text: //===- InstCombineSelect.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 visitSelect function.
  //
  //===----------------------------------------------------------------------===//
  
  #include "InstCombineInternal.h"
  #include "llvm/ADT/APInt.h"
  #include "llvm/ADT/Optional.h"
  #include "llvm/ADT/STLExtras.h"
  #include "llvm/ADT/SmallVector.h"
  #include "llvm/Analysis/AssumptionCache.h"
  #include "llvm/Analysis/CmpInstAnalysis.h"
  #include "llvm/Analysis/InstructionSimplify.h"
  #include "llvm/Analysis/ValueTracking.h"
  #include "llvm/IR/BasicBlock.h"
  #include "llvm/IR/Constant.h"
  #include "llvm/IR/Constants.h"
  #include "llvm/IR/DerivedTypes.h"
  #include "llvm/IR/IRBuilder.h"
  #include "llvm/IR/InstrTypes.h"
  #include "llvm/IR/Instruction.h"
  #include "llvm/IR/Instructions.h"
  #include "llvm/IR/IntrinsicInst.h"
  #include "llvm/IR/Intrinsics.h"
  #include "llvm/IR/Operator.h"
  #include "llvm/IR/PatternMatch.h"
  #include "llvm/IR/Type.h"
  #include "llvm/IR/User.h"
  #include "llvm/IR/Value.h"
  #include "llvm/Support/Casting.h"
  #include "llvm/Support/ErrorHandling.h"
  #include "llvm/Support/KnownBits.h"
  #include "llvm/Transforms/InstCombine/InstCombineWorklist.h"
  #include <cassert>
  #include <utility>
  
  using namespace llvm;
  using namespace PatternMatch;
  
  #define DEBUG_TYPE "instcombine"
  
  static Value *createMinMax(InstCombiner::BuilderTy &Builder,
                             SelectPatternFlavor SPF, Value *A, Value *B) {
    CmpInst::Predicate Pred = getMinMaxPred(SPF);
    assert(CmpInst::isIntPredicate(Pred) && "Expected integer predicate");
    return Builder.CreateSelect(Builder.CreateICmp(Pred, A, B), A, B);
  }
  
  /// Replace a select operand based on an equality comparison with the identity
  /// constant of a binop.
  static Instruction *foldSelectBinOpIdentity(SelectInst &Sel,
                                              const TargetLibraryInfo &TLI,
                                              InstCombiner &IC) {
    // The select condition must be an equality compare with a constant operand.
    Value *X;
    Constant *C;
    CmpInst::Predicate Pred;
    if (!match(Sel.getCondition(), m_Cmp(Pred, m_Value(X), m_Constant(C))))
      return nullptr;
  
    bool IsEq;
    if (ICmpInst::isEquality(Pred))
      IsEq = Pred == ICmpInst::ICMP_EQ;
    else if (Pred == FCmpInst::FCMP_OEQ)
      IsEq = true;
    else if (Pred == FCmpInst::FCMP_UNE)
      IsEq = false;
    else
      return nullptr;
  
    // A select operand must be a binop.
    BinaryOperator *BO;
    if (!match(Sel.getOperand(IsEq ? 1 : 2), m_BinOp(BO)))
      return nullptr;
  
    // The compare constant must be the identity constant for that binop.
    // If this a floating-point compare with 0.0, any zero constant will do.
    Type *Ty = BO->getType();
    Constant *IdC = ConstantExpr::getBinOpIdentity(BO->getOpcode(), Ty, true);
    if (IdC != C) {
      if (!IdC || !CmpInst::isFPPredicate(Pred))
        return nullptr;
      if (!match(IdC, m_AnyZeroFP()) || !match(C, m_AnyZeroFP()))
        return nullptr;
    }
  
    // Last, match the compare variable operand with a binop operand.
    Value *Y;
    if (!BO->isCommutative() && !match(BO, m_BinOp(m_Value(Y), m_Specific(X))))
      return nullptr;
    if (!match(BO, m_c_BinOp(m_Value(Y), m_Specific(X))))
      return nullptr;
  
    // +0.0 compares equal to -0.0, and so it does not behave as required for this
    // transform. Bail out if we can not exclude that possibility.
    if (isa<FPMathOperator>(BO))
      if (!BO->hasNoSignedZeros() && !CannotBeNegativeZero(Y, &TLI))
        return nullptr;
  
    // BO = binop Y, X
    // S = { select (cmp eq X, C), BO, ? } or { select (cmp ne X, C), ?, BO }
    // =>
    // S = { select (cmp eq X, C),  Y, ? } or { select (cmp ne X, C), ?,  Y }
    return IC.replaceOperand(Sel, IsEq ? 1 : 2, Y);
  }
  
  /// This folds:
  ///  select (icmp eq (and X, C1)), TC, FC
  ///    iff C1 is a power 2 and the difference between TC and FC is a power-of-2.
  /// To something like:
  ///  (shr (and (X, C1)), (log2(C1) - log2(TC-FC))) + FC
  /// Or:
  ///  (shl (and (X, C1)), (log2(TC-FC) - log2(C1))) + FC
  /// With some variations depending if FC is larger than TC, or the shift
  /// isn't needed, or the bit widths don't match.
  static Value *foldSelectICmpAnd(SelectInst &Sel, ICmpInst *Cmp,
                                  InstCombiner::BuilderTy &Builder) {
    const APInt *SelTC, *SelFC;
    if (!match(Sel.getTrueValue(), m_APInt(SelTC)) ||
        !match(Sel.getFalseValue(), m_APInt(SelFC)))
      return nullptr;
  
    // If this is a vector select, we need a vector compare.
    Type *SelType = Sel.getType();
    if (SelType->isVectorTy() != Cmp->getType()->isVectorTy())
      return nullptr;
  
    Value *V;
    APInt AndMask;
    bool CreateAnd = false;
    ICmpInst::Predicate Pred = Cmp->getPredicate();
    if (ICmpInst::isEquality(Pred)) {
      if (!match(Cmp->getOperand(1), m_Zero()))
        return nullptr;
  
      V = Cmp->getOperand(0);
      const APInt *AndRHS;
      if (!match(V, m_And(m_Value(), m_Power2(AndRHS))))
        return nullptr;
  
      AndMask = *AndRHS;
    } else if (decomposeBitTestICmp(Cmp->getOperand(0), Cmp->getOperand(1),
                                    Pred, V, AndMask)) {
      assert(ICmpInst::isEquality(Pred) && "Not equality test?");
      if (!AndMask.isPowerOf2())
        return nullptr;
  
      CreateAnd = true;
    } else {
      return nullptr;
    }
  
    // In general, when both constants are non-zero, we would need an offset to
    // replace the select. This would require more instructions than we started
    // with. But there's one special-case that we handle here because it can
    // simplify/reduce the instructions.
    APInt TC = *SelTC;
    APInt FC = *SelFC;
    if (!TC.isNullValue() && !FC.isNullValue()) {
      // If the select constants differ by exactly one bit and that's the same
      // bit that is masked and checked by the select condition, the select can
      // be replaced by bitwise logic to set/clear one bit of the constant result.
      if (TC.getBitWidth() != AndMask.getBitWidth() || (TC ^ FC) != AndMask)
        return nullptr;
      if (CreateAnd) {
        // If we have to create an 'and', then we must kill the cmp to not
        // increase the instruction count.
        if (!Cmp->hasOneUse())
          return nullptr;
        V = Builder.CreateAnd(V, ConstantInt::get(SelType, AndMask));
      }
      bool ExtraBitInTC = TC.ugt(FC);
      if (Pred == ICmpInst::ICMP_EQ) {
        // If the masked bit in V is clear, clear or set the bit in the result:
        // (V & AndMaskC) == 0 ? TC : FC --> (V & AndMaskC) ^ TC
        // (V & AndMaskC) == 0 ? TC : FC --> (V & AndMaskC) | TC
        Constant *C = ConstantInt::get(SelType, TC);
        return ExtraBitInTC ? Builder.CreateXor(V, C) : Builder.CreateOr(V, C);
      }
      if (Pred == ICmpInst::ICMP_NE) {
        // If the masked bit in V is set, set or clear the bit in the result:
        // (V & AndMaskC) != 0 ? TC : FC --> (V & AndMaskC) | FC
        // (V & AndMaskC) != 0 ? TC : FC --> (V & AndMaskC) ^ FC
        Constant *C = ConstantInt::get(SelType, FC);
        return ExtraBitInTC ? Builder.CreateOr(V, C) : Builder.CreateXor(V, C);
      }
      llvm_unreachable("Only expecting equality predicates");
    }
  
    // Make sure one of the select arms is a power-of-2.
    if (!TC.isPowerOf2() && !FC.isPowerOf2())
      return nullptr;
  
    // Determine which shift is needed to transform result of the 'and' into the
    // desired result.
    const APInt &ValC = !TC.isNullValue() ? TC : FC;
    unsigned ValZeros = ValC.logBase2();
    unsigned AndZeros = AndMask.logBase2();
  
    // Insert the 'and' instruction on the input to the truncate.
    if (CreateAnd)
      V = Builder.CreateAnd(V, ConstantInt::get(V->getType(), AndMask));
  
    // If types don't match, we can still convert the select by introducing a zext
    // or a trunc of the 'and'.
    if (ValZeros > AndZeros) {
      V = Builder.CreateZExtOrTrunc(V, SelType);
      V = Builder.CreateShl(V, ValZeros - AndZeros);
    } else if (ValZeros < AndZeros) {
      V = Builder.CreateLShr(V, AndZeros - ValZeros);
      V = Builder.CreateZExtOrTrunc(V, SelType);
    } else {
      V = Builder.CreateZExtOrTrunc(V, SelType);
    }
  
    // Okay, now we know that everything is set up, we just don't know whether we
    // have a icmp_ne or icmp_eq and whether the true or false val is the zero.
    bool ShouldNotVal = !TC.isNullValue();
    ShouldNotVal ^= Pred == ICmpInst::ICMP_NE;
    if (ShouldNotVal)
      V = Builder.CreateXor(V, ValC);
  
    return V;
  }
  
  /// We want to turn code that looks like this:
  ///   %C = or %A, %B
  ///   %D = select %cond, %C, %A
  /// into:
  ///   %C = select %cond, %B, 0
  ///   %D = or %A, %C
  ///
  /// Assuming that the specified instruction is an operand to the select, return
  /// a bitmask indicating which operands of this instruction are foldable if they
  /// equal the other incoming value of the select.
  static unsigned getSelectFoldableOperands(BinaryOperator *I) {
    switch (I->getOpcode()) {
    case Instruction::Add:
    case Instruction::Mul:
    case Instruction::And:
    case Instruction::Or:
    case Instruction::Xor:
      return 3;              // Can fold through either operand.
    case Instruction::Sub:   // Can only fold on the amount subtracted.
    case Instruction::Shl:   // Can only fold on the shift amount.
    case Instruction::LShr:
    case Instruction::AShr:
      return 1;
    default:
      return 0;              // Cannot fold
    }
  }
  
  /// For the same transformation as the previous function, return the identity
  /// constant that goes into the select.
  static APInt getSelectFoldableConstant(BinaryOperator *I) {
    switch (I->getOpcode()) {
    default: llvm_unreachable("This cannot happen!");
    case Instruction::Add:
    case Instruction::Sub:
    case Instruction::Or:
    case Instruction::Xor:
    case Instruction::Shl:
    case Instruction::LShr:
    case Instruction::AShr:
      return APInt::getNullValue(I->getType()->getScalarSizeInBits());
    case Instruction::And:
      return APInt::getAllOnesValue(I->getType()->getScalarSizeInBits());
    case Instruction::Mul:
      return APInt(I->getType()->getScalarSizeInBits(), 1);
    }
  }
  
  /// We have (select c, TI, FI), and we know that TI and FI have the same opcode.
  Instruction *InstCombiner::foldSelectOpOp(SelectInst &SI, Instruction *TI,
                                            Instruction *FI) {
    // Don't break up min/max patterns. The hasOneUse checks below prevent that
    // for most cases, but vector min/max with bitcasts can be transformed. If the
    // one-use restrictions are eased for other patterns, we still don't want to
    // obfuscate min/max.
    if ((match(&SI, m_SMin(m_Value(), m_Value())) ||
         match(&SI, m_SMax(m_Value(), m_Value())) ||
         match(&SI, m_UMin(m_Value(), m_Value())) ||
         match(&SI, m_UMax(m_Value(), m_Value()))))
      return nullptr;
  
    // If this is a cast from the same type, merge.
    Value *Cond = SI.getCondition();
    Type *CondTy = Cond->getType();
    if (TI->getNumOperands() == 1 && TI->isCast()) {
      Type *FIOpndTy = FI->getOperand(0)->getType();
      if (TI->getOperand(0)->getType() != FIOpndTy)
        return nullptr;
  
      // The select condition may be a vector. We may only change the operand
      // type if the vector width remains the same (and matches the condition).
      if (auto *CondVTy = dyn_cast<VectorType>(CondTy)) {
        if (!FIOpndTy->isVectorTy())
          return nullptr;
        if (CondVTy->getNumElements() !=
            cast<VectorType>(FIOpndTy)->getNumElements())
          return nullptr;
  
        // TODO: If the backend knew how to deal with casts better, we could
        // remove this limitation. For now, there's too much potential to create
        // worse codegen by promoting the select ahead of size-altering casts
        // (PR28160).
        //
        // Note that ValueTracking's matchSelectPattern() looks through casts
        // without checking 'hasOneUse' when it matches min/max patterns, so this
        // transform may end up happening anyway.
        if (TI->getOpcode() != Instruction::BitCast &&
            (!TI->hasOneUse() || !FI->hasOneUse()))
          return nullptr;
      } else if (!TI->hasOneUse() || !FI->hasOneUse()) {
        // TODO: The one-use restrictions for a scalar select could be eased if
        // the fold of a select in visitLoadInst() was enhanced to match a pattern
        // that includes a cast.
        return nullptr;
      }
  
      // Fold this by inserting a select from the input values.
      Value *NewSI =
          Builder.CreateSelect(Cond, TI->getOperand(0), FI->getOperand(0),
                               SI.getName() + ".v", &SI);
      return CastInst::Create(Instruction::CastOps(TI->getOpcode()), NewSI,
                              TI->getType());
    }
  
    // Cond ? -X : -Y --> -(Cond ? X : Y)
    Value *X, *Y;
    if (match(TI, m_FNeg(m_Value(X))) && match(FI, m_FNeg(m_Value(Y))) &&
        (TI->hasOneUse() || FI->hasOneUse())) {
      Value *NewSel = Builder.CreateSelect(Cond, X, Y, SI.getName() + ".v", &SI);
      return UnaryOperator::CreateFNegFMF(NewSel, TI);
    }
  
    // Only handle binary operators (including two-operand getelementptr) with
    // one-use here. As with the cast case above, it may be possible to relax the
    // one-use constraint, but that needs be examined carefully since it may not
    // reduce the total number of instructions.
    if (TI->getNumOperands() != 2 || FI->getNumOperands() != 2 ||
        (!isa<BinaryOperator>(TI) && !isa<GetElementPtrInst>(TI)) ||
        !TI->hasOneUse() || !FI->hasOneUse())
      return nullptr;
  
    // Figure out if the operations have any operands in common.
    Value *MatchOp, *OtherOpT, *OtherOpF;
    bool MatchIsOpZero;
    if (TI->getOperand(0) == FI->getOperand(0)) {
      MatchOp  = TI->getOperand(0);
      OtherOpT = TI->getOperand(1);
      OtherOpF = FI->getOperand(1);
      MatchIsOpZero = true;
    } else if (TI->getOperand(1) == FI->getOperand(1)) {
      MatchOp  = TI->getOperand(1);
      OtherOpT = TI->getOperand(0);
      OtherOpF = FI->getOperand(0);
      MatchIsOpZero = false;
    } else if (!TI->isCommutative()) {
      return nullptr;
    } else if (TI->getOperand(0) == FI->getOperand(1)) {
      MatchOp  = TI->getOperand(0);
      OtherOpT = TI->getOperand(1);
      OtherOpF = FI->getOperand(0);
      MatchIsOpZero = true;
    } else if (TI->getOperand(1) == FI->getOperand(0)) {
      MatchOp  = TI->getOperand(1);
      OtherOpT = TI->getOperand(0);
      OtherOpF = FI->getOperand(1);
      MatchIsOpZero = true;
    } else {
      return nullptr;
    }
  
    // If the select condition is a vector, the operands of the original select's
    // operands also must be vectors. This may not be the case for getelementptr
    // for example.
    if (CondTy->isVectorTy() && (!OtherOpT->getType()->isVectorTy() ||
                                 !OtherOpF->getType()->isVectorTy()))
      return nullptr;
  
