[Bug c++/80265] __builtin_{memcmp,memchr,strlen} are not usable in constexpr functions

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80265

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
I think you need to handle some of the builtin folding in the C++ FE.