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[DAGCombiner] refactor folds for fadd (fmul X, -2.0), Y; NFCI 

The transform doesn't work if the vector constant has undef elements.

llvm-svn: 344532
This commit is contained in:
Sanjay Patel 2018-10-15 16:47:01 +00:00
parent 7cf5733f7f
commit 89e2197c33
1 changed files with 18 additions and 16 deletions
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34
llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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@ -10851,14 +10851,6 @@ SDValue DAGCombiner::visitFMULForFMADistributiveCombine(SDNode *N) {
return SDValue();
}
static bool isFMulNegTwo(SDValue &N) {
if (N.getOpcode() != ISD::FMUL)
return false;
if (ConstantFPSDNode *CFP = isConstOrConstSplatFP(N.getOperand(1)))
return CFP->isExactlyValue(-2.0);
return false;
}
SDValue DAGCombiner::visitFADD(SDNode *N) {
SDValue N0 = N->getOperand(0);
SDValue N1 = N->getOperand(1);
@ -10903,14 +10895,24 @@ SDValue DAGCombiner::visitFADD(SDNode *N) {
return DAG.getNode(ISD::FSUB, DL, VT, N1,
GetNegatedExpression(N0, DAG, LegalOperations), Flags);
// fold (fadd A, (fmul B, -2.0)) -> (fsub A, (fadd B, B))
// fold (fadd (fmul B, -2.0), A) -> (fsub A, (fadd B, B))
if ((isFMulNegTwo(N0) && N0.hasOneUse()) ||
(isFMulNegTwo(N1) && N1.hasOneUse())) {
bool N1IsFMul = isFMulNegTwo(N1);
SDValue AddOp = N1IsFMul ? N1.getOperand(0) : N0.getOperand(0);
SDValue Add = DAG.getNode(ISD::FADD, DL, VT, AddOp, AddOp, Flags);
return DAG.getNode(ISD::FSUB, DL, VT, N1IsFMul ? N0 : N1, Add, Flags);
auto isFMulNegTwo = [](SDValue FMul) {
if (!FMul.hasOneUse() || FMul.getOpcode() != ISD::FMUL)
return false;
auto *C = isConstOrConstSplatFP(FMul.getOperand(1));
return C && C->isExactlyValue(-2.0);
};
// fadd (fmul B, -2.0), A --> fsub A, (fadd B, B)
if (isFMulNegTwo(N0)) {
SDValue B = N0.getOperand(0);
SDValue Add = DAG.getNode(ISD::FADD, DL, VT, B, B, Flags);
return DAG.getNode(ISD::FSUB, DL, VT, N1, Add, Flags);
}
// fadd A, (fmul B, -2.0) --> fsub A, (fadd B, B)
if (isFMulNegTwo(N1)) {
SDValue B = N1.getOperand(0);
SDValue Add = DAG.getNode(ISD::FADD, DL, VT, B, B, Flags);
return DAG.getNode(ISD::FSUB, DL, VT, N0, Add, Flags);
}
// No FP constant should be created after legalization as Instruction