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For PR1271:

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Remove a use of getLowBitsSet that caused the mask used for replacement of
shl/lshr pairs with an AND instruction to be computed incorrectly. Its not
clear exactly why this is the case. This solves the disappearing shifts
problem, but it doesn't fix Regression/C/2003-05-21-UnionBitFields. It
seems there is more going on.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@35342 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Reid Spencer 2007-03-25 21:11:44 +00:00
parent db9654e284
commit 55702aaa52
1 changed files with 11 additions and 12 deletions
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23
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -595,7 +595,7 @@ static ConstantInt *Multiply(ConstantInt *C1, ConstantInt *C2) {
/// 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, const APInt& Mask, APInt& KnownZero,
static void ComputeMaskedBits(Value *V, const APInt &Mask, APInt& KnownZero,
APInt& KnownOne, unsigned Depth = 0) {
assert(V && "No Value?");
assert(Depth <= 6 && "Limit Search Depth");
@ -1200,7 +1200,7 @@ bool InstCombiner::SimplifyDemandedBits(Value *V, APInt DemandedMask,
// Figure out what the input bits are. If the top bits of the and result
// are not demanded, then the add doesn't demand them from its input
// either.
unsigned NLZ = DemandedMask.countLeadingZeros();
uint32_t NLZ = DemandedMask.countLeadingZeros();
// If there is a constant on the RHS, there are a variety of xformations
// we can do.
@ -1296,7 +1296,7 @@ bool InstCombiner::SimplifyDemandedBits(Value *V, APInt DemandedMask,
if ((DemandedMask & APInt::getSignBit(BitWidth)) == 0) {
// Right fill the mask of bits for this SUB to demand the most
// significant bit and all those below it.
uint32_t NLZ = DemandedMask.countLeadingZeros();
unsigned NLZ = DemandedMask.countLeadingZeros();
APInt DemandedFromOps(APInt::getAllOnesValue(BitWidth).lshr(NLZ));
if (SimplifyDemandedBits(I->getOperand(0), DemandedFromOps,
LHSKnownZero, LHSKnownOne, Depth+1))
@ -4877,8 +4877,8 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
if (LHSI->hasOneUse()) {
// Otherwise strength reduce the shift into an and.
unsigned ShAmtVal = (unsigned)ShAmt->getZExtValue();
Constant *Mask = ConstantInt::get(APInt::getLowBitsSet(TypeBits,
TypeBits - ShAmtVal));
uint64_t Val = (1ULL << (TypeBits-ShAmtVal))-1;
Constant *Mask = ConstantInt::get(CI->getType(), Val);
Instruction *AndI =
BinaryOperator::createAnd(LHSI->getOperand(0),
@ -5809,7 +5809,7 @@ Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, ConstantInt *Op1,
if (ShiftAmt1 == ShiftAmt2) {
// If we have ((X >>? C) << C), turn this into X & (-1 << C).
if (I.getOpcode() == Instruction::Shl) {
APInt Mask(Ty->getMask().shl(ShiftAmt1));
APInt Mask(APInt::getHighBitsSet(TypeBits, TypeBits - ShiftAmt1));
return BinaryOperator::createAnd(X, ConstantInt::get(Mask));
}
// If we have ((X << C) >>u C), turn this into X & (-1 >>u C).
@ -5847,9 +5847,8 @@ Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, ConstantInt *Op1,
BinaryOperator::createShl(X, ConstantInt::get(Ty, ShiftDiff));
InsertNewInstBefore(Shift, I);
ConstantInt *Mask = ConstantInt::get(
APInt::getHighBitsSet(TypeBits, TypeBits - ShiftAmt2));
return BinaryOperator::createAnd(Shift, Mask);
APInt Mask(APInt::getHighBitsSet(TypeBits, TypeBits - ShiftAmt2));
return BinaryOperator::createAnd(Shift, ConstantInt::get(Mask));
}
// (X << C1) >>u C2 --> X >>u (C2-C1) & (-1 >> C2)
@ -5859,7 +5858,7 @@ Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, ConstantInt *Op1,
BinaryOperator::createLShr(X, ConstantInt::get(Ty, ShiftDiff));
InsertNewInstBefore(Shift, I);
APInt Mask(Ty->getMask().lshr(ShiftAmt2));
APInt Mask(APInt::getHighBitsSet(TypeBits, TypeBits - ShiftAmt2));
return BinaryOperator::createAnd(Shift, ConstantInt::get(Mask));
}
@ -5877,7 +5876,7 @@ Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, ConstantInt *Op1,
ConstantInt::get(Ty, ShiftDiff));
InsertNewInstBefore(Shift, I);
APInt Mask(Ty->getMask().shl(ShiftAmt2));
APInt Mask(APInt::getHighBitsSet(TypeBits, TypeBits - ShiftAmt2));
return BinaryOperator::createAnd(Shift, ConstantInt::get(Mask));
}
@ -5888,7 +5887,7 @@ Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, ConstantInt *Op1,
BinaryOperator::createShl(X, ConstantInt::get(Ty, ShiftDiff));
InsertNewInstBefore(Shift, I);
APInt Mask(Ty->getMask().lshr(ShiftAmt2));
APInt Mask(APInt::getHighBitsSet(TypeBits, TypeBits - ShiftAmt2));
return BinaryOperator::createAnd(Shift, ConstantInt::get(Mask));
}