//===- 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) {

  assert(I.getOperand(1)->getType() == I.getOperand(0)->getType());

  Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);

  // 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;

  // 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.

  Value *A; const APInt *B;

  if (Op1->hasOneUse() && 
match(Op1, m_SRem(m_Value(A), m_Power2(B)))33.9k
) {

    // 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;

}

/// CanEvaluateShifted - 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, the GetShiftedValue function 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 false110
;

  // 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)))128k
) ||

      
(197k
!isLeftShift197k
 && 
match(I, m_Shl(m_Value(), m_ConstantInt(CI)))75.0k
)) {

    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 false132k
;

  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)168
;

  case Instruction::Shl: {

    // We can often fold the shift into shifts-by-a-constant.

    CI = dyn_cast<ConstantInt>(I->getOperand(1));

    if (!CI) 
return false8
;

    // We can always fold shl(c1)+shl(c2) -> shl(c1+c2).

    if (isLeftShift) 
return true0
;

    // We can always turn shl(c)+shr(c) -> and(c2).

    if (CI->getValue() == NumBits) 
return true0
;

    unsigned TypeWidth = I->getType()->getScalarSizeInBits();

    // We can turn shl(c1)+shr(c2) -> shl(c3)+and(c4), but it isn't

    // profitable unless we know the and'd out bits are already zero.

    if (CI->getZExtValue() > NumBits) {

      unsigned LowBits = TypeWidth - CI->getZExtValue();

      if (IC.MaskedValueIsZero(I->getOperand(0),

                       APInt::getLowBitsSet(TypeWidth, NumBits) << LowBits,

                       0, CxtI))

        return true;

    }

    return false;

  }

  case Instruction::LShr: {

    // We can often fold the shift into shifts-by-a-constant.

    CI = dyn_cast<ConstantInt>(I->getOperand(1));

    if (!CI) 
return false136
;

    // We can always fold lshr(c1)+lshr(c2) -> lshr(c1+c2).

    if (!isLeftShift) 
return true0
;

    // We can always turn lshr(c)+shl(c) -> and(c2).

    if (CI->getValue() == NumBits) return true;

    unsigned TypeWidth = I->getType()->getScalarSizeInBits();

    // We can always turn lshr(c1)+shl(c2) -> lshr(c3)+and(c4), but it isn't

    // profitable unless we know the and'd out bits are already zero.

    if (CI->getValue().ult(TypeWidth) && CI->getZExtValue() > NumBits) {

      unsigned LowBits = CI->getZExtValue() - NumBits;

      if (IC.MaskedValueIsZero(I->getOperand(0),

                          APInt::getLowBitsSet(TypeWidth, NumBits) << LowBits,

                          0, CxtI))

        return true;

    }

    return false;

  }

  case Instruction::Select: {

    SelectInst *SI = cast<SelectInst>(I);

    return CanEvaluateShifted(SI->getTrueValue(), NumBits, isLeftShift,

                              IC, SI) &&

           
CanEvaluateShifted(SI->getFalseValue(), NumBits, isLeftShift, IC, SI)112
;

  }

  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;

  }

  }

}

/// GetShiftedValue - When CanEvaluateShifted returned true for an expression,

/// this value 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 (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))

      V = ConstantFoldConstantExpression(CE, DL, IC.getTargetLibraryInfo());

    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: {

    BinaryOperator *BO = cast<BinaryOperator>(I);

    unsigned TypeWidth = BO->getType()->getScalarSizeInBits();

    // We only accept shifts-by-a-constant in CanEvaluateShifted.

    ConstantInt *CI = cast<ConstantInt>(BO->getOperand(1));

    // We can always fold shl(c1)+shl(c2) -> shl(c1+c2).

    if (isLeftShift) {

      // If this is oversized composite shift, then unsigned shifts get 0.

      unsigned NewShAmt = NumBits+CI->getZExtValue();

      if (NewShAmt >= TypeWidth)

        return Constant::getNullValue(I->getType());

      BO->setOperand(1, ConstantInt::get(BO->getType(), NewShAmt));

      BO->setHasNoUnsignedWrap(false);

      BO->setHasNoSignedWrap(false);

      return I;

    }

    // We turn shl(c)+lshr(c) -> and(c2) if the input doesn't already have

    // zeros.

    if (CI->getValue() == NumBits) {

      APInt Mask(APInt::getLowBitsSet(TypeWidth, TypeWidth - NumBits));

      V = IC.Builder->CreateAnd(BO->getOperand(0),

                                ConstantInt::get(BO->getContext(), Mask));

      if (Instruction *VI = dyn_cast<Instruction>(V)) {

        VI->moveBefore(BO);

