[llvm-commits] [llvm] r79560 - /llvm/trunk/lib/VMCore/Attributes.cpp

[Owen Anderson]

Author: resistor
Date: Thu Aug 20 14:03:20 2009
New Revision: 79560

URL: http://llvm.org/viewvc/llvm-project?rev=79560&view=rev
Log:
Reduce contention on the Attributes lock by using atomic operations for reference counting rather than locking.

Modified:
    llvm/trunk/lib/VMCore/Attributes.cpp

Modified: llvm/trunk/lib/VMCore/Attributes.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/VMCore/Attributes.cpp?rev=79560&r1=79559&r2=79560&view=diff

==============================================================================
--- llvm/trunk/lib/VMCore/Attributes.cpp (original)
+++ llvm/trunk/lib/VMCore/Attributes.cpp Thu Aug 20 14:03:20 2009
@@ -15,6 +15,7 @@
 #include "llvm/Type.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/FoldingSet.h"
+#include "llvm/System/Atomic.h"
 #include "llvm/System/Mutex.h"
 #include "llvm/Support/Streams.h"
 #include "llvm/Support/ManagedStatic.h"
@@ -97,7 +98,7 @@
 
 namespace llvm {
 class AttributeListImpl : public FoldingSetNode {
-  unsigned RefCount;
+  sys::cas_flag RefCount;
   
   // AttributesList is uniqued, these should not be publicly available.
   void operator=(const AttributeListImpl &); // Do not implement
@@ -111,8 +112,11 @@
     RefCount = 0;
   }
   
-  void AddRef() { ++RefCount; }
-  void DropRef() { if (--RefCount == 0) delete this; }
+  void AddRef() { sys::AtomicIncrement(&RefCount); }
+  void DropRef() {
+    sys::cas_flag old = sys::AtomicDecrement(&RefCount);
+    if (old == 0) delete this;
+  }
   
   void Profile(FoldingSetNodeID &ID) const {
     Profile(ID, Attrs.data(), Attrs.size());
@@ -175,17 +179,14 @@
 //===----------------------------------------------------------------------===//
 
 AttrListPtr::AttrListPtr(AttributeListImpl *LI) : AttrList(LI) {
-  sys::SmartScopedLock<true> Lock(*ALMutex);
   if (LI) LI->AddRef();
 }
 
 AttrListPtr::AttrListPtr(const AttrListPtr &P) : AttrList(P.AttrList) {
-  sys::SmartScopedLock<true> Lock(*ALMutex);
   if (AttrList) AttrList->AddRef();  
 }
 
 const AttrListPtr &AttrListPtr::operator=(const AttrListPtr &RHS) {
-  sys::SmartScopedLock<true> Lock(*ALMutex);
   if (AttrList == RHS.AttrList) return *this;
   if (AttrList) AttrList->DropRef();
   AttrList = RHS.AttrList;
@@ -194,7 +195,6 @@
 }
 
 AttrListPtr::~AttrListPtr() {
-  sys::SmartScopedLock<true> Lock(*ALMutex);
   if (AttrList) AttrList->DropRef();
 }