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llvm-project/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp

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//===- InstCombineShifts.cpp ----------------------------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the visitShl, visitLShr, and visitAShr functions.
//
//===----------------------------------------------------------------------===//
#include "InstCombineInternal.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/PatternMatch.h"
using namespace llvm;
using namespace PatternMatch;
#define DEBUG_TYPE "instcombine"
Instruction *InstCombiner::commonShiftTransforms(BinaryOperator &I) {
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
assert(Op0->getType() == Op1->getType());
// See if we can fold away this shift.
if (SimplifyDemandedInstructionBits(I))
return &I;
// Try to fold constant and into select arguments.
if (isa<Constant>(Op0))
if (SelectInst *SI = dyn_cast<SelectInst>(Op1))
if (Instruction *R = FoldOpIntoSelect(I, SI))
return R;
if (Constant *CUI = dyn_cast<Constant>(Op1))
if (Instruction *Res = FoldShiftByConstant(Op0, CUI, I))
return Res;
// (C1 shift (A add C2)) -> (C1 shift C2) shift A)
// iff A and C2 are both positive.
Value *A;
Constant *C;
if (match(Op0, m_Constant()) && match(Op1, m_Add(m_Value(A), m_Constant(C))))
if (isKnownNonNegative(A, DL) && isKnownNonNegative(C, DL))
return BinaryOperator::Create(
I.getOpcode(), Builder->CreateBinOp(I.getOpcode(), Op0, C), A);
// X shift (A srem B) -> X shift (A and B-1) iff B is a power of 2.
// Because shifts by negative values (which could occur if A were negative)
// are undefined.
const APInt *B;
if (Op1->hasOneUse() && match(Op1, m_SRem(m_Value(A), m_Power2(B)))) {
// FIXME: Should this get moved into SimplifyDemandedBits by saying we don't
// demand the sign bit (and many others) here??
Value *Rem = Builder->CreateAnd(A, ConstantInt::get(I.getType(), *B-1),
Op1->getName());
I.setOperand(1, Rem);
return &I;
}
return nullptr;
}
/// Return true if we can simplify two logical (either left or right) shifts
/// that have constant shift amounts: OuterShift (InnerShift X, C1), C2.
static bool canEvaluateShiftedShift(unsigned OuterShAmt, bool IsOuterShl,
Instruction *InnerShift, InstCombiner &IC,
Instruction *CxtI) {
assert(InnerShift->isLogicalShift() && "Unexpected instruction type");
// We need constant scalar or constant splat shifts.
const APInt *InnerShiftConst;
if (!match(InnerShift->getOperand(1), m_APInt(InnerShiftConst)))
return false;
// Two logical shifts in the same direction:
// shl (shl X, C1), C2 --> shl X, C1 + C2
// lshr (lshr X, C1), C2 --> lshr X, C1 + C2
bool IsInnerShl = InnerShift->getOpcode() == Instruction::Shl;
if (IsInnerShl == IsOuterShl)
return true;
// Equal shift amounts in opposite directions become bitwise 'and':
// lshr (shl X, C), C --> and X, C'
// shl (lshr X, C), C --> and X, C'
unsigned InnerShAmt = InnerShiftConst->getZExtValue();
if (InnerShAmt == OuterShAmt)
return true;
// If the 2nd shift is bigger than the 1st, we can fold:
// lshr (shl X, C1), C2 --> and (shl X, C1 - C2), C3
// shl (lshr X, C1), C2 --> and (lshr X, C1 - C2), C3
// but it isn't profitable unless we know the and'd out bits are already zero.
