[DAG] Improved target independent vector shuffle folding logic.
This patch teaches the DAGCombiner how to combine shuffles according to rules:
shuffle(shuffle(A, Undef, M0), B, M1) -> shuffle(B, A, M2)
shuffle(shuffle(A, B, M0), B, M1) -> shuffle(B, A, M2)
shuffle(shuffle(A, B, M0), A, M1) -> shuffle(B, A, M2)
llvm-svn: 222090
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 530ced6..342a427 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -11239,6 +11239,26 @@
return DAG.getVectorShuffle(VT, SDLoc(N), SV0, N1, &Mask[0]);
return DAG.getVectorShuffle(VT, SDLoc(N), SV0, SV1, &Mask[0]);
}
+
+ // Compute the commuted shuffle mask.
+ for (unsigned i = 0; i != NumElts; ++i) {
+ int idx = Mask[i];
+ if (idx < 0)
+ continue;
+ else if (idx < (int)NumElts)
+ Mask[i] = idx + NumElts;
+ else
+ Mask[i] = idx - NumElts;
+ }
+
+ if (TLI.isShuffleMaskLegal(Mask, VT)) {
+ if (IsSV1Undef)
+ // shuffle(shuffle(A, Undef, M0), B, M1) -> shuffle(B, A, M2)
+ return DAG.getVectorShuffle(VT, SDLoc(N), N1, SV0, &Mask[0]);
+ // shuffle(shuffle(A, B, M0), B, M1) -> shuffle(B, A, M2)
+ // shuffle(shuffle(A, B, M0), A, M1) -> shuffle(B, A, M2)
+ return DAG.getVectorShuffle(VT, SDLoc(N), SV1, SV0, &Mask[0]);
+ }
}
return SDValue();