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Add some more sign propagation cases

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@28154 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2006-05-06 23:40:29 +00:00
parent 943b9b6651
commit e60351bb72
1 changed files with 77 additions and 10 deletions
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87
lib/CodeGen/SelectionDAG/TargetLowering.cpp
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@ -1068,16 +1068,6 @@ unsigned TargetLowering::ComputeNumSignBits(SDOperand Op, unsigned Depth) const{
return Tmp - C->getValue();
}
break;
case ISD::ADD:
case ISD::SUB:
// Add and sub can have at most one carry bit. Thus we know that the output
// is, at worst, one more bit than the inputs.
Tmp = ComputeNumSignBits(Op.getOperand(0), Depth+1);
if (Tmp == 1) return 1; // Early out.
Tmp2 = ComputeNumSignBits(Op.getOperand(1), Depth+1);
if (Tmp2 == 1) return 1;
return std::min(Tmp, Tmp2)-1;
case ISD::AND:
case ISD::OR:
case ISD::XOR: // NOT is handled here.
@ -1098,6 +1088,83 @@ unsigned TargetLowering::ComputeNumSignBits(SDOperand Op, unsigned Depth) const{
if (getSetCCResultContents() == ZeroOrNegativeOneSetCCResult)
return VTBits;
break;
case ISD::ROTL:
case ISD::ROTR:
if (ConstantSDNode *C = dyn_cast<ConstantSDNode>(Op.getOperand(1))) {
unsigned RotAmt = C->getValue() & (VTBits-1);
// Handle rotate right by N like a rotate left by 32-N.
if (Op.getOpcode() == ISD::ROTR)
RotAmt = (VTBits-RotAmt) & (VTBits-1);
// If we aren't rotating out all of the known-in sign bits, return the
// number that are left. This handles rotl(sext(x), 1) for example.
Tmp = ComputeNumSignBits(Op.getOperand(0), Depth+1);
if (Tmp > RotAmt+1) return Tmp-RotAmt;
}
break;
case ISD::ADD:
// Add can have at most one carry bit. Thus we know that the output
// is, at worst, one more bit than the inputs.
Tmp = ComputeNumSignBits(Op.getOperand(0), Depth+1);
if (Tmp == 1) return 1; // Early out.
// Special case decrementing a value (ADD X, -1):
if (ConstantSDNode *CRHS = dyn_cast<ConstantSDNode>(Op.getOperand(0)))
if (CRHS->isAllOnesValue()) {
uint64_t KnownZero, KnownOne;
uint64_t Mask = MVT::getIntVTBitMask(VT);
ComputeMaskedBits(Op.getOperand(0), Mask, KnownZero, KnownOne, Depth+1);
// If the input is known to be 0 or 1, the output is 0/-1, which is all
// sign bits set.
if ((KnownZero|1) == Mask)
return VTBits;
// If we are subtracting one from a positive number, there is no carry
// out of the result.
if (KnownZero & MVT::getIntVTSignBit(VT))
return Tmp;
}
Tmp2 = ComputeNumSignBits(Op.getOperand(1), Depth+1);
if (Tmp2 == 1) return 1;
return std::min(Tmp, Tmp2)-1;
break;
case ISD::SUB:
Tmp2 = ComputeNumSignBits(Op.getOperand(1), Depth+1);
if (Tmp2 == 1) return 1;
// Handle NEG.
if (ConstantSDNode *CLHS = dyn_cast<ConstantSDNode>(Op.getOperand(0)))
if (CLHS->getValue() == 0) {
uint64_t KnownZero, KnownOne;
uint64_t Mask = MVT::getIntVTBitMask(VT);
ComputeMaskedBits(Op.getOperand(1), Mask, KnownZero, KnownOne, Depth+1);
// If the input is known to be 0 or 1, the output is 0/-1, which is all
// sign bits set.
if ((KnownZero|1) == Mask)
return VTBits;
// If the input is known to be positive (the sign bit is known clear),
// the output of the NEG has the same number of sign bits as the input.
if (KnownZero & MVT::getIntVTSignBit(VT))
return Tmp2;
// Otherwise, we treat this like a SUB.
}
// Sub can have at most one carry bit. Thus we know that the output
// is, at worst, one more bit than the inputs.
Tmp = ComputeNumSignBits(Op.getOperand(0), Depth+1);
if (Tmp == 1) return 1; // Early out.
return std::min(Tmp, Tmp2)-1;
break;
case ISD::TRUNCATE:
// FIXME: it's tricky to do anything useful for this, but it is an important
// case for targets like X86.
break;
}
// Allow the target to implement this method for its nodes.