[DAGCombiner] Add more rules to combine shuffle vector dag nodes.
This patch teaches the DAGCombiner how to fold a pair of shuffles
according to rules:
1. shuffle(shuffle A, B, M0), B, M1) -> shuffle(A, B, M2)
2. shuffle(shuffle A, B, M0), A, M1) -> shuffle(A, B, M3)
The new rules would only trigger if the resulting shuffle has legal type and
legal mask.
Added test 'combine-vec-shuffle-3.ll' to verify that DAGCombiner correctly
folds shuffles on x86 when the resulting mask is legal. Also added some negative
cases to verify that we avoid introducing illegal shuffles.
llvm-svn: 213001
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index c8daea9..a1dd8bf 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -10777,6 +10777,50 @@
}
}
+ // Try to fold according to rules:
+ // shuffle(shuffle A, B, M0), B, M1) -> shuffle(A, B, M2)
+ // shuffle(shuffle A, B, M0), A, M1) -> shuffle(A, B, M2)
+ // Don't try to fold shuffles with illegal type.
+ if (N0.getOpcode() == ISD::VECTOR_SHUFFLE && Level < AfterLegalizeDAG &&
+ TLI.isTypeLegal(VT)) {
+ ShuffleVectorSDNode *OtherSV = cast<ShuffleVectorSDNode>(N0);
+
+ // The incoming shuffle must be of the same type as the result of the
+ // current shuffle.
+ assert(OtherSV->getOperand(0).getValueType() == VT &&
+ "Shuffle types don't match");
+
+ SDValue SV0 = OtherSV->getOperand(0);
+ SDValue SV1 = OtherSV->getOperand(1);
+ bool HasSameOp0 = N1 == SV0;
+ if (!HasSameOp0 && N1 != SV1)
+ // Early exit.
+ return SDValue();
+
+ SmallVector<int, 4> Mask;
+ // Compute the combined shuffle mask for a shuffle with SV0 as the first
+ // operand, and SV1 as the second operand.
+ for (unsigned i = 0; i != NumElts; ++i) {
+ int Idx = SVN->getMaskElt(i);
+ if (Idx < 0) {
+ // Propagate Undef.
+ Mask.push_back(Idx);
+ continue;
+ }
+
+ if (Idx < (int)NumElts)
+ Idx = OtherSV->getMaskElt(Idx);
+ else
+ Idx = HasSameOp0 ? Idx - NumElts : Idx;
+
+ Mask.push_back(Idx);
+ }
+
+ // Avoid introducing shuffles with illegal mask.
+ if (TLI.isShuffleMaskLegal(Mask, VT))
+ return DAG.getVectorShuffle(VT, SDLoc(N), SV0, SV1, &Mask[0]);
+ }
+
return SDValue();
}