.
+@end table
-@table @code
-@item %%
-Substitute one @samp{%} into the program name or argument.
+@item -fopt-info
+@itemx -fopt-info-@var{options}
+@itemx -fopt-info-@var{options}=@var{filename}
+@opindex fopt-info
+Controls optimization dumps from various optimization passes. If the
+@samp{-@var{options}} form is used, @var{options} is a list of
+@samp{-} separated option keywords to select the dump details and
+optimizations.
-@item %i
-Substitute the name of the input file being processed.
+The @var{options} can be divided into two groups: options describing the
+verbosity of the dump, and options describing which optimizations
+should be included. The options from both the groups can be freely
+mixed as they are non-overlapping. However, in case of any conflicts,
+the later options override the earlier options on the command
+line.
-@item %b
-Substitute the basename of the input file being processed.
-This is the substring up to (and not including) the last period
-and not including the directory.
+The following options control the dump verbosity:
-@item %B
-This is the same as @samp{%b}, but include the file suffix (text after
-the last period).
+@table @samp
+@item optimized
+Print information when an optimization is successfully applied. It is
+up to a pass to decide which information is relevant. For example, the
+vectorizer passes print the source location of loops which are
+successfully vectorized.
+@item missed
+Print information about missed optimizations. Individual passes
+control which information to include in the output.
+@item note
+Print verbose information about optimizations, such as certain
+transformations, more detailed messages about decisions etc.
+@item all
+Print detailed optimization information. This includes
+@samp{optimized}, @samp{missed}, and @samp{note}.
+@end table
-@item %d
-Marks the argument containing or following the @samp{%d} as a
-temporary file name, so that that file is deleted if GCC exits
-successfully. Unlike @samp{%g}, this contributes no text to the
-argument.
+One or more of the following option keywords can be used to describe a
+group of optimizations:
-@item %g@var{suffix}
-Substitute a file name that has suffix @var{suffix} and is chosen
-once per compilation, and mark the argument in the same way as
-@samp{%d}. To reduce exposure to denial-of-service attacks, the file
-name is now chosen in a way that is hard to predict even when previously
-chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
-might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
-the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
-treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
-was simply substituted with a file name chosen once per compilation,
-without regard to any appended suffix (which was therefore treated
-just like ordinary text), making such attacks more likely to succeed.
+@table @samp
+@item ipa
+Enable dumps from all interprocedural optimizations.
+@item loop
+Enable dumps from all loop optimizations.
+@item inline
+Enable dumps from all inlining optimizations.
+@item vec
+Enable dumps from all vectorization optimizations.
+@item optall
+Enable dumps from all optimizations. This is a superset of
+the optimization groups listed above.
+@end table
-@item %u@var{suffix}
-Like @samp{%g}, but generates a new temporary file name
-each time it appears instead of once per compilation.
+If @var{options} is
+omitted, it defaults to @samp{optimized-optall}, which means to dump all
+info about successful optimizations from all the passes.
-@item %U@var{suffix}
-Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
-new one if there is no such last file name. In the absence of any
-@samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
-the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
-involves the generation of two distinct file names, one
-for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
-simply substituted with a file name chosen for the previous @samp{%u},
-without regard to any appended suffix.
+If the @var{filename} is provided, then the dumps from all the
+applicable optimizations are concatenated into the @var{filename}.
+Otherwise the dump is output onto @file{stderr}. Though multiple
+@option{-fopt-info} options are accepted, only one of them can include
+a @var{filename}. If other filenames are provided then all but the
+first such option are ignored.
-@item %j@var{suffix}
-Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
-writable, and if @option{-save-temps} is not used;
-otherwise, substitute the name
-of a temporary file, just like @samp{%u}. This temporary file is not
-meant for communication between processes, but rather as a junk
-disposal mechanism.
+Note that the output @var{filename} is overwritten
+in case of multiple translation units. If a combined output from
+multiple translation units is desired, @file{stderr} should be used
+instead.
-@item %|@var{suffix}
-@itemx %m@var{suffix}
-Like @samp{%g}, except if @option{-pipe} is in effect. In that case
-@samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at
-all. These are the two most common ways to instruct a program that it
-should read from standard input or write to standard output. If you
-need something more elaborate you can use an @samp{%@{pipe:@code{X}@}}
-construct: see for example @file{f/lang-specs.h}.
+In the following example, the optimization info is output to
+@file{stderr}:
-@item %.@var{SUFFIX}
-Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
-when it is subsequently output with @samp{%*}. @var{SUFFIX} is
-terminated by the next space or %.
+@smallexample
+gcc -O3 -fopt-info
+@end smallexample
-@item %w
-Marks the argument containing or following the @samp{%w} as the
-designated output file of this compilation. This puts the argument
-into the sequence of arguments that @samp{%o} substitutes.
+This example:
+@smallexample
+gcc -O3 -fopt-info-missed=missed.all
+@end smallexample
-@item %o
-Substitutes the names of all the output files, with spaces
-automatically placed around them. You should write spaces
-around the @samp{%o} as well or the results are undefined.
-@samp{%o} is for use in the specs for running the linker.
-Input files whose names have no recognized suffix are not compiled
-at all, but they are included among the output files, so they are
-linked.
+@noindent
+outputs missed optimization report from all the passes into
+@file{missed.all}, and this one:
-@item %O
-Substitutes the suffix for object files. Note that this is
-handled specially when it immediately follows @samp{%g, %u, or %U},
-because of the need for those to form complete file names. The
-handling is such that @samp{%O} is treated exactly as if it had already
-been substituted, except that @samp{%g, %u, and %U} do not currently
-support additional @var{suffix} characters following @samp{%O} as they do
-following, for example, @samp{.o}.
+@smallexample
+gcc -O2 -ftree-vectorize -fopt-info-vec-missed
+@end smallexample
-@item %p
-Substitutes the standard macro predefinitions for the
-current target machine. Use this when running @command{cpp}.
+@noindent
+prints information about missed optimization opportunities from
+vectorization passes on @file{stderr}.
+Note that @option{-fopt-info-vec-missed} is equivalent to
+@option{-fopt-info-missed-vec}.
-@item %P
-Like @samp{%p}, but puts @samp{__} before and after the name of each
-predefined macro, except for macros that start with @samp{__} or with
-@samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
-C@.
+As another example,
+@smallexample
+gcc -O3 -fopt-info-inline-optimized-missed=inline.txt
+@end smallexample
-@item %I
-Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}),
-@option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}),
-@option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options)
-and @option{-imultilib} as necessary.
+@noindent
+outputs information about missed optimizations as well as
+optimized locations from all the inlining passes into
+@file{inline.txt}.
-@item %s
-Current argument is the name of a library or startup file of some sort.
-Search for that file in a standard list of directories and substitute
-the full name found. The current working directory is included in the
-list of directories scanned.
+Finally, consider:
-@item %T
-Current argument is the name of a linker script. Search for that file
-in the current list of directories to scan for libraries. If the file
-is located insert a @option{--script} option into the command line
-followed by the full path name found. If the file is not found then
-generate an error message. Note: the current working directory is not
-searched.
+@smallexample
+gcc -fopt-info-vec-missed=vec.miss -fopt-info-loop-optimized=loop.opt
+@end smallexample
+
+@noindent
+Here the two output filenames @file{vec.miss} and @file{loop.opt} are
+in conflict since only one output file is allowed. In this case, only
+the first option takes effect and the subsequent options are
+ignored. Thus only @file{vec.miss} is produced which contains
+dumps from the vectorizer about missed opportunities.
+
+@item -fsched-verbose=@var{n}
+@opindex fsched-verbose
+On targets that use instruction scheduling, this option controls the
+amount of debugging output the scheduler prints to the dump files.
+
+For @var{n} greater than zero, @option{-fsched-verbose} outputs the
+same information as @option{-fdump-rtl-sched1} and @option{-fdump-rtl-sched2}.
+For @var{n} greater than one, it also output basic block probabilities,
+detailed ready list information and unit/insn info. For @var{n} greater
+than two, it includes RTL at abort point, control-flow and regions info.
+And for @var{n} over four, @option{-fsched-verbose} also includes
+dependence info.
-@item %e@var{str}
-Print @var{str} as an error message. @var{str} is terminated by a newline.
-Use this when inconsistent options are detected.
-@item %(@var{name})
-Substitute the contents of spec string @var{name} at this point.
-@item %x@{@var{option}@}
-Accumulate an option for @samp{%X}.
+@item -fenable-@var{kind}-@var{pass}
+@itemx -fdisable-@var{kind}-@var{pass}=@var{range-list}
+@opindex fdisable-
+@opindex fenable-
-@item %X
-Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
-spec string.
+This is a set of options that are used to explicitly disable/enable
+optimization passes. These options are intended for use for debugging GCC.
+Compiler users should use regular options for enabling/disabling
+passes instead.
-@item %Y
-Output the accumulated assembler options specified by @option{-Wa}.
+@table @gcctabopt
-@item %Z
-Output the accumulated preprocessor options specified by @option{-Wp}.
+@item -fdisable-ipa-@var{pass}
+Disable IPA pass @var{pass}. @var{pass} is the pass name. If the same pass is
+statically invoked in the compiler multiple times, the pass name should be
+appended with a sequential number starting from 1.
-@item %a
-Process the @code{asm} spec. This is used to compute the
-switches to be passed to the assembler.
+@item -fdisable-rtl-@var{pass}
+@itemx -fdisable-rtl-@var{pass}=@var{range-list}
+Disable RTL pass @var{pass}. @var{pass} is the pass name. If the same pass is
+statically invoked in the compiler multiple times, the pass name should be
+appended with a sequential number starting from 1. @var{range-list} is a
+comma-separated list of function ranges or assembler names. Each range is a number
+pair separated by a colon. The range is inclusive in both ends. If the range
+is trivial, the number pair can be simplified as a single number. If the
+function's call graph node's @var{uid} falls within one of the specified ranges,
+the @var{pass} is disabled for that function. The @var{uid} is shown in the
+function header of a dump file, and the pass names can be dumped by using
+option @option{-fdump-passes}.
-@item %A
-Process the @code{asm_final} spec. This is a spec string for
-passing switches to an assembler post-processor, if such a program is
-needed.
+@item -fdisable-tree-@var{pass}
+@itemx -fdisable-tree-@var{pass}=@var{range-list}
+Disable tree pass @var{pass}. See @option{-fdisable-rtl} for the description of
+option arguments.
-@item %l
-Process the @code{link} spec. This is the spec for computing the
-command line passed to the linker. Typically it makes use of the
-@samp{%L %G %S %D and %E} sequences.
+@item -fenable-ipa-@var{pass}
+Enable IPA pass @var{pass}. @var{pass} is the pass name. If the same pass is
+statically invoked in the compiler multiple times, the pass name should be
+appended with a sequential number starting from 1.
-@item %D
-Dump out a @option{-L} option for each directory that GCC believes might
-contain startup files. If the target supports multilibs then the
-current multilib directory is prepended to each of these paths.
+@item -fenable-rtl-@var{pass}
+@itemx -fenable-rtl-@var{pass}=@var{range-list}
+Enable RTL pass @var{pass}. See @option{-fdisable-rtl} for option argument
+description and examples.
-@item %L
-Process the @code{lib} spec. This is a spec string for deciding which
-libraries are included on the command line to the linker.
+@item -fenable-tree-@var{pass}
+@itemx -fenable-tree-@var{pass}=@var{range-list}
+Enable tree pass @var{pass}. See @option{-fdisable-rtl} for the description
+of option arguments.
-@item %G
-Process the @code{libgcc} spec. This is a spec string for deciding
-which GCC support library is included on the command line to the linker.
+@end table
-@item %S
-Process the @code{startfile} spec. This is a spec for deciding which
-object files are the first ones passed to the linker. Typically
-this might be a file named @file{crt0.o}.
+Here are some examples showing uses of these options.
-@item %E
-Process the @code{endfile} spec. This is a spec string that specifies
-the last object files that are passed to the linker.
+@smallexample
-@item %C
-Process the @code{cpp} spec. This is used to construct the arguments
-to be passed to the C preprocessor.
+# disable ccp1 for all functions
+ -fdisable-tree-ccp1
+# disable complete unroll for function whose cgraph node uid is 1
+ -fenable-tree-cunroll=1
+# disable gcse2 for functions at the following ranges [1,1],
+# [300,400], and [400,1000]
+# disable gcse2 for functions foo and foo2
+ -fdisable-rtl-gcse2=foo,foo2
+# disable early inlining
+ -fdisable-tree-einline
+# disable ipa inlining
+ -fdisable-ipa-inline
+# enable tree full unroll
+ -fenable-tree-unroll
-@item %1
-Process the @code{cc1} spec. This is used to construct the options to be
-passed to the actual C compiler (@command{cc1}).
+@end smallexample
-@item %2
-Process the @code{cc1plus} spec. This is used to construct the options to be
-passed to the actual C++ compiler (@command{cc1plus}).
+@item -fchecking
+@itemx -fchecking=@var{n}
+@opindex fchecking
+@opindex fno-checking
+Enable internal consistency checking. The default depends on
+the compiler configuration. @option{-fchecking=2} enables further
+internal consistency checking that might affect code generation.
-@item %*
-Substitute the variable part of a matched option. See below.
-Note that each comma in the substituted string is replaced by
-a single space.
+@item -frandom-seed=@var{string}
+@opindex frandom-seed
+This option provides a seed that GCC uses in place of
+random numbers in generating certain symbol names
+that have to be different in every compiled file. It is also used to
+place unique stamps in coverage data files and the object files that
+produce them. You can use the @option{-frandom-seed} option to produce
+reproducibly identical object files.
-@item %<@code{S}
-Remove all occurrences of @code{-S} from the command line. Note---this
-command is position dependent. @samp{%} commands in the spec string
-before this one see @code{-S}, @samp{%} commands in the spec string
-after this one do not.
+The @var{string} can either be a number (decimal, octal or hex) or an
+arbitrary string (in which case it's converted to a number by
+computing CRC32).
-@item %:@var{function}(@var{args})
-Call the named function @var{function}, passing it @var{args}.
-@var{args} is first processed as a nested spec string, then split
-into an argument vector in the usual fashion. The function returns
-a string which is processed as if it had appeared literally as part
-of the current spec.
+The @var{string} should be different for every file you compile.
-The following built-in spec functions are provided:
+@item -save-temps
+@itemx -save-temps=cwd
+@opindex save-temps
+Store the usual ``temporary'' intermediate files permanently; place them
+in the current directory and name them based on the source file. Thus,
+compiling @file{foo.c} with @option{-c -save-temps} produces files
+@file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
+preprocessed @file{foo.i} output file even though the compiler now
+normally uses an integrated preprocessor.
-@table @code
-@item @code{getenv}
-The @code{getenv} spec function takes two arguments: an environment
-variable name and a string. If the environment variable is not
-defined, a fatal error is issued. Otherwise, the return value is the
-value of the environment variable concatenated with the string. For
-example, if @env{TOPDIR} is defined as @file{/path/to/top}, then:
+When used in combination with the @option{-x} command-line option,
+@option{-save-temps} is sensible enough to avoid over writing an
+input source file with the same extension as an intermediate file.
+The corresponding intermediate file may be obtained by renaming the
+source file before using @option{-save-temps}.