    // If we reach here, they do have operations in common.
    Value *NewSI = Builder.CreateSelect(Cond, OtherOpT, OtherOpF,
                                        SI.getName() + ".v", &SI);
    Value *Op0 = MatchIsOpZero ? MatchOp : NewSI;
    Value *Op1 = MatchIsOpZero ? NewSI : MatchOp;
    if (auto *BO = dyn_cast<BinaryOperator>(TI)) {
      BinaryOperator *NewBO = BinaryOperator::Create(BO->getOpcode(), Op0, Op1);
      NewBO->copyIRFlags(TI);
      NewBO->andIRFlags(FI);
      return NewBO;
    }
    if (auto *TGEP = dyn_cast<GetElementPtrInst>(TI)) {
      auto *FGEP = cast<GetElementPtrInst>(FI);
      Type *ElementType = TGEP->getResultElementType();
      return TGEP->isInBounds() && FGEP->isInBounds()
                 ? GetElementPtrInst::CreateInBounds(ElementType, Op0, {Op1})
                 : GetElementPtrInst::Create(ElementType, Op0, {Op1});
    }
    llvm_unreachable("Expected BinaryOperator or GEP");
    return nullptr;
  }
  
  static bool isSelect01(const APInt &C1I, const APInt &C2I) {
    if (!C1I.isNullValue() && !C2I.isNullValue()) // One side must be zero.
      return false;
    return C1I.isOneValue() || C1I.isAllOnesValue() ||
           C2I.isOneValue() || C2I.isAllOnesValue();
  }
  
  /// Try to fold the select into one of the operands to allow further
  /// optimization.
  Instruction *InstCombiner::foldSelectIntoOp(SelectInst &SI, Value *TrueVal,
                                              Value *FalseVal) {
    // See the comment above GetSelectFoldableOperands for a description of the
    // transformation we are doing here.
    if (auto *TVI = dyn_cast<BinaryOperator>(TrueVal)) {
      if (TVI->hasOneUse() && !isa<Constant>(FalseVal)) {
        if (unsigned SFO = getSelectFoldableOperands(TVI)) {
          unsigned OpToFold = 0;
          if ((SFO & 1) && FalseVal == TVI->getOperand(0)) {
            OpToFold = 1;
          } else if ((SFO & 2) && FalseVal == TVI->getOperand(1)) {
            OpToFold = 2;
          }
  
          if (OpToFold) {
            APInt CI = getSelectFoldableConstant(TVI);
            Value *OOp = TVI->getOperand(2-OpToFold);
            // Avoid creating select between 2 constants unless it's selecting
            // between 0, 1 and -1.
            const APInt *OOpC;
            bool OOpIsAPInt = match(OOp, m_APInt(OOpC));
            if (!isa<Constant>(OOp) || (OOpIsAPInt && isSelect01(CI, *OOpC))) {
              Value *C = ConstantInt::get(OOp->getType(), CI);
              Value *NewSel = Builder.CreateSelect(SI.getCondition(), OOp, C);
              NewSel->takeName(TVI);
              BinaryOperator *BO = BinaryOperator::Create(TVI->getOpcode(),
                                                          FalseVal, NewSel);
              BO->copyIRFlags(TVI);
              return BO;
            }
          }
        }
      }
    }
  
    if (auto *FVI = dyn_cast<BinaryOperator>(FalseVal)) {
      if (FVI->hasOneUse() && !isa<Constant>(TrueVal)) {
        if (unsigned SFO = getSelectFoldableOperands(FVI)) {
          unsigned OpToFold = 0;
          if ((SFO & 1) && TrueVal == FVI->getOperand(0)) {
            OpToFold = 1;
          } else if ((SFO & 2) && TrueVal == FVI->getOperand(1)) {
            OpToFold = 2;
          }
  
          if (OpToFold) {
            APInt CI = getSelectFoldableConstant(FVI);
            Value *OOp = FVI->getOperand(2-OpToFold);
            // Avoid creating select between 2 constants unless it's selecting
            // between 0, 1 and -1.
            const APInt *OOpC;
            bool OOpIsAPInt = match(OOp, m_APInt(OOpC));
            if (!isa<Constant>(OOp) || (OOpIsAPInt && isSelect01(CI, *OOpC))) {
              Value *C = ConstantInt::get(OOp->getType(), CI);
              Value *NewSel = Builder.CreateSelect(SI.getCondition(), C, OOp);
              NewSel->takeName(FVI);
              BinaryOperator *BO = BinaryOperator::Create(FVI->getOpcode(),
                                                          TrueVal, NewSel);
              BO->copyIRFlags(FVI);
              return BO;
            }
          }
        }
      }
    }
  
    return nullptr;
  }
  
  /// We want to turn:
  ///   (select (icmp eq (and X, Y), 0), (and (lshr X, Z), 1), 1)
  /// into:
  ///   zext (icmp ne i32 (and X, (or Y, (shl 1, Z))), 0)
  /// Note:
  ///   Z may be 0 if lshr is missing.
  /// Worst-case scenario is that we will replace 5 instructions with 5 different
  /// instructions, but we got rid of select.
  static Instruction *foldSelectICmpAndAnd(Type *SelType, const ICmpInst *Cmp,
                                           Value *TVal, Value *FVal,
                                           InstCombiner::BuilderTy &Builder) {
    if (!(Cmp->hasOneUse() && Cmp->getOperand(0)->hasOneUse() &&
          Cmp->getPredicate() == ICmpInst::ICMP_EQ &&
          match(Cmp->getOperand(1), m_Zero()) && match(FVal, m_One())))
      return nullptr;
  
    // The TrueVal has general form of:  and %B, 1
    Value *B;
    if (!match(TVal, m_OneUse(m_And(m_Value(B), m_One()))))
      return nullptr;
  
    // Where %B may be optionally shifted:  lshr %X, %Z.
    Value *X, *Z;
    const bool HasShift = match(B, m_OneUse(m_LShr(m_Value(X), m_Value(Z))));
    if (!HasShift)
      X = B;
  
    Value *Y;
    if (!match(Cmp->getOperand(0), m_c_And(m_Specific(X), m_Value(Y))))
      return nullptr;
  
    // ((X & Y) == 0) ? ((X >> Z) & 1) : 1 --> (X & (Y | (1 << Z))) != 0
    // ((X & Y) == 0) ? (X & 1) : 1 --> (X & (Y | 1)) != 0
    Constant *One = ConstantInt::get(SelType, 1);
    Value *MaskB = HasShift ? Builder.CreateShl(One, Z) : One;
    Value *FullMask = Builder.CreateOr(Y, MaskB);
    Value *MaskedX = Builder.CreateAnd(X, FullMask);
    Value *ICmpNeZero = Builder.CreateIsNotNull(MaskedX);
    return new ZExtInst(ICmpNeZero, SelType);
  }
  
  /// We want to turn:
  ///   (select (icmp sgt x, C), lshr (X, Y), ashr (X, Y)); iff C s>= -1
  ///   (select (icmp slt x, C), ashr (X, Y), lshr (X, Y)); iff C s>= 0
  /// into:
  ///   ashr (X, Y)
  static Value *foldSelectICmpLshrAshr(const ICmpInst *IC, Value *TrueVal,
                                       Value *FalseVal,
                                       InstCombiner::BuilderTy &Builder) {
    ICmpInst::Predicate Pred = IC->getPredicate();
    Value *CmpLHS = IC->getOperand(0);
    Value *CmpRHS = IC->getOperand(1);
    if (!CmpRHS->getType()->isIntOrIntVectorTy())
      return nullptr;
  
    Value *X, *Y;
    unsigned Bitwidth = CmpRHS->getType()->getScalarSizeInBits();
    if ((Pred != ICmpInst::ICMP_SGT ||
         !match(CmpRHS,
                m_SpecificInt_ICMP(ICmpInst::ICMP_SGE, APInt(Bitwidth, -1)))) &&
        (Pred != ICmpInst::ICMP_SLT ||
         !match(CmpRHS,
                m_SpecificInt_ICMP(ICmpInst::ICMP_SGE, APInt(Bitwidth, 0)))))
      return nullptr;
  
    // Canonicalize so that ashr is in FalseVal.
    if (Pred == ICmpInst::ICMP_SLT)
      std::swap(TrueVal, FalseVal);
  
    if (match(TrueVal, m_LShr(m_Value(X), m_Value(Y))) &&
        match(FalseVal, m_AShr(m_Specific(X), m_Specific(Y))) &&
        match(CmpLHS, m_Specific(X))) {
      const auto *Ashr = cast<Instruction>(FalseVal);
      // if lshr is not exact and ashr is, this new ashr must not be exact.
      bool IsExact = Ashr->isExact() && cast<Instruction>(TrueVal)->isExact();
      return Builder.CreateAShr(X, Y, IC->getName(), IsExact);
    }
  
    return nullptr;
  }
  
  /// We want to turn:
  ///   (select (icmp eq (and X, C1), 0), Y, (or Y, C2))
  /// into:
  ///   (or (shl (and X, C1), C3), Y)
  /// iff:
  ///   C1 and C2 are both powers of 2
  /// where:
  ///   C3 = Log(C2) - Log(C1)
  ///
  /// This transform handles cases where:
  /// 1. The icmp predicate is inverted
  /// 2. The select operands are reversed
  /// 3. The magnitude of C2 and C1 are flipped
  static Value *foldSelectICmpAndOr(const ICmpInst *IC, Value *TrueVal,
                                    Value *FalseVal,
                                    InstCombiner::BuilderTy &Builder) {
    // Only handle integer compares. Also, if this is a vector select, we need a
    // vector compare.
    if (!TrueVal->getType()->isIntOrIntVectorTy() ||
        TrueVal->getType()->isVectorTy() != IC->getType()->isVectorTy())
      return nullptr;
  
    Value *CmpLHS = IC->getOperand(0);
    Value *CmpRHS = IC->getOperand(1);
  
    Value *V;
    unsigned C1Log;
    bool IsEqualZero;
    bool NeedAnd = false;
    if (IC->isEquality()) {
      if (!match(CmpRHS, m_Zero()))
        return nullptr;
  
      const APInt *C1;
      if (!match(CmpLHS, m_And(m_Value(), m_Power2(C1))))
        return nullptr;
  
      V = CmpLHS;
      C1Log = C1->logBase2();
      IsEqualZero = IC->getPredicate() == ICmpInst::ICMP_EQ;
    } else if (IC->getPredicate() == ICmpInst::ICMP_SLT ||
               IC->getPredicate() == ICmpInst::ICMP_SGT) {
      // We also need to recognize (icmp slt (trunc (X)), 0) and
      // (icmp sgt (trunc (X)), -1).
      IsEqualZero = IC->getPredicate() == ICmpInst::ICMP_SGT;
      if ((IsEqualZero && !match(CmpRHS, m_AllOnes())) ||
          (!IsEqualZero && !match(CmpRHS, m_Zero())))
        return nullptr;
  
      if (!match(CmpLHS, m_OneUse(m_Trunc(m_Value(V)))))
        return nullptr;
  
      C1Log = CmpLHS->getType()->getScalarSizeInBits() - 1;
      NeedAnd = true;
    } else {
      return nullptr;
    }
  
    const APInt *C2;
    bool OrOnTrueVal = false;
    bool OrOnFalseVal = match(FalseVal, m_Or(m_Specific(TrueVal), m_Power2(C2)));
    if (!OrOnFalseVal)
      OrOnTrueVal = match(TrueVal, m_Or(m_Specific(FalseVal), m_Power2(C2)));
  
    if (!OrOnFalseVal && !OrOnTrueVal)
      return nullptr;
  
    Value *Y = OrOnFalseVal ? TrueVal : FalseVal;
  
    unsigned C2Log = C2->logBase2();
  
    bool NeedXor = (!IsEqualZero && OrOnFalseVal) || (IsEqualZero && OrOnTrueVal);
    bool NeedShift = C1Log != C2Log;
    bool NeedZExtTrunc = Y->getType()->getScalarSizeInBits() !=
                         V->getType()->getScalarSizeInBits();
  
    // Make sure we don't create more instructions than we save.
    Value *Or = OrOnFalseVal ? FalseVal : TrueVal;
    if ((NeedShift + NeedXor + NeedZExtTrunc) >
        (IC->hasOneUse() + Or->hasOneUse()))
      return nullptr;
  
    if (NeedAnd) {
      // Insert the AND instruction on the input to the truncate.
      APInt C1 = APInt::getOneBitSet(V->getType()->getScalarSizeInBits(), C1Log);
      V = Builder.CreateAnd(V, ConstantInt::get(V->getType(), C1));
    }
  
    if (C2Log > C1Log) {
      V = Builder.CreateZExtOrTrunc(V, Y->getType());
      V = Builder.CreateShl(V, C2Log - C1Log);
    } else if (C1Log > C2Log) {
      V = Builder.CreateLShr(V, C1Log - C2Log);
      V = Builder.CreateZExtOrTrunc(V, Y->getType());
    } else
      V = Builder.CreateZExtOrTrunc(V, Y->getType());
  
    if (NeedXor)
      V = Builder.CreateXor(V, *C2);
  
    return Builder.CreateOr(V, Y);
  }
  
  /// Canonicalize a set or clear of a masked set of constant bits to
  /// select-of-constants form.
  static Instruction *foldSetClearBits(SelectInst &Sel,
                                       InstCombiner::BuilderTy &Builder) {
    Value *Cond = Sel.getCondition();
    Value *T = Sel.getTrueValue();
    Value *F = Sel.getFalseValue();
    Type *Ty = Sel.getType();
    Value *X;
    const APInt *NotC, *C;
  
    // Cond ? (X & ~C) : (X | C) --> (X & ~C) | (Cond ? 0 : C)
    if (match(T, m_And(m_Value(X), m_APInt(NotC))) &&
        match(F, m_OneUse(m_Or(m_Specific(X), m_APInt(C)))) && *NotC == ~(*C)) {
      Constant *Zero = ConstantInt::getNullValue(Ty);
      Constant *OrC = ConstantInt::get(Ty, *C);
      Value *NewSel = Builder.CreateSelect(Cond, Zero, OrC, "masksel", &Sel);
      return BinaryOperator::CreateOr(T, NewSel);
    }
  
    // Cond ? (X | C) : (X & ~C) --> (X & ~C) | (Cond ? C : 0)
    if (match(F, m_And(m_Value(X), m_APInt(NotC))) &&
        match(T, m_OneUse(m_Or(m_Specific(X), m_APInt(C)))) && *NotC == ~(*C)) {
      Constant *Zero = ConstantInt::getNullValue(Ty);
      Constant *OrC = ConstantInt::get(Ty, *C);
      Value *NewSel = Builder.CreateSelect(Cond, OrC, Zero, "masksel", &Sel);
      return BinaryOperator::CreateOr(F, NewSel);
    }
  
    return nullptr;
  }
  
  /// Transform patterns such as (a > b) ? a - b : 0 into usub.sat(a, b).
  /// There are 8 commuted/swapped variants of this pattern.
  /// TODO: Also support a - UMIN(a,b) patterns.
  static Value *canonicalizeSaturatedSubtract(const ICmpInst *ICI,
                                              const Value *TrueVal,
                                              const Value *FalseVal,
                                              InstCombiner::BuilderTy &Builder) {
    ICmpInst::Predicate Pred = ICI->getPredicate();
    if (!ICmpInst::isUnsigned(Pred))
      return nullptr;
  
    // (b > a) ? 0 : a - b -> (b <= a) ? a - b : 0
    if (match(TrueVal, m_Zero())) {
      Pred = ICmpInst::getInversePredicate(Pred);
      std::swap(TrueVal, FalseVal);
    }
    if (!match(FalseVal, m_Zero()))
      return nullptr;
  
    Value *A = ICI->getOperand(0);
    Value *B = ICI->getOperand(1);
    if (Pred == ICmpInst::ICMP_ULE || Pred == ICmpInst::ICMP_ULT) {
      // (b < a) ? a - b : 0 -> (a > b) ? a - b : 0
      std::swap(A, B);
      Pred = ICmpInst::getSwappedPredicate(Pred);
    }
  
    assert((Pred == ICmpInst::ICMP_UGE || Pred == ICmpInst::ICMP_UGT) &&
           "Unexpected isUnsigned predicate!");
  
    // Ensure the sub is of the form:
    //  (a > b) ? a - b : 0 -> usub.sat(a, b)
    //  (a > b) ? b - a : 0 -> -usub.sat(a, b)
    // Checking for both a-b and a+(-b) as a constant.
    bool IsNegative = false;
    const APInt *C;
    if (match(TrueVal, m_Sub(m_Specific(B), m_Specific(A))) ||
        (match(A, m_APInt(C)) &&
         match(TrueVal, m_Add(m_Specific(B), m_SpecificInt(-*C)))))
      IsNegative = true;
    else if (!match(TrueVal, m_Sub(m_Specific(A), m_Specific(B))) &&
             !(match(B, m_APInt(C)) &&
               match(TrueVal, m_Add(m_Specific(A), m_SpecificInt(-*C)))))
      return nullptr;
  
    // If we are adding a negate and the sub and icmp are used anywhere else, we
    // would end up with more instructions.
    if (IsNegative && !TrueVal->hasOneUse() && !ICI->hasOneUse())
      return nullptr;
  
    // (a > b) ? a - b : 0 -> usub.sat(a, b)
    // (a > b) ? b - a : 0 -> -usub.sat(a, b)
    Value *Result = Builder.CreateBinaryIntrinsic(Intrinsic::usub_sat, A, B);
    if (IsNegative)
      Result = Builder.CreateNeg(Result);
    return Result;
  }
  
  static Value *canonicalizeSaturatedAdd(ICmpInst *Cmp, Value *TVal, Value *FVal,
                                         InstCombiner::BuilderTy &Builder) {
    if (!Cmp->hasOneUse())
      return nullptr;
  
