ARM: Add doc for ACLE memory barrier intrinsics

Add documentations for ACLE memory barrier intrinsics, describing their motion
barrier characteristics.

llvm-svn: 213733

diff --git a/clang/docs/LanguageExtensions.rst b/clang/docs/LanguageExtensions.rst
index 4c60086..50e1cce 100644 (file)
--- a/clang/docs/LanguageExtensions.rst
+++ b/clang/docs/LanguageExtensions.rst
@@ -1634,6 +1634,19 @@ Target-Specific Extensions
 
 Clang supports some language features conditionally on some targets.
 
+ARM/AArch64 Language Extensions
+-------------------------------
+
+Memory Barrier Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^
+Clang implements the ``__dmb``, ``__dsb`` and ``__isb`` intrinsics as defined
+in the `ARM C Language Extensions Release 2.0
+<http://infocenter.arm.com/help/topic/com.arm.doc.ihi0053c/IHI0053C_acle_2_0.pdf>`_.
+Note that these intrinsics are implemented as motion barriers that block
+reordering of memory accesses and side effect instructions. Other instructions
+like simple arithmatic may be reordered around the intrinsic. If you expect to
+have no reordering at all, use inline assembly instead.
+
 X86/X86-64 Language Extensions
 ------------------------------