+
+If you invoke GCC in parallel, compiling several different source
+files that share a common base name in different subdirectories or the
+same source file compiled for multiple output destinations, it is
+likely that the different parallel compilers will interfere with each
+other, and overwrite the temporary files. For instance:
@smallexample
-%:getenv(TOPDIR /include)
+gcc -save-temps -o outdir1/foo.o indir1/foo.c&
+gcc -save-temps -o outdir2/foo.o indir2/foo.c&
@end smallexample
-expands to @file{/path/to/top/include}.
+may result in @file{foo.i} and @file{foo.o} being written to
+simultaneously by both compilers.
-@item @code{if-exists}
-The @code{if-exists} spec function takes one argument, an absolute
-pathname to a file. If the file exists, @code{if-exists} returns the
-pathname. Here is a small example of its usage:
+@item -save-temps=obj
+@opindex save-temps=obj
+Store the usual ``temporary'' intermediate files permanently. If the
+@option{-o} option is used, the temporary files are based on the
+object file. If the @option{-o} option is not used, the
+@option{-save-temps=obj} switch behaves like @option{-save-temps}.
+
+For example:
@smallexample
-*startfile:
-crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
+gcc -save-temps=obj -c foo.c
+gcc -save-temps=obj -c bar.c -o dir/xbar.o
+gcc -save-temps=obj foobar.c -o dir2/yfoobar
@end smallexample
-@item @code{if-exists-else}
-The @code{if-exists-else} spec function is similar to the @code{if-exists}
-spec function, except that it takes two arguments. The first argument is
-an absolute pathname to a file. If the file exists, @code{if-exists-else}
-returns the pathname. If it does not exist, it returns the second argument.
-This way, @code{if-exists-else} can be used to select one file or another,
-based on the existence of the first. Here is a small example of its usage:
+@noindent
+creates @file{foo.i}, @file{foo.s}, @file{dir/xbar.i},
+@file{dir/xbar.s}, @file{dir2/yfoobar.i}, @file{dir2/yfoobar.s}, and
+@file{dir2/yfoobar.o}.
+
+@item -time@r{[}=@var{file}@r{]}
+@opindex time
+Report the CPU time taken by each subprocess in the compilation
+sequence. For C source files, this is the compiler proper and assembler
+(plus the linker if linking is done).
+
+Without the specification of an output file, the output looks like this:
@smallexample
-*startfile:
-crt0%O%s %:if-exists(crti%O%s) \
-%:if-exists-else(crtbeginT%O%s crtbegin%O%s)
+# cc1 0.12 0.01
+# as 0.00 0.01
@end smallexample
-@item @code{replace-outfile}
-The @code{replace-outfile} spec function takes two arguments. It looks for the
-first argument in the outfiles array and replaces it with the second argument. Here
-is a small example of its usage:
+The first number on each line is the ``user time'', that is time spent
+executing the program itself. The second number is ``system time'',
+time spent executing operating system routines on behalf of the program.
+Both numbers are in seconds.
+
+With the specification of an output file, the output is appended to the
+named file, and it looks like this:
@smallexample
-%@{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)@}
+0.12 0.01 cc1 @var{options}
+0.00 0.01 as @var{options}
@end smallexample
-@item @code{remove-outfile}
-The @code{remove-outfile} spec function takes one argument. It looks for the
-first argument in the outfiles array and removes it. Here is a small example
-its usage:
+The ``user time'' and the ``system time'' are moved before the program
+name, and the options passed to the program are displayed, so that one
+can later tell what file was being compiled, and with which options.
+
+@item -fdump-final-insns@r{[}=@var{file}@r{]}
+@opindex fdump-final-insns
+Dump the final internal representation (RTL) to @var{file}. If the
+optional argument is omitted (or if @var{file} is @code{.}), the name
+of the dump file is determined by appending @code{.gkd} to the
+compilation output file name.
+
+@item -fcompare-debug@r{[}=@var{opts}@r{]}
+@opindex fcompare-debug
+@opindex fno-compare-debug
+If no error occurs during compilation, run the compiler a second time,
+adding @var{opts} and @option{-fcompare-debug-second} to the arguments
+passed to the second compilation. Dump the final internal
+representation in both compilations, and print an error if they differ.
+
+If the equal sign is omitted, the default @option{-gtoggle} is used.
+
+The environment variable @env{GCC_COMPARE_DEBUG}, if defined, non-empty
+and nonzero, implicitly enables @option{-fcompare-debug}. If
+@env{GCC_COMPARE_DEBUG} is defined to a string starting with a dash,
+then it is used for @var{opts}, otherwise the default @option{-gtoggle}
+is used.
+
+@option{-fcompare-debug=}, with the equal sign but without @var{opts},
+is equivalent to @option{-fno-compare-debug}, which disables the dumping
+of the final representation and the second compilation, preventing even
+@env{GCC_COMPARE_DEBUG} from taking effect.
-@smallexample
-%:remove-outfile(-lm)
-@end smallexample
+To verify full coverage during @option{-fcompare-debug} testing, set
+@env{GCC_COMPARE_DEBUG} to say @option{-fcompare-debug-not-overridden},
+which GCC rejects as an invalid option in any actual compilation
+(rather than preprocessing, assembly or linking). To get just a
+warning, setting @env{GCC_COMPARE_DEBUG} to @samp{-w%n-fcompare-debug
+not overridden} will do.
-@item @code{pass-through-libs}
-The @code{pass-through-libs} spec function takes any number of arguments. It
-finds any @option{-l} options and any non-options ending in @file{.a} (which it
-assumes are the names of linker input library archive files) and returns a
-result containing all the found arguments each prepended by
-@option{-plugin-opt=-pass-through=} and joined by spaces. This list is
-intended to be passed to the LTO linker plugin.
+@item -fcompare-debug-second
+@opindex fcompare-debug-second
+This option is implicitly passed to the compiler for the second
+compilation requested by @option{-fcompare-debug}, along with options to
+silence warnings, and omitting other options that would cause
+side-effect compiler outputs to files or to the standard output. Dump
+files and preserved temporary files are renamed so as to contain the
+@code{.gk} additional extension during the second compilation, to avoid
+overwriting those generated by the first.
-@smallexample
-%:pass-through-libs(%G %L %G)
-@end smallexample
+When this option is passed to the compiler driver, it causes the
+@emph{first} compilation to be skipped, which makes it useful for little
+other than debugging the compiler proper.
-@item @code{print-asm-header}
-The @code{print-asm-header} function takes no arguments and simply
-prints a banner like:
+@item -gtoggle
+@opindex gtoggle
+Turn off generation of debug info, if leaving out this option
+generates it, or turn it on at level 2 otherwise. The position of this
+argument in the command line does not matter; it takes effect after all
+other options are processed, and it does so only once, no matter how
+many times it is given. This is mainly intended to be used with
+@option{-fcompare-debug}.
-@smallexample
-Assembler options
-=================
+@item -fvar-tracking-assignments-toggle
+@opindex fvar-tracking-assignments-toggle
+@opindex fno-var-tracking-assignments-toggle
+Toggle @option{-fvar-tracking-assignments}, in the same way that
+@option{-gtoggle} toggles @option{-g}.
-Use "-Wa,OPTION" to pass "OPTION" to the assembler.
-@end smallexample
+@item -Q
+@opindex Q
+Makes the compiler print out each function name as it is compiled, and
+print some statistics about each pass when it finishes.
-It is used to separate compiler options from assembler options
-in the @option{--target-help} output.
-@end table
+@item -ftime-report
+@opindex ftime-report
+Makes the compiler print some statistics about the time consumed by each
+pass when it finishes.
-@item %@{@code{S}@}
-Substitutes the @code{-S} switch, if that switch is given to GCC@.
-If that switch is not specified, this substitutes nothing. Note that
-the leading dash is omitted when specifying this option, and it is
-automatically inserted if the substitution is performed. Thus the spec
-string @samp{%@{foo@}} matches the command-line option @option{-foo}
-and outputs the command-line option @option{-foo}.
+@item -fira-verbose=@var{n}
+@opindex fira-verbose
+Control the verbosity of the dump file for the integrated register allocator.
+The default value is 5. If the value @var{n} is greater or equal to 10,
+the dump output is sent to stderr using the same format as @var{n} minus 10.
-@item %W@{@code{S}@}
-Like %@{@code{S}@} but mark last argument supplied within as a file to be
-deleted on failure.
+@item -flto-report
+@opindex flto-report
+Prints a report with internal details on the workings of the link-time
+optimizer. The contents of this report vary from version to version.
+It is meant to be useful to GCC developers when processing object
+files in LTO mode (via @option{-flto}).
-@item %@{@code{S}*@}
-Substitutes all the switches specified to GCC whose names start
-with @code{-S}, but which also take an argument. This is used for
-switches like @option{-o}, @option{-D}, @option{-I}, etc.
-GCC considers @option{-o foo} as being
-one switch whose name starts with @samp{o}. %@{o*@} substitutes this
-text, including the space. Thus two arguments are generated.
+Disabled by default.
-@item %@{@code{S}*&@code{T}*@}
-Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
-(the order of @code{S} and @code{T} in the spec is not significant).
-There can be any number of ampersand-separated variables; for each the
-wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
+@item -flto-report-wpa
+@opindex flto-report-wpa
+Like @option{-flto-report}, but only print for the WPA phase of Link
+Time Optimization.
-@item %@{@code{S}:@code{X}@}
-Substitutes @code{X}, if the @option{-S} switch is given to GCC@.
+@item -fmem-report
+@opindex fmem-report
+Makes the compiler print some statistics about permanent memory
+allocation when it finishes.
-@item %@{!@code{S}:@code{X}@}
-Substitutes @code{X}, if the @option{-S} switch is @emph{not} given to GCC@.
+@item -fmem-report-wpa
+@opindex fmem-report-wpa
+Makes the compiler print some statistics about permanent memory
+allocation for the WPA phase only.
-@item %@{@code{S}*:@code{X}@}
-Substitutes @code{X} if one or more switches whose names start with
-@code{-S} are specified to GCC@. Normally @code{X} is substituted only
-once, no matter how many such switches appeared. However, if @code{%*}
-appears somewhere in @code{X}, then @code{X} is substituted once
-for each matching switch, with the @code{%*} replaced by the part of
-that switch matching the @code{*}.
+@item -fpre-ipa-mem-report
+@opindex fpre-ipa-mem-report
+@item -fpost-ipa-mem-report
+@opindex fpost-ipa-mem-report
+Makes the compiler print some statistics about permanent memory
+allocation before or after interprocedural optimization.
-If @code{%*} appears as the last part of a spec sequence then a space
-is added after the end of the last substitution. If there is more
-text in the sequence, however, then a space is not generated. This
-allows the @code{%*} substitution to be used as part of a larger
-string. For example, a spec string like this:
+@item -fprofile-report
+@opindex fprofile-report
+Makes the compiler print some statistics about consistency of the
+(estimated) profile and effect of individual passes.
-@smallexample
-%@{mcu=*:--script=%*/memory.ld@}
-@end smallexample
+@item -fstack-usage
+@opindex fstack-usage
+Makes the compiler output stack usage information for the program, on a
+per-function basis. The filename for the dump is made by appending
+@file{.su} to the @var{auxname}. @var{auxname} is generated from the name of
+the output file, if explicitly specified and it is not an executable,
+otherwise it is the basename of the source file. An entry is made up
+of three fields:
-@noindent
-when matching an option like @option{-mcu=newchip} produces:
+@itemize
+@item
+The name of the function.
+@item
+A number of bytes.
+@item
+One or more qualifiers: @code{static}, @code{dynamic}, @code{bounded}.
+@end itemize
-@smallexample
---script=newchip/memory.ld
-@end smallexample
+The qualifier @code{static} means that the function manipulates the stack
+statically: a fixed number of bytes are allocated for the frame on function
+entry and released on function exit; no stack adjustments are otherwise made
+in the function. The second field is this fixed number of bytes.
-@item %@{.@code{S}:@code{X}@}
-Substitutes @code{X}, if processing a file with suffix @code{S}.
+The qualifier @code{dynamic} means that the function manipulates the stack
+dynamically: in addition to the static allocation described above, stack
+adjustments are made in the body of the function, for example to push/pop
+arguments around function calls. If the qualifier @code{bounded} is also
+present, the amount of these adjustments is bounded at compile time and
+the second field is an upper bound of the total amount of stack used by
+the function. If it is not present, the amount of these adjustments is
+not bounded at compile time and the second field only represents the
+bounded part.
-@item %@{!.@code{S}:@code{X}@}
-Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}.
+@item -fstats
+@opindex fstats
+Emit statistics about front-end processing at the end of the compilation.
+This option is supported only by the C++ front end, and
+the information is generally only useful to the G++ development team.
-@item %@{,@code{S}:@code{X}@}
-Substitutes @code{X}, if processing a file for language @code{S}.
+@item -fdbg-cnt-list
+@opindex fdbg-cnt-list
+Print the name and the counter upper bound for all debug counters.
-@item %@{!,@code{S}:@code{X}@}
-Substitutes @code{X}, if not processing a file for language @code{S}.
-@item %@{@code{S}|@code{P}:@code{X}@}
-Substitutes @code{X} if either @code{-S} or @code{-P} is given to
-GCC@. This may be combined with @samp{!}, @samp{.}, @samp{,}, and
-@code{*} sequences as well, although they have a stronger binding than
-the @samp{|}. If @code{%*} appears in @code{X}, all of the
-alternatives must be starred, and only the first matching alternative
-is substituted.
+@item -fdbg-cnt=@var{counter-value-list}
+@opindex fdbg-cnt
+Set the internal debug counter upper bound. @var{counter-value-list}
+is a comma-separated list of @var{name}:@var{value} pairs
+which sets the upper bound of each debug counter @var{name} to @var{value}.
+All debug counters have the initial upper bound of @code{UINT_MAX};
+thus @code{dbg_cnt} returns true always unless the upper bound
+is set by this option.
+For example, with @option{-fdbg-cnt=dce:10,tail_call:0},
+@code{dbg_cnt(dce)} returns true only for first 10 invocations.
-For example, a spec string like this:
+@item -print-file-name=@var{library}
+@opindex print-file-name
+Print the full absolute name of the library file @var{library} that
+would be used when linking---and don't do anything else. With this
+option, GCC does not compile or link anything; it just prints the
+file name.
-@smallexample
-%@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
-@end smallexample
+@item -print-multi-directory
+@opindex print-multi-directory
+Print the directory name corresponding to the multilib selected by any
+other switches present in the command line. This directory is supposed
+to exist in @env{GCC_EXEC_PREFIX}.
-@noindent
-outputs the following command-line options from the following input
-command-line options:
+@item -print-multi-lib
+@opindex print-multi-lib
+Print the mapping from multilib directory names to compiler switches
+that enable them. The directory name is separated from the switches by
+@samp{;}, and each switch starts with an @samp{@@} instead of the
+@samp{-}, without spaces between multiple switches. This is supposed to
+ease shell processing.
-@smallexample
-fred.c -foo -baz
-jim.d -bar -boggle
--d fred.c -foo -baz -boggle
--d jim.d -bar -baz -boggle
-@end smallexample
+@item -print-multi-os-directory
+@opindex print-multi-os-directory
+Print the path to OS libraries for the selected
+multilib, relative to some @file{lib} subdirectory. If OS libraries are
+present in the @file{lib} subdirectory and no multilibs are used, this is
+usually just @file{.}, if OS libraries are present in @file{lib@var{suffix}}
+sibling directories this prints e.g.@: @file{../lib64}, @file{../lib} or
+@file{../lib32}, or if OS libraries are present in @file{lib/@var{subdir}}
+subdirectories it prints e.g.@: @file{amd64}, @file{sparcv9} or @file{ev6}.
