https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116775
--- Comment #9 from Jakub Jelinek <jakub at gcc dot gnu.org> --- Indeed, unevaluated for __builtin_constant_p is not unevaluated in the C++ standard sense, just the behavior that we normally just fold the routine to false if TREE_SIDE_EFFECTS on the operands early. Except for coros it isn't a big deal, it is ok just fold the builtin to 0. As I wrote, one option is when the coro lowering sees __builtin_constant_p look for co_await etc. in the argument and if it is there, fold the builtin manually to 0 instead of handling those and thus pretend co_* wasn't there at all. Or if we see those in __builtin_constant_p (exp), rewrite it into __builtin_constant_p (0 && exp) where we'd somehow force TREE_SIDE_EFFECTS. Note, __builtin_constant_p isn't the only problem, [[assume (exp)]]; is as well, __builtin_has_attribute I think too, maybe __builtin_choose_expr.
