<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/85833>85833</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [InstCombine] Missed optimization: fold chained selects with exclusive condition but one identical arm
        </td>
    </tr>

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

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

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

<pre>
    Alive2 proof: https://alive2.llvm.org/ce/z/ZkjFRM

### Motivating example 

```llvm
define ptr @src(i32 %level, ptr %level.addr) local_unnamed_addr #0 {
entry:
  %c1 = icmp eq i32 %level, 0
  %c2 = icmp eq i32 %level, 1
  %s1 = select i1 %c1, ptr %level.addr, ptr null
 %s2 = select i1 %c2, ptr null, ptr %s1
  ret ptr %s2
}
```
can be folded to:
```llvm
define ptr @tgt(i32 %level, ptr %level.addr) local_unnamed_addr #0 {
entry:
  %cond = icmp eq i32 %level, 0
  %s1 = select i1 %cond, ptr %level.addr, ptr null
  ret ptr %s1
}
```

### Real-world motivation

This snippet of IR is derived from [openssl/crypto/shlib/cmp_util.c@OSSL_CMP_print_to_bio](https://github.com/openssl/openssl/blob/dc9bc6c8e1bd329ead703417a2235ab3e97557ec/crypto/cmp/cmp_util.c#L127) (after O3 pipeline).
The example above is a reduced version. If you're interested in the original suboptimal IR and optimal IR, see also: https://godbolt.org/z/qrh916jj8

**Let me know if you can confirm that it's an optimization opportunity, thanks.**
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJy0Vc1u4zYQfhr6MoghUf8HH5IYBgIk2CLbQ9GLQZEjaxKK1JKUs96nLyi5SZxu070UICTNcPRx5psfCu_pYBA3rLhhxXYlptBbt_njtj-tWqtOm2tNR-QwOms7ll1DH8LoWXbN-I7xnZh311ofh7V1B8Z3Ehnf_WB89-fz0-7xgSVbllyfnzxbFjzYQEcRyBwAv4th1AgXhmWyrIi7qBR2ZBDG4IDliXeS8ZoyDowXGo-oGb9dNs_yWijlGG9AWyn0fjJGDKj2UQuMZwmw6mZBRhPcKQY0SxARZAos2wLJYQT8Bh_PSd6b8k9N03emfkH1qFEGoHQ56V8cX5Rm0vqMEAH4TwD4he0bmH892mF4VfIzwdX2A9OLKIWBFqGzWqGCYF9p-c-MhEP4XzNijfrlnPyUaGvUr1J9wVj6OWMfK_sRhb56sU4rGM5Fbs1709978uANjSMGsB3cPQJ5UOjoiAo6ZwdgxY0d0XivYz-50xgs4zvfa2qjYhj3UyC9lixPvnz9er-_ffhtPzoyYR_sviXLii3j9WWjHij0U7uWdmB894b-9tVqG9GVbFpZyhrTVmW8QaGqJMvTSnCeFaLNsKmKokL53jM5jJd-8ew-5VXMNeO16AI6-JLBSCNqMsh4s_6bC3ztf9HaI0YqBDhUk0QFR3SerFnDXQcnOzFeOQQyAR36gArIQOgRrKMDGaHBT60dAw1CR1aFUfAmxjR7RBDa23-OsYNVrdXhPMLi9Prm-iYtn57qyzTHdY8BBoRnY1-AZs8g9o20piM3QOhFAAqMVx6EWVygH3MdgB1H68JkKJyiQ6EX5tmvF9iV2mSqyRqxwk1apUldJVlZrfpNUqgiaepalnnHS5kkhSibtMmSshRNWuQr2vCE50mWNmmVl0m1zlFVssjzriw7Vaua5QkOgvTrnF6R9xNu6qLOspUWLWo_XwCcG3yBeZNxHu8Dt4n_XLXTwbM80eSDf0MJFPR8c9wZH27t0MbsFlt4IO9RXYQeOY9jBWQvyKA6d6eHFwo94HepJ09HjCwqmrlqpwDWIJBCE0gKDcINq8npzSeVPY-n5XU1OvuEMjC-mwPyjO_mgP8KAAD__xE-HTM">