<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/135557>135557</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [ConstraintElim] Failure to eliminate cmp of usub.sat
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            llvm:optimizations,
            missed-optimization
      </td>
    </tr>

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

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

<pre>
    https://alive2.llvm.org/ce/z/4ZG-nD
```llvm
define i1 @src(i64 %index, i64 %limit) {
  %precond = icmp ult i64 %index, %limit
 call void @llvm.assume(i1 %precond)
  %sub.sat = call i64 @llvm.usub.sat.i64(i64 %index, i64 1)
  %cmp = icmp ult i64 %sub.sat, %limit
  ret i1 %cmp
}

define i1 @tgt(i64 %index, i64 %limit) {
  ret i1 true
}
```

I think we should be able to handle this by adding a fact that the usub.sat result is ule its first argument, similar to what we do for min/max/abs.
</pre>
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