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Add a fold for add that exchanges it with a constant shift if possible, so 

that the shift may be more easily folded into other operations.

llvm-svn: 26286
This commit is contained in:
Nate Begeman 2006-02-18 02:43:25 +00:00
parent 19fa8ac938
commit 983ca89714
1 changed files with 24 additions and 6 deletions
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28
llvm/lib/Target/TargetLowering.cpp
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@ -459,6 +459,24 @@ bool TargetLowering::SimplifyDemandedBits(SDOperand Op, uint64_t DemandedMask,
CountTrailingZeros_64(~KnownZero2));
KnownZero = (1ULL << KnownZeroOut) - 1;
KnownOne = 0;
SDOperand SH = Op.getOperand(0);
// fold (add (shl x, c1), (shl c2, c1)) -> (shl (add x, c2), c1)
if (KnownZero && SH.getOpcode() == ISD::SHL && SH.Val->hasOneUse() &&
Op.Val->hasOneUse()) {
if (ConstantSDNode *SA = dyn_cast<ConstantSDNode>(SH.getOperand(1))) {
MVT::ValueType VT = Op.getValueType();
unsigned ShiftAmt = SA->getValue();
uint64_t AddAmt = AA->getValue();
uint64_t AddShr = AddAmt >> ShiftAmt;
if (AddAmt == (AddShr << ShiftAmt)) {
SDOperand ADD = TLO.DAG.getNode(ISD::ADD, VT, SH.getOperand(0),
TLO.DAG.getConstant(AddShr, VT));
SDOperand SHL = TLO.DAG.getNode(ISD::SHL, VT, ADD,SH.getOperand(1));
return TLO.CombineTo(Op, SHL);
}
}
}
}
break;
case ISD::CTTZ:
@ -577,7 +595,7 @@ void TargetLowering::ComputeMaskedBits(SDOperand Op, uint64_t Mask,
KnownOne <<= SA->getValue();
KnownZero |= (1ULL << SA->getValue())-1; // low bits known zero.
}
break;
return;
case ISD::SRL:
// (ushr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0
if (ConstantSDNode *SA = dyn_cast<ConstantSDNode>(Op.getOperand(1))) {
@ -590,7 +608,7 @@ void TargetLowering::ComputeMaskedBits(SDOperand Op, uint64_t Mask,
KnownOne >>= SA->getValue();
KnownZero |= HighBits; // high bits known zero.
}
break;
return;
case ISD::SRA:
if (ConstantSDNode *SA = dyn_cast<ConstantSDNode>(Op.getOperand(1))) {
uint64_t HighBits = (1ULL << SA->getValue())-1;
@ -611,7 +629,7 @@ void TargetLowering::ComputeMaskedBits(SDOperand Op, uint64_t Mask,
KnownOne |= HighBits;
}
}
break;
return;
case ISD::CTTZ:
case ISD::CTLZ:
case ISD::CTPOP: {
@ -666,12 +684,12 @@ void TargetLowering::ComputeMaskedBits(SDOperand Op, uint64_t Mask,
// We know that the top bits of C-X are clear if X contains less bits
// than C (i.e. no wrap-around can happen). For example, 20-X is
// positive if we can prove that X is >= 0 and < 16.
break;
return;
default:
// Allow the target to implement this method for its nodes.
if (Op.getOpcode() >= ISD::BUILTIN_OP_END)
computeMaskedBitsForTargetNode(Op, Mask, KnownZero, KnownOne);
break;
return;
}
}