// Also, check that the inner shift is valid (less than the type width) or
// we'll crash trying to produce the bit mask for the 'and'.
unsigned TypeWidth = InnerShift->getType()->getScalarSizeInBits();
if (InnerShAmt > OuterShAmt && InnerShAmt < TypeWidth) {
unsigned MaskShift =
IsInnerShl ? TypeWidth - InnerShAmt : InnerShAmt - OuterShAmt;
APInt Mask = APInt::getLowBitsSet(TypeWidth, OuterShAmt) << MaskShift;
if (IC.MaskedValueIsZero(InnerShift->getOperand(0), Mask, 0, CxtI))
return true;
}
return false;
}
/// See if we can compute the specified value, but shifted logically to the left
/// or right by some number of bits. This should return true if the expression
/// can be computed for the same cost as the current expression tree. This is
/// used to eliminate extraneous shifting from things like:
/// %C = shl i128 %A, 64
/// %D = shl i128 %B, 96
/// %E = or i128 %C, %D
/// %F = lshr i128 %E, 64
/// where the client will ask if E can be computed shifted right by 64-bits. If
/// this succeeds, getShiftedValue() will be called to produce the value.
static bool canEvaluateShifted(Value *V, unsigned NumBits, bool IsLeftShift,
InstCombiner &IC, Instruction *CxtI) {
// We can always evaluate constants shifted.
if (isa<Constant>(V))
return true;
Instruction *I = dyn_cast<Instruction>(V);
if (!I) return false;
// If this is the opposite shift, we can directly reuse the input of the shift
// if the needed bits are already zero in the input. This allows us to reuse
// the value which means that we don't care if the shift has multiple uses.
// TODO: Handle opposite shift by exact value.
ConstantInt *CI = nullptr;
if ((IsLeftShift && match(I, m_LShr(m_Value(), m_ConstantInt(CI)))) ||
(!IsLeftShift && match(I, m_Shl(m_Value(), m_ConstantInt(CI))))) {
if (CI->getZExtValue() == NumBits) {
// TODO: Check that the input bits are already zero with MaskedValueIsZero
#if 0
// If this is a truncate of a logical shr, we can truncate it to a smaller
// lshr iff we know that the bits we would otherwise be shifting in are
// already zeros.
uint32_t OrigBitWidth = OrigTy->getScalarSizeInBits();
uint32_t BitWidth = Ty->getScalarSizeInBits();
if (MaskedValueIsZero(I->getOperand(0),
APInt::getHighBitsSet(OrigBitWidth, OrigBitWidth-BitWidth)) &&
CI->getLimitedValue(BitWidth) < BitWidth) {
return CanEvaluateTruncated(I->getOperand(0), Ty);
}
#endif
}
}
// We can't mutate something that has multiple uses: doing so would
// require duplicating the instruction in general, which isn't profitable.
if (!I->hasOneUse()) return false;
switch (I->getOpcode()) {
default: return false;
case Instruction::And:
case Instruction::Or:
case Instruction::Xor:
// Bitwise operators can all arbitrarily be arbitrarily evaluated shifted.
return canEvaluateShifted(I->getOperand(0), NumBits, IsLeftShift, IC, I) &&
canEvaluateShifted(I->getOperand(1), NumBits, IsLeftShift, IC, I);
case Instruction::Shl:
case Instruction::LShr:
return canEvaluateShiftedShift(NumBits, IsLeftShift, I, IC, CxtI);
case Instruction::Select: {
SelectInst *SI = cast<SelectInst>(I);
Value *TrueVal = SI->getTrueValue();
Value *FalseVal = SI->getFalseValue();
return canEvaluateShifted(TrueVal, NumBits, IsLeftShift, IC, SI) &&
canEvaluateShifted(FalseVal, NumBits, IsLeftShift, IC, SI);
}
case Instruction::PHI: {
// We can change a phi if we can change all operands. Note that we never
// get into trouble with cyclic PHIs here because we only consider
// instructions with a single use.
PHINode *PN = cast<PHINode>(I);
for (Value *IncValue : PN->incoming_values())
if (!canEvaluateShifted(IncValue, NumBits, IsLeftShift, IC, PN))
return false;
return true;
}
}
}
/// Fold OuterShift (InnerShift X, C1), C2.
