text: //===- SimplifyCFG.cpp - Code to perform CFG simplification ---------------===//
  //
  // 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
  //
  //===----------------------------------------------------------------------===//
  //
  // Peephole optimize the CFG.
  //
  //===----------------------------------------------------------------------===//
  
  #include "llvm/ADT/APInt.h"
  #include "llvm/ADT/ArrayRef.h"
  #include "llvm/ADT/DenseMap.h"
  #include "llvm/ADT/MapVector.h"
  #include "llvm/ADT/Optional.h"
  #include "llvm/ADT/STLExtras.h"
  #include "llvm/ADT/ScopeExit.h"
  #include "llvm/ADT/Sequence.h"
  #include "llvm/ADT/SetOperations.h"
  #include "llvm/ADT/SetVector.h"
  #include "llvm/ADT/SmallPtrSet.h"
  #include "llvm/ADT/SmallVector.h"
  #include "llvm/ADT/Statistic.h"
  #include "llvm/ADT/StringRef.h"
  #include "llvm/Analysis/AssumptionCache.h"
  #include "llvm/Analysis/CaptureTracking.h"
  #include "llvm/Analysis/ConstantFolding.h"
  #include "llvm/Analysis/DomTreeUpdater.h"
  #include "llvm/Analysis/GuardUtils.h"
  #include "llvm/Analysis/InstructionSimplify.h"
  #include "llvm/Analysis/MemorySSA.h"
  #include "llvm/Analysis/MemorySSAUpdater.h"
  #include "llvm/Analysis/TargetTransformInfo.h"
  #include "llvm/Analysis/ValueTracking.h"
  #include "llvm/IR/Attributes.h"
  #include "llvm/IR/BasicBlock.h"
  #include "llvm/IR/CFG.h"
  #include "llvm/IR/Constant.h"
  #include "llvm/IR/ConstantRange.h"
  #include "llvm/IR/Constants.h"
  #include "llvm/IR/DataLayout.h"
  #include "llvm/IR/DerivedTypes.h"
  #include "llvm/IR/Function.h"
  #include "llvm/IR/GlobalValue.h"
  #include "llvm/IR/GlobalVariable.h"
  #include "llvm/IR/IRBuilder.h"
  #include "llvm/IR/InstrTypes.h"
  #include "llvm/IR/Instruction.h"
  #include "llvm/IR/Instructions.h"
  #include "llvm/IR/IntrinsicInst.h"
  #include "llvm/IR/LLVMContext.h"
  #include "llvm/IR/MDBuilder.h"
  #include "llvm/IR/Metadata.h"
  #include "llvm/IR/Module.h"
  #include "llvm/IR/NoFolder.h"
  #include "llvm/IR/Operator.h"
  #include "llvm/IR/PatternMatch.h"
  #include "llvm/IR/Type.h"
  #include "llvm/IR/Use.h"
  #include "llvm/IR/User.h"
  #include "llvm/IR/Value.h"
  #include "llvm/IR/ValueHandle.h"
  #include "llvm/Support/BranchProbability.h"
  #include "llvm/Support/Casting.h"
  #include "llvm/Support/CommandLine.h"
  #include "llvm/Support/Debug.h"
  #include "llvm/Support/ErrorHandling.h"
  #include "llvm/Support/KnownBits.h"
  #include "llvm/Support/MathExtras.h"
  #include "llvm/Support/raw_ostream.h"
  #include "llvm/Transforms/Utils/BasicBlockUtils.h"
  #include "llvm/Transforms/Utils/Local.h"
  #include "llvm/Transforms/Utils/ValueMapper.h"
  #include <algorithm>
  #include <cassert>
  #include <climits>
  #include <cstddef>
  #include <cstdint>
  #include <iterator>
  #include <map>
  #include <set>
  #include <tuple>
  #include <utility>
  #include <vector>
  
  using namespace llvm;
  using namespace PatternMatch;
  
