IGCInstCombiner/7.0/InstCombineShifts.cpp

/*========================== begin_copyright_notice ============================

Copyright (C) 2018-2021 Intel Corporation

SPDX-License-Identifier: MIT

============================= end_copyright_notice ===========================*/

/*========================== begin_copyright_notice ============================

This file is distributed under the University of Illinois Open Source License.
See LICENSE.TXT for details.

============================= end_copyright_notice ===========================*/

// This file implements the visitShl, visitLShr, and visitAShr functions.

#include "common/LLVMWarningsPush.hpp"
#include "InstCombineInternal.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/PatternMatch.h"
#include "Probe/Assertion.h"

using namespace llvm;
using namespace PatternMatch;
using namespace IGCombiner;

#define DEBUG_TYPE "instcombine"

Instruction* InstCombiner::commonShiftTransforms(BinaryOperator& I) {
    Value* Op0 = I.getOperand(0), * Op1 = I.getOperand(1);
    IGC_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, 0, &AC, &I, &DT) &&
            isKnownNonNegative(C, DL, 0, &AC, &I, &DT))
            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) {
    IGC_ASSERT_MESSAGE(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'
    if (*InnerShiftConst == 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 (InnerShiftConst->ugt(OuterShAmt) && InnerShiftConst->ult(TypeWidth)) {
        unsigned InnerShAmt = InnerShiftConst->getZExtValue();
        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->getValue() == 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;
    }

    IGC_ASSERT_MESSAGE(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: IGC_ASSERT_EXIT_MESSAGE(0, "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;
    }
    }
}

// If this is a bitwise operator or add with a constant RHS we might be able
// to pull it through a shift.
static bool canShiftBinOpWithConstantRHS(BinaryOperator& Shift,
    BinaryOperator* BO,
    const APInt& C) {
    bool IsValid = true;     // Valid only for And, Or Xor,
    bool HighBitSet = false; // Transform ifhigh bit of constant set?

    switch (BO->getOpcode()) {
    default: IsValid = false; break;   // Do not perform transform!
    case Instruction::Add:
        IsValid = Shift.getOpcode() == Instruction::Shl;
        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 && Shift.getOpcode() == Instruction::AShr)
        IsValid = C.isNegative() == HighBitSet;

    return IsValid;
}

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)) {
        LLVM_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();

    IGC_ASSERT_MESSAGE(!Op1C->uge(TypeBits), "Shift over the type width should have been removed already");

    if (Instruction * FoldedShift = foldBinOpIntoSelectOrPhi(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 {
                IGC_ASSERT_MESSAGE(I.getOpcode() == Instruction::LShr, "Unknown logical shift");
                MaskV.lshrInPlace(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.
            const APInt* Op0C;
            if (match(Op0BO->getOperand(1), m_APInt(Op0C))) {
                if (canShiftBinOpWithConstantRHS(I, Op0BO, *Op0C)) {
                    Constant* NewRHS = ConstantExpr::get(I.getOpcode(),
                        cast<Constant>(Op0BO->getOperand(1)), Op1);

                    Value* NewShift =
                        Builder.CreateBinOp(I.getOpcode(), Op0BO->getOperand(0), Op1);
                    NewShift->takeName(Op0BO);

                    return BinaryOperator::Create(Op0BO->getOpcode(), NewShift,
                        NewRHS);
                }
            }

            // If the operand is a subtract with a constant LHS, and the shift
            // is the only use, we can pull it out of the shift.
            // This folds (shl (sub C1, X), C2) -> (sub (C1 << C2), (shl X, C2))
            if (isLeftShift && Op0BO->getOpcode() == Instruction::Sub &&
                match(Op0BO->getOperand(0), m_APInt(Op0C))) {
                Constant* NewRHS = ConstantExpr::get(I.getOpcode(),
                    cast<Constant>(Op0BO->getOperand(0)), Op1);