/// See canEvaluateShiftedShift() for the constraints on these instructions.
static Value *foldShiftedShift(BinaryOperator *InnerShift, unsigned OuterShAmt,
bool IsOuterShl,
InstCombiner::BuilderTy &Builder) {
bool IsInnerShl = InnerShift->getOpcode() == Instruction::Shl;
Type *ShType = InnerShift->getType();
unsigned TypeWidth = ShType->getScalarSizeInBits();
// We only accept shifts-by-a-constant in canEvaluateShifted().
const APInt *C1;
match(InnerShift->getOperand(1), m_APInt(C1));
unsigned InnerShAmt = C1->getZExtValue();
// Change the shift amount and clear the appropriate IR flags.
auto NewInnerShift = [&](unsigned ShAmt) {
InnerShift->setOperand(1, ConstantInt::get(ShType, ShAmt));
if (IsInnerShl) {
InnerShift->setHasNoUnsignedWrap(false);
InnerShift->setHasNoSignedWrap(false);
} else {
InnerShift->setIsExact(false);
}
return InnerShift;
};
// Two logical shifts in the same direction:
// shl (shl X, C1), C2 --> shl X, C1 + C2
// lshr (lshr X, C1), C2 --> lshr X, C1 + C2
if (IsInnerShl == IsOuterShl) {
// If this is an oversized composite shift, then unsigned shifts get 0.
if (InnerShAmt + OuterShAmt >= TypeWidth)
return Constant::getNullValue(ShType);
return NewInnerShift(InnerShAmt + OuterShAmt);
}
// Equal shift amounts in opposite directions become bitwise 'and':
// lshr (shl X, C), C --> and X, C'
// shl (lshr X, C), C --> and X, C'
if (InnerShAmt == OuterShAmt) {
APInt Mask = IsInnerShl
? APInt::getLowBitsSet(TypeWidth, TypeWidth - OuterShAmt)
: APInt::getHighBitsSet(TypeWidth, TypeWidth - OuterShAmt);
Value *And = Builder.CreateAnd(InnerShift->getOperand(0),
ConstantInt::get(ShType, Mask));
if (auto *AndI = dyn_cast<Instruction>(And)) {
AndI->moveBefore(InnerShift);
AndI->takeName(InnerShift);
}
return And;
}
assert(InnerShAmt > OuterShAmt &&
"Unexpected opposite direction logical shift pair");
// In general, we would need an 'and' for this transform, but
// canEvaluateShiftedShift() guarantees that the masked-off bits are not used.
// lshr (shl X, C1), C2 --> shl X, C1 - C2
// shl (lshr X, C1), C2 --> lshr X, C1 - C2
return NewInnerShift(InnerShAmt - OuterShAmt);
}
/// When canEvaluateShifted() returns true for an expression, this function
/// inserts the new computation that produces the shifted value.
static Value *getShiftedValue(Value *V, unsigned NumBits, bool isLeftShift,
InstCombiner &IC, const DataLayout &DL) {
// We can always evaluate constants shifted.
if (Constant *C = dyn_cast<Constant>(V)) {
if (isLeftShift)
V = IC.Builder->CreateShl(C, NumBits);
else
V = IC.Builder->CreateLShr(C, NumBits);
// If we got a constantexpr back, try to simplify it with TD info.
if (auto *C = dyn_cast<Constant>(V))
if (auto *FoldedC =
ConstantFoldConstant(C, DL, &IC.getTargetLibraryInfo()))
V = FoldedC;
return V;
}
Instruction *I = cast<Instruction>(V);
IC.Worklist.Add(I);
switch (I->getOpcode()) {
default: llvm_unreachable("Inconsistency with CanEvaluateShifted");
case Instruction::And:
case Instruction::Or:
case Instruction::Xor:
// Bitwise operators can all arbitrarily be arbitrarily evaluated shifted.
I->setOperand(
0, getShiftedValue(I->getOperand(0), NumBits, isLeftShift, IC, DL));
I->setOperand(
1, getShiftedValue(I->getOperand(1), NumBits, isLeftShift, IC, DL));
return I;
case Instruction::Shl:
case Instruction::LShr:
return foldShiftedShift(cast<BinaryOperator>(I), NumBits, isLeftShift,
*(IC.Builder));
case Instruction::Select:
I->setOperand(
1, getShiftedValue(I->getOperand(1), NumBits, isLeftShift, IC, DL));
I->setOperand(
2, getShiftedValue(I->getOperand(2), NumBits, isLeftShift, IC, DL));
return I;
case Instruction::PHI: {
// We can change a phi if we can change all operands. Note that we never
// get into trouble with cyclic PHIs here because we only consider
// instructions with a single use.