  #define DEBUG_TYPE "simplifycfg"
  
  cl::opt<bool> llvm::RequireAndPreserveDomTree(
      "simplifycfg-require-and-preserve-domtree", cl::Hidden, cl::ZeroOrMore,
      cl::init(false),
      cl::desc("Temorary development switch used to gradually uplift SimplifyCFG "
               "into preserving DomTree,"));
  
  // Chosen as 2 so as to be cheap, but still to have enough power to fold
  // a select, so the "clamp" idiom (of a min followed by a max) will be caught.
  // To catch this, we need to fold a compare and a select, hence '2' being the
  // minimum reasonable default.
  static cl::opt<unsigned> PHINodeFoldingThreshold(
      "phi-node-folding-threshold", cl::Hidden, cl::init(2),
      cl::desc(
          "Control the amount of phi node folding to perform (default = 2)"));
  
  static cl::opt<unsigned> TwoEntryPHINodeFoldingThreshold(
      "two-entry-phi-node-folding-threshold", cl::Hidden, cl::init(4),
      cl::desc("Control the maximal total instruction cost that we are willing "
               "to speculatively execute to fold a 2-entry PHI node into a "
               "select (default = 4)"));
  
  static cl::opt<bool>
      HoistCommon("simplifycfg-hoist-common", cl::Hidden, cl::init(true),
                  cl::desc("Hoist common instructions up to the parent block"));
  
  static cl::opt<bool>
      SinkCommon("simplifycfg-sink-common", cl::Hidden, cl::init(true),
                 cl::desc("Sink common instructions down to the end block"));
  
  static cl::opt<bool> HoistCondStores(
      "simplifycfg-hoist-cond-stores", cl::Hidden, cl::init(true),
      cl::desc("Hoist conditional stores if an unconditional store precedes"));
  
  static cl::opt<bool> MergeCondStores(
      "simplifycfg-merge-cond-stores", cl::Hidden, cl::init(true),
      cl::desc("Hoist conditional stores even if an unconditional store does not "
               "precede - hoist multiple conditional stores into a single "
               "predicated store"));
  
  static cl::opt<bool> MergeCondStoresAggressively(
      "simplifycfg-merge-cond-stores-aggressively", cl::Hidden, cl::init(false),
      cl::desc("When merging conditional stores, do so even if the resultant "
               "basic blocks are unlikely to be if-converted as a result"));
  
  static cl::opt<bool> SpeculateOneExpensiveInst(
      "speculate-one-expensive-inst", cl::Hidden, cl::init(true),
      cl::desc("Allow exactly one expensive instruction to be speculatively "
               "executed"));
  
  static cl::opt<unsigned> MaxSpeculationDepth(
      "max-speculation-depth", cl::Hidden, cl::init(10),
      cl::desc("Limit maximum recursion depth when calculating costs of "
               "speculatively executed instructions"));
  
  static cl::opt<int>
      MaxSmallBlockSize("simplifycfg-max-small-block-size", cl::Hidden,
                        cl::init(10),
                        cl::desc("Max size of a block which is still considered "
                                 "small enough to thread through"));
  
  // Two is chosen to allow one negation and a logical combine.
  static cl::opt<unsigned>
      BranchFoldThreshold("simplifycfg-branch-fold-threshold", cl::Hidden,
                          cl::init(2),
                          cl::desc("Maximum cost of combining conditions when "
                                   "folding branches"));
  
  static cl::opt<unsigned> BranchFoldToCommonDestVectorMultiplier(
      "simplifycfg-branch-fold-common-dest-vector-multiplier", cl::Hidden,
      cl::init(2),
      cl::desc("Multiplier to apply to threshold when determining whether or not "
               "to fold branch to common destination when vector operations are "
               "present"));
  
  static cl::opt<bool> EnableMergeCompatibleInvokes(
      "simplifycfg-merge-compatible-invokes", cl::Hidden, cl::init(true),
      cl::desc("Allow SimplifyCFG to merge invokes together when appropriate"));
  
