<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/102823>102823</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [IR] A question about the ordering of allocas
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            question,
            documentation,
            llvm:ir
      </td>
    </tr>

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

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

<pre>
    See the following stack growth direction detection idiom: https://github.com/google/googletest/blob/ff233bdd4cac0a0bf6e5cd45bda3406814cb2796/googletest/src/gtest-death-test.cc#L1213-L1247

LLVM IR for `testing::internal::StackGrowsDown()`:
```
; Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn memory(none) uwtable
define hidden noundef zeroext i1 @_ZN7testing8internal14StackGrowsDownEv() local_unnamed_addr #4 {
entry:
  %dummy.i = alloca i32, align 4
  %dummy = alloca i32, align 4
  call void @llvm.lifetime.start.p0(i64 4, ptr nonnull %dummy.i)
  %cmp.i = icmp ult ptr %dummy.i, %dummy
  call void @llvm.lifetime.end.p0(i64 4, ptr nonnull %dummy.i)
  ret i1 %cmp.i
}
```

Is it a well-defined behavior? If we swap these two allocas, does it produce the opposite result? If so, are we allowed to constant fold the pointer comparison based on `TargetFrameLowering::getStackGrowthDirection`?

I cannot find any information from LangRef.

cc @RKSimon @topperc @nikic 
</pre>
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