text: //===- InstCombineShifts.cpp ----------------------------------------------===//
  //
  // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  // See https://llvm.org/LICENSE.txt for license information.
  // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
  //
  //===----------------------------------------------------------------------===//
  //
  // 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"
  
  // Given pattern:
  //   (x shiftopcode Q) shiftopcode K
  // we should rewrite it as
  //   x shiftopcode (Q+K)  iff (Q+K) u< bitwidth(x)
  // This is valid for any shift, but they must be identical.
  //
  // AnalyzeForSignBitExtraction indicates that we will only analyze whether this
  // pattern has any 2 right-shifts that sum to 1 less than original bit width.
  Value *InstCombiner::reassociateShiftAmtsOfTwoSameDirectionShifts(
      BinaryOperator *Sh0, const SimplifyQuery &SQ,
      bool AnalyzeForSignBitExtraction) {
    // Look for a shift of some instruction, ignore zext of shift amount if any.
    Instruction *Sh0Op0;
    Value *ShAmt0;
    if (!match(Sh0,
               m_Shift(m_Instruction(Sh0Op0), m_ZExtOrSelf(m_Value(ShAmt0)))))
      return nullptr;
  
    // If there is a truncation between the two shifts, we must make note of it
    // and look through it. The truncation imposes additional constraints on the
    // transform.
    Instruction *Sh1;
    Value *Trunc = nullptr;
    match(Sh0Op0,
          m_CombineOr(m_CombineAnd(m_Trunc(m_Instruction(Sh1)), m_Value(Trunc)),
                      m_Instruction(Sh1)));
  
    // Inner shift: (x shiftopcode ShAmt1)
    // Like with other shift, ignore zext of shift amount if any.
    Value *X, *ShAmt1;
    if (!match(Sh1, m_Shift(m_Value(X), m_ZExtOrSelf(m_Value(ShAmt1)))))
      return nullptr;
  
    // We have two shift amounts from two different shifts. The types of those
    // shift amounts may not match. If that's the case let's bailout now..
    if (ShAmt0->getType() != ShAmt1->getType())
      return nullptr;
  
    // We are only looking for signbit extraction if we have two right shifts.
    bool HadTwoRightShifts = match(Sh0, m_Shr(m_Value(), m_Value())) &&
                             match(Sh1, m_Shr(m_Value(), m_Value()));
    // ... and if it's not two right-shifts, we know the answer already.
    if (AnalyzeForSignBitExtraction && !HadTwoRightShifts)
      return nullptr;
  
    // The shift opcodes must be identical, unless we are just checking whether
    // this pattern can be interpreted as a sign-bit-extraction.
    Instruction::BinaryOps ShiftOpcode = Sh0->getOpcode();
    bool IdenticalShOpcodes = Sh0->getOpcode() == Sh1->getOpcode();
    if (!IdenticalShOpcodes && !AnalyzeForSignBitExtraction)
      return nullptr;
  
    // If we saw truncation, we'll need to produce extra instruction,
    // and for that one of the operands of the shift must be one-use,
    // unless of course we don't actually plan to produce any instructions here.
    if (Trunc && !AnalyzeForSignBitExtraction &&
        !match(Sh0, m_c_BinOp(m_OneUse(m_Value()), m_Value())))
      return nullptr;
  
    // Can we fold (ShAmt0+ShAmt1) ?
    auto *NewShAmt = dyn_cast_or_null<Constant>(
        SimplifyAddInst(ShAmt0, ShAmt1, /*isNSW=*/false, /*isNUW=*/false,
                        SQ.getWithInstruction(Sh0)));
    if (!NewShAmt)
      return nullptr; // Did not simplify.
    unsigned NewShAmtBitWidth = NewShAmt->getType()->getScalarSizeInBits();
    unsigned XBitWidth = X->getType()->getScalarSizeInBits();
    // Is the new shift amount smaller than the bit width of inner/new shift?
    if (!match(NewShAmt, m_SpecificInt_ICMP(ICmpInst::Predicate::ICMP_ULT,
                                            APInt(NewShAmtBitWidth, XBitWidth))))
      return nullptr; // FIXME: could perform constant-folding.
  
