return DAG.getVectorShuffle(VT, SDLoc(SVN), S0, S1, SVN->getMask());
}
-// Tries to turn a shuffle of two CONCAT_VECTORS into a single concat.
+// Tries to turn a shuffle of two CONCAT_VECTORS into a single concat,
+// or turn a shuffle of a single concat into simpler shuffle then concat.
static SDValue partitionShuffleOfConcats(SDNode *N, SelectionDAG &DAG) {
EVT VT = N->getValueType(0);
unsigned NumElts = VT.getVectorNumElements();
unsigned NumElemsPerConcat = ConcatVT.getVectorNumElements();
unsigned NumConcats = NumElts / NumElemsPerConcat;
+ // Special case: shuffle(concat(A,B)) can be more efficiently represented
+ // as concat(shuffle(A,B),UNDEF) if the shuffle doesn't set any of the high
+ // half vector elements.
+ if (NumElemsPerConcat * 2 == NumElts && N1.getOpcode() == ISD::UNDEF &&
+ std::all_of(SVN->getMask().begin() + NumElemsPerConcat,
+ SVN->getMask().end(), [](int i) { return i == -1; })) {
+ N0 = DAG.getVectorShuffle(ConcatVT, SDLoc(N), N0.getOperand(0), N0.getOperand(1),
+ ArrayRef<int>(SVN->getMask().begin(), NumElemsPerConcat));
+ N1 = DAG.getUNDEF(ConcatVT);
+ return DAG.getNode(ISD::CONCAT_VECTORS, SDLoc(N), VT, N0, N1);
+ }
+
// Look at every vector that's inserted. We're looking for exact
// subvector-sized copies from a concatenated vector
for (unsigned I = 0; I != NumConcats; ++I) {