[X86] combineKSHIFT - pull out common operands. NFC. (#194326)

static SDValue combineKSHIFT(SDNode *N, SelectionDAG &DAG,

                             TargetLowering::DAGCombinerInfo &DCI) {

  EVT VT = N->getValueType(0);

  SDValue Src = N->getOperand(0);

  uint64_t Amt = N->getConstantOperandVal(1);

  unsigned Opcode = N->getOpcode();

  const TargetLowering &TLI = DAG.getTargetLoweringInfo();

  if (ISD::isBuildVectorAllZeros(N->getOperand(0).getNode()))

  if (ISD::isBuildVectorAllZeros(Src.getNode()))

    return DAG.getConstant(0, SDLoc(N), VT);

  // Fold kshiftr(extract_subvector(X,C1),C2)

  //  --> extract_subvector(kshiftr(X,C1+C2),0)

  // Fold kshiftr(kshiftr(X,C1),C2) --> kshiftr(X,C1+C2)

  if (N->getOpcode() == X86ISD::KSHIFTR) {

  if (Opcode == X86ISD::KSHIFTR) {

    SDLoc DL(N);

    if (N->getOperand(0).getOpcode() == ISD::EXTRACT_SUBVECTOR ||

        N->getOperand(0).getOpcode() == X86ISD::KSHIFTR) {

      SDValue Src = N->getOperand(0).getOperand(0);

      uint64_t Amt = N->getConstantOperandVal(1) +

                     N->getOperand(0).getConstantOperandVal(1);

      EVT SrcVT = Src.getValueType();

      if (TLI.isTypeLegal(SrcVT) && Amt < SrcVT.getVectorNumElements()) {

        SDValue Shift = DAG.getNode(X86ISD::KSHIFTR, DL, SrcVT, Src,

                                    DAG.getTargetConstant(Amt, DL, MVT::i8));

    if (Src.getOpcode() == ISD::EXTRACT_SUBVECTOR ||

        Src.getOpcode() == X86ISD::KSHIFTR) {

      SDValue Inner = Src.getOperand(0);

      EVT InnerVT = Inner.getValueType();

      uint64_t NewAmt = Amt + Src.getConstantOperandVal(1);

      if (TLI.isTypeLegal(InnerVT) && NewAmt < InnerVT.getVectorNumElements()) {

        SDValue Shift = DAG.getNode(X86ISD::KSHIFTR, DL, InnerVT, Inner,

                                    DAG.getTargetConstant(NewAmt, DL, MVT::i8));

        return DAG.getNode(ISD::EXTRACT_SUBVECTOR, DL, VT, Shift,

                           DAG.getVectorIdxConstant(0, DL));

      }