text: //===- GVN.cpp - Eliminate redundant values and loads ---------------------===//
  //
  // 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 pass performs global value numbering to eliminate fully redundant
  // instructions.  It also performs simple dead load elimination.
  //
  // Note that this pass does the value numbering itself; it does not use the
  // ValueNumbering analysis passes.
  //
  //===----------------------------------------------------------------------===//
  
  #include "llvm/Transforms/Scalar/GVN.h"
  #include "llvm/ADT/DenseMap.h"
  #include "llvm/ADT/DepthFirstIterator.h"
  #include "llvm/ADT/Hashing.h"
  #include "llvm/ADT/MapVector.h"
  #include "llvm/ADT/PointerIntPair.h"
  #include "llvm/ADT/PostOrderIterator.h"
  #include "llvm/ADT/STLExtras.h"
  #include "llvm/ADT/SetVector.h"
  #include "llvm/ADT/SmallPtrSet.h"
  #include "llvm/ADT/SmallVector.h"
  #include "llvm/ADT/Statistic.h"
  #include "llvm/Analysis/AliasAnalysis.h"
  #include "llvm/Analysis/AssumptionCache.h"
  #include "llvm/Analysis/CFG.h"
  #include "llvm/Analysis/DomTreeUpdater.h"
  #include "llvm/Analysis/GlobalsModRef.h"
  #include "llvm/Analysis/InstructionSimplify.h"
  #include "llvm/Analysis/LoopInfo.h"
  #include "llvm/Analysis/MemoryBuiltins.h"
  #include "llvm/Analysis/MemoryDependenceAnalysis.h"
  #include "llvm/Analysis/OptimizationRemarkEmitter.h"
  #include "llvm/Analysis/PHITransAddr.h"
  #include "llvm/Analysis/TargetLibraryInfo.h"
  #include "llvm/Analysis/ValueTracking.h"
  #include "llvm/Config/llvm-config.h"
  #include "llvm/IR/Attributes.h"
  #include "llvm/IR/BasicBlock.h"
  #include "llvm/IR/CallSite.h"
  #include "llvm/IR/Constant.h"
  #include "llvm/IR/Constants.h"
  #include "llvm/IR/DataLayout.h"
  #include "llvm/IR/DebugInfoMetadata.h"
  #include "llvm/IR/DebugLoc.h"
  #include "llvm/IR/Dominators.h"
  #include "llvm/IR/Function.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/LLVMContext.h"
  #include "llvm/IR/Metadata.h"
  #include "llvm/IR/Module.h"
  #include "llvm/IR/Operator.h"
  #include "llvm/IR/PassManager.h"
  #include "llvm/IR/PatternMatch.h"
  #include "llvm/IR/Type.h"
  #include "llvm/IR/Use.h"
  #include "llvm/IR/Value.h"
  #include "llvm/Pass.h"
  #include "llvm/Support/Casting.h"
  #include "llvm/Support/CommandLine.h"
  #include "llvm/Support/Compiler.h"
  #include "llvm/Support/Debug.h"
  #include "llvm/Support/raw_ostream.h"
  #include "llvm/Transforms/Utils.h"
  #include "llvm/Transforms/Utils/BasicBlockUtils.h"
  #include "llvm/Transforms/Utils/Local.h"
  #include "llvm/Transforms/Utils/SSAUpdater.h"
  #include "llvm/Transforms/Utils/VNCoercion.h"
  #include <algorithm>
  #include <cassert>
  #include <cstdint>
  #include <utility>
  #include <vector>
  
  using namespace llvm;
  using namespace llvm::gvn;
  using namespace llvm::VNCoercion;
  using namespace PatternMatch;
  
  #define DEBUG_TYPE "gvn"
  
  STATISTIC(NumGVNInstr,  "Number of instructions deleted");
  STATISTIC(NumGVNLoad,   "Number of loads deleted");
  STATISTIC(NumGVNPRE,    "Number of instructions PRE'd");
  STATISTIC(NumGVNBlocks, "Number of blocks merged");
  STATISTIC(NumGVNSimpl,  "Number of instructions simplified");
  STATISTIC(NumGVNEqProp, "Number of equalities propagated");
  STATISTIC(NumPRELoad,   "Number of loads PRE'd");
  
  static cl::opt<bool> EnablePRE("enable-pre",
                                 cl::init(true), cl::Hidden);
  static cl::opt<bool> EnableLoadPRE("enable-load-pre", cl::init(true));
  static cl::opt<bool> EnableMemDep("enable-gvn-memdep", cl::init(true));
  
  // Maximum allowed recursion depth.
  static cl::opt<uint32_t>
  MaxRecurseDepth("gvn-max-recurse-depth", cl::Hidden, cl::init(1000), cl::ZeroOrMore,
                  cl::desc("Max recurse depth in GVN (default = 1000)"));
  
  static cl::opt<uint32_t> MaxNumDeps(
      "gvn-max-num-deps", cl::Hidden, cl::init(100), cl::ZeroOrMore,
      cl::desc("Max number of dependences to attempt Load PRE (default = 100)"));
  
  struct llvm::GVN::Expression {
    uint32_t opcode;
    Type *type;
    bool commutative = false;
    SmallVector<uint32_t, 4> varargs;
  
    Expression(uint32_t o = ~2U) : opcode(o) {}
  
    bool operator==(const Expression &other) const {
      if (opcode != other.opcode)
        return false;
      if (opcode == ~0U || opcode == ~1U)
        return true;
      if (type != other.type)
        return false;
      if (varargs != other.varargs)
        return false;
      return true;
    }
  
    friend hash_code hash_value(const Expression &Value) {
      return hash_combine(
          Value.opcode, Value.type,
          hash_combine_range(Value.varargs.begin(), Value.varargs.end()));
    }
  };
  
  namespace llvm {
  
  template <> struct DenseMapInfo<GVN::Expression> {
    static inline GVN::Expression getEmptyKey() { return ~0U; }
    static inline GVN::Expression getTombstoneKey() { return ~1U; }
  
    static unsigned getHashValue(const GVN::Expression &e) {
      using llvm::hash_value;
  
      return static_cast<unsigned>(hash_value(e));
    }
  
    static bool isEqual(const GVN::Expression &LHS, const GVN::Expression &RHS) {
      return LHS == RHS;
    }
  };
  
  } // end namespace llvm
  
  /// Represents a particular available value that we know how to materialize.
  /// Materialization of an AvailableValue never fails.  An AvailableValue is
  /// implicitly associated with a rematerialization point which is the
  /// location of the instruction from which it was formed.
  struct llvm::gvn::AvailableValue {
    enum ValType {
      SimpleVal, // A simple offsetted value that is accessed.
      LoadVal,   // A value produced by a load.
      MemIntrin, // A memory intrinsic which is loaded from.
      UndefVal   // A UndefValue representing a value from dead block (which
                 // is not yet physically removed from the CFG).
    };
  
    /// V - The value that is live out of the block.
    PointerIntPair<Value *, 2, ValType> Val;
  
    /// Offset - The byte offset in Val that is interesting for the load query.
    unsigned Offset;
  
    static AvailableValue get(Value *V, unsigned Offset = 0) {
      AvailableValue Res;
      Res.Val.setPointer(V);
      Res.Val.setInt(SimpleVal);
      Res.Offset = Offset;
      return Res;
    }
  
    static AvailableValue getMI(MemIntrinsic *MI, unsigned Offset = 0) {
      AvailableValue Res;
      Res.Val.setPointer(MI);
      Res.Val.setInt(MemIntrin);
      Res.Offset = Offset;
      return Res;
    }
  
    static AvailableValue getLoad(LoadInst *LI, unsigned Offset = 0) {
      AvailableValue Res;
      Res.Val.setPointer(LI);
      Res.Val.setInt(LoadVal);
      Res.Offset = Offset;
      return Res;
    }
  
    static AvailableValue getUndef() {
      AvailableValue Res;
      Res.Val.setPointer(nullptr);
      Res.Val.setInt(UndefVal);
      Res.Offset = 0;
      return Res;
    }
  
    bool isSimpleValue() const { return Val.getInt() == SimpleVal; }
    bool isCoercedLoadValue() const { return Val.getInt() == LoadVal; }
    bool isMemIntrinValue() const { return Val.getInt() == MemIntrin; }
    bool isUndefValue() const { return Val.getInt() == UndefVal; }
  
    Value *getSimpleValue() const {
      assert(isSimpleValue() && "Wrong accessor");
      return Val.getPointer();
    }
  
    LoadInst *getCoercedLoadValue() const {
      assert(isCoercedLoadValue() && "Wrong accessor");
      return cast<LoadInst>(Val.getPointer());
    }
  
    MemIntrinsic *getMemIntrinValue() const {
      assert(isMemIntrinValue() && "Wrong accessor");
      return cast<MemIntrinsic>(Val.getPointer());
    }
  
    /// Emit code at the specified insertion point to adjust the value defined
    /// here to the specified type. This handles various coercion cases.
    Value *MaterializeAdjustedValue(LoadInst *LI, Instruction *InsertPt,
                                    GVN &gvn) const;
  };
  
  /// Represents an AvailableValue which can be rematerialized at the end of
  /// the associated BasicBlock.
  struct llvm::gvn::AvailableValueInBlock {
    /// BB - The basic block in question.
    BasicBlock *BB;
  
    /// AV - The actual available value
    AvailableValue AV;
  
    static AvailableValueInBlock get(BasicBlock *BB, AvailableValue &&AV) {
      AvailableValueInBlock Res;
      Res.BB = BB;
      Res.AV = std::move(AV);
      return Res;
    }
  
    static AvailableValueInBlock get(BasicBlock *BB, Value *V,
                                     unsigned Offset = 0) {
      return get(BB, AvailableValue::get(V, Offset));
    }
  
    static AvailableValueInBlock getUndef(BasicBlock *BB) {
      return get(BB, AvailableValue::getUndef());
    }
  
    /// Emit code at the end of this block to adjust the value defined here to
    /// the specified type. This handles various coercion cases.
    Value *MaterializeAdjustedValue(LoadInst *LI, GVN &gvn) const {
      return AV.MaterializeAdjustedValue(LI, BB->getTerminator(), gvn);
    }
  };
  
  //===----------------------------------------------------------------------===//
  //                     ValueTable Internal Functions
  //===----------------------------------------------------------------------===//
  
  GVN::Expression GVN::ValueTable::createExpr(Instruction *I) {
    Expression e;
    e.type = I->getType();
    e.opcode = I->getOpcode();
    for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end();
         OI != OE; ++OI)
      e.varargs.push_back(lookupOrAdd(*OI));
    if (I->isCommutative()) {
      // Ensure that commutative instructions that only differ by a permutation
      // of their operands get the same value number by sorting the operand value
      // numbers.  Since all commutative instructions have two operands it is more
      // efficient to sort by hand rather than using, say, std::sort.
      assert(I->getNumOperands() == 2 && "Unsupported commutative instruction!");
      if (e.varargs[0] > e.varargs[1])
        std::swap(e.varargs[0], e.varargs[1]);
      e.commutative = true;
    }
  
    if (CmpInst *C = dyn_cast<CmpInst>(I)) {
      // Sort the operand value numbers so x<y and y>x get the same value number.
      CmpInst::Predicate Predicate = C->getPredicate();
      if (e.varargs[0] > e.varargs[1]) {
        std::swap(e.varargs[0], e.varargs[1]);
        Predicate = CmpInst::getSwappedPredicate(Predicate);
      }
      e.opcode = (C->getOpcode() << 8) | Predicate;
      e.commutative = true;
    } else if (InsertValueInst *E = dyn_cast<InsertValueInst>(I)) {
      for (InsertValueInst::idx_iterator II = E->idx_begin(), IE = E->idx_end();
           II != IE; ++II)
        e.varargs.push_back(*II);
    }
  
    return e;
  }
  
  GVN::Expression GVN::ValueTable::createCmpExpr(unsigned Opcode,
                                                 CmpInst::Predicate Predicate,
                                                 Value *LHS, Value *RHS) {
    assert((Opcode == Instruction::ICmp || Opcode == Instruction::FCmp) &&
           "Not a comparison!");
    Expression e;
    e.type = CmpInst::makeCmpResultType(LHS->getType());
    e.varargs.push_back(lookupOrAdd(LHS));
    e.varargs.push_back(lookupOrAdd(RHS));
  
    // Sort the operand value numbers so x<y and y>x get the same value number.
    if (e.varargs[0] > e.varargs[1]) {
      std::swap(e.varargs[0], e.varargs[1]);
      Predicate = CmpInst::getSwappedPredicate(Predicate);
    }
    e.opcode = (Opcode << 8) | Predicate;
    e.commutative = true;
    return e;
  }
  
  GVN::Expression GVN::ValueTable::createExtractvalueExpr(ExtractValueInst *EI) {
    assert(EI && "Not an ExtractValueInst?");
    Expression e;
    e.type = EI->getType();
    e.opcode = 0;
  
    WithOverflowInst *WO = dyn_cast<WithOverflowInst>(EI->getAggregateOperand());
    if (WO != nullptr && EI->getNumIndices() == 1 && *EI->idx_begin() == 0) {
      // EI is an extract from one of our with.overflow intrinsics. Synthesize
      // a semantically equivalent expression instead of an extract value
      // expression.
      e.opcode = WO->getBinaryOp();
      e.varargs.push_back(lookupOrAdd(WO->getLHS()));
      e.varargs.push_back(lookupOrAdd(WO->getRHS()));
      return e;
    }
  
