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[DAGCombiner] Combine shuffles of BUILD_VECTOR and SCALAR_TO_VECTOR

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This patch attempts to fold the shuffling of 'scalar source' inputs - BUILD_VECTOR and SCALAR_TO_VECTOR nodes - if the shuffle node is the only user. This folds away a lot of unnecessary shuffle nodes, and allows quite a bit of constant folding that was being missed.

Differential Revision: http://reviews.llvm.org/D8516

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@234004 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Simon Pilgrim
2015-04-03 10:02:21 +00:00
parent c39f5dd0e2
commit 4e60da755a
11 changed files with 140 additions and 224 deletions
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37
lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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@@ -11980,6 +11980,43 @@ SDValue DAGCombiner::visitVECTOR_SHUFFLE(SDNode *N) {
return V;
}
// Attempt to combine a shuffle of 2 inputs of 'scalar sources' -
// BUILD_VECTOR or SCALAR_TO_VECTOR into a single BUILD_VECTOR.
if (Level < AfterLegalizeVectorOps && TLI.isTypeLegal(VT)) {
SmallVector<SDValue, 8> Ops;
for (int M : SVN->getMask()) {
SDValue Op = DAG.getUNDEF(VT.getScalarType());
if (M >= 0) {
int Idx = M % NumElts;
SDValue &S = (M < (int)NumElts ? N0 : N1);
if (S.getOpcode() == ISD::BUILD_VECTOR && S.hasOneUse()) {
Op = S.getOperand(Idx);
} else if (S.getOpcode() == ISD::SCALAR_TO_VECTOR && S.hasOneUse()) {
if (Idx == 0)
Op = S.getOperand(0);
} else {
// Operand can't be combined - bail out.
break;
}
}
Ops.push_back(Op);
}
if (Ops.size() == VT.getVectorNumElements()) {
// BUILD_VECTOR requires all inputs to be of the same type, find the
// maximum type and extend them all.
EVT SVT = VT.getScalarType();
if (SVT.isInteger())
for (SDValue &Op : Ops)
SVT = (SVT.bitsLT(Op.getValueType()) ? Op.getValueType() : SVT);
if (SVT != VT.getScalarType())
for (SDValue &Op : Ops)
Op = TLI.isZExtFree(Op.getValueType(), SVT)
? DAG.getZExtOrTrunc(Op, SDLoc(N), SVT)
: DAG.getSExtOrTrunc(Op, SDLoc(N), SVT);
return DAG.getNode(ISD::BUILD_VECTOR, SDLoc(N), VT, Ops);
}
}
// If this shuffle only has a single input that is a bitcasted shuffle,
// attempt to merge the 2 shuffles and suitably bitcast the inputs/output
// back to their original types.