[X86] truncateVectorWithPACKUS - use getZeroExtendInReg helper. NFCI.

  return truncateVectorWithPACK(Opcode, DstVT, Res, DL, DAG, Subtarget);

}

/// Truncate using ISD::AND mask and X86ISD::PACKUS.

/// Truncate using inreg zero extension (AND mask) and X86ISD::PACKUS.

/// e.g. trunc <8 x i32> X to <8 x i16> -->

/// MaskX = X & 0xffff (clear high bits to prevent saturation)

/// packus (extract_subv MaskX, 0), (extract_subv MaskX, 1)

static SDValue truncateVectorWithPACKUS(EVT DstVT, SDValue In, const SDLoc &DL,

                                        const X86Subtarget &Subtarget,

                                        SelectionDAG &DAG) {

  EVT SrcVT = In.getValueType();

  APInt Mask = APInt::getLowBitsSet(SrcVT.getScalarSizeInBits(),

                                    DstVT.getScalarSizeInBits());

  In = DAG.getNode(ISD::AND, DL, SrcVT, In, DAG.getConstant(Mask, DL, SrcVT));

  In = DAG.getZeroExtendInReg(In, DL, DstVT);

  return truncateVectorWithPACK(X86ISD::PACKUS, DstVT, In, DL, DAG, Subtarget);

}