    // Not a recognised intrinsic. Fall back to producing an extract value
    // expression.
    e.opcode = EI->getOpcode();
    for (Instruction::op_iterator OI = EI->op_begin(), OE = EI->op_end();
         OI != OE; ++OI)
      e.varargs.push_back(lookupOrAdd(*OI));
  
    for (ExtractValueInst::idx_iterator II = EI->idx_begin(), IE = EI->idx_end();
           II != IE; ++II)
      e.varargs.push_back(*II);
  
    return e;
  }
  
  //===----------------------------------------------------------------------===//
  //                     ValueTable External Functions
  //===----------------------------------------------------------------------===//
  
  GVN::ValueTable::ValueTable() = default;
  GVN::ValueTable::ValueTable(const ValueTable &) = default;
  GVN::ValueTable::ValueTable(ValueTable &&) = default;
  GVN::ValueTable::~ValueTable() = default;
  
  /// add - Insert a value into the table with a specified value number.
  void GVN::ValueTable::add(Value *V, uint32_t num) {
    valueNumbering.insert(std::make_pair(V, num));
    if (PHINode *PN = dyn_cast<PHINode>(V))
      NumberingPhi[num] = PN;
  }
  
  uint32_t GVN::ValueTable::lookupOrAddCall(CallInst *C) {
    if (AA->doesNotAccessMemory(C)) {
      Expression exp = createExpr(C);
      uint32_t e = assignExpNewValueNum(exp).first;
      valueNumbering[C] = e;
      return e;
    } else if (MD && AA->onlyReadsMemory(C)) {
      Expression exp = createExpr(C);
      auto ValNum = assignExpNewValueNum(exp);
      if (ValNum.second) {
        valueNumbering[C] = ValNum.first;
        return ValNum.first;
      }
  
      MemDepResult local_dep = MD->getDependency(C);
  
      if (!local_dep.isDef() && !local_dep.isNonLocal()) {
        valueNumbering[C] =  nextValueNumber;
        return nextValueNumber++;
      }
  
      if (local_dep.isDef()) {
        CallInst* local_cdep = cast<CallInst>(local_dep.getInst());
  
        if (local_cdep->getNumArgOperands() != C->getNumArgOperands()) {
          valueNumbering[C] = nextValueNumber;
          return nextValueNumber++;
        }
  
        for (unsigned i = 0, e = C->getNumArgOperands(); i < e; ++i) {
          uint32_t c_vn = lookupOrAdd(C->getArgOperand(i));
          uint32_t cd_vn = lookupOrAdd(local_cdep->getArgOperand(i));
          if (c_vn != cd_vn) {
            valueNumbering[C] = nextValueNumber;
            return nextValueNumber++;
          }
        }
  
        uint32_t v = lookupOrAdd(local_cdep);
        valueNumbering[C] = v;
        return v;
      }
  
      // Non-local case.
      const MemoryDependenceResults::NonLocalDepInfo &deps =
          MD->getNonLocalCallDependency(C);
      // FIXME: Move the checking logic to MemDep!
      CallInst* cdep = nullptr;
  
      // Check to see if we have a single dominating call instruction that is
      // identical to C.
      for (unsigned i = 0, e = deps.size(); i != e; ++i) {
        const NonLocalDepEntry *I = &deps[i];
        if (I->getResult().isNonLocal())
          continue;
  
        // We don't handle non-definitions.  If we already have a call, reject
        // instruction dependencies.
        if (!I->getResult().isDef() || cdep != nullptr) {
          cdep = nullptr;
          break;
        }
  
        CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->getResult().getInst());
        // FIXME: All duplicated with non-local case.
        if (NonLocalDepCall && DT->properlyDominates(I->getBB(), C->getParent())){
          cdep = NonLocalDepCall;
          continue;
        }
  
        cdep = nullptr;
        break;
      }
  
      if (!cdep) {
        valueNumbering[C] = nextValueNumber;
        return nextValueNumber++;
      }
  
      if (cdep->getNumArgOperands() != C->getNumArgOperands()) {
        valueNumbering[C] = nextValueNumber;
        return nextValueNumber++;
      }
      for (unsigned i = 0, e = C->getNumArgOperands(); i < e; ++i) {
        uint32_t c_vn = lookupOrAdd(C->getArgOperand(i));
        uint32_t cd_vn = lookupOrAdd(cdep->getArgOperand(i));
        if (c_vn != cd_vn) {
          valueNumbering[C] = nextValueNumber;
          return nextValueNumber++;
        }
      }
  
      uint32_t v = lookupOrAdd(cdep);
      valueNumbering[C] = v;
      return v;
    } else {
      valueNumbering[C] = nextValueNumber;
      return nextValueNumber++;
    }
  }
  
  /// Returns true if a value number exists for the specified value.
  bool GVN::ValueTable::exists(Value *V) const { return valueNumbering.count(V) != 0; }
  
  /// lookup_or_add - Returns the value number for the specified value, assigning
  /// it a new number if it did not have one before.
  uint32_t GVN::ValueTable::lookupOrAdd(Value *V) {
    DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
    if (VI != valueNumbering.end())
      return VI->second;
  
    if (!isa<Instruction>(V)) {
      valueNumbering[V] = nextValueNumber;
      return nextValueNumber++;
    }
  
    Instruction* I = cast<Instruction>(V);
    Expression exp;
    switch (I->getOpcode()) {
      case Instruction::Call:
        return lookupOrAddCall(cast<CallInst>(I));
      case Instruction::FNeg:
      case Instruction::Add:
      case Instruction::FAdd:
      case Instruction::Sub:
      case Instruction::FSub:
      case Instruction::Mul:
      case Instruction::FMul:
      case Instruction::UDiv:
      case Instruction::SDiv:
      case Instruction::FDiv:
      case Instruction::URem:
      case Instruction::SRem:
      case Instruction::FRem:
      case Instruction::Shl:
      case Instruction::LShr:
      case Instruction::AShr:
      case Instruction::And:
      case Instruction::Or:
      case Instruction::Xor:
      case Instruction::ICmp:
      case Instruction::FCmp:
      case Instruction::Trunc:
      case Instruction::ZExt:
      case Instruction::SExt:
      case Instruction::FPToUI:
      case Instruction::FPToSI:
      case Instruction::UIToFP:
      case Instruction::SIToFP:
      case Instruction::FPTrunc:
      case Instruction::FPExt:
      case Instruction::PtrToInt:
      case Instruction::IntToPtr:
      case Instruction::AddrSpaceCast:
      case Instruction::BitCast:
      case Instruction::Select:
      case Instruction::ExtractElement:
      case Instruction::InsertElement:
      case Instruction::ShuffleVector:
      case Instruction::InsertValue:
      case Instruction::GetElementPtr:
        exp = createExpr(I);
        break;
      case Instruction::ExtractValue:
        exp = createExtractvalueExpr(cast<ExtractValueInst>(I));
        break;
      case Instruction::PHI:
        valueNumbering[V] = nextValueNumber;
        NumberingPhi[nextValueNumber] = cast<PHINode>(V);
        return nextValueNumber++;
      default:
        valueNumbering[V] = nextValueNumber;
        return nextValueNumber++;
    }
  
    uint32_t e = assignExpNewValueNum(exp).first;
    valueNumbering[V] = e;
    return e;
  }
  
  /// Returns the value number of the specified value. Fails if
  /// the value has not yet been numbered.
  uint32_t GVN::ValueTable::lookup(Value *V, bool Verify) const {
    DenseMap<Value*, uint32_t>::const_iterator VI = valueNumbering.find(V);
    if (Verify) {
      assert(VI != valueNumbering.end() && "Value not numbered?");
      return VI->second;
    }
    return (VI != valueNumbering.end()) ? VI->second : 0;
  }
  
  /// Returns the value number of the given comparison,
  /// assigning it a new number if it did not have one before.  Useful when
  /// we deduced the result of a comparison, but don't immediately have an
  /// instruction realizing that comparison to hand.
  uint32_t GVN::ValueTable::lookupOrAddCmp(unsigned Opcode,
                                           CmpInst::Predicate Predicate,
                                           Value *LHS, Value *RHS) {
    Expression exp = createCmpExpr(Opcode, Predicate, LHS, RHS);
    return assignExpNewValueNum(exp).first;
  }
  
  /// Remove all entries from the ValueTable.
  void GVN::ValueTable::clear() {
    valueNumbering.clear();
    expressionNumbering.clear();
    NumberingPhi.clear();
    PhiTranslateTable.clear();
    nextValueNumber = 1;
    Expressions.clear();
    ExprIdx.clear();
    nextExprNumber = 0;
  }
  
  /// Remove a value from the value numbering.
  void GVN::ValueTable::erase(Value *V) {
    uint32_t Num = valueNumbering.lookup(V);
    valueNumbering.erase(V);
    // If V is PHINode, V <--> value number is an one-to-one mapping.
    if (isa<PHINode>(V))
      NumberingPhi.erase(Num);
  }
  
  /// verifyRemoved - Verify that the value is removed from all internal data
  /// structures.
  void GVN::ValueTable::verifyRemoved(const Value *V) const {
    for (DenseMap<Value*, uint32_t>::const_iterator
           I = valueNumbering.begin(), E = valueNumbering.end(); I != E; ++I) {
      assert(I->first != V && "Inst still occurs in value numbering map!");
    }
  }
  
  //===----------------------------------------------------------------------===//
  //                                GVN Pass
  //===----------------------------------------------------------------------===//
  
  PreservedAnalyses GVN::run(Function &F, FunctionAnalysisManager &AM) {
    // FIXME: The order of evaluation of these 'getResult' calls is very
    // significant! Re-ordering these variables will cause GVN when run alone to
    // be less effective! We should fix memdep and basic-aa to not exhibit this
    // behavior, but until then don't change the order here.
    auto &AC = AM.getResult<AssumptionAnalysis>(F);
    auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
    auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
    auto &AA = AM.getResult<AAManager>(F);
    auto &MemDep = AM.getResult<MemoryDependenceAnalysis>(F);
    auto *LI = AM.getCachedResult<LoopAnalysis>(F);
    auto &ORE = AM.getResult<OptimizationRemarkEmitterAnalysis>(F);
    bool Changed = runImpl(F, AC, DT, TLI, AA, &MemDep, LI, &ORE);
    if (!Changed)
      return PreservedAnalyses::all();
    PreservedAnalyses PA;
    PA.preserve<DominatorTreeAnalysis>();
    PA.preserve<GlobalsAA>();
    PA.preserve<TargetLibraryAnalysis>();
    if (LI)
      PA.preserve<LoopAnalysis>();
    return PA;
  }
  
  #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
  LLVM_DUMP_METHOD void GVN::dump(DenseMap<uint32_t, Value*>& d) const {
    errs() << "{\n";
    for (DenseMap<uint32_t, Value*>::iterator I = d.begin(),
         E = d.end(); I != E; ++I) {
        errs() << I->first << "\n";
        I->second->dump();
    }
    errs() << "}\n";
  }
  #endif
  
  /// Return true if we can prove that the value
  /// we're analyzing is fully available in the specified block.  As we go, keep
  /// track of which blocks we know are fully alive in FullyAvailableBlocks.  This
  /// map is actually a tri-state map with the following values:
  ///   0) we know the block *is not* fully available.
  ///   1) we know the block *is* fully available.
  ///   2) we do not know whether the block is fully available or not, but we are
  ///      currently speculating that it will be.
  ///   3) we are speculating for this block and have used that to speculate for
  ///      other blocks.
  static bool IsValueFullyAvailableInBlock(BasicBlock *BB,
                              DenseMap<BasicBlock*, char> &FullyAvailableBlocks,
                              uint32_t RecurseDepth) {
    if (RecurseDepth > MaxRecurseDepth)
      return false;
  
    // Optimistically assume that the block is fully available and check to see
    // if we already know about this block in one lookup.
    std::pair<DenseMap<BasicBlock*, char>::iterator, bool> IV =
      FullyAvailableBlocks.insert(std::make_pair(BB, 2));
  
    // If the entry already existed for this block, return the precomputed value.
    if (!IV.second) {
      // If this is a speculative "available" value, mark it as being used for
      // speculation of other blocks.
      if (IV.first->second == 2)
        IV.first->second = 3;
      return IV.first->second != 0;
    }
  
    // Otherwise, see if it is fully available in all predecessors.
    pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
  
    // If this block has no predecessors, it isn't live-in here.
    if (PI == PE)
      goto SpeculationFailure;
  
    for (; PI != PE; ++PI)
      // If the value isn't fully available in one of our predecessors, then it
      // isn't fully available in this block either.  Undo our previous
      // optimistic assumption and bail out.
      if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks,RecurseDepth+1))
        goto SpeculationFailure;
  
    return true;
  
  // If we get here, we found out that this is not, after
  // all, a fully-available block.  We have a problem if we speculated on this and
  // used the speculation to mark other blocks as available.
  SpeculationFailure:
    char &BBVal = FullyAvailableBlocks[BB];
  
    // If we didn't speculate on this, just return with it set to false.
    if (BBVal == 2) {
      BBVal = 0;
      return false;
    }
  
    // If we did speculate on this value, we could have blocks set to 1 that are
    // incorrect.  Walk the (transitive) successors of this block and mark them as
    // 0 if set to one.
    SmallVector<BasicBlock*, 32> BBWorklist;
    BBWorklist.push_back(BB);
  
    do {
      BasicBlock *Entry = BBWorklist.pop_back_val();
      // Note that this sets blocks to 0 (unavailable) if they happen to not
      // already be in FullyAvailableBlocks.  This is safe.
      char &EntryVal = FullyAvailableBlocks[Entry];
      if (EntryVal == 0) continue;  // Already unavailable.
  
