commit f40c4026253e65cfda3e0c8e6cfced4933aa48d4
Author: Nathan Froyd <froydnj@mozilla.com>
Date:   Wed May 6 14:45:45 2015 -0400

    support new-style __atomic_* primitives
    
    Recent versions of GCC/clang feature a new set of compiler intrinsics
    for performing atomic operations, motivated by the operations needed to
    support the C++11 memory model.  These intrinsics are more flexible than
    the old __sync_* intrinstics and offer efficient support for atomic load
    and store operations.

diff --git a/configure.ac b/configure.ac
index 965a06c..3c736a6 100644
--- a/configure.ac
+++ b/configure.ac
@@ -387,6 +387,22 @@ AM_CONDITIONAL(HAVE_CORETEXT, $have_coretext)
 
 dnl ===========================================================================
 
+AC_CACHE_CHECK([for C++11 atomic primitives], hb_cv_have_cxx11_atomic_primitives, [
+	hb_cv_have_cxx11_atomic_primitives=false
+	AC_TRY_LINK([
+		void memory_barrier (void) { __sync_synchronize (); }
+		int atomic_add (int *i) { return __atomic_fetch_add (i, 1, __ATOMIC_SEQ_CST); }
+		int mutex_trylock (int *m) { return __atomic_test_and_set (m, __ATOMIC_SEQ_CST); }
+		void mutex_unlock (int *m) { __atomic_clear (m, __ATOMIC_SEQ_CST); }
+		], [], hb_cv_have_cxx11_atomic_primitives=true
+	)
+])
+if $hb_cv_have_cxx11_atomic_primitives; then
+	AC_DEFINE(HAVE_CXX11_ATOMIC_PRIMITIVES, 1, [Have C++11 __atomic_* atomic primitives])
+fi
+
+dnl ===========================================================================
+
 AC_CACHE_CHECK([for Intel atomic primitives], hb_cv_have_intel_atomic_primitives, [
 	hb_cv_have_intel_atomic_primitives=false
 	AC_TRY_LINK([
diff --git a/src/hb-atomic-private.hh b/src/hb-atomic-private.hh
index 8179571..8581cc4 100644
--- a/src/hb-atomic-private.hh
+++ b/src/hb-atomic-private.hh
@@ -96,6 +96,26 @@ typedef int32_t hb_atomic_int_impl_t;
 #endif
 
 
+/* Must come before the HAVE_INTEL_ATOMIC_PRIMITIVES check because the Intel
+ * primitives and the CXX11 primitives can coexist in the same compiler and
+ * we prefer the CXX11 primitives. */
+#elif !defined(HB_NO_MT) && defined(HAVE_CXX11_ATOMIC_PRIMITIVES)
+
+typedef int hb_atomic_int_impl_t;
+#define HB_ATOMIC_INT_IMPL_INIT(V) (V)
+#define hb_atomic_int_impl_add(AI, V)   	__atomic_fetch_add(&(AI), (V), __ATOMIC_SEQ_CST)
+
+#define hb_atomic_ptr_impl_get(P)		__atomic_load_n((P), __ATOMIC_SEQ_CST)
+
+static inline bool
+hb_atomic_ptr_impl_cmplexch_impl(void **ptr, void *oldv, void *newv)
+{
+  void *expected = oldv;
+  return __atomic_compare_exchange_n(ptr, &expected, newv, 0, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST);
+}
+#define hb_atomic_ptr_impl_cmpexch(P,O,N)	hb_atomic_ptr_impl_cmplexch_impl((void**)(P), (void*)(O), (void*)(N))
+
+
 #elif !defined(HB_NO_MT) && defined(HAVE_INTEL_ATOMIC_PRIMITIVES)
 
 typedef int hb_atomic_int_impl_t;