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From: "jlame646 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/107039] New: GCC not diagnosing UB in constant expression
Date: Mon, 26 Sep 2022 08:44:16 +0000
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X-Bugzilla-Version: 12.2.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107039

            Bug ID: 107039
           Summary: GCC not diagnosing UB in constant expression
           Product: gcc
           Version: 12.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jlame646 at gmail dot com
  Target Milestone: ---

GCC doesn't give diagnostic for the following program while clang and msvc =
do.
Demo: https://godbolt.org/z/o3K57fjeE

```
struct S
{
    int a, b;
};

constexpr void fn( S &s )
{
    (&s.b)[-1] =3D 123;
}

constexpr auto test =3D ([]{
    S s;
    fn(s);
}(), 0);
```

There should be a diagnostic for the above code.=