[Bug libstdc++/78420] [6/7/8 Regression] std::less<T*> is not a total order with -O2 enabled

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78420

--- Comment #25 from Jason Merrill <jason at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #23)
> One possibility would be a __builtin_constant_p-like builtin that would fold
> to false much earlier than the current __builtin_constant_p, e.g. during
> gimplification.

I think this would only be useful for C++ constexpr evaluation, since most uses
in C depend on being folded after inlining.