<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/122439>122439</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [DAG] SDPatternMatch - add m_Undef matcher
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            good first issue,
            llvm:SelectionDAG
      </td>
    </tr>

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

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

<pre>
    Add SDPatternMatch matcher and unit test coverage for ISD::UNDEF opcode

e.g.
```
m_InsertSubVector(m_Undef(), m_Value(), m_Zero()) // subvector widening pattern
```
</pre>
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