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[RISCV] Combine (ADDI (ADDI X, C1), C2) -> (ADDI X, C1+C2) #157416

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[RISCV] Combine (ADDI (ADDI X, C1), C2) -> (ADDI X, C1+C2) #157416

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2 changes: 1 addition & 1 deletion llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4019,7 +4019,7 @@ void SelectionDAGBuilder::visitBitCast(const User &I) {
// constant integer as an opaque constant.
else if(ConstantInt *C = dyn_cast<ConstantInt>(I.getOperand(0)))
setValue(&I, DAG.getConstant(C->getValue(), dl, DestVT, /*isTarget=*/false,
/*isOpaque*/true));
/*isOpaque*/false));
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Why did we have an opaque constant here?

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The ConstantHoisting pass adds a NOP bitcast to mark the constants that have been hoisted. bitcasts of constants normally should be optimized out before the codegen pipeline starts. So the only cases that SelectionDAG should see come from the ConstantHoisting pass.

else
setValue(&I, N); // noop cast.
}
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16 changes: 13 additions & 3 deletions llvm/lib/Target/RISCV/RISCVISelLowering.cpp
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Expand Up @@ -9421,7 +9421,17 @@ SDValue RISCVTargetLowering::lowerSELECT(SDValue Op, SelectionDAG &DAG) const {
// Efficient only if the constant and its negation fit into `ADDI`
// Prefer Add/Sub over Xor since can be compressed for small immediates
if (isInt<12>(RawConstVal)) {
SDValue SubOp = DAG.getNode(ISD::SUB, DL, VT, RegV, ConstVal);
SDValue SubOp;
using namespace llvm::SDPatternMatch;
SDValue ShAmt;
if (sd_match(RegV, m_OneUse(m_Not(m_OneUse(m_Shl(m_AllOnes(), m_Value(ShAmt))))))) {
SDValue One = DAG.getConstant(1, DL, VT);
SDValue Shl = DAG.getNode(ISD::SHL, DL, VT, One, ShAmt);
SDValue SubAmt = DAG.getConstant(1 + RawConstVal, DL, VT);
SubOp = DAG.getNode(ISD::SUB, DL, VT, Shl, SubAmt);
} else {
SubOp = DAG.getNode(ISD::SUB, DL, VT, RegV, ConstVal);
}
SDValue CMOV =
DAG.getNode(IsCZERO_NEZ ? RISCVISD::CZERO_NEZ : RISCVISD::CZERO_EQZ,
DL, VT, SubOp, CondV);
Expand Down Expand Up @@ -16257,8 +16267,8 @@ static SDValue performXORCombine(SDNode *N, SelectionDAG &DAG,
SDValue Op0 = DAG.getNode(ISD::ANY_EXTEND, DL, MVT::i64, N0.getOperand(0));
SDValue Op1 = DAG.getNode(ISD::ZERO_EXTEND, DL, MVT::i64, N0.getOperand(1));
SDValue Shl = DAG.getNode(ISD::SHL, DL, MVT::i64, Op0, Op1);
SDValue And = DAG.getNOT(DL, Shl, MVT::i64);
return DAG.getNode(ISD::TRUNCATE, DL, MVT::i32, And);
SDValue Not = DAG.getNOT(DL, Shl, MVT::i64);
return DAG.getNode(ISD::TRUNCATE, DL, MVT::i32, Not);
}

// fold (xor (sllw 1, x), -1) -> (rolw ~1, x)
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