https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64225
--- Comment #8 from joseph at codesourcery dot com <joseph at codesourcery dot com> --- Expanding x * x (or any such multiplication) to a call to pow is inherently dubious because the semantics of multiplication never include clobbering errno, though maybe it's OK with -funsafe-math-optimizations to introduce such a clobber. I think it would be useful to have no-errno-setting-needed versions of libm function builtins that users can call explicitly, as well as for internal use by GCC when it generates a built-in function call from code that doesn't set errno. (For example: glibc uses __builtin_fma to expand to an fma instruction when _FP_FAST_FMA indicates one is available. But strictly it's incorrect to expand fma / __builtin_fma calls to such an instruction without considering errno, unless -fno-math-errno. None of those glibc uses require fma to set errno (and glibc fma has its own bug where it fails to do so), so it would be beneficial to have __builtin_fma_noerrno to reflect what's actually required - this function would expand inline if possible, and failing that would call an fma function that might or might not end up settting errno.)
