[llvm-dev] single-threaded code-gen and how to make it support multi-thread

Doerfert, Johannes via llvm-dev llvm-dev at lists.llvm.org
Wed Apr 3 19:18:47 PDT 2019

I thought isolation is guaranteed per LLVMContext, but I might be wrong. Maybe somebody else can help.

From: pongba <pongba at gmail.com>
Sent: Wednesday, April 3, 2019 21:12
To: Doerfert, Johannes
Cc: llvm-dev at lists.llvm.org
Subject: Re: [llvm-dev] single-threaded code-gen and how to make it support multi-thread

Thank you Johannes, I looked it up and it seems that we're creating one LLVMContext per compilation "unit", not sure if that matters. i.e. there's no single globally shared LLVMContext object.

Is LLVMContext *the* concurrency isolation (or unit) here?

On Wed, Apr 3, 2019 at 6:34 PM Doerfert, Johannes <jdoerfert at anl.gov<mailto:jdoerfert at anl.gov>> wrote:
Do you use one llvm context or one per thread that interacts with llvm? I'm not an expert but the former might not be supported.


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From: llvm-dev <llvm-dev-bounces at lists.llvm.org<mailto:llvm-dev-bounces at lists.llvm.org>> on behalf of pongba via llvm-dev <llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>>
Sent: Wednesday, April 3, 2019 7:24:25 PM
To: llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>
Subject: [llvm-dev] single-threaded code-gen and how to make it support multi-thread

Hi llvm-dev,

Our code base has a ancient copy of llvm (ver 3.5.1), and it uses the LLVM code gen for some domain-specific language.

The previous dev left a global lock around the usage of LLVM code gen stating that because LLVM code gen can only be accessed single-threaded it needs to be protected with this global lock.

But now this lock has caused some perf issues as we pretty much lose concurrency when having to compile a large number of source files.

I've tried to remove the global lock and what I have observed in crashing stack is something like below:

(I did make sure LLVM_ENABLE_THREADS is defined to be 1, apparently it didn't seem to help)

The document around this seems vague, I have not found a clear instruction as to how to solve this, hence this post. Can anyone help with some pointers?

Any guidance is appreciated:)

  ntdll.dll!RtlReportCriticalFailure(long StatusCode, void * FailureInfo, unsigned long BreakIfDbgPresent) Line 201 C
  ntdll.dll!RtlpHeapHandleError(long ErrorLevel) Line 344 C
  ntdll.dll!RtlpHpHeapHandleError(_HEAP_FAILURE_TYPE FailureType, unsigned __int64 HeapAddress, unsigned __int64 Address) Line 670 C
  ntdll.dll!RtlpLogHeapFailure(_HEAP_FAILURE_TYPE FailureType, void * HeapAddress, void * Address, void * Param1, void * Param2, void * Param3) Line 158 C
  ntdll.dll!RtlFreeHeap(void * HeapHandle, unsigned long Flags, void * BaseAddress) Line 352 C
  ucrtbase.dll!_free_base(void * block) Line 105 C++
  XXXTest.exe!llvm::StringMapImpl::RehashTable(unsigned int BucketNo) Line 238 C++
  XXXTest.exe!llvm::StringMap<llvm::ConstantDataSequential * __ptr64,llvm::MallocAllocator>::insert(std::pair<llvm::StringRef,llvm::ConstantDataSequential *> KV) Line 344 C++
  [Inline Frame] XXXTest.exe!llvm::StringMap<llvm::Value *,llvm::MallocAllocator>::GetOrCreateValue(llvm::StringRef) Line 371 C++
  [Inline Frame] XXXTest.exe!llvm::StringMap<llvm::Value *,llvm::MallocAllocator>::GetOrCreateValue(llvm::StringRef) Line 375 C++
  XXXTest.exe!llvm::ValueSymbolTable::createValueName(llvm::StringRef Name, llvm::Value * V) Line 98 C++
  XXXTest.exe!llvm::Value::setName(const llvm::Twine & NewName) Line 236 C++
  XXXTest.exe!llvm::IRBuilder<1,llvm::ConstantFolder,llvm::IRBuilderDefaultInserter<1> >::Insert<llvm::GetElementPtrInst>(llvm::GetElementPtrInst * I, const llvm::Twine & Name) Line 497 C++
  XXXTest.exe!llvm::IRBuilder<1,llvm::ConstantFolder,llvm::IRBuilderDefaultInserter<1> >::CreateConstInBoundsGEP1_32(llvm::Value * Ptr, unsigned int Idx0, const llvm::Twine & Name) Line 1014 C++
> XXXTest.exe!XXX::LlvmCodeGenerator::Visit(const XXX::FeatureRefExpression & p_expr) Line 953 C++
  XXXTest.exe!XXX::FeatureRefExpression::Accept(XXX::Visitor & p_visitor) Line 46 C++


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