Optimizing swizzles of complex shuffles may generate additional complex shuffles.
Do not try to optimize swizzles of shuffles if the source shuffle has more than
a single user, except when the source shuffle is also a swizzle.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153864 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 5e88fcb..0894607 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -7792,6 +7792,14 @@
SmallVector<int, 8> NewMask;
ShuffleVectorSDNode *OtherSV = cast<ShuffleVectorSDNode>(N0);
+ // If the source shuffle has more than one user then do not try to optimize
+ // it because it may generate a more complex shuffle node. However, if the
+ // source shuffle is also a swizzle (a single source shuffle), our
+ // transformation is still likely to reduce the number of shuffles and only
+ // generate a simple shuffle node.
+ if (N0.getOperand(1).getOpcode() != ISD::UNDEF && !N0.hasOneUse())
+ return SDValue();
+
EVT InVT = N0.getValueType();
int InNumElts = InVT.getVectorNumElements();
@@ -7808,7 +7816,7 @@
NewMask.push_back(Idx);
}
-
+ assert(NewMask.size() == VT.getVectorNumElements() && "Invalid mask size");
return DAG.getVectorShuffle(VT, N->getDebugLoc(), OtherSV->getOperand(0),
OtherSV->getOperand(1), &NewMask[0]);
}