PHINode *PN = cast<PHINode>(I);
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
PN->setIncomingValue(i, getShiftedValue(PN->getIncomingValue(i), NumBits,
isLeftShift, IC, DL));
return PN;
}
}
}
Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, Constant *Op1,
BinaryOperator &I) {
bool isLeftShift = I.getOpcode() == Instruction::Shl;
const APInt *Op1C;
if (!match(Op1, m_APInt(Op1C)))
return nullptr;
// See if we can propagate this shift into the input, this covers the trivial
// cast of lshr(shl(x,c1),c2) as well as other more complex cases.
if (I.getOpcode() != Instruction::AShr &&
canEvaluateShifted(Op0, Op1C->getZExtValue(), isLeftShift, *this, &I)) {
DEBUG(dbgs() << "ICE: GetShiftedValue propagating shift through expression"
" to eliminate shift:\n IN: " << *Op0 << "\n SH: " << I <<"\n");
return replaceInstUsesWith(
I, getShiftedValue(Op0, Op1C->getZExtValue(), isLeftShift, *this, DL));
}
// See if we can simplify any instructions used by the instruction whose sole
// purpose is to compute bits we don't care about.
unsigned TypeBits = Op0->getType()->getScalarSizeInBits();
assert(!Op1C->uge(TypeBits) &&
"Shift over the type width should have been removed already");
if (Instruction *FoldedShift = foldOpWithConstantIntoOperand(I))
return FoldedShift;
// Fold shift2(trunc(shift1(x,c1)), c2) -> trunc(shift2(shift1(x,c1),c2))
if (TruncInst *TI = dyn_cast<TruncInst>(Op0)) {
Instruction *TrOp = dyn_cast<Instruction>(TI->getOperand(0));
// If 'shift2' is an ashr, we would have to get the sign bit into a funny
// place. Don't try to do this transformation in this case. Also, we
// require that the input operand is a shift-by-constant so that we have
// confidence that the shifts will get folded together. We could do this
// xform in more cases, but it is unlikely to be profitable.
if (TrOp && I.isLogicalShift() && TrOp->isShift() &&
isa<ConstantInt>(TrOp->getOperand(1))) {
// Okay, we'll do this xform. Make the shift of shift.
Constant *ShAmt =
ConstantExpr::getZExt(cast<Constant>(Op1), TrOp->getType());
// (shift2 (shift1 & 0x00FF), c2)
Value *NSh = Builder->CreateBinOp(I.getOpcode(), TrOp, ShAmt,I.getName());
// For logical shifts, the truncation has the effect of making the high
// part of the register be zeros. Emulate this by inserting an AND to
// clear the top bits as needed. This 'and' will usually be zapped by
// other xforms later if dead.
unsigned SrcSize = TrOp->getType()->getScalarSizeInBits();
unsigned DstSize = TI->getType()->getScalarSizeInBits();
APInt MaskV(APInt::getLowBitsSet(SrcSize, DstSize));
// The mask we constructed says what the trunc would do if occurring
// between the shifts. We want to know the effect *after* the second
// shift. We know that it is a logical shift by a constant, so adjust the
// mask as appropriate.
if (I.getOpcode() == Instruction::Shl)
MaskV <<= Op1C->getZExtValue();
else {
assert(I.getOpcode() == Instruction::LShr && "Unknown logical shift");
MaskV = MaskV.lshr(Op1C->getZExtValue());
}
// shift1 & 0x00FF
Value *And = Builder->CreateAnd(NSh,
ConstantInt::get(I.getContext(), MaskV),
TI->getName());
// Return the value truncated to the interesting size.
return new TruncInst(And, I.getType());
}
}
if (Op0->hasOneUse()) {
if (BinaryOperator *Op0BO = dyn_cast<BinaryOperator>(Op0)) {
// Turn ((X >> C) + Y) << C -> (X + (Y << C)) & (~0 << C)
Value *V1, *V2;
ConstantInt *CC;
switch (Op0BO->getOpcode()) {
default: break;
case Instruction::Add:
case Instruction::And:
case Instruction::Or:
case Instruction::Xor: {
// These operators commute.
