> Le 23 oct. 2019 à 07:33, Akim Demaille <a...@lrde.epita.fr> a écrit : > >> Le 22 oct. 2019 à 20:10, Paul Eggert <egg...@cs.ucla.edu> a écrit : >> >> On 10/21/19 2:07 AM, Akim Demaille wrote: >> > >> GCC 9 should have the necessary primitives to bypass the code eliciting the >> warnings you mentioned; besides, recent GCCs are better at avoiding false >> alarms with options like -Wtype-limits. I don't see why macOS GCC 9 would >> differ from GNU/Linux GCC 9 in this area. > > I know. That's why I wrote > >>> Except that on this mac GCC 7 to 9 shows the warning. I don't understand >>> [why] there's a difference with GNU/Linux.
So I had a closer look at intprops.h, and the problem is actually coming from limits.h (the system's one, not gnulib's): $ cat intprops.h #include <limits.h> $ gcc-mp-9 -Wextra -E intprops.h -dM | grep _has_buil #define __has_builtin(x) 0 which ruins all your efforts on has_builtin in intprops.h: /* If the compiler lacks __has_builtin, define it well enough for this source file only. */ #ifndef __has_builtin # define __has_builtin(x) _GL_HAS_##x # if 5 <= __GNUC__ && !defined __ICC # define _GL_HAS___builtin_add_overflow 1 # else # define _GL_HAS___builtin_add_overflow 0 # endif # define _GL_TEMPDEF___has_builtin #endif It seems to come from /opt/local/lib/gcc9/gcc/x86_64-apple-darwin18/9.2.0/include-fixed/os/base.h which starts with #include <sys/cdefs.h> #ifndef __has_builtin #define __has_builtin(x) 0 #endif #ifndef __has_include #define __has_include(x) 0 #endif #ifndef __has_feature #define __has_feature(x) 0 #endif #ifndef __has_attribute #define __has_attribute(x) 0 #endif #ifndef __has_extension #define __has_extension(x) 0 #endif #ifndef __has_extension #define __has_extension(x) 0 #endif which seems consistent with the fact that GCC 9 does not support __has_builtin (contrary to what I believed) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66970 I guess that since macOS's "native" compiler is Clang, which does support __has_builtin, GCC folks want to emulate that compiler. By emasculating theirs. Unfortunately on __has_builtin(__has_builtin) clang returns 0.
