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Add some more simple sign bit propagation cases. 

llvm-svn: 28149
This commit is contained in:
Chris Lattner 2006-05-06 22:39:59 +00:00
parent ce9b9fe6eb
commit f86075731d
1 changed files with 67 additions and 27 deletions
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94
llvm/lib/Target/TargetLowering.cpp
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@ -1010,19 +1010,7 @@ unsigned TargetLowering::ComputeNumSignBits(SDOperand Op, unsigned Depth) const{
return 1; // Limit search depth.
switch (Op.getOpcode()) {
default:
// Allow the target to implement this method for its nodes.
if (Op.getOpcode() >= ISD::BUILTIN_OP_END) {
case ISD::INTRINSIC_WO_CHAIN:
case ISD::INTRINSIC_W_CHAIN:
case ISD::INTRINSIC_VOID:
unsigned NumBits = ComputeNumSignBitsForTargetNode(Op, Depth);
if (NumBits > 1) return NumBits;
}
// FIXME: Should use computemaskedbits to look at the top bits.
return 1;
default: break;
case ISD::AssertSext:
Tmp = MVT::getSizeInBits(cast<VTSDNode>(Op.getOperand(1))->getVT());
return VTBits-Tmp+1;
@ -1030,6 +1018,31 @@ unsigned TargetLowering::ComputeNumSignBits(SDOperand Op, unsigned Depth) const{
Tmp = MVT::getSizeInBits(cast<VTSDNode>(Op.getOperand(1))->getVT());
return VTBits-Tmp;
case ISD::SEXTLOAD: // '17' bits known
Tmp = MVT::getSizeInBits(cast<VTSDNode>(Op.getOperand(3))->getVT());
return VTBits-Tmp+1;
case ISD::ZEXTLOAD: // '16' bits known
Tmp = MVT::getSizeInBits(cast<VTSDNode>(Op.getOperand(3))->getVT());
return VTBits-Tmp;
case ISD::Constant: {
uint64_t Val = cast<ConstantSDNode>(Op)->getValue();
// If negative, invert the bits, then look at it.
if (Val & MVT::getIntVTSignBit(VT))
Val = ~Val;
// Shift the bits so they are the leading bits in the int64_t.
Val <<= 64-VTBits;
// Return # leading zeros. We use 'min' here in case Val was zero before
// shifting. We don't want to return '64' as for an i32 "0".
return std::min(VTBits, CountLeadingZeros_64(Val));
}
case ISD::SIGN_EXTEND:
Tmp = VTBits-MVT::getSizeInBits(Op.getOperand(0).getValueType());
return ComputeNumSignBits(Op.getOperand(0), Depth+1) + Tmp;
case ISD::SIGN_EXTEND_INREG:
// Max of the input and what this extends.
Tmp = MVT::getSizeInBits(cast<VTSDNode>(Op.getOperand(1))->getVT());
@ -1046,31 +1059,58 @@ unsigned TargetLowering::ComputeNumSignBits(SDOperand Op, unsigned Depth) const{
if (Tmp > VTBits) Tmp = VTBits;
}
return Tmp;
case ISD::SHL:
if (ConstantSDNode *C = dyn_cast<ConstantSDNode>(Op.getOperand(1))) {
// shl destroys sign bits.
Tmp = ComputeNumSignBits(Op.getOperand(0), Depth+1);
if (C->getValue() >= VTBits || // Bad shift.
C->getValue() >= Tmp) break; // Shifted all sign bits out.
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;
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::ZEXTLOAD: // 16 bits known
//case ISD::SEXTLOAD: // 17 bits known
//case ISD::Constant:
//case ISD::SIGN_EXTEND:
//
case ISD::AND:
case ISD::OR:
case ISD::XOR: // NOT is handled here.
// Logical binary ops preserve the number of sign bits.
Tmp = ComputeNumSignBits(Op.getOperand(0), Depth+1);
if (Tmp == 1) return 1; // Early out.
Tmp2 = ComputeNumSignBits(Op.getOperand(1), Depth+1);
return std::min(Tmp, Tmp2);
case ISD::SELECT:
Tmp = ComputeNumSignBits(Op.getOperand(0), Depth+1);
if (Tmp == 1) return 1; // Early out.
Tmp2 = ComputeNumSignBits(Op.getOperand(1), Depth+1);
return std::min(Tmp, Tmp2);
case ISD::SETCC:
// If setcc returns 0/-1, all bits are sign bits.
if (getSetCCResultContents() == ZeroOrNegativeOneSetCCResult)
return VTBits;
break;
}
#if 0
// fold (sext_in_reg (setcc x)) -> setcc x iff (setcc x) == 0 or -1
if (N0.getOpcode() == ISD::SETCC &&
TLI.getSetCCResultContents() ==
TargetLowering::ZeroOrNegativeOneSetCCResult)
return N0;
#endif
// Allow the target to implement this method for its nodes.
if (Op.getOpcode() >= ISD::BUILTIN_OP_END ||
Op.getOpcode() == ISD::INTRINSIC_WO_CHAIN ||
Op.getOpcode() == ISD::INTRINSIC_W_CHAIN ||
Op.getOpcode() == ISD::INTRINSIC_VOID) {
unsigned NumBits = ComputeNumSignBitsForTargetNode(Op, Depth);
if (NumBits > 1) return NumBits;
}
// FIXME: Should use computemaskedbits to look at the top bits.
return 1;
}