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From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/112296] __builtin_constant_p doesn't propagate through
 member functions
Date: Mon, 30 Oct 2023 14:49:58 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D112296

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Barry Revzin from comment #0)
> inline int direct(Span span) {
>     return __builtin_constant_p(span.size());
> }
>=20
> inline int indirect(Span span) {
>     size_t s =3D span.size();
>     return __builtin_constant_p(s);
> }

If the problem is that bcp is limited by inlining, you'd think that the fir=
st
one would be more likely to work. It does less.

Clearly inlining can see through the member function, because in 'indirect'=
 it
can propagate its return value through 's' and to the bcp call.

But in 'direct' the return value is somehow not constant when used directly=
. It
is only constant if propagated through a local variable. That seems like an
unnecessary limitation.=