PNaCl documentation: improve some of the SIMD documentation.

native_client_sdk/src/doc/reference/pnacl-c-cpp-language-support.rst

 ============================
 PNaCl C/C++ Language Support
 ============================
 
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 Source language support
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 ===============
 
 Inline assembly isn't supported by PNaCl because it isn't portable. The
 one current exception is the common compiler barrier idiom
 ``asm("":::"memory")``, which gets transformed to a sequentially
 consistent memory barrier (equivalent to ``__sync_synchronize()``). In
 PNaCl this barrier is only guaranteed to order ``volatile`` and atomic
 memory accesses, though in practice the implementation attempts to also
 prevent reordering of memory accesses to objects which may escape.
 
+PNaCl supports :ref:`Portable SIMD Vectors <portable_simd_vectors>`,
+which are traditionally expressed through target-specific intrinsics or
+inline assembly.
+
 NaCl supports a fairly wide subset of inline assembly through GCC's
 inline assembly syntax, with the restriction that the sandboxing model
 for the target architecture has to be respected.
 
 .. _portable_simd_vectors:
 
 Portable SIMD Vectors
 =====================
 
 SIMD vectors aren't part of the C/C++ standards and are traditionally
 very hardware-specific. Portable Native Client offers a portable version
 of SIMD vector datatypes and operations which map well to modern
 architectures and offer performance which matches or approaches
 hardware-specific uses.
 
-SIMD vector support was added to Portable Native Client for version 36
-of Chrome, and more features are expected to be added in subsequent
-releases.
+SIMD vector support was added to Portable Native Client for version 37
+of Chrome and more features, including performance enhancements, are
+expected to be added in subsequent releases.
 
 Hand-Coding Vector Extensions
 -----------------------------
 
 The initial vector support in Portable Native Client adds `LLVM vectors
 <http://clang.llvm.org/docs/LanguageExtensions.html#vectors-and-extended-vectors>`_
 and `GCC vectors
 <http://gcc.gnu.org/onlinedocs/gcc/Vector-Extensions.html>`_ since these
 are well supported by different hardware platforms and don't require any
 new compiler intrinsics.
@@ skipping 213 matching lines @@
   A similar feature is **thread suspension**: The ability to
   asynchronously suspend and resume a thread and inspect or modify its
   execution state (such as register state).
 
   Neither PNaCl nor NaCl currently support asynchronous interruption
   or suspension of threads.
 
 If PNaCl were to support either of these, the interaction of
 ``volatile`` and atomics with same-thread signal handling would need
 to be carefully detailed.