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Clean up codes in ComputeMaskedBits(): 

1. Line out nested use of zext/trunc.
2. Make more use of getHighBitsSet/getLowBitsSet.
3. Use APInt[] != 0 instead of "(APInt & SignBit) != 0".

llvm-svn: 35408
This commit is contained in:
Zhou Sheng 2007-03-28 02:19:03 +00:00
parent 4388043b25
commit 57e3f7324b
1 changed files with 27 additions and 29 deletions
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56
llvm/lib/Transforms/Scalar/InstructionCombining.cpp
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@ -600,11 +600,10 @@ static void ComputeMaskedBits(Value *V, const APInt &Mask, APInt& KnownZero,
assert(V && "No Value?");
assert(Depth <= 6 && "Limit Search Depth");
uint32_t BitWidth = Mask.getBitWidth();
const IntegerType *VTy = cast<IntegerType>(V->getType());
assert(VTy->getBitWidth() == BitWidth &&
assert(cast<IntegerType>(V->getType())->getBitWidth() == BitWidth &&
KnownZero.getBitWidth() == BitWidth &&
KnownOne.getBitWidth() == BitWidth &&
"VTy, Mask, KnownOne and KnownZero should have same BitWidth");
"V, Mask, KnownOne and KnownZero should have same BitWidth");
if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
// We know all of the bits for a constant!
KnownOne = CI->getValue() & Mask;
@ -685,8 +684,11 @@ static void ComputeMaskedBits(Value *V, const APInt &Mask, APInt& KnownZero,
// All these have integer operands
uint32_t SrcBitWidth =
cast<IntegerType>(I->getOperand(0)->getType())->getBitWidth();
ComputeMaskedBits(I->getOperand(0), APInt(Mask).zext(SrcBitWidth),
KnownZero.zext(SrcBitWidth), KnownOne.zext(SrcBitWidth), Depth+1);
APInt MaskIn(Mask);
MaskIn.zext(SrcBitWidth);
KnownZero.zext(SrcBitWidth);
KnownOne.zext(SrcBitWidth);
ComputeMaskedBits(I->getOperand(0), MaskIn, KnownZero, KnownOne, Depth+1);
KnownZero.trunc(BitWidth);
KnownOne.trunc(BitWidth);
return;
@ -703,43 +705,40 @@ static void ComputeMaskedBits(Value *V, const APInt &Mask, APInt& KnownZero,
// Compute the bits in the result that are not present in the input.
const IntegerType *SrcTy = cast<IntegerType>(I->getOperand(0)->getType());
uint32_t SrcBitWidth = SrcTy->getBitWidth();
APInt NewBits(APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth));
ComputeMaskedBits(I->getOperand(0), APInt(Mask).trunc(SrcBitWidth),
KnownZero.trunc(SrcBitWidth), KnownOne.trunc(SrcBitWidth), Depth+1);
APInt MaskIn(Mask);
MaskIn.trunc(SrcBitWidth);
KnownZero.trunc(SrcBitWidth);
KnownOne.trunc(SrcBitWidth);
ComputeMaskedBits(I->getOperand(0), MaskIn, KnownZero, KnownOne, Depth+1);
assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
// The top bits are known to be zero.
KnownZero.zext(BitWidth);
KnownOne.zext(BitWidth);
KnownZero |= NewBits;
KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth);
return;
}
case Instruction::SExt: {
// Compute the bits in the result that are not present in the input.
const IntegerType *SrcTy = cast<IntegerType>(I->getOperand(0)->getType());
uint32_t SrcBitWidth = SrcTy->getBitWidth();
APInt NewBits(APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth));
ComputeMaskedBits(I->getOperand(0), APInt(Mask).trunc(SrcBitWidth),
KnownZero.trunc(SrcBitWidth), KnownOne.trunc(SrcBitWidth), Depth+1);
APInt MaskIn(Mask);
MaskIn.trunc(SrcBitWidth);
KnownZero.trunc(SrcBitWidth);
KnownOne.trunc(SrcBitWidth);
ComputeMaskedBits(I->getOperand(0), MaskIn, KnownZero, KnownOne, Depth+1);
assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
KnownZero.zext(BitWidth);
KnownOne.zext(BitWidth);
// If the sign bit of the input is known set or clear, then we know the
// top bits of the result.
APInt InSignBit(APInt::getSignBit(SrcTy->getBitWidth()));
InSignBit.zext(BitWidth);
if ((KnownZero & InSignBit) != 0) { // Input sign bit known zero
APInt NewBits(APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth));
if (KnownZero[SrcBitWidth-1]) // Input sign bit known zero
KnownZero |= NewBits;
KnownOne &= ~NewBits;
} else if ((KnownOne & InSignBit) != 0) { // Input sign bit known set
else if (KnownOne[SrcBitWidth-1]) // Input sign bit known set
KnownOne |= NewBits;
KnownZero &= ~NewBits;
} else { // Input sign bit unknown
KnownZero &= ~NewBits;
KnownOne &= ~NewBits;
}
return;
}
case Instruction::Shl:
@ -760,7 +759,6 @@ static void ComputeMaskedBits(Value *V, const APInt &Mask, APInt& KnownZero,
if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
// Compute the new bits that are at the top now.
uint64_t ShiftAmt = SA->getZExtValue();
APInt HighBits(APInt::getHighBitsSet(BitWidth, ShiftAmt));
// Unsigned shift right.
APInt Mask2(Mask.shl(ShiftAmt));
@ -768,16 +766,16 @@ static void ComputeMaskedBits(Value *V, const APInt &Mask, APInt& KnownZero,
assert((KnownZero & KnownOne) == 0&&"Bits known to be one AND zero?");
KnownZero = APIntOps::lshr(KnownZero, ShiftAmt);
KnownOne = APIntOps::lshr(KnownOne, ShiftAmt);
KnownZero |= HighBits; // high bits known zero.
// high bits known zero.
KnownZero |= APInt::getHighBitsSet(BitWidth, ShiftAmt);
return;
}
break;
case Instruction::AShr:
// (ushr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0
// (ashr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0
if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
// Compute the new bits that are at the top now.
uint64_t ShiftAmt = SA->getZExtValue();
APInt HighBits(APInt::getHighBitsSet(BitWidth, ShiftAmt));
// Signed shift right.
APInt Mask2(Mask.shl(ShiftAmt));
@ -789,11 +787,11 @@ static void ComputeMaskedBits(Value *V, const APInt &Mask, APInt& KnownZero,
// Handle the sign bits and adjust to where it is now in the mask.
APInt SignBit(APInt::getSignBit(BitWidth).lshr(ShiftAmt));
if ((KnownZero & SignBit) != 0) { // New bits are known zero.
APInt HighBits(APInt::getHighBitsSet(BitWidth, ShiftAmt));
if (KnownZero[BitWidth-ShiftAmt-1]) // New bits are known zero.
KnownZero |= HighBits;
} else if ((KnownOne & SignBit) != 0) { // New bits are known one.
else if (KnownOne[BitWidth-ShiftAmt-1]) // New bits are known one.
KnownOne |= HighBits;
}
return;
}
break;