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[RISCV] Introduce add_vl combine for identity operand #139742

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Merged
merged 1 commit into from
May 13, 2025
Merged

[RISCV] Introduce add_vl combine for identity operand #139742

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35 changes: 23 additions & 12 deletions llvm/lib/Target/RISCV/RISCVISelLowering.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -16619,6 +16619,25 @@ NodeExtensionHelper::getSupportedFoldings(const SDNode *Root) {
}
} // End anonymous namespace.

static SDValue simplifyOp_VL(SDNode *N) {
// TODO: Extend this to other binops using generic identity logic
assert(N->getOpcode() == RISCVISD::ADD_VL);
SDValue A = N->getOperand(0);
SDValue B = N->getOperand(1);
SDValue Passthru = N->getOperand(2);
if (!Passthru.isUndef())
// TODO:This could be a vmerge instead
return SDValue();
;
if (ISD::isConstantSplatVectorAllZeros(B.getNode()))
return A;
// Peek through fixed to scalable
if (B.getOpcode() == ISD::INSERT_SUBVECTOR && B.getOperand(0).isUndef() &&
ISD::isConstantSplatVectorAllZeros(B.getOperand(1).getNode()))
return A;
return SDValue();
}

/// Combine a binary or FMA operation to its equivalent VW or VW_W form.
/// The supported combines are:
/// add | add_vl | or disjoint | or_vl disjoint -> vwadd(u) | vwadd(u)_w
Expand Down Expand Up @@ -18515,20 +18534,10 @@ static SDValue combineVqdotAccum(SDNode *N, SelectionDAG &DAG,
return SDValue();

SDValue AccumOp = DotOp.getOperand(2);
bool IsNullAdd = ISD::isConstantSplatVectorAllZeros(AccumOp.getNode());
// Peek through fixed to scalable
if (!IsNullAdd && AccumOp.getOpcode() == ISD::INSERT_SUBVECTOR &&
AccumOp.getOperand(0).isUndef())
IsNullAdd =
ISD::isConstantSplatVectorAllZeros(AccumOp.getOperand(1).getNode());

SDLoc DL(N);
EVT VT = N->getValueType(0);
// The manual constant folding is required, this case is not constant folded
// or combined.
if (!IsNullAdd)
Addend = DAG.getNode(RISCVISD::ADD_VL, DL, VT, AccumOp, Addend,
DAG.getUNDEF(VT), AddMask, AddVL);
Addend = DAG.getNode(RISCVISD::ADD_VL, DL, VT, Addend, AccumOp,
DAG.getUNDEF(VT), AddMask, AddVL);

SDValue Ops[] = {DotOp.getOperand(0), DotOp.getOperand(1), Addend,
DotOp.getOperand(3), DotOp->getOperand(4)};
Expand Down Expand Up @@ -19657,6 +19666,8 @@ SDValue RISCVTargetLowering::PerformDAGCombine(SDNode *N,
break;
}
case RISCVISD::ADD_VL:
if (SDValue V = simplifyOp_VL(N))
return V;
if (SDValue V = combineOp_VLToVWOp_VL(N, DCI, Subtarget))
return V;
if (SDValue V = combineVqdotAccum(N, DAG, Subtarget))
Expand Down