On Thu, Jun 10, 2021 at 11:24:43AM +0100, Jonathan Wakely wrote:
> > And I'm not changing the libstdc++ side, where perhaps we could change
> > std::is_constant_evaluated definition for
> > #ifdef __cpp_if_consteval
> > case to if consteval { return true; } else { return false; }
> > but we need to keep it defined to __builtin_is_constant_evaluated ()
> > for C++20 or older.
>
> Is there any advantage to changing that (cheaper for GCC to evaluate?)
I guess compile-time lost in the noise.
> or should we just continue to use the __builtin unconditionally?
>
> I suppose it's theoretically possible that there could be a non-GCC
> compiler where defined(__cpp_if_consteval) is true but
> __has_builtin(__builtin_is_constant_evaluated) is false.
Up to you. The wording says Equivalent to
if consteval { return true; } else { return false; }
and return __builtin_is_constant_evaluated (); is equivalent to that.
Perhaps some people could appreciate to see it literally there, but we
can't use it for C++20 (due to the -Wpedantic warnings or -pedantic-errors
errors) and for C++17 and earlier (consteval is not a keyword).
Jakub