      // Mark as unavailable.
      EntryVal = 0;
  
      BBWorklist.append(succ_begin(Entry), succ_end(Entry));
    } while (!BBWorklist.empty());
  
    return false;
  }
  
  /// Given a set of loads specified by ValuesPerBlock,
  /// construct SSA form, allowing us to eliminate LI.  This returns the value
  /// that should be used at LI's definition site.
  static Value *ConstructSSAForLoadSet(LoadInst *LI,
                           SmallVectorImpl<AvailableValueInBlock> &ValuesPerBlock,
                                       GVN &gvn) {
    // Check for the fully redundant, dominating load case.  In this case, we can
    // just use the dominating value directly.
    if (ValuesPerBlock.size() == 1 &&
        gvn.getDominatorTree().properlyDominates(ValuesPerBlock[0].BB,
                                                 LI->getParent())) {
      assert(!ValuesPerBlock[0].AV.isUndefValue() &&
             "Dead BB dominate this block");
      return ValuesPerBlock[0].MaterializeAdjustedValue(LI, gvn);
    }
  
    // Otherwise, we have to construct SSA form.
    SmallVector<PHINode*, 8> NewPHIs;
    SSAUpdater SSAUpdate(&NewPHIs);
    SSAUpdate.Initialize(LI->getType(), LI->getName());
  
    for (const AvailableValueInBlock &AV : ValuesPerBlock) {
      BasicBlock *BB = AV.BB;
  
      if (SSAUpdate.HasValueForBlock(BB))
        continue;
  
      // If the value is the load that we will be eliminating, and the block it's
      // available in is the block that the load is in, then don't add it as
      // SSAUpdater will resolve the value to the relevant phi which may let it
      // avoid phi construction entirely if there's actually only one value.
      if (BB == LI->getParent() &&
          ((AV.AV.isSimpleValue() && AV.AV.getSimpleValue() == LI) ||
           (AV.AV.isCoercedLoadValue() && AV.AV.getCoercedLoadValue() == LI)))
        continue;
  
      SSAUpdate.AddAvailableValue(BB, AV.MaterializeAdjustedValue(LI, gvn));
    }
  
    // Perform PHI construction.
    return SSAUpdate.GetValueInMiddleOfBlock(LI->getParent());
  }
  
  Value *AvailableValue::MaterializeAdjustedValue(LoadInst *LI,
                                                  Instruction *InsertPt,
                                                  GVN &gvn) const {
    Value *Res;
    Type *LoadTy = LI->getType();
    const DataLayout &DL = LI->getModule()->getDataLayout();
    if (isSimpleValue()) {
      Res = getSimpleValue();
      if (Res->getType() != LoadTy) {
        Res = getStoreValueForLoad(Res, Offset, LoadTy, InsertPt, DL);
  
        LLVM_DEBUG(dbgs() << "GVN COERCED NONLOCAL VAL:\nOffset: " << Offset
                          << "  " << *getSimpleValue() << '\n'
                          << *Res << '\n'
                          << "\n\n\n");
      }
    } else if (isCoercedLoadValue()) {
      LoadInst *Load = getCoercedLoadValue();
      if (Load->getType() == LoadTy && Offset == 0) {
        Res = Load;
      } else {
        Res = getLoadValueForLoad(Load, Offset, LoadTy, InsertPt, DL);
        // We would like to use gvn.markInstructionForDeletion here, but we can't
        // because the load is already memoized into the leader map table that GVN
        // tracks.  It is potentially possible to remove the load from the table,
        // but then there all of the operations based on it would need to be
        // rehashed.  Just leave the dead load around.
        gvn.getMemDep().removeInstruction(Load);
        LLVM_DEBUG(dbgs() << "GVN COERCED NONLOCAL LOAD:\nOffset: " << Offset
                          << "  " << *getCoercedLoadValue() << '\n'
                          << *Res << '\n'
                          << "\n\n\n");
      }
    } else if (isMemIntrinValue()) {
      Res = getMemInstValueForLoad(getMemIntrinValue(), Offset, LoadTy,
                                   InsertPt, DL);
      LLVM_DEBUG(dbgs() << "GVN COERCED NONLOCAL MEM INTRIN:\nOffset: " << Offset
                        << "  " << *getMemIntrinValue() << '\n'
                        << *Res << '\n'
                        << "\n\n\n");
    } else {
      assert(isUndefValue() && "Should be UndefVal");
      LLVM_DEBUG(dbgs() << "GVN COERCED NONLOCAL Undef:\n";);
      return UndefValue::get(LoadTy);
    }
    assert(Res && "failed to materialize?");
    return Res;
  }
  
  static bool isLifetimeStart(const Instruction *Inst) {
    if (const IntrinsicInst* II = dyn_cast<IntrinsicInst>(Inst))
      return II->getIntrinsicID() == Intrinsic::lifetime_start;
    return false;
  }
  
  /// Try to locate the three instruction involved in a missed
  /// load-elimination case that is due to an intervening store.
  static void reportMayClobberedLoad(LoadInst *LI, MemDepResult DepInfo,
                                     DominatorTree *DT,
                                     OptimizationRemarkEmitter *ORE) {
    using namespace ore;
  
    User *OtherAccess = nullptr;
  
    OptimizationRemarkMissed R(DEBUG_TYPE, "LoadClobbered", LI);
    R << "load of type " << NV("Type", LI->getType()) << " not eliminated"
      << setExtraArgs();
  
    for (auto *U : LI->getPointerOperand()->users())
      if (U != LI && (isa<LoadInst>(U) || isa<StoreInst>(U)) &&
          DT->dominates(cast<Instruction>(U), LI)) {
        // FIXME: for now give up if there are multiple memory accesses that
        // dominate the load.  We need further analysis to decide which one is
        // that we're forwarding from.
        if (OtherAccess)
          OtherAccess = nullptr;
        else
          OtherAccess = U;
      }
  
    if (OtherAccess)
      R << " in favor of " << NV("OtherAccess", OtherAccess);
  
    R << " because it is clobbered by " << NV("ClobberedBy", DepInfo.getInst());
  
    ORE->emit(R);
  }
  
  bool GVN::AnalyzeLoadAvailability(LoadInst *LI, MemDepResult DepInfo,
                                    Value *Address, AvailableValue &Res) {
    assert((DepInfo.isDef() || DepInfo.isClobber()) &&
           "expected a local dependence");
    assert(LI->isUnordered() && "rules below are incorrect for ordered access");
  
    const DataLayout &DL = LI->getModule()->getDataLayout();
  
    Instruction *DepInst = DepInfo.getInst();
    if (DepInfo.isClobber()) {
      // If the dependence is to a store that writes to a superset of the bits
      // read by the load, we can extract the bits we need for the load from the
      // stored value.
      if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) {
        // Can't forward from non-atomic to atomic without violating memory model.
        if (Address && LI->isAtomic() <= DepSI->isAtomic()) {
          int Offset =
            analyzeLoadFromClobberingStore(LI->getType(), Address, DepSI, DL);
          if (Offset != -1) {
            Res = AvailableValue::get(DepSI->getValueOperand(), Offset);
            return true;
          }
        }
      }
  
      // Check to see if we have something like this:
      //    load i32* P
      //    load i8* (P+1)
      // if we have this, replace the later with an extraction from the former.
      if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) {
        // If this is a clobber and L is the first instruction in its block, then
        // we have the first instruction in the entry block.
        // Can't forward from non-atomic to atomic without violating memory model.
        if (DepLI != LI && Address && LI->isAtomic() <= DepLI->isAtomic()) {
          int Offset =
            analyzeLoadFromClobberingLoad(LI->getType(), Address, DepLI, DL);
  
          if (Offset != -1) {
            Res = AvailableValue::getLoad(DepLI, Offset);
            return true;
          }
        }
      }
  
      // If the clobbering value is a memset/memcpy/memmove, see if we can
      // forward a value on from it.
      if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(DepInst)) {
        if (Address && !LI->isAtomic()) {
          int Offset = analyzeLoadFromClobberingMemInst(LI->getType(), Address,
                                                        DepMI, DL);
          if (Offset != -1) {
            Res = AvailableValue::getMI(DepMI, Offset);
            return true;
          }
        }
      }
      // Nothing known about this clobber, have to be conservative
      LLVM_DEBUG(
          // fast print dep, using operator<< on instruction is too slow.
          dbgs() << "GVN: load "; LI->printAsOperand(dbgs());
          dbgs() << " is clobbered by " << *DepInst << '\n';);
      if (ORE->allowExtraAnalysis(DEBUG_TYPE))
        reportMayClobberedLoad(LI, DepInfo, DT, ORE);
  
      return false;
    }
    assert(DepInfo.isDef() && "follows from above");
  
    // Loading the allocation -> undef.
    if (isa<AllocaInst>(DepInst) || isMallocLikeFn(DepInst, TLI) ||
        // Loading immediately after lifetime begin -> undef.
        isLifetimeStart(DepInst)) {
      Res = AvailableValue::get(UndefValue::get(LI->getType()));
      return true;
    }
  
    // Loading from calloc (which zero initializes memory) -> zero
    if (isCallocLikeFn(DepInst, TLI)) {
      Res = AvailableValue::get(Constant::getNullValue(LI->getType()));
      return true;
    }
  
    if (StoreInst *S = dyn_cast<StoreInst>(DepInst)) {
      // Reject loads and stores that are to the same address but are of
      // different types if we have to. If the stored value is larger or equal to
      // the loaded value, we can reuse it.
      if (!canCoerceMustAliasedValueToLoad(S->getValueOperand(), LI->getType(),
                                           DL))
        return false;
  
      // Can't forward from non-atomic to atomic without violating memory model.
      if (S->isAtomic() < LI->isAtomic())
        return false;
  
      Res = AvailableValue::get(S->getValueOperand());
      return true;
    }
  
    if (LoadInst *LD = dyn_cast<LoadInst>(DepInst)) {
      // If the types mismatch and we can't handle it, reject reuse of the load.
      // If the stored value is larger or equal to the loaded value, we can reuse
      // it.
      if (!canCoerceMustAliasedValueToLoad(LD, LI->getType(), DL))
        return false;
  
      // Can't forward from non-atomic to atomic without violating memory model.
      if (LD->isAtomic() < LI->isAtomic())
        return false;
  
      Res = AvailableValue::getLoad(LD);
      return true;
    }
  
    // Unknown def - must be conservative
    LLVM_DEBUG(
        // fast print dep, using operator<< on instruction is too slow.
        dbgs() << "GVN: load "; LI->printAsOperand(dbgs());
        dbgs() << " has unknown def " << *DepInst << '\n';);
    return false;
  }
  
  void GVN::AnalyzeLoadAvailability(LoadInst *LI, LoadDepVect &Deps,
                                    AvailValInBlkVect &ValuesPerBlock,
                                    UnavailBlkVect &UnavailableBlocks) {
    // Filter out useless results (non-locals, etc).  Keep track of the blocks
    // where we have a value available in repl, also keep track of whether we see
    // dependencies that produce an unknown value for the load (such as a call
    // that could potentially clobber the load).
    unsigned NumDeps = Deps.size();
    for (unsigned i = 0, e = NumDeps; i != e; ++i) {
      BasicBlock *DepBB = Deps[i].getBB();
      MemDepResult DepInfo = Deps[i].getResult();
  
      if (DeadBlocks.count(DepBB)) {
        // Dead dependent mem-op disguise as a load evaluating the same value
        // as the load in question.
        ValuesPerBlock.push_back(AvailableValueInBlock::getUndef(DepBB));
        continue;
      }
  
      if (!DepInfo.isDef() && !DepInfo.isClobber()) {
        UnavailableBlocks.push_back(DepBB);
        continue;
      }
  
      // The address being loaded in this non-local block may not be the same as
      // the pointer operand of the load if PHI translation occurs.  Make sure
      // to consider the right address.
      Value *Address = Deps[i].getAddress();
  
      AvailableValue AV;
      if (AnalyzeLoadAvailability(LI, DepInfo, Address, AV)) {
        // subtlety: because we know this was a non-local dependency, we know
        // it's safe to materialize anywhere between the instruction within
        // DepInfo and the end of it's block.
        ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB,
                                                            std::move(AV)));
      } else {
        UnavailableBlocks.push_back(DepBB);
      }
    }
  
    assert(NumDeps == ValuesPerBlock.size() + UnavailableBlocks.size() &&
           "post condition violation");
  }
  
  bool GVN::PerformLoadPRE(LoadInst *LI, AvailValInBlkVect &ValuesPerBlock,
                           UnavailBlkVect &UnavailableBlocks) {
    // Okay, we have *some* definitions of the value.  This means that the value
    // is available in some of our (transitive) predecessors.  Lets think about
    // doing PRE of this load.  This will involve inserting a new load into the
    // predecessor when it's not available.  We could do this in general, but
    // prefer to not increase code size.  As such, we only do this when we know
    // that we only have to insert *one* load (which means we're basically moving
    // the load, not inserting a new one).
  
