<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/223249>223249</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [InstCombine] Fold equality with self-dependent select to constant set membership
        </td>
    </tr>

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

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

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

<pre>
    ## Description

InstCombine appears to miss:

```text
X == select(X >s 0, C1, C2)
  ->
(X == C1) || (X == C2)
```
when C1 >s 0 and C2 <=s 0.

Example:

define i1 @src(i32 %x) {
  %cond = icmp sgt i32 %x, 0
  %s = select i1 %cond, i32 2, i32 0
  %r = icmp eq i32 %x, %s
  ret i1 %r
}

define i1 @tgt(i32 %x) {
  %a = icmp eq i32 %x, 0
  %b = icmp eq i32 %x, 2
  %r = or i1 %a, %b
  ret i1 %r
}

Alive2: https://alive2.llvm.org/ce/z/LMpt7A

Generalized Alive2 proof: https://alive2.llvm.org/ce/z/ZMrWVm

The source is true exactly for X = 0 or X = 2, so the select can be replaced by a constant set-membership check.
</pre>
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