1 files changed, 27 insertions, 3 deletions
diff --git a/include/llvm/ADT/IntrusiveRefCntPtr.h b/include/llvm/ADT/IntrusiveRefCntPtr.h
index b8b8861..729e37f 100644
--- a/include/llvm/ADT/IntrusiveRefCntPtr.h
+++ b/include/llvm/ADT/IntrusiveRefCntPtr.h
@@ -23,6 +23,7 @@
 
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/Compiler.h"
+#include <atomic>
 #include <memory>
 
 namespace llvm {
@@ -88,6 +89,31 @@ namespace llvm {
     static void retain(T *obj) { obj->Retain(); }
     static void release(T *obj) { obj->Release(); }
   };
+
+/// \brief A thread-safe version of \c llvm::RefCountedBase.
+///
+/// A generic base class for objects that wish to have their lifetimes managed
+/// using reference counts. Classes subclass \c ThreadSafeRefCountedBase to
+/// obtain such functionality, and are typically handled with
+/// \c IntrusiveRefCntPtr "smart pointers" which automatically handle the
+/// management of reference counts.
+template <class Derived>
+class ThreadSafeRefCountedBase {
+  mutable std::atomic<int> RefCount;
+
+protected:
+  ThreadSafeRefCountedBase() : RefCount(0) {}
+
+public:
+  void Retain() const { ++RefCount; }
+
+  void Release() const {
+    int NewRefCount = --RefCount;
+    assert(NewRefCount >= 0 && "Reference count was already zero.");
+    if (NewRefCount == 0)
+      delete static_cast<const Derived*>(this);
+  }
+};
   
 //===----------------------------------------------------------------------===//
 /// IntrusiveRefCntPtr - A template class that implements a "smart pointer"
@@ -109,7 +135,7 @@ namespace llvm {
   template <typename T>
   class IntrusiveRefCntPtr {
     T* Obj;
-    typedef IntrusiveRefCntPtr this_type;
+
   public:
     typedef T element_type;
 
@@ -123,7 +149,6 @@ namespace llvm {
       retain();
     }
 
-#if LLVM_HAS_RVALUE_REFERENCES
     IntrusiveRefCntPtr(IntrusiveRefCntPtr&& S) : Obj(S.Obj) {
       S.Obj = 0;
     }
@@ -132,7 +157,6 @@ namespace llvm {
     IntrusiveRefCntPtr(IntrusiveRefCntPtr<X>&& S) : Obj(S.getPtr()) {
       S.Obj = 0;
     }
-#endif
 
     template <class X>
     IntrusiveRefCntPtr(const IntrusiveRefCntPtr<X>& S)