    SmallPtrSet<BasicBlock *, 4> Blockers(UnavailableBlocks.begin(),
                                          UnavailableBlocks.end());
  
    // Let's find the first basic block with more than one predecessor.  Walk
    // backwards through predecessors if needed.
    BasicBlock *LoadBB = LI->getParent();
    BasicBlock *TmpBB = LoadBB;
    bool IsSafeToSpeculativelyExecute = isSafeToSpeculativelyExecute(LI);
  
    // Check that there is no implicit control flow instructions above our load in
    // its block. If there is an instruction that doesn't always pass the
    // execution to the following instruction, then moving through it may become
    // invalid. For example:
    //
    // int arr[LEN];
    // int index = ???;
    // ...
    // guard(0 <= index && index < LEN);
    // use(arr[index]);
    //
    // It is illegal to move the array access to any point above the guard,
    // because if the index is out of bounds we should deoptimize rather than
    // access the array.
    // Check that there is no guard in this block above our instruction.
    if (!IsSafeToSpeculativelyExecute && ICF->isDominatedByICFIFromSameBlock(LI))
      return false;
    while (TmpBB->getSinglePredecessor()) {
      TmpBB = TmpBB->getSinglePredecessor();
      if (TmpBB == LoadBB) // Infinite (unreachable) loop.
        return false;
      if (Blockers.count(TmpBB))
        return false;
  
      // If any of these blocks has more than one successor (i.e. if the edge we
      // just traversed was critical), then there are other paths through this
      // block along which the load may not be anticipated.  Hoisting the load
      // above this block would be adding the load to execution paths along
      // which it was not previously executed.
      if (TmpBB->getTerminator()->getNumSuccessors() != 1)
        return false;
  
      // Check that there is no implicit control flow in a block above.
      if (!IsSafeToSpeculativelyExecute && ICF->hasICF(TmpBB))
        return false;
    }
  
    assert(TmpBB);
    LoadBB = TmpBB;
  
    // Check to see how many predecessors have the loaded value fully
    // available.
    MapVector<BasicBlock *, Value *> PredLoads;
    DenseMap<BasicBlock*, char> FullyAvailableBlocks;
    for (const AvailableValueInBlock &AV : ValuesPerBlock)
      FullyAvailableBlocks[AV.BB] = true;
    for (BasicBlock *UnavailableBB : UnavailableBlocks)
      FullyAvailableBlocks[UnavailableBB] = false;
  
    SmallVector<BasicBlock *, 4> CriticalEdgePred;
    for (BasicBlock *Pred : predecessors(LoadBB)) {
      // If any predecessor block is an EH pad that does not allow non-PHI
      // instructions before the terminator, we can't PRE the load.
      if (Pred->getTerminator()->isEHPad()) {
        LLVM_DEBUG(
            dbgs() << "COULD NOT PRE LOAD BECAUSE OF AN EH PAD PREDECESSOR '"
                   << Pred->getName() << "': " << *LI << '\n');
        return false;
      }
  
      if (IsValueFullyAvailableInBlock(Pred, FullyAvailableBlocks, 0)) {
        continue;
      }
  
      if (Pred->getTerminator()->getNumSuccessors() != 1) {
        if (isa<IndirectBrInst>(Pred->getTerminator())) {
          LLVM_DEBUG(
              dbgs() << "COULD NOT PRE LOAD BECAUSE OF INDBR CRITICAL EDGE '"
                     << Pred->getName() << "': " << *LI << '\n');
          return false;
        }
  
        // FIXME: Can we support the fallthrough edge?
        if (isa<CallBrInst>(Pred->getTerminator())) {
          LLVM_DEBUG(
              dbgs() << "COULD NOT PRE LOAD BECAUSE OF CALLBR CRITICAL EDGE '"
                     << Pred->getName() << "': " << *LI << '\n');
          return false;
        }
  
        if (LoadBB->isEHPad()) {
          LLVM_DEBUG(
              dbgs() << "COULD NOT PRE LOAD BECAUSE OF AN EH PAD CRITICAL EDGE '"
                     << Pred->getName() << "': " << *LI << '\n');
          return false;
        }
  
        CriticalEdgePred.push_back(Pred);
      } else {
        // Only add the predecessors that will not be split for now.
        PredLoads[Pred] = nullptr;
      }
    }
  
    // Decide whether PRE is profitable for this load.
    unsigned NumUnavailablePreds = PredLoads.size() + CriticalEdgePred.size();
    assert(NumUnavailablePreds != 0 &&
           "Fully available value should already be eliminated!");
  
    // If this load is unavailable in multiple predecessors, reject it.
    // FIXME: If we could restructure the CFG, we could make a common pred with
    // all the preds that don't have an available LI and insert a new load into
    // that one block.
    if (NumUnavailablePreds != 1)
        return false;
  
    // Split critical edges, and update the unavailable predecessors accordingly.
    for (BasicBlock *OrigPred : CriticalEdgePred) {
      BasicBlock *NewPred = splitCriticalEdges(OrigPred, LoadBB);
      assert(!PredLoads.count(OrigPred) && "Split edges shouldn't be in map!");
      PredLoads[NewPred] = nullptr;
      LLVM_DEBUG(dbgs() << "Split critical edge " << OrigPred->getName() << "->"
                        << LoadBB->getName() << '\n');
    }
  
    // Check if the load can safely be moved to all the unavailable predecessors.
    bool CanDoPRE = true;
    const DataLayout &DL = LI->getModule()->getDataLayout();
    SmallVector<Instruction*, 8> NewInsts;
    for (auto &PredLoad : PredLoads) {
      BasicBlock *UnavailablePred = PredLoad.first;
  
      // Do PHI translation to get its value in the predecessor if necessary.  The
      // returned pointer (if non-null) is guaranteed to dominate UnavailablePred.
      // We do the translation for each edge we skipped by going from LI's block
      // to LoadBB, otherwise we might miss pieces needing translation.
  
      // If all preds have a single successor, then we know it is safe to insert
      // the load on the pred (?!?), so we can insert code to materialize the
      // pointer if it is not available.
      Value *LoadPtr = LI->getPointerOperand();
      BasicBlock *Cur = LI->getParent();
      while (Cur != LoadBB) {
        PHITransAddr Address(LoadPtr, DL, AC);
        LoadPtr = Address.PHITranslateWithInsertion(
            Cur, Cur->getSinglePredecessor(), *DT, NewInsts);
        if (!LoadPtr) {
          CanDoPRE = false;
          break;
        }
        Cur = Cur->getSinglePredecessor();
      }
  
      if (LoadPtr) {
        PHITransAddr Address(LoadPtr, DL, AC);
        LoadPtr = Address.PHITranslateWithInsertion(LoadBB, UnavailablePred, *DT,
                                                    NewInsts);
      }
      // If we couldn't find or insert a computation of this phi translated value,
      // we fail PRE.
      if (!LoadPtr) {
        LLVM_DEBUG(dbgs() << "COULDN'T INSERT PHI TRANSLATED VALUE OF: "
                          << *LI->getPointerOperand() << "\n");
        CanDoPRE = false;
        break;
      }
  
      PredLoad.second = LoadPtr;
    }
  
    if (!CanDoPRE) {
      while (!NewInsts.empty()) {
        // Erase instructions generated by the failed PHI translation before
        // trying to number them. PHI translation might insert instructions
        // in basic blocks other than the current one, and we delete them
        // directly, as markInstructionForDeletion only allows removing from the
        // current basic block.
        NewInsts.pop_back_val()->eraseFromParent();
      }
      // HINT: Don't revert the edge-splitting as following transformation may
      // also need to split these critical edges.
      return !CriticalEdgePred.empty();
    }
  
    // Okay, we can eliminate this load by inserting a reload in the predecessor
    // and using PHI construction to get the value in the other predecessors, do
    // it.
    LLVM_DEBUG(dbgs() << "GVN REMOVING PRE LOAD: " << *LI << '\n');
    LLVM_DEBUG(if (!NewInsts.empty()) dbgs()
               << "INSERTED " << NewInsts.size() << " INSTS: " << *NewInsts.back()
               << '\n');
  
    // Assign value numbers to the new instructions.
    for (Instruction *I : NewInsts) {
      // Instructions that have been inserted in predecessor(s) to materialize
      // the load address do not retain their original debug locations. Doing
      // so could lead to confusing (but correct) source attributions.
      if (const DebugLoc &DL = I->getDebugLoc())
        I->setDebugLoc(DebugLoc::get(0, 0, DL.getScope(), DL.getInlinedAt()));
  
      // FIXME: We really _ought_ to insert these value numbers into their
      // parent's availability map.  However, in doing so, we risk getting into
      // ordering issues.  If a block hasn't been processed yet, we would be
      // marking a value as AVAIL-IN, which isn't what we intend.
      VN.lookupOrAdd(I);
    }
  
    for (const auto &PredLoad : PredLoads) {
      BasicBlock *UnavailablePred = PredLoad.first;
      Value *LoadPtr = PredLoad.second;
  
      auto *NewLoad =
          new LoadInst(LI->getType(), LoadPtr, LI->getName() + ".pre",
                       LI->isVolatile(), LI->getAlignment(), LI->getOrdering(),
                       LI->getSyncScopeID(), UnavailablePred->getTerminator());
      NewLoad->setDebugLoc(LI->getDebugLoc());
  
      // Transfer the old load's AA tags to the new load.
      AAMDNodes Tags;
      LI->getAAMetadata(Tags);
      if (Tags)
        NewLoad->setAAMetadata(Tags);
  
      if (auto *MD = LI->getMetadata(LLVMContext::MD_invariant_load))
        NewLoad->setMetadata(LLVMContext::MD_invariant_load, MD);
      if (auto *InvGroupMD = LI->getMetadata(LLVMContext::MD_invariant_group))
        NewLoad->setMetadata(LLVMContext::MD_invariant_group, InvGroupMD);
      if (auto *RangeMD = LI->getMetadata(LLVMContext::MD_range))
        NewLoad->setMetadata(LLVMContext::MD_range, RangeMD);
  
      // We do not propagate the old load's debug location, because the new
      // load now lives in a different BB, and we want to avoid a jumpy line
      // table.
      // FIXME: How do we retain source locations without causing poor debugging
      // behavior?
  
      // Add the newly created load.
      ValuesPerBlock.push_back(AvailableValueInBlock::get(UnavailablePred,
                                                          NewLoad));
      MD->invalidateCachedPointerInfo(LoadPtr);
      LLVM_DEBUG(dbgs() << "GVN INSERTED " << *NewLoad << '\n');
    }
  
    // Perform PHI construction.
    Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, *this);
    LI->replaceAllUsesWith(V);
    if (isa<PHINode>(V))
      V->takeName(LI);
    if (Instruction *I = dyn_cast<Instruction>(V))
      I->setDebugLoc(LI->getDebugLoc());
    if (V->getType()->isPtrOrPtrVectorTy())
      MD->invalidateCachedPointerInfo(V);
    markInstructionForDeletion(LI);
    ORE->emit([&]() {
      return OptimizationRemark(DEBUG_TYPE, "LoadPRE", LI)
             << "load eliminated by PRE";
    });
    ++NumPRELoad;
    return true;
  }
  
  static void reportLoadElim(LoadInst *LI, Value *AvailableValue,
                             OptimizationRemarkEmitter *ORE) {
    using namespace ore;
  
    ORE->emit([&]() {
      return OptimizationRemark(DEBUG_TYPE, "LoadElim", LI)
             << "load of type " << NV("Type", LI->getType()) << " eliminated"
             << setExtraArgs() << " in favor of "
             << NV("InfavorOfValue", AvailableValue);
    });
  }
  
  /// Attempt to eliminate a load whose dependencies are
  /// non-local by performing PHI construction.
  bool GVN::processNonLocalLoad(LoadInst *LI) {
    // non-local speculations are not allowed under asan.
    if (LI->getParent()->getParent()->hasFnAttribute(
            Attribute::SanitizeAddress) ||
        LI->getParent()->getParent()->hasFnAttribute(
            Attribute::SanitizeHWAddress))
      return false;
  
    // Step 1: Find the non-local dependencies of the load.
    LoadDepVect Deps;
    MD->getNonLocalPointerDependency(LI, Deps);
  
    // If we had to process more than one hundred blocks to find the
    // dependencies, this load isn't worth worrying about.  Optimizing
    // it will be too expensive.
    unsigned NumDeps = Deps.size();
    if (NumDeps > MaxNumDeps)
      return false;
  
    // If we had a phi translation failure, we'll have a single entry which is a
    // clobber in the current block.  Reject this early.
    if (NumDeps == 1 &&
        !Deps[0].getResult().isDef() && !Deps[0].getResult().isClobber()) {
      LLVM_DEBUG(dbgs() << "GVN: non-local load "; LI->printAsOperand(dbgs());
                 dbgs() << " has unknown dependencies\n";);
      return false;
    }
  
