<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/54851>54851</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            GVN hoists loads over unknown intrinsics
        </td>
    </tr>

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

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

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

<pre>
    Originally reported here: https://discourse.llvm.org/t/bug-gvn-memdep-bug-in-the-presence-of-intrinsics/59402

> GVN, or probably memdep analysis, seem to think intrinsics are somewhat special
> and consequently assume they cannot "effectively clobber" a memory location. It
> might also be globals-mod-ref or something else that provides AA information.
> 
> The following example ([https://godbolt.org/z/TG6dYvP6M 1](https://godbolt.org/z/TG6dYvP6M)) shows how an unknown function
> prevents an invalid load hoist while an unknown intrinsic does not. Again, the preload
> is not sound in a multi-thread environment.

The simple reproducer can be found here: https://godbolt.org/z/cKMEezbjY
Compiled with `-globals-aa -gvn` the below code will hoist the load above the barrier but not the unknown function.

```
@G = internal global i32 undef

define void @test_barrier(i1 %c) {
  br i1 %c, label %init, label %check
init:
  store i32 0, ptr @G
  br label %check
check:
  call void @llvm.amdgcn.s.barrier()
  %v = load i32, ptr @G
  %cmp = icmp eq i32 %v, 0
  call void @llvm.assume(i1 %cmp)
  ret void
}

define void @test_unknown(i1 %c) {
  br i1 %c, label %init, label %check
init:
  store i32 0, ptr @G
  br label %check
check:
  call void @unknown()
  %v = load i32, ptr @G
  %cmp = icmp eq i32 %v, 0
  call void @llvm.assume(i1 %cmp)
  ret void
}

declare void @unknown()
declare void @llvm.amdgcn.s.barrier()
declare void @llvm.assume(i1 noundef)
```
</pre>
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