  STATISTIC(NumBitMaps, "Number of switch instructions turned into bitmaps");
  STATISTIC(NumLinearMaps,
            "Number of switch instructions turned into linear mapping");
  STATISTIC(NumLookupTables,
            "Number of switch instructions turned into lookup tables");
  STATISTIC(
      NumLookupTablesHoles,
      "Number of switch instructions turned into lookup tables (holes checked)");
  STATISTIC(NumTableCmpReuses, "Number of reused switch table lookup compares");
  STATISTIC(NumFoldValueComparisonIntoPredecessors,
            "Number of value comparisons folded into predecessor basic blocks");
  STATISTIC(NumFoldBranchToCommonDest,
            "Number of branches folded into predecessor basic block");
  STATISTIC(
      NumHoistCommonCode,
      "Number of common instruction 'blocks' hoisted up to the begin block");
  STATISTIC(NumHoistCommonInstrs,
            "Number of common instructions hoisted up to the begin block");
  STATISTIC(NumSinkCommonCode,
            "Number of common instruction 'blocks' sunk down to the end block");
  STATISTIC(NumSinkCommonInstrs,
            "Number of common instructions sunk down to the end block");
  STATISTIC(NumSpeculations, "Number of speculative executed instructions");
  STATISTIC(NumInvokes,
            "Number of invokes with empty resume blocks simplified into calls");
  STATISTIC(NumInvokesMerged, "Number of invokes that were merged together");
  STATISTIC(NumInvokeSetsFormed, "Number of invoke sets that were formed");
  
  namespace {
  
  // The first field contains the value that the switch produces when a certain
  // case group is selected, and the second field is a vector containing the
  // cases composing the case group.
  using SwitchCaseResultVectorTy =
      SmallVector<std::pair<Constant *, SmallVector<ConstantInt *, 4>>, 2>;
  
  // The first field contains the phi node that generates a result of the switch
  // and the second field contains the value generated for a certain case in the
  // switch for that PHI.
  using SwitchCaseResultsTy = SmallVector<std::pair<PHINode *, Constant *>, 4>;
  
  /// ValueEqualityComparisonCase - Represents a case of a switch.
  struct ValueEqualityComparisonCase {
    ConstantInt *Value;
    BasicBlock *Dest;
  
    ValueEqualityComparisonCase(ConstantInt *Value, BasicBlock *Dest)
        : Value(Value), Dest(Dest) {}
  
    bool operator<(ValueEqualityComparisonCase RHS) const {
      // Comparing pointers is ok as we only rely on the order for uniquing.
      return Value < RHS.Value;
    }
  
    bool operator==(BasicBlock *RHSDest) const { return Dest == RHSDest; }
  };
  
  class SimplifyCFGOpt {
    const TargetTransformInfo &TTI;
    DomTreeUpdater *DTU;
    const DataLayout &DL;
    ArrayRef<WeakVH> LoopHeaders;
    const SimplifyCFGOptions &Options;
    bool Resimplify;
  
    Value *isValueEqualityComparison(Instruction *TI);
    BasicBlock *GetValueEqualityComparisonCases(
        Instruction *TI, std::vector<ValueEqualityComparisonCase> &Cases);
    bool SimplifyEqualityComparisonWithOnlyPredecessor(Instruction *TI,
                                                       BasicBlock *Pred,
                                                       IRBuilder<> &Builder);
    bool PerformValueComparisonIntoPredecessorFolding(Instruction *TI, Value *&CV,
                                                      Instruction *PTI,
                                                      IRBuilder<> &Builder);
    bool FoldValueComparisonIntoPredecessors(Instruction *TI,
                                             IRBuilder<> &Builder);
  
    bool simplifyResume(ResumeInst *RI, IRBuilder<> &Builder);
    bool simplifySingleResume(ResumeInst *RI);
    bool simplifyCommonResume(ResumeInst *RI);
    bool simplifyCleanupReturn(CleanupReturnInst *RI);
    bool simplifyUnreachable(UnreachableInst *UI);
    bool simplifySwitch(SwitchInst *SI, IRBuilder<> &Builder);
    bool simplifyIndirectBr(IndirectBrInst *IBI);
    bool simplifyBranch(BranchInst *Branch, IRBuilder<> &Builder);
    bool simplifyUncondBranch(BranchInst *BI, IRBuilder<> &Builder);
    bool simplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder);
  
