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[TargetLowering][InstCombine] Simplify BSwap demanded bits code a little. NFC 

Use alignDown instead of &= ~7.

Replace ResultBit with NLZ. (BitWidth - NLZ - NTZ == 8) so
(BitWidth - NTZ - 8 == NLZ).

Reviewed By: spatel

Differential Revision: https://reviews.llvm.org/D117804
This commit is contained in:
Craig Topper 2022-01-20 10:36:21 -08:00
parent eb6c6e6058
commit 9abc593e98
2 changed files with 14 additions and 19 deletions
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12
llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
View File

@ -1815,20 +1815,16 @@ bool TargetLowering::SimplifyDemandedBits(
// Round NTZ down to the next byte. If we have 11 trailing zeros, then
// we need all the bits down to bit 8. Likewise, round NLZ. If we
// have 14 leading zeros, round to 8.
NLZ &= ~7;
NTZ &= ~7;
NLZ = alignDown(NLZ, 8);
NTZ = alignDown(NTZ, 8);
// If we need exactly one byte, we can do this transformation.
if (BitWidth - NLZ - NTZ == 8) {
unsigned ResultBit = NTZ;
unsigned InputBit = BitWidth - NTZ - 8;
// Replace this with either a left or right shift to get the byte into
// the right place.
unsigned ShiftOpcode = InputBit > ResultBit ? ISD::SRL : ISD::SHL;
unsigned ShiftOpcode = NLZ > NTZ ? ISD::SRL : ISD::SHL;
if (!TLO.LegalOperations() || isOperationLegal(ShiftOpcode, VT)) {
EVT ShiftAmtTy = getShiftAmountTy(VT, DL);
unsigned ShiftAmount =
InputBit > ResultBit ? InputBit - ResultBit : ResultBit - InputBit;
unsigned ShiftAmount = NLZ > NTZ ? NLZ - NTZ : NTZ - NLZ;
SDValue ShAmt = TLO.DAG.getConstant(ShiftAmount, dl, ShiftAmtTy);
SDValue NewOp = TLO.DAG.getNode(ShiftOpcode, dl, VT, Src, ShAmt);
return TLO.CombineTo(Op, NewOp);

21
llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
View File

@ -800,22 +800,21 @@ Value *InstCombinerImpl::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
// Round NTZ down to the next byte. If we have 11 trailing zeros, then
// we need all the bits down to bit 8. Likewise, round NLZ. If we
// have 14 leading zeros, round to 8.
NLZ &= ~7;
NTZ &= ~7;
NLZ = alignDown(NLZ, 8);
NTZ = alignDown(NTZ, 8);
// If we need exactly one byte, we can do this transformation.
if (BitWidth-NLZ-NTZ == 8) {
unsigned ResultBit = NTZ;
unsigned InputBit = BitWidth-NTZ-8;
if (BitWidth - NLZ - NTZ == 8) {
// Replace this with either a left or right shift to get the byte into
// the right place.
Instruction *NewVal;
if (InputBit > ResultBit)
NewVal = BinaryOperator::CreateLShr(II->getArgOperand(0),
ConstantInt::get(I->getType(), InputBit-ResultBit));
if (NLZ > NTZ)
NewVal = BinaryOperator::CreateLShr(
II->getArgOperand(0),
ConstantInt::get(I->getType(), NLZ - NTZ));
else
NewVal = BinaryOperator::CreateShl(II->getArgOperand(0),
ConstantInt::get(I->getType(), ResultBit-InputBit));
NewVal = BinaryOperator::CreateShl(
II->getArgOperand(0),
ConstantInt::get(I->getType(), NTZ - NLZ));
NewVal->takeName(I);
return InsertNewInstWith(NewVal, *I);
}