+SDValue X86TargetLowering::lowerTRUNCATE(SDValue Op, SelectionDAG &DAG) const {
+ DebugLoc DL = Op.getDebugLoc();
+ EVT VT = Op.getValueType();
+ EVT SVT = Op.getOperand(0).getValueType();
+
+ if (!VT.is128BitVector() || !SVT.is256BitVector() ||
+ VT.getVectorNumElements() != SVT.getVectorNumElements())
+ return SDValue();
+
+ assert(Subtarget->hasAVX() && "256-bit vector is observed without AVX!");
+
+ unsigned NumElems = VT.getVectorNumElements();
+ EVT NVT = EVT::getVectorVT(*DAG.getContext(), VT.getVectorElementType(),
+ NumElems * 2);
+
+ SDValue In = Op.getOperand(0);
+ SmallVector<int, 16> MaskVec(NumElems * 2, -1);
+ // Prepare truncation shuffle mask
+ for (unsigned i = 0; i != NumElems; ++i)
+ MaskVec[i] = i * 2;
+ SDValue V = DAG.getVectorShuffle(NVT, DL,
+ DAG.getNode(ISD::BITCAST, DL, NVT, In),
+ DAG.getUNDEF(NVT), &MaskVec[0]);
+ return DAG.getNode(ISD::EXTRACT_SUBVECTOR, DL, VT, V,
+ DAG.getIntPtrConstant(0));
+}
+