    // Match unsigned saturated add with constant.
    Value *Cmp0 = Cmp->getOperand(0);
    Value *Cmp1 = Cmp->getOperand(1);
    ICmpInst::Predicate Pred = Cmp->getPredicate();
    Value *X;
    const APInt *C, *CmpC;
    if (Pred == ICmpInst::ICMP_ULT &&
        match(TVal, m_Add(m_Value(X), m_APInt(C))) && X == Cmp0 &&
        match(FVal, m_AllOnes()) && match(Cmp1, m_APInt(CmpC)) && *CmpC == ~*C) {
      // (X u< ~C) ? (X + C) : -1 --> uadd.sat(X, C)
      return Builder.CreateBinaryIntrinsic(
          Intrinsic::uadd_sat, X, ConstantInt::get(X->getType(), *C));
    }
  
    // Match unsigned saturated add of 2 variables with an unnecessary 'not'.
    // There are 8 commuted variants.
    // Canonicalize -1 (saturated result) to true value of the select. Just
    // swapping the compare operands is legal, because the selected value is the
    // same in case of equality, so we can interchange u< and u<=.
    if (match(FVal, m_AllOnes())) {
      std::swap(TVal, FVal);
      std::swap(Cmp0, Cmp1);
    }
    if (!match(TVal, m_AllOnes()))
      return nullptr;
  
    // Canonicalize predicate to 'ULT'.
    if (Pred == ICmpInst::ICMP_UGT) {
      Pred = ICmpInst::ICMP_ULT;
      std::swap(Cmp0, Cmp1);
    }
    if (Pred != ICmpInst::ICMP_ULT)
      return nullptr;
  
    // Match unsigned saturated add of 2 variables with an unnecessary 'not'.
    Value *Y;
    if (match(Cmp0, m_Not(m_Value(X))) &&
        match(FVal, m_c_Add(m_Specific(X), m_Value(Y))) && Y == Cmp1) {
      // (~X u< Y) ? -1 : (X + Y) --> uadd.sat(X, Y)
      // (~X u< Y) ? -1 : (Y + X) --> uadd.sat(X, Y)
      return Builder.CreateBinaryIntrinsic(Intrinsic::uadd_sat, X, Y);
    }
    // The 'not' op may be included in the sum but not the compare.
    X = Cmp0;
    Y = Cmp1;
    if (match(FVal, m_c_Add(m_Not(m_Specific(X)), m_Specific(Y)))) {
      // (X u< Y) ? -1 : (~X + Y) --> uadd.sat(~X, Y)
      // (X u< Y) ? -1 : (Y + ~X) --> uadd.sat(Y, ~X)
      BinaryOperator *BO = cast<BinaryOperator>(FVal);
      return Builder.CreateBinaryIntrinsic(
          Intrinsic::uadd_sat, BO->getOperand(0), BO->getOperand(1));
    }
    // The overflow may be detected via the add wrapping round.
    if (match(Cmp0, m_c_Add(m_Specific(Cmp1), m_Value(Y))) &&
        match(FVal, m_c_Add(m_Specific(Cmp1), m_Specific(Y)))) {
      // ((X + Y) u< X) ? -1 : (X + Y) --> uadd.sat(X, Y)
      // ((X + Y) u< Y) ? -1 : (X + Y) --> uadd.sat(X, Y)
      return Builder.CreateBinaryIntrinsic(Intrinsic::uadd_sat, Cmp1, Y);
    }
  
    return nullptr;
  }
  
  /// Fold the following code sequence:
  /// \code
  ///   int a = ctlz(x & -x);
  //    x ? 31 - a : a;
  /// \code
  ///
  /// into:
  ///   cttz(x)
  static Instruction *foldSelectCtlzToCttz(ICmpInst *ICI, Value *TrueVal,
                                           Value *FalseVal,
                                           InstCombiner::BuilderTy &Builder) {
    unsigned BitWidth = TrueVal->getType()->getScalarSizeInBits();
    if (!ICI->isEquality() || !match(ICI->getOperand(1), m_Zero()))
      return nullptr;
  
    if (ICI->getPredicate() == ICmpInst::ICMP_NE)
      std::swap(TrueVal, FalseVal);
  
    if (!match(FalseVal,
               m_Xor(m_Deferred(TrueVal), m_SpecificInt(BitWidth - 1))))
      return nullptr;
  
    if (!match(TrueVal, m_Intrinsic<Intrinsic::ctlz>()))
      return nullptr;
  
    Value *X = ICI->getOperand(0);
    auto *II = cast<IntrinsicInst>(TrueVal);
    if (!match(II->getOperand(0), m_c_And(m_Specific(X), m_Neg(m_Specific(X)))))
      return nullptr;
  
    Function *F = Intrinsic::getDeclaration(II->getModule(), Intrinsic::cttz,
                                            II->getType());
    return CallInst::Create(F, {X, II->getArgOperand(1)});
  }
  
  /// Attempt to fold a cttz/ctlz followed by a icmp plus select into a single
  /// call to cttz/ctlz with flag 'is_zero_undef' cleared.
  ///
  /// For example, we can fold the following code sequence:
  /// \code
  ///   %0 = tail call i32 @llvm.cttz.i32(i32 %x, i1 true)
  ///   %1 = icmp ne i32 %x, 0
  ///   %2 = select i1 %1, i32 %0, i32 32
  /// \code
  ///
  /// into:
  ///   %0 = tail call i32 @llvm.cttz.i32(i32 %x, i1 false)
  static Value *foldSelectCttzCtlz(ICmpInst *ICI, Value *TrueVal, Value *FalseVal,
                                   InstCombiner::BuilderTy &Builder) {
    ICmpInst::Predicate Pred = ICI->getPredicate();
    Value *CmpLHS = ICI->getOperand(0);
    Value *CmpRHS = ICI->getOperand(1);
  
    // Check if the condition value compares a value for equality against zero.
    if (!ICI->isEquality() || !match(CmpRHS, m_Zero()))
      return nullptr;
  
    Value *SelectArg = FalseVal;
    Value *ValueOnZero = TrueVal;
    if (Pred == ICmpInst::ICMP_NE)
      std::swap(SelectArg, ValueOnZero);
  
    // Skip zero extend/truncate.
    Value *Count = nullptr;
    if (!match(SelectArg, m_ZExt(m_Value(Count))) &&
        !match(SelectArg, m_Trunc(m_Value(Count))))
      Count = SelectArg;
  
    // Check that 'Count' is a call to intrinsic cttz/ctlz. Also check that the
    // input to the cttz/ctlz is used as LHS for the compare instruction.
    if (!match(Count, m_Intrinsic<Intrinsic::cttz>(m_Specific(CmpLHS))) &&
        !match(Count, m_Intrinsic<Intrinsic::ctlz>(m_Specific(CmpLHS))))
      return nullptr;
  
    IntrinsicInst *II = cast<IntrinsicInst>(Count);
  
    // Check if the value propagated on zero is a constant number equal to the
    // sizeof in bits of 'Count'.
    unsigned SizeOfInBits = Count->getType()->getScalarSizeInBits();
    if (match(ValueOnZero, m_SpecificInt(SizeOfInBits))) {
      // Explicitly clear the 'undef_on_zero' flag. It's always valid to go from
      // true to false on this flag, so we can replace it for all users.
      II->setArgOperand(1, ConstantInt::getFalse(II->getContext()));
      return SelectArg;
    }
  
    // The ValueOnZero is not the bitwidth. But if the cttz/ctlz (and optional
    // zext/trunc) have one use (ending at the select), the cttz/ctlz result will
    // not be used if the input is zero. Relax to 'undef_on_zero' for that case.
    if (II->hasOneUse() && SelectArg->hasOneUse() &&
        !match(II->getArgOperand(1), m_One()))
      II->setArgOperand(1, ConstantInt::getTrue(II->getContext()));
  
    return nullptr;
  }
  
  /// Return true if we find and adjust an icmp+select pattern where the compare
  /// is with a constant that can be incremented or decremented to match the
  /// minimum or maximum idiom.
  static bool adjustMinMax(SelectInst &Sel, ICmpInst &Cmp) {
    ICmpInst::Predicate Pred = Cmp.getPredicate();
    Value *CmpLHS = Cmp.getOperand(0);
    Value *CmpRHS = Cmp.getOperand(1);
    Value *TrueVal = Sel.getTrueValue();
    Value *FalseVal = Sel.getFalseValue();
  
    // We may move or edit the compare, so make sure the select is the only user.
    const APInt *CmpC;
    if (!Cmp.hasOneUse() || !match(CmpRHS, m_APInt(CmpC)))
      return false;
  
    // These transforms only work for selects of integers or vector selects of
    // integer vectors.
    Type *SelTy = Sel.getType();
    auto *SelEltTy = dyn_cast<IntegerType>(SelTy->getScalarType());
    if (!SelEltTy || SelTy->isVectorTy() != Cmp.getType()->isVectorTy())
      return false;
  
    Constant *AdjustedRHS;
    if (Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_SGT)
      AdjustedRHS = ConstantInt::get(CmpRHS->getType(), *CmpC + 1);
    else if (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_SLT)
      AdjustedRHS = ConstantInt::get(CmpRHS->getType(), *CmpC - 1);
    else
      return false;
  
    // X > C ? X : C+1  -->  X < C+1 ? C+1 : X
    // X < C ? X : C-1  -->  X > C-1 ? C-1 : X
    if ((CmpLHS == TrueVal && AdjustedRHS == FalseVal) ||
        (CmpLHS == FalseVal && AdjustedRHS == TrueVal)) {
      ; // Nothing to do here. Values match without any sign/zero extension.
    }
    // Types do not match. Instead of calculating this with mixed types, promote
    // all to the larger type. This enables scalar evolution to analyze this
    // expression.
    else if (CmpRHS->getType()->getScalarSizeInBits() < SelEltTy->getBitWidth()) {
      Constant *SextRHS = ConstantExpr::getSExt(AdjustedRHS, SelTy);
  
      // X = sext x; x >s c ? X : C+1 --> X = sext x; X <s C+1 ? C+1 : X
      // X = sext x; x <s c ? X : C-1 --> X = sext x; X >s C-1 ? C-1 : X
      // X = sext x; x >u c ? X : C+1 --> X = sext x; X <u C+1 ? C+1 : X
      // X = sext x; x <u c ? X : C-1 --> X = sext x; X >u C-1 ? C-1 : X
      if (match(TrueVal, m_SExt(m_Specific(CmpLHS))) && SextRHS == FalseVal) {
        CmpLHS = TrueVal;
        AdjustedRHS = SextRHS;
      } else if (match(FalseVal, m_SExt(m_Specific(CmpLHS))) &&
                 SextRHS == TrueVal) {
        CmpLHS = FalseVal;
        AdjustedRHS = SextRHS;
      } else if (Cmp.isUnsigned()) {
        Constant *ZextRHS = ConstantExpr::getZExt(AdjustedRHS, SelTy);
        // X = zext x; x >u c ? X : C+1 --> X = zext x; X <u C+1 ? C+1 : X
        // X = zext x; x <u c ? X : C-1 --> X = zext x; X >u C-1 ? C-1 : X
        // zext + signed compare cannot be changed:
        //    0xff <s 0x00, but 0x00ff >s 0x0000
        if (match(TrueVal, m_ZExt(m_Specific(CmpLHS))) && ZextRHS == FalseVal) {
          CmpLHS = TrueVal;
          AdjustedRHS = ZextRHS;
        } else if (match(FalseVal, m_ZExt(m_Specific(CmpLHS))) &&
                   ZextRHS == TrueVal) {
          CmpLHS = FalseVal;
          AdjustedRHS = ZextRHS;
        } else {
          return false;
        }
      } else {
        return false;
      }
    } else {
      return false;
    }
  
    Pred = ICmpInst::getSwappedPredicate(Pred);
    CmpRHS = AdjustedRHS;
    std::swap(FalseVal, TrueVal);
    Cmp.setPredicate(Pred);
    Cmp.setOperand(0, CmpLHS);
    Cmp.setOperand(1, CmpRHS);
    Sel.setOperand(1, TrueVal);
    Sel.setOperand(2, FalseVal);
    Sel.swapProfMetadata();
  
    // Move the compare instruction right before the select instruction. Otherwise
    // the sext/zext value may be defined after the compare instruction uses it.
    Cmp.moveBefore(&Sel);
  
    return true;
  }
  
  /// If this is an integer min/max (icmp + select) with a constant operand,
  /// create the canonical icmp for the min/max operation and canonicalize the
  /// constant to the 'false' operand of the select:
  /// select (icmp Pred X, C1), C2, X --> select (icmp Pred' X, C2), X, C2
  /// Note: if C1 != C2, this will change the icmp constant to the existing
  /// constant operand of the select.
  static Instruction *
  canonicalizeMinMaxWithConstant(SelectInst &Sel, ICmpInst &Cmp,
                                 InstCombiner &IC) {
    if (!Cmp.hasOneUse() || !isa<Constant>(Cmp.getOperand(1)))
      return nullptr;
  
    // Canonicalize the compare predicate based on whether we have min or max.
    Value *LHS, *RHS;
    SelectPatternResult SPR = matchSelectPattern(&Sel, LHS, RHS);
    if (!SelectPatternResult::isMinOrMax(SPR.Flavor))
      return nullptr;
  
    // Is this already canonical?
    ICmpInst::Predicate CanonicalPred = getMinMaxPred(SPR.Flavor);
    if (Cmp.getOperand(0) == LHS && Cmp.getOperand(1) == RHS &&
        Cmp.getPredicate() == CanonicalPred)
      return nullptr;
  
    // Bail out on unsimplified X-0 operand (due to some worklist management bug),
    // as this may cause an infinite combine loop. Let the sub be folded first.
    if (match(LHS, m_Sub(m_Value(), m_Zero())) ||
        match(RHS, m_Sub(m_Value(), m_Zero())))
      return nullptr;
  
    // Create the canonical compare and plug it into the select.
    IC.replaceOperand(Sel, 0, IC.Builder.CreateICmp(CanonicalPred, LHS, RHS));
  
    // If the select operands did not change, we're done.
    if (Sel.getTrueValue() == LHS && Sel.getFalseValue() == RHS)
      return &Sel;
  
    // If we are swapping the select operands, swap the metadata too.
    assert(Sel.getTrueValue() == RHS && Sel.getFalseValue() == LHS &&
           "Unexpected results from matchSelectPattern");
    Sel.swapValues();
    Sel.swapProfMetadata();
    return &Sel;
  }
  
  /// There are many select variants for each of ABS/NABS.
  /// In matchSelectPattern(), there are different compare constants, compare
  /// predicates/operands and select operands.
  /// In isKnownNegation(), there are different formats of negated operands.
  /// Canonicalize all these variants to 1 pattern.
  /// This makes CSE more likely.
  static Instruction *canonicalizeAbsNabs(SelectInst &Sel, ICmpInst &Cmp,
                                          InstCombiner &IC) {
    if (!Cmp.hasOneUse() || !isa<Constant>(Cmp.getOperand(1)))
      return nullptr;
  
    // Choose a sign-bit check for the compare (likely simpler for codegen).
    // ABS:  (X <s 0) ? -X : X
    // NABS: (X <s 0) ? X : -X
    Value *LHS, *RHS;
    SelectPatternFlavor SPF = matchSelectPattern(&Sel, LHS, RHS).Flavor;
    if (SPF != SelectPatternFlavor::SPF_ABS &&
        SPF != SelectPatternFlavor::SPF_NABS)
      return nullptr;
  
    Value *TVal = Sel.getTrueValue();
    Value *FVal = Sel.getFalseValue();
    assert(isKnownNegation(TVal, FVal) &&
           "Unexpected result from matchSelectPattern");
  
    // The compare may use the negated abs()/nabs() operand, or it may use
    // negation in non-canonical form such as: sub A, B.
    bool CmpUsesNegatedOp = match(Cmp.getOperand(0), m_Neg(m_Specific(TVal))) ||
                            match(Cmp.getOperand(0), m_Neg(m_Specific(FVal)));
  
    bool CmpCanonicalized = !CmpUsesNegatedOp &&
                            match(Cmp.getOperand(1), m_ZeroInt()) &&
                            Cmp.getPredicate() == ICmpInst::ICMP_SLT;
    bool RHSCanonicalized = match(RHS, m_Neg(m_Specific(LHS)));
  
    // Is this already canonical?
    if (CmpCanonicalized && RHSCanonicalized)
      return nullptr;
  
    // If RHS is not canonical but is used by other instructions, don't
    // canonicalize it and potentially increase the instruction count.
    if (!RHSCanonicalized)
      if (!(RHS->hasOneUse() || (RHS->hasNUses(2) && CmpUsesNegatedOp)))
        return nullptr;
  
    // Create the canonical compare: icmp slt LHS 0.
    if (!CmpCanonicalized) {
      Cmp.setPredicate(ICmpInst::ICMP_SLT);
      Cmp.setOperand(1, ConstantInt::getNullValue(Cmp.getOperand(0)->getType()));
      if (CmpUsesNegatedOp)
        Cmp.setOperand(0, LHS);
    }
  