    // If there was a truncation, and we have a right-shift, we can only fold if
    // we are left with the original sign bit. Likewise, if we were just checking
    // that this is a sighbit extraction, this is the place to check it.
    // FIXME: zero shift amount is also legal here, but we can't *easily* check
    // more than one predicate so it's not really worth it.
    if (HadTwoRightShifts && (Trunc || AnalyzeForSignBitExtraction)) {
      // If it's not a sign bit extraction, then we're done.
      if (!match(NewShAmt,
                 m_SpecificInt_ICMP(ICmpInst::Predicate::ICMP_EQ,
                                    APInt(NewShAmtBitWidth, XBitWidth - 1))))
        return nullptr;
      // If it is, and that was the question, return the base value.
      if (AnalyzeForSignBitExtraction)
        return X;
    }
  
    assert(IdenticalShOpcodes && "Should not get here with different shifts.");
  
    // All good, we can do this fold.
    NewShAmt = ConstantExpr::getZExtOrBitCast(NewShAmt, X->getType());
  
    BinaryOperator *NewShift = BinaryOperator::Create(ShiftOpcode, X, NewShAmt);
  
    // The flags can only be propagated if there wasn't a trunc.
    if (!Trunc) {
      // If the pattern did not involve trunc, and both of the original shifts
      // had the same flag set, preserve the flag.
      if (ShiftOpcode == Instruction::BinaryOps::Shl) {
        NewShift->setHasNoUnsignedWrap(Sh0->hasNoUnsignedWrap() &&
                                       Sh1->hasNoUnsignedWrap());
        NewShift->setHasNoSignedWrap(Sh0->hasNoSignedWrap() &&
                                     Sh1->hasNoSignedWrap());
      } else {
        NewShift->setIsExact(Sh0->isExact() && Sh1->isExact());
      }
    }
  
    Instruction *Ret = NewShift;
    if (Trunc) {
      Builder.Insert(NewShift);
      Ret = CastInst::Create(Instruction::Trunc, NewShift, Sh0->getType());
    }
  
    return Ret;
  }
  
  // If we have some pattern that leaves only some low bits set, and then performs
  // left-shift of those bits, if none of the bits that are left after the final
  // shift are modified by the mask, we can omit the mask.
  //
  // There are many variants to this pattern:
  //   a)  (x & ((1 << MaskShAmt) - 1)) << ShiftShAmt
  //   b)  (x & (~(-1 << MaskShAmt))) << ShiftShAmt
  //   c)  (x & (-1 >> MaskShAmt)) << ShiftShAmt
  //   d)  (x & ((-1 << MaskShAmt) >> MaskShAmt)) << ShiftShAmt
  //   e)  ((x << MaskShAmt) l>> MaskShAmt) << ShiftShAmt
  //   f)  ((x << MaskShAmt) a>> MaskShAmt) << ShiftShAmt
  // All these patterns can be simplified to just:
  //   x << ShiftShAmt
  // iff:
  //   a,b)     (MaskShAmt+ShiftShAmt) u>= bitwidth(x)
  //   c,d,e,f) (ShiftShAmt-MaskShAmt) s>= 0 (i.e. ShiftShAmt u>= MaskShAmt)
  static Instruction *
  dropRedundantMaskingOfLeftShiftInput(BinaryOperator *OuterShift,
                                       const SimplifyQuery &Q,
                                       InstCombiner::BuilderTy &Builder) {
    assert(OuterShift->getOpcode() == Instruction::BinaryOps::Shl &&
           "The input must be 'shl'!");
  
    Value *Masked, *ShiftShAmt;
    match(OuterShift, m_Shift(m_Value(Masked), m_Value(ShiftShAmt)));
  
    Type *NarrowestTy = OuterShift->getType();
    Type *WidestTy = Masked->getType();
    // The mask must be computed in a type twice as wide to ensure
    // that no bits are lost if the sum-of-shifts is wider than the base type.
    Type *ExtendedTy = WidestTy->getExtendedType();
  
    Value *MaskShAmt;
  