        VI->takeName(BO);

      }

      return V;

    }

    // We turn shl(c1)+shr(c2) -> shl(c3)+and(c4), but only when we know that

    // the and won't be needed.

    assert(CI->getZExtValue() > NumBits);

    BO->setOperand(1, ConstantInt::get(BO->getType(),

                                       CI->getZExtValue() - NumBits));

    BO->setHasNoUnsignedWrap(false);

    BO->setHasNoSignedWrap(false);

    return BO;

  }

  case Instruction::LShr: {

    BinaryOperator *BO = cast<BinaryOperator>(I);

    unsigned TypeWidth = BO->getType()->getScalarSizeInBits();

    // We only accept shifts-by-a-constant in CanEvaluateShifted.

    ConstantInt *CI = cast<ConstantInt>(BO->getOperand(1));

    // We can always fold lshr(c1)+lshr(c2) -> lshr(c1+c2).

    if (!isLeftShift) {

      // If this is oversized composite shift, then unsigned shifts get 0.

      unsigned NewShAmt = NumBits+CI->getZExtValue();

      if (NewShAmt >= TypeWidth)

        return Constant::getNullValue(BO->getType());

      BO->setOperand(1, ConstantInt::get(BO->getType(), NewShAmt));

      BO->setIsExact(false);

      return I;

    }

    // We turn lshr(c)+shl(c) -> and(c2) if the input doesn't already have

    // zeros.

    if (CI->getValue() == NumBits) {

      APInt Mask(APInt::getHighBitsSet(TypeWidth, TypeWidth - NumBits));

      V = IC.Builder->CreateAnd(I->getOperand(0),

                                ConstantInt::get(BO->getContext(), Mask));

      if (Instruction *VI = dyn_cast<Instruction>(V)) {

        VI->moveBefore(I);

        VI->takeName(I);

      }

      return V;

    }

    // We turn lshr(c1)+shl(c2) -> lshr(c3)+and(c4), but only when we know that

    // the and won't be needed.

    assert(CI->getZExtValue() > NumBits);

    BO->setOperand(1, ConstantInt::get(BO->getType(),

                                       CI->getZExtValue() - NumBits));

    BO->setIsExact(false);

    return BO;

  }

  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;

  ConstantInt *COp1 = nullptr;

  if (ConstantDataVector *CV = dyn_cast<ConstantDataVector>(Op1))

    COp1 = dyn_cast_or_null<ConstantInt>(CV->getSplatValue());

  else if (ConstantVector *CV = dyn_cast<ConstantVector>(Op1))

    COp1 = dyn_cast_or_null<ConstantInt>(CV->getSplatValue());

  else

    COp1 = dyn_cast<ConstantInt>(Op1);

  if (!COp1)

    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, COp1->getZExtValue(), isLeftShift, *this, &I)195k
) {

    DEBUG(dbgs() << "ICE: GetShiftedValue propagating shift through expression"

              " to eliminate shift:\n  IN: " << *Op0 << "\n  SH: " << I <<"\n");

    return ReplaceInstUsesWith(

        I, GetShiftedValue(Op0, COp1->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.

  uint32_t TypeBits = Op0->getType()->getScalarSizeInBits();

  assert(!COp1->uge(TypeBits) &&

         "Shift over the type width should have been removed already");

  // ((X*C1) << C2) == (X * (C1 << C2))

  if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Op0))

    if (BO->getOpcode() == Instruction::Mul && 
isLeftShift5.40k
)

      if (Constant *BOOp = dyn_cast<Constant>(BO->getOperand(1)))

        return BinaryOperator::CreateMul(BO->getOperand(0),

                                        ConstantExpr::getShl(BOOp, Op1));

  // Try to fold constant and into select arguments.

  if (SelectInst *SI = dyn_cast<SelectInst>(Op0))

    if (Instruction *R = FoldOpIntoSelect(I, SI))

      return R;

  if (isa<PHINode>(Op0))

    if (Instruction *NV = FoldOpIntoPhi(I))

      return NV;

  // 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(COp1, 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 <<= COp1->getZExtValue();

      else {

        assert(I.getOpcode() == Instruction::LShr && "Unknown logical shift");

        MaskV = MaskV.lshr(COp1->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()4.67k
 &&

            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());

          uint32_t Op1Val = COp1->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()4.67k
 &&

            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; // HLSL CHANGE

      case Instruction::Sub: {

        // Turn ((X >> C) + Y) << C  ->  (X + (Y << C)) & (~0 << C)

        if (isLeftShift && 
Op0BO->getOperand(0)->hasOneUse()5.91k
 &&

            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());

          uint32_t Op1Val = COp1->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()5.91k
 &&

            match(Op0BO->getOperand(0),

                  m_And(m_OneUse(m_Shr(m_Value(V1), m_Value(V2))),

                        m_ConstantInt(CC))) && 
V2 == Op10
) {

          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::AShr3.05k
)

          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);

        }

      }

    }

  }

  // Find out if this is a shift of a shift by a constant.