    bool tryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI,
                                               IRBuilder<> &Builder);
  
    bool HoistThenElseCodeToIf(BranchInst *BI, const TargetTransformInfo &TTI,
                               bool EqTermsOnly);
    bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB,
                                const TargetTransformInfo &TTI);
    bool SimplifyTerminatorOnSelect(Instruction *OldTerm, Value *Cond,
                                    BasicBlock *TrueBB, BasicBlock *FalseBB,
                                    uint32_t TrueWeight, uint32_t FalseWeight);
    bool SimplifyBranchOnICmpChain(BranchInst *BI, IRBuilder<> &Builder,
                                   const DataLayout &DL);
    bool SimplifySwitchOnSelect(SwitchInst *SI, SelectInst *Select);
    bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI);
    bool TurnSwitchRangeIntoICmp(SwitchInst *SI, IRBuilder<> &Builder);
  
  public:
    SimplifyCFGOpt(const TargetTransformInfo &TTI, DomTreeUpdater *DTU,
                   const DataLayout &DL, ArrayRef<WeakVH> LoopHeaders,
                   const SimplifyCFGOptions &Opts)
        : TTI(TTI), DTU(DTU), DL(DL), LoopHeaders(LoopHeaders), Options(Opts) {
      assert((!DTU || !DTU->hasPostDomTree()) &&
             "SimplifyCFG is not yet capable of maintaining validity of a "
             "PostDomTree, so don't ask for it.");
    }
  
    bool simplifyOnce(BasicBlock *BB);
    bool run(BasicBlock *BB);
  
    // Helper to set Resimplify and return change indication.
    bool requestResimplify() {
      Resimplify = true;
      return true;
    }
  };
  
  } // end anonymous namespace
  
  /// Return true if all the PHI nodes in the basic block \p BB
  /// receive compatible (identical) incoming values when coming from
  /// all of the predecessor blocks that are specified in \p IncomingBlocks.
  ///
  /// Note that if the values aren't exactly identical, but \p EquivalenceSet
  /// is provided, and *both* of the values are present in the set,
  /// then they are considered equal.
  static bool IncomingValuesAreCompatible(
      BasicBlock *BB, ArrayRef<BasicBlock *> IncomingBlocks,
      SmallPtrSetImpl<Value *> *EquivalenceSet = nullptr) {
    assert(IncomingBlocks.size() == 2 &&
           "Only for a pair of incoming blocks at the time!");
  
    // FIXME: it is okay if one of the incoming values is an `undef` value,
    //        iff the other incoming value is guaranteed to be a non-poison value.
    // FIXME: it is okay if one of the incoming values is a `poison` value.
    return all_of(BB->phis(), [IncomingBlocks, EquivalenceSet](PHINode &PN) {
      Value *IV0 = PN.getIncomingValueForBlock(IncomingBlocks[0]);
      Value *IV1 = PN.getIncomingValueForBlock(IncomingBlocks[1]);
      if (IV0 == IV1)
        return true;
      if (EquivalenceSet && EquivalenceSet->contains(IV0) &&
          EquivalenceSet->contains(IV1))
        return true;
      return false;
    });
  }
  
  /// Return true if it is safe to merge these two
  /// terminator instructions together.
  static bool
  SafeToMergeTerminators(Instruction *SI1, Instruction *SI2,
                         SmallSetVector<BasicBlock *, 4> *FailBlocks = nullptr) {
    if (SI1 == SI2)
      return false; // Can't merge with self!
  