    // ((1 << MaskShAmt) - 1)
    auto MaskA = m_Add(m_Shl(m_One(), m_Value(MaskShAmt)), m_AllOnes());
    // (~(-1 << maskNbits))
    auto MaskB = m_Xor(m_Shl(m_AllOnes(), m_Value(MaskShAmt)), m_AllOnes());
    // (-1 >> MaskShAmt)
    auto MaskC = m_Shr(m_AllOnes(), m_Value(MaskShAmt));
    // ((-1 << MaskShAmt) >> MaskShAmt)
    auto MaskD =
        m_Shr(m_Shl(m_AllOnes(), m_Value(MaskShAmt)), m_Deferred(MaskShAmt));
  
    Value *X;
    Constant *NewMask;
  
    if (match(Masked, m_c_And(m_CombineOr(MaskA, MaskB), m_Value(X)))) {
      // Can we simplify (MaskShAmt+ShiftShAmt) ?
      auto *SumOfShAmts = dyn_cast_or_null<Constant>(SimplifyAddInst(
          MaskShAmt, ShiftShAmt, /*IsNSW=*/false, /*IsNUW=*/false, Q));
      if (!SumOfShAmts)
        return nullptr; // Did not simplify.
      // In this pattern SumOfShAmts correlates with the number of low bits
      // that shall remain in the root value (OuterShift).
  
      // An extend of an undef value becomes zero because the high bits are never
      // completely unknown. Replace the the `undef` shift amounts with final
      // shift bitwidth to ensure that the value remains undef when creating the
      // subsequent shift op.
      SumOfShAmts = Constant::replaceUndefsWith(
          SumOfShAmts, ConstantInt::get(SumOfShAmts->getType()->getScalarType(),
                                        ExtendedTy->getScalarSizeInBits()));
      auto *ExtendedSumOfShAmts = ConstantExpr::getZExt(SumOfShAmts, ExtendedTy);
      // And compute the mask as usual: ~(-1 << (SumOfShAmts))
      auto *ExtendedAllOnes = ConstantExpr::getAllOnesValue(ExtendedTy);
      auto *ExtendedInvertedMask =
          ConstantExpr::getShl(ExtendedAllOnes, ExtendedSumOfShAmts);
      NewMask = ConstantExpr::getNot(ExtendedInvertedMask);
    } else if (match(Masked, m_c_And(m_CombineOr(MaskC, MaskD), m_Value(X))) ||
               match(Masked, m_Shr(m_Shl(m_Value(X), m_Value(MaskShAmt)),
                                   m_Deferred(MaskShAmt)))) {
      // Can we simplify (ShiftShAmt-MaskShAmt) ?
      auto *ShAmtsDiff = dyn_cast_or_null<Constant>(SimplifySubInst(
          ShiftShAmt, MaskShAmt, /*IsNSW=*/false, /*IsNUW=*/false, Q));
      if (!ShAmtsDiff)
        return nullptr; // Did not simplify.
      // In this pattern ShAmtsDiff correlates with the number of high bits that
      // shall be unset in the root value (OuterShift).
  
      // An extend of an undef value becomes zero because the high bits are never
      // completely unknown. Replace the the `undef` shift amounts with negated
      // bitwidth of innermost shift to ensure that the value remains undef when
      // creating the subsequent shift op.
      unsigned WidestTyBitWidth = WidestTy->getScalarSizeInBits();
      ShAmtsDiff = Constant::replaceUndefsWith(
          ShAmtsDiff, ConstantInt::get(ShAmtsDiff->getType()->getScalarType(),
                                       -WidestTyBitWidth));
      auto *ExtendedNumHighBitsToClear = ConstantExpr::getZExt(
          ConstantExpr::getSub(ConstantInt::get(ShAmtsDiff->getType(),
                                                WidestTyBitWidth,
                                                /*isSigned=*/false),
                               ShAmtsDiff),
          ExtendedTy);
      // And compute the mask as usual: (-1 l>> (NumHighBitsToClear))
      auto *ExtendedAllOnes = ConstantExpr::getAllOnesValue(ExtendedTy);
      NewMask =
          ConstantExpr::getLShr(ExtendedAllOnes, ExtendedNumHighBitsToClear);
    } else
      return nullptr; // Don't know anything about this pattern.
  