    // If this load follows a GEP, see if we can PRE the indices before analyzing.
    if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(LI->getOperand(0))) {
      for (GetElementPtrInst::op_iterator OI = GEP->idx_begin(),
                                          OE = GEP->idx_end();
           OI != OE; ++OI)
        if (Instruction *I = dyn_cast<Instruction>(OI->get()))
          performScalarPRE(I);
    }
  
    // Step 2: Analyze the availability of the load
    AvailValInBlkVect ValuesPerBlock;
    UnavailBlkVect UnavailableBlocks;
    AnalyzeLoadAvailability(LI, Deps, ValuesPerBlock, UnavailableBlocks);
  
    // If we have no predecessors that produce a known value for this load, exit
    // early.
    if (ValuesPerBlock.empty())
      return false;
  
    // Step 3: Eliminate fully redundancy.
    //
    // If all of the instructions we depend on produce a known value for this
    // load, then it is fully redundant and we can use PHI insertion to compute
    // its value.  Insert PHIs and remove the fully redundant value now.
    if (UnavailableBlocks.empty()) {
      LLVM_DEBUG(dbgs() << "GVN REMOVING NONLOCAL LOAD: " << *LI << '\n');
  
      // Perform PHI construction.
      Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, *this);
      LI->replaceAllUsesWith(V);
  
      if (isa<PHINode>(V))
        V->takeName(LI);
      if (Instruction *I = dyn_cast<Instruction>(V))
        // If instruction I has debug info, then we should not update it.
        // Also, if I has a null DebugLoc, then it is still potentially incorrect
        // to propagate LI's DebugLoc because LI may not post-dominate I.
        if (LI->getDebugLoc() && LI->getParent() == I->getParent())
          I->setDebugLoc(LI->getDebugLoc());
      if (V->getType()->isPtrOrPtrVectorTy())
        MD->invalidateCachedPointerInfo(V);
      markInstructionForDeletion(LI);
      ++NumGVNLoad;
      reportLoadElim(LI, V, ORE);
      return true;
    }
  
    // Step 4: Eliminate partial redundancy.
    if (!EnablePRE || !EnableLoadPRE)
      return false;
  
    return PerformLoadPRE(LI, ValuesPerBlock, UnavailableBlocks);
  }
  
  bool GVN::processAssumeIntrinsic(IntrinsicInst *IntrinsicI) {
    assert(IntrinsicI->getIntrinsicID() == Intrinsic::assume &&
           "This function can only be called with llvm.assume intrinsic");
    Value *V = IntrinsicI->getArgOperand(0);
  
    if (ConstantInt *Cond = dyn_cast<ConstantInt>(V)) {
      if (Cond->isZero()) {
        Type *Int8Ty = Type::getInt8Ty(V->getContext());
        // Insert a new store to null instruction before the load to indicate that
        // this code is not reachable.  FIXME: We could insert unreachable
        // instruction directly because we can modify the CFG.
        new StoreInst(UndefValue::get(Int8Ty),
                      Constant::getNullValue(Int8Ty->getPointerTo()),
                      IntrinsicI);
      }
      markInstructionForDeletion(IntrinsicI);
      return false;
    } else if (isa<Constant>(V)) {
      // If it's not false, and constant, it must evaluate to true. This means our
      // assume is assume(true), and thus, pointless, and we don't want to do
      // anything more here.
      return false;
    }
  
    Constant *True = ConstantInt::getTrue(V->getContext());
    bool Changed = false;
  
    for (BasicBlock *Successor : successors(IntrinsicI->getParent())) {
      BasicBlockEdge Edge(IntrinsicI->getParent(), Successor);
  
      // This property is only true in dominated successors, propagateEquality
      // will check dominance for us.
      Changed |= propagateEquality(V, True, Edge, false);
    }
  
    // We can replace assume value with true, which covers cases like this:
    // call void @llvm.assume(i1 %cmp)
    // br i1 %cmp, label %bb1, label %bb2 ; will change %cmp to true
    ReplaceWithConstMap[V] = True;
  
    // If one of *cmp *eq operand is const, adding it to map will cover this:
    // %cmp = fcmp oeq float 3.000000e+00, %0 ; const on lhs could happen
    // call void @llvm.assume(i1 %cmp)
    // ret float %0 ; will change it to ret float 3.000000e+00
    if (auto *CmpI = dyn_cast<CmpInst>(V)) {
      if (CmpI->getPredicate() == CmpInst::Predicate::ICMP_EQ ||
          CmpI->getPredicate() == CmpInst::Predicate::FCMP_OEQ ||
          (CmpI->getPredicate() == CmpInst::Predicate::FCMP_UEQ &&
           CmpI->getFastMathFlags().noNaNs())) {
        Value *CmpLHS = CmpI->getOperand(0);
        Value *CmpRHS = CmpI->getOperand(1);
        if (isa<Constant>(CmpLHS))
          std::swap(CmpLHS, CmpRHS);
        auto *RHSConst = dyn_cast<Constant>(CmpRHS);
  
        // If only one operand is constant.
        if (RHSConst != nullptr && !isa<Constant>(CmpLHS))
          ReplaceWithConstMap[CmpLHS] = RHSConst;
      }
    }
    return Changed;
  }
  
  static void patchAndReplaceAllUsesWith(Instruction *I, Value *Repl) {
    patchReplacementInstruction(I, Repl);
    I->replaceAllUsesWith(Repl);
  }
  
  /// Attempt to eliminate a load, first by eliminating it
  /// locally, and then attempting non-local elimination if that fails.
  bool GVN::processLoad(LoadInst *L) {
    if (!MD)
      return false;
  
    // This code hasn't been audited for ordered or volatile memory access
    if (!L->isUnordered())
      return false;
  
    if (L->use_empty()) {
      markInstructionForDeletion(L);
      return true;
    }
  
    // ... to a pointer that has been loaded from before...
    MemDepResult Dep = MD->getDependency(L);
  
    // If it is defined in another block, try harder.
    if (Dep.isNonLocal())
      return processNonLocalLoad(L);
  
    // Only handle the local case below
    if (!Dep.isDef() && !Dep.isClobber()) {
      // This might be a NonFuncLocal or an Unknown
      LLVM_DEBUG(
          // fast print dep, using operator<< on instruction is too slow.
          dbgs() << "GVN: load "; L->printAsOperand(dbgs());
          dbgs() << " has unknown dependence\n";);
      return false;
    }
  
    AvailableValue AV;
    if (AnalyzeLoadAvailability(L, Dep, L->getPointerOperand(), AV)) {
      Value *AvailableValue = AV.MaterializeAdjustedValue(L, L, *this);
  
      // Replace the load!
      patchAndReplaceAllUsesWith(L, AvailableValue);
      markInstructionForDeletion(L);
      ++NumGVNLoad;
      reportLoadElim(L, AvailableValue, ORE);
      // Tell MDA to rexamine the reused pointer since we might have more
      // information after forwarding it.
      if (MD && AvailableValue->getType()->isPtrOrPtrVectorTy())
        MD->invalidateCachedPointerInfo(AvailableValue);
      return true;
    }
  
    return false;
  }
  
  /// Return a pair the first field showing the value number of \p Exp and the
  /// second field showing whether it is a value number newly created.
  std::pair<uint32_t, bool>
  GVN::ValueTable::assignExpNewValueNum(Expression &Exp) {
    uint32_t &e = expressionNumbering[Exp];
    bool CreateNewValNum = !e;
    if (CreateNewValNum) {
      Expressions.push_back(Exp);
      if (ExprIdx.size() < nextValueNumber + 1)
        ExprIdx.resize(nextValueNumber * 2);
      e = nextValueNumber;
      ExprIdx[nextValueNumber++] = nextExprNumber++;
    }
    return {e, CreateNewValNum};
  }
  
  /// Return whether all the values related with the same \p num are
  /// defined in \p BB.
  bool GVN::ValueTable::areAllValsInBB(uint32_t Num, const BasicBlock *BB,
                                       GVN &Gvn) {
    LeaderTableEntry *Vals = &Gvn.LeaderTable[Num];
    while (Vals && Vals->BB == BB)
      Vals = Vals->Next;
    return !Vals;
  }
  
  /// Wrap phiTranslateImpl to provide caching functionality.
  uint32_t GVN::ValueTable::phiTranslate(const BasicBlock *Pred,
                                         const BasicBlock *PhiBlock, uint32_t Num,
                                         GVN &Gvn) {
    auto FindRes = PhiTranslateTable.find({Num, Pred});
    if (FindRes != PhiTranslateTable.end())
      return FindRes->second;
    uint32_t NewNum = phiTranslateImpl(Pred, PhiBlock, Num, Gvn);
    PhiTranslateTable.insert({{Num, Pred}, NewNum});
    return NewNum;
  }
  
  // Return true if the value number \p Num and NewNum have equal value.
  // Return false if the result is unknown.
  bool GVN::ValueTable::areCallValsEqual(uint32_t Num, uint32_t NewNum,
                                         const BasicBlock *Pred,
                                         const BasicBlock *PhiBlock, GVN &Gvn) {
    CallInst *Call = nullptr;
    LeaderTableEntry *Vals = &Gvn.LeaderTable[Num];
    while (Vals) {
      Call = dyn_cast<CallInst>(Vals->Val);
      if (Call && Call->getParent() == PhiBlock)
        break;
      Vals = Vals->Next;
    }
  
    if (AA->doesNotAccessMemory(Call))
      return true;
  
    if (!MD || !AA->onlyReadsMemory(Call))
      return false;
  
    MemDepResult local_dep = MD->getDependency(Call);
    if (!local_dep.isNonLocal())
      return false;
  
    const MemoryDependenceResults::NonLocalDepInfo &deps =
        MD->getNonLocalCallDependency(Call);
  
    // Check to see if the Call has no function local clobber.
    for (unsigned i = 0; i < deps.size(); i++) {
      if (deps[i].getResult().isNonFuncLocal())
        return true;
    }
    return false;
  }
  
  /// Translate value number \p Num using phis, so that it has the values of
  /// the phis in BB.
  uint32_t GVN::ValueTable::phiTranslateImpl(const BasicBlock *Pred,
                                             const BasicBlock *PhiBlock,
                                             uint32_t Num, GVN &Gvn) {
    if (PHINode *PN = NumberingPhi[Num]) {
      for (unsigned i = 0; i != PN->getNumIncomingValues(); ++i) {
        if (PN->getParent() == PhiBlock && PN->getIncomingBlock(i) == Pred)
          if (uint32_t TransVal = lookup(PN->getIncomingValue(i), false))
            return TransVal;
      }
      return Num;
    }
  
    // If there is any value related with Num is defined in a BB other than
    // PhiBlock, it cannot depend on a phi in PhiBlock without going through
    // a backedge. We can do an early exit in that case to save compile time.
    if (!areAllValsInBB(Num, PhiBlock, Gvn))
      return Num;
  
    if (Num >= ExprIdx.size() || ExprIdx[Num] == 0)
      return Num;
    Expression Exp = Expressions[ExprIdx[Num]];
  
    for (unsigned i = 0; i < Exp.varargs.size(); i++) {
      // For InsertValue and ExtractValue, some varargs are index numbers
      // instead of value numbers. Those index numbers should not be
      // translated.
      if ((i > 1 && Exp.opcode == Instruction::InsertValue) ||
          (i > 0 && Exp.opcode == Instruction::ExtractValue))
        continue;
      Exp.varargs[i] = phiTranslate(Pred, PhiBlock, Exp.varargs[i], Gvn);
    }
  
    if (Exp.commutative) {
      assert(Exp.varargs.size() == 2 && "Unsupported commutative expression!");
      if (Exp.varargs[0] > Exp.varargs[1]) {
        std::swap(Exp.varargs[0], Exp.varargs[1]);
        uint32_t Opcode = Exp.opcode >> 8;
        if (Opcode == Instruction::ICmp || Opcode == Instruction::FCmp)
          Exp.opcode = (Opcode << 8) |
                       CmpInst::getSwappedPredicate(
                           static_cast<CmpInst::Predicate>(Exp.opcode & 255));
      }
    }
  
    if (uint32_t NewNum = expressionNumbering[Exp]) {
      if (Exp.opcode == Instruction::Call && NewNum != Num)
        return areCallValsEqual(Num, NewNum, Pred, PhiBlock, Gvn) ? NewNum : Num;
      return NewNum;
    }
    return Num;
  }
  
  /// Erase stale entry from phiTranslate cache so phiTranslate can be computed
  /// again.
  void GVN::ValueTable::eraseTranslateCacheEntry(uint32_t Num,
                                                 const BasicBlock &CurrBlock) {
    for (const BasicBlock *Pred : predecessors(&CurrBlock)) {
      auto FindRes = PhiTranslateTable.find({Num, Pred});
      if (FindRes != PhiTranslateTable.end())
        PhiTranslateTable.erase(FindRes);
    }
  }
  
  // In order to find a leader for a given value number at a
  // specific basic block, we first obtain the list of all Values for that number,
  // and then scan the list to find one whose block dominates the block in
  // question.  This is fast because dominator tree queries consist of only
  // a few comparisons of DFS numbers.
  Value *GVN::findLeader(const BasicBlock *BB, uint32_t num) {
    LeaderTableEntry Vals = LeaderTable[num];
    if (!Vals.Val) return nullptr;
  
