[DAGCombine] Slightly improve lowering of BUILD_VECTOR into a shuffle.
This handles the case of a BUILD_VECTOR being constructed out of elements extracted from a vector twice the size of the result vector. Previously this was always scalarized. Now, we try to construct a shuffle node that feeds on extract_subvectors.
This fixes PR15872 and provides a partial fix for PR21711.
Differential Revision: http://reviews.llvm.org/D6678
llvm-svn: 224429
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index ed3d06c..8297e84 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -10783,9 +10783,6 @@
SDValue ExtVal = Extract.getOperand(1);
unsigned ExtIndex = cast<ConstantSDNode>(ExtVal)->getZExtValue();
if (Extract.getOperand(0) == VecIn1) {
- if (ExtIndex > VT.getVectorNumElements())
- return SDValue();
-
Mask.push_back(ExtIndex);
continue;
}
@@ -10805,20 +10802,34 @@
if (VecIn2.getNode())
return SDValue();
- // We only support widening of vectors which are half the size of the
- // output registers. For example XMM->YMM widening on X86 with AVX.
- if (VecIn1.getValueType().getSizeInBits()*2 != VT.getSizeInBits())
- return SDValue();
-
// If the input vector type has a different base type to the output
// vector type, bail out.
if (VecIn1.getValueType().getVectorElementType() !=
VT.getVectorElementType())
return SDValue();
- // Widen the input vector by adding undef values.
- VecIn1 = DAG.getNode(ISD::CONCAT_VECTORS, dl, VT,
- VecIn1, DAG.getUNDEF(VecIn1.getValueType()));
+ // If the input vector is too small, widen it.
+ // We only support widening of vectors which are half the size of the
+ // output registers. For example XMM->YMM widening on X86 with AVX.
+ EVT VecInT = VecIn1.getValueType();
+ if (VecInT.getSizeInBits() * 2 == VT.getSizeInBits()) {
+ // Widen the input vector by adding undef values.
+ VecIn1 = DAG.getNode(ISD::CONCAT_VECTORS, dl, VT,
+ VecIn1, DAG.getUNDEF(VecIn1.getValueType()));
+ } else if (VecInT.getSizeInBits() == VT.getSizeInBits() * 2) {
+ // If the input vector is too large, try to split it.
+ if (!TLI.isExtractSubvectorCheap(VT, VT.getVectorNumElements()))
+ return SDValue();
+
+ // Try to replace VecIn1 with two extract_subvectors
+ // No need to update the masks, they should still be correct.
+ VecIn2 = DAG.getNode(ISD::EXTRACT_SUBVECTOR, dl, VT, VecIn1,
+ 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();
}
if (UsesZeroVector)