Define likely()/unlikely() macros

It serves as nice "hotspot" annotations, and can also help things, so
why not.

Signed-off-by: Ran Benita <ran234@gmail.com>

diff --git a/configure.ac b/configure.ac
index 5f317ed..853ffe3 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -81,6 +81,8 @@ AS_IF([test "x$ac_cv_func_secure_getenv" = xno -a \
     AC_MSG_WARN([C library does not support secure_getenv, using getenv instead])
 ])
 
+AX_GCC_BUILTIN(__builtin_expect)
+
 # Some tests use Linux-specific headers
 AC_CHECK_HEADER([linux/input.h])
 AM_CONDITIONAL(BUILD_LINUX_TESTS, [test "x$ac_cv_header_linux_input_h" = xyes])

diff --git a/m4/ax_gcc_builtin.m4 b/m4/ax_gcc_builtin.m4
new file mode 100644 (file)
index 0000000..b28a91b
--- /dev/null
+++ b/m4/ax_gcc_builtin.m4
@@ -0,0 +1,168 @@
+# ===========================================================================
+#      http://www.gnu.org/software/autoconf-archive/ax_gcc_builtin.html
+# ===========================================================================
+#
+# SYNOPSIS
+#
+#   AX_GCC_BUILTIN(BUILTIN)
+#
+# DESCRIPTION
+#
+#   This macro checks if the compiler supports one of GCC's built-in
+#   functions; many other compilers also provide those same built-ins.
+#
+#   The BUILTIN parameter is the name of the built-in function.
+#
+#   If BUILTIN is supported define HAVE_<BUILTIN>. Keep in mind that since
+#   builtins usually start with two underscores they will be copied over
+#   into the HAVE_<BUILTIN> definition (e.g. HAVE___BUILTIN_EXPECT for
+#   __builtin_expect()).
+#
+#   The macro caches its result in the ax_cv_have_<BUILTIN> variable (e.g.
+#   ax_cv_have___builtin_expect).
+#
+#   The macro currently supports the following built-in functions:
+#
+#    __builtin_assume_aligned
+#    __builtin_bswap32
+#    __builtin_bswap64
+#    __builtin_choose_expr
+#    __builtin___clear_cache
+#    __builtin_clrsb
+#    __builtin_clrsbl
+#    __builtin_clrsbll
+#    __builtin_clz
+#    __builtin_clzl
+#    __builtin_clzll
+#    __builtin_complex
+#    __builtin_constant_p
+#    __builtin_ctz
+#    __builtin_ctzl
+#    __builtin_ctzll
+#    __builtin_expect
+#    __builtin_ffs
+#    __builtin_ffsl
+#    __builtin_ffsll
+#    __builtin_fpclassify
+#    __builtin_huge_val
+#    __builtin_huge_valf
+#    __builtin_huge_vall
+#    __builtin_inf
+#    __builtin_infd128
+#    __builtin_infd32
+#    __builtin_infd64
+#    __builtin_inff
+#    __builtin_infl
+#    __builtin_isinf_sign
+#    __builtin_nan
+#    __builtin_nand128
+#    __builtin_nand32
+#    __builtin_nand64
+#    __builtin_nanf
+#    __builtin_nanl
+#    __builtin_nans
+#    __builtin_nansf
+#    __builtin_nansl
+#    __builtin_object_size
+#    __builtin_parity
+#    __builtin_parityl
+#    __builtin_parityll
+#    __builtin_popcount
+#    __builtin_popcountl
+#    __builtin_popcountll
+#    __builtin_powi
+#    __builtin_powif
+#    __builtin_powil
+#    __builtin_prefetch
+#    __builtin_trap
+#    __builtin_types_compatible_p
+#    __builtin_unreachable
+#
+#   Unsuppored built-ins will be tested with an empty parameter set and the
+#   result of the check might be wrong or meaningless so use with care.
+#
+# LICENSE
+#
+#   Copyright (c) 2013 Gabriele Svelto <gabriele.svelto@gmail.com>
+#
+#   Copying and distribution of this file, with or without modification, are
+#   permitted in any medium without royalty provided the copyright notice
+#   and this notice are preserved.  This file is offered as-is, without any
+#   warranty.
+
+#serial 2
+
+AC_DEFUN([AX_GCC_BUILTIN], [
+    AS_VAR_PUSHDEF([ac_var], [ax_cv_have_$1])
+
+    AC_CACHE_CHECK([for $1], [ac_var], [
