[Driver] Don't make -gsplit-dwarf imply -g2

RFC: http://lists.llvm.org/pipermail/cfe-dev/2020-May/065430.html
Agreement from GCC: https://sourceware.org/pipermail/gcc-patches/2020-May/545688.html

g_flags_Group options generally don't affect the amount of debugging
information. -gsplit-dwarf is an exception. Its order dependency with
other gN_Group options make it inconvenient in a build system:

* -g0 -gsplit-dwarf -> level 2
   -gsplit-dwarf "upgrades" the amount of debugging information despite
   the previous intention (-g0) to drop debugging information
* -g1 -gsplit-dwarf -> level 2
  -gsplit-dwarf "upgrades" the amount of debugging information.
* If we have a higher-level -gN, -gN -gsplit-dwarf will supposedly decrease the
  amount of debugging information. This happens with GCC -g3.

The non-orthogonality has confused many users. GCC 11 will change the semantics
(-gsplit-dwarf no longer implies -g2) despite the backwards compatibility break.
This patch matches its behavior.

New semantics:

* If there is a g_Group, allow split DWARF if useful
  (none of: -g0, -gline-directives-only, -g1 -fno-split-dwarf-inlining)
* Otherwise, no-op.

To restore the original behavior, replace -gsplit-dwarf with -gsplit-dwarf -g.

Reviewed By: dblaikie

Differential Revision: https://reviews.llvm.org/D80391

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index d90d059..7d68cdb 100644 (file)
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -117,6 +117,7 @@ Modified Compiler Flags
 - Now that `this` pointers are tagged with `nonnull` and `dereferenceable(N)`,
   `-fno-delete-null-pointer-checks` has gained the power to remove the
   `nonnull` attribute on `this` for configurations that need it to be nullable.
+- ``-gsplit-dwarf`` no longer implies ``-g2``.
 
 New Pragmas in Clang
 --------------------

diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index baf7d5c..f3a6b12 100644 (file)
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -3750,20 +3750,15 @@ static void RenderDebugOptions(const ToolChain &TC, const Driver &D,
       Args.hasFlag(options::OPT_fsplit_dwarf_inlining,
                    options::OPT_fno_split_dwarf_inlining, false);
 
-  Args.ClaimAllArgs(options::OPT_g_Group);
-
-  Arg* SplitDWARFArg;
-  DwarfFission = getDebugFissionKind(D, Args, SplitDWARFArg);
-
-  if (DwarfFission != DwarfFissionKind::None &&
-      !checkDebugInfoOption(SplitDWARFArg, Args, D, TC)) {
-    DwarfFission = DwarfFissionKind::None;
-    SplitDWARFInlining = false;
-  }
+  if (const Arg *A = Args.getLastArg(options::OPT_g_Group)) {
+    Arg *SplitDWARFArg;
+    DwarfFission = getDebugFissionKind(D, Args, SplitDWARFArg);
+    if (DwarfFission != DwarfFissionKind::None &&
+        !checkDebugInfoOption(SplitDWARFArg, Args, D, TC)) {
+      DwarfFission = DwarfFissionKind::None;
+      SplitDWARFInlining = false;
+    }
 
-  if (const Arg *A =
-          Args.getLastArg(options::OPT_g_Group, options::OPT_gsplit_dwarf,
-                          options::OPT_gsplit_dwarf_EQ)) {
     DebugInfoKind = codegenoptions::LimitedDebugInfo;
 
     // If the last option explicitly specified a debug-info level, use it.
@@ -4896,7 +4891,7 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   if (D.IsCLMode())
     AddClangCLArgs(Args, InputType, CmdArgs, &DebugInfoKind, &EmitCodeView);
 
-  DwarfFissionKind DwarfFission;
+  DwarfFissionKind DwarfFission = DwarfFissionKind::None;
   RenderDebugOptions(TC, D, RawTriple, Args, EmitCodeView, CmdArgs,
                      DebugInfoKind, DwarfFission);
 

diff --git a/clang/test/Driver/split-debug.c b/clang/test/Driver/split-debug.c
index 4b644c8..bd9ec32 100644 (file)
--- a/clang/test/Driver/split-debug.c
+++ b/clang/test/Driver/split-debug.c
@@ -20,8 +20,8 @@
 // RUN: %clang -### -c -target x86_64-apple-darwin  -gsplit-dwarf -g %s 2>&1 | FileCheck %s --check-prefix=NOSPLIT
 // NOSPLIT-NOT: "-split-dwarf
 
-/// -gsplit-dwarf currently enables debug fission even without -g.
-// RUN: %clang -### -c -target x86_64 -gsplit-dwarf %s 2>&1 | FileCheck %s --check-prefix=SPLIT
+/// -gsplit-dwarf is a no-op if no -g is specified.
+// RUN: %clang -### -c -target x86_64 -gsplit-dwarf %s 2>&1 | FileCheck %s --check-prefix=G0
 
 /// Test -gsplit-dwarf=single.
 // RUN: %clang -### -c -target x86_64 -gsplit-dwarf=single -g %s 2>&1 | FileCheck %s --check-prefix=SINGLE
@@ -59,8 +59,8 @@
 /// Interaction with -g0.
 // RUN: %clang -### -c -target x86_64 -gsplit-dwarf -g0 -### %s 2>&1 | FileCheck %s --check-prefix=G0
 // RUN: %clang -### -c -target x86_64 -gsplit-dwarf=single -g0 %s 2>&1 | FileCheck %s --check-prefix=G0
-// RUN: %clang -### -c -target x86_64 -g0 -gsplit-dwarf %s 2>&1 | FileCheck %s --check-prefixes=NOINLINE,SPLIT
-// RUN: %clang -### -c -target x86_64 -g0 -gsplit-dwarf=single %s 2>&1 | FileCheck %s --check-prefix=SINGLE
+// RUN: %clang -### -c -target x86_64 -g0 -gsplit-dwarf %s 2>&1 | FileCheck %s --check-prefixes=G0
+// RUN: %clang -### -c -target x86_64 -g0 -gsplit-dwarf=single %s 2>&1 | FileCheck %s --check-prefix=G0
 // RUN: %clang -### -c -target x86_64 -gsplit-dwarf=single -g0 -fsplit-dwarf-inlining %s 2>&1 | FileCheck %s --check-prefix=G0
 
 // G0-NOT: "-debug-info-kind=
@@ -69,7 +69,7 @@
 /// Interaction with -g1 (-gmlt).
 // RUN: %clang -### -S -target x86_64 -gsplit-dwarf -g1 %s 2>&1 | FileCheck %s --check-prefix=G1_WITH_SPLIT
 // RUN: %clang -### -S -target x86_64 -gsplit-dwarf -g1 -fno-split-dwarf-inlining %s 2>&1 | FileCheck %s --check-prefix=G1_WITH_SPLIT
-// RUN: %clang -### -S -target x86_64 -gmlt -gsplit-dwarf -fno-split-dwarf-inlining %s 2>&1 | FileCheck %s --check-prefix=SPLIT
+// RUN: %clang -### -S -target x86_64 -gmlt -gsplit-dwarf -fno-split-dwarf-inlining %s 2>&1 | FileCheck %s --check-prefix=G1_WITH_SPLIT
 
 // G1_WITH_SPLIT: "-debug-info-kind=line-tables-only"
 // G1_WITH_SPLIT: "-split-dwarf-file"