[InstCombine] use unary shuffle creator to reduce code duplication; NFC

Author: rotateright

llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp

@@ -2075,9 +2075,8 @@ static Instruction *narrowVectorSelect(ShuffleVectorInst &Shuf,
 
   // shuf (sel (shuf NarrowCond, undef, WideMask), X, Y), undef, NarrowMask) -->
   // sel NarrowCond, (shuf X, undef, NarrowMask), (shuf Y, undef, NarrowMask)
-  Value *Undef = UndefValue::get(X->getType());
-  Value *NarrowX = Builder.CreateShuffleVector(X, Undef, Shuf.getShuffleMask());
-  Value *NarrowY = Builder.CreateShuffleVector(Y, Undef, Shuf.getShuffleMask());
+  Value *NarrowX = Builder.CreateShuffleVector(X, Shuf.getShuffleMask());
+  Value *NarrowY = Builder.CreateShuffleVector(Y, Shuf.getShuffleMask());
   return SelectInst::Create(NarrowCond, NarrowX, NarrowY);
 }
 
@@ -2444,8 +2443,7 @@ Instruction *InstCombinerImpl::visitShuffleVectorInst(ShuffleVectorInst &SVI) {
         SmallVector<int, 16> ShuffleMask(SrcNumElems, -1);
         for (unsigned I = 0, E = MaskElems, Idx = BegIdx; I != E; ++Idx, ++I)
           ShuffleMask[I] = Idx;
-        V = Builder.CreateShuffleVector(V, UndefValue::get(V->getType()),
-                                        ShuffleMask,
+        V = Builder.CreateShuffleVector(V, ShuffleMask,
                                         SVI.getName() + ".extract");
         BegIdx = 0;
       }

llvm/lib/Transforms/InstCombine/InstructionCombining.cpp

@@ -1712,9 +1712,8 @@ Instruction *InstCombinerImpl::foldVectorBinop(BinaryOperator &Inst) {
     // values followed by a splat followed by the 2nd binary operation:
     // bo (splat X), (bo Y, OtherOp) --> bo (splat (bo X, Y)), OtherOp
     Value *NewBO = Builder.CreateBinOp(Opcode, X, Y);
-    UndefValue *Undef = UndefValue::get(Inst.getType());
     SmallVector<int, 8> NewMask(MaskC.size(), SplatIndex);
-    Value *NewSplat = Builder.CreateShuffleVector(NewBO, Undef, NewMask);
+    Value *NewSplat = Builder.CreateShuffleVector(NewBO, NewMask);
     Instruction *R = BinaryOperator::Create(Opcode, NewSplat, OtherOp);
 
     // Intersect FMF on both new binops. Other (poison-generating) flags are