ARM: Add doc for ACLE memory barrier intrinsics

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

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@213733 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/docs/LanguageExtensions.rst b/docs/LanguageExtensions.rst
index 4c600868e9ece52dc043ce9fc3a69cc664abf368..50e1ccebe87171146ba6016950eba04f8aee7dd7 100644 (file)
--- a/docs/LanguageExtensions.rst
+++ b/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
 ------------------------------