m4/atomic.m4

   1 AC_DEFUN([DISPATCH_C_ATOMIC_BUILTINS], [
   2 #
   3 # This is a bit subtle: on i386 systems without at least -march=i486 defined,
   4 # certain built-in atomics fall back to depending on undefined symbols if
   5 # their return values are used.
   6 #
   7 AC_CACHE_CHECK([for gcc atomic builtins],[dispatch_cv_atomic],
   8 [AC_LINK_IFELSE([AC_LANG_PROGRAM([],[[
   9 int i, x =0;
  10 i = __sync_add_and_fetch(&x,1);
  11 return x;]])],[dispatch_cv_atomic=yes],
  12   [saveCFLAGS="$CFLAGS"
  13   CFLAGS="$CFLAGS -march=i486"
  14   AC_LINK_IFELSE([AC_LANG_PROGRAM([],[[
  15   int i, x =0;
  16   i = __sync_add_and_fetch(&x,1);
  17   return x;]])],[CFLAGS="$saveCFLAGS"
  18 dispatch_cv_atomic="-march=i486"
  19 ])])])
  20
  21 ])