<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/139818>139818</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [clang] constant evaluation of `for` loop does not run destructor for condition variable
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            good first issue,
            clang:frontend,
            accepts-invalid,
            c++23
      </td>
    </tr>

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

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

<pre>
    If a condition variable is declared in the second clause of a three-clause `for` loop, clang doesn't destroy it when constant-evaluating the loop. For example:
```c++
struct X {
  constexpr ~X() noexcept(false) { throw "oops"; }
  constexpr operator bool() {
    return b;
  }
  bool b;
};
constexpr bool f() {
  for (bool b = false; X x = {b}; b = true) {}
  return true;
}
static_assert(f());
```
Clang treats this as constant, but the destructor for `x` throws an exception.

It looks like the problem is that we fail to call `IterScope.destroy()` [here](https://github.com/llvm/llvm-project/blob/5f41928689125667cf645835fa9fefee97511d8a/clang/lib/AST/ExprConstant.cpp#L5742), when terminating a loop iteration because the condition evaluated to `false`.
</pre>
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