-@item %@{S:X; T:Y; :D@}
+@item -print-multiarch
+@opindex print-multiarch
+Print the path to OS libraries for the selected multiarch,
+relative to some @file{lib} subdirectory.
-If @code{S} is given to GCC, substitutes @code{X}; else if @code{T} is
-given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can
-be as many clauses as you need. This may be combined with @code{.},
-@code{,}, @code{!}, @code{|}, and @code{*} as needed.
+@item -print-prog-name=@var{program}
+@opindex print-prog-name
+Like @option{-print-file-name}, but searches for a program such as @command{cpp}.
+@item -print-libgcc-file-name
+@opindex print-libgcc-file-name
+Same as @option{-print-file-name=libgcc.a}.
-@end table
+This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
+but you do want to link with @file{libgcc.a}. You can do:
-The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar
-construct may contain other nested @samp{%} constructs or spaces, or
-even newlines. They are processed as usual, as described above.
-Trailing white space in @code{X} is ignored. White space may also
-appear anywhere on the left side of the colon in these constructs,
-except between @code{.} or @code{*} and the corresponding word.
+@smallexample
+gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
+@end smallexample
-The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are
-handled specifically in these constructs. If another value of
-@option{-O} or the negated form of a @option{-f}, @option{-m}, or
-@option{-W} switch is found later in the command line, the earlier
-switch value is ignored, except with @{@code{S}*@} where @code{S} is
-just one letter, which passes all matching options.
+@item -print-search-dirs
+@opindex print-search-dirs
+Print the name of the configured installation directory and a list of
+program and library directories @command{gcc} searches---and don't do anything else.
-The character @samp{|} at the beginning of the predicate text is used to
-indicate that a command should be piped to the following command, but
-only if @option{-pipe} is specified.
+This is useful when @command{gcc} prints the error message
+@samp{installation problem, cannot exec cpp0: No such file or directory}.
+To resolve this you either need to put @file{cpp0} and the other compiler
+components where @command{gcc} expects to find them, or you can set the environment
+variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
+Don't forget the trailing @samp{/}.
+@xref{Environment Variables}.
-It is built into GCC which switches take arguments and which do not.
-(You might think it would be useful to generalize this to allow each
-compiler's spec to say which switches take arguments. But this cannot
-be done in a consistent fashion. GCC cannot even decide which input
-files have been specified without knowing which switches take arguments,
-and it must know which input files to compile in order to tell which
-compilers to run).
+@item -print-sysroot
+@opindex print-sysroot
+Print the target sysroot directory that is used during
+compilation. This is the target sysroot specified either at configure
+time or using the @option{--sysroot} option, possibly with an extra
+suffix that depends on compilation options. If no target sysroot is
+specified, the option prints nothing.
-GCC also knows implicitly that arguments starting in @option{-l} are to be
-treated as compiler output files, and passed to the linker in their
-proper position among the other output files.
+@item -print-sysroot-headers-suffix
+@opindex print-sysroot-headers-suffix
+Print the suffix added to the target sysroot when searching for
+headers, or give an error if the compiler is not configured with such
+a suffix---and don't do anything else.
-@c man begin OPTIONS
+@item -dumpmachine
+@opindex dumpmachine
+Print the compiler's target machine (for example,
+@samp{i686-pc-linux-gnu})---and don't do anything else.
-@node Target Options
-@section Specifying Target Machine and Compiler Version
-@cindex target options
-@cindex cross compiling
-@cindex specifying machine version
-@cindex specifying compiler version and target machine
-@cindex compiler version, specifying
-@cindex target machine, specifying
+@item -dumpversion
+@opindex dumpversion
+Print the compiler version (for example, @code{3.0})---and don't do
+anything else.
-The usual way to run GCC is to run the executable called @command{gcc}, or
-@command{@var{machine}-gcc} when cross-compiling, or
-@command{@var{machine}-gcc-@var{version}} to run a version other than the
-one that was installed last.
+@item -dumpspecs
+@opindex dumpspecs
+Print the compiler's built-in specs---and don't do anything else. (This
+is used when GCC itself is being built.) @xref{Spec Files}.
+@end table
@node Submodel Options
-@section Hardware Models and Configurations
+@section Machine-Dependent Options
@cindex submodel options
@cindex specifying hardware config
@cindex hardware models and configurations, specifying
-@cindex machine dependent options
+@cindex target-dependent options
+@cindex machine-dependent options
-Each target machine types can have its own
-special options, starting with @samp{-m}, to choose among various
-hardware models or configurations---for example, 68010 vs 68020,
-floating coprocessor or none. A single installed version of the
-compiler can compile for any model or configuration, according to the
-options specified.
+Each target machine supported by GCC can have its own options---for
+example, to allow you to compile for a particular processor variant or
+ABI, or to control optimizations specific to that machine. By
+convention, the names of machine-specific options start with
+@samp{-m}.
-Some configurations of the compiler also support additional special
+Some configurations of the compiler also support additional target-specific
options, usually for compatibility with other compilers on the same
platform.
@item -mgeneral-regs-only
@opindex mgeneral-regs-only
-Generate code which uses only the general-purpose registers. This is equivalent
-to feature modifier @option{nofp} of @option{-march} or @option{-mcpu}, except
-that @option{-mgeneral-regs-only} takes precedence over any conflicting feature
-modifier regardless of sequence.
+Generate code which uses only the general-purpose registers. This will prevent
+the compiler from using floating-point and Advanced SIMD registers but will not
+impose any restrictions on the assembler.
@item -mlittle-endian
@opindex mlittle-endian
@itemx -mno-omit-leaf-frame-pointer
@opindex momit-leaf-frame-pointer
@opindex mno-omit-leaf-frame-pointer
-Omit or keep the frame pointer in leaf functions. The former behaviour is the
+Omit or keep the frame pointer in leaf functions. The former behavior is the
default.
@item -mtls-dialect=desc
This erratum workaround is made at link time and this will only pass the
corresponding flag to the linker.
+@item -mlow-precision-recip-sqrt
+@item -mno-low-precision-recip-sqrt
+@opindex -mlow-precision-recip-sqrt
+@opindex -mno-low-precision-recip-sqrt
+When calculating the reciprocal square root approximation,
+uses one less step than otherwise, thus reducing latency and precision.
+This is only relevant if @option{-ffast-math} enables the reciprocal square root
+approximation, which in turn depends on the target processor.
+
@item -march=@var{name}
@opindex march
-Specify the name of the target architecture, optionally suffixed by one or
+Specify the name of the target architecture and, optionally, one or
more feature modifiers. This option has the form
@option{-march=@var{arch}@r{@{}+@r{[}no@r{]}@var{feature}@r{@}*}}.
-The permissible values for @var{arch} are @samp{armv8-a} or
-@samp{armv8.1-a}.
+The permissible values for @var{arch} are @samp{armv8-a},
+@samp{armv8.1-a} or @var{native}.
-For the permissible values for @var{feature}, see the sub-section on
-@ref{aarch64-feature-modifiers,,@option{-march} and @option{-mcpu}
+The value @samp{armv8.1-a} implies @samp{armv8-a} and enables compiler
+support for the ARMv8.1 architecture extension. In particular, it
+enables the @samp{+crc} and @samp{+lse} features.
+
+The value @samp{native} is available on native AArch64 GNU/Linux and
+causes the compiler to pick the architecture of the host system. This
+option has no effect if the compiler is unable to recognize the
+architecture of the host system,
+
+The permissible values for @var{feature} are listed in the sub-section
+on @ref{aarch64-feature-modifiers,,@option{-march} and @option{-mcpu}
Feature Modifiers}. Where conflicting feature modifiers are
specified, the right-most feature is used.
-Additionally on native AArch64 GNU/Linux systems the value
-@samp{native} is available. This option causes the compiler to pick the
-architecture of the host system. If the compiler is unable to recognize the
-architecture of the host system this option has no effect.
-
GCC uses @var{name} to determine what kind of instructions it can emit
when generating assembly code. If @option{-march} is specified
without either of @option{-mtune} or @option{-mcpu} also being
@opindex mtune
Specify the name of the target processor for which GCC should tune the
performance of the code. Permissible values for this option are:
-@samp{generic}, @samp{cortex-a53}, @samp{cortex-a57}, @samp{cortex-a72},
-@samp{exynos-m1}, @samp{thunderx}, @samp{xgene1}.
+@samp{generic}, @samp{cortex-a35}, @samp{cortex-a53}, @samp{cortex-a57},
+@samp{cortex-a72}, @samp{exynos-m1}, @samp{qdf24xx}, @samp{thunderx},
+@samp{xgene1}.
Additionally, this option can specify that GCC should tune the performance
of the code for a big.LITTLE system. Permissible values for this
Additionally on native AArch64 GNU/Linux systems the value
@samp{native} is available. This option causes the compiler to pick
the architecture of and tune the performance of the code for the
-processor of the host system. If the compiler is unable to recognize
-the processor of the host system this option has no effect.
+processor of the host system. This option has no effect if the
+compiler is unable to recognize the architecture of the host system.
Where none of @option{-mtune=}, @option{-mcpu=} or @option{-march=}
are specified, the code is tuned to perform well across a range
Additionally on native AArch64 GNU/Linux systems the value
@samp{native} is available. This option causes the compiler to tune
-the performance of the code for the processor of the host system. If
-the compiler is unable to recognize the processor of the host system
-this option has no effect.
+the performance of the code for the processor of the host system.
+This option has no effect if the compiler is unable to recognize the
+architecture of the host system.
GCC uses @var{name} to determine what kind of instructions it can emit when
generating assembly code (as if by @option{-march}) and to determine
@table @samp
@item crc
-Enable CRC extension.
+Enable CRC extension. This is on by default for
+@option{-march=armv8.1-a}.
@item crypto
Enable Crypto extension. This also enables Advanced SIMD and floating-point
instructions.
instructions. This is on by default for all possible values for options
@option{-march} and @option{-mcpu}.
@item lse
-Enable Large System Extension instructions.
-@item pan
-Enable Privileged Access Never support.
-@item lor
-Enable Limited Ordering Regions support.
-@item rdma
-Enable ARMv8.1 Advanced SIMD instructions. This implies Advanced SIMD
-is enabled.
+Enable Large System Extension instructions. This is on by default for
+@option{-march=armv8.1-a}.
@end table
@item -mprefer-short-insn-regs
@opindex mprefer-short-insn-regs
-Preferrentially allocate registers that allow short instruction generation.
+Preferentially allocate registers that allow short instruction generation.
This can result in increased instruction count, so this may either reduce or
increase overall code size.
@item -mbarrel-shifter
@opindex mbarrel-shifter
Generate instructions supported by barrel shifter. This is the default
-unless @option{-mcpu=ARC601} is in effect.
+unless @option{-mcpu=ARC601} or @samp{-mcpu=ARCEM} is in effect.
@item -mcpu=@var{cpu}
@opindex mcpu
@opindex mA6
@opindex mARC600
@item ARC600
+@item arc600
Compile for ARC600. Aliases: @option{-mA6}, @option{-mARC600}.
@item ARC601
+@item arc601
@opindex mARC601
Compile for ARC601. Alias: @option{-mARC601}.
@item ARC700
+@item arc700
@opindex mA7
@opindex mARC700
Compile for ARC700. Aliases: @option{-mA7}, @option{-mARC700}.
This is the default when configured with @option{--with-cpu=arc700}@.
+
+@item ARCEM
+@item arcem
+Compile for ARC EM.
+
+@item ARCHS
+@item archs
+Compile for ARC HS.
@end table
@item -mdpfp
@opindex mswap
Generate swap instructions.
+@item -matomic
+@opindex matomic
+This enables Locked Load/Store Conditional extension to implement
+atomic memopry built-in functions. Not available for ARC 6xx or ARC
+EM cores.
+
+@item -mdiv-rem
+@opindex mdiv-rem
+Enable DIV/REM instructions for ARCv2 cores.
+
+@item -mcode-density
+@opindex mcode-density
+Enable code density instructions for ARC EM, default on for ARC HS.
+
+@item -mll64
+@opindex mll64
+Enable double load/store operations for ARC HS cores.
+
+@item -mmpy-option=@var{multo}
+@opindex mmpy-option
+Compile ARCv2 code with a multiplier design option. @samp{wlh1} is
+the default value. The recognized values for @var{multo} are:
+
+@table @samp
+@item 0
+No multiplier available.
+
+@item 1
+@opindex w
+The multiply option is set to w: 16x16 multiplier, fully pipelined.
+The following instructions are enabled: MPYW, and MPYUW.
+
+@item 2
+@opindex wlh1
+The multiply option is set to wlh1: 32x32 multiplier, fully
+pipelined (1 stage). The following instructions are additionally
+enabled: MPY, MPYU, MPYM, MPYMU, and MPY_S.
+
+@item 3
+@opindex wlh2
+The multiply option is set to wlh2: 32x32 multiplier, fully pipelined
+(2 stages). The following instructions are additionally enabled: MPY,
+MPYU, MPYM, MPYMU, and MPY_S.
+
+@item 4
+@opindex wlh3
+The multiply option is set to wlh3: Two 16x16 multiplier, blocking,
+sequential. The following instructions are additionally enabled: MPY,
+MPYU, MPYM, MPYMU, and MPY_S.
+
+@item 5
+@opindex wlh4
+The multiply option is set to wlh4: One 16x16 multiplier, blocking,
+sequential. The following instructions are additionally enabled: MPY,
+MPYU, MPYM, MPYMU, and MPY_S.
+
+@item 6
+@opindex wlh5
+The multiply option is set to wlh5: One 32x4 multiplier, blocking,
+sequential. The following instructions are additionally enabled: MPY,
+MPYU, MPYM, MPYMU, and MPY_S.
+
+@end table
+
+This option is only available for ARCv2 cores@.
+
+@item -mfpu=@var{fpu}
+@opindex mfpu
+Enables specific floating-point hardware extension for ARCv2
+core. Supported values for @var{fpu} are:
+
+@table @samp
+
+@item fpus
+@opindex fpus
+Enables support for single precision floating point hardware
+extensions@.
+
+@item fpud
+@opindex fpud
+Enables support for double precision floating point hardware
+extensions. The single precision floating point extension is also
+enabled. Not available for ARC EM@.
+
+@item fpuda
+@opindex fpuda
+Enables support for double precision floating point hardware
+extensions using double precision assist instructions. The single
+precision floating point extension is also enabled. This option is
+only available for ARC EM@.
+
+@item fpuda_div
+@opindex fpuda_div
+Enables support for double precision floating point hardware
+extensions using double precision assist instructions, and simple
+precision square-root and divide hardware extensions. The single
+precision floating point extension is also enabled. This option is
+only available for ARC EM@.
+
+@item fpuda_fma
+@opindex fpuda_fma
+Enables support for double precision floating point hardware
+extensions using double precision assist instructions, and simple
+precision fused multiple and add hardware extension. The single
+precision floating point extension is also enabled. This option is
+only available for ARC EM@.
+
+@item fpuda_all
+@opindex fpuda_all
+Enables support for double precision floating point hardware
+extensions using double precision assist instructions, and all simple
+precision hardware extensions. The single precision floating point
+extension is also enabled. This option is only available for ARC EM@.
+
+@item fpus_div
+@opindex fpus_div
+Enables support for single precision floating point, and single
+precision square-root and divide hardware extensions@.
+
+@item fpud_div
+@opindex fpud_div
+Enables support for double precision floating point, and double
+precision square-root and divide hardware extensions. This option
+includes option @samp{fpus_div}. Not available for ARC EM@.
