<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/133507>133507</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            clang 19 or 20 miscompiles llvm::MergeBasicBlockIntoOnlyPred for PPC32
        </td>
    </tr>

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

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

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

<pre>
    For target powerpc-unknown-openbsd, clang-19 or clang-20 miscompiles the function llvm::MergeBasicBlockIntoOnlyPred in llvm 19. clang-18 works. This means that clang-19 miscompiles itself for 32-bit PowerPC. If my target clang-19 contains a miscompiled MergeBasicBlockIntoOnlyPred, then it will (with most .c files) either crash SIGSEGV or get stuck in an infinite loop.

My target clang-19's source tree has a few modifications. One of them moves MergeBasicBlockIntoOnlyPred from llvm/lib/Transforms/Utils/Local.cpp to its own file. The attached [emini.zip](https://github.com/user-attachments/files/19510915/emini.zip) contains

- emini.cpp, a MergeBasicBlockIntoOnlyPred preprocessed by clang-16 with OpenBSD/macppc headers.
- ecompile.sh, a script to cross-compile emini.cpp,

$ sh ecompile.sh -c emini.cpp -o whatever.o

You can build emini.cpp with clang 16 to 20. It doesn't work with git main, because clang-21 seems to drop support for __is_referencable in my libc++ headers.

I have started a git bisect of llvm-project on my fast AMD64 machine. I can cross-compile emini.cpp on the AMD64 and copy the .o to my slow PPC32 machine, where I link it into my target clang-19, then try to compile and run OpenBSD date(1) with my target clang-19. If it works, git bisect good. If it crashes or times out, git bisect bad. I know that releases/20.x is bad and releases/18.x is good. I need about 2 hours to build each git commit, so I might take a few more days to finish my bisect.
</pre>
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