<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=http://email.email.llvm.org/c/eJzdVcFu4zYQ_Rr5QsSQKEsWDz44sdMGSDdBNrvNjaDIkc2GFgWSyjp_3yHtJN5m0aBd9FJBkEhq9Pg475HTWvW8uN9qTzzAzpNgSQtE98FZNUpQpH0mdTGrYSa7hqlWVYrVdC5nNZtB3oJgaibzTtbYmWb5KsuX19Y-6n5DRCBhC0RBp3sdtO0RlmTVOf_mxMB1ADfdZtUqo802hMFn5TKjl3hvdNiO7VTaHXaMeXp5nQ3O_gEyYLc1tsVXDqpjjFU51LScFRWTjM2LvCmbjhaqrClT86oWXQTQrdzvsaF7aUYF2OKJgwjWYeeUEy2v51VGWaIvZBiFIcJ7vel30AfiAwwEE7YZhVOYIbERuvc4DqY7jVt-WmEuYyZgD3IMGDr2ChzJ6pzzSGjAKT2XFv8WfeDwJMwoMA4DyBm5wvl1_5hYGBGQG_FbOxpFbG-eD9MfM9yOGxKckCnvRj9GBYnFb47sYNfiqxt7GTXwR5EOzyXp9B55PYHzUSCZ4A0KmFCiJIfoOj_cMqPn8U6jBC9-fXV-cXvLf71arfnl3c1vfHl-9Tp6cfPp8_364faOLy_v13f84uGhKE5-frNCRmtih6McZTRFSstfQzhHDdkbQjY_4RIv3RH8N0RDZ7RAJMK_fr5fxZWUS6GUA-8tGqI5Ip2C_RDwDRTxPpAtxryHfLk430Dgqj2EnWXl-s2BiDY8H4ln9OJj0uUPaCIcSSvm-ym238Vk89X3Aw7C6HBP0mWa9zT-NfZV-lPf3DgiDFLvRdBPgGZEbh53FrzbBIdTZSvczuAioi2TNlJ4SMtYnsL-b22GQXXE_RkL_Sf2-X6ajwz0r_3yOx7pdgzp5Dtqtlqff_mFX6-_rq_jnHFaGs-9eKDF1Zya6EUxktLd6N1gtNTBPMfUYn0Ro0m5uyDeJgCsFK2BHVEWPOltQAMOA0TvgYPpRC1KxUomJmJEXm4hexh3ou8nozOLf1yMtPcjYNovK8pyOtkuFAXW1GXb1U3VlJ3M2zqfqbKDmgGbz4uJES0Yv8BamFHawzeSILCN5XDy8wz0gua0KChtirqc02ba5M2siBQqxspazbNZDjuhzTTiTK3bTNwiQWId8fjRaB_828eDEgCJMDIMmPrUiU4-7tRqRZKbYT-49_p1WGFk2nLRki-uPYYkhbaxch3K4985ZJKWukjr_BOtzqMF>52902</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [libc++] constexpr copy assignment of vector::iterator assigns nothing under _LIBCPP_DEBUG_LEVEL == 2
        </td>
    </tr>

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

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

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

<pre>
    This seems to be introduced by 6146e4cf89dbd5d9627c4694e0bea9d4c0fc6e0b.
Looking at the definition in [_wrap_iter.h](https://github.com/llvm/llvm-project/blob/0edf99950e6234159c99710838f21d3629d756af/libcxx/include/__iterator/wrap_iter.h#L75) the actual assignment step is guarded against self assignment AND being executed under `__libcpp_is_constant_evaluated` - I think the latter should only guard the debug tracking like in other member functions.

A fixed version could look like:
```c++
    _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX11
    __wrap_iter& operator=(const __wrap_iter& __x)
    {
        if (this != _VSTD::addressof(__x))
        {
            if (!__libcpp_is_constant_evaluated())
                __get_db()->__iterator_copy(this, _VSTD::addressof(__x));
            __i = __x.__i;
        }
        return *this;
    }
```

Or alternatively (since self assignment seems harmless in this case):

```c++
    _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX11
    __wrap_iter& operator=(const __wrap_iter& __x)
    {
        if (this != _VSTD::addressof(__x) && !__libcpp_is_constant_evaluated())
            __get_db()->__iterator_copy(this, _VSTD::addressof(__x));

        __i = __x.__i;
        return *this;
    }
```

Without `_LIBCPP_DEBUG_LEVEL == 2` the copy assignment operator is (implicitly) defaulted, so the problem does not happen there.
</pre>
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