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[InstCombine] Teach SimplifyMultipleUseDemandedBits to handle And/Or/Xor known bits using the LHS/RHS known bits it already acquired without recursing back into computeKnownBits. 

This replicates the known bits and constant creation code from the single use case for these instructions and adds it here. The computeKnownBits and constant creation code for other instructions is now in the default case of the opcode switch.

llvm-svn: 300094
This commit is contained in:
Craig Topper 2017-04-12 19:32:47 +00:00
parent cf3641fd57
commit c75f94bfa5
1 changed files with 46 additions and 11 deletions
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57
llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
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@ -770,6 +770,12 @@ Value *InstCombiner::SimplifyMultipleUseDemandedBits(Instruction *I,
computeKnownBits(I->getOperand(0), LHSKnownZero, LHSKnownOne, Depth + 1,
CxtI);
// If the client is only demanding bits that we know, return the known
// constant.
if ((DemandedMask & ((RHSKnownZero | LHSKnownZero)|
(RHSKnownOne & LHSKnownOne))) == DemandedMask)
return Constant::getIntegerValue(ITy, RHSKnownOne & LHSKnownOne);
// If all of the demanded bits are known 1 on one side, return the other.
// These bits cannot contribute to the result of the 'and' in this
// context.
@ -780,10 +786,10 @@ Value *InstCombiner::SimplifyMultipleUseDemandedBits(Instruction *I,
(DemandedMask & ~RHSKnownZero))
return I->getOperand(1);
// If all of the demanded bits in the inputs are known zeros, return zero.
if ((DemandedMask & (RHSKnownZero|LHSKnownZero)) == DemandedMask)
return Constant::getNullValue(ITy);
// Output known-1 bits are only known if set in both the LHS & RHS.
KnownOne = RHSKnownOne & LHSKnownOne;
// Output known-0 are known to be clear if zero in either the LHS | RHS.
KnownZero = RHSKnownZero | LHSKnownZero;
break;
case Instruction::Or:
@ -796,6 +802,12 @@ Value *InstCombiner::SimplifyMultipleUseDemandedBits(Instruction *I,
computeKnownBits(I->getOperand(0), LHSKnownZero, LHSKnownOne, Depth + 1,
CxtI);
// If the client is only demanding bits that we know, return the known
// constant.
if ((DemandedMask & ((RHSKnownZero & LHSKnownZero)|
(RHSKnownOne | LHSKnownOne))) == DemandedMask)
return Constant::getIntegerValue(ITy, RHSKnownOne | LHSKnownOne);
// If all of the demanded bits are known zero on one side, return the
// other. These bits cannot contribute to the result of the 'or' in this
// context.
@ -815,9 +827,13 @@ Value *InstCombiner::SimplifyMultipleUseDemandedBits(Instruction *I,
(DemandedMask & (~LHSKnownZero)))
return I->getOperand(1);
// Output known-0 bits are only known if clear in both the LHS & RHS.
KnownZero = RHSKnownZero & LHSKnownZero;
// Output known-1 are known to be set if set in either the LHS | RHS.
KnownOne = RHSKnownOne | LHSKnownOne;
break;
case Instruction::Xor:
case Instruction::Xor: {
// We can simplify (X^Y) -> X or Y in the user's context if we know that
// only bits from X or Y are demanded.
@ -826,6 +842,18 @@ Value *InstCombiner::SimplifyMultipleUseDemandedBits(Instruction *I,
computeKnownBits(I->getOperand(0), LHSKnownZero, LHSKnownOne, Depth + 1,
CxtI);
// Output known-0 bits are known if clear or set in both the LHS & RHS.
APInt IKnownZero = (RHSKnownZero & LHSKnownZero) |
(RHSKnownOne & LHSKnownOne);
// Output known-1 are known to be set if set in only one of the LHS, RHS.
APInt IKnownOne = (RHSKnownZero & LHSKnownOne) |
(RHSKnownOne & LHSKnownZero);
// If the client is only demanding bits that we know, return the known
// constant.
if ((DemandedMask & (IKnownZero|IKnownOne)) == DemandedMask)
return Constant::getIntegerValue(ITy, IKnownOne);
// If all of the demanded bits are known zero on one side, return the
// other.
if ((DemandedMask & RHSKnownZero) == DemandedMask)
@ -833,16 +861,23 @@ Value *InstCombiner::SimplifyMultipleUseDemandedBits(Instruction *I,
if ((DemandedMask & LHSKnownZero) == DemandedMask)
return I->getOperand(1);
// Output known-0 bits are known if clear or set in both the LHS & RHS.
KnownZero = std::move(IKnownZero);
// Output known-1 are known to be set if set in only one of the LHS, RHS.
KnownOne = std::move(IKnownOne);
break;
}
default:
// Compute the KnownZero/KnownOne bits to simplify things downstream.
computeKnownBits(I, KnownZero, KnownOne, Depth, CxtI);
// Compute the KnownZero/KnownOne bits to simplify things downstream.
computeKnownBits(I, KnownZero, KnownOne, Depth, CxtI);
// If this user is only demanding bits that we know, return the known
// constant.
if ((DemandedMask & (KnownZero|KnownOne)) == DemandedMask)
return Constant::getIntegerValue(ITy, KnownOne);
// If this user is only demanding bits that we know, return the known
// constant.
if ((DemandedMask & (KnownZero|KnownOne)) == DemandedMask)
return Constant::getIntegerValue(ITy, KnownOne);
break;
}
return nullptr;
}