[PATCH] Make LLVM profiling thread-safe

[Matthew Dempsky]

On Mon, Jun 24, 2013 at 12:17:17PM -0700, Matthew Dempsky wrote:
> Instead of emitting separate read-modify-write instructions to
> increment the profiling counters, an monotonically ordered atomic add
> instruction should be emitted.

Oops, need to fix the tests too!


Index: llvm/lib/Transforms/Instrumentation/ProfilingUtils.cpp
===================================================================
--- llvm/lib/Transforms/Instrumentation/ProfilingUtils.cpp	(revision 184494)
+++ llvm/lib/Transforms/Instrumentation/ProfilingUtils.cpp	(working copy)
@@ -121,12 +121,10 @@
   Constant *ElementPtr =
     ConstantExpr::getGetElementPtr(CounterArray, Indices);
 
-  // Load, increment and store the value back.
-  Value *OldVal = new LoadInst(ElementPtr, "OldFuncCounter", InsertPos);
-  Value *NewVal = BinaryOperator::Create(Instruction::Add, OldVal,
-                                 ConstantInt::get(Type::getInt32Ty(Context), 1),
-                                         "NewFuncCounter", InsertPos);
-  new StoreInst(NewVal, ElementPtr, InsertPos);
+  // Atomically increment the counter by one.
+  Constant *One = ConstantInt::get(Type::getInt32Ty(Context), 1);
+  new AtomicRMWInst(AtomicRMWInst::Add, ElementPtr, One, Monotonic,
+                    CrossThread, InsertPos);
 }
 
 void llvm::InsertProfilingShutdownCall(Function *Callee, Module *Mod) {
Index: llvm/test/Analysis/Profiling/edge-profiling.ll
===================================================================
--- llvm/test/Analysis/Profiling/edge-profiling.ll	(revision 184494)
+++ llvm/test/Analysis/Profiling/edge-profiling.ll	(working copy)
@@ -16,19 +16,14 @@
 define void @oneblock() nounwind {
 entry:
 ; CHECK:entry:
-; CHECK:%OldFuncCounter
-; CHECK:load 
+; CHECK:atomicrmw
+; CHECK:add
 ; CHECK:getelementptr
 ; CHECK:@EdgeProfCounters
 ; CHECK:i32 0
 ; CHECK:i32 0
-; CHECK:%NewFuncCounter
-; CHECK:add
-; CHECK:%OldFuncCounter
-; CHECK:store 
-; CHECK:%NewFuncCounter
-; CHECK:getelementptr
-; CHECK:@EdgeProfCounters
+; CHECK:i32 1
+; CHECK:monotonic
   %0 = call i32 @puts(i8* getelementptr inbounds ([12 x i8]* @.str, i64 0, i64 0)) nounwind ; <i32> [#uses=0]
   ret void
 }