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Convert a vselect into a concat_vector if possible

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Summary:
If both vector args to vselect are concat_vectors and the condition is
constant and picks half a vector from each argument, convert the vselect
into a concat_vectors.

Added a test.

The ConvertSelectToConcatVector is assuming it doesn't get vselects with
arguments of, for example, <undef, undef, true, true>. Those get taken
care of in the checks above its call.

Reviewers: nadav, delena, grosbach, hfinkel

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D3916

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209929 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Filipe Cabecinhas
2014-05-30 23:03:11 +00:00
parent 96241f26fc
commit d99cefbad1
3 changed files with 75 additions and 1 deletions
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61
lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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@@ -4592,6 +4592,56 @@ std::pair<SDValue, SDValue> SplitVSETCC(const SDNode *N, SelectionDAG &DAG) {
return std::make_pair(Lo, Hi);
}
// This function assumes all the vselect's arguments are CONCAT_VECTOR
// nodes and that the condition is a BV of ConstantSDNodes (or undefs).
static SDValue ConvertSelectToConcatVector(SDNode *N, SelectionDAG &DAG) {
SDLoc dl(N);
SDValue Cond = N->getOperand(0);
SDValue LHS = N->getOperand(1);
SDValue RHS = N->getOperand(2);
MVT VT = N->getSimpleValueType(0);
int NumElems = VT.getVectorNumElements();
assert(LHS.getOpcode() == ISD::CONCAT_VECTORS &&
RHS.getOpcode() == ISD::CONCAT_VECTORS &&
Cond.getOpcode() == ISD::BUILD_VECTOR);
// We're sure we have an even number of elements due to the
// concat_vectors we have as arguments to vselect.
// Skip BV elements until we find one that's not an UNDEF
// After we find an UNDEF element, keep looping until we get to half the
// length of the BV and see if all the non-undef nodes are the same.
ConstantSDNode *BottomHalf = nullptr;
for (int i = 0; i < NumElems / 2; ++i) {
if (Cond->getOperand(i)->getOpcode() == ISD::UNDEF)
continue;
if (BottomHalf == nullptr)
BottomHalf = cast<ConstantSDNode>(Cond.getOperand(i));
else if (Cond->getOperand(i).getNode() != BottomHalf)
return SDValue();
}
// Do the same for the second half of the BuildVector
ConstantSDNode *TopHalf = nullptr;
for (int i = NumElems / 2; i < NumElems; ++i) {
if (Cond->getOperand(i)->getOpcode() == ISD::UNDEF)
continue;
if (TopHalf == nullptr)
TopHalf = cast<ConstantSDNode>(Cond.getOperand(i));
else if (Cond->getOperand(i).getNode() != TopHalf)
return SDValue();
}
assert(TopHalf && BottomHalf &&
"One half of the selector was all UNDEFs and the other was all the "
"same value. This should have been addressed before this function.");
return DAG.getNode(
ISD::CONCAT_VECTORS, dl, VT,
BottomHalf->isNullValue() ? RHS->getOperand(0) : LHS->getOperand(0),
TopHalf->isNullValue() ? RHS->getOperand(1) : LHS->getOperand(1));
}
SDValue DAGCombiner::visitVSELECT(SDNode *N) {
SDValue N0 = N->getOperand(0);
SDValue N1 = N->getOperand(1);
@@ -4664,6 +4714,17 @@ SDValue DAGCombiner::visitVSELECT(SDNode *N) {
if (ISD::isBuildVectorAllZeros(N0.getNode()))
return N2;
// The ConvertSelectToConcatVector function is assuming both the above
// checks for (vselect (build_vector all{ones,zeros) ...) have been made
// and addressed.
if (N1.getOpcode() == ISD::CONCAT_VECTORS &&
N2.getOpcode() == ISD::CONCAT_VECTORS &&
ISD::isBuildVectorOfConstantSDNodes(N0.getNode())) {
SDValue CV = ConvertSelectToConcatVector(N, DAG);
if (CV.getNode())
return CV;
}
return SDValue();
}