Reorder shuffle and binary operation.

This patch enables transformations:

    BinOp(shuffle(v1), shuffle(v2)) -> shuffle(BinOp(v1, v2))
    BinOp(shuffle(v1), const1) -> shuffle(BinOp, const2)

They allow to eliminate extra shuffles in some cases.

Differential Revision: http://reviews.llvm.org/D3525

llvm-svn: 208488
diff --git a/llvm/lib/Transforms/InstCombine/InstCombine.h b/llvm/lib/Transforms/InstCombine/InstCombine.h
index 4a5517a..0fbc7a4 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombine.h
+++ b/llvm/lib/Transforms/InstCombine/InstCombine.h
@@ -358,6 +358,8 @@
   Value *SimplifyDemandedVectorElts(Value *V, APInt DemandedElts,
                                     APInt &UndefElts, unsigned Depth = 0);
 
+  Value *SimplifyVectorOp(BinaryOperator &Inst);
+
   // FoldOpIntoPhi - Given a binary operator, cast instruction, or select
   // which has a PHI node as operand #0, see if we can fold the instruction
   // into the PHI (which is only possible if all operands to the PHI are