Re: undefined behaviour findings in bitset

[Akim Demaille]

Le 17 mars 2019 à 20:27, Bruno Haible <br...@clisp.org> a écrit : Hi Akim, But GCC 4.7 does not support [[noreturn]] yet, even in gnu++11 mode. I need something like the following changes. -# if 201103 <= (defined __cplusplus ? __cplusplus : 0) +# if (201103 <= (defined __cplusplus ? __cplusplus : 0) \ +      && 4 < __GNUC__ + (8 <= __GNUC_MINOR__)) Something like this is OK. But this change drops support for [[noreturn]] in compilers other than GCC and clang. 😱 Shouldn't it be like this:  # if (201103 <= (defined __cplusplus ? __cplusplus : 0) \        && (!defined __GNUC__ || 4 < __GNUC__ + (8 <= __GNUC_MINOR__))) Yes, of course :(  Thanks!  Fixed and pushed, Wouldn't it be useful to have a file that defines macros such as GL_GCC_VERSION (that is defined on GCC only, not clang, nor icc), GL_ICC_VERSION, etc.? The effort to distribute (in a module) and include this file may well be larger than the gain, no? Actually I was thinking about putting this in config.h, so that we would even benefit from it at configure-time. It would also help casual gnulib contributors like me be shielded from compilers that pretend to be GCC.  For instance we should probably tune the snippet above even further, since Clang 7 pretends to be GCC 4.2 (__GNUC__ __GNUC_MINOR__). Also, in this case the code duplication is between a file in m4/ and a file in lib/. However, we don't have a good way to share code between m4/ and lib/, because an include statement in a .m4 file #include "$srcdir/lib/foo.h" would need to reference the gnulib-tool --source-base value instead of 'lib'. Yep, I can see the problem.  But I would probably have tried to deal with it the other way round: generate the *.h file from the macro. Yet I don't know all the places where _Noreturn.h is used, so maybe it's not (easily) doable. Also, the relationship with noreturn.h is not completely clear for me either.  For instance I see it already has the above fix for GCC 4.7, but in a different way.  /* Use ISO C++11 syntax when the compiler supports it.  */ # if (__cplusplus >= 201103 && !(__GNUC__ == 4 && __GNUC_MINOR__ == 7)) \     || (_MSC_VER >= 1900) #  define _GL_NORETURN_FUNC [[noreturn]] And I just discovered stdnoreturn.in.h which has a third approach, configure-based.