if (N1.getOpcode() == ISD::UNDEF)
commuteShuffle(N1, N2, MaskVec);
+ // If shuffling a splat, try to blend the splat instead. We do this here so
+ // that even when this arises during lowering we don't have to re-handle it.
+ auto BlendSplat = [&](BuildVectorSDNode *BV, int Offset) {
+ BitVector UndefElements;
+ SDValue Splat = BV->getSplatValue(&UndefElements);
+ if (!Splat)
+ return;
+
+ for (int i = 0; i < (int)NElts; ++i) {
+ if (MaskVec[i] < Offset || MaskVec[i] >= (Offset + (int)NElts))
+ continue;
+
+ // If this input comes from undef, mark it as such.
+ if (UndefElements[MaskVec[i] - Offset]) {
+ MaskVec[i] = -1;
+ continue;
+ }
+
+ // If we can blend a non-undef lane, use that instead.
+ if (!UndefElements[i])
+ MaskVec[i] = i + Offset;
+ }
+ };
+ if (auto *N1BV = dyn_cast<BuildVectorSDNode>(N1))
+ BlendSplat(N1BV, 0);
+ if (auto *N2BV = dyn_cast<BuildVectorSDNode>(N2))
+ BlendSplat(N2BV, NElts);
+
// Canonicalize all index into lhs, -> shuffle lhs, undef
// Canonicalize all index into rhs, -> shuffle rhs, undef
bool AllLHS = true, AllRHS = true;