<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/107673>107673</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Seemingly incorrect treatment of constexpr member functions in modules
        </td>
    </tr>

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

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

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

<pre>
    According to the standard, member functions defined within a class definition are implicitly `inline` in the global module, but not so within a module purview. However, the standard also states that `constexpr` member functions are implicitly inline, and in this case makes no exception for modules. 

[11.4.2/1 [class.mfct] - see also Note 1](https://eel.is/c++draft/class.mfct#1)
[9.2.6/1 [dcl.constexpr]](https://eel.is/c++draft/dcl.constexpr#1)

As such all `constexpr` member functions should be `inline`, regardless of modules. From what I can see, clang is not respecting this. I'm seeing linker errors for such member functions when using modules with shared libraries. 

I believe the difference between clang and gcc [seen here](https://godbolt.org/z/GGW1fjMT1) is fundamentally the cause. Clang is generating code for a function marked `constexpr` but not for one marked `inline constexpr`, yet if I'm interpreting the standard correctly these cases should be equivalent.
</pre>
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