[PATCH] [x86] Teach the X86 backend to DAG-combine SSE2 shuffles that are trivially redundant.

[Chandler Carruth]

Thanks, will submit once the other lands.

================
Comment at: lib/Target/X86/X86ISelLowering.cpp:18826
@@ +18825,3 @@
+/// \brief Try to combine x86 target specific shuffles.
+static SDValue PerformTargetShuffleCombine(SDValue N, SelectionDAG &DAG,
+                                           TargetLowering::DAGCombinerInfo &DCI,
----------------
Filipe Cabecinhas wrote:
> Since we're already on the X86 backend, could we start calling these functions PerformX86ShuffleCombine? It's not like they're generic for more targets.
> 
> I know “Target” is what's being used everywhere else, but I'd prefer more specific naming.
I don't entirely disagree, but don't feel confident enough to cleanup the entire backend this way, and don't want to be inconsistent at this point, so I'd rather leave it.

http://reviews.llvm.org/D4240