    Value *Val = nullptr;
    if (DT->dominates(Vals.BB, BB)) {
      Val = Vals.Val;
      if (isa<Constant>(Val)) return Val;
    }
  
    LeaderTableEntry* Next = Vals.Next;
    while (Next) {
      if (DT->dominates(Next->BB, BB)) {
        if (isa<Constant>(Next->Val)) return Next->Val;
        if (!Val) Val = Next->Val;
      }
  
      Next = Next->Next;
    }
  
    return Val;
  }
  
  /// There is an edge from 'Src' to 'Dst'.  Return
  /// true if every path from the entry block to 'Dst' passes via this edge.  In
  /// particular 'Dst' must not be reachable via another edge from 'Src'.
  static bool isOnlyReachableViaThisEdge(const BasicBlockEdge &E,
                                         DominatorTree *DT) {
    // While in theory it is interesting to consider the case in which Dst has
    // more than one predecessor, because Dst might be part of a loop which is
    // only reachable from Src, in practice it is pointless since at the time
    // GVN runs all such loops have preheaders, which means that Dst will have
    // been changed to have only one predecessor, namely Src.
    const BasicBlock *Pred = E.getEnd()->getSinglePredecessor();
    assert((!Pred || Pred == E.getStart()) &&
           "No edge between these basic blocks!");
    return Pred != nullptr;
  }
  
  void GVN::assignBlockRPONumber(Function &F) {
    BlockRPONumber.clear();
    uint32_t NextBlockNumber = 1;
    ReversePostOrderTraversal<Function *> RPOT(&F);
    for (BasicBlock *BB : RPOT)
      BlockRPONumber[BB] = NextBlockNumber++;
    InvalidBlockRPONumbers = false;
  }
  
  // Tries to replace instruction with const, using information from
  // ReplaceWithConstMap.
  bool GVN::replaceOperandsWithConsts(Instruction *Instr) const {
    bool Changed = false;
    for (unsigned OpNum = 0; OpNum < Instr->getNumOperands(); ++OpNum) {
      Value *Operand = Instr->getOperand(OpNum);
      auto it = ReplaceWithConstMap.find(Operand);
      if (it != ReplaceWithConstMap.end()) {
        assert(!isa<Constant>(Operand) &&
               "Replacing constants with constants is invalid");
        LLVM_DEBUG(dbgs() << "GVN replacing: " << *Operand << " with "
                          << *it->second << " in instruction " << *Instr << '\n');
        Instr->setOperand(OpNum, it->second);
        Changed = true;
      }
    }
    return Changed;
  }
  
  /// The given values are known to be equal in every block
  /// dominated by 'Root'.  Exploit this, for example by replacing 'LHS' with
  /// 'RHS' everywhere in the scope.  Returns whether a change was made.
  /// If DominatesByEdge is false, then it means that we will propagate the RHS
  /// value starting from the end of Root.Start.
  bool GVN::propagateEquality(Value *LHS, Value *RHS, const BasicBlockEdge &Root,
                              bool DominatesByEdge) {
    SmallVector<std::pair<Value*, Value*>, 4> Worklist;
    Worklist.push_back(std::make_pair(LHS, RHS));
    bool Changed = false;
    // For speed, compute a conservative fast approximation to
    // DT->dominates(Root, Root.getEnd());
    const bool RootDominatesEnd = isOnlyReachableViaThisEdge(Root, DT);
  
    while (!Worklist.empty()) {
      std::pair<Value*, Value*> Item = Worklist.pop_back_val();
      LHS = Item.first; RHS = Item.second;
  
      if (LHS == RHS)
        continue;
      assert(LHS->getType() == RHS->getType() && "Equality but unequal types!");
  
      // Don't try to propagate equalities between constants.
      if (isa<Constant>(LHS) && isa<Constant>(RHS))
        continue;
  
      // Prefer a constant on the right-hand side, or an Argument if no constants.
      if (isa<Constant>(LHS) || (isa<Argument>(LHS) && !isa<Constant>(RHS)))
        std::swap(LHS, RHS);
      assert((isa<Argument>(LHS) || isa<Instruction>(LHS)) && "Unexpected value!");
  
      // If there is no obvious reason to prefer the left-hand side over the
      // right-hand side, ensure the longest lived term is on the right-hand side,
      // so the shortest lived term will be replaced by the longest lived.
      // This tends to expose more simplifications.
      uint32_t LVN = VN.lookupOrAdd(LHS);
      if ((isa<Argument>(LHS) && isa<Argument>(RHS)) ||
          (isa<Instruction>(LHS) && isa<Instruction>(RHS))) {
        // Move the 'oldest' value to the right-hand side, using the value number
        // as a proxy for age.
        uint32_t RVN = VN.lookupOrAdd(RHS);
        if (LVN < RVN) {
          std::swap(LHS, RHS);
          LVN = RVN;
        }
      }
  
      // If value numbering later sees that an instruction in the scope is equal
      // to 'LHS' then ensure it will be turned into 'RHS'.  In order to preserve
      // the invariant that instructions only occur in the leader table for their
      // own value number (this is used by removeFromLeaderTable), do not do this
      // if RHS is an instruction (if an instruction in the scope is morphed into
      // LHS then it will be turned into RHS by the next GVN iteration anyway, so
      // using the leader table is about compiling faster, not optimizing better).
      // The leader table only tracks basic blocks, not edges. Only add to if we
      // have the simple case where the edge dominates the end.
      if (RootDominatesEnd && !isa<Instruction>(RHS))
        addToLeaderTable(LVN, RHS, Root.getEnd());
  
      // Replace all occurrences of 'LHS' with 'RHS' everywhere in the scope.  As
      // LHS always has at least one use that is not dominated by Root, this will
      // never do anything if LHS has only one use.
      if (!LHS->hasOneUse()) {
        unsigned NumReplacements =
            DominatesByEdge
                ? replaceDominatedUsesWith(LHS, RHS, *DT, Root)
                : replaceDominatedUsesWith(LHS, RHS, *DT, Root.getStart());
  
        Changed |= NumReplacements > 0;
        NumGVNEqProp += NumReplacements;
        // Cached information for anything that uses LHS will be invalid.
        if (MD)
          MD->invalidateCachedPointerInfo(LHS);
      }
  
      // Now try to deduce additional equalities from this one. For example, if
      // the known equality was "(A != B)" == "false" then it follows that A and B
      // are equal in the scope. Only boolean equalities with an explicit true or
      // false RHS are currently supported.
      if (!RHS->getType()->isIntegerTy(1))
        // Not a boolean equality - bail out.
        continue;
      ConstantInt *CI = dyn_cast<ConstantInt>(RHS);
      if (!CI)
        // RHS neither 'true' nor 'false' - bail out.
        continue;
      // Whether RHS equals 'true'.  Otherwise it equals 'false'.
      bool isKnownTrue = CI->isMinusOne();
      bool isKnownFalse = !isKnownTrue;
  
      // If "A && B" is known true then both A and B are known true.  If "A || B"
      // is known false then both A and B are known false.
      Value *A, *B;
      if ((isKnownTrue && match(LHS, m_And(m_Value(A), m_Value(B)))) ||
          (isKnownFalse && match(LHS, m_Or(m_Value(A), m_Value(B))))) {
        Worklist.push_back(std::make_pair(A, RHS));
        Worklist.push_back(std::make_pair(B, RHS));
        continue;
      }
  
      // If we are propagating an equality like "(A == B)" == "true" then also
      // propagate the equality A == B.  When propagating a comparison such as
      // "(A >= B)" == "true", replace all instances of "A < B" with "false".
      if (CmpInst *Cmp = dyn_cast<CmpInst>(LHS)) {
        Value *Op0 = Cmp->getOperand(0), *Op1 = Cmp->getOperand(1);
  
        // If "A == B" is known true, or "A != B" is known false, then replace
        // A with B everywhere in the scope.
        if ((isKnownTrue && Cmp->getPredicate() == CmpInst::ICMP_EQ) ||
            (isKnownFalse && Cmp->getPredicate() == CmpInst::ICMP_NE))
          Worklist.push_back(std::make_pair(Op0, Op1));
  
        // Handle the floating point versions of equality comparisons too.
        if ((isKnownTrue && Cmp->getPredicate() == CmpInst::FCMP_OEQ) ||
            (isKnownFalse && Cmp->getPredicate() == CmpInst::FCMP_UNE)) {
  
          // Floating point -0.0 and 0.0 compare equal, so we can only
          // propagate values if we know that we have a constant and that
          // its value is non-zero.
  
          // FIXME: We should do this optimization if 'no signed zeros' is
          // applicable via an instruction-level fast-math-flag or some other
          // indicator that relaxed FP semantics are being used.
  
          if (isa<ConstantFP>(Op1) && !cast<ConstantFP>(Op1)->isZero())
            Worklist.push_back(std::make_pair(Op0, Op1));
        }
  
        // If "A >= B" is known true, replace "A < B" with false everywhere.
        CmpInst::Predicate NotPred = Cmp->getInversePredicate();
        Constant *NotVal = ConstantInt::get(Cmp->getType(), isKnownFalse);
        // Since we don't have the instruction "A < B" immediately to hand, work
        // out the value number that it would have and use that to find an
        // appropriate instruction (if any).
        uint32_t NextNum = VN.getNextUnusedValueNumber();
        uint32_t Num = VN.lookupOrAddCmp(Cmp->getOpcode(), NotPred, Op0, Op1);
        // If the number we were assigned was brand new then there is no point in
        // looking for an instruction realizing it: there cannot be one!
        if (Num < NextNum) {
          Value *NotCmp = findLeader(Root.getEnd(), Num);
          if (NotCmp && isa<Instruction>(NotCmp)) {
            unsigned NumReplacements =
                DominatesByEdge
                    ? replaceDominatedUsesWith(NotCmp, NotVal, *DT, Root)
                    : replaceDominatedUsesWith(NotCmp, NotVal, *DT,
                                               Root.getStart());
            Changed |= NumReplacements > 0;
            NumGVNEqProp += NumReplacements;
            // Cached information for anything that uses NotCmp will be invalid.
            if (MD)
              MD->invalidateCachedPointerInfo(NotCmp);
          }
        }
        // Ensure that any instruction in scope that gets the "A < B" value number
        // is replaced with false.
        // The leader table only tracks basic blocks, not edges. Only add to if we
        // have the simple case where the edge dominates the end.
        if (RootDominatesEnd)
          addToLeaderTable(Num, NotVal, Root.getEnd());
  
        continue;
      }
    }
  
    return Changed;
  }
  
  /// When calculating availability, handle an instruction
  /// by inserting it into the appropriate sets
  bool GVN::processInstruction(Instruction *I) {
    // Ignore dbg info intrinsics.
    if (isa<DbgInfoIntrinsic>(I))
      return false;
  
    // If the instruction can be easily simplified then do so now in preference
    // to value numbering it.  Value numbering often exposes redundancies, for
    // example if it determines that %y is equal to %x then the instruction
    // "%z = and i32 %x, %y" becomes "%z = and i32 %x, %x" which we now simplify.
    const DataLayout &DL = I->getModule()->getDataLayout();
    if (Value *V = SimplifyInstruction(I, {DL, TLI, DT, AC})) {
      bool Changed = false;
      if (!I->use_empty()) {
        I->replaceAllUsesWith(V);
        Changed = true;
      }
      if (isInstructionTriviallyDead(I, TLI)) {
        markInstructionForDeletion(I);
        Changed = true;
      }
      if (Changed) {
        if (MD && V->getType()->isPtrOrPtrVectorTy())
          MD->invalidateCachedPointerInfo(V);
        ++NumGVNSimpl;
        return true;
      }
    }
  
    if (IntrinsicInst *IntrinsicI = dyn_cast<IntrinsicInst>(I))
      if (IntrinsicI->getIntrinsicID() == Intrinsic::assume)
        return processAssumeIntrinsic(IntrinsicI);
  
    if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
      if (processLoad(LI))
        return true;
  
      unsigned Num = VN.lookupOrAdd(LI);
      addToLeaderTable(Num, LI, LI->getParent());
      return false;
    }
  
    // For conditional branches, we can perform simple conditional propagation on
    // the condition value itself.
    if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
      if (!BI->isConditional())
        return false;
  
      if (isa<Constant>(BI->getCondition()))
        return processFoldableCondBr(BI);
  
      Value *BranchCond = BI->getCondition();
      BasicBlock *TrueSucc = BI->getSuccessor(0);
      BasicBlock *FalseSucc = BI->getSuccessor(1);
      // Avoid multiple edges early.
      if (TrueSucc == FalseSucc)
        return false;
  
      BasicBlock *Parent = BI->getParent();
      bool Changed = false;
  
      Value *TrueVal = ConstantInt::getTrue(TrueSucc->getContext());
      BasicBlockEdge TrueE(Parent, TrueSucc);
      Changed |= propagateEquality(BranchCond, TrueVal, TrueE, true);
  
