m4/builtin-expect.m4

   1 dnl Check for __builtin_expect.
   2
   3 dnl Copyright 2016-2020 Free Software Foundation, Inc.
   4 dnl This file is free software; the Free Software Foundation
   5 dnl gives unlimited permission to copy and/or distribute it,
   6 dnl with or without modifications, as long as this notice is preserved.
   7
   8 dnl Written by Paul Eggert.
   9
  10 AC_DEFUN([gl___BUILTIN_EXPECT],
  11 [
  12   AC_CACHE_CHECK([for __builtin_expect],
  13     [gl_cv___builtin_expect],
  14     [AC_LINK_IFELSE(
  15        [AC_LANG_SOURCE([[
  16          int
  17          main (int argc, char **argv)
  18          {
  19            argc = __builtin_expect (argc, 100);
  20            return argv[argc != 100][0];
  21          }]])],
  22        [gl_cv___builtin_expect=yes],
  23        [AC_LINK_IFELSE(
  24           [AC_LANG_SOURCE([[
  25              #include <builtins.h>
  26              int
  27              main (int argc, char **argv)
  28              {
  29                argc = __builtin_expect (argc, 100);
  30                return argv[argc != 100][0];
  31              }]])],
  32           [gl_cv___builtin_expect="in <builtins.h>"],
  33           [gl_cv___builtin_expect=no])])])
  34   if test "$gl_cv___builtin_expect" = yes; then
  35     AC_DEFINE([HAVE___BUILTIN_EXPECT], [1])
  36   elif test "$gl_cv___builtin_expect" = "in <builtins.h>"; then
  37     AC_DEFINE([HAVE___BUILTIN_EXPECT], [2])
  38   fi
  39   AH_VERBATIM([HAVE___BUILTIN_EXPECT],
  40     [/* Define to 1 if the compiler supports __builtin_expect,
  41    and to 2 if <builtins.h> does.  */
  42 #undef HAVE___BUILTIN_EXPECT
  43 #ifndef HAVE___BUILTIN_EXPECT
  44 # define __builtin_expect(e, c) (e)
  45 #elif HAVE___BUILTIN_EXPECT == 2
  46 # include <builtins.h>
  47 #endif
  48     ])
  49 ])