[DAGCombine] Fix a bug in a BUILD_VECTOR combine
When trying to convert a BUILD_VECTOR into a shuffle, we try to split a single source vector that is twice as wide as the destination vector.
We can not do this when we also need the zero vector to create a blend.
This fixes PR22774.
Differential Revision: http://reviews.llvm.org/D8040
llvm-svn: 231219
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index c7a9df5..4a074a0 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -11358,7 +11358,9 @@
} else if (VecInT.getSizeInBits() == VT.getSizeInBits() * 2) {
// If the input vector is too large, try to split it.
// We don't support having two input vectors that are too large.
- if (VecIn2.getNode())
+ // If the zero vector was used, we can not split the vector,
+ // since we'd need 3 inputs.
+ if (UsesZeroVector || VecIn2.getNode())
return SDValue();
if (!TLI.isExtractSubvectorCheap(VT, VT.getVectorNumElements()))
@@ -11370,7 +11372,6 @@
DAG.getConstant(VT.getVectorNumElements(), TLI.getVectorIdxTy()));
VecIn1 = DAG.getNode(ISD::EXTRACT_SUBVECTOR, dl, VT, VecIn1,
DAG.getConstant(0, TLI.getVectorIdxTy()));
- UsesZeroVector = false;
} else
return SDValue();
}