<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/62944>62944</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Example from C++ standard is rejected as part of constant expression
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            new issue
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          Fedr
      </td>
    </tr>
</table>

<pre>
    [OK example](https://timsong-cpp.github.io/cppwp/n4868/class.mem.general#25) from C++ standard is rejected by Clang if it is evaluated as constant expression:
```
struct T1 { int a, b; };
struct T2 { int c; double d; };
union U { T1 t1; T2 t2; };

constexpr int f() {
  U u = { { 1, 2 } };   // active member is t1
  return u.t2.c;        // OK, as if u.t1.a were nominated
}

constexpr int x = f();
```
with the error:
```
read of member 't2' of union with active member 't1' is not allowed in a constant expression
```
Other compilers reject it as well (https://gcc.godbolt.org/z/YTds3Grd5), but since Clang is typically most standard conforming, I decided to ask you first.

Related discussion: https://stackoverflow.com/q/76323477/7325599
</pre>
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