  BinaryOperator *ShiftOp = dyn_cast<BinaryOperator>(Op0);

  if (ShiftOp && 
!ShiftOp->isShift()59.1k
)

    ShiftOp = nullptr;

  if (ShiftOp && 
isa<ConstantInt>(ShiftOp->getOperand(1))18.4k
) {

    // This is a constant shift of a constant shift. 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 transforms applied to shl are very similar to the transforms applied

    // to mul by constant. We can be more aggressive about optimizing right

    // shifts.

    //

    // Combinations of right and left shifts will still be optimized in

    // DAGCombine where scalar evolution no longer applies.

    ConstantInt *ShiftAmt1C = cast<ConstantInt>(ShiftOp->getOperand(1));

    uint32_t ShiftAmt1 = ShiftAmt1C->getLimitedValue(TypeBits);

    uint32_t ShiftAmt2 = COp1->getLimitedValue(TypeBits);

    assert(ShiftAmt2 != 0 && "Should have been simplified earlier");

    if (ShiftAmt1 == 0) 
return nullptr0
;  // Will be simplified in the future.

    Value *X = ShiftOp->getOperand(0);

    IntegerType *Ty = cast<IntegerType>(I.getType());

    // Check for (X << c1) << c2  and  (X >> c1) >> c2

    if (I.getOpcode() == ShiftOp->getOpcode()) {

      uint32_t AmtSum = ShiftAmt1+ShiftAmt2;   // Fold into one big shift.

      // If this is oversized composite shift, then unsigned shifts get 0, ashr

      // saturates.

      if (AmtSum >= TypeBits) {

        if (I.getOpcode() != Instruction::AShr)

          return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));

        AmtSum = TypeBits-1;  // Saturate to 31 for i32 ashr.

      }

      return BinaryOperator::Create(I.getOpcode(), X,

                                    ConstantInt::get(Ty, AmtSum));

    }

    if (ShiftAmt1 == ShiftAmt2) {

      // If we have ((X << C) >>u C), turn this into X & (-1 >>u C).

      if (I.getOpcode() == Instruction::LShr &&

          
ShiftOp->getOpcode() == Instruction::Shl10
) {

        APInt Mask(APInt::getLowBitsSet(TypeBits, TypeBits - ShiftAmt1));

        return BinaryOperator::CreateAnd(X,

                                        ConstantInt::get(I.getContext(), Mask));

      }

    } else 
if (796
ShiftAmt1 < ShiftAmt2796
) {

      uint32_t ShiftDiff = ShiftAmt2-ShiftAmt1;

      // (X >>?,exact C1) << C2 --> X << (C2-C1)

      // The inexact version is deferred to DAGCombine so we don't hide shl

      // behind a bit mask.

      if (I.getOpcode() == Instruction::Shl &&

          
ShiftOp->getOpcode() != Instruction::Shl376
 &&

          
ShiftOp->isExact()376
) {

        assert(ShiftOp->getOpcode() == Instruction::LShr ||

               ShiftOp->getOpcode() == Instruction::AShr);

        ConstantInt *ShiftDiffCst = ConstantInt::get(Ty, ShiftDiff);

        BinaryOperator *NewShl = BinaryOperator::Create(Instruction::Shl,

                                                        X, ShiftDiffCst);

        NewShl->setHasNoUnsignedWrap(I.hasNoUnsignedWrap());

        NewShl->setHasNoSignedWrap(I.hasNoSignedWrap());

        return NewShl;

      }

      // (X << C1) >>u C2  --> X >>u (C2-C1) & (-1 >> C2)

      if (I.getOpcode() == Instruction::LShr &&

          
ShiftOp->getOpcode() == Instruction::Shl24
) {

        ConstantInt *ShiftDiffCst = ConstantInt::get(Ty, ShiftDiff);

        // (X <<nuw C1) >>u C2 --> X >>u (C2-C1)

        if (ShiftOp->hasNoUnsignedWrap()) {

          BinaryOperator *NewLShr = BinaryOperator::Create(Instruction::LShr,

                                                           X, ShiftDiffCst);