+
+@item fpus_fma
+@opindex fpus_fma
+Enables support for single precision floating point, and single
+precision fused multiple and add hardware extensions@.
+
+@item fpud_fma
+@opindex fpud_fma
+Enables support for double precision floating point, and double
+precision fused multiple and add hardware extensions. This option
+includes option @samp{fpus_fma}. Not available for ARC EM@.
+
+@item fpus_all
+@opindex fpus_all
+Enables support for all single precision floating point hardware
+extensions@.
+
+@item fpud_all
+@opindex fpud_all
+Enables support for all single and double precision floating point
+hardware extensions. Not available for ARC EM@.
+
+@end table
+
@end table
The following options are passed through to the assembler, and also
@c semantically relevant code generation options
@table @gcctabopt
-@item -mepilogue-cfi
-@opindex mepilogue-cfi
-Enable generation of call frame information for epilogues.
-
-@item -mno-epilogue-cfi
-@opindex mno-epilogue-cfi
-Disable generation of call frame information for epilogues.
-
@item -mlong-calls
@opindex mlong-calls
Generate call insns as register indirect calls, thus providing access
@item -mlra-priority-noncompact
@opindex mlra-priority-noncompact
-Reduce target regsiter priority for r0..r3 / r12..r15.
+Reduce target register priority for r0..r3 / r12..r15.
@item -mno-millicode
@opindex mno-millicode
@samp{armv6}, @samp{armv6j},
@samp{armv6t2}, @samp{armv6z}, @samp{armv6kz}, @samp{armv6-m},
@samp{armv7}, @samp{armv7-a}, @samp{armv7-r}, @samp{armv7-m}, @samp{armv7e-m},
-@samp{armv7ve}, @samp{armv8-a}, @samp{armv8-a+crc},
-@samp{iwmmxt}, @samp{iwmmxt2}, @samp{ep9312}.
+@samp{armv7ve}, @samp{armv8-a}, @samp{armv8-a+crc}, @samp{armv8.1-a},
+@samp{armv8.1-a+crc}, @samp{iwmmxt}, @samp{iwmmxt2}, @samp{ep9312}.
+
+Architecture revisions older than @option{armv4t} are deprecated.
@option{-march=armv7ve} is the armv7-a architecture with virtualization
extensions.
@samp{arm1156t2-s}, @samp{arm1156t2f-s}, @samp{arm1176jz-s}, @samp{arm1176jzf-s},
@samp{generic-armv7-a}, @samp{cortex-a5}, @samp{cortex-a7}, @samp{cortex-a8},
@samp{cortex-a9}, @samp{cortex-a12}, @samp{cortex-a15}, @samp{cortex-a17},
-@samp{cortex-a53}, @samp{cortex-a57}, @samp{cortex-a72},
-@samp{cortex-r4},
-@samp{cortex-r4f}, @samp{cortex-r5}, @samp{cortex-r7}, @samp{cortex-m7},
+@samp{cortex-a32}, @samp{cortex-a35}, @samp{cortex-a53}, @samp{cortex-a57},
+@samp{cortex-a72}, @samp{cortex-r4},
+@samp{cortex-r4f}, @samp{cortex-r5}, @samp{cortex-r7}, @samp{cortex-r8},
+@samp{cortex-m7},
@samp{cortex-m4},
@samp{cortex-m3},
@samp{cortex-m1},
@samp{cortex-m0.small-multiply},
@samp{cortex-m0plus.small-multiply},
@samp{exynos-m1},
+@samp{qdf24xx},
@samp{marvell-pj4},
@samp{xscale}, @samp{iwmmxt}, @samp{iwmmxt2}, @samp{ep9312},
@samp{fa526}, @samp{fa626},
@samp{vfpv3xd-fp16}, @samp{neon}, @samp{neon-fp16}, @samp{vfpv4},
@samp{vfpv4-d16}, @samp{fpv4-sp-d16}, @samp{neon-vfpv4},
@samp{fpv5-d16}, @samp{fpv5-sp-d16},
-@samp{fp-armv8}, @samp{neon-fp-armv8}, and @samp{crypto-neon-fp-armv8}.
+@samp{fp-armv8}, @samp{neon-fp-armv8} and @samp{crypto-neon-fp-armv8}.
If @option{-msoft-float} is specified this specifies the format of
floating-point values.
floating-point arithmetic (in particular denormal values are treated as
zero), so the use of NEON instructions may lead to a loss of precision.
+You can also set the fpu name at function level by using the @code{target("fpu=")} function attributes (@pxref{ARM Function Attributes}) or pragmas (@pxref{Function Specific Option Pragmas}).
+
@item -mfp16-format=@var{name}
@opindex mfp16-format
Specify the format of the @code{__fp16} half-precision floating-point type.
@item -masm-syntax-unified
@opindex masm-syntax-unified
Assume inline assembler is using unified asm syntax. The default is
-currently off which implies divided syntax. Currently this option is
-available only for Thumb1 and has no effect on ARM state and Thumb2.
-However, this may change in future releases of GCC. Divided syntax
-should be considered deprecated.
+currently off which implies divided syntax. This option has no impact
+on Thumb2. However, this may change in future releases of GCC.
+Divided syntax should be considered deprecated.
@item -mrestrict-it
@opindex mrestrict-it
The compiler never sets @code{EIND}.
@item
-The compiler uses @code{EIND} implicitely in @code{EICALL}/@code{EIJMP}
+The compiler uses @code{EIND} implicitly in @code{EICALL}/@code{EIJMP}
instructions or might read @code{EIND} directly in order to emulate an
indirect call/jump by means of a @code{RET} instruction.
Enable Local Register Allocation. This is still experimental for FT32,
so by default the compiler uses standard reload.
+@item -mnodiv
+@opindex mnodiv
+Do not use div and mod instructions.
+
@end table
@node FRV Options
@itemx -mdwarf2-asm
@opindex mno-dwarf2-asm
@opindex mdwarf2-asm
-Don't (or do) generate assembler code for the DWARF 2 line number debugging
+Don't (or do) generate assembler code for the DWARF line number debugging
info. This may be useful when not using the GNU assembler.
@item -mearly-stop-bits
(Dis/En)able data speculative scheduling before reload.
This results in generation of @code{ld.a} instructions and
the corresponding check instructions (@code{ld.c} / @code{chk.a}).
-The default is 'disable'.
+The default setting is disabled.
@item -msched-ar-data-spec
@itemx -mno-sched-ar-data-spec
(En/Dis)able data speculative scheduling after reload.
This results in generation of @code{ld.a} instructions and
the corresponding check instructions (@code{ld.c} / @code{chk.a}).
-The default is 'enable'.
+The default setting is enabled.
@item -mno-sched-control-spec
@itemx -msched-control-spec
available only during region scheduling (i.e.@: before reload).
This results in generation of the @code{ld.s} instructions and
the corresponding check instructions @code{chk.s}.
-The default is 'disable'.
+The default setting is disabled.
@item -msched-br-in-data-spec
@itemx -mno-sched-br-in-data-spec
(En/Dis)able speculative scheduling of the instructions that
are dependent on the data speculative loads before reload.
This is effective only with @option{-msched-br-data-spec} enabled.
-The default is 'enable'.
+The default setting is enabled.
@item -msched-ar-in-data-spec
@itemx -mno-sched-ar-in-data-spec
(En/Dis)able speculative scheduling of the instructions that
are dependent on the data speculative loads after reload.
This is effective only with @option{-msched-ar-data-spec} enabled.
-The default is 'enable'.
+The default setting is enabled.
@item -msched-in-control-spec
@itemx -mno-sched-in-control-spec
(En/Dis)able speculative scheduling of the instructions that
are dependent on the control speculative loads.
This is effective only with @option{-msched-control-spec} enabled.
-The default is 'enable'.
+The default setting is enabled.
@item -mno-sched-prefer-non-data-spec-insns
@itemx -msched-prefer-non-data-spec-insns
If enabled, data-speculative instructions are chosen for schedule
only if there are no other choices at the moment. This makes
the use of the data speculation much more conservative.
-The default is 'disable'.
+The default setting is disabled.
@item -mno-sched-prefer-non-control-spec-insns
@itemx -msched-prefer-non-control-spec-insns
If enabled, control-speculative instructions are chosen for schedule
only if there are no other choices at the moment. This makes
the use of the control speculation much more conservative.
-The default is 'disable'.
+The default setting is disabled.
@item -mno-sched-count-spec-in-critical-path
@itemx -msched-count-spec-in-critical-path
If enabled, speculative dependencies are considered during
computation of the instructions priorities. This makes the use of the
speculation a bit more conservative.
-The default is 'disable'.
+The default setting is disabled.
@item -msched-spec-ldc
@opindex msched-spec-ldc
support these registers. When using the o32 FPXX ABI, @option{-mno-odd-spreg}
is set by default.
-@item -mcompact-branches=never
-@itemx -mcompact-branches=optimal
-@itemx -mcompact-branches=always
-@opindex mcompact-branches=never
-@opindex mcompact-branches=optimal
-@opindex mcompact-branches=always
-These options control which form of branches will be generated. The
-default is @option{-mcompact-branches=optimal}.
-
-The @option{-mcompact-branches=never} option ensures that compact branch
-instructions will never be generated.
-
-The @option{-mcompact-branches=always} option ensures that a compact
-branch instruction will be generated if available. If a compact branch
-instruction is not available, a delay slot form of the branch will be
-used instead.
-
-This option is supported from MIPS Release 6 onwards.
-
-The @option{-mcompact-branches=optimal} option will cause a delay slot
-branch to be used if one is available in the current ISA and the delay
-slot is successfully filled. If the delay slot is not filled, a compact
-branch will be chosen if one is available.
-
@item -mabs=2008
@itemx -mabs=legacy
@opindex mabs=2008
Likely instructions are not be generated by default because the MIPS32
and MIPS64 architectures specifically deprecate their use.
+@item -mcompact-branches=never
+@itemx -mcompact-branches=optimal
+@itemx -mcompact-branches=always
+@opindex mcompact-branches=never
+@opindex mcompact-branches=optimal
+@opindex mcompact-branches=always
+These options control which form of branches will be generated. The
+default is @option{-mcompact-branches=optimal}.
+
+The @option{-mcompact-branches=never} option ensures that compact branch
+instructions will never be generated.
+
+The @option{-mcompact-branches=always} option ensures that a compact
+branch instruction will be generated if available. If a compact branch
+instruction is not available, a delay slot form of the branch will be
+used instead.
+
+This option is supported from MIPS Release 6 onwards.
+
+The @option{-mcompact-branches=optimal} option will cause a delay slot
+branch to be used if one is available in the current ISA and the delay
+slot is successfully filled. If the delay slot is not filled, a compact
+branch will be chosen if one is available.
+
@item -mfp-exceptions
@itemx -mno-fp-exceptions
@opindex mfp-exceptions
@opindex mrelax-pic-calls
Try to turn PIC calls that are normally dispatched via register
@code{$25} into direct calls. This is only possible if the linker can
-resolve the destination at link-time and if the destination is within
+resolve the destination at link time and if the destination is within
range for a direct call.
@option{-mrelax-pic-calls} is the default if GCC was configured to use
This option is also passed on to the assembler.
+@item -mwarn-mcu
+@itemx -mno-warn-mcu
+@opindex mwarn-mcu
+@opindex mno-warn-mcu
+This option enables or disables warnings about conflicts between the
+MCU name specified by the @option{-mmcu} option and the ISA set by the
+@option{-mcpu} option and/or the hardware multiply support set by the
+@option{-mhwmult} option. It also toggles warnings about unrecognized
+MCU names. This option is on by default.
+
@item -mcpu=
@opindex mcpu=
Specifies the ISA to use. Accepted values are @samp{msp430},
@samp{f5series} for the 16/32-bit multiply supported by F5-series MCUs.
A value of @samp{auto} can also be given. This tells GCC to deduce
the hardware multiply support based upon the MCU name provided by the
-@option{-mmcu} option. If no @option{-mmcu} option is specified then
-@samp{32bit} hardware multiply support is assumed. If the MCU name is
-not recognised then no hardware multiply support is assumed.
-@code{auto} is the default setting.
+@option{-mmcu} option. If no @option{-mmcu} option is specified or if
+the MCU name is not recognized then no hardware multiply support is
+assumed. @code{auto} is the default setting.
Hardware multiplies are normally performed by calling a library
routine. This saves space in the generated code. When compiling at
@code{upper}, @code{either} or @code{any}. The first three behave
like the corresponding attribute. The fourth possible value -
@code{any} - is the default. It leaves placement entirely up to the
-linker script and how it assigns the standard sections (.text, .data
-etc) to the memory regions.
+linker script and how it assigns the standard sections
+(@code{.text}, @code{.data}, etc) to the memory regions.
@item -msilicon-errata=
@opindex msilicon-errata
Generate GP-relative accesses for all data objects in the program. If you
use this option, the entire data and BSS segments
of your program must fit in 64K of memory and you must use an appropriate
-linker script to allocate them within the addressible range of the
+linker script to allocate them within the addressable range of the
global pointer.
@item all
Generate GP-relative addresses for function pointers as well as data
pointers. If you use this option, the entire text, data, and BSS segments
of your program must fit in 64K of memory and you must use an appropriate
-linker script to allocate them within the addressible range of the
+linker script to allocate them within the addressable range of the
global pointer.
@end table
Link in code for a __main kernel. This is for stand-alone instead of
offloading execution.
+@item -moptimize
+@opindex moptimize
+Apply partitioned execution optimizations. This is the default when any
+level of optimization is selected.
+
@end table
@node PDP-11 Options
@option{-mmul=none} option on the command line. Thus specifying
@option{-mcpu=g13} enables the use of the G13 hardware multiply
peripheral and specifying @option{-mcpu=g10} disables the use of
-hardware multipications altogether.
+hardware multiplications altogether.
Note, although the RL78/G14 core is the default target, specifying
@option{-mcpu=g14} or @option{-mcpu=rl78} on the command line does
-change the behaviour of the toolchain since it also enables G14
+change the behavior of the toolchain since it also enables G14
hardware multiply support. If these options are not specified on the
command line then software multiplication routines will be used even
though the code targets the RL78 core. This is for backwards
@samp{e300c3}, @samp{e500mc}, @samp{e500mc64}, @samp{e5500},
@samp{e6500}, @samp{ec603e}, @samp{G3}, @samp{G4}, @samp{G5},
@samp{titan}, @samp{power3}, @samp{power4}, @samp{power5}, @samp{power5+},
-@samp{power6}, @samp{power6x}, @samp{power7}, @samp{power8}, @samp{powerpc},
-@samp{powerpc64}, @samp{powerpc64le}, and @samp{rs64}.
+@samp{power6}, @samp{power6x}, @samp{power7}, @samp{power8},
+@samp{power9}, @samp{powerpc}, @samp{powerpc64}, @samp{powerpc64le},
+and @samp{rs64}.
@option{-mcpu=powerpc}, @option{-mcpu=powerpc64}, and
@option{-mcpu=powerpc64le} specify pure 32-bit PowerPC (either
-mpowerpc-gpopt -mpowerpc-gfxopt -msingle-float -mdouble-float @gol
-msimple-fpu -mstring -mmulhw -mdlmzb -mmfpgpr -mvsx @gol
-mcrypto -mdirect-move -mpower8-fusion -mpower8-vector @gol
--mquad-memory -mquad-memory-atomic}
+-mquad-memory -mquad-memory-atomic -mmodulo -mfloat128 -mfloat128-hardware @gol
+-mpower9-fusion -mpower9-vector}
The particular options set for any particular CPU varies between
compiler versions, depending on what setting seems to produce optimal
enhancements.
