<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/135996>135996</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Crash on LLVM MachineFunctionPass Plugin with `opt`
        </td>
    </tr>

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

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

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

<pre>
    I've written the following empty MachineFunctionPass:
    
    #include "llvm/CodeGen/MachineFunctionPass.h"
    #include "llvm/CodeGen/MachineFunction.h"
    #include "llvm/Passes/PassBuilder.h"
    #include "llvm/Passes/PassPlugin.h"
    #include "llvm/CodeGen/MachinePassManager.h"
    #include "llvm/CodeGen/MachineFunctionPass.h"
    #include "llvm/Support/raw_ostream.h"
    
    using namespace llvm;
    
    struct MyMachineFunctionPass : PassInfoMixin<MyMachineFunctionPass> {
    
        static StringRef name() { return "MyMachineFunctionPass"; }
           
        // Doing transformations here...
        PreservedAnalyses run(MachineFunction &MF, MachineFunctionAnalysisManager &AM) {
            errs() << "Running MyMachineFunctionPass\n";
    
            return PreservedAnalyses::none();
        }
    
        /// (2) Optional initialization before any MachineFunction runs
        static Error doInitialization(Module &M, MachineFunctionAnalysisManager &AM) {
            errs() << "Initializing MyMachineFunctionPass on module: " << M.getName() << "\n";
            return Error::success();
        }
    
        /// (3) Optional finalization after all MachineFunctions have run
        static Error doFinalization(Module &M, MachineFunctionAnalysisManager &AM) {
            errs() << "Finalizing MyMachineFunctionPass on module: " << M.getName() << "\n";
            return Error::success();
        }
    
        /// (4) Fallback: runs on module if invoked incorrectly as an IR pass (shouldn't happen in proper use)
        static Error run(Module &M, MachineFunctionAnalysisManager &AM) {
            errs() << "WARNING: MyMachineFunctionPass called on Module — skipping\n";
            return Error::success();
        }
    
    };
    
    extern "C" LLVM_ATTRIBUTE_WEAK ::llvm::PassPluginLibraryInfo llvmGetPassPluginInfo() {
        errs() << "[+] Running llvmGetPassPluginInfo()\n";
    
        return {
            LLVM_PLUGIN_API_VERSION, "MyMachineFunctionPass", LLVM_VERSION_STRING,
            [](PassBuilder &PB) {
                PB.registerPipelineParsingCallback(
                    [](StringRef Name, MachineFunctionPassManager &MFPM, ArrayRef<PassBuilder::PipelineElement>) {
                        errs() << "[+] Running registerPipelineParsingCallback()\n";
    
                        if (Name == "MyMachineFunctionPass") {
                            errs() << "    - Name is MyMachineFunctionPass\n";
                            MFPM.addPass(MyMachineFunctionPass());
                            return true;
                        }
    
                        return false;
                    }
                );
            }
        };
    }

However, `opt` segfaults on compilation using this plugin:

    root@5c9cdbf4bf7a:/tmp/workdir# clang -O0 -emit-llvm -c beacon/test.c -o builds/test.bc
    root@5c9cdbf4bf7a:/tmp/workdir# llc -O0 -stop-after=finalize-isel -march=x86-64 -o builds/test.mir builds/test.bc
    root@5c9cdbf4bf7a:/tmp/workdir# opt -load-pass-plugin=./transpiler/build/libMyMachineFunctionPass.so -passes=MyMachineFunctionPass -S ./builds/test.bc -o ./builds/test.ll
    [+] Running llvmGetPassPluginInfo()
    [+] Running registerPipelineParsingCallback()
        - Name is MyMachineFunctionPass
    [+] Running registerPipelineParsingCallback()
        - Name is MyMachineFunctionPass
    PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
    Stack dump:
    0.      Program arguments: opt -load-pass-plugin=./transpiler/build/libMyMachineFunctionPass.so -passes=MyMachineFunctionPass -S ./builds/test.bc -o ./builds/test.ll
    1.      Running pass "function(machine-function(MyMachineFunctionPass))" on module "./builds/test.bc"
    2.      Running pass "machine-function(MyMachineFunctionPass)" on function "main"
     #0 0x00007f2b019c7d46 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/usr/lib/llvm-20/bin/../lib/libLLVM.so.20.1+0x1025d46)
     #1 0x00007f2b019c59d0 llvm::sys::RunSignalHandlers() (/usr/lib/llvm-20/bin/../lib/libLLVM.so.20.1+0x10239d0)
     #2 0x00007f2b019c83fb (/usr/lib/llvm-20/bin/../lib/libLLVM.so.20.1+0x10263fb)
     #3 0x00007f2b004dd050 (/lib/x86_64-linux-gnu/libc.so.6+0x3c050)
     #4 0x00007f2b01b57ffe llvm::AnalysisManager<llvm::Function>::getResultImpl(llvm::AnalysisKey*, llvm::Function&) (/usr/lib/llvm-20/bin/../lib/libLLVM.so.20.1+0x11b5ffe)
     #5 0x00007f2b01e0613e llvm::FunctionToMachineFunctionPassAdaptor::run(llvm::Function&, llvm::AnalysisManager<llvm::Function>&) (/usr/lib/llvm-20/bin/../lib/libLLVM.so.20.1+0x146413e)
     #6 0x00007f2b03d7b80d (/usr/lib/llvm-20/bin/../lib/libLLVM.so.20.1+0x33d980d)
     #7 0x00007f2b01b55349 llvm::PassManager<llvm::Function, llvm::AnalysisManager<llvm::Function>>::run(llvm::Function&, llvm::AnalysisManager<llvm::Function>&) (/usr/lib/llvm-20/bin/../lib/libLLVM.so.20.1+0x11b3349)
     #8 0x00007f2b03d6da1d (/usr/lib/llvm-20/bin/../lib/libLLVM.so.20.1+0x33cba1d)
     #9 0x00007f2b01b59306 llvm::ModuleToFunctionPassAdaptor::run(llvm::Module&, llvm::AnalysisManager<llvm::Module>&) (/usr/lib/llvm-20/bin/../lib/libLLVM.so.20.1+0x11b7306)
    #10 0x00007f2b03d7765d (/usr/lib/llvm-20/bin/../lib/libLLVM.so.20.1+0x33d565d)
    #11 0x00007f2b01b54057 llvm::PassManager<llvm::Module, llvm::AnalysisManager<llvm::Module>>::run(llvm::Module&, llvm::AnalysisManager<llvm::Module>&) (/usr/lib/llvm-20/bin/../lib/libLLVM.so.20.1+0x11b2057)
    #12 0x000055d5e57d6b61 llvm::runPassPipeline(llvm::StringRef, llvm::Module&, llvm::TargetMachine*, llvm::TargetLibraryInfoImpl*, llvm::ToolOutputFile*, llvm::ToolOutputFile*, llvm::ToolOutputFile*, llvm::StringRef, llvm::ArrayRef<llvm::PassPlugin>, llvm::ArrayRef<std::function<void (llvm::PassBuilder&)>>, llvm::opt_tool::OutputKind, llvm::opt_tool::VerifierKind, bool, bool, bool, bool, bool, bool, bool) (/usr/lib/llvm-20/bin/opt+0x29b61)
    #13 0x000055d5e57cbc2e optMain (/usr/lib/llvm-20/bin/opt+0x1ec2e)
    #14 0x00007f2b004c824a (/lib/x86_64-linux-gnu/libc.so.6+0x2724a)
    #15 0x00007f2b004c8305 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x27305)
    #16 0x000055d5e57c60b1 _start (/usr/lib/llvm-20/bin/opt+0x190b1)
    Segmentation fault (core dumped)

I wonder if anyone could guide me in the right direction.
</pre>
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