    NewMask = ConstantExpr::getTrunc(NewMask, NarrowestTy);
  
    // Does this mask has any unset bits? If not then we can just not apply it.
    bool NeedMask = !match(NewMask, m_AllOnes());
  
    // If we need to apply a mask, there are several more restrictions we have.
    if (NeedMask) {
      // The old masking instruction must go away.
      if (!Masked->hasOneUse())
        return nullptr;
      // The original "masking" instruction must not have been`ashr`.
      if (match(Masked, m_AShr(m_Value(), m_Value())))
        return nullptr;
    }
  
    // No 'NUW'/'NSW'! We no longer know that we won't shift-out non-0 bits.
    auto *NewShift = BinaryOperator::Create(OuterShift->getOpcode(), X,
                                            OuterShift->getOperand(1));
  
    if (!NeedMask)
      return NewShift;
  
    Builder.Insert(NewShift);
    return BinaryOperator::Create(Instruction::And, NewShift, NewMask);
  }
  
  Instruction *InstCombiner::commonShiftTransforms(BinaryOperator &I) {
    Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
    assert(Op0->getType() == Op1->getType());
  
    // If the shift amount is a one-use `sext`, we can demote it to `zext`.
    Value *Y;
    if (match(Op1, m_OneUse(m_SExt(m_Value(Y))))) {
      Value *NewExt = Builder.CreateZExt(Y, I.getType(), Op1->getName());
      return BinaryOperator::Create(I.getOpcode(), Op0, NewExt);
    }
  
    // 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;
  
    if (auto *NewShift = cast_or_null<Instruction>(
            reassociateShiftAmtsOfTwoSameDirectionShifts(&I, SQ)))
      return NewShift;
  
    // (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) {
    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'
    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;
    }
  
    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;
    }
    }
  }
  
  // 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) {
    switch (BO->getOpcode()) {
    default:
      return false; // Do not perform transform!
    case Instruction::Add:
      return Shift.getOpcode() == Instruction::Shl;
    case Instruction::Or:
    case Instruction::Xor:
    case Instruction::And:
      return true;
    }
  }
  
  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();
  
    assert(!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 {
          assert(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)) {
            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)) {
          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)) {
          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) {
    const SimplifyQuery Q = SQ.getWithInstruction(&I);
  
    if (Value *V = SimplifyShlInst(I.getOperand(0), I.getOperand(1),
                                   I.hasNoSignedWrap(), I.hasNoUnsignedWrap(), Q))
      return replaceInstUsesWith(I, V);
  
    if (Instruction *X = foldVectorBinop(I))
      return X;
  
    if (Instruction *V = commonShiftTransforms(I))
      return V;
  
    if (Instruction *V = dropRedundantMaskingOfLeftShiftInput(&I, Q, Builder))
      return V;
  
    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))) {
      unsigned ShAmt = ShAmtAPInt->getZExtValue();
  
      // 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_OneUse(m_ZExt(m_Value(X))))) {
        unsigned SrcWidth = X->getType()->getScalarSizeInBits();
        if (ShAmt < SrcWidth &&
            MaskedValueIsZero(X, APInt::getHighBitsSet(SrcWidth, ShAmt), 0, &I))
          return new ZExtInst(Builder.CreateShl(X, ShAmt), Ty);
      }
  
      // (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));
  
      // shl (zext i1 X), C1 --> select (X, 1 << C1, 0)
      if (match(Op0, m_ZExt(m_Value(X))) && X->getType()->isIntOrIntVectorTy(1)) {
        auto *NewC = ConstantExpr::getShl(ConstantInt::get(Ty, 1), C1);
        return SelectInst::Create(X, NewC, ConstantInt::getNullValue(Ty));
      }
    }
  
    // (1 << (C - x)) -> ((1 << C) >> x) if C is bitwidth - 1
    if (match(Op0, m_One()) &&
        match(Op1, m_Sub(m_SpecificInt(BitWidth - 1), m_Value(X))))
      return BinaryOperator::CreateLShr(
          ConstantInt::get(Ty, APInt::getSignMask(BitWidth)), X);
  
