<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/63316>63316</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Instcombine incorrectly optimizes `fcmp uno`
        </td>
    </tr>

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

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

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

<pre>
    After this commit: https://github.com/llvm/llvm-project/commit/e47b76a82a0300900dbf3c2d3a50552a76305a8c running `opt -passes=instcombine` on the following IR:
```
define i1 @test(i64 %arg) {
  %sitofp = sitofp i64 %arg to float
  %fmul = fmul float %sitofp, 0x7FF0000000000000
  %fcmp = fcmp uno float %fmul, 0.000000e+00
  ret i1 %fcmp
}
```
results in
```
define i1 @test(i64 %arg) {
  ret i1 false
}
```
That's not correct because `fcmp uno` returns true if either argument is NaN and by IEEE-754 multiplication of infinity (aka `0x7FF0000000000000`) and 0 (`sitofp i64 %arg to float` with `%arg == 0`) is NaN. Alive2 points out exactly this case: https://alive2.llvm.org/ce/z/5rPFgH
</pre>
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