// Turn (Y + (X >> C)) << C -> (X + (Y << C)) & (~0 << C)
if (isLeftShift && Op0BO->getOperand(1)->hasOneUse() &&
match(Op0BO->getOperand(1), m_Shr(m_Value(V1),
m_Specific(Op1)))) {
Value *YS = // (Y << C)
Builder->CreateShl(Op0BO->getOperand(0), Op1, Op0BO->getName());
// (X + (Y << C))
Value *X = Builder->CreateBinOp(Op0BO->getOpcode(), YS, V1,
Op0BO->getOperand(1)->getName());
unsigned Op1Val = Op1C->getLimitedValue(TypeBits);
APInt Bits = APInt::getHighBitsSet(TypeBits, TypeBits - Op1Val);
Constant *Mask = ConstantInt::get(I.getContext(), Bits);
if (VectorType *VT = dyn_cast<VectorType>(X->getType()))
Mask = ConstantVector::getSplat(VT->getNumElements(), Mask);
return BinaryOperator::CreateAnd(X, Mask);
}
// Turn (Y + ((X >> C) & CC)) << C -> ((X & (CC << C)) + (Y << C))
Value *Op0BOOp1 = Op0BO->getOperand(1);
if (isLeftShift && Op0BOOp1->hasOneUse() &&
match(Op0BOOp1,
m_And(m_OneUse(m_Shr(m_Value(V1), m_Specific(Op1))),
m_ConstantInt(CC)))) {
Value *YS = // (Y << C)
Builder->CreateShl(Op0BO->getOperand(0), Op1,
Op0BO->getName());
// X & (CC << C)
Value *XM = Builder->CreateAnd(V1, ConstantExpr::getShl(CC, Op1),
V1->getName()+".mask");
return BinaryOperator::Create(Op0BO->getOpcode(), YS, XM);
}
LLVM_FALLTHROUGH;
}
case Instruction::Sub: {
// Turn ((X >> C) + Y) << C -> (X + (Y << C)) & (~0 << C)
if (isLeftShift && Op0BO->getOperand(0)->hasOneUse() &&
match(Op0BO->getOperand(0), m_Shr(m_Value(V1),
m_Specific(Op1)))) {
Value *YS = // (Y << C)
Builder->CreateShl(Op0BO->getOperand(1), Op1, Op0BO->getName());
// (X + (Y << C))
Value *X = Builder->CreateBinOp(Op0BO->getOpcode(), V1, YS,
Op0BO->getOperand(0)->getName());
unsigned Op1Val = Op1C->getLimitedValue(TypeBits);
APInt Bits = APInt::getHighBitsSet(TypeBits, TypeBits - Op1Val);
Constant *Mask = ConstantInt::get(I.getContext(), Bits);
if (VectorType *VT = dyn_cast<VectorType>(X->getType()))
Mask = ConstantVector::getSplat(VT->getNumElements(), Mask);
return BinaryOperator::CreateAnd(X, Mask);
}
// Turn (((X >> C)&CC) + Y) << C -> (X + (Y << C)) & (CC << C)
if (isLeftShift && Op0BO->getOperand(0)->hasOneUse() &&
match(Op0BO->getOperand(0),
m_And(m_OneUse(m_Shr(m_Value(V1), m_Value(V2))),
m_ConstantInt(CC))) && V2 == Op1) {
Value *YS = // (Y << C)
Builder->CreateShl(Op0BO->getOperand(1), Op1, Op0BO->getName());
// X & (CC << C)
Value *XM = Builder->CreateAnd(V1, ConstantExpr::getShl(CC, Op1),
V1->getName()+".mask");
return BinaryOperator::Create(Op0BO->getOpcode(), XM, YS);
}
break;
}
}
// If the operand is a bitwise operator with a constant RHS, and the
// shift is the only use, we can pull it out of the shift.
if (ConstantInt *Op0C = dyn_cast<ConstantInt>(Op0BO->getOperand(1))) {
bool isValid = true; // Valid only for And, Or, Xor
bool highBitSet = false; // Transform if high bit of constant set?
switch (Op0BO->getOpcode()) {
default: isValid = false; break; // Do not perform transform!
case Instruction::Add:
isValid = isLeftShift;
break;
case Instruction::Or:
case Instruction::Xor:
highBitSet = false;
break;
case Instruction::And:
highBitSet = true;
break;
}
// If this is a signed shift right, and the high bit is modified
// by the logical operation, do not perform the transformation.