      Value *FalseVal = ConstantInt::getFalse(FalseSucc->getContext());
      BasicBlockEdge FalseE(Parent, FalseSucc);
      Changed |= propagateEquality(BranchCond, FalseVal, FalseE, true);
  
      return Changed;
    }
  
    // For switches, propagate the case values into the case destinations.
    if (SwitchInst *SI = dyn_cast<SwitchInst>(I)) {
      Value *SwitchCond = SI->getCondition();
      BasicBlock *Parent = SI->getParent();
      bool Changed = false;
  
      // Remember how many outgoing edges there are to every successor.
      SmallDenseMap<BasicBlock *, unsigned, 16> SwitchEdges;
      for (unsigned i = 0, n = SI->getNumSuccessors(); i != n; ++i)
        ++SwitchEdges[SI->getSuccessor(i)];
  
      for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
           i != e; ++i) {
        BasicBlock *Dst = i->getCaseSuccessor();
        // If there is only a single edge, propagate the case value into it.
        if (SwitchEdges.lookup(Dst) == 1) {
          BasicBlockEdge E(Parent, Dst);
          Changed |= propagateEquality(SwitchCond, i->getCaseValue(), E, true);
        }
      }
      return Changed;
    }
  
    // Instructions with void type don't return a value, so there's
    // no point in trying to find redundancies in them.
    if (I->getType()->isVoidTy())
      return false;
  
    uint32_t NextNum = VN.getNextUnusedValueNumber();
    unsigned Num = VN.lookupOrAdd(I);
  
    // Allocations are always uniquely numbered, so we can save time and memory
    // by fast failing them.
    if (isa<AllocaInst>(I) || I->isTerminator() || isa<PHINode>(I)) {
      addToLeaderTable(Num, I, I->getParent());
      return false;
    }
  
    // If the number we were assigned was a brand new VN, then we don't
    // need to do a lookup to see if the number already exists
    // somewhere in the domtree: it can't!
    if (Num >= NextNum) {
      addToLeaderTable(Num, I, I->getParent());
      return false;
    }
  
    // Perform fast-path value-number based elimination of values inherited from
    // dominators.
    Value *Repl = findLeader(I->getParent(), Num);
    if (!Repl) {
      // Failure, just remember this instance for future use.
      addToLeaderTable(Num, I, I->getParent());
      return false;
    } else if (Repl == I) {
      // If I was the result of a shortcut PRE, it might already be in the table
      // and the best replacement for itself. Nothing to do.
      return false;
    }
  
    // Remove it!
    patchAndReplaceAllUsesWith(I, Repl);
    if (MD && Repl->getType()->isPtrOrPtrVectorTy())
      MD->invalidateCachedPointerInfo(Repl);
    markInstructionForDeletion(I);
    return true;
  }
  
  /// runOnFunction - This is the main transformation entry point for a function.
  bool GVN::runImpl(Function &F, AssumptionCache &RunAC, DominatorTree &RunDT,
                    const TargetLibraryInfo &RunTLI, AAResults &RunAA,
                    MemoryDependenceResults *RunMD, LoopInfo *LI,
                    OptimizationRemarkEmitter *RunORE) {
    AC = &RunAC;
    DT = &RunDT;
    VN.setDomTree(DT);
    TLI = &RunTLI;
    VN.setAliasAnalysis(&RunAA);
    MD = RunMD;
    ImplicitControlFlowTracking ImplicitCFT(DT);
    ICF = &ImplicitCFT;
    this->LI = LI;
    VN.setMemDep(MD);
    ORE = RunORE;
    InvalidBlockRPONumbers = true;
  
    bool Changed = false;
    bool ShouldContinue = true;
  
    DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Eager);
    // Merge unconditional branches, allowing PRE to catch more
    // optimization opportunities.
    for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) {
      BasicBlock *BB = &*FI++;
  
      bool removedBlock = MergeBlockIntoPredecessor(BB, &DTU, LI, nullptr, MD);
      if (removedBlock)
        ++NumGVNBlocks;
  
      Changed |= removedBlock;
    }
  
    unsigned Iteration = 0;
    while (ShouldContinue) {
      LLVM_DEBUG(dbgs() << "GVN iteration: " << Iteration << "\n");
      ShouldContinue = iterateOnFunction(F);
      Changed |= ShouldContinue;
      ++Iteration;
    }
  
    if (EnablePRE) {
      // Fabricate val-num for dead-code in order to suppress assertion in
      // performPRE().
      assignValNumForDeadCode();
      bool PREChanged = true;
      while (PREChanged) {
        PREChanged = performPRE(F);
        Changed |= PREChanged;
      }
    }
  
    // FIXME: Should perform GVN again after PRE does something.  PRE can move
    // computations into blocks where they become fully redundant.  Note that
    // we can't do this until PRE's critical edge splitting updates memdep.
    // Actually, when this happens, we should just fully integrate PRE into GVN.
  
    cleanupGlobalSets();
    // Do not cleanup DeadBlocks in cleanupGlobalSets() as it's called for each
    // iteration.
    DeadBlocks.clear();
  
    return Changed;
  }
  
  bool GVN::processBlock(BasicBlock *BB) {
    // FIXME: Kill off InstrsToErase by doing erasing eagerly in a helper function
    // (and incrementing BI before processing an instruction).
    assert(InstrsToErase.empty() &&
           "We expect InstrsToErase to be empty across iterations");
    if (DeadBlocks.count(BB))
      return false;
  
    // Clearing map before every BB because it can be used only for single BB.
    ReplaceWithConstMap.clear();
    bool ChangedFunction = false;
  
    for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
         BI != BE;) {
      if (!ReplaceWithConstMap.empty())
        ChangedFunction |= replaceOperandsWithConsts(&*BI);
      ChangedFunction |= processInstruction(&*BI);
  
      if (InstrsToErase.empty()) {
        ++BI;
        continue;
      }
  
      // If we need some instructions deleted, do it now.
      NumGVNInstr += InstrsToErase.size();
  
      // Avoid iterator invalidation.
      bool AtStart = BI == BB->begin();
      if (!AtStart)
        --BI;
  
      for (auto *I : InstrsToErase) {
        assert(I->getParent() == BB && "Removing instruction from wrong block?");
        LLVM_DEBUG(dbgs() << "GVN removed: " << *I << '\n');
        salvageDebugInfo(*I);
        if (MD) MD->removeInstruction(I);
        LLVM_DEBUG(verifyRemoved(I));
        ICF->removeInstruction(I);
        I->eraseFromParent();
      }
      InstrsToErase.clear();
  
      if (AtStart)
        BI = BB->begin();
      else
        ++BI;
    }
  
    return ChangedFunction;
  }
  
  // Instantiate an expression in a predecessor that lacked it.
  bool GVN::performScalarPREInsertion(Instruction *Instr, BasicBlock *Pred,
                                      BasicBlock *Curr, unsigned int ValNo) {
    // Because we are going top-down through the block, all value numbers
    // will be available in the predecessor by the time we need them.  Any
    // that weren't originally present will have been instantiated earlier
    // in this loop.
    bool success = true;
    for (unsigned i = 0, e = Instr->getNumOperands(); i != e; ++i) {
      Value *Op = Instr->getOperand(i);
      if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op))
        continue;
      // This could be a newly inserted instruction, in which case, we won't
      // find a value number, and should give up before we hurt ourselves.
      // FIXME: Rewrite the infrastructure to let it easier to value number
      // and process newly inserted instructions.
      if (!VN.exists(Op)) {
        success = false;
        break;
      }
      uint32_t TValNo =
          VN.phiTranslate(Pred, Curr, VN.lookup(Op), *this);
      if (Value *V = findLeader(Pred, TValNo)) {
        Instr->setOperand(i, V);
      } else {
        success = false;
        break;
      }
    }
  
    // Fail out if we encounter an operand that is not available in
    // the PRE predecessor.  This is typically because of loads which
    // are not value numbered precisely.
    if (!success)
      return false;
  
    Instr->insertBefore(Pred->getTerminator());
    Instr->setName(Instr->getName() + ".pre");
    Instr->setDebugLoc(Instr->getDebugLoc());
  
    unsigned Num = VN.lookupOrAdd(Instr);
    VN.add(Instr, Num);
  
    // Update the availability map to include the new instruction.
    addToLeaderTable(Num, Instr, Pred);
    return true;
  }
  
  bool GVN::performScalarPRE(Instruction *CurInst) {
    if (isa<AllocaInst>(CurInst) || CurInst->isTerminator() ||
        isa<PHINode>(CurInst) || CurInst->getType()->isVoidTy() ||
        CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() ||
        isa<DbgInfoIntrinsic>(CurInst))
      return false;
  
    // Don't do PRE on compares. The PHI would prevent CodeGenPrepare from
    // sinking the compare again, and it would force the code generator to
    // move the i1 from processor flags or predicate registers into a general
    // purpose register.
    if (isa<CmpInst>(CurInst))
      return false;
  
    // Don't do PRE on GEPs. The inserted PHI would prevent CodeGenPrepare from
    // sinking the addressing mode computation back to its uses. Extending the
    // GEP's live range increases the register pressure, and therefore it can
    // introduce unnecessary spills.
    //
    // This doesn't prevent Load PRE. PHI translation will make the GEP available
    // to the load by moving it to the predecessor block if necessary.
    if (isa<GetElementPtrInst>(CurInst))
      return false;
  
    // We don't currently value number ANY inline asm calls.
    if (auto *CallB = dyn_cast<CallBase>(CurInst))
      if (CallB->isInlineAsm())
        return false;
  
    uint32_t ValNo = VN.lookup(CurInst);
  
    // Look for the predecessors for PRE opportunities.  We're
    // only trying to solve the basic diamond case, where
    // a value is computed in the successor and one predecessor,
    // but not the other.  We also explicitly disallow cases
    // where the successor is its own predecessor, because they're
    // more complicated to get right.
    unsigned NumWith = 0;
    unsigned NumWithout = 0;
    BasicBlock *PREPred = nullptr;
    BasicBlock *CurrentBlock = CurInst->getParent();
  
    // Update the RPO numbers for this function.
    if (InvalidBlockRPONumbers)
      assignBlockRPONumber(*CurrentBlock->getParent());
  
    SmallVector<std::pair<Value *, BasicBlock *>, 8> predMap;
    for (BasicBlock *P : predecessors(CurrentBlock)) {
      // We're not interested in PRE where blocks with predecessors that are
      // not reachable.
      if (!DT->isReachableFromEntry(P)) {
        NumWithout = 2;
        break;
      }
      // It is not safe to do PRE when P->CurrentBlock is a loop backedge, and
      // when CurInst has operand defined in CurrentBlock (so it may be defined
      // by phi in the loop header).
      assert(BlockRPONumber.count(P) && BlockRPONumber.count(CurrentBlock) &&
             "Invalid BlockRPONumber map.");
      if (BlockRPONumber[P] >= BlockRPONumber[CurrentBlock] &&
          llvm::any_of(CurInst->operands(), [&](const Use &U) {
            if (auto *Inst = dyn_cast<Instruction>(U.get()))
              return Inst->getParent() == CurrentBlock;
            return false;
          })) {
        NumWithout = 2;
        break;
      }
  
      uint32_t TValNo = VN.phiTranslate(P, CurrentBlock, ValNo, *this);
      Value *predV = findLeader(P, TValNo);
      if (!predV) {
        predMap.push_back(std::make_pair(static_cast<Value *>(nullptr), P));
        PREPred = P;
        ++NumWithout;
      } else if (predV == CurInst) {
        /* CurInst dominates this predecessor. */
        NumWithout = 2;
        break;
      } else {
        predMap.push_back(std::make_pair(predV, P));
        ++NumWith;
      }
    }
  
    // Don't do PRE when it might increase code size, i.e. when
    // we would need to insert instructions in more than one pred.
    if (NumWithout > 1 || NumWith == 0)
      return false;
  
    // We may have a case where all predecessors have the instruction,
    // and we just need to insert a phi node. Otherwise, perform
    // insertion.
    Instruction *PREInstr = nullptr;
  
    if (NumWithout != 0) {
      if (!isSafeToSpeculativelyExecute(CurInst)) {
        // It is only valid to insert a new instruction if the current instruction
        // is always executed. An instruction with implicit control flow could
        // prevent us from doing it. If we cannot speculate the execution, then
        // PRE should be prohibited.
        if (ICF->isDominatedByICFIFromSameBlock(CurInst))
          return false;
      }
  
      // Don't do PRE across indirect branch.
      if (isa<IndirectBrInst>(PREPred->getTerminator()))
        return false;
  
      // Don't do PRE across callbr.
      // FIXME: Can we do this across the fallthrough edge?
      if (isa<CallBrInst>(PREPred->getTerminator()))
        return false;
  
      // We can't do PRE safely on a critical edge, so instead we schedule
      // the edge to be split and perform the PRE the next time we iterate
      // on the function.
      unsigned SuccNum = GetSuccessorNumber(PREPred, CurrentBlock);
      if (isCriticalEdge(PREPred->getTerminator(), SuccNum)) {
        toSplit.push_back(std::make_pair(PREPred->getTerminator(), SuccNum));
        return false;
      }
      // We need to insert somewhere, so let's give it a shot
      PREInstr = CurInst->clone();
      if (!performScalarPREInsertion(PREInstr, PREPred, CurrentBlock, ValNo)) {
        // If we failed insertion, make sure we remove the instruction.
        LLVM_DEBUG(verifyRemoved(PREInstr));
        PREInstr->deleteValue();
        return false;
      }
    }
  
