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Make sure to correctly clear the exact/nuw/nsw flags off of shifts when they are combined together. <rdar://problem/9859829>

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llvm-svn: 136435
This commit is contained in:
Eli Friedman 2011-07-29 00:18:19 +00:00
parent f7890e34b9
commit a07aa98eff
2 changed files with 43 additions and 20 deletions
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46
lib/Transforms/InstCombine/InstCombineShifts.cpp
View File

@ -208,11 +208,12 @@ static Value *GetShiftedValue(Value *V, unsigned NumBits, bool isLeftShift,
return I;
case Instruction::Shl: {
unsigned TypeWidth = I->getType()->getScalarSizeInBits();
BinaryOperator *BO = cast<BinaryOperator>(I);
unsigned TypeWidth = BO->getType()->getScalarSizeInBits();
// We only accept shifts-by-a-constant in CanEvaluateShifted.
ConstantInt *CI = cast<ConstantInt>(I->getOperand(1));
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.
@ -220,7 +221,9 @@ static Value *GetShiftedValue(Value *V, unsigned NumBits, bool isLeftShift,
if (NewShAmt >= TypeWidth)
return Constant::getNullValue(I->getType());
I->setOperand(1, ConstantInt::get(I->getType(), NewShAmt));
BO->setOperand(1, ConstantInt::get(BO->getType(), NewShAmt));
BO->setHasNoUnsignedWrap(false);
BO->setHasNoSignedWrap(false);
return I;
}
@ -228,11 +231,11 @@ static Value *GetShiftedValue(Value *V, unsigned NumBits, bool isLeftShift,
// zeros.
if (CI->getValue() == NumBits) {
APInt Mask(APInt::getLowBitsSet(TypeWidth, TypeWidth - NumBits));
V = IC.Builder->CreateAnd(I->getOperand(0),
ConstantInt::get(I->getContext(), Mask));
V = IC.Builder->CreateAnd(BO->getOperand(0),
ConstantInt::get(BO->getContext(), Mask));
if (Instruction *VI = dyn_cast<Instruction>(V)) {
VI->moveBefore(I);
VI->takeName(I);
VI->moveBefore(BO);
VI->takeName(BO);
}
return V;
}
@ -240,23 +243,27 @@ static Value *GetShiftedValue(Value *V, unsigned NumBits, bool isLeftShift,
// 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);
I->setOperand(1, ConstantInt::get(I->getType(),
CI->getZExtValue() - NumBits));
return I;
BO->setOperand(1, ConstantInt::get(BO->getType(),
CI->getZExtValue() - NumBits));
BO->setHasNoUnsignedWrap(false);
BO->setHasNoSignedWrap(false);
return BO;
}
case Instruction::LShr: {
unsigned TypeWidth = I->getType()->getScalarSizeInBits();
BinaryOperator *BO = cast<BinaryOperator>(I);
unsigned TypeWidth = BO->getType()->getScalarSizeInBits();
// We only accept shifts-by-a-constant in CanEvaluateShifted.
ConstantInt *CI = cast<ConstantInt>(I->getOperand(1));
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(I->getType());
return Constant::getNullValue(BO->getType());
I->setOperand(1, ConstantInt::get(I->getType(), NewShAmt));
BO->setOperand(1, ConstantInt::get(BO->getType(), NewShAmt));
BO->setIsExact(false);
return I;
}
@ -265,7 +272,7 @@ static Value *GetShiftedValue(Value *V, unsigned NumBits, bool isLeftShift,
if (CI->getValue() == NumBits) {
APInt Mask(APInt::getHighBitsSet(TypeWidth, TypeWidth - NumBits));
V = IC.Builder->CreateAnd(I->getOperand(0),
ConstantInt::get(I->getContext(), Mask));
ConstantInt::get(BO->getContext(), Mask));
if (Instruction *VI = dyn_cast<Instruction>(V)) {
VI->moveBefore(I);
VI->takeName(I);
@ -276,9 +283,10 @@ static Value *GetShiftedValue(Value *V, unsigned NumBits, bool isLeftShift,
// 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);
I->setOperand(1, ConstantInt::get(I->getType(),
CI->getZExtValue() - NumBits));
return I;
BO->setOperand(1, ConstantInt::get(BO->getType(),
CI->getZExtValue() - NumBits));
BO->setIsExact(false);
return BO;
}
case Instruction::Select:

17
test/Transforms/InstCombine/shift.ll
View File

@ -525,5 +525,20 @@ define i32 @test43(i32 %a, i32 %b) nounwind {
; CHECK-NEXT: ret
}
define i32 @test44(i32 %a) nounwind {
%y = shl nuw i32 %a, 1
%z = shl i32 %y, 4
ret i32 %z
; CHECK: @test44
; CHECK-NEXT: %y = shl i32 %a, 5
; CHECK-NEXT: ret i32 %y
}
define i32 @test45(i32 %a) nounwind {
%y = lshr exact i32 %a, 1
%z = lshr i32 %y, 4
ret i32 %z
; CHECK: @test45
; CHECK-NEXT: %y = lshr i32 %a, 5
; CHECK-NEXT: ret i32 %y
}