<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/92366>92366</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [RISCV][LoopUnroll/CostModel] Loops with Insert/Extract element using induction variable without vector are not unrolled
        </td>
    </tr>

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

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

    <tr>
      <th>Reporter</th>
      <td>
          joe-img
      </td>
    </tr>
</table>

<pre>
    Without vector, extractelement/insertelement with non-constant index can be very costly. 
This was factored into the cost model in https://github.com/llvm/llvm-project/pull/67334

However, in the case of full canonical loop unrolling and the index being the induction variable, the index _will_ be constant, but is not at the time of estimating the cost of unrolling the loop.

Example before and after this change: (llvm 17 vs 18)
https://compiler-explorer.com/z/Mh6eWKjr7

I had a go at fixing this myself, but could not see a good fix. I ended up abusing ephemeral values that get passed into UnrollCostEstimator.
</pre>
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