[PATCH] CodeGen: improve ms instrincics support

[Saleem Abdulrasool]

================
Comment at: lib/CodeGen/CGBuiltin.cpp:1540
@@ +1539,3 @@
+
+    Value *Result = Builder.CreateAtomicCmpXchg(Destination, Comparend,
+                                                Exchange,
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Reid Kleckner wrote:
> Saleem Abdulrasool wrote:
> > Reid Kleckner wrote:
> > > MSDN says the 'Dest' is volatile, so I'd call Result->setVolatile(true) here.
> > Dest itself is volatile, the returned value is not.  We dont strip volatility off of Destination.  Oh, and I dont see a llvm::Value::setVolatile either.
> CreateAtomicCmpXchg should return an AtomicRMWInst* which can be made volatile.  It's not the result that's volatile, it's the memory update.
Done (thanks for the clarification!); although needed an additional extract value due to a recent change to the cmpxchg change.

http://reviews.llvm.org/D4182