[VE] Revert mis-modifications from merge conflicts #49
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kaz7
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May 22, 2023
…callback
The `TypeSystemMap::m_mutex` guards against concurrent modifications
of members of `TypeSystemMap`. In particular, `m_map`.
`TypeSystemMap::ForEach` iterates through the entire `m_map` calling
a user-specified callback for each entry. This is all done while
`m_mutex` is locked. However, there's nothing that guarantees that
the callback itself won't call back into `TypeSystemMap` APIs on the
same thread. This lead to double-locking `m_mutex`, which is undefined
behaviour. We've seen this cause a deadlock in the swift plugin with
following backtrace:
```
int main() {
std::unique_ptr<int> up = std::make_unique<int>(5);
volatile int val = *up;
return val;
}
clang++ -std=c++2a -g -O1 main.cpp
./bin/lldb -o “br se -p return” -o run -o “v *up” -o “expr *up” -b
```
```
frame #4: std::lock_guard<std::mutex>::lock_guard
frame #5: lldb_private::TypeSystemMap::GetTypeSystemForLanguage <<<< Lock #2
frame #6: lldb_private::TypeSystemMap::GetTypeSystemForLanguage
frame #7: lldb_private::Target::GetScratchTypeSystemForLanguage
...
frame #26: lldb_private::SwiftASTContext::LoadLibraryUsingPaths
frame #27: lldb_private::SwiftASTContext::LoadModule
frame #30: swift::ModuleDecl::collectLinkLibraries
frame #31: lldb_private::SwiftASTContext::LoadModule
frame #34: lldb_private::SwiftASTContext::GetCompileUnitImportsImpl
frame #35: lldb_private::SwiftASTContext::PerformCompileUnitImports
frame #36: lldb_private::TypeSystemSwiftTypeRefForExpressions::GetSwiftASTContext
frame #37: lldb_private::TypeSystemSwiftTypeRefForExpressions::GetPersistentExpressionState
frame #38: lldb_private::Target::GetPersistentSymbol
frame #41: lldb_private::TypeSystemMap::ForEach <<<< Lock #1
frame #42: lldb_private::Target::GetPersistentSymbol
frame #43: lldb_private::IRExecutionUnit::FindInUserDefinedSymbols
frame #44: lldb_private::IRExecutionUnit::FindSymbol
frame #45: lldb_private::IRExecutionUnit::MemoryManager::GetSymbolAddressAndPresence
frame #46: lldb_private::IRExecutionUnit::MemoryManager::findSymbol
frame #47: non-virtual thunk to lldb_private::IRExecutionUnit::MemoryManager::findSymbol
frame #48: llvm::LinkingSymbolResolver::findSymbol
frame #49: llvm::LegacyJITSymbolResolver::lookup
frame #50: llvm::RuntimeDyldImpl::resolveExternalSymbols
frame #51: llvm::RuntimeDyldImpl::resolveRelocations
frame #52: llvm::MCJIT::finalizeLoadedModules
frame #53: llvm::MCJIT::finalizeObject
frame #54: lldb_private::IRExecutionUnit::ReportAllocations
frame #55: lldb_private::IRExecutionUnit::GetRunnableInfo
frame #56: lldb_private::ClangExpressionParser::PrepareForExecution
frame #57: lldb_private::ClangUserExpression::TryParse
frame #58: lldb_private::ClangUserExpression::Parse
```
Our solution is to simply iterate over a local copy of `m_map`.
**Testing**
* Confirmed on manual reproducer (would reproduce 100% of the time
before the patch)
Differential Revision: https://reviews.llvm.org/D149949
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Old days, LoopAccessAnalysis.cpp is modified by d5a79ec.
After that, this file is not correctly merged even the
modifications on d5a79ec is removed. This time, I've
synced LoopAccessAnalysis.cpp with upstream.
Pass regression tests.