// The highBitSet boolean indicates the value of the high bit of
// the constant which would cause it to be modified for this
// operation.
//
if (isValid && I.getOpcode() == Instruction::AShr)
isValid = Op0C->getValue()[TypeBits-1] == highBitSet;
if (isValid) {
Constant *NewRHS = ConstantExpr::get(I.getOpcode(), Op0C, Op1);
Value *NewShift =
Builder->CreateBinOp(I.getOpcode(), Op0BO->getOperand(0), Op1);
NewShift->takeName(Op0BO);
return BinaryOperator::Create(Op0BO->getOpcode(), NewShift,
NewRHS);
}
}
}
}
return nullptr;
}
Instruction *InstCombiner::visitShl(BinaryOperator &I) {
if (Value *V = SimplifyVectorOp(I))
return replaceInstUsesWith(I, V);
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
if (Value *V = SimplifyShlInst(Op0, Op1, I.hasNoSignedWrap(),
I.hasNoUnsignedWrap(), DL, &TLI, &DT, &AC))
return replaceInstUsesWith(I, V);
if (Instruction *V = commonShiftTransforms(I))
return V;
const APInt *ShAmtAPInt;
if (match(Op1, m_APInt(ShAmtAPInt))) {
unsigned ShAmt = ShAmtAPInt->getZExtValue();
unsigned BitWidth = I.getType()->getScalarSizeInBits();
Type *Ty = I.getType();
// shl (zext X), ShAmt --> zext (shl X, ShAmt)
// This is only valid if X would have zeros shifted out.
Value *X;
if (match(Op0, 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);
}
// (X >>u C) << C --> X & (-1 << C)
if (match(Op0, m_LShr(m_Value(X), m_Specific(Op1)))) {
APInt Mask(APInt::getHighBitsSet(BitWidth, BitWidth - ShAmt));
return BinaryOperator::CreateAnd(X, ConstantInt::get(Ty, Mask));
}
// Be careful about hiding shl instructions behind bit masks. They are used
// to represent multiplies by a constant, and it is important that simple
// arithmetic expressions are still recognizable by scalar evolution.
// The inexact versions are deferred to DAGCombine, so we don't hide shl
// behind a bit mask.
const APInt *ShOp1;
if (match(Op0, m_CombineOr(m_Exact(m_LShr(m_Value(X), m_APInt(ShOp1))),
m_Exact(m_AShr(m_Value(X), m_APInt(ShOp1)))))) {
unsigned ShrAmt = ShOp1->getZExtValue();
if (ShrAmt < ShAmt) {
// If C1 < C2: (X >>?,exact C1) << C2 --> X << (C2 - C1)
Constant *ShiftDiff = ConstantInt::get(Ty, ShAmt - 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);
auto *NewShr = BinaryOperator::Create(
cast<BinaryOperator>(Op0)->getOpcode(), X, ShiftDiff);
NewShr->setIsExact(true);
return NewShr;
}
}
if (match(Op0, m_Shl(m_Value(X), m_APInt(ShOp1)))) {
unsigned AmtSum = ShAmt + ShOp1->getZExtValue();
// Oversized shifts are simplified to zero in InstSimplify.
