<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/91619>91619</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Missed optimization in bounds analysis in unsigned arithmetic that cannot underflow
        </td>
    </tr>

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

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

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

<pre>
    Clang doesn't seem to be able to optimize the following out:

```
bool f(size_t a, size_t b) {
 __builtin_assume(a <= b);
    __builtin_assume(b <= PTRDIFF_MAX);
 // This can be deleted, because:
    //   1. 0 <= a <= b implies that b - a <= b
    //   2. b - a <= b <= PTRDIFF_MAX
    return b - a <= PTRDIFF_MAX;
}
```
https://godbolt.org/z/vzE7qb7Gb

I ran into this while exploring what combination of `__builtin_assume`s would dispatch some unnecessary assertions in `std::string_view`. (A separate bug while I'll file after this.)
</pre>
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