    // Create the canonical RHS: RHS = sub (0, LHS).
    if (!RHSCanonicalized) {
      assert(RHS->hasOneUse() && "RHS use number is not right");
      RHS = IC.Builder.CreateNeg(LHS);
      if (TVal == LHS) {
        // Replace false value.
        IC.replaceOperand(Sel, 2, RHS);
        FVal = RHS;
      } else {
        // Replace true value.
        IC.replaceOperand(Sel, 1, RHS);
        TVal = RHS;
      }
    }
  
    // If the select operands do not change, we're done.
    if (SPF == SelectPatternFlavor::SPF_NABS) {
      if (TVal == LHS)
        return &Sel;
      assert(FVal == LHS && "Unexpected results from matchSelectPattern");
    } else {
      if (FVal == LHS)
        return &Sel;
      assert(TVal == LHS && "Unexpected results from matchSelectPattern");
    }
  
    // We are swapping the select operands, so swap the metadata too.
    Sel.swapValues();
    Sel.swapProfMetadata();
    return &Sel;
  }
  
  static Value *simplifyWithOpReplaced(Value *V, Value *Op, Value *ReplaceOp,
                                       const SimplifyQuery &Q) {
    // If this is a binary operator, try to simplify it with the replaced op
    // because we know Op and ReplaceOp are equivalant.
    // For example: V = X + 1, Op = X, ReplaceOp = 42
    // Simplifies as: add(42, 1) --> 43
    if (auto *BO = dyn_cast<BinaryOperator>(V)) {
      if (BO->getOperand(0) == Op)
        return SimplifyBinOp(BO->getOpcode(), ReplaceOp, BO->getOperand(1), Q);
      if (BO->getOperand(1) == Op)
        return SimplifyBinOp(BO->getOpcode(), BO->getOperand(0), ReplaceOp, Q);
    }
  
    return nullptr;
  }
  
  /// If we have a select with an equality comparison, then we know the value in
  /// one of the arms of the select. See if substituting this value into an arm
  /// and simplifying the result yields the same value as the other arm.
  ///
  /// To make this transform safe, we must drop poison-generating flags
  /// (nsw, etc) if we simplified to a binop because the select may be guarding
  /// that poison from propagating. If the existing binop already had no
  /// poison-generating flags, then this transform can be done by instsimplify.
  ///
  /// Consider:
  ///   %cmp = icmp eq i32 %x, 2147483647
  ///   %add = add nsw i32 %x, 1
  ///   %sel = select i1 %cmp, i32 -2147483648, i32 %add
  ///
  /// We can't replace %sel with %add unless we strip away the flags.
  /// TODO: Wrapping flags could be preserved in some cases with better analysis.
  static Value *foldSelectValueEquivalence(SelectInst &Sel, ICmpInst &Cmp,
                                           const SimplifyQuery &Q) {
    if (!Cmp.isEquality())
      return nullptr;
  
    // Canonicalize the pattern to ICMP_EQ by swapping the select operands.
    Value *TrueVal = Sel.getTrueValue(), *FalseVal = Sel.getFalseValue();
    if (Cmp.getPredicate() == ICmpInst::ICMP_NE)
      std::swap(TrueVal, FalseVal);
  
    // Try each equivalence substitution possibility.
    // We have an 'EQ' comparison, so the select's false value will propagate.
    // Example:
    // (X == 42) ? 43 : (X + 1) --> (X == 42) ? (X + 1) : (X + 1) --> X + 1
    // (X == 42) ? (X + 1) : 43 --> (X == 42) ? (42 + 1) : 43 --> 43
    Value *CmpLHS = Cmp.getOperand(0), *CmpRHS = Cmp.getOperand(1);
    if (simplifyWithOpReplaced(FalseVal, CmpLHS, CmpRHS, Q) == TrueVal ||
        simplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, Q) == TrueVal ||
        simplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, Q) == FalseVal ||
        simplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, Q) == FalseVal) {
      if (auto *FalseInst = dyn_cast<Instruction>(FalseVal))
        FalseInst->dropPoisonGeneratingFlags();
      return FalseVal;
    }
    return nullptr;
  }
  
  // See if this is a pattern like:
  //   %old_cmp1 = icmp slt i32 %x, C2
  //   %old_replacement = select i1 %old_cmp1, i32 %target_low, i32 %target_high
  //   %old_x_offseted = add i32 %x, C1
  //   %old_cmp0 = icmp ult i32 %old_x_offseted, C0
  //   %r = select i1 %old_cmp0, i32 %x, i32 %old_replacement
  // This can be rewritten as more canonical pattern:
  //   %new_cmp1 = icmp slt i32 %x, -C1
  //   %new_cmp2 = icmp sge i32 %x, C0-C1
  //   %new_clamped_low = select i1 %new_cmp1, i32 %target_low, i32 %x
  //   %r = select i1 %new_cmp2, i32 %target_high, i32 %new_clamped_low
  // Iff -C1 s<= C2 s<= C0-C1
  // Also ULT predicate can also be UGT iff C0 != -1 (+invert result)
  //      SLT predicate can also be SGT iff C2 != INT_MAX (+invert res.)
  static Instruction *canonicalizeClampLike(SelectInst &Sel0, ICmpInst &Cmp0,
                                            InstCombiner::BuilderTy &Builder) {
    Value *X = Sel0.getTrueValue();
    Value *Sel1 = Sel0.getFalseValue();
  
    // First match the condition of the outermost select.
    // Said condition must be one-use.
    if (!Cmp0.hasOneUse())
      return nullptr;
    Value *Cmp00 = Cmp0.getOperand(0);
    Constant *C0;
    if (!match(Cmp0.getOperand(1),
               m_CombineAnd(m_AnyIntegralConstant(), m_Constant(C0))))
      return nullptr;
    // Canonicalize Cmp0 into the form we expect.
    // FIXME: we shouldn't care about lanes that are 'undef' in the end?
    switch (Cmp0.getPredicate()) {
    case ICmpInst::Predicate::ICMP_ULT:
      break; // Great!
    case ICmpInst::Predicate::ICMP_ULE:
      // We'd have to increment C0 by one, and for that it must not have all-ones
      // element, but then it would have been canonicalized to 'ult' before
      // we get here. So we can't do anything useful with 'ule'.
      return nullptr;
    case ICmpInst::Predicate::ICMP_UGT:
      // We want to canonicalize it to 'ult', so we'll need to increment C0,
      // which again means it must not have any all-ones elements.
      if (!match(C0,
                 m_SpecificInt_ICMP(ICmpInst::Predicate::ICMP_NE,
                                    APInt::getAllOnesValue(
                                        C0->getType()->getScalarSizeInBits()))))
        return nullptr; // Can't do, have all-ones element[s].
      C0 = AddOne(C0);
      std::swap(X, Sel1);
      break;
    case ICmpInst::Predicate::ICMP_UGE:
      // The only way we'd get this predicate if this `icmp` has extra uses,
      // but then we won't be able to do this fold.
      return nullptr;
    default:
      return nullptr; // Unknown predicate.
    }
  
    // Now that we've canonicalized the ICmp, we know the X we expect;
    // the select in other hand should be one-use.
    if (!Sel1->hasOneUse())
      return nullptr;
  
    // We now can finish matching the condition of the outermost select:
    // it should either be the X itself, or an addition of some constant to X.
    Constant *C1;
    if (Cmp00 == X)
      C1 = ConstantInt::getNullValue(Sel0.getType());
    else if (!match(Cmp00,
                    m_Add(m_Specific(X),
                          m_CombineAnd(m_AnyIntegralConstant(), m_Constant(C1)))))
      return nullptr;
  
    Value *Cmp1;
    ICmpInst::Predicate Pred1;
    Constant *C2;
    Value *ReplacementLow, *ReplacementHigh;
    if (!match(Sel1, m_Select(m_Value(Cmp1), m_Value(ReplacementLow),
                              m_Value(ReplacementHigh))) ||
        !match(Cmp1,
               m_ICmp(Pred1, m_Specific(X),
                      m_CombineAnd(m_AnyIntegralConstant(), m_Constant(C2)))))
      return nullptr;
  
    if (!Cmp1->hasOneUse() && (Cmp00 == X || !Cmp00->hasOneUse()))
      return nullptr; // Not enough one-use instructions for the fold.
    // FIXME: this restriction could be relaxed if Cmp1 can be reused as one of
    //        two comparisons we'll need to build.
  
    // Canonicalize Cmp1 into the form we expect.
    // FIXME: we shouldn't care about lanes that are 'undef' in the end?
    switch (Pred1) {
    case ICmpInst::Predicate::ICMP_SLT:
      break;
    case ICmpInst::Predicate::ICMP_SLE:
      // We'd have to increment C2 by one, and for that it must not have signed
      // max element, but then it would have been canonicalized to 'slt' before
      // we get here. So we can't do anything useful with 'sle'.
      return nullptr;
    case ICmpInst::Predicate::ICMP_SGT:
      // We want to canonicalize it to 'slt', so we'll need to increment C2,
      // which again means it must not have any signed max elements.
      if (!match(C2,
                 m_SpecificInt_ICMP(ICmpInst::Predicate::ICMP_NE,
                                    APInt::getSignedMaxValue(
                                        C2->getType()->getScalarSizeInBits()))))
        return nullptr; // Can't do, have signed max element[s].
      C2 = AddOne(C2);
      LLVM_FALLTHROUGH;
    case ICmpInst::Predicate::ICMP_SGE:
      // Also non-canonical, but here we don't need to change C2,
      // so we don't have any restrictions on C2, so we can just handle it.
      std::swap(ReplacementLow, ReplacementHigh);
      break;
    default:
      return nullptr; // Unknown predicate.
    }
  
    // The thresholds of this clamp-like pattern.
    auto *ThresholdLowIncl = ConstantExpr::getNeg(C1);
    auto *ThresholdHighExcl = ConstantExpr::getSub(C0, C1);
  
    // The fold has a precondition 1: C2 s>= ThresholdLow
    auto *Precond1 = ConstantExpr::getICmp(ICmpInst::Predicate::ICMP_SGE, C2,
                                           ThresholdLowIncl);
    if (!match(Precond1, m_One()))
      return nullptr;
    // The fold has a precondition 2: C2 s<= ThresholdHigh
    auto *Precond2 = ConstantExpr::getICmp(ICmpInst::Predicate::ICMP_SLE, C2,
                                           ThresholdHighExcl);
    if (!match(Precond2, m_One()))
      return nullptr;
  
    // All good, finally emit the new pattern.
    Value *ShouldReplaceLow = Builder.CreateICmpSLT(X, ThresholdLowIncl);
    Value *ShouldReplaceHigh = Builder.CreateICmpSGE(X, ThresholdHighExcl);
    Value *MaybeReplacedLow =
        Builder.CreateSelect(ShouldReplaceLow, ReplacementLow, X);
    Instruction *MaybeReplacedHigh =
        SelectInst::Create(ShouldReplaceHigh, ReplacementHigh, MaybeReplacedLow);
  
    return MaybeReplacedHigh;
  }
  
  // If we have
  //  %cmp = icmp [canonical predicate] i32 %x, C0
  //  %r = select i1 %cmp, i32 %y, i32 C1
  // Where C0 != C1 and %x may be different from %y, see if the constant that we
  // will have if we flip the strictness of the predicate (i.e. without changing
  // the result) is identical to the C1 in select. If it matches we can change
  // original comparison to one with swapped predicate, reuse the constant,
  // and swap the hands of select.
  static Instruction *
  tryToReuseConstantFromSelectInComparison(SelectInst &Sel, ICmpInst &Cmp,
                                           InstCombiner &IC) {
    ICmpInst::Predicate Pred;
    Value *X;
    Constant *C0;
    if (!match(&Cmp, m_OneUse(m_ICmp(
                         Pred, m_Value(X),
                         m_CombineAnd(m_AnyIntegralConstant(), m_Constant(C0))))))
      return nullptr;
  
    // If comparison predicate is non-relational, we won't be able to do anything.
    if (ICmpInst::isEquality(Pred))
      return nullptr;
  
    // If comparison predicate is non-canonical, then we certainly won't be able
    // to make it canonical; canonicalizeCmpWithConstant() already tried.
    if (!isCanonicalPredicate(Pred))
      return nullptr;
  
    // If the [input] type of comparison and select type are different, lets abort
    // for now. We could try to compare constants with trunc/[zs]ext though.
    if (C0->getType() != Sel.getType())
      return nullptr;
  
    // FIXME: are there any magic icmp predicate+constant pairs we must not touch?
  
    Value *SelVal0, *SelVal1; // We do not care which one is from where.
    match(&Sel, m_Select(m_Value(), m_Value(SelVal0), m_Value(SelVal1)));
    // At least one of these values we are selecting between must be a constant
    // else we'll never succeed.
    if (!match(SelVal0, m_AnyIntegralConstant()) &&
        !match(SelVal1, m_AnyIntegralConstant()))
      return nullptr;
  
    // Does this constant C match any of the `select` values?
    auto MatchesSelectValue = [SelVal0, SelVal1](Constant *C) {
      return C->isElementWiseEqual(SelVal0) || C->isElementWiseEqual(SelVal1);
    };
  
    // If C0 *already* matches true/false value of select, we are done.
    if (MatchesSelectValue(C0))
      return nullptr;
  
    // Check the constant we'd have with flipped-strictness predicate.
    auto FlippedStrictness = getFlippedStrictnessPredicateAndConstant(Pred, C0);
    if (!FlippedStrictness)
      return nullptr;
  
    // If said constant doesn't match either, then there is no hope,
    if (!MatchesSelectValue(FlippedStrictness->second))
      return nullptr;
  
    // It matched! Lets insert the new comparison just before select.
    InstCombiner::BuilderTy::InsertPointGuard Guard(IC.Builder);
    IC.Builder.SetInsertPoint(&Sel);
  
    Pred = ICmpInst::getSwappedPredicate(Pred); // Yes, swapped.
    Value *NewCmp = IC.Builder.CreateICmp(Pred, X, FlippedStrictness->second,
                                          Cmp.getName() + ".inv");
    IC.replaceOperand(Sel, 0, NewCmp);
    Sel.swapValues();
    Sel.swapProfMetadata();
  
    return &Sel;
  }
  
  /// Visit a SelectInst that has an ICmpInst as its first operand.
  Instruction *InstCombiner::foldSelectInstWithICmp(SelectInst &SI,
                                                    ICmpInst *ICI) {
    if (Value *V = foldSelectValueEquivalence(SI, *ICI, SQ))
      return replaceInstUsesWith(SI, V);
  
    if (Instruction *NewSel = canonicalizeMinMaxWithConstant(SI, *ICI, *this))
      return NewSel;
  
    if (Instruction *NewAbs = canonicalizeAbsNabs(SI, *ICI, *this))
      return NewAbs;
  
    if (Instruction *NewAbs = canonicalizeClampLike(SI, *ICI, Builder))
      return NewAbs;
  
    if (Instruction *NewSel =
            tryToReuseConstantFromSelectInComparison(SI, *ICI, *this))
      return NewSel;
  
    bool Changed = adjustMinMax(SI, *ICI);
  
    if (Value *V = foldSelectICmpAnd(SI, ICI, Builder))
      return replaceInstUsesWith(SI, V);
  
    // NOTE: if we wanted to, this is where to detect integer MIN/MAX
    Value *TrueVal = SI.getTrueValue();
    Value *FalseVal = SI.getFalseValue();
    ICmpInst::Predicate Pred = ICI->getPredicate();
    Value *CmpLHS = ICI->getOperand(0);
    Value *CmpRHS = ICI->getOperand(1);
    if (CmpRHS != CmpLHS && isa<Constant>(CmpRHS)) {
      if (CmpLHS == TrueVal && Pred == ICmpInst::ICMP_EQ) {
        // Transform (X == C) ? X : Y -> (X == C) ? C : Y
        SI.setOperand(1, CmpRHS);
        Changed = true;
      } else if (CmpLHS == FalseVal && Pred == ICmpInst::ICMP_NE) {
        // Transform (X != C) ? Y : X -> (X != C) ? Y : C
        SI.setOperand(2, CmpRHS);
        Changed = true;
      }
    }
  
