[PATCH] D11579: [InstrProfiling] Fix data race on profile counters by using AtomicRMW.

[Alexey Samsonov]

samsonov created this revision.
samsonov added reviewers: dnovillo, bogner.
samsonov added a subscriber: llvm-commits.

Since we introduced counters for functions in COMDAT sections (e.g.
inline functions from STL headers), these headers can easily be
incremented concurrently by multiple threads. Replace load-add-store
with a single "atomicrmw add" with monotonic memory ordering.

http://reviews.llvm.org/D11579

Files:
  lib/Transforms/Instrumentation/InstrProfiling.cpp

Index: lib/Transforms/Instrumentation/InstrProfiling.cpp
===================================================================
--- lib/Transforms/Instrumentation/InstrProfiling.cpp
+++ lib/Transforms/Instrumentation/InstrProfiling.cpp
@@ -147,9 +147,9 @@
   IRBuilder<> Builder(Inc->getParent(), *Inc);
   uint64_t Index = Inc->getIndex()->getZExtValue();
   Value *Addr = Builder.CreateConstInBoundsGEP2_64(Counters, 0, Index);
-  Value *Count = Builder.CreateLoad(Addr, "pgocount");
-  Count = Builder.CreateAdd(Count, Builder.getInt64(1));
-  Inc->replaceAllUsesWith(Builder.CreateStore(Count, Addr));
+  Builder.CreateAtomicRMW(AtomicRMWInst::Add, Addr, Builder.getInt64(1),
+                          llvm::Monotonic);
+  assert(Inc->use_empty() && "InstrProfIncrementInst has uses!");
   Inc->eraseFromParent();
 }
 


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