if (AmtSum < BitWidth)
// (X << C1) << C2 --> X << (C1 + C2)
return BinaryOperator::CreateShl(X, ConstantInt::get(Ty, AmtSum));
}
// 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)) {
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) {
I.setHasNoSignedWrap();
return &I;
}
}
Constant *C1;
if (match(Op1, m_Constant(C1))) {
Constant *C2;
Value *X;
// (C2 << X) << C1 --> (C2 << C1) << X
if (match(Op0, m_OneUse(m_Shl(m_Constant(C2), m_Value(X)))))
return BinaryOperator::CreateShl(ConstantExpr::getShl(C2, C1), X);
// (X * C2) << C1 --> X * (C2 << C1)
if (match(Op0, m_Mul(m_Value(X), m_Constant(C2))))
return BinaryOperator::CreateMul(X, ConstantExpr::getShl(C2, C1));
}
return nullptr;
}
Instruction *InstCombiner::visitLShr(BinaryOperator &I) {
if (Value *V = SimplifyVectorOp(I))
return replaceInstUsesWith(I, V);
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
if (Value *V = SimplifyLShrInst(Op0, Op1, I.isExact(), DL, &TLI, &DT, &AC))
return replaceInstUsesWith(I, V);
if (Instruction *R = commonShiftTransforms(I))
return R;
Type *Ty = I.getType();
const APInt *ShAmtAPInt;
if (match(Op1, m_APInt(ShAmtAPInt))) {
unsigned ShAmt = ShAmtAPInt->getZExtValue();
unsigned BitWidth = Ty->getScalarSizeInBits();
auto *II = dyn_cast<IntrinsicInst>(Op0);
if (II && isPowerOf2_32(BitWidth) && Log2_32(BitWidth) == ShAmt &&
(II->getIntrinsicID() == Intrinsic::ctlz ||
II->getIntrinsicID() == Intrinsic::cttz ||
II->getIntrinsicID() == Intrinsic::ctpop)) {
// ctlz.i32(x)>>5 --> zext(x == 0)
// cttz.i32(x)>>5 --> zext(x == 0)
// ctpop.i32(x)>>5 --> zext(x == -1)
bool IsPop = II->getIntrinsicID() == Intrinsic::ctpop;
Constant *RHS = ConstantInt::getSigned(Ty, IsPop ? -1 : 0);
Value *Cmp = Builder->CreateICmpEQ(II->getArgOperand(0), RHS);
return new ZExtInst(Cmp, Ty);
}
Value *X;
const APInt *ShOp1;
if (match(Op0, m_Shl(m_Value(X), m_APInt(ShOp1)))) {
unsigned ShlAmt = ShOp1->getZExtValue();
if (ShlAmt < ShAmt) {
Constant *ShiftDiff = ConstantInt::get(Ty, ShAmt - ShlAmt);
if (cast<BinaryOperator>(Op0)->hasNoUnsignedWrap()) {
// (X <<nuw C1) >>u C2 --> X >>u (C2 - C1)
auto *NewLShr = BinaryOperator::CreateLShr(X, ShiftDiff);
NewLShr->setIsExact(I.isExact());
return NewLShr;
}
// (X << C1) >>u C2 --> (X >>u (C2 - C1)) & (-1 >> C2)
Value *NewLShr = Builder->CreateLShr(X, ShiftDiff, "", I.isExact());
APInt Mask(APInt::getLowBitsSet(BitWidth, BitWidth - ShAmt));
return BinaryOperator::CreateAnd(NewLShr, ConstantInt::get(Ty, Mask));
}
if (ShlAmt > ShAmt) {
Constant *ShiftDiff = ConstantInt::get(Ty, ShlAmt - ShAmt);
if (cast<BinaryOperator>(Op0)->hasNoUnsignedWrap()) {
// (X <<nuw C1) >>u C2 --> X <<nuw (C1 - C2)
auto *NewShl = BinaryOperator::CreateShl(X, ShiftDiff);
NewShl->setHasNoUnsignedWrap(true);
return NewShl;
}
// (X << C1) >>u C2 --> X << (C1 - C2) & (-1 >> C2)
Value *NewShl = Builder->CreateShl(X, ShiftDiff);
APInt Mask(APInt::getLowBitsSet(BitWidth, BitWidth - ShAmt));
return BinaryOperator::CreateAnd(NewShl, ConstantInt::get(Ty, Mask));
}
assert(ShlAmt == ShAmt);
// (X << C) >>u C --> X & (-1 >>u C)
APInt Mask(APInt::getLowBitsSet(BitWidth, BitWidth - ShAmt));
return BinaryOperator::CreateAnd(X, ConstantInt::get(Ty, Mask));
}
if (match(Op0, m_LShr(m_Value(X), m_APInt(ShOp1)))) {
unsigned AmtSum = ShAmt + ShOp1->getZExtValue();
// Oversized shifts are simplified to zero in InstSimplify.
