https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82318
--- Comment #7 from Rich Felker <bugdal at aerifal dot cx> --- I'll inquire about it. Note that F.6 already requires this for C functions; the loophole is just that the implementation itself does not inherently have to consist of C functions. If it's determined that C won't require the library functions not bound to IEEE operations to return values representable in their nominal type, then GCC needs to be aware of whether the target libc can be expected to do so, and if not, it needs to, as a special case, assume there might be excess precision in the return value, so that (double)retval==retval can't be assumed to be true in the optimizer. Note that such an option would be nice to have anyway, for arbitrary functions, since it's necessary for being able to call code that was compiled with -fexcess-precision=fast from code that can't accept the non-conforming/optimizer-unsafe behavior and safely use the return value. It should probably be an attribute, with a flag to set the global default. For example, __attribute__((__returns_excess_precision__)).
