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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/86369] constexpr const char* comparison fails
Date: Fri, 04 Nov 2022 13:27:19 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D86369

--- Comment #10 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Aaron Ballman from comment #9)
> Doesn't [expr.eq] make it unspecified though?

Will defer that answer to Jason.
But please have a look at the comment 6 testcase.  I strongly hope that
constexpr const char *p =3D "abc";
constexpr const char *q =3D p;
static_assert (p =3D=3D q, "");
doesn't actually mean the string literal is evaluated multiple times, becau=
se
if it would be, then one pretty much can't use string literals for anything
reliably.
I bet the wording in there is for the
constexpr const char *r =3D "abc";
constexpr const char *s =3D "abc";
case, where the standard doesn't force implementations to unify same string
literals within the same TU but allows it (and also allows say tail merging=
 of
them).  From what I can see in the LLVM constant expression evaluation
behavior, it doesn't track what comes from which evaluation of a string lit=
eral
(GCC doesn't track that either) and just assumes that it could be different
evaluation, while GCC assumes it is not.=