<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/62532>62532</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            D146051 breaks some reductions in AMD GPU offload if -O0
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
      </td>
    </tr>

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

    <tr>
      <th>Reporter</th>
      <td>
          jdenny-ornl
      </td>
    </tr>
</table>

<pre>
    I expect the following reproducer to print i=18:

```
#include <stdio.h>

int main() {
  int i = 10;
  #pragma omp target teams num_teams(1) reduction(+:i)
  {   
    #pragma omp distribute parallel for num_threads(1) reduction(+: i)
    for (int x = 0; x < 4; ++x)
 i += 1;
    #pragma omp distribute parallel for num_threads(1) reduction(+: i)
    for (int x = 0; x < 4; ++x)
      i += 1;
 }
  printf("i=%d\n", i);
  return i != 18;
}
```

Working at 8b8466fd31e5 (a main commit from today) while offloading to a gfx906, I saw the wrong result:

```
$ clang -fopenmp -fopenmp-targets=amdgcn-amd-amdhsa test.c
$ ./a.out
i=10
```

The test also reproduced the bug without num_threads(1) and num_teams(1), which I added just to see if parallelism mattered.

I found some workarounds that caused the test to print i=18 as expected:

- Add -O1 or higher to the clang command line.
- Offload to nvptx64 or x86_64 instead.
- Revert fb5683449e97 (D146051), a commit from March that I identified via git bisect.  That commit just relocates DeadArgumentEliminationPass

I configured as follows, and check-all succeeded with or without the revert:

```
$ cmake \
 -DCMAKE_BUILD_TYPE=Release \
  -DLLVM_ENABLE_PROJECTS='clang;lld' \
 -DLLVM_ENABLE_RUNTIMES=openmp \
  -DLLVM_TARGETS_TO_BUILD='host;AMDGPU' \
  -DCMAKE_C_COMPILER=gcc \
  -DCMAKE_CXX_COMPILER=g++ \
 ../llvm 
```
</pre>
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