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Do not recombine FMA when that is not needed. 

Summary: As per title. This creates useless recombines.

Reviewers: jyknight, nemanjai, mkuper, spatel, RKSimon, zvi, bkramer

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D33848

llvm-svn: 309578
This commit is contained in:
Amaury Sechet 2017-07-31 16:56:25 +00:00
parent a3ad61d874
commit 4358c5217d
1 changed files with 16 additions and 4 deletions
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20
llvm/lib/Target/X86/X86ISelLowering.cpp
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@ -34517,6 +34517,7 @@ static SDValue combineFMA(SDNode *N, SelectionDAG &DAG,
// Negative multiplication when NegA xor NegB
bool NegMul = (NegA != NegB);
bool HasNeg = NegA || NegB || NegC;
unsigned NewOpcode;
if (!NegMul)
@ -34524,6 +34525,14 @@ static SDValue combineFMA(SDNode *N, SelectionDAG &DAG,
else
NewOpcode = (!NegC) ? X86ISD::FNMADD : X86ISD::FNMSUB;
// For FMA and FAMDD, we risk reconstructing the node we started with.
// In order to avoid this, we check for negation or opcode change. If
// one of the two happened, then it is a new node and we return it.
if (N->getOpcode() == X86ISD::FMADD || N->getOpcode() == ISD::FMA) {
if (HasNeg || NewOpcode != N->getOpcode())
return DAG.getNode(NewOpcode, dl, VT, A, B, C);
return SDValue();
}
if (N->getOpcode() == X86ISD::FMADD_RND) {
switch (NewOpcode) {
@ -34547,12 +34556,15 @@ static SDValue combineFMA(SDNode *N, SelectionDAG &DAG,
case X86ISD::FNMSUB: NewOpcode = X86ISD::FNMSUBS3_RND; break;
}
} else {
assert((N->getOpcode() == X86ISD::FMADD || N->getOpcode() == ISD::FMA) &&
"Unexpected opcode!");
return DAG.getNode(NewOpcode, dl, VT, A, B, C);
llvm_unreachable("Unexpected opcode!");
}
return DAG.getNode(NewOpcode, dl, VT, A, B, C, N->getOperand(3));
// Only return the node is the opcode was changed or one of the
// operand was negated. If not, we'll just recreate the same node.
if (HasNeg || NewOpcode != N->getOpcode())
return DAG.getNode(NewOpcode, dl, VT, A, B, C, N->getOperand(3));
return SDValue();
}
static SDValue combineZext(SDNode *N, SelectionDAG &DAG,