    // Either we should have filled in the PRE instruction, or we should
    // not have needed insertions.
    assert(PREInstr != nullptr || NumWithout == 0);
  
    ++NumGVNPRE;
  
    // Create a PHI to make the value available in this block.
    PHINode *Phi =
        PHINode::Create(CurInst->getType(), predMap.size(),
                        CurInst->getName() + ".pre-phi", &CurrentBlock->front());
    for (unsigned i = 0, e = predMap.size(); i != e; ++i) {
      if (Value *V = predMap[i].first) {
        // If we use an existing value in this phi, we have to patch the original
        // value because the phi will be used to replace a later value.
        patchReplacementInstruction(CurInst, V);
        Phi->addIncoming(V, predMap[i].second);
      } else
        Phi->addIncoming(PREInstr, PREPred);
    }
  
    VN.add(Phi, ValNo);
    // After creating a new PHI for ValNo, the phi translate result for ValNo will
    // be changed, so erase the related stale entries in phi translate cache.
    VN.eraseTranslateCacheEntry(ValNo, *CurrentBlock);
    addToLeaderTable(ValNo, Phi, CurrentBlock);
    Phi->setDebugLoc(CurInst->getDebugLoc());
    CurInst->replaceAllUsesWith(Phi);
    if (MD && Phi->getType()->isPtrOrPtrVectorTy())
      MD->invalidateCachedPointerInfo(Phi);
    VN.erase(CurInst);
    removeFromLeaderTable(ValNo, CurInst, CurrentBlock);
  
    LLVM_DEBUG(dbgs() << "GVN PRE removed: " << *CurInst << '\n');
    if (MD)
      MD->removeInstruction(CurInst);
    LLVM_DEBUG(verifyRemoved(CurInst));
    // FIXME: Intended to be markInstructionForDeletion(CurInst), but it causes
    // some assertion failures.
    ICF->removeInstruction(CurInst);
    CurInst->eraseFromParent();
    ++NumGVNInstr;
  
    return true;
  }
  
  /// Perform a purely local form of PRE that looks for diamond
  /// control flow patterns and attempts to perform simple PRE at the join point.
  bool GVN::performPRE(Function &F) {
    bool Changed = false;
    for (BasicBlock *CurrentBlock : depth_first(&F.getEntryBlock())) {
      // Nothing to PRE in the entry block.
      if (CurrentBlock == &F.getEntryBlock())
        continue;
  
      // Don't perform PRE on an EH pad.
      if (CurrentBlock->isEHPad())
        continue;
  
      for (BasicBlock::iterator BI = CurrentBlock->begin(),
                                BE = CurrentBlock->end();
           BI != BE;) {
        Instruction *CurInst = &*BI++;
        Changed |= performScalarPRE(CurInst);
      }
    }
  
    if (splitCriticalEdges())
      Changed = true;
  
    return Changed;
  }
  
  /// Split the critical edge connecting the given two blocks, and return
  /// the block inserted to the critical edge.
  BasicBlock *GVN::splitCriticalEdges(BasicBlock *Pred, BasicBlock *Succ) {
    BasicBlock *BB =
        SplitCriticalEdge(Pred, Succ, CriticalEdgeSplittingOptions(DT, LI));
    if (MD)
      MD->invalidateCachedPredecessors();
    InvalidBlockRPONumbers = true;
    return BB;
  }
  
  /// Split critical edges found during the previous
  /// iteration that may enable further optimization.
  bool GVN::splitCriticalEdges() {
    if (toSplit.empty())
      return false;
    do {
      std::pair<Instruction *, unsigned> Edge = toSplit.pop_back_val();
      SplitCriticalEdge(Edge.first, Edge.second,
                        CriticalEdgeSplittingOptions(DT, LI));
    } while (!toSplit.empty());
    if (MD) MD->invalidateCachedPredecessors();
    InvalidBlockRPONumbers = true;
    return true;
  }
  
  /// Executes one iteration of GVN
  bool GVN::iterateOnFunction(Function &F) {
    cleanupGlobalSets();
  
    // Top-down walk of the dominator tree
    bool Changed = false;
    // Needed for value numbering with phi construction to work.
    // RPOT walks the graph in its constructor and will not be invalidated during
    // processBlock.
    ReversePostOrderTraversal<Function *> RPOT(&F);
  
    for (BasicBlock *BB : RPOT)
      Changed |= processBlock(BB);
  
    return Changed;
  }
  
  void GVN::cleanupGlobalSets() {
    VN.clear();
    LeaderTable.clear();
    BlockRPONumber.clear();
    TableAllocator.Reset();
    ICF->clear();
    InvalidBlockRPONumbers = true;
  }
  
  /// Verify that the specified instruction does not occur in our
  /// internal data structures.
  void GVN::verifyRemoved(const Instruction *Inst) const {
    VN.verifyRemoved(Inst);
  
    // Walk through the value number scope to make sure the instruction isn't
    // ferreted away in it.
    for (DenseMap<uint32_t, LeaderTableEntry>::const_iterator
         I = LeaderTable.begin(), E = LeaderTable.end(); I != E; ++I) {
      const LeaderTableEntry *Node = &I->second;
      assert(Node->Val != Inst && "Inst still in value numbering scope!");
  
      while (Node->Next) {
        Node = Node->Next;
        assert(Node->Val != Inst && "Inst still in value numbering scope!");
      }
    }
  }
  
  /// BB is declared dead, which implied other blocks become dead as well. This
  /// function is to add all these blocks to "DeadBlocks". For the dead blocks'
  /// live successors, update their phi nodes by replacing the operands
  /// corresponding to dead blocks with UndefVal.
  void GVN::addDeadBlock(BasicBlock *BB) {
    SmallVector<BasicBlock *, 4> NewDead;
    SmallSetVector<BasicBlock *, 4> DF;
  
    NewDead.push_back(BB);
    while (!NewDead.empty()) {
      BasicBlock *D = NewDead.pop_back_val();
      if (DeadBlocks.count(D))
        continue;
  
      // All blocks dominated by D are dead.
      SmallVector<BasicBlock *, 8> Dom;
      DT->getDescendants(D, Dom);
      DeadBlocks.insert(Dom.begin(), Dom.end());
  
      // Figure out the dominance-frontier(D).
      for (BasicBlock *B : Dom) {
        for (BasicBlock *S : successors(B)) {
          if (DeadBlocks.count(S))
            continue;
  
          bool AllPredDead = true;
          for (BasicBlock *P : predecessors(S))
            if (!DeadBlocks.count(P)) {
              AllPredDead = false;
              break;
            }
  
          if (!AllPredDead) {
            // S could be proved dead later on. That is why we don't update phi
            // operands at this moment.
            DF.insert(S);
          } else {
            // While S is not dominated by D, it is dead by now. This could take
            // place if S already have a dead predecessor before D is declared
            // dead.
            NewDead.push_back(S);
          }
        }
      }
    }
  
    // For the dead blocks' live successors, update their phi nodes by replacing
    // the operands corresponding to dead blocks with UndefVal.
    for(SmallSetVector<BasicBlock *, 4>::iterator I = DF.begin(), E = DF.end();
          I != E; I++) {
      BasicBlock *B = *I;
      if (DeadBlocks.count(B))
        continue;
  
      // First, split the critical edges. This might also create additional blocks
      // to preserve LoopSimplify form and adjust edges accordingly.
      SmallVector<BasicBlock *, 4> Preds(pred_begin(B), pred_end(B));
      for (BasicBlock *P : Preds) {
        if (!DeadBlocks.count(P))
          continue;
  
        if (llvm::any_of(successors(P),
                         [B](BasicBlock *Succ) { return Succ == B; }) &&
            isCriticalEdge(P->getTerminator(), B)) {
          if (BasicBlock *S = splitCriticalEdges(P, B))
            DeadBlocks.insert(P = S);
        }
      }
  
      // Now undef the incoming values from the dead predecessors.
      for (BasicBlock *P : predecessors(B)) {
        if (!DeadBlocks.count(P))
          continue;
        for (PHINode &Phi : B->phis()) {
          Phi.setIncomingValueForBlock(P, UndefValue::get(Phi.getType()));
          if (MD)
            MD->invalidateCachedPointerInfo(&Phi);
        }
      }
    }
  }
  
  // If the given branch is recognized as a foldable branch (i.e. conditional
  // branch with constant condition), it will perform following analyses and
  // transformation.
  //  1) If the dead out-coming edge is a critical-edge, split it. Let
  //     R be the target of the dead out-coming edge.
  //  1) Identify the set of dead blocks implied by the branch's dead outcoming
  //     edge. The result of this step will be {X| X is dominated by R}
  //  2) Identify those blocks which haves at least one dead predecessor. The
  //     result of this step will be dominance-frontier(R).
  //  3) Update the PHIs in DF(R) by replacing the operands corresponding to
  //     dead blocks with "UndefVal" in an hope these PHIs will optimized away.
  //
  // Return true iff *NEW* dead code are found.
  bool GVN::processFoldableCondBr(BranchInst *BI) {
    if (!BI || BI->isUnconditional())
      return false;
  
    // If a branch has two identical successors, we cannot declare either dead.
    if (BI->getSuccessor(0) == BI->getSuccessor(1))
      return false;
  
    ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition());
    if (!Cond)
      return false;
  
    BasicBlock *DeadRoot =
        Cond->getZExtValue() ? BI->getSuccessor(1) : BI->getSuccessor(0);
    if (DeadBlocks.count(DeadRoot))
      return false;
  
    if (!DeadRoot->getSinglePredecessor())
      DeadRoot = splitCriticalEdges(BI->getParent(), DeadRoot);
  
    addDeadBlock(DeadRoot);
    return true;
  }
  
  // performPRE() will trigger assert if it comes across an instruction without
  // associated val-num. As it normally has far more live instructions than dead
  // instructions, it makes more sense just to "fabricate" a val-number for the
  // dead code than checking if instruction involved is dead or not.
  void GVN::assignValNumForDeadCode() {
    for (BasicBlock *BB : DeadBlocks) {
      for (Instruction &Inst : *BB) {
        unsigned ValNum = VN.lookupOrAdd(&Inst);
        addToLeaderTable(ValNum, &Inst, BB);
      }
    }
  }
  
  class llvm::gvn::GVNLegacyPass : public FunctionPass {
  public:
    static char ID; // Pass identification, replacement for typeid
  
    explicit GVNLegacyPass(bool NoMemDepAnalysis = !EnableMemDep)
        : FunctionPass(ID), NoMemDepAnalysis(NoMemDepAnalysis) {
      initializeGVNLegacyPassPass(*PassRegistry::getPassRegistry());
    }
  
    bool runOnFunction(Function &F) override {
      if (skipFunction(F))
        return false;
  
      auto *LIWP = getAnalysisIfAvailable<LoopInfoWrapperPass>();
  
      return Impl.runImpl(
          F, getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F),
          getAnalysis<DominatorTreeWrapperPass>().getDomTree(),
          getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(),
          getAnalysis<AAResultsWrapperPass>().getAAResults(),
          NoMemDepAnalysis ? nullptr
                  : &getAnalysis<MemoryDependenceWrapperPass>().getMemDep(),
          LIWP ? &LIWP->getLoopInfo() : nullptr,
          &getAnalysis<OptimizationRemarkEmitterWrapperPass>().getORE());
    }
  
    void getAnalysisUsage(AnalysisUsage &AU) const override {
      AU.addRequired<AssumptionCacheTracker>();
      AU.addRequired<DominatorTreeWrapperPass>();
      AU.addRequired<TargetLibraryInfoWrapperPass>();
      AU.addRequired<LoopInfoWrapperPass>();
      if (!NoMemDepAnalysis)
        AU.addRequired<MemoryDependenceWrapperPass>();
      AU.addRequired<AAResultsWrapperPass>();
  
      AU.addPreserved<DominatorTreeWrapperPass>();
      AU.addPreserved<GlobalsAAWrapperPass>();
      AU.addPreserved<TargetLibraryInfoWrapperPass>();
      AU.addPreserved<LoopInfoWrapperPass>();
      AU.addPreservedID(LoopSimplifyID);
      AU.addRequired<OptimizationRemarkEmitterWrapperPass>();
    }
  
  private:
    bool NoMemDepAnalysis;
    GVN Impl;
  };
  
  char GVNLegacyPass::ID = 0;
  
  INITIALIZE_PASS_BEGIN(GVNLegacyPass, "gvn", "Global Value Numbering", false, false)
  INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
  INITIALIZE_PASS_DEPENDENCY(MemoryDependenceWrapperPass)
  INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
  INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
  INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
  INITIALIZE_PASS_DEPENDENCY(GlobalsAAWrapperPass)
  INITIALIZE_PASS_DEPENDENCY(OptimizationRemarkEmitterWrapperPass)
  INITIALIZE_PASS_END(GVNLegacyPass, "gvn", "Global Value Numbering", false, false)
  
  // The public interface to this file...
  FunctionPass *llvm::createGVNPass(bool NoMemDepAnalysis) {
    return new GVNLegacyPass(NoMemDepAnalysis);
  }
  