+        AC_LINK_IFELSE([AC_LANG_PROGRAM([], [
+            m4_case([$1],
+                [__builtin_assume_aligned], [$1("", 0)],
+                [__builtin_bswap32], [$1(0)],
+                [__builtin_bswap64], [$1(0)],
+                [__builtin_choose_expr], [$1(0, 0, 0)],
+                [__builtin___clear_cache], [$1("", "")],
+                [__builtin_clrsb], [$1(0)],
+                [__builtin_clrsbl], [$1(0)],
+                [__builtin_clrsbll], [$1(0)],
+                [__builtin_clz], [$1(0)],
+                [__builtin_clzl], [$1(0)],
+                [__builtin_clzll], [$1(0)],
+                [__builtin_complex], [$1(0.0, 0.0)],
+                [__builtin_constant_p], [$1(0)],
+                [__builtin_ctz], [$1(0)],
+                [__builtin_ctzl], [$1(0)],
+                [__builtin_ctzll], [$1(0)],
+                [__builtin_expect], [$1(0, 0)],
+                [__builtin_ffs], [$1(0)],
+                [__builtin_ffsl], [$1(0)],
+                [__builtin_ffsll], [$1(0)],
+                [__builtin_fpclassify], [$1(0, 1, 2, 3, 4, 0.0)],
+                [__builtin_huge_val], [$1()],
+                [__builtin_huge_valf], [$1()],
+                [__builtin_huge_vall], [$1()],
+                [__builtin_inf], [$1()],
+                [__builtin_infd128], [$1()],
+                [__builtin_infd32], [$1()],
+                [__builtin_infd64], [$1()],
+                [__builtin_inff], [$1()],
+                [__builtin_infl], [$1()],
+                [__builtin_isinf_sign], [$1(0.0)],
+                [__builtin_nan], [$1("")],
+                [__builtin_nand128], [$1("")],
+                [__builtin_nand32], [$1("")],
+                [__builtin_nand64], [$1("")],
+                [__builtin_nanf], [$1("")],
+                [__builtin_nanl], [$1("")],
+                [__builtin_nans], [$1("")],
+                [__builtin_nansf], [$1("")],
+                [__builtin_nansl], [$1("")],
+                [__builtin_object_size], [$1("", 0)],
+                [__builtin_parity], [$1(0)],
+                [__builtin_parityl], [$1(0)],
+                [__builtin_parityll], [$1(0)],
+                [__builtin_popcount], [$1(0)],
+                [__builtin_popcountl], [$1(0)],
+                [__builtin_popcountll], [$1(0)],
+                [__builtin_powi], [$1(0, 0)],
+                [__builtin_powif], [$1(0, 0)],
+                [__builtin_powil], [$1(0, 0)],
+                [__builtin_prefetch], [$1("")],
+                [__builtin_trap], [$1()],
+                [__builtin_types_compatible_p], [$1(int, int)],
+                [__builtin_unreachable], [$1()],
+                [m4_warn([syntax], [Unsupported built-in $1, the test may fail])
+                 $1()]
+            )
+            ])],
+            [AS_VAR_SET([ac_var], [yes])],
+            [AS_VAR_SET([ac_var], [no])])
+    ])
+
+    AS_IF([test yes = AS_VAR_GET([ac_var])],
+        [AC_DEFINE_UNQUOTED(AS_TR_CPP(HAVE_$1), 1,
+            [Define to 1 if the system has the `$1' built-in function])], [])
+
+    AS_VAR_POPDEF([ac_var])
+])

diff --git a/src/utils.h b/src/utils.h
index f7fc7a5..6affee1 100644 (file)
--- a/src/utils.h
+++ b/src/utils.h
@@ -195,6 +195,14 @@ unmap_file(const char *str, size_t size);
 # define secure_getenv getenv
 #endif
 
+#if defined(HAVE___BUILTIN_EXPECT)
+# define likely(x)   __builtin_expect(!!(x), 1)
+# define unlikely(x) __builtin_expect(!!(x), 0)
+#else
+# define likely(x)   (x)
+# define unlikely(x) (x)
+#endif
+
 /* Compiler Attributes */
 
 #if defined(__GNUC__) && (__GNUC__ >= 4) && !defined(__CYGWIN__)