                Value* NewShift = Builder.CreateShl(Op0BO->getOperand(1), Op1);
                NewShift->takeName(Op0BO);

                return BinaryOperator::CreateSub(NewRHS, NewShift);
            }
        }

        // If we have a select that conditionally executes some binary operator,
        // see if we can pull it the select and operator through the shift.
        //
        // For example, turning:
        //   shl (select C, (add X, C1), X), C2
        // Into:
        //   Y = shl X, C2
        //   select C, (add Y, C1 << C2), Y
        Value* Cond;
        BinaryOperator* TBO;
        Value* FalseVal;
        if (match(Op0, m_Select(m_Value(Cond), m_OneUse(m_BinOp(TBO)),
            m_Value(FalseVal)))) {
            const APInt* C;
            if (!isa<Constant>(FalseVal) && TBO->getOperand(0) == FalseVal &&
                match(TBO->getOperand(1), m_APInt(C)) &&
                canShiftBinOpWithConstantRHS(I, TBO, *C)) {
                Constant* NewRHS = ConstantExpr::get(I.getOpcode(),
                    cast<Constant>(TBO->getOperand(1)), Op1);

                Value* NewShift =
                    Builder.CreateBinOp(I.getOpcode(), FalseVal, Op1);
                Value* NewOp = Builder.CreateBinOp(TBO->getOpcode(), NewShift,
                    NewRHS);
                return SelectInst::Create(Cond, NewOp, NewShift);
            }
        }

        BinaryOperator* FBO;
        Value* TrueVal;
        if (match(Op0, m_Select(m_Value(Cond), m_Value(TrueVal),
            m_OneUse(m_BinOp(FBO))))) {
            const APInt* C;
            if (!isa<Constant>(TrueVal) && FBO->getOperand(0) == TrueVal &&
                match(FBO->getOperand(1), m_APInt(C)) &&
                canShiftBinOpWithConstantRHS(I, FBO, *C)) {
                Constant* NewRHS = ConstantExpr::get(I.getOpcode(),
                    cast<Constant>(FBO->getOperand(1)), Op1);

                Value* NewShift =
                    Builder.CreateBinOp(I.getOpcode(), TrueVal, Op1);
                Value* NewOp = Builder.CreateBinOp(FBO->getOpcode(), NewShift,
                    NewRHS);
                return SelectInst::Create(Cond, NewShift, NewOp);
            }
        }
    }

    return nullptr;
}

Instruction* InstCombiner::visitShl(BinaryOperator& I) {
    if (Value * V = SimplifyShlInst(I.getOperand(0), I.getOperand(1),
        I.hasNoSignedWrap(), I.hasNoUnsignedWrap(),
        SQ.getWithInstruction(&I)))
        return replaceInstUsesWith(I, V);

    if (Instruction * X = foldShuffledBinop(I))
        return X;

    if (Instruction * V = commonShiftTransforms(I))
        return V;

    Value* Op0 = I.getOperand(0), * Op1 = I.getOperand(1);
    Type* Ty = I.getType();
    const APInt* ShAmtAPInt;
    if (match(Op1, m_APInt(ShAmtAPInt))) {
        unsigned ShAmt = ShAmtAPInt->getZExtValue();
        unsigned BitWidth = Ty->getScalarSizeInBits();

        // 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 >> C) << C --> X & (-1 << C)
        if (match(Op0, m_Shr(m_Value(X), m_Specific(Op1)))) {
            APInt Mask(APInt::getHighBitsSet(BitWidth, BitWidth - ShAmt));
            return BinaryOperator::CreateAnd(X, ConstantInt::get(Ty, Mask));
        }

        // FIXME: we do not yet transform non-exact shr's. The backend (DAGCombine)
        // needs a few fixes for the rotate pattern recognition first.
        const APInt* ShOp1;
        if (match(Op0, m_Exact(m_Shr(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;
        }
    }

    // Transform  (x >> y) << y  to  x & (-1 << y)
    // Valid for any type of right-shift.
    Value* X;
    if (match(Op0, m_OneUse(m_Shr(m_Value(X), m_Specific(Op1))))) {
        Constant* AllOnes = ConstantInt::getAllOnesValue(Ty);
        Value* Mask = Builder.CreateShl(AllOnes, Op1);
        return BinaryOperator::CreateAnd(Mask, X);
    }

    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 = SimplifyLShrInst(I.getOperand(0), I.getOperand(1), I.isExact(),
        SQ.getWithInstruction(&I)))
        return replaceInstUsesWith(I, V);

    if (Instruction * X = foldShuffledBinop(I))
        return X;

    if (Instruction * R = commonShiftTransforms(I))
        return R;

