<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/132609>132609</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            add `-Wmacro-redefined-duplicate`
        </td>
    </tr>

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

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

    <tr>
      <th>Reporter</th>
      <td>
          kasperk81
      </td>
    </tr>
</table>

<pre>
    C language allows macro redefinition as long as the values are the same. when values are different clang issues `-Wmacro-redefined`.

a new diagnostic `-Wmarco-redefined-duplicate` would help with code cleanup. clang already has that information (it clearly "skips" `-Wmacro-redefined` when values are the same), so it should be able to expose it in pedantic mode.

there is an indirect way to detect it using `-Wunused-macros`:
https://godbolt.org/z/dxG8K1cPb
but it only flags the first occurrence of same-value-duplicate as unused and doesn't show the _other_ occurrence(s).
</pre>
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