Relax C++11 atomic ops memory order to acquire-release

src/hb-atomic-private.hh

@@ -53,14 +53,14 @@
 #include <atomic>
 
 typedef int hb_atomic_int_impl_t;
-#define hb_atomic_int_impl_add(AI, V)		(reinterpret_cast<std::atomic<int> *> (&AI)->fetch_add (V))
+#define hb_atomic_int_impl_add(AI, V)		(reinterpret_cast<std::atomic<int> *> (&AI)->fetch_add (V, std::memory_order_acq_rel))
 
-#define hb_atomic_ptr_impl_get(P)		(reinterpret_cast<std::atomic<void*> *> (P)->load ())
+#define hb_atomic_ptr_impl_get(P)		(reinterpret_cast<std::atomic<void*> *> (P)->load (std::memory_order_acquire))
 static inline bool
 _hb_atomic_ptr_impl_cmplexch (const void **P, const void *O_, const void *N)
 {
   const void *O = O_; // Need lvalue
-  return reinterpret_cast<std::atomic<const void*> *> (P)->compare_exchange_weak ((O), (N));
+  return reinterpret_cast<std::atomic<const void*> *> (P)->compare_exchange_weak ((O), (N), std::memory_order_acq_rel);
 }
 #define hb_atomic_ptr_impl_cmpexch(P,O,N)	(_hb_atomic_ptr_impl_cmplexch ((const void **) (P), (O), (N)))