When @option{-maltivec} is used, rather than @option{-maltivec=le} or
-@option{-maltivec=be}, the element order for Altivec intrinsics such
+@option{-maltivec=be}, the element order for AltiVec intrinsics such
as @code{vec_splat}, @code{vec_extract}, and @code{vec_insert}
match array element order corresponding to the endianness of the
target. That is, element zero identifies the leftmost element in a
@item -maltivec=be
@opindex maltivec=be
-Generate Altivec instructions using big-endian element order,
+Generate AltiVec instructions using big-endian element order,
regardless of whether the target is big- or little-endian. This is
the default when targeting a big-endian platform.
-The element order is used to interpret element numbers in Altivec
+The element order is used to interpret element numbers in AltiVec
intrinsics such as @code{vec_splat}, @code{vec_extract}, and
@code{vec_insert}. By default, these match array element order
corresponding to the endianness for the target.
@item -maltivec=le
@opindex maltivec=le
-Generate Altivec instructions using little-endian element order,
+Generate AltiVec instructions using little-endian element order,
regardless of whether the target is big- or little-endian. This is
the default when targeting a little-endian platform. This option is
currently ignored when targeting a big-endian platform.
-The element order is used to interpret element numbers in Altivec
+The element order is used to interpret element numbers in AltiVec
intrinsics such as @code{vec_splat}, @code{vec_extract}, and
@code{vec_insert}. By default, these match array element order
corresponding to the endianness for the target.
If the @option{-mno-upper-regs} option is used, it turns off both
@option{-mupper-regs-sf} and @option{-mupper-regs-df} options.
+@item -mfloat128
+@itemx -mno-float128
+@opindex mfloat128
+@opindex mno-float128
+Enable/disable the @var{__float128} keyword for IEEE 128-bit floating point
+and use either software emulation for IEEE 128-bit floating point or
+hardware instructions.
+
+The VSX instruction set (@option{-mvsx}, @option{-mcpu=power7}, or
+@option{-mcpu=power8}) must be enabled to use the @option{-mfloat128}
+option. The @code{-mfloat128} option only works on PowerPC 64-bit
+Linux systems.
+
+@item -mfloat128-hardware
+@itemx -mno-float128-hardware
+@opindex mfloat128-hardware
+@opindex mno-float128-hardware
+Enable/disable using ISA 3.0 hardware instructions to support the
+@var{__float128} data type.
+
+@item -mmodulo
+@itemx -mno-modulo
+@opindex mmodulo
+@opindex mno-module
+Generate code that uses (does not use) the ISA 3.0 integer modulo
+instructions. The @option{-mmodulo} option is enabled by default
+with the @option{-mcpu=power9} option.
+
+@item -mpower9-fusion
+@itemx -mno-power9-fusion
+@opindex mpower9-fusion
+@opindex mno-power9-fusion
+Generate code that keeps (does not keeps) some operations adjacent so
+that the instructions can be fused together on power9 and later
+processors.
+
+@item -mpower9-vector
+@itemx -mno-power9-vector
+@opindex mpower9-vector
+@opindex mno-power9-vector
+Generate code that uses (does not use) the vector and scalar
+instructions that were added in version 2.07 of the PowerPC ISA. Also
+enable the use of built-in functions that allow more direct access to
+the vector instructions.
+
@item -mfloat-gprs=@var{yes/single/double/no}
@itemx -mfloat-gprs
@opindex mfloat-gprs
square root and divide for floating-point arguments. You should use
the @option{-ffast-math} option when using @option{-mrecip} (or at
least @option{-funsafe-math-optimizations},
-@option{-finite-math-only}, @option{-freciprocal-math} and
+@option{-ffinite-math-only}, @option{-freciprocal-math} and
@option{-fno-trapping-math}). Note that while the throughput of the
sequence is generally higher than the throughput of the non-reciprocal
instruction, the precision of the sequence can be decreased by up to 2
When the instructions are enabled GCC defines the C preprocessor
symbol @code{__RX_ALLOW_STRING_INSNS__}, otherwise it defines the
symbol @code{__RX_DISALLOW_STRING_INSNS__}.
+
+@item -mjsr
+@itemx -mno-jsr
+@opindex mjsr
+@opindex mno-jsr
+Use only (or not only) @code{JSR} instructions to access functions.
+This option can be used when code size exceeds the range of @code{BSR}
+instructions. Note that @option{-mno-jsr} does not mean to not use
+@code{JSR} but instead means that any type of branch may be used.
@end table
@emph{Note:} The generic GCC command-line option @option{-ffixed-@var{reg}}
Store (do not store) the address of the caller's frame as backchain pointer
into the callee's stack frame.
A backchain may be needed to allow debugging using tools that do not understand
-DWARF 2 call frame information.
+DWARF call frame information.
When @option{-mno-packed-stack} is in effect, the backchain pointer is stored
at the bottom of the stack frame; when @option{-mpacked-stack} is in effect,
the backchain is placed into the topmost word of the 96/160 byte register
available when GNU extensions are enabled. It will not be expanded
when requesting strict standard compliance e.g. with @option{-std=c99}.
In addition to the GCC low-level builtins @option{-mzvector} enables
-a set of builtins added for compatibility with Altivec-style
+a set of builtins added for compatibility with AltiVec-style
implementations like Power and Cell. In order to make use of these
builtins the header file @file{vecintrin.h} needs to be included.
@option{-mzvector} is disabled by default.
@item -march=@var{cpu-type}
@opindex march
-Generate code that runs on @var{cpu-type}, which is the name of a system
-representing a certain processor type. Possible values for
-@var{cpu-type} are @samp{g5}, @samp{g6}, @samp{z900}, @samp{z990},
-@samp{z9-109}, @samp{z9-ec}, @samp{z10}, @samp{z196}, @samp{zEC12},
-and @samp{z13}.
-When generating code using the instructions available on z/Architecture,
-the default is @option{-march=z900}. Otherwise, the default is
-@option{-march=g5}.
+Generate code that runs on @var{cpu-type}, which is the name of a
+system representing a certain processor type. Possible values for
+@var{cpu-type} are @samp{z900}, @samp{z990}, @samp{z9-109},
+@samp{z9-ec}, @samp{z10}, @samp{z196}, @samp{zEC12}, and @samp{z13}.
+The default is @option{-march=z900}. @samp{g5} and @samp{g6} are
+deprecated and will be removed with future releases.
@item -mtune=@var{cpu-type}
@opindex mtune
handling of cases where the result of a comparison is unordered. By default
@option{-mieee} is implicitly enabled. If @option{-ffinite-math-only} is
enabled @option{-mno-ieee} is implicitly set, which results in faster
-floating-point greater-equal and less-equal comparisons. The implcit settings
+floating-point greater-equal and less-equal comparisons. The implicit settings
can be overridden by specifying either @option{-mieee} or @option{-mno-ieee}.
@item -minline-ic_invalidate
only for the @code{casa} instruction emitted for the LEON3 processor. This
is the default.
-@item -mno-faster-structs
-@itemx -mfaster-structs
-@opindex mno-faster-structs
+@item -mfaster-structs
+@itemx -mno-faster-structs
@opindex mfaster-structs
+@opindex mno-faster-structs
With @option{-mfaster-structs}, the compiler assumes that structures
should have 8-byte alignment. This enables the use of pairs of
@code{ldd} and @code{std} instructions for copies in structure
acknowledges that their resulting code is not directly in line with
the rules of the ABI@.
+@item -mstd-struct-return
+@itemx -mno-std-struct-return
+@opindex mstd-struct-return
+@opindex mno-std-struct-return
+With @option{-mstd-struct-return}, the compiler generates checking code
+in functions returning structures or unions to detect size mismatches
+between the two sides of function calls, as per the 32-bit ABI@.
+
+The default is @option{-mno-std-struct-return}. This option has no effect
+in 64-bit mode.
+
@item -mcpu=@var{cpu_type}
@opindex mcpu
Set the instruction set, register set, and instruction scheduling parameters
@item skylake-avx512
Intel Skylake Server CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3,
-SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA,
+SSSE3, SSE4.1, SSE4.2, POPCNT, PKU, AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA,
BMI, BMI2, F16C, RDSEED, ADCX, PREFETCHW, CLFLUSHOPT, XSAVEC, XSAVES, AVX512F,
AVX512VL, AVX512BW, AVX512DQ and AVX512CD instruction set support.
@itemx -mfma4
@opindex mfma4
@need 200
-@itemx -mno-fma4
-@opindex mno-fma4
-@need 200
@itemx -mprefetchwt1
@opindex mprefetchwt1
@need 200
@need 200
@itemx -mmwaitx
@opindex mmwaitx
+@need 200
+@itemx -mclzero
+@opindex mclzero
+@itemx -mpku
+@opindex mpku
These switches enable the use of instructions in the MMX, SSE,
SSE2, SSE3, SSSE3, SSE4.1, AVX, AVX2, AVX512F, AVX512PF, AVX512ER, AVX512CD,
SHA, AES, PCLMUL, FSGSBASE, RDRND, F16C, FMA, SSE4A, FMA4, XOP, LWP, ABM,
AVX512VL, AVX512BW, AVX512DQ, AVX512IFMA AVX512VBMI, BMI, BMI2, FXSR,
-XSAVE, XSAVEOPT, LZCNT, RTM, MPX, MWAITX or 3DNow!@:
+XSAVE, XSAVEOPT, LZCNT, RTM, MPX, MWAITX, PKU or 3DNow!@:
extended instruction sets. Each has a corresponding @option{-mno-} option
to disable use of these instructions.
(and their vectorized
variants) for single-precision floating-point arguments. These instructions
are generated only when @option{-funsafe-math-optimizations} is enabled
-together with @option{-finite-math-only} and @option{-fno-trapping-math}.
+together with @option{-ffinite-math-only} and @option{-fno-trapping-math}.
Note that while the throughput of the sequence is higher than the throughput
of the non-reciprocal instruction, the precision of the sequence can be
decreased by up to 2 ulp (i.e. the inverse of 1.0 equals 0.99999994).
@option{-D_MT}; when linking, it links in a special thread helper library
@option{-lmingwthrd} which cleans up per-thread exception-handling data.
+@item -mms-bitfields
+@itemx -mno-ms-bitfields
+@opindex mms-bitfields
+@opindex mno-ms-bitfields
+
+Enable/disable bit-field layout compatible with the native Microsoft
+Windows compiler.
+
+If @code{packed} is used on a structure, or if bit-fields are used,
+it may be that the Microsoft ABI lays out the structure differently
+than the way GCC normally does. Particularly when moving packed
+data between functions compiled with GCC and the native Microsoft compiler
+(either via function call or as data in a file), it may be necessary to access
+either format.
+
+This option is enabled by default for Microsoft Windows
+targets. This behavior can also be controlled locally by use of variable
+or type attributes. For more information, see @ref{x86 Variable Attributes}
+and @ref{x86 Type Attributes}.
+
+The Microsoft structure layout algorithm is fairly simple with the exception
+of the bit-field packing.
+The padding and alignment of members of structures and whether a bit-field
+can straddle a storage-unit boundary are determine by these rules:
+
+@enumerate
+@item Structure members are stored sequentially in the order in which they are
+declared: the first member has the lowest memory address and the last member
+the highest.
+
+@item Every data object has an alignment requirement. The alignment requirement
+for all data except structures, unions, and arrays is either the size of the
+object or the current packing size (specified with either the
+@code{aligned} attribute or the @code{pack} pragma),
+whichever is less. For structures, unions, and arrays,
+the alignment requirement is the largest alignment requirement of its members.
+Every object is allocated an offset so that:
+
+@smallexample
+offset % alignment_requirement == 0
+@end smallexample
+
+@item Adjacent bit-fields are packed into the same 1-, 2-, or 4-byte allocation
+unit if the integral types are the same size and if the next bit-field fits
+into the current allocation unit without crossing the boundary imposed by the
+common alignment requirements of the bit-fields.
+@end enumerate
+
+MSVC interprets zero-length bit-fields in the following ways:
+
+@enumerate
+@item If a zero-length bit-field is inserted between two bit-fields that
+are normally coalesced, the bit-fields are not coalesced.
+
+For example:
+
+@smallexample
+struct
+ @{
+ unsigned long bf_1 : 12;
+ unsigned long : 0;
+ unsigned long bf_2 : 12;
+ @} t1;
+@end smallexample
+
+@noindent
+The size of @code{t1} is 8 bytes with the zero-length bit-field. If the
+zero-length bit-field were removed, @code{t1}'s size would be 4 bytes.
+
+@item If a zero-length bit-field is inserted after a bit-field, @code{foo}, and the
+alignment of the zero-length bit-field is greater than the member that follows it,
+@code{bar}, @code{bar} is aligned as the type of the zero-length bit-field.
+
+For example:
+
+@smallexample
+struct
+ @{
+ char foo : 4;
+ short : 0;
+ char bar;
+ @} t2;
+
+struct
+ @{
+ char foo : 4;
+ short : 0;
+ double bar;
+ @} t3;
+@end smallexample
+
+@noindent
+For @code{t2}, @code{bar} is placed at offset 2, rather than offset 1.
+Accordingly, the size of @code{t2} is 4. For @code{t3}, the zero-length
+bit-field does not affect the alignment of @code{bar} or, as a result, the size
+of the structure.
+
+Taking this into account, it is important to note the following:
+
+@enumerate
+@item If a zero-length bit-field follows a normal bit-field, the type of the
+zero-length bit-field may affect the alignment of the structure as whole. For
+example, @code{t2} has a size of 4 bytes, since the zero-length bit-field follows a
+normal bit-field, and is of type short.
+
+@item Even if a zero-length bit-field is not followed by a normal bit-field, it may
+still affect the alignment of the structure:
+
+@smallexample
+struct
+ @{
+ char foo : 6;
+ long : 0;
+ @} t4;
+@end smallexample
+
+@noindent
+Here, @code{t4} takes up 4 bytes.
+@end enumerate
+
+@item Zero-length bit-fields following non-bit-field members are ignored:
+
+@smallexample
+struct
+ @{
+ char foo;
+ long : 0;
+ char bar;
+ @} t5;
+@end smallexample
+
+@noindent
+Here, @code{t5} takes up 2 bytes.
+@end enumerate
+
+
@item -mno-align-stringops
@opindex mno-align-stringops
Do not align the destination of inlined string operations. This switch reduces
@itemx -mno-skip-rax-setup
@opindex mskip-rax-setup
When generating code for the x86-64 architecture with SSE extensions
-disabled, @option{-skip-rax-setup} can be used to skip setting up RAX
+disabled, @option{-mskip-rax-setup} can be used to skip setting up RAX
register when there are no variable arguments passed in vector registers.
@strong{Warning:} Since RAX register is used to avoid unnecessarily
canary in the TLS block (the default). This option has effect only when
@option{-fstack-protector} or @option{-fstack-protector-all} is specified.
+@item -mmitigate-rop
+@opindex mmitigate-rop
+Try to avoid generating code sequences that contain unintended return
+opcodes, to mitigate against certain forms of attack. At the moment,
+this option is limited in what it can do and should not be relied
+on to provide serious protection.
+
@end table
These @samp{-m} switches are supported in addition to the above
@item -fwritable-relocated-rdata
@opindex fno-writable-relocated-rdata
This option is available for MinGW and Cygwin targets. It specifies
-that relocated-data in read-only section is put into .data
+that relocated-data in read-only section is put into the @code{.data}
section. This is a necessary for older runtimes not supporting
-modification of .rdata sections for pseudo-relocation.
