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For PR1205:

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Add a new ComputeMaskedBits function that is APIntified. We'll slowly
convert things over to use this version. When its all done, we'll remove
the existing version.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@35018 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Reid Spencer 2007-03-08 01:46:38 +00:00
parent 98ded765c2
commit 3e7594f187
1 changed files with 206 additions and 1 deletions
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207
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -566,11 +566,216 @@ static ConstantInt *SubOne(ConstantInt *C) {
ConstantInt::get(C->getType(), 1)));
}
/// ComputeMaskedBits - Determine which of the bits specified in Mask are
/// known to be either zero or one and return them in the KnownZero/KnownOne
/// bit sets. This code only analyzes bits in Mask, in order to short-circuit
/// processing.
/// NOTE: we cannot consider 'undef' to be "IsZero" here. The problem is that
/// we cannot optimize based on the assumption that it is zero without changing
/// it to be an explicit zero. If we don't change it to zero, other code could
/// optimized based on the contradictory assumption that it is non-zero.
/// Because instcombine aggressively folds operations with undef args anyway,
/// this won't lose us code quality.
static void ComputeMaskedBits(Value *V, APInt Mask, APInt& KnownZero,
APInt& KnownOne, unsigned Depth = 0) {
uint32_t BitWidth = Mask.getBitWidth();
assert(KnownZero.getBitWidth() == BitWidth &&
KnownOne.getBitWidth() == BitWidth &&
"Mask, KnownOne and KnownZero should have same BitWidth");
if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
// We know all of the bits for a constant!
APInt Tmp(CI->getValue());
Tmp.zextOrTrunc(BitWidth);
KnownOne = Tmp & Mask;
KnownZero = ~KnownOne & Mask;
return;
}
KnownZero.clear(); KnownOne.clear(); // Don't know anything.
if (Depth == 6 || Mask == 0)
return; // Limit search depth.
Instruction *I = dyn_cast<Instruction>(V);
if (!I) return;
APInt KnownZero2(KnownZero), KnownOne2(KnownOne);
Mask &= APInt::getAllOnesValue(
cast<IntegerType>(V->getType())->getBitWidth()).zextOrTrunc(BitWidth);
switch (I->getOpcode()) {
case Instruction::And:
// If either the LHS or the RHS are Zero, the result is zero.
ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, Depth+1);
Mask &= ~KnownZero;
ComputeMaskedBits(I->getOperand(0), Mask, KnownZero2, KnownOne2, Depth+1);
assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
// Output known-1 bits are only known if set in both the LHS & RHS.
KnownOne &= KnownOne2;
// Output known-0 are known to be clear if zero in either the LHS | RHS.
KnownZero |= KnownZero2;
return;
case Instruction::Or:
ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, Depth+1);
Mask &= ~KnownOne;
ComputeMaskedBits(I->getOperand(0), Mask, KnownZero2, KnownOne2, Depth+1);
assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
// Output known-0 bits are only known if clear in both the LHS & RHS.
KnownZero &= KnownZero2;
// Output known-1 are known to be set if set in either the LHS | RHS.
KnownOne |= KnownOne2;
return;
case Instruction::Xor: {
ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, Depth+1);
ComputeMaskedBits(I->getOperand(0), Mask, KnownZero2, KnownOne2, Depth+1);
assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
// Output known-0 bits are known if clear or set in both the LHS & RHS.
APInt KnownZeroOut = (KnownZero & KnownZero2) | (KnownOne & KnownOne2);
// Output known-1 are known to be set if set in only one of the LHS, RHS.
KnownOne = (KnownZero & KnownOne2) | (KnownOne & KnownZero2);
KnownZero = KnownZeroOut;
return;
}
case Instruction::Select:
ComputeMaskedBits(I->getOperand(2), Mask, KnownZero, KnownOne, Depth+1);
ComputeMaskedBits(I->getOperand(1), Mask, KnownZero2, KnownOne2, Depth+1);
assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
// Only known if known in both the LHS and RHS.
