llvm / llvm/llvm-project

Clang trunk (x86): assertion in TwoAddressInstructionImpl::processTiedPairs (duplicate tied reg) during backend lowering of inline asm with multiple tied outputs/inputs

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crash generated by fuzzer inline-asm llvm:codegen
Dominant language
LLVM
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Description

## Compiler Explorer: https://godbolt.org/z/nK9aseMGa

- clang start crashing on `Trunk`
- generated by fuzzer

## Console
```console
clang: /root/llvm-project/llvm/lib/CodeGen/TwoAddressInstructionPass.cpp:1605: void {anonymous}::TwoAddressInstructionImpl::processTiedPairs(llvm::MachineInstr*, {anonymous}::TwoAddressInstructionImpl::TiedPairList&, unsigned int&): Assertion `i == DstIdx || !MI->getOperand(i).isReg() || MI->getOperand(i).getReg() != RegA' failed.
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:
0. Program arguments: /opt/compiler-explorer/clang-assertions-trunk/bin/clang -g -o /app/output.s -mllvm --x86-asm-syntax=intel -fno-verbose-asm -S --gcc-toolchain=/opt/compiler-explorer/gcc-snapshot -fcolor-diagnostics -fno-crash-diagnostics
1. parser at end of file
2. Code generation
3. Running pass 'Function Pass Manager' on module ''.
4. Running pass 'Two-Address instruction pass' on function '@foo'
#0 0x00000000042ecab8 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x42ecab8)
#1 0x00000000042e9ee4 llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x42e9ee4)
#2 0x000000000422ec88 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
#3 0x0000797a93842520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
#4 0x0000797a938969fc pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x969fc)
#5 0x0000797a93842476 gsignal (/lib/x86_64-linux-gnu/libc.so.6+0x42476)
#6 0x0000797a938287f3 abort (/lib/x86_64-linux-gnu/libc.so.6+0x287f3)
#7 0x0000797a9382871b (/lib/x86_64-linux-gnu/libc.so.6+0x2871b)
#8 0x0000797a93839e96 (/lib/x86_64-linux-gnu/libc.so.6+0x39e96)
#9 0x00000000038b9caf (anonymous namespace)::TwoAddressInstructionImpl::processTiedPairs(llvm::MachineInstr*, llvm::SmallVector, 4u>&, unsigned int&) TwoAddressInstructionPass.cpp:0:0
#10 0x00000000038bb110 (anonymous namespace)::TwoAddressInstructionImpl::run() TwoAddressInstructionPass.cpp:0:0
#11 0x00000000038bd4f7 (anonymous namespace)::TwoAddressInstructionLegacyPass::runOnMachineFunction(llvm::MachineFunction&) TwoAddressInstructionPass.cpp:0:0
#12 0x00000000035843d9 llvm::MachineFunctionPass::runOnFunction(llvm::Function&) (.part.0) MachineFunctionPass.cpp:0:0
#13 0x0000000003bda986 llvm::FPPassManager::runOnFunction(llvm::Function&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x3bda986)
#14 0x0000000003bdad31 llvm::FPPassManager::runOnModule(llvm::Module&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x3bdad31)
#15 0x0000000003bdb59f llvm::legacy::PassManagerImpl::run(llvm::Module&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x3bdb59f)
#16 0x00000000045ae49c (anonymous namespace)::EmitAssemblyHelper::RunCodegenPipeline(clang::BackendAction, std::unique_ptr>&, std::unique_ptr>&) BackendUtil.cpp:0:0
#17 0x00000000045aedd0 clang::emitBackendOutput(clang::CompilerInstance&, clang::CodeGenOptions&, llvm::StringRef, llvm::Module*, clang::BackendAction, llvm::IntrusiveRefCntPtr, std::unique_ptr>, clang::BackendConsumer*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x45aedd0)
#18 0x0000000004c4d987 clang::BackendConsumer::HandleTranslationUnit(clang::ASTContext&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x4c4d987)
#19 0x0000000006a08fec clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x6a08fec)
#20 0x0000000004c4dde8 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x4c4dde8)
#21 0x0000000004f446e5 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x4f446e5)
#22 0x0000000004ec497e clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x4ec497e)
#23 0x000000000503ea6d clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x503ea6d)
#24 0x0000000000de5b4c cc1_main(llvm::ArrayRef, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0xde5b4c)
#25 0x0000000000ddc59a ExecuteCC1Tool(llvm::SmallVectorImpl&, llvm::ToolContext const&, llvm::IntrusiveRefCntPtr) driver.cpp:0:0
#26 0x0000000000ddc71d int llvm::function_ref&)>::callback_fn&)>(long, llvm::SmallVectorImpl&) driver.cpp:0:0
#27 0x0000000004cc0739 void llvm::function_ref::callback_fn>, std::__cxx11::basic_string, std::allocator>*, bool*) const::'lambda'()>(long) Job.cpp:0:0
#28 0x000000000422f124 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x422f124)
#29 0x0000000004cc0d4f clang::driver::CC1Command::Execute(llvm::ArrayRef>, std::__cxx11::basic_string, std::allocator>*, bool*) const (.part.0) Job.cpp:0:0
#30 0x0000000004c81832 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x4c81832)
#31 0x0000000004c827de clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl>&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x4c827de)
#32 0x0000000004c89c35 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0x4c89c35)
#33 0x0000000000de1f41 clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0xde1f41)
#34 0x0000000000c8cf94 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0xc8cf94)
#35 0x0000797a93829d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#36 0x0000797a93829e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#37 0x0000000000ddc035 _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+0xddc035)
clang: error: clang frontend command failed with exit code 134 (use -v to see invocation)
Compiler returned: 134
```

## Code
```c
void foo(void) {
unsigned char e[16];
unsigned long a, b, c, d;
__asm__ __volatile__(""
: "=d"(a), "=&c"(c), "=&D"(d), "=&a"(b)
: "D0"(-1U), "mr"(e), "1"(128 >> 5), "2"(e), "3"(-1U));
}
```

Contributor guide

Open the contributing guide

Research direction

Reproduce the crash with the supplied C inline-assembly example using the Compiler Explorer link or the shown clang command. Start at llvm/lib/CodeGen/TwoAddressInstructionPass.cpp, especially processTiedPairs; done means the input no longer hits the duplicate-tied-register assertion and the failure is covered by a regression test.

Written by the indexing model from the issue text.

Assessment

Tech stack
c
Domain
compilers
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Needs clarification
Newbie friendliness
30/100

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