[Bug c/120850] provide an special __builtin_memset_explicit

[xry111 at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120850

--- Comment #12 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
I.e. on the contrary the normal memset() *can* be optimized away *just because*
we have a __builtin_memset.