Call CreateShuffleVector without the poison

If we call CreateShuffleVector with only one value as
an argument, it will create a poison vector internally
and it shuffled.

Author: ParkHanbum

llvm/lib/Transforms/Vectorize/VectorCombine.cpp

@@ -715,8 +715,7 @@ bool VectorCombine::foldInsExtFNeg(Instruction &I) {
   Value *VecFNeg = Builder.CreateFNegFMF(SrcVec, FNeg);
   if (NeedLenChg) {
     // shuffle DestVec, (shuffle (fneg SrcVec), poison, SrcMask), Mask
-    Value *LenChgShuf = Builder.CreateShuffleVector(
-        SrcVec, PoisonValue::get(SrcVecTy), SrcMask);
+    Value *LenChgShuf = Builder.CreateShuffleVector(SrcVec, SrcMask);
     NewShuf = Builder.CreateShuffleVector(DestVec, LenChgShuf, Mask);
   } else {
     // shuffle DestVec, (fneg SrcVec), Mask