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[InstCombine] match variable names and code comments; NFC 

Similar to:
29c09c7

Planned follow-up is to add a transform here to allow removing
a common shift fold that is conflicting with D110170.
This commit is contained in:
Sanjay Patel 2021-09-26 12:02:46 -04:00
parent 1f5b60ad47
commit 025a805d7c
1 changed files with 34 additions and 33 deletions
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67
llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
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@ -902,41 +902,41 @@ Instruction *InstCombinerImpl::visitShl(BinaryOperator &I) {
Type *Ty = I.getType();
unsigned BitWidth = Ty->getScalarSizeInBits();
const APInt *ShAmtAPInt;
if (match(Op1, m_APInt(ShAmtAPInt))) {
unsigned ShAmt = ShAmtAPInt->getZExtValue();
const APInt *C;
if (match(Op1, m_APInt(C))) {
unsigned ShAmtC = C->getZExtValue();
// shl (zext X), ShAmt --> zext (shl X, ShAmt)
// shl (zext X), C --> zext (shl X, C)
// This is only valid if X would have zeros shifted out.
Value *X;
if (match(Op0, m_OneUse(m_ZExt(m_Value(X))))) {
unsigned SrcWidth = X->getType()->getScalarSizeInBits();
if (ShAmt < SrcWidth &&
MaskedValueIsZero(X, APInt::getHighBitsSet(SrcWidth, ShAmt), 0, &I))
return new ZExtInst(Builder.CreateShl(X, ShAmt), Ty);
if (ShAmtC < SrcWidth &&
MaskedValueIsZero(X, APInt::getHighBitsSet(SrcWidth, ShAmtC), 0, &I))
return new ZExtInst(Builder.CreateShl(X, ShAmtC), Ty);
}
// (X >> C) << C --> X & (-1 << C)
if (match(Op0, m_Shr(m_Value(X), m_Specific(Op1)))) {
APInt Mask(APInt::getHighBitsSet(BitWidth, BitWidth - ShAmt));
APInt Mask(APInt::getHighBitsSet(BitWidth, BitWidth - ShAmtC));
return BinaryOperator::CreateAnd(X, ConstantInt::get(Ty, Mask));
}
const APInt *ShOp1;
if (match(Op0, m_Exact(m_Shr(m_Value(X), m_APInt(ShOp1)))) &&
ShOp1->ult(BitWidth)) {
unsigned ShrAmt = ShOp1->getZExtValue();
if (ShrAmt < ShAmt) {
// If C1 < C2: (X >>?,exact C1) << C2 --> X << (C2 - C1)
Constant *ShiftDiff = ConstantInt::get(Ty, ShAmt - ShrAmt);
const APInt *C1;
if (match(Op0, m_Exact(m_Shr(m_Value(X), m_APInt(C1)))) &&
C1->ult(BitWidth)) {
unsigned ShrAmt = C1->getZExtValue();
if (ShrAmt < ShAmtC) {
// If C1 < C: (X >>?,exact C1) << C --> X << (C - C1)
Constant *ShiftDiff = ConstantInt::get(Ty, ShAmtC - ShrAmt);
auto *NewShl = BinaryOperator::CreateShl(X, ShiftDiff);
NewShl->setHasNoUnsignedWrap(I.hasNoUnsignedWrap());
NewShl->setHasNoSignedWrap(I.hasNoSignedWrap());
return NewShl;
}
if (ShrAmt > ShAmt) {
// If C1 > C2: (X >>?exact C1) << C2 --> X >>?exact (C1 - C2)
Constant *ShiftDiff = ConstantInt::get(Ty, ShrAmt - ShAmt);
if (ShrAmt > ShAmtC) {
// If C1 > C: (X >>?exact C1) << C --> X >>?exact (C1 - C)
Constant *ShiftDiff = ConstantInt::get(Ty, ShrAmt - ShAmtC);
