https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56592
--- Comment #5 from Oleg Endo <olegendo at gcc dot gnu.org> --- (In reply to Oleg Endo from comment #0) > In order to > minimize mode switches the function signature can be taken into account when > deciding the default FPU precision for a particular function. E.g. when a > function has any double precision arguments, it can be assumed that the > function will use the double values in some way. Thus the default entry > mode for such a function should be 'double'. Similarly, for functions that > return double values it can be better to leave the function with 'double' > mode. I think this idea is going to be problematic in the general case. Although implicit function declarations have been obsoleted and are being phased out, there's still quite some code out there that relies on it. The same goes for the va_args handling of the current GNU vs. Renesas ABI. The GNU ABI works for implicit function declarations because arguments are passed always in the same way, regardless of argument type/count.