    // FIXME: This code is nearly duplicated in InstSimplify. Using/refactoring
    // decomposeBitTestICmp() might help.
    {
      unsigned BitWidth =
          DL.getTypeSizeInBits(TrueVal->getType()->getScalarType());
      APInt MinSignedValue = APInt::getSignedMinValue(BitWidth);
      Value *X;
      const APInt *Y, *C;
      bool TrueWhenUnset;
      bool IsBitTest = false;
      if (ICmpInst::isEquality(Pred) &&
          match(CmpLHS, m_And(m_Value(X), m_Power2(Y))) &&
          match(CmpRHS, m_Zero())) {
        IsBitTest = true;
        TrueWhenUnset = Pred == ICmpInst::ICMP_EQ;
      } else if (Pred == ICmpInst::ICMP_SLT && match(CmpRHS, m_Zero())) {
        X = CmpLHS;
        Y = &MinSignedValue;
        IsBitTest = true;
        TrueWhenUnset = false;
      } else if (Pred == ICmpInst::ICMP_SGT && match(CmpRHS, m_AllOnes())) {
        X = CmpLHS;
        Y = &MinSignedValue;
        IsBitTest = true;
        TrueWhenUnset = true;
      }
      if (IsBitTest) {
        Value *V = nullptr;
        // (X & Y) == 0 ? X : X ^ Y  --> X & ~Y
        if (TrueWhenUnset && TrueVal == X &&
            match(FalseVal, m_Xor(m_Specific(X), m_APInt(C))) && *Y == *C)
          V = Builder.CreateAnd(X, ~(*Y));
        // (X & Y) != 0 ? X ^ Y : X  --> X & ~Y
        else if (!TrueWhenUnset && FalseVal == X &&
                 match(TrueVal, m_Xor(m_Specific(X), m_APInt(C))) && *Y == *C)
          V = Builder.CreateAnd(X, ~(*Y));
        // (X & Y) == 0 ? X ^ Y : X  --> X | Y
        else if (TrueWhenUnset && FalseVal == X &&
                 match(TrueVal, m_Xor(m_Specific(X), m_APInt(C))) && *Y == *C)
          V = Builder.CreateOr(X, *Y);
        // (X & Y) != 0 ? X : X ^ Y  --> X | Y
        else if (!TrueWhenUnset && TrueVal == X &&
                 match(FalseVal, m_Xor(m_Specific(X), m_APInt(C))) && *Y == *C)
          V = Builder.CreateOr(X, *Y);
  
        if (V)
          return replaceInstUsesWith(SI, V);
      }
    }
  
    if (Instruction *V =
            foldSelectICmpAndAnd(SI.getType(), ICI, TrueVal, FalseVal, Builder))
      return V;
  
    if (Instruction *V = foldSelectCtlzToCttz(ICI, TrueVal, FalseVal, Builder))
      return V;
  
    if (Value *V = foldSelectICmpAndOr(ICI, TrueVal, FalseVal, Builder))
      return replaceInstUsesWith(SI, V);
  
    if (Value *V = foldSelectICmpLshrAshr(ICI, TrueVal, FalseVal, Builder))
      return replaceInstUsesWith(SI, V);
  
    if (Value *V = foldSelectCttzCtlz(ICI, TrueVal, FalseVal, Builder))
      return replaceInstUsesWith(SI, V);
  
    if (Value *V = canonicalizeSaturatedSubtract(ICI, TrueVal, FalseVal, Builder))
      return replaceInstUsesWith(SI, V);
  
    if (Value *V = canonicalizeSaturatedAdd(ICI, TrueVal, FalseVal, Builder))
      return replaceInstUsesWith(SI, V);
  
    return Changed ? &SI : nullptr;
  }
  
  /// SI is a select whose condition is a PHI node (but the two may be in
  /// different blocks). See if the true/false values (V) are live in all of the
  /// predecessor blocks of the PHI. For example, cases like this can't be mapped:
  ///
  ///   X = phi [ C1, BB1], [C2, BB2]
  ///   Y = add
  ///   Z = select X, Y, 0
  ///
  /// because Y is not live in BB1/BB2.
  static bool canSelectOperandBeMappingIntoPredBlock(const Value *V,
                                                     const SelectInst &SI) {
    // If the value is a non-instruction value like a constant or argument, it
    // can always be mapped.
    const Instruction *I = dyn_cast<Instruction>(V);
    if (!I) return true;
  
    // If V is a PHI node defined in the same block as the condition PHI, we can
    // map the arguments.
    const PHINode *CondPHI = cast<PHINode>(SI.getCondition());
  
    if (const PHINode *VP = dyn_cast<PHINode>(I))
      if (VP->getParent() == CondPHI->getParent())
        return true;
  
    // Otherwise, if the PHI and select are defined in the same block and if V is
    // defined in a different block, then we can transform it.
    if (SI.getParent() == CondPHI->getParent() &&
        I->getParent() != CondPHI->getParent())
      return true;
  
    // Otherwise we have a 'hard' case and we can't tell without doing more
    // detailed dominator based analysis, punt.
    return false;
  }
  
  /// We have an SPF (e.g. a min or max) of an SPF of the form:
  ///   SPF2(SPF1(A, B), C)
  Instruction *InstCombiner::foldSPFofSPF(Instruction *Inner,
                                          SelectPatternFlavor SPF1,
                                          Value *A, Value *B,
                                          Instruction &Outer,
                                          SelectPatternFlavor SPF2, Value *C) {
    if (Outer.getType() != Inner->getType())
      return nullptr;
  
    if (C == A || C == B) {
      // MAX(MAX(A, B), B) -> MAX(A, B)
      // MIN(MIN(a, b), a) -> MIN(a, b)
      // TODO: This could be done in instsimplify.
      if (SPF1 == SPF2 && SelectPatternResult::isMinOrMax(SPF1))
        return replaceInstUsesWith(Outer, Inner);
  
      // MAX(MIN(a, b), a) -> a
      // MIN(MAX(a, b), a) -> a
      // TODO: This could be done in instsimplify.
      if ((SPF1 == SPF_SMIN && SPF2 == SPF_SMAX) ||
          (SPF1 == SPF_SMAX && SPF2 == SPF_SMIN) ||
          (SPF1 == SPF_UMIN && SPF2 == SPF_UMAX) ||
          (SPF1 == SPF_UMAX && SPF2 == SPF_UMIN))
        return replaceInstUsesWith(Outer, C);
    }
  
    if (SPF1 == SPF2) {
      const APInt *CB, *CC;
      if (match(B, m_APInt(CB)) && match(C, m_APInt(CC))) {
        // MIN(MIN(A, 23), 97) -> MIN(A, 23)
        // MAX(MAX(A, 97), 23) -> MAX(A, 97)
        // TODO: This could be done in instsimplify.
        if ((SPF1 == SPF_UMIN && CB->ule(*CC)) ||
            (SPF1 == SPF_SMIN && CB->sle(*CC)) ||
            (SPF1 == SPF_UMAX && CB->uge(*CC)) ||
            (SPF1 == SPF_SMAX && CB->sge(*CC)))
          return replaceInstUsesWith(Outer, Inner);
  
        // MIN(MIN(A, 97), 23) -> MIN(A, 23)
        // MAX(MAX(A, 23), 97) -> MAX(A, 97)
        if ((SPF1 == SPF_UMIN && CB->ugt(*CC)) ||
            (SPF1 == SPF_SMIN && CB->sgt(*CC)) ||
            (SPF1 == SPF_UMAX && CB->ult(*CC)) ||
            (SPF1 == SPF_SMAX && CB->slt(*CC))) {
          Outer.replaceUsesOfWith(Inner, A);
          return &Outer;
        }
      }
    }
  
    // max(max(A, B), min(A, B)) --> max(A, B)
    // min(min(A, B), max(A, B)) --> min(A, B)
    // TODO: This could be done in instsimplify.
    if (SPF1 == SPF2 &&
        ((SPF1 == SPF_UMIN && match(C, m_c_UMax(m_Specific(A), m_Specific(B)))) ||
         (SPF1 == SPF_SMIN && match(C, m_c_SMax(m_Specific(A), m_Specific(B)))) ||
         (SPF1 == SPF_UMAX && match(C, m_c_UMin(m_Specific(A), m_Specific(B)))) ||
         (SPF1 == SPF_SMAX && match(C, m_c_SMin(m_Specific(A), m_Specific(B))))))
      return replaceInstUsesWith(Outer, Inner);
  
    // ABS(ABS(X)) -> ABS(X)
    // NABS(NABS(X)) -> NABS(X)
    // TODO: This could be done in instsimplify.
    if (SPF1 == SPF2 && (SPF1 == SPF_ABS || SPF1 == SPF_NABS)) {
      return replaceInstUsesWith(Outer, Inner);
    }
  
    // ABS(NABS(X)) -> ABS(X)
    // NABS(ABS(X)) -> NABS(X)
    if ((SPF1 == SPF_ABS && SPF2 == SPF_NABS) ||
        (SPF1 == SPF_NABS && SPF2 == SPF_ABS)) {
      SelectInst *SI = cast<SelectInst>(Inner);
      Value *NewSI =
          Builder.CreateSelect(SI->getCondition(), SI->getFalseValue(),
                               SI->getTrueValue(), SI->getName(), SI);
      return replaceInstUsesWith(Outer, NewSI);
    }
  
    auto IsFreeOrProfitableToInvert =
        [&](Value *V, Value *&NotV, bool &ElidesXor) {
      if (match(V, m_Not(m_Value(NotV)))) {
        // If V has at most 2 uses then we can get rid of the xor operation
        // entirely.
        ElidesXor |= !V->hasNUsesOrMore(3);
        return true;
      }
  
      if (isFreeToInvert(V, !V->hasNUsesOrMore(3))) {
        NotV = nullptr;
        return true;
      }
  
      return false;
    };
  
    Value *NotA, *NotB, *NotC;
    bool ElidesXor = false;
  
    // MIN(MIN(~A, ~B), ~C) == ~MAX(MAX(A, B), C)
    // MIN(MAX(~A, ~B), ~C) == ~MAX(MIN(A, B), C)
    // MAX(MIN(~A, ~B), ~C) == ~MIN(MAX(A, B), C)
    // MAX(MAX(~A, ~B), ~C) == ~MIN(MIN(A, B), C)
    //
    // This transform is performance neutral if we can elide at least one xor from
    // the set of three operands, since we'll be tacking on an xor at the very
    // end.
    if (SelectPatternResult::isMinOrMax(SPF1) &&
        SelectPatternResult::isMinOrMax(SPF2) &&
        IsFreeOrProfitableToInvert(A, NotA, ElidesXor) &&
        IsFreeOrProfitableToInvert(B, NotB, ElidesXor) &&
        IsFreeOrProfitableToInvert(C, NotC, ElidesXor) && ElidesXor) {
      if (!NotA)
        NotA = Builder.CreateNot(A);
      if (!NotB)
        NotB = Builder.CreateNot(B);
      if (!NotC)
        NotC = Builder.CreateNot(C);
  
      Value *NewInner = createMinMax(Builder, getInverseMinMaxFlavor(SPF1), NotA,
                                     NotB);
      Value *NewOuter = Builder.CreateNot(
          createMinMax(Builder, getInverseMinMaxFlavor(SPF2), NewInner, NotC));
      return replaceInstUsesWith(Outer, NewOuter);
    }
  
    return nullptr;
  }
  
  /// Turn select C, (X + Y), (X - Y) --> (X + (select C, Y, (-Y))).
  /// This is even legal for FP.
  static Instruction *foldAddSubSelect(SelectInst &SI,
                                       InstCombiner::BuilderTy &Builder) {
    Value *CondVal = SI.getCondition();
    Value *TrueVal = SI.getTrueValue();
    Value *FalseVal = SI.getFalseValue();
    auto *TI = dyn_cast<Instruction>(TrueVal);
    auto *FI = dyn_cast<Instruction>(FalseVal);
    if (!TI || !FI || !TI->hasOneUse() || !FI->hasOneUse())
      return nullptr;
  
    Instruction *AddOp = nullptr, *SubOp = nullptr;
    if ((TI->getOpcode() == Instruction::Sub &&
         FI->getOpcode() == Instruction::Add) ||
        (TI->getOpcode() == Instruction::FSub &&
         FI->getOpcode() == Instruction::FAdd)) {
      AddOp = FI;
      SubOp = TI;
    } else if ((FI->getOpcode() == Instruction::Sub &&
                TI->getOpcode() == Instruction::Add) ||
               (FI->getOpcode() == Instruction::FSub &&
                TI->getOpcode() == Instruction::FAdd)) {
      AddOp = TI;
      SubOp = FI;
    }
  
    if (AddOp) {
      Value *OtherAddOp = nullptr;
      if (SubOp->getOperand(0) == AddOp->getOperand(0)) {
        OtherAddOp = AddOp->getOperand(1);
      } else if (SubOp->getOperand(0) == AddOp->getOperand(1)) {
        OtherAddOp = AddOp->getOperand(0);
      }
  
      if (OtherAddOp) {
        // So at this point we know we have (Y -> OtherAddOp):
        //        select C, (add X, Y), (sub X, Z)
        Value *NegVal; // Compute -Z
        if (SI.getType()->isFPOrFPVectorTy()) {
          NegVal = Builder.CreateFNeg(SubOp->getOperand(1));
          if (Instruction *NegInst = dyn_cast<Instruction>(NegVal)) {
            FastMathFlags Flags = AddOp->getFastMathFlags();
            Flags &= SubOp->getFastMathFlags();
            NegInst->setFastMathFlags(Flags);
          }
        } else {
          NegVal = Builder.CreateNeg(SubOp->getOperand(1));
        }
  
        Value *NewTrueOp = OtherAddOp;
        Value *NewFalseOp = NegVal;
        if (AddOp != TI)
          std::swap(NewTrueOp, NewFalseOp);
        Value *NewSel = Builder.CreateSelect(CondVal, NewTrueOp, NewFalseOp,
                                             SI.getName() + ".p", &SI);
  
        if (SI.getType()->isFPOrFPVectorTy()) {
          Instruction *RI =
              BinaryOperator::CreateFAdd(SubOp->getOperand(0), NewSel);
  
          FastMathFlags Flags = AddOp->getFastMathFlags();
          Flags &= SubOp->getFastMathFlags();
          RI->setFastMathFlags(Flags);
          return RI;
        } else
          return BinaryOperator::CreateAdd(SubOp->getOperand(0), NewSel);
      }
    }
    return nullptr;
  }
  
  /// Turn X + Y overflows ? -1 : X + Y -> uadd_sat X, Y
  /// And X - Y overflows ? 0 : X - Y -> usub_sat X, Y
  /// Along with a number of patterns similar to:
  /// X + Y overflows ? (X < 0 ? INTMIN : INTMAX) : X + Y --> sadd_sat X, Y
  /// X - Y overflows ? (X > 0 ? INTMAX : INTMIN) : X - Y --> ssub_sat X, Y
  static Instruction *
  foldOverflowingAddSubSelect(SelectInst &SI, InstCombiner::BuilderTy &Builder) {
    Value *CondVal = SI.getCondition();
    Value *TrueVal = SI.getTrueValue();
    Value *FalseVal = SI.getFalseValue();
  
    WithOverflowInst *II;
    if (!match(CondVal, m_ExtractValue<1>(m_WithOverflowInst(II))) ||
        !match(FalseVal, m_ExtractValue<0>(m_Specific(II))))
      return nullptr;
  
    Value *X = II->getLHS();
    Value *Y = II->getRHS();
  
    auto IsSignedSaturateLimit = [&](Value *Limit, bool IsAdd) {
      Type *Ty = Limit->getType();
  
      ICmpInst::Predicate Pred;
      Value *TrueVal, *FalseVal, *Op;
      const APInt *C;
      if (!match(Limit, m_Select(m_ICmp(Pred, m_Value(Op), m_APInt(C)),
                                 m_Value(TrueVal), m_Value(FalseVal))))
        return false;
  
      auto IsZeroOrOne = [](const APInt &C) {
        return C.isNullValue() || C.isOneValue();
      };
      auto IsMinMax = [&](Value *Min, Value *Max) {
        APInt MinVal = APInt::getSignedMinValue(Ty->getScalarSizeInBits());
        APInt MaxVal = APInt::getSignedMaxValue(Ty->getScalarSizeInBits());
        return match(Min, m_SpecificInt(MinVal)) &&
               match(Max, m_SpecificInt(MaxVal));
      };
  
      if (Op != X && Op != Y)
        return false;
  
      if (IsAdd) {
        // X + Y overflows ? (X <s 0 ? INTMIN : INTMAX) : X + Y --> sadd_sat X, Y
        // X + Y overflows ? (X <s 1 ? INTMIN : INTMAX) : X + Y --> sadd_sat X, Y
        // X + Y overflows ? (Y <s 0 ? INTMIN : INTMAX) : X + Y --> sadd_sat X, Y
        // X + Y overflows ? (Y <s 1 ? INTMIN : INTMAX) : X + Y --> sadd_sat X, Y
        if (Pred == ICmpInst::ICMP_SLT && IsZeroOrOne(*C) &&
            IsMinMax(TrueVal, FalseVal))
          return true;
        // X + Y overflows ? (X >s 0 ? INTMAX : INTMIN) : X + Y --> sadd_sat X, Y
        // X + Y overflows ? (X >s -1 ? INTMAX : INTMIN) : X + Y --> sadd_sat X, Y
        // X + Y overflows ? (Y >s 0 ? INTMAX : INTMIN) : X + Y --> sadd_sat X, Y
        // X + Y overflows ? (Y >s -1 ? INTMAX : INTMIN) : X + Y --> sadd_sat X, Y
        if (Pred == ICmpInst::ICMP_SGT && IsZeroOrOne(*C + 1) &&
            IsMinMax(FalseVal, TrueVal))
          return true;
      } else {
        // X - Y overflows ? (X <s 0 ? INTMIN : INTMAX) : X - Y --> ssub_sat X, Y
        // X - Y overflows ? (X <s -1 ? INTMIN : INTMAX) : X - Y --> ssub_sat X, Y
        if (Op == X && Pred == ICmpInst::ICMP_SLT && IsZeroOrOne(*C + 1) &&
            IsMinMax(TrueVal, FalseVal))
          return true;
        // X - Y overflows ? (X >s -1 ? INTMAX : INTMIN) : X - Y --> ssub_sat X, Y
        // X - Y overflows ? (X >s -2 ? INTMAX : INTMIN) : X - Y --> ssub_sat X, Y
        if (Op == X && Pred == ICmpInst::ICMP_SGT && IsZeroOrOne(*C + 2) &&
            IsMinMax(FalseVal, TrueVal))
          return true;
        // X - Y overflows ? (Y <s 0 ? INTMAX : INTMIN) : X - Y --> ssub_sat X, Y
        // X - Y overflows ? (Y <s 1 ? INTMAX : INTMIN) : X - Y --> ssub_sat X, Y
        if (Op == Y && Pred == ICmpInst::ICMP_SLT && IsZeroOrOne(*C) &&
            IsMinMax(FalseVal, TrueVal))
          return true;
        // X - Y overflows ? (Y >s 0 ? INTMIN : INTMAX) : X - Y --> ssub_sat X, Y
        // X - Y overflows ? (Y >s -1 ? INTMIN : INTMAX) : X - Y --> ssub_sat X, Y
        if (Op == Y && Pred == ICmpInst::ICMP_SGT && IsZeroOrOne(*C + 1) &&
            IsMinMax(TrueVal, FalseVal))
          return true;
      }
  
      return false;
    };
  