          NewLShr->setIsExact(I.isExact());

          return NewLShr;

        }

        Value *Shift = Builder->CreateLShr(X, ShiftDiffCst);

        APInt Mask(APInt::getLowBitsSet(TypeBits, TypeBits - ShiftAmt2));

        return BinaryOperator::CreateAnd(Shift,

                                         ConstantInt::get(I.getContext(),Mask));

      }

      // 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.

      if (I.getOpcode() == Instruction::AShr &&

          
ShiftOp->getOpcode() == Instruction::Shl48
) {

        if (ShiftOp->hasNoSignedWrap()) {

          // (X <<nsw C1) >>s C2 --> X >>s (C2-C1)

          ConstantInt *ShiftDiffCst = ConstantInt::get(Ty, ShiftDiff);

          BinaryOperator *NewAShr = BinaryOperator::Create(Instruction::AShr,

                                                           X, ShiftDiffCst);

          NewAShr->setIsExact(I.isExact());

          return NewAShr;

        }

      }

    } else {

      assert(ShiftAmt2 < ShiftAmt1);

      uint32_t ShiftDiff = ShiftAmt1-ShiftAmt2;

      // (X >>?exact C1) << C2 --> X >>?exact (C1-C2)

      // The inexact version is deferred to DAGCombine so we don't hide shl

      // behind a bit mask.

      if (I.getOpcode() == Instruction::Shl &&

          
ShiftOp->getOpcode() != Instruction::Shl216
 &&

          
ShiftOp->isExact()216
) {

        ConstantInt *ShiftDiffCst = ConstantInt::get(Ty, ShiftDiff);

        BinaryOperator *NewShr = BinaryOperator::Create(ShiftOp->getOpcode(),

                                                        X, ShiftDiffCst);

        NewShr->setIsExact(true);

        return NewShr;

      }

      // (X << C1) >>u C2  --> X << (C1-C2) & (-1 >> C2)

      if (I.getOpcode() == Instruction::LShr &&

          
ShiftOp->getOpcode() == Instruction::Shl12
) {

        ConstantInt *ShiftDiffCst = ConstantInt::get(Ty, ShiftDiff);

        if (ShiftOp->hasNoUnsignedWrap()) {

          // (X <<nuw C1) >>u C2 --> X <<nuw (C1-C2)

          BinaryOperator *NewShl = BinaryOperator::Create(Instruction::Shl,

                                                          X, ShiftDiffCst);

          NewShl->setHasNoUnsignedWrap(true);

          return NewShl;

        }

        Value *Shift = Builder->CreateShl(X, ShiftDiffCst);

        APInt Mask(APInt::getLowBitsSet(TypeBits, TypeBits - ShiftAmt2));

        return BinaryOperator::CreateAnd(Shift,

                                         ConstantInt::get(I.getContext(),Mask));

      }

      // 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.

      if (I.getOpcode() == Instruction::AShr &&

          
ShiftOp->getOpcode() == Instruction::Shl120
) {

        if (ShiftOp->hasNoSignedWrap()) {

          // (X <<nsw C1) >>s C2 --> X <<nsw (C1-C2)

          ConstantInt *ShiftDiffCst = ConstantInt::get(Ty, ShiftDiff);

          BinaryOperator *NewShl = BinaryOperator::Create(Instruction::Shl,

                                                          X, ShiftDiffCst);

          NewShl->setHasNoSignedWrap(true);

          return NewShl;

        }

      }

    }

  }

  return nullptr;

}

Instruction *InstCombiner::visitShl(BinaryOperator &I) {

  if (Value *V = SimplifyVectorOp(I))

    return ReplaceInstUsesWith(I, V);

  if (Value *V =

          SimplifyShlInst(I.getOperand(0), I.getOperand(1), I.hasNoSignedWrap(),

                          I.hasNoUnsignedWrap(), DL, TLI, DT, AC))

    return ReplaceInstUsesWith(I, V);

  if (Instruction *V = commonShiftTransforms(I))

    return V;

  if (ConstantInt *Op1C = dyn_cast<ConstantInt>(I.getOperand(1))) {

    unsigned ShAmt = Op1C->getZExtValue();

    // If the shifted-out value is known-zero, then this is a NUW shift.

    if (!I.hasNoUnsignedWrap() &&

        MaskedValueIsZero(I.getOperand(0),

                          APInt::getHighBitsSet(Op1C->getBitWidth(), ShAmt),

                          0, &I)) {

          I.setHasNoUnsignedWrap();

          return &I;