    // It is not safe to merge these two switch instructions if they have a common
    // successor, and if that successor has a PHI node, and if *that* PHI node has
    // conflicting incoming values from the two switch blocks.
    BasicBlock *SI1BB = SI1->getParent();
    BasicBlock *SI2BB = SI2->getParent();
  
    SmallPtrSet<BasicBlock *, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
    bool Fail = false;
    for (BasicBlock *Succ : successors(SI2BB)) {
      if (!SI1Succs.count(Succ))
        continue;
      if (IncomingValuesAreCompatible(Succ, {SI1BB, SI2BB}))
        continue;
      Fail = true;
      if (FailBlocks)
        FailBlocks->insert(Succ);
      else
        break;
    }
  
    return !Fail;
  }
  
  /// Update PHI nodes in Succ to indicate that there will now be entries in it
  /// from the 'NewPred' block. The values that will be flowing into the PHI nodes
  /// will be the same as those coming in from ExistPred, an existing predecessor
  /// of Succ.
  static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
                                    BasicBlock *ExistPred,
                                    MemorySSAUpdater *MSSAU = nullptr) {
    for (PHINode &PN : Succ->phis())
      PN.addIncoming(PN.getIncomingValueForBlock(ExistPred), NewPred);
    if (MSSAU)
      if (auto *MPhi = MSSAU->getMemorySSA()->getMemoryAccess(Succ))
        MPhi->addIncoming(MPhi->getIncomingValueForBlock(ExistPred), NewPred);
  }
  
  /// Compute an abstract "cost" of speculating the given instruction,
  /// which is assumed to be safe to speculate. TCC_Free means cheap,
  /// TCC_Basic means less cheap, and TCC_Expensive means prohibitively
  /// expensive.
  static InstructionCost computeSpeculationCost(const User *I,
                                                const TargetTransformInfo &TTI) {
    assert(isSafeToSpeculativelyExecute(I) &&
           "Instruction is not safe to speculatively execute!");
    return TTI.getUserCost(I, TargetTransformInfo::TCK_SizeAndLatency);
  }
  
  /// If we have a merge point of an "if condition" as accepted above,
  /// return true if the specified value dominates the block.  We
  /// don't handle the true generality of domination here, just a special case
  /// which works well enough for us.
  ///
  /// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
  /// see if V (which must be an instruction) and its recursive operands
  /// that do not dominate BB have a combined cost lower than Budget and
  /// are non-trapping.  If both are true, the instruction is inserted into the
  /// set and true is returned.
  ///
  /// The cost for most non-trapping instructions is defined as 1 except for
  /// Select whose cost is 2.
  ///
  /// After this function returns, Cost is increased by the cost of
  /// V plus its non-dominating operands.  If that cost is greater than
  /// Budget, false is returned and Cost is undefined.
  static bool dominatesMergePoint(Value *V, BasicBlock *BB,
                                  SmallPtrSetImpl<Instruction *> &AggressiveInsts,
                                  InstructionCost &Cost,
                                  InstructionCost Budget,
                                  const TargetTransformInfo &TTI,
                                  unsigned Depth = 0) {
    // It is possible to hit a zero-cost cycle (phi/gep instructions for example),
    // so limit the recursion depth.
    // TODO: While this recursion limit does prevent pathological behavior, it
    // would be better to track visited instructions to avoid cycles.
    if (Depth == MaxSpeculationDepth)
      return false;
  
    Instruction *I = dyn_cast<Instruction>(V);
    if (!I) {
      // Non-instructions all dominate instructions, but not all constantexprs
      // can be executed unconditionally.
      if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
        if (C->canTrap())
          return false;
      return true;
    }
    BasicBlock *PBB = I->getParent();
  
    // We don't want to allow weird loops that might have the "if condition" in
    // the bottom of this block.
    if (PBB == BB)
      return false;
  
    // If this instruction is defined in a block that contains an unconditional
    // branch to BB, then it must be in the 'conditional' part of the "if
    // statement".  If not, it definitely dominates the region.
    BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator());
    if (!BI || BI->isConditional() || BI->getSuccessor(0) != BB)
      return true;
  
    // If we have seen this instruction before, don't count it again.
    if (AggressiveInsts.count(I))
      return true;
  
    // Okay, it looks like the instruction IS in the "condition".  Check to
    // see if it's a cheap instruction to unconditionally compute, and if it
    // only uses stuff defined outside of the condition.  If so, hoist it out.
    if (!isSafeToSpeculativelyExecute(I))
      return false;
  
    Cost += computeSpeculationCost(I, TTI);
  
