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[InstCombine] move/adjust comments about demanded bits; NFC 

The code has been moved/copied around, but the comments were not updated to match.
This commit is contained in:
Sanjay Patel 2022-09-09 11:46:50 -04:00
parent 02f3fec391
commit 6113e6738d
1 changed files with 13 additions and 26 deletions
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39
llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
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@ -525,7 +525,7 @@ Value *InstCombinerImpl::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
SimplifyDemandedBits(I, 0, DemandedFromLHS, LHSKnown, Depth + 1))
return disableWrapFlagsBasedOnUnusedHighBits(I, NLZ);
// If we are known to be adding/subtracting zeros to every bit below
// If we are known to be adding zeros to every bit below
// the highest demanded bit, we just return the other side.
if (DemandedFromOps.isSubsetOf(RHSKnown.Zero))
return I->getOperand(0);
@ -549,7 +549,7 @@ Value *InstCombinerImpl::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
SimplifyDemandedBits(I, 0, DemandedFromOps, LHSKnown, Depth + 1))
return disableWrapFlagsBasedOnUnusedHighBits(I, NLZ);
// If we are known to be adding/subtracting zeros to every bit below
// If we are known to be subtracting zeros from every bit below
// the highest demanded bit, we just return the other side.
if (DemandedFromOps.isSubsetOf(RHSKnown.Zero))
return I->getOperand(0);
@ -1005,11 +1005,8 @@ Value *InstCombinerImpl::SimplifyMultipleUseDemandedBits(
// this instruction has a simpler value in that context.
switch (I->getOpcode()) {
case Instruction::And: {
// If either the LHS or the RHS are Zero, the result is zero.
computeKnownBits(I->getOperand(1), RHSKnown, Depth + 1, CxtI);
computeKnownBits(I->getOperand(0), LHSKnown, Depth + 1,
CxtI);
computeKnownBits(I->getOperand(0), LHSKnown, Depth + 1, CxtI);
Known = LHSKnown & RHSKnown;
// If the client is only demanding bits that we know, return the known
@ -1018,8 +1015,7 @@ Value *InstCombinerImpl::SimplifyMultipleUseDemandedBits(
return Constant::getIntegerValue(ITy, Known.One);
// 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.
// These bits cannot contribute to the result of the 'and' in this context.
if (DemandedMask.isSubsetOf(LHSKnown.Zero | RHSKnown.One))
return I->getOperand(0);
if (DemandedMask.isSubsetOf(RHSKnown.Zero | LHSKnown.One))
@ -1028,14 +1024,8 @@ Value *InstCombinerImpl::SimplifyMultipleUseDemandedBits(
break;
}
case Instruction::Or: {
// 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.
// If either the LHS or the RHS are One, the result is One.
computeKnownBits(I->getOperand(1), RHSKnown, Depth + 1, CxtI);
computeKnownBits(I->getOperand(0), LHSKnown, Depth + 1,
CxtI);
computeKnownBits(I->getOperand(0), LHSKnown, Depth + 1, CxtI);
Known = LHSKnown | RHSKnown;
// If the client is only demanding bits that we know, return the known
@ -1043,9 +1033,10 @@ Value *InstCombinerImpl::SimplifyMultipleUseDemandedBits(
if (DemandedMask.isSubsetOf(Known.Zero | Known.One))
return Constant::getIntegerValue(ITy, Known.One);
// 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.
// 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.
// 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.
if (DemandedMask.isSubsetOf(LHSKnown.One | RHSKnown.Zero))
return I->getOperand(0);
if (DemandedMask.isSubsetOf(RHSKnown.One | LHSKnown.Zero))
@ -1054,13 +1045,8 @@ Value *InstCombinerImpl::SimplifyMultipleUseDemandedBits(
break;
}
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.
computeKnownBits(I->getOperand(1), RHSKnown, Depth + 1, CxtI);
computeKnownBits(I->getOperand(0), LHSKnown, Depth + 1,
CxtI);
computeKnownBits(I->getOperand(0), LHSKnown, Depth + 1, CxtI);
Known = LHSKnown ^ RHSKnown;
// If the client is only demanding bits that we know, return the known
@ -1068,8 +1054,9 @@ Value *InstCombinerImpl::SimplifyMultipleUseDemandedBits(
if (DemandedMask.isSubsetOf(Known.Zero | Known.One))
return Constant::getIntegerValue(ITy, Known.One);
// If all of the demanded bits are known zero on one side, return the
// other.
// 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.
// If all of the demanded bits are known zero on one side, return the other.
if (DemandedMask.isSubsetOf(RHSKnown.Zero))
return I->getOperand(0);
if (DemandedMask.isSubsetOf(LHSKnown.Zero))