    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 = foldVectorBinop(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))) && ShOp1->ult(BitWidth)) {
        if (ShOp1->ult(ShAmt)) {
          unsigned ShlAmt = ShOp1->getZExtValue();
          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 (ShOp1->ugt(ShAmt)) {
          unsigned ShlAmt = ShOp1->getZExtValue();
          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(*ShOp1 == 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()))) {
        assert(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::foldVariableSignZeroExtensionOfVariableHighBitExtract(
      BinaryOperator &OldAShr) {
    assert(OldAShr.getOpcode() == Instruction::AShr &&
           "Must be called with arithmetic right-shift instruction only.");
  
    // Check that constant C is a splat of the element-wise bitwidth of V.
    auto BitWidthSplat = [](Constant *C, Value *V) {
      return match(
          C, m_SpecificInt_ICMP(ICmpInst::Predicate::ICMP_EQ,
                                APInt(C->getType()->getScalarSizeInBits(),
                                      V->getType()->getScalarSizeInBits())));
    };
  
    // It should look like variable-length sign-extension on the outside:
    //   (Val << (bitwidth(Val)-Nbits)) a>> (bitwidth(Val)-Nbits)
    Value *NBits;
    Instruction *MaybeTrunc;
    Constant *C1, *C2;
    if (!match(&OldAShr,
               m_AShr(m_Shl(m_Instruction(MaybeTrunc),
                            m_ZExtOrSelf(m_Sub(m_Constant(C1),
                                               m_ZExtOrSelf(m_Value(NBits))))),
                      m_ZExtOrSelf(m_Sub(m_Constant(C2),
                                         m_ZExtOrSelf(m_Deferred(NBits)))))) ||
        !BitWidthSplat(C1, &OldAShr) || !BitWidthSplat(C2, &OldAShr))
      return nullptr;
  
    // There may or may not be a truncation after outer two shifts.
    Instruction *HighBitExtract;
    match(MaybeTrunc, m_TruncOrSelf(m_Instruction(HighBitExtract)));
    bool HadTrunc = MaybeTrunc != HighBitExtract;
  
    // And finally, the innermost part of the pattern must be a right-shift.
    Value *X, *NumLowBitsToSkip;
    if (!match(HighBitExtract, m_Shr(m_Value(X), m_Value(NumLowBitsToSkip))))
      return nullptr;
  
    // Said right-shift must extract high NBits bits - C0 must be it's bitwidth.
    Constant *C0;
    if (!match(NumLowBitsToSkip,
               m_ZExtOrSelf(
                   m_Sub(m_Constant(C0), m_ZExtOrSelf(m_Specific(NBits))))) ||
        !BitWidthSplat(C0, HighBitExtract))
      return nullptr;
  
    // Since the NBits is identical for all shifts, if the outermost and
    // innermost shifts are identical, then outermost shifts are redundant.
    // If we had truncation, do keep it though.
    if (HighBitExtract->getOpcode() == OldAShr.getOpcode())
      return replaceInstUsesWith(OldAShr, MaybeTrunc);
  
    // Else, if there was a truncation, then we need to ensure that one
    // instruction will go away.
    if (HadTrunc && !match(&OldAShr, m_c_BinOp(m_OneUse(m_Value()), m_Value())))
      return nullptr;
  
    // Finally, bypass two innermost shifts, and perform the outermost shift on
    // the operands of the innermost shift.
    Instruction *NewAShr =
        BinaryOperator::Create(OldAShr.getOpcode(), X, NumLowBitsToSkip);
    NewAShr->copyIRFlags(HighBitExtract); // We can preserve 'exact'-ness.
    if (!HadTrunc)
      return NewAShr;
  
    Builder.Insert(NewAShr);
    return TruncInst::CreateTruncOrBitCast(NewAShr, OldAShr.getType());
  }
  
  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 = foldVectorBinop(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;
      }
    }
  
    if (Instruction *R = foldVariableSignZeroExtensionOfVariableHighBitExtract(I))
      return R;
  
    // 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;
  }
  