    // Allow exactly one instruction to be speculated regardless of its cost
    // (as long as it is safe to do so).
    // This is intended to flatten the CFG even if the instruction is a division
    // or other expensive operation. The speculation of an expensive instruction
    // is expected to be undone in CodeGenPrepare if the speculation has not
    // enabled further IR optimizations.
    if (Cost > Budget &&
        (!SpeculateOneExpensiveInst || !AggressiveInsts.empty() || Depth > 0 ||
         !Cost.isValid()))
      return false;
  
    // Okay, we can only really hoist these out if their operands do
    // not take us over the cost threshold.
    for (Use &Op : I->operands())
      if (!dominatesMergePoint(Op, BB, AggressiveInsts, Cost, Budget, TTI,
                               Depth + 1))
        return false;
    // Okay, it's safe to do this!  Remember this instruction.
    AggressiveInsts.insert(I);
    return true;
  }
  
  /// Extract ConstantInt from value, looking through IntToPtr
  /// and PointerNullValue. Return NULL if value is not a constant int.
  static ConstantInt *GetConstantInt(Value *V, const DataLayout &DL) {
    // Normal constant int.
    ConstantInt *CI = dyn_cast<ConstantInt>(V);
    if (CI || !isa<Constant>(V) || !V->getType()->isPointerTy())
      return CI;
  
    // This is some kind of pointer constant. Turn it into a pointer-sized
    // ConstantInt if possible.
    IntegerType *PtrTy = cast<IntegerType>(DL.getIntPtrType(V->getType()));
  
    // Null pointer means 0, see SelectionDAGBuilder::getValue(const Value*).
    if (isa<ConstantPointerNull>(V))
      return ConstantInt::get(PtrTy, 0);
  
    // IntToPtr const int.
    if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
      if (CE->getOpcode() == Instruction::IntToPtr)
        if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(0))) {
          // The constant is very likely to have the right type already.
          if (CI->getType() == PtrTy)
            return CI;
          else
            return cast<ConstantInt>(
                ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false));
        }
    return nullptr;
  }
  
  namespace {
  
  /// Given a chain of or (||) or and (&&) comparison of a value against a
  /// constant, this will try to recover the information required for a switch
  /// structure.
  /// It will depth-first traverse the chain of comparison, seeking for patterns
  /// like %a == 12 or %a < 4 and combine them to produce a set of integer
  /// representing the different cases for the switch.
  /// Note that if the chain is composed of '||' it will build the set of elements
  /// that matches the comparisons (i.e. any of this value validate the chain)
  /// while for a chain of '&&' it will build the set elements that make the test
  /// fail.
  struct ConstantComparesGatherer {
    const DataLayout &DL;
  
    /// Value found for the switch comparison
    Value *CompValue = nullptr;
  
    /// Extra clause to be checked before the switch
    Value *Extra = nullptr;
  
    /// Set of integers to match in switch
    SmallVector<ConstantInt *, 8> Vals;
  
    /// Number of comparisons matched in the and/or chain
    unsigned UsedICmps = 0;
  
    /// Construct and compute the result for the comparison instruction Cond
    ConstantComparesGatherer(Instruction *Cond, const DataLayout &DL) : DL(DL) {
      gather(Cond);
    }
  
    ConstantComparesGatherer(const ConstantComparesGatherer &) = delete;
    ConstantComparesGatherer &
    operator=(const ConstantComparesGatherer &) = delete;
  
  private:
    /// Try to set the current value used for the comparison, it succeeds only if
    /// it wasn't set before or if the new value is the same as the old one
    bool setValueOnce(Value *NewVal) {
      if (CompValue && CompValue != NewVal)
        return false;
      CompValue = NewVal;
      return (CompValue != nullptr);
    }
  
    /// Try to match Instruction "I" as a comparison against a constant and
    /// populates the array Vals with the set of values that match (or do not
    /// match depending on isEQ).
    /// Return false on failure. On success, the Value the comparison matched
    /// against is placed in CompValue.
    /// If CompValue is already set, the function is expected to fail if a match
    /// is found but the value compared to is different.
    bool matchInstruction(Instruction *I, bool isEQ) {
      // If this is an icmp against a constant, handle this as one of the cases.
      ICmpInst *ICI;
      ConstantInt *C;
      if (!((ICI = dyn_cast<ICmpInst>(I)) &&
            (C = GetConstantInt(I->getOperand(1), DL)))) {
        return false;
      }
  
