[Bug c++/86369] constexpr const char* comparison fails

[aaron at aaronballman dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86369

--- Comment #11 from Aaron Ballman <aaron at aaronballman dot com> ---
(In reply to Jakub Jelinek from comment #10)
> (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 = "abc";
> constexpr const char *q = p;
> static_assert (p == q, "");
> doesn't actually mean the string literal is evaluated multiple times, because
> if it would be, then one pretty much can't use string literals for anything
> reliably.

Oh yeah, I agree with you in that case. I was talking about the summary example
with function calls returning a string literal. Sorry for not being more clear!

> I bet the wording in there is for the
> constexpr const char *r = "abc";
> constexpr const char *s = "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
> literal (GCC doesn't track that either) and just assumes that it could be
> different evaluation, while GCC assumes it is not.

Yeah, that sounds plausible.