builtins: Implement the functions from stdatomic.h

Talking to John and Doug, we concluded that these functions from
stdatomic really do belong here in compiler-rt rather than in libc,
since the compiler owns stdatomic.h and these need to refer to
clang-specific builtins. Nonetheless, I've only added these on darwin
for now - other platforms should probably do the same unless their
libc does implement these functions.

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@236805 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 19 insertions, 0 deletions

diff --git a/lib/builtins/atomic_thread_fence.c b/lib/builtins/atomic_thread_fence.c
new file mode 100644
index 000000000..71f698c9d
--- /dev/null
+++ b/lib/builtins/atomic_thread_fence.c
@@ -0,0 +1,19 @@
+/*===-- atomic_thread_fence.c -----------------------------------------------===
+ *
+ *                     The LLVM Compiler Infrastructure
+ *
+ * This file is dual licensed under the MIT and the University of Illinois Open
+ * Source Licenses. See LICENSE.TXT for details.
+ *
+ *===------------------------------------------------------------------------===
+ *
+ * This file implements atomic_thread_fence from C11's stdatomic.h.
+ *
+ *===------------------------------------------------------------------------===
+ */
+
+#include <stdatomic.h>
+#undef atomic_thread_fence
+void atomic_thread_fence(memory_order order) {
+  __c11_atomic_thread_fence(order);
+}