    Intrinsic::ID NewIntrinsicID;
    if (II->getIntrinsicID() == Intrinsic::uadd_with_overflow &&
        match(TrueVal, m_AllOnes()))
      // X + Y overflows ? -1 : X + Y -> uadd_sat X, Y
      NewIntrinsicID = Intrinsic::uadd_sat;
    else if (II->getIntrinsicID() == Intrinsic::usub_with_overflow &&
             match(TrueVal, m_Zero()))
      // X - Y overflows ? 0 : X - Y -> usub_sat X, Y
      NewIntrinsicID = Intrinsic::usub_sat;
    else if (II->getIntrinsicID() == Intrinsic::sadd_with_overflow &&
             IsSignedSaturateLimit(TrueVal, /*IsAdd=*/true))
      // X + Y overflows ? (X <s 0 ? INTMIN : INTMAX) : X + Y --> sadd_sat X, Y
      // X + Y overflows ? (X <s 1 ? INTMIN : INTMAX) : X + Y --> sadd_sat X, Y
      // X + Y overflows ? (X >s 0 ? INTMAX : INTMIN) : X + Y --> sadd_sat X, Y
      // X + Y overflows ? (X >s -1 ? INTMAX : INTMIN) : X + Y --> sadd_sat X, Y
      // X + Y overflows ? (Y <s 0 ? INTMIN : INTMAX) : X + Y --> sadd_sat X, Y
      // X + Y overflows ? (Y <s 1 ? INTMIN : INTMAX) : X + Y --> sadd_sat X, Y
      // X + Y overflows ? (Y >s 0 ? INTMAX : INTMIN) : X + Y --> sadd_sat X, Y
      // X + Y overflows ? (Y >s -1 ? INTMAX : INTMIN) : X + Y --> sadd_sat X, Y
      NewIntrinsicID = Intrinsic::sadd_sat;
    else if (II->getIntrinsicID() == Intrinsic::ssub_with_overflow &&
             IsSignedSaturateLimit(TrueVal, /*IsAdd=*/false))
      // X - Y overflows ? (X <s 0 ? INTMIN : INTMAX) : X - Y --> ssub_sat X, Y
      // X - Y overflows ? (X <s -1 ? INTMIN : INTMAX) : X - Y --> ssub_sat X, Y
      // X - Y overflows ? (X >s -1 ? INTMAX : INTMIN) : X - Y --> ssub_sat X, Y
      // X - Y overflows ? (X >s -2 ? INTMAX : INTMIN) : X - Y --> ssub_sat X, Y
      // X - Y overflows ? (Y <s 0 ? INTMAX : INTMIN) : X - Y --> ssub_sat X, Y
      // X - Y overflows ? (Y <s 1 ? INTMAX : INTMIN) : X - Y --> ssub_sat X, Y
      // X - Y overflows ? (Y >s 0 ? INTMIN : INTMAX) : X - Y --> ssub_sat X, Y
      // X - Y overflows ? (Y >s -1 ? INTMIN : INTMAX) : X - Y --> ssub_sat X, Y
      NewIntrinsicID = Intrinsic::ssub_sat;
    else
      return nullptr;
  
    Function *F =
        Intrinsic::getDeclaration(SI.getModule(), NewIntrinsicID, SI.getType());
    return CallInst::Create(F, {X, Y});
  }
  
  Instruction *InstCombiner::foldSelectExtConst(SelectInst &Sel) {
    Constant *C;
    if (!match(Sel.getTrueValue(), m_Constant(C)) &&
        !match(Sel.getFalseValue(), m_Constant(C)))
      return nullptr;
  
    Instruction *ExtInst;
    if (!match(Sel.getTrueValue(), m_Instruction(ExtInst)) &&
        !match(Sel.getFalseValue(), m_Instruction(ExtInst)))
      return nullptr;
  
    auto ExtOpcode = ExtInst->getOpcode();
    if (ExtOpcode != Instruction::ZExt && ExtOpcode != Instruction::SExt)
      return nullptr;
  
    // If we are extending from a boolean type or if we can create a select that
    // has the same size operands as its condition, try to narrow the select.
    Value *X = ExtInst->getOperand(0);
    Type *SmallType = X->getType();
    Value *Cond = Sel.getCondition();
    auto *Cmp = dyn_cast<CmpInst>(Cond);
    if (!SmallType->isIntOrIntVectorTy(1) &&
        (!Cmp || Cmp->getOperand(0)->getType() != SmallType))
      return nullptr;
  
    // If the constant is the same after truncation to the smaller type and
    // extension to the original type, we can narrow the select.
    Type *SelType = Sel.getType();
    Constant *TruncC = ConstantExpr::getTrunc(C, SmallType);
    Constant *ExtC = ConstantExpr::getCast(ExtOpcode, TruncC, SelType);
    if (ExtC == C) {
      Value *TruncCVal = cast<Value>(TruncC);
      if (ExtInst == Sel.getFalseValue())
        std::swap(X, TruncCVal);
  
      // select Cond, (ext X), C --> ext(select Cond, X, C')
      // select Cond, C, (ext X) --> ext(select Cond, C', X)
      Value *NewSel = Builder.CreateSelect(Cond, X, TruncCVal, "narrow", &Sel);
      return CastInst::Create(Instruction::CastOps(ExtOpcode), NewSel, SelType);
    }
  
    // If one arm of the select is the extend of the condition, replace that arm
    // with the extension of the appropriate known bool value.
    if (Cond == X) {
      if (ExtInst == Sel.getTrueValue()) {
        // select X, (sext X), C --> select X, -1, C
        // select X, (zext X), C --> select X,  1, C
        Constant *One = ConstantInt::getTrue(SmallType);
        Constant *AllOnesOrOne = ConstantExpr::getCast(ExtOpcode, One, SelType);
        return SelectInst::Create(Cond, AllOnesOrOne, C, "", nullptr, &Sel);
      } else {
        // select X, C, (sext X) --> select X, C, 0
        // select X, C, (zext X) --> select X, C, 0
        Constant *Zero = ConstantInt::getNullValue(SelType);
        return SelectInst::Create(Cond, C, Zero, "", nullptr, &Sel);
      }
    }
  
    return nullptr;
  }
  
  /// Try to transform a vector select with a constant condition vector into a
  /// shuffle for easier combining with other shuffles and insert/extract.
  static Instruction *canonicalizeSelectToShuffle(SelectInst &SI) {
    Value *CondVal = SI.getCondition();
    Constant *CondC;
    if (!CondVal->getType()->isVectorTy() || !match(CondVal, m_Constant(CondC)))
      return nullptr;
  
    unsigned NumElts = cast<VectorType>(CondVal->getType())->getNumElements();
    SmallVector<int, 16> Mask;
    Mask.reserve(NumElts);
    for (unsigned i = 0; i != NumElts; ++i) {
      Constant *Elt = CondC->getAggregateElement(i);
      if (!Elt)
        return nullptr;
  
      if (Elt->isOneValue()) {
        // If the select condition element is true, choose from the 1st vector.
        Mask.push_back(i);
      } else if (Elt->isNullValue()) {
        // If the select condition element is false, choose from the 2nd vector.
        Mask.push_back(i + NumElts);
      } else if (isa<UndefValue>(Elt)) {
        // Undef in a select condition (choose one of the operands) does not mean
        // the same thing as undef in a shuffle mask (any value is acceptable), so
        // give up.
        return nullptr;
      } else {
        // Bail out on a constant expression.
        return nullptr;
      }
    }
  
    return new ShuffleVectorInst(SI.getTrueValue(), SI.getFalseValue(), Mask);
  }
  
  /// If we have a select of vectors with a scalar condition, try to convert that
  /// to a vector select by splatting the condition. A splat may get folded with
  /// other operations in IR and having all operands of a select be vector types
  /// is likely better for vector codegen.
  static Instruction *canonicalizeScalarSelectOfVecs(
      SelectInst &Sel, InstCombiner &IC) {
    auto *Ty = dyn_cast<VectorType>(Sel.getType());
    if (!Ty)
      return nullptr;
  
    // We can replace a single-use extract with constant index.
    Value *Cond = Sel.getCondition();
    if (!match(Cond, m_OneUse(m_ExtractElt(m_Value(), m_ConstantInt()))))
      return nullptr;
  
    // select (extelt V, Index), T, F --> select (splat V, Index), T, F
    // Splatting the extracted condition reduces code (we could directly create a
    // splat shuffle of the source vector to eliminate the intermediate step).
    unsigned NumElts = Ty->getNumElements();
    return IC.replaceOperand(Sel, 0, IC.Builder.CreateVectorSplat(NumElts, Cond));
  }
  
  /// Reuse bitcasted operands between a compare and select:
  /// select (cmp (bitcast C), (bitcast D)), (bitcast' C), (bitcast' D) -->
  /// bitcast (select (cmp (bitcast C), (bitcast D)), (bitcast C), (bitcast D))
  static Instruction *foldSelectCmpBitcasts(SelectInst &Sel,
                                            InstCombiner::BuilderTy &Builder) {
    Value *Cond = Sel.getCondition();
    Value *TVal = Sel.getTrueValue();
    Value *FVal = Sel.getFalseValue();
  
    CmpInst::Predicate Pred;
    Value *A, *B;
    if (!match(Cond, m_Cmp(Pred, m_Value(A), m_Value(B))))
      return nullptr;
  
    // The select condition is a compare instruction. If the select's true/false
    // values are already the same as the compare operands, there's nothing to do.
    if (TVal == A || TVal == B || FVal == A || FVal == B)
      return nullptr;
  
    Value *C, *D;
    if (!match(A, m_BitCast(m_Value(C))) || !match(B, m_BitCast(m_Value(D))))
      return nullptr;
  
    // select (cmp (bitcast C), (bitcast D)), (bitcast TSrc), (bitcast FSrc)
    Value *TSrc, *FSrc;
    if (!match(TVal, m_BitCast(m_Value(TSrc))) ||
        !match(FVal, m_BitCast(m_Value(FSrc))))
      return nullptr;
  
    // If the select true/false values are *different bitcasts* of the same source
    // operands, make the select operands the same as the compare operands and
    // cast the result. This is the canonical select form for min/max.
    Value *NewSel;
    if (TSrc == C && FSrc == D) {
      // select (cmp (bitcast C), (bitcast D)), (bitcast' C), (bitcast' D) -->
      // bitcast (select (cmp A, B), A, B)
      NewSel = Builder.CreateSelect(Cond, A, B, "", &Sel);
    } else if (TSrc == D && FSrc == C) {
      // select (cmp (bitcast C), (bitcast D)), (bitcast' D), (bitcast' C) -->
      // bitcast (select (cmp A, B), B, A)
      NewSel = Builder.CreateSelect(Cond, B, A, "", &Sel);
    } else {
      return nullptr;
    }
    return CastInst::CreateBitOrPointerCast(NewSel, Sel.getType());
  }
  
  /// Try to eliminate select instructions that test the returned flag of cmpxchg
  /// instructions.
  ///
  /// If a select instruction tests the returned flag of a cmpxchg instruction and
  /// selects between the returned value of the cmpxchg instruction its compare
  /// operand, the result of the select will always be equal to its false value.
  /// For example:
  ///
  ///   %0 = cmpxchg i64* %ptr, i64 %compare, i64 %new_value seq_cst seq_cst
  ///   %1 = extractvalue { i64, i1 } %0, 1
  ///   %2 = extractvalue { i64, i1 } %0, 0
  ///   %3 = select i1 %1, i64 %compare, i64 %2
  ///   ret i64 %3
  ///
  /// The returned value of the cmpxchg instruction (%2) is the original value
  /// located at %ptr prior to any update. If the cmpxchg operation succeeds, %2
  /// must have been equal to %compare. Thus, the result of the select is always
  /// equal to %2, and the code can be simplified to:
  ///
  ///   %0 = cmpxchg i64* %ptr, i64 %compare, i64 %new_value seq_cst seq_cst
  ///   %1 = extractvalue { i64, i1 } %0, 0
  ///   ret i64 %1
  ///
  static Value *foldSelectCmpXchg(SelectInst &SI) {
    // A helper that determines if V is an extractvalue instruction whose
    // aggregate operand is a cmpxchg instruction and whose single index is equal
    // to I. If such conditions are true, the helper returns the cmpxchg
    // instruction; otherwise, a nullptr is returned.
    auto isExtractFromCmpXchg = [](Value *V, unsigned I) -> AtomicCmpXchgInst * {
      auto *Extract = dyn_cast<ExtractValueInst>(V);
      if (!Extract)
        return nullptr;
      if (Extract->getIndices()[0] != I)
        return nullptr;
      return dyn_cast<AtomicCmpXchgInst>(Extract->getAggregateOperand());
    };
  
    // If the select has a single user, and this user is a select instruction that
    // we can simplify, skip the cmpxchg simplification for now.
    if (SI.hasOneUse())
      if (auto *Select = dyn_cast<SelectInst>(SI.user_back()))
        if (Select->getCondition() == SI.getCondition())
          if (Select->getFalseValue() == SI.getTrueValue() ||
              Select->getTrueValue() == SI.getFalseValue())
            return nullptr;
  
    // Ensure the select condition is the returned flag of a cmpxchg instruction.
    auto *CmpXchg = isExtractFromCmpXchg(SI.getCondition(), 1);
    if (!CmpXchg)
      return nullptr;
  
    // Check the true value case: The true value of the select is the returned
    // value of the same cmpxchg used by the condition, and the false value is the
    // cmpxchg instruction's compare operand.
    if (auto *X = isExtractFromCmpXchg(SI.getTrueValue(), 0))
      if (X == CmpXchg && X->getCompareOperand() == SI.getFalseValue())
        return SI.getFalseValue();
  
    // Check the false value case: The false value of the select is the returned
    // value of the same cmpxchg used by the condition, and the true value is the
    // cmpxchg instruction's compare operand.
    if (auto *X = isExtractFromCmpXchg(SI.getFalseValue(), 0))
      if (X == CmpXchg && X->getCompareOperand() == SI.getTrueValue())
        return SI.getFalseValue();
  
    return nullptr;
  }
  
  static Instruction *moveAddAfterMinMax(SelectPatternFlavor SPF, Value *X,
                                         Value *Y,
                                         InstCombiner::BuilderTy &Builder) {
    assert(SelectPatternResult::isMinOrMax(SPF) && "Expected min/max pattern");
    bool IsUnsigned = SPF == SelectPatternFlavor::SPF_UMIN ||
                      SPF == SelectPatternFlavor::SPF_UMAX;
    // TODO: If InstSimplify could fold all cases where C2 <= C1, we could change
    // the constant value check to an assert.
    Value *A;
    const APInt *C1, *C2;
    if (IsUnsigned && match(X, m_NUWAdd(m_Value(A), m_APInt(C1))) &&
        match(Y, m_APInt(C2)) && C2->uge(*C1) && X->hasNUses(2)) {
      // umin (add nuw A, C1), C2 --> add nuw (umin A, C2 - C1), C1
      // umax (add nuw A, C1), C2 --> add nuw (umax A, C2 - C1), C1
      Value *NewMinMax = createMinMax(Builder, SPF, A,
                                      ConstantInt::get(X->getType(), *C2 - *C1));
      return BinaryOperator::CreateNUW(BinaryOperator::Add, NewMinMax,
                                       ConstantInt::get(X->getType(), *C1));
    }
  
    if (!IsUnsigned && match(X, m_NSWAdd(m_Value(A), m_APInt(C1))) &&
        match(Y, m_APInt(C2)) && X->hasNUses(2)) {
      bool Overflow;
      APInt Diff = C2->ssub_ov(*C1, Overflow);
      if (!Overflow) {
        // smin (add nsw A, C1), C2 --> add nsw (smin A, C2 - C1), C1
        // smax (add nsw A, C1), C2 --> add nsw (smax A, C2 - C1), C1
        Value *NewMinMax = createMinMax(Builder, SPF, A,
                                        ConstantInt::get(X->getType(), Diff));
        return BinaryOperator::CreateNSW(BinaryOperator::Add, NewMinMax,
                                         ConstantInt::get(X->getType(), *C1));
      }
    }
  
    return nullptr;
  }
  
  /// Match a sadd_sat or ssub_sat which is using min/max to clamp the value.
  Instruction *InstCombiner::matchSAddSubSat(SelectInst &MinMax1) {
    Type *Ty = MinMax1.getType();
  