        }

    // If the shifted out value is all signbits, this is a NSW shift.

    if (!I.hasNoSignedWrap() &&

        
ComputeNumSignBits(I.getOperand(0), 0, &I) > ShAmt115k
) {

      I.setHasNoSignedWrap();

      return &I;

    }

  }

  // (C1 << A) << C2 -> (C1 << C2) << A

  Constant *C1, *C2;

  Value *A;

  if (match(I.getOperand(0), m_OneUse(m_Shl(m_Constant(C1), m_Value(A)))) &&

      
match(I.getOperand(1), m_Constant(C2))8
)

    return BinaryOperator::CreateShl(ConstantExpr::getShl(C1, C2), A);

  return nullptr;

}

Instruction *InstCombiner::visitLShr(BinaryOperator &I) {

  if (Value *V = SimplifyVectorOp(I))

    return ReplaceInstUsesWith(I, V);

  if (Value *V = SimplifyLShrInst(I.getOperand(0), I.getOperand(1), I.isExact(),

                                  DL, TLI, DT, AC))

    return ReplaceInstUsesWith(I, V);

  if (Instruction *R = commonShiftTransforms(I))

    return R;

  Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);

  if (ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {

    unsigned ShAmt = Op1C->getZExtValue();

    if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Op0)) {

      unsigned BitWidth = Op0->getType()->getScalarSizeInBits();

      // ctlz.i32(x)>>5  --> zext(x == 0)

      // cttz.i32(x)>>5  --> zext(x == 0)

      // ctpop.i32(x)>>5 --> zext(x == -1)

      if ((II->getIntrinsicID() == Intrinsic::ctlz ||

           II->getIntrinsicID() == Intrinsic::cttz ||

           II->getIntrinsicID() == Intrinsic::ctpop) &&

          isPowerOf2_32(BitWidth) && Log2_32(BitWidth) == ShAmt) {

        bool isCtPop = II->getIntrinsicID() == Intrinsic::ctpop;

        Constant *RHS = ConstantInt::getSigned(Op0->getType(), isCtPop ? -1:0);

        Value *Cmp = Builder->CreateICmpEQ(II->getArgOperand(0), RHS);

        return new ZExtInst(Cmp, II->getType());

      }

    }

    // If the shifted-out value is known-zero, then this is an exact shift.

    if (!I.isExact() &&

        MaskedValueIsZero(Op0, APInt::getLowBitsSet(Op1C->getBitWidth(), ShAmt),

                          0, &I)){

      I.setIsExact();

      return &I;

    }

  }

  return nullptr;

}

Instruction *InstCombiner::visitAShr(BinaryOperator &I) {

  if (Value *V = SimplifyVectorOp(I))

    return ReplaceInstUsesWith(I, V);

  if (Value *V = SimplifyAShrInst(I.getOperand(0), I.getOperand(1), I.isExact(),

                                  DL, TLI, DT, AC))

    return ReplaceInstUsesWith(I, V);

  if (Instruction *R = commonShiftTransforms(I))

    return R;

  Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);

  if (ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {

    unsigned ShAmt = Op1C->getZExtValue();

    // If the input is a SHL by the same constant (ashr (shl X, C), C), then we

    // have a sign-extend idiom.

    Value *X;

    if (match(Op0, m_Shl(m_Value(X), m_Specific(Op1)))) {

      // If the input is an extension from the shifted amount value, e.g.

      //   %x = zext i8 %A to i32

      //   %y = shl i32 %x, 24

      //   %z = ashr %y, 24

      // then turn this into "z = sext i8 A to i32".

      if (ZExtInst *ZI = dyn_cast<ZExtInst>(X)) {

        uint32_t SrcBits = ZI->getOperand(0)->getType()->getScalarSizeInBits();

        uint32_t DestBits = ZI->getType()->getScalarSizeInBits();

        if (Op1C->getZExtValue() == DestBits-SrcBits)

          return new SExtInst(ZI->getOperand(0), ZI->getType());

      }

    }

    // If the shifted-out value is known-zero, then this is an exact shift.

    if (!I.isExact() &&

        MaskedValueIsZero(Op0,APInt::getLowBitsSet(Op1C->getBitWidth(),ShAmt),

                          0, &I)){

      I.setIsExact();

      return &I;

    }

  }

  // See if we can turn a signed shr into an unsigned shr.

  if (MaskedValueIsZero(Op0,

                        APInt::getSignBit(I.getType()->getScalarSizeInBits()),

                        0, &I))

    return BinaryOperator::CreateLShr(Op0, Op1);

  return nullptr;

}