+modification of @code{.rdata} sections for pseudo-relocation.
@item -mpe-aligned-commons
@opindex mpe-aligned-commons
These are listed under @xref{S/390 and zSeries Options}.
-@node Code Gen Options
-@section Options for Code Generation Conventions
-@cindex code generation conventions
-@cindex options, code generation
-@cindex run-time options
-These machine-independent options control the interface conventions
-used in code generation.
+@c man end
+
+@node Spec Files
+@section Specifying Subprocesses and the Switches to Pass to Them
+@cindex Spec Files
+
+@command{gcc} is a driver program. It performs its job by invoking a
+sequence of other programs to do the work of compiling, assembling and
+linking. GCC interprets its command-line parameters and uses these to
+deduce which programs it should invoke, and which command-line options
+it ought to place on their command lines. This behavior is controlled
+by @dfn{spec strings}. In most cases there is one spec string for each
+program that GCC can invoke, but a few programs have multiple spec
+strings to control their behavior. The spec strings built into GCC can
+be overridden by using the @option{-specs=} command-line switch to specify
+a spec file.
-Most of them have both positive and negative forms; the negative form
-of @option{-ffoo} is @option{-fno-foo}. In the table below, only
-one of the forms is listed---the one that is not the default. You
-can figure out the other form by either removing @samp{no-} or adding
-it.
+@dfn{Spec files} are plain-text files that are used to construct spec
+strings. They consist of a sequence of directives separated by blank
+lines. The type of directive is determined by the first non-whitespace
+character on the line, which can be one of the following:
-@table @gcctabopt
-@item -fbounds-check
-@opindex fbounds-check
-For front ends that support it, generate additional code to check that
-indices used to access arrays are within the declared range. This is
-currently only supported by the Java and Fortran front ends, where
-this option defaults to true and false respectively.
+@table @code
+@item %@var{command}
+Issues a @var{command} to the spec file processor. The commands that can
+appear here are:
-@item -fstack-reuse=@var{reuse-level}
-@opindex fstack_reuse
-This option controls stack space reuse for user declared local/auto variables
-and compiler generated temporaries. @var{reuse_level} can be @samp{all},
-@samp{named_vars}, or @samp{none}. @samp{all} enables stack reuse for all
-local variables and temporaries, @samp{named_vars} enables the reuse only for
-user defined local variables with names, and @samp{none} disables stack reuse
-completely. The default value is @samp{all}. The option is needed when the
-program extends the lifetime of a scoped local variable or a compiler generated
-temporary beyond the end point defined by the language. When a lifetime of
-a variable ends, and if the variable lives in memory, the optimizing compiler
-has the freedom to reuse its stack space with other temporaries or scoped
-local variables whose live range does not overlap with it. Legacy code extending
-local lifetime is likely to break with the stack reuse optimization.
+@table @code
+@item %include <@var{file}>
+@cindex @code{%include}
+Search for @var{file} and insert its text at the current point in the
+specs file.
-For example,
+@item %include_noerr <@var{file}>
+@cindex @code{%include_noerr}
+Just like @samp{%include}, but do not generate an error message if the include
+file cannot be found.
-@smallexample
- int *p;
- @{
- int local1;
+@item %rename @var{old_name} @var{new_name}
+@cindex @code{%rename}
+Rename the spec string @var{old_name} to @var{new_name}.
- p = &local1;
- local1 = 10;
- ....
- @}
- @{
- int local2;
- local2 = 20;
- ...
- @}
+@end table
- if (*p == 10) // out of scope use of local1
- @{
+@item *[@var{spec_name}]:
+This tells the compiler to create, override or delete the named spec
+string. All lines after this directive up to the next directive or
+blank line are considered to be the text for the spec string. If this
+results in an empty string then the spec is deleted. (Or, if the
+spec did not exist, then nothing happens.) Otherwise, if the spec
+does not currently exist a new spec is created. If the spec does
+exist then its contents are overridden by the text of this
+directive, unless the first character of that text is the @samp{+}
+character, in which case the text is appended to the spec.
- @}
-@end smallexample
+@item [@var{suffix}]:
+Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
+and up to the next directive or blank line are considered to make up the
+spec string for the indicated suffix. When the compiler encounters an
+input file with the named suffix, it processes the spec string in
+order to work out how to compile that file. For example:
-Another example:
@smallexample
+.ZZ:
+z-compile -input %i
+@end smallexample
- struct A
- @{
- A(int k) : i(k), j(k) @{ @}
- int i;
- int j;
- @};
-
- A *ap;
-
- void foo(const A& ar)
- @{
- ap = &ar;
- @}
+This says that any input file whose name ends in @samp{.ZZ} should be
+passed to the program @samp{z-compile}, which should be invoked with the
+command-line switch @option{-input} and with the result of performing the
+@samp{%i} substitution. (See below.)
- void bar()
- @{
- foo(A(10)); // temp object's lifetime ends when foo returns
+As an alternative to providing a spec string, the text following a
+suffix directive can be one of the following:
- @{
- A a(20);
- ....
- @}
- ap->i+= 10; // ap references out of scope temp whose space
- // is reused with a. What is the value of ap->i?
- @}
+@table @code
+@item @@@var{language}
+This says that the suffix is an alias for a known @var{language}. This is
+similar to using the @option{-x} command-line switch to GCC to specify a
+language explicitly. For example:
+@smallexample
+.ZZ:
+@@c++
@end smallexample
-The lifetime of a compiler generated temporary is well defined by the C++
-standard. When a lifetime of a temporary ends, and if the temporary lives
-in memory, the optimizing compiler has the freedom to reuse its stack
-space with other temporaries or scoped local variables whose live range
-does not overlap with it. However some of the legacy code relies on
-the behavior of older compilers in which temporaries' stack space is
-not reused, the aggressive stack reuse can lead to runtime errors. This
-option is used to control the temporary stack reuse optimization.
+Says that .ZZ files are, in fact, C++ source files.
-@item -ftrapv
-@opindex ftrapv
-This option generates traps for signed overflow on addition, subtraction,
-multiplication operations.
-The options @option{-ftrapv} and @option{-fwrapv} override each other, so using
-@option{-ftrapv} @option{-fwrapv} on the command-line results in
-@option{-fwrapv} being effective. Note that only active options override, so
-using @option{-ftrapv} @option{-fwrapv} @option{-fno-wrapv} on the command-line
-results in @option{-ftrapv} being effective.
+@item #@var{name}
+This causes an error messages saying:
-@item -fwrapv
-@opindex fwrapv
-This option instructs the compiler to assume that signed arithmetic
-overflow of addition, subtraction and multiplication wraps around
-using twos-complement representation. This flag enables some optimizations
-and disables others. This option is enabled by default for the Java
-front end, as required by the Java language specification.
-The options @option{-ftrapv} and @option{-fwrapv} override each other, so using
-@option{-ftrapv} @option{-fwrapv} on the command-line results in
-@option{-fwrapv} being effective. Note that only active options override, so
-using @option{-ftrapv} @option{-fwrapv} @option{-fno-wrapv} on the command-line
-results in @option{-ftrapv} being effective.
+@smallexample
+@var{name} compiler not installed on this system.
+@end smallexample
+@end table
-@item -fexceptions
-@opindex fexceptions
-Enable exception handling. Generates extra code needed to propagate
-exceptions. For some targets, this implies GCC generates frame
-unwind information for all functions, which can produce significant data
-size overhead, although it does not affect execution. If you do not
-specify this option, GCC enables it by default for languages like
-C++ that normally require exception handling, and disables it for
-languages like C that do not normally require it. However, you may need
-to enable this option when compiling C code that needs to interoperate
-properly with exception handlers written in C++. You may also wish to
-disable this option if you are compiling older C++ programs that don't
-use exception handling.
+GCC already has an extensive list of suffixes built into it.
+This directive adds an entry to the end of the list of suffixes, but
+since the list is searched from the end backwards, it is effectively
+possible to override earlier entries using this technique.
-@item -fnon-call-exceptions
-@opindex fnon-call-exceptions
-Generate code that allows trapping instructions to throw exceptions.
-Note that this requires platform-specific runtime support that does
-not exist everywhere. Moreover, it only allows @emph{trapping}
-instructions to throw exceptions, i.e.@: memory references or floating-point
-instructions. It does not allow exceptions to be thrown from
-arbitrary signal handlers such as @code{SIGALRM}.
+@end table
-@item -fdelete-dead-exceptions
-@opindex fdelete-dead-exceptions
-Consider that instructions that may throw exceptions but don't otherwise
-contribute to the execution of the program can be optimized away.
-This option is enabled by default for the Ada front end, as permitted by
-the Ada language specification.
-Optimization passes that cause dead exceptions to be removed are enabled independently at different optimization levels.
+GCC has the following spec strings built into it. Spec files can
+override these strings or create their own. Note that individual
+targets can also add their own spec strings to this list.
-@item -funwind-tables
-@opindex funwind-tables
-Similar to @option{-fexceptions}, except that it just generates any needed
-static data, but does not affect the generated code in any other way.
-You normally do not need to enable this option; instead, a language processor
-that needs this handling enables it on your behalf.
+@smallexample
+asm Options to pass to the assembler
+asm_final Options to pass to the assembler post-processor
+cpp Options to pass to the C preprocessor
+cc1 Options to pass to the C compiler
+cc1plus Options to pass to the C++ compiler
+endfile Object files to include at the end of the link
+link Options to pass to the linker
+lib Libraries to include on the command line to the linker
+libgcc Decides which GCC support library to pass to the linker
+linker Sets the name of the linker
+predefines Defines to be passed to the C preprocessor
+signed_char Defines to pass to CPP to say whether @code{char} is signed
+ by default
+startfile Object files to include at the start of the link
+@end smallexample
-@item -fasynchronous-unwind-tables
-@opindex fasynchronous-unwind-tables
-Generate unwind table in DWARF 2 format, if supported by target machine. The
-table is exact at each instruction boundary, so it can be used for stack
-unwinding from asynchronous events (such as debugger or garbage collector).
+Here is a small example of a spec file:
-@item -fno-gnu-unique
-@opindex fno-gnu-unique
-On systems with recent GNU assembler and C library, the C++ compiler
-uses the @code{STB_GNU_UNIQUE} binding to make sure that definitions
-of template static data members and static local variables in inline
-functions are unique even in the presence of @code{RTLD_LOCAL}; this
-is necessary to avoid problems with a library used by two different
-@code{RTLD_LOCAL} plugins depending on a definition in one of them and
-therefore disagreeing with the other one about the binding of the
-symbol. But this causes @code{dlclose} to be ignored for affected
-DSOs; if your program relies on reinitialization of a DSO via
-@code{dlclose} and @code{dlopen}, you can use
-@option{-fno-gnu-unique}.
+@smallexample
+%rename lib old_lib
-@item -fpcc-struct-return
-@opindex fpcc-struct-return
-Return ``short'' @code{struct} and @code{union} values in memory like
-longer ones, rather than in registers. This convention is less
-efficient, but it has the advantage of allowing intercallability between
-GCC-compiled files and files compiled with other compilers, particularly
-the Portable C Compiler (pcc).
+*lib:
+--start-group -lgcc -lc -leval1 --end-group %(old_lib)
+@end smallexample
-The precise convention for returning structures in memory depends
-on the target configuration macros.
+This example renames the spec called @samp{lib} to @samp{old_lib} and
+then overrides the previous definition of @samp{lib} with a new one.
+The new definition adds in some extra command-line options before
+including the text of the old definition.
-Short structures and unions are those whose size and alignment match
-that of some integer type.
+@dfn{Spec strings} are a list of command-line options to be passed to their
+corresponding program. In addition, the spec strings can contain
+@samp{%}-prefixed sequences to substitute variable text or to
+conditionally insert text into the command line. Using these constructs
+it is possible to generate quite complex command lines.
-@strong{Warning:} code compiled with the @option{-fpcc-struct-return}
-switch is not binary compatible with code compiled with the
-@option{-freg-struct-return} switch.
-Use it to conform to a non-default application binary interface.
+Here is a table of all defined @samp{%}-sequences for spec
+strings. Note that spaces are not generated automatically around the
+results of expanding these sequences. Therefore you can concatenate them
+together or combine them with constant text in a single argument.
-@item -freg-struct-return
-@opindex freg-struct-return
-Return @code{struct} and @code{union} values in registers when possible.
-This is more efficient for small structures than
-@option{-fpcc-struct-return}.
+@table @code
+@item %%
+Substitute one @samp{%} into the program name or argument.
-If you specify neither @option{-fpcc-struct-return} nor
-@option{-freg-struct-return}, GCC defaults to whichever convention is
-standard for the target. If there is no standard convention, GCC
-defaults to @option{-fpcc-struct-return}, except on targets where GCC is
-the principal compiler. In those cases, we can choose the standard, and
-we chose the more efficient register return alternative.
+@item %i
+Substitute the name of the input file being processed.
-@strong{Warning:} code compiled with the @option{-freg-struct-return}
-switch is not binary compatible with code compiled with the
-@option{-fpcc-struct-return} switch.
-Use it to conform to a non-default application binary interface.
+@item %b
+Substitute the basename of the input file being processed.
+This is the substring up to (and not including) the last period
+and not including the directory.
-@item -fshort-enums
-@opindex fshort-enums
-Allocate to an @code{enum} type only as many bytes as it needs for the
-declared range of possible values. Specifically, the @code{enum} type
-is equivalent to the smallest integer type that has enough room.
+@item %B
+This is the same as @samp{%b}, but include the file suffix (text after
+the last period).
-@strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
-code that is not binary compatible with code generated without that switch.
-Use it to conform to a non-default application binary interface.
+@item %d
+Marks the argument containing or following the @samp{%d} as a
+temporary file name, so that that file is deleted if GCC exits
+successfully. Unlike @samp{%g}, this contributes no text to the
+argument.
-@item -fshort-double
-@opindex fshort-double
-Use the same size for @code{double} as for @code{float}.
+@item %g@var{suffix}
+Substitute a file name that has suffix @var{suffix} and is chosen
+once per compilation, and mark the argument in the same way as
+@samp{%d}. To reduce exposure to denial-of-service attacks, the file
+name is now chosen in a way that is hard to predict even when previously
+chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
+might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
+the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
+treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
+was simply substituted with a file name chosen once per compilation,
+without regard to any appended suffix (which was therefore treated
+just like ordinary text), making such attacks more likely to succeed.
-@strong{Warning:} the @option{-fshort-double} switch causes GCC to generate
-code that is not binary compatible with code generated without that switch.
-Use it to conform to a non-default application binary interface.
+@item %u@var{suffix}
+Like @samp{%g}, but generates a new temporary file name
+each time it appears instead of once per compilation.
-@item -fshort-wchar
-@opindex fshort-wchar
-Override the underlying type for @code{wchar_t} to be @code{short
-unsigned int} instead of the default for the target. This option is
-useful for building programs to run under WINE@.
+@item %U@var{suffix}
+Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
+new one if there is no such last file name. In the absence of any
+@samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
+the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
+involves the generation of two distinct file names, one
+for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
+simply substituted with a file name chosen for the previous @samp{%u},
+without regard to any appended suffix.
-@strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
-code that is not binary compatible with code generated without that switch.
-Use it to conform to a non-default application binary interface.