      Value *RHSVal;
      const APInt *RHSC;
  
      // Pattern match a special case
      // (x & ~2^z) == y --> x == y || x == y|2^z
      // This undoes a transformation done by instcombine to fuse 2 compares.
      if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ : ICmpInst::ICMP_NE)) {
        // It's a little bit hard to see why the following transformations are
        // correct. Here is a CVC3 program to verify them for 64-bit values:
  
        /*
           ONE  : BITVECTOR(64) = BVZEROEXTEND(0bin1, 63);
           x    : BITVECTOR(64);
           y    : BITVECTOR(64);
           z    : BITVECTOR(64);
           mask : BITVECTOR(64) = BVSHL(ONE, z);
           QUERY( (y & ~mask = y) =>
                  ((x & ~mask = y) <=> (x = y OR x = (y |  mask)))
           );
           QUERY( (y |  mask = y) =>
                  ((x |  mask = y) <=> (x = y OR x = (y & ~mask)))
           );
        */
  
        // Please note that each pattern must be a dual implication (<--> or
        // iff). One directional implication can create spurious matches. If the
        // implication is only one-way, an unsatisfiable condition on the left
        // side can imply a satisfiable condition on the right side. Dual
        // implication ensures that satisfiable conditions are transformed to
        // other satisfiable conditions and unsatisfiable conditions are
        // transformed to other unsatisfiable conditions.
  
        // Here is a concrete example of a unsatisfiable condition on the left
        // implying a satisfiable condition on the right:
        //
        // mask = (1 << z)
        // (x & ~mask) == y  --> (x == y || x == (y | mask))
        //
        // Substituting y = 3, z = 0 yields:
        // (x & -2) == 3 --> (x == 3 || x == 2)
  
        // Pattern match a special case:
        /*
          QUERY( (y & ~mask = y) =>
                 ((x & ~mask = y) <=> (x = y OR x = (y |  mask)))
          );
        */
        if (match(ICI->getOperand(0),
                  m_And(m_Value(RHSVal), m_APInt(RHSC)))) {
          APInt Mask = ~*RHSC;
          if (Mask.isPowerOf2() && (C->getValue() & ~Mask) == C->getValue()) {
            // If we already have a value for the switch, it has to match!
            if (!setValueOnce(RHSVal))
              return false;
  
            Vals.push_back(C);
            Vals.push_back(
                ConstantInt::get(C->getContext(),
                                 C->getValue() | Mask));
            UsedICmps++;
            return true;
          }
        }
  
        // Pattern match a special case:
        /*
          QUERY( (y |  mask = y) =>
                 ((x |  mask = y) <=> (x = y OR x = (y & ~mask)))
          );
        */
        if (match(ICI->getOperand(0),
                  m_Or(m_Value(RHSVal), m_APInt(RHSC)))) {
          APInt Mask = *RHSC;
          if (Mask.isPowerOf2() && (C->getValue() | Mask) == C->getValue()) {
            // If we already have a value for the switch, it has to match!
            if (!setValueOnce(RHSVal))
              return false;
  
            Vals.push_back(C);
            Vals.push_back(ConstantInt::get(C->getContext(),
                                            C->getValue() & ~Mask));
            UsedICmps++;
            return true;
          }
        }
  
        // If we already have a value for the switch, it has to match!
        if (!setValueOnce(ICI->getOperand(0)))
          return false;
  
        UsedICmps++;
        Vals.push_back(C);
        return ICI->getOperand(0);
      }
  
      // If we have "x ult 3", for example, then we can add 0,1,2 to the set.
      ConstantRange Span =
          ConstantRange::makeExactICmpRegion(ICI->getPredicate(), C->getValue());
  