    Value* Op0 = I.getOperand(0), * Op1 = I.getOperand(1);
    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));
            }
            IGC_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_OneUse(m_ZExt(m_Value(X)))) &&
            (!Ty->isIntegerTy() || shouldChangeType(Ty, X->getType()))) {
            IGC_ASSERT_MESSAGE(ShAmt < X->getType()->getScalarSizeInBits(), "Big shift not simplified to zero?");
            // lshr (zext iM X to iN), C --> zext (lshr X, C) to iN
            Value* NewLShr = Builder.CreateLShr(X, ShAmt);
            return new ZExtInst(NewLShr, Ty);
        }

        if (match(Op0, m_SExt(m_Value(X))) &&
            (!Ty->isIntegerTy() || shouldChangeType(Ty, X->getType()))) {
            // Are we moving the sign bit to the low bit and widening with high zeros?
            unsigned SrcTyBitWidth = X->getType()->getScalarSizeInBits();
            if (ShAmt == BitWidth - 1) {
                // lshr (sext i1 X to iN), N-1 --> zext X to iN
                if (SrcTyBitWidth == 1)
                    return new ZExtInst(X, Ty);

                // lshr (sext iM X to iN), N-1 --> zext (lshr X, M-1) to iN
                if (Op0->hasOneUse()) {
                    Value* NewLShr = Builder.CreateLShr(X, SrcTyBitWidth - 1);
                    return new ZExtInst(NewLShr, Ty);
                }
            }

            // lshr (sext iM X to iN), N-M --> zext (ashr X, min(N-M, M-1)) to iN
            if (ShAmt == BitWidth - SrcTyBitWidth && Op0->hasOneUse()) {
                // The new shift amount can't be more than the narrow source type.
                unsigned NewShAmt = std::min(ShAmt, SrcTyBitWidth - 1);
                Value* AShr = Builder.CreateAShr(X, NewShAmt);
                return new ZExtInst(AShr, Ty);
            }
        }

        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;
        }
    }

    // Transform  (x << y) >> y  to  x & (-1 >> y)
    Value* X;
    if (match(Op0, m_OneUse(m_Shl(m_Value(X), m_Specific(Op1))))) {
        Constant* AllOnes = ConstantInt::getAllOnesValue(Ty);
        Value* Mask = Builder.CreateLShr(AllOnes, Op1);
        return BinaryOperator::CreateAnd(Mask, X);
    }

    return nullptr;
}

Instruction* InstCombiner::visitAShr(BinaryOperator& I) {
    if (Value * V = SimplifyAShrInst(I.getOperand(0), I.getOperand(1), I.isExact(),
        SQ.getWithInstruction(&I)))
        return replaceInstUsesWith(I, V);

    if (Instruction * X = foldShuffledBinop(I))
        return X;

    if (Instruction * R = commonShiftTransforms(I))
        return R;

    Value* Op0 = I.getOperand(0), * Op1 = I.getOperand(1);
    Type* Ty = I.getType();
    unsigned BitWidth = Ty->getScalarSizeInBits();
    const APInt* ShAmtAPInt;
    if (match(Op1, m_APInt(ShAmtAPInt)) && ShAmtAPInt->ult(BitWidth)) {
        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))) &&
            ShOp1->ult(BitWidth)) {
            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))) &&
            ShOp1->ult(BitWidth)) {
            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 (match(Op0, m_OneUse(m_SExt(m_Value(X)))) &&
            (Ty->isVectorTy() || shouldChangeType(Ty, X->getType()))) {
            // ashr (sext X), C --> sext (ashr X, C')
            Type* SrcTy = X->getType();
            ShAmt = std::min(ShAmt, SrcTy->getScalarSizeInBits() - 1);
            Value* NewSh = Builder.CreateAShr(X, ConstantInt::get(SrcTy, ShAmt));
            return new SExtInst(NewSh, Ty);
        }

        // 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::getSignMask(BitWidth), 0, &I))
        return BinaryOperator::CreateLShr(Op0, Op1);

    return nullptr;
}
#include "common/LLVMWarningsPop.hpp"