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From: "tim at klingt dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/107521] New: clang rejects invalid code in libstdc++
Date: Fri, 04 Nov 2022 04:17:34 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Version: 12.1.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107521

            Bug ID: 107521
           Summary: clang rejects invalid code in libstdc++
           Product: gcc
           Version: 12.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tim at klingt dot org
  Target Milestone: ---

compare https://github.com/llvm/llvm-project/issues/58754

https://github.com/gcc-mirror/gcc/blob/master/libstdc%2B%2B-v3/include/bits=
/char_traits.h#L216-L217
```
          if (__s1 =3D=3D __s2) // unlikely, but saves a lot of work
            return __s1;
```

according to aaron ballman:

> Heh, that's a fun one. http://eel.is/c++draft/lex.string#9 is what that c=
ode is referring to and I believe Clang is correct to reject it as a core c=
onstant expression per http://eel.is/c++draft/expr.const#5.24 because the e=
quality operator's results are unspecified.

according to jonathan wakely:
> This is a libstdc++ bug.
> And a g++ bug, for letting me do it.=