PNaCl documentation: add SIMD vectors.

native_client_sdk/src/doc/reference/pnacl-undefined-behavior.rst

Index: native_client_sdk/src/doc/reference/pnacl-undefined-behavior.rst
diff --git a/native_client_sdk/src/doc/reference/pnacl-undefined-behavior.rst b/native_client_sdk/src/doc/reference/pnacl-undefined-behavior.rst
index 30d95f91fbf2ddbc21648d30e824af3c5fcdc638..3ee94bd143ef914c5fa6698c8889797260af12e7 100644
--- a/native_client_sdk/src/doc/reference/pnacl-undefined-behavior.rst
+++ b/native_client_sdk/src/doc/reference/pnacl-undefined-behavior.rst
@@ -177,6 +177,19 @@ sources of undefined behavior which are believed to be fixable:
   function implementation isn't, e.g. ``std::min`` and ``std::max``), is
   well-defined in the *pexe*.
 
+SIMD Vectors
+^^^^^^^^^^^^
+
+SIMD vector instructions aren't specified by the C/C++ standard and as
+such their behavior isn't specified at all in C/C++, it is usually left

[Derek Schuff, 2014/04/24 16:06:20]

maybe "SIMD vector types aren't included in the C/C++ standard and as such their
behavior isn't specified at all in C/C++; it is usually left up to the target
architecture to specify behavior"

[JF, 2014/04/24 16:16:30]

Done. I went for "part of the C/C++ standards".

+up to the target architecture to specify behavior. Portable Native
+Client instead exposed :ref:`Portable SIMD Vectors
+<portable_simd_vectors>` and offers the same guarantees on these vectors
+as the guarantees offered by the contained elements. Of notable interest
+amongst these guarantees are those of alignment for load/store
+instructions on vectors: they have the same alignment restriction as the
+contained elements.
+
 Hard to Fix
 ^^^^^^^^^^^