    // We are looking for a tree of:
    // max(INT_MIN, min(INT_MAX, add(sext(A), sext(B))))
    // Where the min and max could be reversed
    Instruction *MinMax2;
    BinaryOperator *AddSub;
    const APInt *MinValue, *MaxValue;
    if (match(&MinMax1, m_SMin(m_Instruction(MinMax2), m_APInt(MaxValue)))) {
      if (!match(MinMax2, m_SMax(m_BinOp(AddSub), m_APInt(MinValue))))
        return nullptr;
    } else if (match(&MinMax1,
                     m_SMax(m_Instruction(MinMax2), m_APInt(MinValue)))) {
      if (!match(MinMax2, m_SMin(m_BinOp(AddSub), m_APInt(MaxValue))))
        return nullptr;
    } else
      return nullptr;
  
    // Check that the constants clamp a saturate, and that the new type would be
    // sensible to convert to.
    if (!(*MaxValue + 1).isPowerOf2() || -*MinValue != *MaxValue + 1)
      return nullptr;
    // In what bitwidth can this be treated as saturating arithmetics?
    unsigned NewBitWidth = (*MaxValue + 1).logBase2() + 1;
    // FIXME: This isn't quite right for vectors, but using the scalar type is a
    // good first approximation for what should be done there.
    if (!shouldChangeType(Ty->getScalarType()->getIntegerBitWidth(), NewBitWidth))
      return nullptr;
  
    // Also make sure that the number of uses is as expected. The "3"s are for the
    // the two items of min/max (the compare and the select).
    if (MinMax2->hasNUsesOrMore(3) || AddSub->hasNUsesOrMore(3))
      return nullptr;
  
    // Create the new type (which can be a vector type)
    Type *NewTy = Ty->getWithNewBitWidth(NewBitWidth);
    // Match the two extends from the add/sub
    Value *A, *B;
    if(!match(AddSub, m_BinOp(m_SExt(m_Value(A)), m_SExt(m_Value(B)))))
      return nullptr;
    // And check the incoming values are of a type smaller than or equal to the
    // size of the saturation. Otherwise the higher bits can cause different
    // results.
    if (A->getType()->getScalarSizeInBits() > NewBitWidth ||
        B->getType()->getScalarSizeInBits() > NewBitWidth)
      return nullptr;
  
    Intrinsic::ID IntrinsicID;
    if (AddSub->getOpcode() == Instruction::Add)
      IntrinsicID = Intrinsic::sadd_sat;
    else if (AddSub->getOpcode() == Instruction::Sub)
      IntrinsicID = Intrinsic::ssub_sat;
    else
      return nullptr;
  
    // Finally create and return the sat intrinsic, truncated to the new type
    Function *F = Intrinsic::getDeclaration(MinMax1.getModule(), IntrinsicID, NewTy);
    Value *AT = Builder.CreateSExt(A, NewTy);
    Value *BT = Builder.CreateSExt(B, NewTy);
    Value *Sat = Builder.CreateCall(F, {AT, BT});
    return CastInst::Create(Instruction::SExt, Sat, Ty);
  }
  
  /// Reduce a sequence of min/max with a common operand.
  static Instruction *factorizeMinMaxTree(SelectPatternFlavor SPF, Value *LHS,
                                          Value *RHS,
                                          InstCombiner::BuilderTy &Builder) {
    assert(SelectPatternResult::isMinOrMax(SPF) && "Expected a min/max");
    // TODO: Allow FP min/max with nnan/nsz.
    if (!LHS->getType()->isIntOrIntVectorTy())
      return nullptr;
  
    // Match 3 of the same min/max ops. Example: umin(umin(), umin()).
    Value *A, *B, *C, *D;
    SelectPatternResult L = matchSelectPattern(LHS, A, B);
    SelectPatternResult R = matchSelectPattern(RHS, C, D);
    if (SPF != L.Flavor || L.Flavor != R.Flavor)
      return nullptr;
  
    // Look for a common operand. The use checks are different than usual because
    // a min/max pattern typically has 2 uses of each op: 1 by the cmp and 1 by
    // the select.
    Value *MinMaxOp = nullptr;
    Value *ThirdOp = nullptr;
    if (!LHS->hasNUsesOrMore(3) && RHS->hasNUsesOrMore(3)) {
      // If the LHS is only used in this chain and the RHS is used outside of it,
      // reuse the RHS min/max because that will eliminate the LHS.
      if (D == A || C == A) {
        // min(min(a, b), min(c, a)) --> min(min(c, a), b)
        // min(min(a, b), min(a, d)) --> min(min(a, d), b)
        MinMaxOp = RHS;
        ThirdOp = B;
      } else if (D == B || C == B) {
        // min(min(a, b), min(c, b)) --> min(min(c, b), a)
        // min(min(a, b), min(b, d)) --> min(min(b, d), a)
        MinMaxOp = RHS;
        ThirdOp = A;
      }
    } else if (!RHS->hasNUsesOrMore(3)) {
      // Reuse the LHS. This will eliminate the RHS.
      if (D == A || D == B) {
        // min(min(a, b), min(c, a)) --> min(min(a, b), c)
        // min(min(a, b), min(c, b)) --> min(min(a, b), c)
        MinMaxOp = LHS;
        ThirdOp = C;
      } else if (C == A || C == B) {
        // min(min(a, b), min(b, d)) --> min(min(a, b), d)
        // min(min(a, b), min(c, b)) --> min(min(a, b), d)
        MinMaxOp = LHS;
        ThirdOp = D;
      }
    }
    if (!MinMaxOp || !ThirdOp)
      return nullptr;
  
    CmpInst::Predicate P = getMinMaxPred(SPF);
    Value *CmpABC = Builder.CreateICmp(P, MinMaxOp, ThirdOp);
    return SelectInst::Create(CmpABC, MinMaxOp, ThirdOp);
  }
  
  /// Try to reduce a rotate pattern that includes a compare and select into a
  /// funnel shift intrinsic. Example:
  /// rotl32(a, b) --> (b == 0 ? a : ((a >> (32 - b)) | (a << b)))
  ///              --> call llvm.fshl.i32(a, a, b)
  static Instruction *foldSelectRotate(SelectInst &Sel) {
    // The false value of the select must be a rotate of the true value.
    Value *Or0, *Or1;
    if (!match(Sel.getFalseValue(), m_OneUse(m_Or(m_Value(Or0), m_Value(Or1)))))
      return nullptr;
  
    Value *TVal = Sel.getTrueValue();
    Value *SA0, *SA1;
    if (!match(Or0, m_OneUse(m_LogicalShift(m_Specific(TVal), m_Value(SA0)))) ||
        !match(Or1, m_OneUse(m_LogicalShift(m_Specific(TVal), m_Value(SA1)))))
      return nullptr;
  
    auto ShiftOpcode0 = cast<BinaryOperator>(Or0)->getOpcode();
    auto ShiftOpcode1 = cast<BinaryOperator>(Or1)->getOpcode();
    if (ShiftOpcode0 == ShiftOpcode1)
      return nullptr;
  
    // We have one of these patterns so far:
    // select ?, TVal, (or (lshr TVal, SA0), (shl TVal, SA1))
    // select ?, TVal, (or (shl TVal, SA0), (lshr TVal, SA1))
    // This must be a power-of-2 rotate for a bitmasking transform to be valid.
    unsigned Width = Sel.getType()->getScalarSizeInBits();
    if (!isPowerOf2_32(Width))
      return nullptr;
  
    // Check the shift amounts to see if they are an opposite pair.
    Value *ShAmt;
    if (match(SA1, m_OneUse(m_Sub(m_SpecificInt(Width), m_Specific(SA0)))))
      ShAmt = SA0;
    else if (match(SA0, m_OneUse(m_Sub(m_SpecificInt(Width), m_Specific(SA1)))))
      ShAmt = SA1;
    else
      return nullptr;
  
    // Finally, see if the select is filtering out a shift-by-zero.
    Value *Cond = Sel.getCondition();
    ICmpInst::Predicate Pred;
    if (!match(Cond, m_OneUse(m_ICmp(Pred, m_Specific(ShAmt), m_ZeroInt()))) ||
        Pred != ICmpInst::ICMP_EQ)
      return nullptr;
  
    // This is a rotate that avoids shift-by-bitwidth UB in a suboptimal way.
    // Convert to funnel shift intrinsic.
    bool IsFshl = (ShAmt == SA0 && ShiftOpcode0 == BinaryOperator::Shl) ||
                  (ShAmt == SA1 && ShiftOpcode1 == BinaryOperator::Shl);
    Intrinsic::ID IID = IsFshl ? Intrinsic::fshl : Intrinsic::fshr;
    Function *F = Intrinsic::getDeclaration(Sel.getModule(), IID, Sel.getType());
    return IntrinsicInst::Create(F, { TVal, TVal, ShAmt });
  }
  
  static Instruction *foldSelectToCopysign(SelectInst &Sel,
                                           InstCombiner::BuilderTy &Builder) {
    Value *Cond = Sel.getCondition();
    Value *TVal = Sel.getTrueValue();
    Value *FVal = Sel.getFalseValue();
    Type *SelType = Sel.getType();
  
    // Match select ?, TC, FC where the constants are equal but negated.
    // TODO: Generalize to handle a negated variable operand?
    const APFloat *TC, *FC;
    if (!match(TVal, m_APFloat(TC)) || !match(FVal, m_APFloat(FC)) ||
        !abs(*TC).bitwiseIsEqual(abs(*FC)))
      return nullptr;
  
    assert(TC != FC && "Expected equal select arms to simplify");
  
    Value *X;
    const APInt *C;
    bool IsTrueIfSignSet;
    ICmpInst::Predicate Pred;
    if (!match(Cond, m_OneUse(m_ICmp(Pred, m_BitCast(m_Value(X)), m_APInt(C)))) ||
        !isSignBitCheck(Pred, *C, IsTrueIfSignSet) || X->getType() != SelType)
      return nullptr;
  
    // If needed, negate the value that will be the sign argument of the copysign:
    // (bitcast X) <  0 ? -TC :  TC --> copysign(TC,  X)
    // (bitcast X) <  0 ?  TC : -TC --> copysign(TC, -X)
    // (bitcast X) >= 0 ? -TC :  TC --> copysign(TC, -X)
    // (bitcast X) >= 0 ?  TC : -TC --> copysign(TC,  X)
    if (IsTrueIfSignSet ^ TC->isNegative())
      X = Builder.CreateFNegFMF(X, &Sel);
  
    // Canonicalize the magnitude argument as the positive constant since we do
    // not care about its sign.
    Value *MagArg = TC->isNegative() ? FVal : TVal;
    Function *F = Intrinsic::getDeclaration(Sel.getModule(), Intrinsic::copysign,
                                            Sel.getType());
    Instruction *CopySign = IntrinsicInst::Create(F, { MagArg, X });
    CopySign->setFastMathFlags(Sel.getFastMathFlags());
    return CopySign;
  }
  
  Instruction *InstCombiner::foldVectorSelect(SelectInst &Sel) {
    auto *VecTy = dyn_cast<FixedVectorType>(Sel.getType());
    if (!VecTy)
      return nullptr;
  
    unsigned NumElts = VecTy->getNumElements();
    APInt UndefElts(NumElts, 0);
    APInt AllOnesEltMask(APInt::getAllOnesValue(NumElts));
    if (Value *V = SimplifyDemandedVectorElts(&Sel, AllOnesEltMask, UndefElts)) {
      if (V != &Sel)
        return replaceInstUsesWith(Sel, V);
      return &Sel;
    }
  
    return nullptr;
  }
  
  Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
    Value *CondVal = SI.getCondition();
    Value *TrueVal = SI.getTrueValue();
    Value *FalseVal = SI.getFalseValue();
    Type *SelType = SI.getType();
  
    // FIXME: Remove this workaround when freeze related patches are done.
    // For select with undef operand which feeds into an equality comparison,
    // don't simplify it so loop unswitch can know the equality comparison
    // may have an undef operand. This is a workaround for PR31652 caused by
    // descrepancy about branch on undef between LoopUnswitch and GVN.
    if (isa<UndefValue>(TrueVal) || isa<UndefValue>(FalseVal)) {
      if (llvm::any_of(SI.users(), [&](User *U) {
            ICmpInst *CI = dyn_cast<ICmpInst>(U);
            if (CI && CI->isEquality())
              return true;
            return false;
          })) {
        return nullptr;
      }
    }
  
    if (Value *V = SimplifySelectInst(CondVal, TrueVal, FalseVal,
                                      SQ.getWithInstruction(&SI)))
      return replaceInstUsesWith(SI, V);
  
    if (Instruction *I = canonicalizeSelectToShuffle(SI))
      return I;
  
    if (Instruction *I = canonicalizeScalarSelectOfVecs(SI, *this))
      return I;
  
    // Canonicalize a one-use integer compare with a non-canonical predicate by
    // inverting the predicate and swapping the select operands. This matches a
    // compare canonicalization for conditional branches.
    // TODO: Should we do the same for FP compares?
    CmpInst::Predicate Pred;
    if (match(CondVal, m_OneUse(m_ICmp(Pred, m_Value(), m_Value()))) &&
        !isCanonicalPredicate(Pred)) {
      // Swap true/false values and condition.
      CmpInst *Cond = cast<CmpInst>(CondVal);
      Cond->setPredicate(CmpInst::getInversePredicate(Pred));
      SI.swapValues();
      SI.swapProfMetadata();
      Worklist.push(Cond);
      return &SI;
    }
  
    if (SelType->isIntOrIntVectorTy(1) &&
        TrueVal->getType() == CondVal->getType()) {
      if (match(TrueVal, m_One())) {
        // Change: A = select B, true, C --> A = or B, C
        return BinaryOperator::CreateOr(CondVal, FalseVal);
      }
      if (match(TrueVal, m_Zero())) {
        // Change: A = select B, false, C --> A = and !B, C
        Value *NotCond = Builder.CreateNot(CondVal, "not." + CondVal->getName());
        return BinaryOperator::CreateAnd(NotCond, FalseVal);
      }
      if (match(FalseVal, m_Zero())) {
        // Change: A = select B, C, false --> A = and B, C
        return BinaryOperator::CreateAnd(CondVal, TrueVal);
      }
      if (match(FalseVal, m_One())) {
        // Change: A = select B, C, true --> A = or !B, C
        Value *NotCond = Builder.CreateNot(CondVal, "not." + CondVal->getName());
        return BinaryOperator::CreateOr(NotCond, TrueVal);
      }
  
      // select a, a, b  -> a | b
      // select a, b, a  -> a & b
      if (CondVal == TrueVal)
        return BinaryOperator::CreateOr(CondVal, FalseVal);
      if (CondVal == FalseVal)
        return BinaryOperator::CreateAnd(CondVal, TrueVal);
  
      // select a, ~a, b -> (~a) & b
      // select a, b, ~a -> (~a) | b
      if (match(TrueVal, m_Not(m_Specific(CondVal))))
        return BinaryOperator::CreateAnd(TrueVal, FalseVal);
      if (match(FalseVal, m_Not(m_Specific(CondVal))))
        return BinaryOperator::CreateOr(TrueVal, FalseVal);
    }
  
    // Selecting between two integer or vector splat integer constants?
    //
    // Note that we don't handle a scalar select of vectors:
    // select i1 %c, <2 x i8> <1, 1>, <2 x i8> <0, 0>
    // because that may need 3 instructions to splat the condition value:
    // extend, insertelement, shufflevector.
    if (SelType->isIntOrIntVectorTy() &&
        CondVal->getType()->isVectorTy() == SelType->isVectorTy()) {
      // select C, 1, 0 -> zext C to int
      if (match(TrueVal, m_One()) && match(FalseVal, m_Zero()))
        return new ZExtInst(CondVal, SelType);
  
      // select C, -1, 0 -> sext C to int
      if (match(TrueVal, m_AllOnes()) && match(FalseVal, m_Zero()))
        return new SExtInst(CondVal, SelType);
  
      // select C, 0, 1 -> zext !C to int
      if (match(TrueVal, m_Zero()) && match(FalseVal, m_One())) {
        Value *NotCond = Builder.CreateNot(CondVal, "not." + CondVal->getName());
        return new ZExtInst(NotCond, SelType);
      }
  
      // select C, 0, -1 -> sext !C to int
      if (match(TrueVal, m_Zero()) && match(FalseVal, m_AllOnes())) {
        Value *NotCond = Builder.CreateNot(CondVal, "not." + CondVal->getName());
        return new SExtInst(NotCond, SelType);
      }
    }
  
