[PATCH] [DAGCombine] Don't generate atrocious shuffles for constant vectors

[Michael Kuperstein]

Thanks, Simon!


================
Comment at: test/CodeGen/X86/widen_shuffle-1.ll:92
@@ -91,2 +91,2 @@
   ret void
 }
----------------
RKSimon wrote:
> This looks like its leaving a shuffle of a constant vector - shouldn't this be constant folded away?
It should, but that would require an additional DAGCombine.

What this code test up generating is two vector_shuffle nodes, one comes directly from the shufflevector and the other appears during type legalization. This patch simplifies the first one, but the other one remains.

http://reviews.llvm.org/D7093

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