<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/122688>122688</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            GlobalISel sdiv/sext shift right heavy
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            backend:AMDGPU,
            llvm:globalisel
      </td>
    </tr>

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

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

<pre>
    [reduced.gisel.txt](https://github.com/user-attachments/files/18395905/reduced.gisel.txt)
[reduced.sdisel.txt](https://github.com/user-attachments/files/18395904/reduced.sdisel.txt)
[reduced.txt](https://github.com/user-attachments/files/18395903/reduced.txt)

Given input IR like:

```
  %i78 = sdiv i32 %i, 128
  %i80 = sext i32 %i78 to i64
  %i83 = sdiv i64 %i80, 4
```

I see many more `ashr` and `lshr` instructions in the result with global-isel. I believe SDIsel is instead using `v_bfe` instead of some 2-4 SHR instructions.

I've been looking at this and reducing with the instruction `llc -O3 -march=amdgcn -mcpu=gfx942 -mtriple amdgcn-amd-hmcsa  ./reduced.ll  -global-isel={true,false}`
</pre>
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