diff --git a/lib/Support/Atomic.cpp b/lib/Support/Atomic.cpp
index 3001f6c468a..9559ad72957 100644
--- a/lib/Support/Atomic.cpp
+++ b/lib/Support/Atomic.cpp
@@ -21,11 +21,15 @@ using namespace llvm;
 #undef MemoryFence
 #endif
 
+#if defined(__GNUC__) || (defined(__IBMCPP__) && __IBMCPP__ >= 1210)
+#define GNU_ATOMICS
+#endif
+
 void sys::MemoryFence() {
 #if LLVM_HAS_ATOMICS == 0
   return;
 #else
-#  if defined(__GNUC__)
+#  if defined(GNU_ATOMICS)
   __sync_synchronize();
 #  elif defined(_MSC_VER)
   MemoryBarrier();
@@ -43,7 +47,7 @@ sys::cas_flag sys::CompareAndSwap(volatile sys::cas_flag* ptr,
   if (result == old_value)
     *ptr = new_value;
   return result;
-#elif defined(__GNUC__)
+#elif defined(GNU_ATOMICS)
   return __sync_val_compare_and_swap(ptr, old_value, new_value);
 #elif defined(_MSC_VER)
   return InterlockedCompareExchange(ptr, new_value, old_value);
@@ -56,7 +60,7 @@ sys::cas_flag sys::AtomicIncrement(volatile sys::cas_flag* ptr) {
 #if LLVM_HAS_ATOMICS == 0
   ++(*ptr);
   return *ptr;
-#elif defined(__GNUC__)
+#elif defined(GNU_ATOMICS)
   return __sync_add_and_fetch(ptr, 1);
 #elif defined(_MSC_VER)
   return InterlockedIncrement(ptr);
@@ -69,7 +73,7 @@ sys::cas_flag sys::AtomicDecrement(volatile sys::cas_flag* ptr) {
 #if LLVM_HAS_ATOMICS == 0
   --(*ptr);
   return *ptr;
-#elif defined(__GNUC__)
+#elif defined(GNU_ATOMICS)
   return __sync_sub_and_fetch(ptr, 1);
 #elif defined(_MSC_VER)
   return InterlockedDecrement(ptr);
@@ -82,7 +86,7 @@ sys::cas_flag sys::AtomicAdd(volatile sys::cas_flag* ptr, sys::cas_flag val) {
 #if LLVM_HAS_ATOMICS == 0
   *ptr += val;
   return *ptr;
-#elif defined(__GNUC__)
+#elif defined(GNU_ATOMICS)
   return __sync_add_and_fetch(ptr, val);
 #elif defined(_MSC_VER)
   return InterlockedExchangeAdd(ptr, val) + val;