+@item %j@var{suffix}
+Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
+writable, and if @option{-save-temps} is not used;
+otherwise, substitute the name
+of a temporary file, just like @samp{%u}. This temporary file is not
+meant for communication between processes, but rather as a junk
+disposal mechanism.
-@item -fno-common
-@opindex fno-common
-In C code, controls the placement of uninitialized global variables.
-Unix C compilers have traditionally permitted multiple definitions of
-such variables in different compilation units by placing the variables
-in a common block.
-This is the behavior specified by @option{-fcommon}, and is the default
-for GCC on most targets.
-On the other hand, this behavior is not required by ISO C, and on some
-targets may carry a speed or code size penalty on variable references.
-The @option{-fno-common} option specifies that the compiler should place
-uninitialized global variables in the data section of the object file,
-rather than generating them as common blocks.
-This has the effect that if the same variable is declared
-(without @code{extern}) in two different compilations,
-you get a multiple-definition error when you link them.
-In this case, you must compile with @option{-fcommon} instead.
-Compiling with @option{-fno-common} is useful on targets for which
-it provides better performance, or if you wish to verify that the
-program will work on other systems that always treat uninitialized
-variable declarations this way.
+@item %|@var{suffix}
+@itemx %m@var{suffix}
+Like @samp{%g}, except if @option{-pipe} is in effect. In that case
+@samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at
+all. These are the two most common ways to instruct a program that it
+should read from standard input or write to standard output. If you
+need something more elaborate you can use an @samp{%@{pipe:@code{X}@}}
+construct: see for example @file{f/lang-specs.h}.
-@item -fno-ident
-@opindex fno-ident
-Ignore the @code{#ident} directive.
+@item %.@var{SUFFIX}
+Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
+when it is subsequently output with @samp{%*}. @var{SUFFIX} is
+terminated by the next space or %.
-@item -finhibit-size-directive
-@opindex finhibit-size-directive
-Don't output a @code{.size} assembler directive, or anything else that
-would cause trouble if the function is split in the middle, and the
-two halves are placed at locations far apart in memory. This option is
-used when compiling @file{crtstuff.c}; you should not need to use it
-for anything else.
+@item %w
+Marks the argument containing or following the @samp{%w} as the
+designated output file of this compilation. This puts the argument
+into the sequence of arguments that @samp{%o} substitutes.
-@item -fverbose-asm
-@opindex fverbose-asm
-Put extra commentary information in the generated assembly code to
-make it more readable. This option is generally only of use to those
-who actually need to read the generated assembly code (perhaps while
-debugging the compiler itself).
+@item %o
+Substitutes the names of all the output files, with spaces
+automatically placed around them. You should write spaces
+around the @samp{%o} as well or the results are undefined.
+@samp{%o} is for use in the specs for running the linker.
+Input files whose names have no recognized suffix are not compiled
+at all, but they are included among the output files, so they are
+linked.
-@option{-fno-verbose-asm}, the default, causes the
-extra information to be omitted and is useful when comparing two assembler
-files.
+@item %O
+Substitutes the suffix for object files. Note that this is
+handled specially when it immediately follows @samp{%g, %u, or %U},
+because of the need for those to form complete file names. The
+handling is such that @samp{%O} is treated exactly as if it had already
+been substituted, except that @samp{%g, %u, and %U} do not currently
+support additional @var{suffix} characters following @samp{%O} as they do
+following, for example, @samp{.o}.
-@item -frecord-gcc-switches
-@opindex frecord-gcc-switches
-This switch causes the command line used to invoke the
-compiler to be recorded into the object file that is being created.
-This switch is only implemented on some targets and the exact format
-of the recording is target and binary file format dependent, but it
-usually takes the form of a section containing ASCII text. This
-switch is related to the @option{-fverbose-asm} switch, but that
-switch only records information in the assembler output file as
-comments, so it never reaches the object file.
-See also @option{-grecord-gcc-switches} for another
-way of storing compiler options into the object file.
+@item %p
+Substitutes the standard macro predefinitions for the
+current target machine. Use this when running @command{cpp}.
-@item -fpic
-@opindex fpic
-@cindex global offset table
-@cindex PIC
-Generate position-independent code (PIC) suitable for use in a shared
-library, if supported for the target machine. Such code accesses all
-constant addresses through a global offset table (GOT)@. The dynamic
-loader resolves the GOT entries when the program starts (the dynamic
-loader is not part of GCC; it is part of the operating system). If
-the GOT size for the linked executable exceeds a machine-specific
-maximum size, you get an error message from the linker indicating that
-@option{-fpic} does not work; in that case, recompile with @option{-fPIC}
-instead. (These maximums are 8k on the SPARC and 32k
-on the m68k and RS/6000. The x86 has no such limit.)
+@item %P
+Like @samp{%p}, but puts @samp{__} before and after the name of each
+predefined macro, except for macros that start with @samp{__} or with
+@samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
+C@.
-Position-independent code requires special support, and therefore works
-only on certain machines. For the x86, GCC supports PIC for System V
-but not for the Sun 386i. Code generated for the IBM RS/6000 is always
-position-independent.
+@item %I
+Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}),
+@option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}),
+@option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options)
+and @option{-imultilib} as necessary.
-When this flag is set, the macros @code{__pic__} and @code{__PIC__}
-are defined to 1.
+@item %s
+Current argument is the name of a library or startup file of some sort.
+Search for that file in a standard list of directories and substitute
+the full name found. The current working directory is included in the
+list of directories scanned.
-@item -fPIC
-@opindex fPIC
-If supported for the target machine, emit position-independent code,
-suitable for dynamic linking and avoiding any limit on the size of the
-global offset table. This option makes a difference on the m68k,
-PowerPC and SPARC@.
+@item %T
+Current argument is the name of a linker script. Search for that file
+in the current list of directories to scan for libraries. If the file
+is located insert a @option{--script} option into the command line
+followed by the full path name found. If the file is not found then
+generate an error message. Note: the current working directory is not
+searched.
-Position-independent code requires special support, and therefore works
-only on certain machines.
+@item %e@var{str}
+Print @var{str} as an error message. @var{str} is terminated by a newline.
+Use this when inconsistent options are detected.
-When this flag is set, the macros @code{__pic__} and @code{__PIC__}
-are defined to 2.
+@item %(@var{name})
+Substitute the contents of spec string @var{name} at this point.
-@item -fpie
-@itemx -fPIE
-@opindex fpie
-@opindex fPIE
-These options are similar to @option{-fpic} and @option{-fPIC}, but
-generated position independent code can be only linked into executables.
-Usually these options are used when @option{-pie} GCC option is
-used during linking.
+@item %x@{@var{option}@}
+Accumulate an option for @samp{%X}.
-@option{-fpie} and @option{-fPIE} both define the macros
-@code{__pie__} and @code{__PIE__}. The macros have the value 1
-for @option{-fpie} and 2 for @option{-fPIE}.
+@item %X
+Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
+spec string.
-@item -fno-plt
-@opindex fno-plt
-Do not use PLT for external function calls in position-independent code.
-Instead, load callee address at call site from GOT and branch to it.
-This leads to more efficient code by eliminating PLT stubs and exposing
-GOT load to optimizations. On architectures such as 32-bit x86 where
-PLT stubs expect GOT pointer in a specific register, this gives more
-register allocation freedom to the compiler. Lazy binding requires PLT:
-with @option{-fno-plt} all external symbols are resolved at load time.
+@item %Y
+Output the accumulated assembler options specified by @option{-Wa}.
-Alternatively, function attribute @code{noplt} can be used to avoid PLT
-for calls to specific external functions by marking those functions with
-this attribute.
+@item %Z
+Output the accumulated preprocessor options specified by @option{-Wp}.
-Additionally, a few targets also convert calls to those functions that are
-marked to not use the PLT to use the GOT instead for non-position independent
-code.
+@item %a
+Process the @code{asm} spec. This is used to compute the
+switches to be passed to the assembler.
-@item -fno-jump-tables
-@opindex fno-jump-tables
-Do not use jump tables for switch statements even where it would be
-more efficient than other code generation strategies. This option is
-of use in conjunction with @option{-fpic} or @option{-fPIC} for
-building code that forms part of a dynamic linker and cannot
-reference the address of a jump table. On some targets, jump tables
-do not require a GOT and this option is not needed.
+@item %A
+Process the @code{asm_final} spec. This is a spec string for
+passing switches to an assembler post-processor, if such a program is
+needed.
-@item -ffixed-@var{reg}
-@opindex ffixed
-Treat the register named @var{reg} as a fixed register; generated code
-should never refer to it (except perhaps as a stack pointer, frame
-pointer or in some other fixed role).
+@item %l
+Process the @code{link} spec. This is the spec for computing the
+command line passed to the linker. Typically it makes use of the
+@samp{%L %G %S %D and %E} sequences.
-@var{reg} must be the name of a register. The register names accepted
-are machine-specific and are defined in the @code{REGISTER_NAMES}
-macro in the machine description macro file.
+@item %D
+Dump out a @option{-L} option for each directory that GCC believes might
+contain startup files. If the target supports multilibs then the
+current multilib directory is prepended to each of these paths.
-This flag does not have a negative form, because it specifies a
-three-way choice.
+@item %L
+Process the @code{lib} spec. This is a spec string for deciding which
+libraries are included on the command line to the linker.
-@item -fcall-used-@var{reg}
-@opindex fcall-used
-Treat the register named @var{reg} as an allocable register that is
-clobbered by function calls. It may be allocated for temporaries or
-variables that do not live across a call. Functions compiled this way
-do not save and restore the register @var{reg}.
+@item %G
+Process the @code{libgcc} spec. This is a spec string for deciding
+which GCC support library is included on the command line to the linker.
-It is an error to use this flag with the frame pointer or stack pointer.
-Use of this flag for other registers that have fixed pervasive roles in
-the machine's execution model produces disastrous results.
+@item %S
+Process the @code{startfile} spec. This is a spec for deciding which
+object files are the first ones passed to the linker. Typically
+this might be a file named @file{crt0.o}.
-This flag does not have a negative form, because it specifies a
-three-way choice.
+@item %E
+Process the @code{endfile} spec. This is a spec string that specifies
+the last object files that are passed to the linker.
-@item -fcall-saved-@var{reg}
-@opindex fcall-saved
-Treat the register named @var{reg} as an allocable register saved by
-functions. It may be allocated even for temporaries or variables that
-live across a call. Functions compiled this way save and restore
-the register @var{reg} if they use it.
+@item %C
+Process the @code{cpp} spec. This is used to construct the arguments
+to be passed to the C preprocessor.
-It is an error to use this flag with the frame pointer or stack pointer.
-Use of this flag for other registers that have fixed pervasive roles in
-the machine's execution model produces disastrous results.
+@item %1
+Process the @code{cc1} spec. This is used to construct the options to be
+passed to the actual C compiler (@command{cc1}).
-A different sort of disaster results from the use of this flag for
-a register in which function values may be returned.
+@item %2
+Process the @code{cc1plus} spec. This is used to construct the options to be
+passed to the actual C++ compiler (@command{cc1plus}).
-This flag does not have a negative form, because it specifies a
-three-way choice.
+@item %*
+Substitute the variable part of a matched option. See below.
+Note that each comma in the substituted string is replaced by
+a single space.
-@item -fpack-struct[=@var{n}]
-@opindex fpack-struct
-Without a value specified, pack all structure members together without
-holes. When a value is specified (which must be a small power of two), pack
-structure members according to this value, representing the maximum
-alignment (that is, objects with default alignment requirements larger than
-this are output potentially unaligned at the next fitting location.
+@item %<@code{S}
+Remove all occurrences of @code{-S} from the command line. Note---this
+command is position dependent. @samp{%} commands in the spec string
+before this one see @code{-S}, @samp{%} commands in the spec string
+after this one do not.
-@strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
-code that is not binary compatible with code generated without that switch.
-Additionally, it makes the code suboptimal.
-Use it to conform to a non-default application binary interface.
+@item %:@var{function}(@var{args})
+Call the named function @var{function}, passing it @var{args}.
+@var{args} is first processed as a nested spec string, then split
+into an argument vector in the usual fashion. The function returns
+a string which is processed as if it had appeared literally as part
+of the current spec.
-@item -finstrument-functions
-@opindex finstrument-functions
-Generate instrumentation calls for entry and exit to functions. Just
-after function entry and just before function exit, the following
-profiling functions are called with the address of the current
-function and its call site. (On some platforms,
-@code{__builtin_return_address} does not work beyond the current
-function, so the call site information may not be available to the
-profiling functions otherwise.)
+The following built-in spec functions are provided:
+
+@table @code
+@item @code{getenv}
+The @code{getenv} spec function takes two arguments: an environment
+variable name and a string. If the environment variable is not
+defined, a fatal error is issued. Otherwise, the return value is the
+value of the environment variable concatenated with the string. For
+example, if @env{TOPDIR} is defined as @file{/path/to/top}, then:
@smallexample
-void __cyg_profile_func_enter (void *this_fn,
- void *call_site);
-void __cyg_profile_func_exit (void *this_fn,
- void *call_site);
+%:getenv(TOPDIR /include)
@end smallexample
-The first argument is the address of the start of the current function,
-which may be looked up exactly in the symbol table.
+expands to @file{/path/to/top/include}.
-This instrumentation is also done for functions expanded inline in other
-functions. The profiling calls indicate where, conceptually, the
-inline function is entered and exited. This means that addressable
-versions of such functions must be available. If all your uses of a
-function are expanded inline, this may mean an additional expansion of
-code size. If you use @code{extern inline} in your C code, an
-addressable version of such functions must be provided. (This is
-normally the case anyway, but if you get lucky and the optimizer always
-expands the functions inline, you might have gotten away without
-providing static copies.)
+@item @code{if-exists}
+The @code{if-exists} spec function takes one argument, an absolute
+pathname to a file. If the file exists, @code{if-exists} returns the
+pathname. Here is a small example of its usage:
-A function may be given the attribute @code{no_instrument_function}, in
-which case this instrumentation is not done. This can be used, for
-example, for the profiling functions listed above, high-priority
-interrupt routines, and any functions from which the profiling functions
-cannot safely be called (perhaps signal handlers, if the profiling
-routines generate output or allocate memory).
+@smallexample
+*startfile:
+crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
+@end smallexample
-@item -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{}
-@opindex finstrument-functions-exclude-file-list
+@item @code{if-exists-else}
+The @code{if-exists-else} spec function is similar to the @code{if-exists}
+spec function, except that it takes two arguments. The first argument is
+an absolute pathname to a file. If the file exists, @code{if-exists-else}
+returns the pathname. If it does not exist, it returns the second argument.
+This way, @code{if-exists-else} can be used to select one file or another,
+based on the existence of the first. Here is a small example of its usage:
-Set the list of functions that are excluded from instrumentation (see
-the description of @option{-finstrument-functions}). If the file that
-contains a function definition matches with one of @var{file}, then
-that function is not instrumented. The match is done on substrings:
-if the @var{file} parameter is a substring of the file name, it is
-considered to be a match.
+@smallexample
+*startfile:
+crt0%O%s %:if-exists(crti%O%s) \
+%:if-exists-else(crtbeginT%O%s crtbegin%O%s)
+@end smallexample
-For example:
+@item @code{replace-outfile}
+The @code{replace-outfile} spec function takes two arguments. It looks for the
+first argument in the outfiles array and replaces it with the second argument. Here
+is a small example of its usage:
@smallexample
--finstrument-functions-exclude-file-list=/bits/stl,include/sys
+%@{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)@}
@end smallexample
-@noindent
-excludes any inline function defined in files whose pathnames
-contain @file{/bits/stl} or @file{include/sys}.