KnownOne &= KnownOne2;
KnownZero &= KnownZero2;
return;
case Instruction::FPTrunc:
case Instruction::FPExt:
case Instruction::FPToUI:
case Instruction::FPToSI:
case Instruction::SIToFP:
case Instruction::PtrToInt:
case Instruction::UIToFP:
case Instruction::IntToPtr:
return; // Can't work with floating point or pointers
case Instruction::Trunc:
// All these have integer operands
ComputeMaskedBits(I->getOperand(0), Mask, KnownZero, KnownOne, Depth+1);
return;
case Instruction::BitCast: {
const Type *SrcTy = I->getOperand(0)->getType();
if (SrcTy->isInteger()) {
ComputeMaskedBits(I->getOperand(0), Mask, KnownZero, KnownOne, Depth+1);
return;
}
break;
}
case Instruction::ZExt: {
// Compute the bits in the result that are not present in the input.
const IntegerType *SrcTy = cast<IntegerType>(I->getOperand(0)->getType());
APInt NotIn(~SrcTy->getMask());
APInt NewBits = APInt::getAllOnesValue(BitWidth) &
NotIn.zext(BitWidth);
Mask &= ~NotIn;
ComputeMaskedBits(I->getOperand(0), Mask, KnownZero, KnownOne, Depth+1);
assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
// The top bits are known to be zero.
KnownZero |= NewBits;
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());
APInt NotIn(~SrcTy->getMask());
APInt NewBits = APInt::getAllOnesValue(BitWidth) &
NotIn.zext(BitWidth);
Mask &= ~NotIn;
ComputeMaskedBits(I->getOperand(0), Mask, KnownZero, KnownOne, Depth+1);
assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
// If the sign bit of the input is known set or clear, then we know the
// top bits of the result.
APInt InSignBit(APInt::getSignedMinValue(SrcTy->getBitWidth()));
InSignBit.zextOrTrunc(BitWidth);
if ((KnownZero & InSignBit) != 0) { // Input sign bit known zero
KnownZero |= NewBits;
KnownOne &= ~NewBits;
} else if ((KnownOne & InSignBit) != 0) { // Input sign bit known set
KnownOne |= NewBits;
KnownZero &= ~NewBits;
} else { // Input sign bit unknown
KnownZero &= ~NewBits;
KnownOne &= ~NewBits;
}
return;
}
case Instruction::Shl:
// (shl X, C1) & C2 == 0 iff (X & C2 >>u C1) == 0
if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
uint64_t ShiftAmt = SA->getZExtValue();
Mask = APIntOps::lshr(Mask, ShiftAmt);
ComputeMaskedBits(I->getOperand(0), Mask, KnownZero, KnownOne, Depth+1);
assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
KnownZero = APIntOps::shl(KnownZero, ShiftAmt);
KnownOne = APIntOps::shl(KnownOne, ShiftAmt);
KnownZero |= APInt(BitWidth, 1ULL).shl(ShiftAmt)-1; // low bits known zero.
return;
}
break;
case Instruction::LShr:
// (ushr 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::getAllOnesValue(BitWidth).shl(BitWidth-ShiftAmt));
// Unsigned shift right.
Mask = APIntOps::shl(Mask, ShiftAmt);
ComputeMaskedBits(I->getOperand(0), Mask, KnownZero,KnownOne,Depth+1);
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.
return;
}
break;
case Instruction::AShr:
// (ushr 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::getAllOnesValue(BitWidth).shl(BitWidth-ShiftAmt));
// Signed shift right.
Mask = APIntOps::shl(Mask, ShiftAmt);
ComputeMaskedBits(I->getOperand(0), Mask, KnownZero,KnownOne,Depth+1);
assert((KnownZero & KnownOne) == 0&&"Bits known to be one AND zero?");
KnownZero = APIntOps::lshr(KnownZero, ShiftAmt);
KnownOne = APIntOps::lshr(KnownOne, ShiftAmt);
// Handle the sign bits and adjust to where it is now in the mask.
APInt SignBit = APInt::getSignedMinValue(BitWidth).lshr(ShiftAmt);
if ((KnownZero & SignBit) != 0) { // New bits are known zero.
KnownZero |= HighBits;
} else if ((KnownOne & SignBit) != 0) { // New bits are known one.
KnownOne |= HighBits;
}
return;
}
break;
}
}
/// ComputeMaskedBits - Determine which of the bits specified in Mask are
/// known to be either zero or one and return them in the KnownZero/KnownOne
/// bitsets. This code only analyzes bits in Mask, in order to short-circuit
/// processing.
static void ComputeMaskedBits(Value *V, uint64_t Mask, uint64_t &KnownZero,
static void ComputeMaskedBits(Value *V, uint64_t Mask, uint64_t &KnownZero,
uint64_t &KnownOne, unsigned Depth = 0) {
// Note, we cannot consider 'undef' to be "IsZero" here. The problem is that
// we cannot optimize based on the assumption that it is zero without changing