auto *NewShr = BinaryOperator::Create(
cast<BinaryOperator>(Op0)->getOpcode(), X, ShiftDiff);
NewShr->setIsExact(true);
@ -944,34 +944,34 @@ Instruction *InstCombinerImpl::visitShl(BinaryOperator &I) {
}
}
if (match(Op0, m_OneUse(m_Shr(m_Value(X), m_APInt(ShOp1)))) &&
ShOp1->ult(BitWidth)) {
unsigned ShrAmt = ShOp1->getZExtValue();
if (ShrAmt < ShAmt) {
// If C1 < C2: (X >>? C1) << C2 --> X << (C2 - C1) & (-1 << C2)
Constant *ShiftDiff = ConstantInt::get(Ty, ShAmt - ShrAmt);
if (match(Op0, m_OneUse(m_Shr(m_Value(X), m_APInt(C1)))) &&
C1->ult(BitWidth)) {
unsigned ShrAmt = C1->getZExtValue();
if (ShrAmt < ShAmtC) {
// If C1 < C: (X >>? C1) << C --> (X << (C - C1)) & (-1 << C)
Constant *ShiftDiff = ConstantInt::get(Ty, ShAmtC - ShrAmt);
auto *NewShl = BinaryOperator::CreateShl(X, ShiftDiff);
NewShl->setHasNoUnsignedWrap(I.hasNoUnsignedWrap());
NewShl->setHasNoSignedWrap(I.hasNoSignedWrap());
Builder.Insert(NewShl);
APInt Mask(APInt::getHighBitsSet(BitWidth, BitWidth - ShAmt));
APInt Mask(APInt::getHighBitsSet(BitWidth, BitWidth - ShAmtC));
return BinaryOperator::CreateAnd(NewShl, ConstantInt::get(Ty, Mask));
}
if (ShrAmt > ShAmt) {
// If C1 > C2: (X >>? C1) << C2 --> X >>? (C1 - C2) & (-1 << C2)
Constant *ShiftDiff = ConstantInt::get(Ty, ShrAmt - ShAmt);
if (ShrAmt > ShAmtC) {
// If C1 > C: (X >>? C1) << C --> (X >>? (C1 - C)) & (-1 << C)
Constant *ShiftDiff = ConstantInt::get(Ty, ShrAmt - ShAmtC);
auto *OldShr = cast<BinaryOperator>(Op0);
auto *NewShr =
BinaryOperator::Create(OldShr->getOpcode(), X, ShiftDiff);
NewShr->setIsExact(OldShr->isExact());
Builder.Insert(NewShr);
APInt Mask(APInt::getHighBitsSet(BitWidth, BitWidth - ShAmt));
APInt Mask(APInt::getHighBitsSet(BitWidth, BitWidth - ShAmtC));
return BinaryOperator::CreateAnd(NewShr, ConstantInt::get(Ty, Mask));
}
}
if (match(Op0, m_Shl(m_Value(X), m_APInt(ShOp1))) && ShOp1->ult(BitWidth)) {
unsigned AmtSum = ShAmt + ShOp1->getZExtValue();
if (match(Op0, m_Shl(m_Value(X), m_APInt(C1))) && C1->ult(BitWidth)) {
unsigned AmtSum = ShAmtC + C1->getZExtValue();
// Oversized shifts are simplified to zero in InstSimplify.
if (AmtSum < BitWidth)
// (X << C1) << C2 --> X << (C1 + C2)
@ -980,13 +980,14 @@ Instruction *InstCombinerImpl::visitShl(BinaryOperator &I) {
// If the shifted-out value is known-zero, then this is a NUW shift.
if (!I.hasNoUnsignedWrap() &&
MaskedValueIsZero(Op0, APInt::getHighBitsSet(BitWidth, ShAmt), 0, &I)) {
MaskedValueIsZero(Op0, APInt::getHighBitsSet(BitWidth, ShAmtC), 0,
&I)) {
I.setHasNoUnsignedWrap();
return &I;
}
// If the shifted-out value is all signbits, then this is a NSW shift.
if (!I.hasNoSignedWrap() && ComputeNumSignBits(Op0, 0, &I) > ShAmt) {
if (!I.hasNoSignedWrap() && ComputeNumSignBits(Op0, 0, &I) > ShAmtC) {
I.setHasNoSignedWrap();
return &I;
}