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[InstCombine] refactor shift-of-shift folds; NFCI

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Reduces code duplication and makes it easier to extend these folds for vectors.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@292145 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Sanjay Patel 2017-01-16 17:27:50 +00:00
parent 50d76a80ed
commit 0f258723e9
1 changed files with 66 additions and 83 deletions
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149
lib/Transforms/InstCombine/InstCombineShifts.cpp
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@ -190,6 +190,68 @@ static bool canEvaluateShifted(Value *V, unsigned NumBits, bool IsLeftShift,
}
}
/// Fold OuterShift (InnerShift X, C1), C2.
/// See canEvaluateShiftedShift() for the constraints on these instructions.
static Value *foldShiftedShift(BinaryOperator *InnerShift, unsigned OuterShAmt,
bool IsOuterShl,
InstCombiner::BuilderTy &Builder) {
bool IsInnerShl = InnerShift->getOpcode() == Instruction::Shl;
Type *ShType = InnerShift->getType();
unsigned TypeWidth = ShType->getScalarSizeInBits();
// We only accept shifts-by-a-constant in canEvaluateShifted().
ConstantInt *C1 = cast<ConstantInt>(InnerShift->getOperand(1));
unsigned InnerShAmt = C1->getZExtValue();
// Change the shift amount and clear the appropriate IR flags.
auto NewInnerShift = [&](unsigned ShAmt) {
InnerShift->setOperand(1, ConstantInt::get(ShType, ShAmt));
if (IsInnerShl) {
InnerShift->setHasNoUnsignedWrap(false);
InnerShift->setHasNoSignedWrap(false);
} else {
InnerShift->setIsExact(false);
}
return InnerShift;
};
// Two logical shifts in the same direction:
// shl (shl X, C1), C2 --> shl X, C1 + C2
// lshr (lshr X, C1), C2 --> lshr X, C1 + C2
if (IsInnerShl == IsOuterShl) {
// If this is an oversized composite shift, then unsigned shifts get 0.
if (InnerShAmt + OuterShAmt >= TypeWidth)
return Constant::getNullValue(ShType);
return NewInnerShift(InnerShAmt + OuterShAmt);
}
// Equal shift amounts in opposite directions become bitwise 'and':
// lshr (shl X, C), C --> and X, C'
// shl (lshr X, C), C --> and X, C'
if (InnerShAmt == OuterShAmt) {
APInt Mask = IsInnerShl
? APInt::getLowBitsSet(TypeWidth, TypeWidth - OuterShAmt)
: APInt::getHighBitsSet(TypeWidth, TypeWidth - OuterShAmt);
Value *And = Builder.CreateAnd(InnerShift->getOperand(0),
ConstantInt::get(ShType, Mask));
if (auto *AndI = dyn_cast<Instruction>(And)) {
AndI->moveBefore(InnerShift);
AndI->takeName(InnerShift);
}
return And;
}
assert(InnerShAmt > OuterShAmt &&
"Unexpected opposite direction logical shift pair");
// In general, we would need an 'and' for this transform, but
// canEvaluateShiftedShift() guarantees that the masked-off bits are not used.
// lshr (shl X, C1), C2 --> shl X, C1 - C2
// shl (lshr X, C1), C2 --> lshr X, C1 - C2
return NewInnerShift(InnerShAmt - OuterShAmt);
}
/// When canEvaluateShifted() returns true for an expression, this function
/// inserts the new computation that produces the shifted value.
static Value *getShiftedValue(Value *V, unsigned NumBits, bool isLeftShift,
@ -223,89 +285,10 @@ static Value *getShiftedValue(Value *V, unsigned NumBits, bool isLeftShift,
1, getShiftedValue(I->getOperand(1), NumBits, isLeftShift, IC, DL));
return I;
case Instruction::Shl: {
BinaryOperator *BO = cast<BinaryOperator>(I);
unsigned TypeWidth = BO->getType()->getScalarSizeInBits();
// We only accept shifts-by-a-constant in CanEvaluateShifted.
ConstantInt *CI = cast<ConstantInt>(BO->getOperand(1));
// We can always fold shl(c1)+shl(c2) -> shl(c1+c2).
if (isLeftShift) {
// If this is oversized composite shift, then unsigned shifts get 0.
unsigned NewShAmt = NumBits+CI->getZExtValue();
if (NewShAmt >= TypeWidth)
return Constant::getNullValue(I->getType());
BO->setOperand(1, ConstantInt::get(BO->getType(), NewShAmt));
BO->setHasNoUnsignedWrap(false);
BO->setHasNoSignedWrap(false);
return I;
}
// We turn shl(c)+lshr(c) -> and(c2) if the input doesn't already have
// zeros.
if (CI->getValue() == NumBits) {
APInt Mask(APInt::getLowBitsSet(TypeWidth, TypeWidth - NumBits));
V = IC.Builder->CreateAnd(BO->getOperand(0),
ConstantInt::get(BO->getContext(), Mask));
if (Instruction *VI = dyn_cast<Instruction>(V)) {
VI->moveBefore(BO);
VI->takeName(BO);
}
return V;
}
// We turn shl(c1)+shr(c2) -> shl(c3)+and(c4), but only when we know that
// the and won't be needed.
assert(CI->getZExtValue() > NumBits);
BO->setOperand(1, ConstantInt::get(BO->getType(),
CI->getZExtValue() - NumBits));
BO->setHasNoUnsignedWrap(false);
BO->setHasNoSignedWrap(false);
return BO;
}
// FIXME: This is almost identical to the SHL case. Refactor both cases into
// a helper function.
case Instruction::LShr: {
BinaryOperator *BO = cast<BinaryOperator>(I);
unsigned TypeWidth = BO->getType()->getScalarSizeInBits();
// We only accept shifts-by-a-constant in CanEvaluateShifted.
ConstantInt *CI = cast<ConstantInt>(BO->getOperand(1));
// We can always fold lshr(c1)+lshr(c2) -> lshr(c1+c2).
if (!isLeftShift) {
// If this is oversized composite shift, then unsigned shifts get 0.
unsigned NewShAmt = NumBits+CI->getZExtValue();
if (NewShAmt >= TypeWidth)
return Constant::getNullValue(BO->getType());
BO->setOperand(1, ConstantInt::get(BO->getType(), NewShAmt));
BO->setIsExact(false);
return I;
}
// We turn lshr(c)+shl(c) -> and(c2) if the input doesn't already have
// zeros.
if (CI->getValue() == NumBits) {
APInt Mask(APInt::getHighBitsSet(TypeWidth, TypeWidth - NumBits));
V = IC.Builder->CreateAnd(I->getOperand(0),
ConstantInt::get(BO->getContext(), Mask));
if (Instruction *VI = dyn_cast<Instruction>(V)) {
VI->moveBefore(I);
VI->takeName(I);
}
return V;
}
// We turn lshr(c1)+shl(c2) -> lshr(c3)+and(c4), but only when we know that
// the and won't be needed.
assert(CI->getZExtValue() > NumBits);
BO->setOperand(1, ConstantInt::get(BO->getType(),
CI->getZExtValue() - NumBits));
BO->setIsExact(false);
return BO;
}
case Instruction::Shl:
case Instruction::LShr:
return foldShiftedShift(cast<BinaryOperator>(I), NumBits, isLeftShift,
*(IC.Builder));
case Instruction::Select:
I->setOperand(