+/// EltsFromConsecutiveLoads - Given the initializing elements 'Elts' of a
+/// vector of type 'VT', see if the elements can be replaced by a single large
+/// load which has the same value as a build_vector whose operands are 'elts'.
+///
+/// Example: <load i32 *a, load i32 *a+4, undef, undef> -> zextload a
+///
+/// FIXME: we'd also like to handle the case where the last elements are zero
+/// rather than undef via VZEXT_LOAD, but we do not detect that case today.
+/// There's even a handy isZeroNode for that purpose.
+static SDValue EltsFromConsecutiveLoads(EVT VT, SmallVectorImpl<SDValue> &Elts,
+ DebugLoc &dl, SelectionDAG &DAG) {
+ EVT EltVT = VT.getVectorElementType();
+ unsigned NumElems = Elts.size();
+
+ LoadSDNode *LDBase = NULL;
+ unsigned LastLoadedElt = -1U;
+
+ // For each element in the initializer, see if we've found a load or an undef.
+ // If we don't find an initial load element, or later load elements are
+ // non-consecutive, bail out.
+ for (unsigned i = 0; i < NumElems; ++i) {
+ SDValue Elt = Elts[i];
+
+ if (!Elt.getNode() ||
+ (Elt.getOpcode() != ISD::UNDEF && !ISD::isNON_EXTLoad(Elt.getNode())))
+ return SDValue();
+ if (!LDBase) {
+ if (Elt.getNode()->getOpcode() == ISD::UNDEF)
+ return SDValue();
+ LDBase = cast<LoadSDNode>(Elt.getNode());
+ LastLoadedElt = i;
+ continue;
+ }
+ if (Elt.getOpcode() == ISD::UNDEF)
+ continue;
+
+ LoadSDNode *LD = cast<LoadSDNode>(Elt);
+ if (!DAG.isConsecutiveLoad(LD, LDBase, EltVT.getSizeInBits()/8, i))
+ return SDValue();
+ LastLoadedElt = i;
+ }
+
+ // If we have found an entire vector of loads and undefs, then return a large
+ // load of the entire vector width starting at the base pointer. If we found
+ // consecutive loads for the low half, generate a vzext_load node.
+ if (LastLoadedElt == NumElems - 1) {
+ if (DAG.InferPtrAlignment(LDBase->getBasePtr()) >= 16)
+ return DAG.getLoad(VT, dl, LDBase->getChain(), LDBase->getBasePtr(),
+ LDBase->getSrcValue(), LDBase->getSrcValueOffset(),
+ LDBase->isVolatile(), LDBase->isNonTemporal(), 0);
+ return DAG.getLoad(VT, dl, LDBase->getChain(), LDBase->getBasePtr(),
+ LDBase->getSrcValue(), LDBase->getSrcValueOffset(),
+ LDBase->isVolatile(), LDBase->isNonTemporal(),
+ LDBase->getAlignment());
+ } else if (NumElems == 4 && LastLoadedElt == 1) {
+ SDVTList Tys = DAG.getVTList(MVT::v2i64, MVT::Other);
+ SDValue Ops[] = { LDBase->getChain(), LDBase->getBasePtr() };
+ SDValue ResNode = DAG.getNode(X86ISD::VZEXT_LOAD, dl, Tys, Ops, 2);
+ return DAG.getNode(ISD::BIT_CONVERT, dl, VT, ResNode);
+ }
+ return SDValue();
+}
+