<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/146990>146990</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [MLIR][SCF] pipelining pass use of uninitialized value
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            mlir
      </td>
    </tr>

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

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

<pre>
    Here in the code:

https://github.com/llvm/llvm-project/blob/61529d9e36fa86782a2458e6bdeedf7f376ef4b5/mlir/lib/Dialect/SCF/Transforms/LoopPipelining.cpp#L127

https://github.com/llvm/llvm-project/blob/61529d9e36fa86782a2458e6bdeedf7f376ef4b5/mlir/lib/Dialect/SCF/Transforms/LoopPipelining.cpp#L148-L153

`maxStage` is used before initialized.

When it checks `numIteration > maxStage` at line-127, maxStage is always 0 as default. So it will mistakenly decide if the loop trip count is actually greater than stage number, and thus pipelining a loop that should not have done.

---
At older llvm version(17), it was correct. The problem is introduced in this commit: https://github.com/llvm/llvm-project/commit/ef112833e11e94ea049f98bec4a29b4fe96a25dd
</pre>
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