if (AmtSum < BitWidth)
// (X >>u C1) >>u C2 --> X >>u (C1 + C2)
return BinaryOperator::CreateLShr(X, ConstantInt::get(Ty, AmtSum));
}
// If the shifted-out value is known-zero, then this is an exact shift.
if (!I.isExact() &&
MaskedValueIsZero(Op0, APInt::getLowBitsSet(BitWidth, ShAmt), 0, &I)) {
I.setIsExact();
return &I;
}
}
return nullptr;
}
Instruction *InstCombiner::visitAShr(BinaryOperator &I) {
if (Value *V = SimplifyVectorOp(I))
return replaceInstUsesWith(I, V);
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
if (Value *V = SimplifyAShrInst(Op0, Op1, I.isExact(), DL, &TLI, &DT, &AC))
return replaceInstUsesWith(I, V);
if (Instruction *R = commonShiftTransforms(I))
return R;
Type *Ty = I.getType();
unsigned BitWidth = Ty->getScalarSizeInBits();
const APInt *ShAmtAPInt;
if (match(Op1, m_APInt(ShAmtAPInt))) {
unsigned ShAmt = ShAmtAPInt->getZExtValue();
// If the shift amount equals the difference in width of the destination
// and source scalar types:
// ashr (shl (zext X), C), C --> sext X
Value *X;
if (match(Op0, m_Shl(m_ZExt(m_Value(X)), m_Specific(Op1))) &&
ShAmt == BitWidth - X->getType()->getScalarSizeInBits())
return new SExtInst(X, Ty);
// We can't handle (X << C1) >>s C2. It shifts arbitrary bits in. However,
// we can handle (X <<nsw C1) >>s C2 since it only shifts in sign bits.
const APInt *ShOp1;
if (match(Op0, m_NSWShl(m_Value(X), m_APInt(ShOp1)))) {
unsigned ShlAmt = ShOp1->getZExtValue();
if (ShlAmt < ShAmt) {
// (X <<nsw C1) >>s C2 --> X >>s (C2 - C1)
Constant *ShiftDiff = ConstantInt::get(Ty, ShAmt - ShlAmt);
auto *NewAShr = BinaryOperator::CreateAShr(X, ShiftDiff);
NewAShr->setIsExact(I.isExact());
return NewAShr;
}
if (ShlAmt > ShAmt) {
// (X <<nsw C1) >>s C2 --> X <<nsw (C1 - C2)
Constant *ShiftDiff = ConstantInt::get(Ty, ShlAmt - ShAmt);
auto *NewShl = BinaryOperator::Create(Instruction::Shl, X, ShiftDiff);
NewShl->setHasNoSignedWrap(true);
return NewShl;
}
}
if (match(Op0, m_AShr(m_Value(X), m_APInt(ShOp1)))) {
unsigned AmtSum = ShAmt + ShOp1->getZExtValue();
// Oversized arithmetic shifts replicate the sign bit.
AmtSum = std::min(AmtSum, BitWidth - 1);
// (X >>s C1) >>s C2 --> X >>s (C1 + C2)
return BinaryOperator::CreateAShr(X, ConstantInt::get(Ty, AmtSum));
}
// If the shifted-out value is known-zero, then this is an exact shift.
if (!I.isExact() &&
MaskedValueIsZero(Op0, APInt::getLowBitsSet(BitWidth, ShAmt), 0, &I)) {
I.setIsExact();
return &I;
}
}
// See if we can turn a signed shr into an unsigned shr.
if (MaskedValueIsZero(Op0, APInt::getSignBit(BitWidth), 0, &I))
return BinaryOperator::CreateLShr(Op0, Op1);
return nullptr;
}
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