    // See if we are selecting two values based on a comparison of the two values.
    if (FCmpInst *FCI = dyn_cast<FCmpInst>(CondVal)) {
      Value *Cmp0 = FCI->getOperand(0), *Cmp1 = FCI->getOperand(1);
      if ((Cmp0 == TrueVal && Cmp1 == FalseVal) ||
          (Cmp0 == FalseVal && Cmp1 == TrueVal)) {
        // Canonicalize to use ordered comparisons by swapping the select
        // operands.
        //
        // e.g.
        // (X ugt Y) ? X : Y -> (X ole Y) ? Y : X
        if (FCI->hasOneUse() && FCmpInst::isUnordered(FCI->getPredicate())) {
          FCmpInst::Predicate InvPred = FCI->getInversePredicate();
          IRBuilder<>::FastMathFlagGuard FMFG(Builder);
          // FIXME: The FMF should propagate from the select, not the fcmp.
          Builder.setFastMathFlags(FCI->getFastMathFlags());
          Value *NewCond = Builder.CreateFCmp(InvPred, Cmp0, Cmp1,
                                              FCI->getName() + ".inv");
          Value *NewSel = Builder.CreateSelect(NewCond, FalseVal, TrueVal);
          return replaceInstUsesWith(SI, NewSel);
        }
  
        // NOTE: if we wanted to, this is where to detect MIN/MAX
      }
    }
  
    // Canonicalize select with fcmp to fabs(). -0.0 makes this tricky. We need
    // fast-math-flags (nsz) or fsub with +0.0 (not fneg) for this to work. We
    // also require nnan because we do not want to unintentionally change the
    // sign of a NaN value.
    // FIXME: These folds should test/propagate FMF from the select, not the
    //        fsub or fneg.
    // (X <= +/-0.0) ? (0.0 - X) : X --> fabs(X)
    Instruction *FSub;
    if (match(CondVal, m_FCmp(Pred, m_Specific(FalseVal), m_AnyZeroFP())) &&
        match(TrueVal, m_FSub(m_PosZeroFP(), m_Specific(FalseVal))) &&
        match(TrueVal, m_Instruction(FSub)) && FSub->hasNoNaNs() &&
        (Pred == FCmpInst::FCMP_OLE || Pred == FCmpInst::FCMP_ULE)) {
      Value *Fabs = Builder.CreateUnaryIntrinsic(Intrinsic::fabs, FalseVal, FSub);
      return replaceInstUsesWith(SI, Fabs);
    }
    // (X >  +/-0.0) ? X : (0.0 - X) --> fabs(X)
    if (match(CondVal, m_FCmp(Pred, m_Specific(TrueVal), m_AnyZeroFP())) &&
        match(FalseVal, m_FSub(m_PosZeroFP(), m_Specific(TrueVal))) &&
        match(FalseVal, m_Instruction(FSub)) && FSub->hasNoNaNs() &&
        (Pred == FCmpInst::FCMP_OGT || Pred == FCmpInst::FCMP_UGT)) {
      Value *Fabs = Builder.CreateUnaryIntrinsic(Intrinsic::fabs, TrueVal, FSub);
      return replaceInstUsesWith(SI, Fabs);
    }
    // With nnan and nsz:
    // (X <  +/-0.0) ? -X : X --> fabs(X)
    // (X <= +/-0.0) ? -X : X --> fabs(X)
    Instruction *FNeg;
    if (match(CondVal, m_FCmp(Pred, m_Specific(FalseVal), m_AnyZeroFP())) &&
        match(TrueVal, m_FNeg(m_Specific(FalseVal))) &&
        match(TrueVal, m_Instruction(FNeg)) &&
        FNeg->hasNoNaNs() && FNeg->hasNoSignedZeros() &&
        (Pred == FCmpInst::FCMP_OLT || Pred == FCmpInst::FCMP_OLE ||
         Pred == FCmpInst::FCMP_ULT || Pred == FCmpInst::FCMP_ULE)) {
      Value *Fabs = Builder.CreateUnaryIntrinsic(Intrinsic::fabs, FalseVal, FNeg);
      return replaceInstUsesWith(SI, Fabs);
    }
    // With nnan and nsz:
    // (X >  +/-0.0) ? X : -X --> fabs(X)
    // (X >= +/-0.0) ? X : -X --> fabs(X)
    if (match(CondVal, m_FCmp(Pred, m_Specific(TrueVal), m_AnyZeroFP())) &&
        match(FalseVal, m_FNeg(m_Specific(TrueVal))) &&
        match(FalseVal, m_Instruction(FNeg)) &&
        FNeg->hasNoNaNs() && FNeg->hasNoSignedZeros() &&
        (Pred == FCmpInst::FCMP_OGT || Pred == FCmpInst::FCMP_OGE ||
         Pred == FCmpInst::FCMP_UGT || Pred == FCmpInst::FCMP_UGE)) {
      Value *Fabs = Builder.CreateUnaryIntrinsic(Intrinsic::fabs, TrueVal, FNeg);
      return replaceInstUsesWith(SI, Fabs);
    }
  
    // See if we are selecting two values based on a comparison of the two values.
    if (ICmpInst *ICI = dyn_cast<ICmpInst>(CondVal))
      if (Instruction *Result = foldSelectInstWithICmp(SI, ICI))
        return Result;
  
    if (Instruction *Add = foldAddSubSelect(SI, Builder))
      return Add;
    if (Instruction *Add = foldOverflowingAddSubSelect(SI, Builder))
      return Add;
    if (Instruction *Or = foldSetClearBits(SI, Builder))
      return Or;
  
    // Turn (select C, (op X, Y), (op X, Z)) -> (op X, (select C, Y, Z))
    auto *TI = dyn_cast<Instruction>(TrueVal);
    auto *FI = dyn_cast<Instruction>(FalseVal);
    if (TI && FI && TI->getOpcode() == FI->getOpcode())
      if (Instruction *IV = foldSelectOpOp(SI, TI, FI))
        return IV;
  
    if (Instruction *I = foldSelectExtConst(SI))
      return I;
  
    // See if we can fold the select into one of our operands.
    if (SelType->isIntOrIntVectorTy() || SelType->isFPOrFPVectorTy()) {
      if (Instruction *FoldI = foldSelectIntoOp(SI, TrueVal, FalseVal))
        return FoldI;
  
      Value *LHS, *RHS;
      Instruction::CastOps CastOp;
      SelectPatternResult SPR = matchSelectPattern(&SI, LHS, RHS, &CastOp);
      auto SPF = SPR.Flavor;
      if (SPF) {
        Value *LHS2, *RHS2;
        if (SelectPatternFlavor SPF2 = matchSelectPattern(LHS, LHS2, RHS2).Flavor)
          if (Instruction *R = foldSPFofSPF(cast<Instruction>(LHS), SPF2, LHS2,
                                            RHS2, SI, SPF, RHS))
            return R;
        if (SelectPatternFlavor SPF2 = matchSelectPattern(RHS, LHS2, RHS2).Flavor)
          if (Instruction *R = foldSPFofSPF(cast<Instruction>(RHS), SPF2, LHS2,
                                            RHS2, SI, SPF, LHS))
            return R;
        // TODO.
        // ABS(-X) -> ABS(X)
      }
  
      if (SelectPatternResult::isMinOrMax(SPF)) {
        // Canonicalize so that
        // - type casts are outside select patterns.
        // - float clamp is transformed to min/max pattern
  
        bool IsCastNeeded = LHS->getType() != SelType;
        Value *CmpLHS = cast<CmpInst>(CondVal)->getOperand(0);
        Value *CmpRHS = cast<CmpInst>(CondVal)->getOperand(1);
        if (IsCastNeeded ||
            (LHS->getType()->isFPOrFPVectorTy() &&
             ((CmpLHS != LHS && CmpLHS != RHS) ||
              (CmpRHS != LHS && CmpRHS != RHS)))) {
          CmpInst::Predicate MinMaxPred = getMinMaxPred(SPF, SPR.Ordered);
  
          Value *Cmp;
          if (CmpInst::isIntPredicate(MinMaxPred)) {
            Cmp = Builder.CreateICmp(MinMaxPred, LHS, RHS);
          } else {
            IRBuilder<>::FastMathFlagGuard FMFG(Builder);
            auto FMF =
                cast<FPMathOperator>(SI.getCondition())->getFastMathFlags();
            Builder.setFastMathFlags(FMF);
            Cmp = Builder.CreateFCmp(MinMaxPred, LHS, RHS);
          }
  
          Value *NewSI = Builder.CreateSelect(Cmp, LHS, RHS, SI.getName(), &SI);
          if (!IsCastNeeded)
            return replaceInstUsesWith(SI, NewSI);
  
          Value *NewCast = Builder.CreateCast(CastOp, NewSI, SelType);
          return replaceInstUsesWith(SI, NewCast);
        }
  
        // MAX(~a, ~b) -> ~MIN(a, b)
        // MAX(~a, C)  -> ~MIN(a, ~C)
        // MIN(~a, ~b) -> ~MAX(a, b)
        // MIN(~a, C)  -> ~MAX(a, ~C)
        auto moveNotAfterMinMax = [&](Value *X, Value *Y) -> Instruction * {
          Value *A;
          if (match(X, m_Not(m_Value(A))) && !X->hasNUsesOrMore(3) &&
              !isFreeToInvert(A, A->hasOneUse()) &&
              // Passing false to only consider m_Not and constants.
              isFreeToInvert(Y, false)) {
            Value *B = Builder.CreateNot(Y);
            Value *NewMinMax = createMinMax(Builder, getInverseMinMaxFlavor(SPF),
                                            A, B);
            // Copy the profile metadata.
            if (MDNode *MD = SI.getMetadata(LLVMContext::MD_prof)) {
              cast<SelectInst>(NewMinMax)->setMetadata(LLVMContext::MD_prof, MD);
              // Swap the metadata if the operands are swapped.
              if (X == SI.getFalseValue() && Y == SI.getTrueValue())
                cast<SelectInst>(NewMinMax)->swapProfMetadata();
            }
  
            return BinaryOperator::CreateNot(NewMinMax);
          }
  
          return nullptr;
        };
  
        if (Instruction *I = moveNotAfterMinMax(LHS, RHS))
          return I;
        if (Instruction *I = moveNotAfterMinMax(RHS, LHS))
          return I;
  
        if (Instruction *I = moveAddAfterMinMax(SPF, LHS, RHS, Builder))
          return I;
  
        if (Instruction *I = factorizeMinMaxTree(SPF, LHS, RHS, Builder))
          return I;
        if (Instruction *I = matchSAddSubSat(SI))
          return I;
      }
    }
  
    // Canonicalize select of FP values where NaN and -0.0 are not valid as
    // minnum/maxnum intrinsics.
    if (isa<FPMathOperator>(SI) && SI.hasNoNaNs() && SI.hasNoSignedZeros()) {
      Value *X, *Y;
      if (match(&SI, m_OrdFMax(m_Value(X), m_Value(Y))))
        return replaceInstUsesWith(
            SI, Builder.CreateBinaryIntrinsic(Intrinsic::maxnum, X, Y, &SI));
  
      if (match(&SI, m_OrdFMin(m_Value(X), m_Value(Y))))
        return replaceInstUsesWith(
            SI, Builder.CreateBinaryIntrinsic(Intrinsic::minnum, X, Y, &SI));
    }
  
    // See if we can fold the select into a phi node if the condition is a select.
    if (auto *PN = dyn_cast<PHINode>(SI.getCondition()))
      // The true/false values have to be live in the PHI predecessor's blocks.
      if (canSelectOperandBeMappingIntoPredBlock(TrueVal, SI) &&
          canSelectOperandBeMappingIntoPredBlock(FalseVal, SI))
        if (Instruction *NV = foldOpIntoPhi(SI, PN))
          return NV;
  
    if (SelectInst *TrueSI = dyn_cast<SelectInst>(TrueVal)) {
      if (TrueSI->getCondition()->getType() == CondVal->getType()) {
        // select(C, select(C, a, b), c) -> select(C, a, c)
        if (TrueSI->getCondition() == CondVal) {
          if (SI.getTrueValue() == TrueSI->getTrueValue())
            return nullptr;
          return replaceOperand(SI, 1, TrueSI->getTrueValue());
        }
        // select(C0, select(C1, a, b), b) -> select(C0&C1, a, b)
        // We choose this as normal form to enable folding on the And and shortening
        // paths for the values (this helps GetUnderlyingObjects() for example).
        if (TrueSI->getFalseValue() == FalseVal && TrueSI->hasOneUse()) {
          Value *And = Builder.CreateAnd(CondVal, TrueSI->getCondition());
          replaceOperand(SI, 0, And);
          replaceOperand(SI, 1, TrueSI->getTrueValue());
          return &SI;
        }
      }
    }
    if (SelectInst *FalseSI = dyn_cast<SelectInst>(FalseVal)) {
      if (FalseSI->getCondition()->getType() == CondVal->getType()) {
        // select(C, a, select(C, b, c)) -> select(C, a, c)
        if (FalseSI->getCondition() == CondVal) {
          if (SI.getFalseValue() == FalseSI->getFalseValue())
            return nullptr;
          return replaceOperand(SI, 2, FalseSI->getFalseValue());
        }
        // select(C0, a, select(C1, a, b)) -> select(C0|C1, a, b)
        if (FalseSI->getTrueValue() == TrueVal && FalseSI->hasOneUse()) {
          Value *Or = Builder.CreateOr(CondVal, FalseSI->getCondition());
          replaceOperand(SI, 0, Or);
          replaceOperand(SI, 2, FalseSI->getFalseValue());
          return &SI;
        }
      }
    }
  
    auto canMergeSelectThroughBinop = [](BinaryOperator *BO) {
      // The select might be preventing a division by 0.
      switch (BO->getOpcode()) {
      default:
        return true;
      case Instruction::SRem:
      case Instruction::URem:
      case Instruction::SDiv:
      case Instruction::UDiv:
        return false;
      }
    };
  
    // Try to simplify a binop sandwiched between 2 selects with the same
    // condition.
    // select(C, binop(select(C, X, Y), W), Z) -> select(C, binop(X, W), Z)
    BinaryOperator *TrueBO;
    if (match(TrueVal, m_OneUse(m_BinOp(TrueBO))) &&
        canMergeSelectThroughBinop(TrueBO)) {
      if (auto *TrueBOSI = dyn_cast<SelectInst>(TrueBO->getOperand(0))) {
        if (TrueBOSI->getCondition() == CondVal) {
          replaceOperand(*TrueBO, 0, TrueBOSI->getTrueValue());
          Worklist.push(TrueBO);
          return &SI;
        }
      }
      if (auto *TrueBOSI = dyn_cast<SelectInst>(TrueBO->getOperand(1))) {
        if (TrueBOSI->getCondition() == CondVal) {
          replaceOperand(*TrueBO, 1, TrueBOSI->getTrueValue());
          Worklist.push(TrueBO);
          return &SI;
        }
      }
    }
  
    // select(C, Z, binop(select(C, X, Y), W)) -> select(C, Z, binop(Y, W))
    BinaryOperator *FalseBO;
    if (match(FalseVal, m_OneUse(m_BinOp(FalseBO))) &&
        canMergeSelectThroughBinop(FalseBO)) {
      if (auto *FalseBOSI = dyn_cast<SelectInst>(FalseBO->getOperand(0))) {
        if (FalseBOSI->getCondition() == CondVal) {
          replaceOperand(*FalseBO, 0, FalseBOSI->getFalseValue());
          Worklist.push(FalseBO);
          return &SI;
        }
      }
      if (auto *FalseBOSI = dyn_cast<SelectInst>(FalseBO->getOperand(1))) {
        if (FalseBOSI->getCondition() == CondVal) {
          replaceOperand(*FalseBO, 1, FalseBOSI->getFalseValue());
          Worklist.push(FalseBO);
          return &SI;
        }
      }
    }
  
    Value *NotCond;
    if (match(CondVal, m_Not(m_Value(NotCond)))) {
      replaceOperand(SI, 0, NotCond);
      SI.swapValues();
      SI.swapProfMetadata();
      return &SI;
    }
  
    if (Instruction *I = foldVectorSelect(SI))
      return I;
  
    // If we can compute the condition, there's no need for a select.
    // Like the above fold, we are attempting to reduce compile-time cost by
    // putting this fold here with limitations rather than in InstSimplify.
    // The motivation for this call into value tracking is to take advantage of
    // the assumption cache, so make sure that is populated.
    if (!CondVal->getType()->isVectorTy() && !AC.assumptions().empty()) {
      KnownBits Known(1);
      computeKnownBits(CondVal, Known, 0, &SI);
      if (Known.One.isOneValue())
        return replaceInstUsesWith(SI, TrueVal);
      if (Known.Zero.isOneValue())
        return replaceInstUsesWith(SI, FalseVal);
    }
  
    if (Instruction *BitCastSel = foldSelectCmpBitcasts(SI, Builder))
      return BitCastSel;
  
    // Simplify selects that test the returned flag of cmpxchg instructions.
    if (Value *V = foldSelectCmpXchg(SI))
      return replaceInstUsesWith(SI, V);
  
    if (Instruction *Select = foldSelectBinOpIdentity(SI, TLI, *this))
      return Select;
  
    if (Instruction *Rot = foldSelectRotate(SI))
      return Rot;
  
    if (Instruction *Copysign = foldSelectToCopysign(SI, Builder))
      return Copysign;
  
    return nullptr;
  }
  