Do not define AO_GCC_FORCE_HAVE_CAS for Clang 3.8+ (Aarch64)

(Cherry-pick commits 83fca68, baa9851 from 'master' branch.)

Clang now defines __GCC_HAVE_SYNC_COMPARE_AND_SWAP_n macros (so,
the workaround is not needed anymore).

* src/atomic_ops/sysdeps/gcc/aarch64.h (AO_GCC_FORCE_HAVE_CAS):
Do not define if AO_CLANG_PREREQ(3, 8) (unless __APPLE_CC__).

diff --git a/src/atomic_ops/sysdeps/gcc/aarch64.h b/src/atomic_ops/sysdeps/gcc/aarch64.h
index 08680ce..1204816 100644 (file)
--- a/src/atomic_ops/sysdeps/gcc/aarch64.h
+++ b/src/atomic_ops/sysdeps/gcc/aarch64.h
@@ -204,12 +204,17 @@
 
 #endif /* !AO_PREFER_BUILTIN_ATOMICS */
 
+/* As of clang-5.0, __GCC_HAVE_SYNC_COMPARE_AND_SWAP_16                 */
+/* macro is still missing (while the double-word CAS is available).     */
 #if defined(__clang__)
-  /* As of clang-3.6/arm64, __GCC_HAVE_SYNC_COMPARE_AND_SWAP_n are missing. */
-# define AO_GCC_FORCE_HAVE_CAS
 # define AO_GCC_HAVE_double_SYNC_CAS
 #endif
 
+#if (defined(__clang__) && !AO_CLANG_PREREQ(3, 8)) || defined(__APPLE_CC__)
+  /* __GCC_HAVE_SYNC_COMPARE_AND_SWAP_n macros are missing.     */
+# define AO_GCC_FORCE_HAVE_CAS
+#endif
+
 #include "generic.h"
 
 #undef AO_GCC_FORCE_HAVE_CAS