+@item @code{remove-outfile}
+The @code{remove-outfile} spec function takes one argument. It looks for the
+first argument in the outfiles array and removes it. Here is a small example
+its usage:
-If, for some reason, you want to include letter @samp{,} in one of
-@var{sym}, write @samp{\,}. For example,
-@option{-finstrument-functions-exclude-file-list='\,\,tmp'}
-(note the single quote surrounding the option).
+@smallexample
+%:remove-outfile(-lm)
+@end smallexample
-@item -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{}
-@opindex finstrument-functions-exclude-function-list
+@item @code{pass-through-libs}
+The @code{pass-through-libs} spec function takes any number of arguments. It
+finds any @option{-l} options and any non-options ending in @file{.a} (which it
+assumes are the names of linker input library archive files) and returns a
+result containing all the found arguments each prepended by
+@option{-plugin-opt=-pass-through=} and joined by spaces. This list is
+intended to be passed to the LTO linker plugin.
-This is similar to @option{-finstrument-functions-exclude-file-list},
-but this option sets the list of function names to be excluded from
-instrumentation. The function name to be matched is its user-visible
-name, such as @code{vector<int> blah(const vector<int> &)}, not the
-internal mangled name (e.g., @code{_Z4blahRSt6vectorIiSaIiEE}). The
-match is done on substrings: if the @var{sym} parameter is a substring
-of the function name, it is considered to be a match. For C99 and C++
-extended identifiers, the function name must be given in UTF-8, not
-using universal character names.
+@smallexample
+%:pass-through-libs(%G %L %G)
+@end smallexample
-@item -fstack-check
-@opindex fstack-check
-Generate code to verify that you do not go beyond the boundary of the
-stack. You should specify this flag if you are running in an
-environment with multiple threads, but you only rarely need to specify it in
-a single-threaded environment since stack overflow is automatically
-detected on nearly all systems if there is only one stack.
+@item @code{print-asm-header}
+The @code{print-asm-header} function takes no arguments and simply
+prints a banner like:
-Note that this switch does not actually cause checking to be done; the
-operating system or the language runtime must do that. The switch causes
-generation of code to ensure that they see the stack being extended.
+@smallexample
+Assembler options
+=================
-You can additionally specify a string parameter: @samp{no} means no
-checking, @samp{generic} means force the use of old-style checking,
-@samp{specific} means use the best checking method and is equivalent
-to bare @option{-fstack-check}.
+Use "-Wa,OPTION" to pass "OPTION" to the assembler.
+@end smallexample
-Old-style checking is a generic mechanism that requires no specific
-target support in the compiler but comes with the following drawbacks:
+It is used to separate compiler options from assembler options
+in the @option{--target-help} output.
+@end table
-@enumerate
-@item
-Modified allocation strategy for large objects: they are always
-allocated dynamically if their size exceeds a fixed threshold.
+@item %@{@code{S}@}
+Substitutes the @code{-S} switch, if that switch is given to GCC@.
+If that switch is not specified, this substitutes nothing. Note that
+the leading dash is omitted when specifying this option, and it is
+automatically inserted if the substitution is performed. Thus the spec
+string @samp{%@{foo@}} matches the command-line option @option{-foo}
+and outputs the command-line option @option{-foo}.
-@item
-Fixed limit on the size of the static frame of functions: when it is
-topped by a particular function, stack checking is not reliable and
-a warning is issued by the compiler.
+@item %W@{@code{S}@}
+Like %@{@code{S}@} but mark last argument supplied within as a file to be
+deleted on failure.
-@item
-Inefficiency: because of both the modified allocation strategy and the
-generic implementation, code performance is hampered.
-@end enumerate
+@item %@{@code{S}*@}
+Substitutes all the switches specified to GCC whose names start
+with @code{-S}, but which also take an argument. This is used for
+switches like @option{-o}, @option{-D}, @option{-I}, etc.
+GCC considers @option{-o foo} as being
+one switch whose name starts with @samp{o}. %@{o*@} substitutes this
+text, including the space. Thus two arguments are generated.
-Note that old-style stack checking is also the fallback method for
-@samp{specific} if no target support has been added in the compiler.
+@item %@{@code{S}*&@code{T}*@}
+Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
+(the order of @code{S} and @code{T} in the spec is not significant).
+There can be any number of ampersand-separated variables; for each the
+wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
-@item -fstack-limit-register=@var{reg}
-@itemx -fstack-limit-symbol=@var{sym}
-@itemx -fno-stack-limit
-@opindex fstack-limit-register
-@opindex fstack-limit-symbol
-@opindex fno-stack-limit
-Generate code to ensure that the stack does not grow beyond a certain value,
-either the value of a register or the address of a symbol. If a larger
-stack is required, a signal is raised at run time. For most targets,
-the signal is raised before the stack overruns the boundary, so
-it is possible to catch the signal without taking special precautions.
+@item %@{@code{S}:@code{X}@}
+Substitutes @code{X}, if the @option{-S} switch is given to GCC@.
-For instance, if the stack starts at absolute address @samp{0x80000000}
-and grows downwards, you can use the flags
-@option{-fstack-limit-symbol=__stack_limit} and
-@option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
-of 128KB@. Note that this may only work with the GNU linker.
+@item %@{!@code{S}:@code{X}@}
+Substitutes @code{X}, if the @option{-S} switch is @emph{not} given to GCC@.
-@item -fsplit-stack
-@opindex fsplit-stack
-Generate code to automatically split the stack before it overflows.
-The resulting program has a discontiguous stack which can only
-overflow if the program is unable to allocate any more memory. This
-is most useful when running threaded programs, as it is no longer
-necessary to calculate a good stack size to use for each thread. This
-is currently only implemented for the x86 targets running
-GNU/Linux.
+@item %@{@code{S}*:@code{X}@}
+Substitutes @code{X} if one or more switches whose names start with
+@code{-S} are specified to GCC@. Normally @code{X} is substituted only
+once, no matter how many such switches appeared. However, if @code{%*}
+appears somewhere in @code{X}, then @code{X} is substituted once
+for each matching switch, with the @code{%*} replaced by the part of
+that switch matching the @code{*}.
-When code compiled with @option{-fsplit-stack} calls code compiled
-without @option{-fsplit-stack}, there may not be much stack space
-available for the latter code to run. If compiling all code,
-including library code, with @option{-fsplit-stack} is not an option,
-then the linker can fix up these calls so that the code compiled
-without @option{-fsplit-stack} always has a large stack. Support for
-this is implemented in the gold linker in GNU binutils release 2.21
-and later.
+If @code{%*} appears as the last part of a spec sequence then a space
+is added after the end of the last substitution. If there is more
+text in the sequence, however, then a space is not generated. This
+allows the @code{%*} substitution to be used as part of a larger
+string. For example, a spec string like this:
-@item -fleading-underscore
-@opindex fleading-underscore
-This option and its counterpart, @option{-fno-leading-underscore}, forcibly
-change the way C symbols are represented in the object file. One use
-is to help link with legacy assembly code.
+@smallexample
+%@{mcu=*:--script=%*/memory.ld@}
+@end smallexample
-@strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
-generate code that is not binary compatible with code generated without that
-switch. Use it to conform to a non-default application binary interface.
-Not all targets provide complete support for this switch.
+@noindent
+when matching an option like @option{-mcu=newchip} produces:
-@item -ftls-model=@var{model}
-@opindex ftls-model
-Alter the thread-local storage model to be used (@pxref{Thread-Local}).
-The @var{model} argument should be one of @samp{global-dynamic},
-@samp{local-dynamic}, @samp{initial-exec} or @samp{local-exec}.
-Note that the choice is subject to optimization: the compiler may use
-a more efficient model for symbols not visible outside of the translation
-unit, or if @option{-fpic} is not given on the command line.
+@smallexample
+--script=newchip/memory.ld
+@end smallexample
-The default without @option{-fpic} is @samp{initial-exec}; with
-@option{-fpic} the default is @samp{global-dynamic}.
+@item %@{.@code{S}:@code{X}@}
+Substitutes @code{X}, if processing a file with suffix @code{S}.
-@item -fvisibility=@r{[}default@r{|}internal@r{|}hidden@r{|}protected@r{]}
-@opindex fvisibility
-Set the default ELF image symbol visibility to the specified option---all
-symbols are marked with this unless overridden within the code.
-Using this feature can very substantially improve linking and
-load times of shared object libraries, produce more optimized
-code, provide near-perfect API export and prevent symbol clashes.
-It is @strong{strongly} recommended that you use this in any shared objects
-you distribute.
+@item %@{!.@code{S}:@code{X}@}
+Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}.
-Despite the nomenclature, @samp{default} always means public; i.e.,
-available to be linked against from outside the shared object.
-@samp{protected} and @samp{internal} are pretty useless in real-world
-usage so the only other commonly used option is @samp{hidden}.
-The default if @option{-fvisibility} isn't specified is
-@samp{default}, i.e., make every symbol public.
+@item %@{,@code{S}:@code{X}@}
+Substitutes @code{X}, if processing a file for language @code{S}.
-A good explanation of the benefits offered by ensuring ELF
-symbols have the correct visibility is given by ``How To Write
-Shared Libraries'' by Ulrich Drepper (which can be found at
-@w{@uref{http://www.akkadia.org/drepper/}})---however a superior
-solution made possible by this option to marking things hidden when
-the default is public is to make the default hidden and mark things
-public. This is the norm with DLLs on Windows and with @option{-fvisibility=hidden}
-and @code{__attribute__ ((visibility("default")))} instead of
-@code{__declspec(dllexport)} you get almost identical semantics with
-identical syntax. This is a great boon to those working with
-cross-platform projects.
+@item %@{!,@code{S}:@code{X}@}
+Substitutes @code{X}, if not processing a file for language @code{S}.
-For those adding visibility support to existing code, you may find
-@code{#pragma GCC visibility} of use. This works by you enclosing
-the declarations you wish to set visibility for with (for example)
-@code{#pragma GCC visibility push(hidden)} and
-@code{#pragma GCC visibility pop}.
-Bear in mind that symbol visibility should be viewed @strong{as
-part of the API interface contract} and thus all new code should
-always specify visibility when it is not the default; i.e., declarations
-only for use within the local DSO should @strong{always} be marked explicitly
-as hidden as so to avoid PLT indirection overheads---making this
-abundantly clear also aids readability and self-documentation of the code.
-Note that due to ISO C++ specification requirements, @code{operator new} and
-@code{operator delete} must always be of default visibility.
+@item %@{@code{S}|@code{P}:@code{X}@}
+Substitutes @code{X} if either @code{-S} or @code{-P} is given to
+GCC@. This may be combined with @samp{!}, @samp{.}, @samp{,}, and
+@code{*} sequences as well, although they have a stronger binding than
+the @samp{|}. If @code{%*} appears in @code{X}, all of the
+alternatives must be starred, and only the first matching alternative
+is substituted.
-Be aware that headers from outside your project, in particular system
-headers and headers from any other library you use, may not be
-expecting to be compiled with visibility other than the default. You
-may need to explicitly say @code{#pragma GCC visibility push(default)}
-before including any such headers.
+For example, a spec string like this:
-@code{extern} declarations are not affected by @option{-fvisibility}, so
-a lot of code can be recompiled with @option{-fvisibility=hidden} with
-no modifications. However, this means that calls to @code{extern}
-functions with no explicit visibility use the PLT, so it is more
-effective to use @code{__attribute ((visibility))} and/or
-@code{#pragma GCC visibility} to tell the compiler which @code{extern}
-declarations should be treated as hidden.
+@smallexample
+%@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
+@end smallexample
-Note that @option{-fvisibility} does affect C++ vague linkage
-entities. This means that, for instance, an exception class that is
-be thrown between DSOs must be explicitly marked with default
-visibility so that the @samp{type_info} nodes are unified between
-the DSOs.
+@noindent
+outputs the following command-line options from the following input
+command-line options:
-An overview of these techniques, their benefits and how to use them
-is at @uref{http://gcc.gnu.org/@/wiki/@/Visibility}.
+@smallexample
+fred.c -foo -baz
+jim.d -bar -boggle
+-d fred.c -foo -baz -boggle
+-d jim.d -bar -baz -boggle
+@end smallexample
-@item -fstrict-volatile-bitfields
-@opindex fstrict-volatile-bitfields
-This option should be used if accesses to volatile bit-fields (or other
-structure fields, although the compiler usually honors those types
-anyway) should use a single access of the width of the
-field's type, aligned to a natural alignment if possible. For
-example, targets with memory-mapped peripheral registers might require
-all such accesses to be 16 bits wide; with this flag you can
-declare all peripheral bit-fields as @code{unsigned short} (assuming short
-is 16 bits on these targets) to force GCC to use 16-bit accesses
-instead of, perhaps, a more efficient 32-bit access.
+@item %@{S:X; T:Y; :D@}
-If this option is disabled, the compiler uses the most efficient
-instruction. In the previous example, that might be a 32-bit load
-instruction, even though that accesses bytes that do not contain
-any portion of the bit-field, or memory-mapped registers unrelated to
-the one being updated.
+If @code{S} is given to GCC, substitutes @code{X}; else if @code{T} is
+given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can
+be as many clauses as you need. This may be combined with @code{.},
+@code{,}, @code{!}, @code{|}, and @code{*} as needed.
-In some cases, such as when the @code{packed} attribute is applied to a
-structure field, it may not be possible to access the field with a single
-read or write that is correctly aligned for the target machine. In this
-case GCC falls back to generating multiple accesses rather than code that
-will fault or truncate the result at run time.
-Note: Due to restrictions of the C/C++11 memory model, write accesses are
-not allowed to touch non bit-field members. It is therefore recommended
-to define all bits of the field's type as bit-field members.
+@end table
-The default value of this option is determined by the application binary
-interface for the target processor.
+The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar
+construct may contain other nested @samp{%} constructs or spaces, or
+even newlines. They are processed as usual, as described above.
+Trailing white space in @code{X} is ignored. White space may also
+appear anywhere on the left side of the colon in these constructs,
+except between @code{.} or @code{*} and the corresponding word.
-@item -fsync-libcalls
-@opindex fsync-libcalls
-This option controls whether any out-of-line instance of the @code{__sync}
-family of functions may be used to implement the C++11 @code{__atomic}
-family of functions.
+The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are
+handled specifically in these constructs. If another value of
+@option{-O} or the negated form of a @option{-f}, @option{-m}, or
+@option{-W} switch is found later in the command line, the earlier
+switch value is ignored, except with @{@code{S}*@} where @code{S} is
+just one letter, which passes all matching options.
-The default value of this option is enabled, thus the only useful form
-of the option is @option{-fno-sync-libcalls}. This option is used in
-the implementation of the @file{libatomic} runtime library.
+The character @samp{|} at the beginning of the predicate text is used to
+indicate that a command should be piped to the following command, but
+only if @option{-pipe} is specified.
-@end table
+It is built into GCC which switches take arguments and which do not.
+(You might think it would be useful to generalize this to allow each
+compiler's spec to say which switches take arguments. But this cannot
+be done in a consistent fashion. GCC cannot even decide which input
+files have been specified without knowing which switches take arguments,
+and it must know which input files to compile in order to tell which
+compilers to run).
-@c man end
+GCC also knows implicitly that arguments starting in @option{-l} are to be
+treated as compiler output files, and passed to the linker in their
+proper position among the other output files.
@node Environment Variables
@section Environment Variables Affecting GCC
projects / platform / upstream / gcc.git / blobdiff