      // Shift the range if the compare is fed by an add. This is the range
      // compare idiom as emitted by instcombine.
      Value *CandidateVal = I->getOperand(0);
      if (match(I->getOperand(0), m_Add(m_Value(RHSVal), m_APInt(RHSC)))) {
        Span = Span.subtract(*RHSC);
        CandidateVal = RHSVal;
      }
  
      // If this is an and/!= check, then we are looking to build the set of
      // value that *don't* pass the and chain. I.e. to turn "x ugt 2" into
      // x != 0 && x != 1.
      if (!isEQ)
        Span = Span.inverse();
  
      // If there are a ton of values, we don't want to make a ginormous switch.
      if (Span.isSizeLargerThan(8) || Span.isEmptySet()) {
        return false;
      }
  
      // If we already have a value for the switch, it has to match!
      if (!setValueOnce(CandidateVal))
        return false;
  
      // Add all values from the range to the set
      for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp)
        Vals.push_back(ConstantInt::get(I->getContext(), Tmp));
  
      UsedICmps++;
      return true;
    }
  
    /// Given a potentially 'or'd or 'and'd together collection of icmp
    /// eq/ne/lt/gt instructions that compare a value against a constant, extract
    /// the value being compared, and stick the list constants into the Vals
    /// vector.
    /// One "Extra" case is allowed to differ from the other.
    void gather(Value *V) {
      bool isEQ = match(V, m_LogicalOr(m_Value(), m_Value()));
  
      // Keep a stack (SmallVector for efficiency) for depth-first traversal
      SmallVector<Value *, 8> DFT;
      SmallPtrSet<Value *, 8> Visited;
  
      // Initialize
      Visited.insert(V);
      DFT.push_back(V);
  
      while (!DFT.empty()) {
        V = DFT.pop_back_val();
  
        if (Instruction *I = dyn_cast<Instruction>(V)) {
          // If it is a || (or && depending on isEQ), process the operands.
          Value *Op0, *Op1;
          if (isEQ ? match(I, m_LogicalOr(m_Value(Op0), m_Value(Op1)))
                   : match(I, m_LogicalAnd(m_Value(Op0), m_Value(Op1)))) {
            if (Visited.insert(Op1).second)
              DFT.push_back(Op1);
            if (Visited.insert(Op0).second)
              DFT.push_back(Op0);
  
            continue;
          }
  
          // Try to match the current instruction
          if (matchInstruction(I, isEQ))
            // Match succeed, continue the loop
            continue;
        }
  
        // One element of the sequence of || (or &&) could not be match as a
        // comparison against the same value as the others.
        // We allow only one "Extra" case to be checked before the switch
        if (!Extra) {
          Extra = V;
          continue;
        }
        // Failed to parse a proper sequence, abort now
        CompValue = nullptr;
        break;
      }
    }
  };
  
  } // end anonymous namespace
  
  static void EraseTerminatorAndDCECond(Instruction *TI,
                                        MemorySSAUpdater *MSSAU = nullptr) {
    Instruction *Cond = nullptr;
    if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
      Cond = dyn_cast<Instruction>(SI->getCondition());
    } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
      if (BI->isConditional())
        Cond = dyn_cast<Instruction>(BI->getCondition());
    } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) {
      Cond = dyn_cast<Instruction>(IBI->getAddress());
    }
  
    TI->eraseFromParent();
    if (Cond)
      RecursivelyDeleteTriviallyDeadInstructions(Cond, nullptr, MSSAU);
  }
  
  /// Return true if the specified terminator checks
  /// to see if a value is equal to constant integer value.
  Value *SimplifyCFGOpt::isValueEqualityComparison(Instruction *TI) {
    Value *CV = nullptr;
    if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
      // Do not permit merging of large switch instructions into their
      // predecessors unless there is only one predecessor.
      if (!SI->getParent()->hasNPredecessorsOrMore(128 / SI->getNumSuccessors()))
        CV = SI->getCondition();
    } else if (BranchInst *BI = dyn_cast<BranchInst>(TI))
      if (BI->isConditional() && BI->getCondition()->hasOneUse())
        if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition())) {
          if (ICI->isEquality() && GetConstantInt(ICI->getOperand(1), DL))
            CV = ICI->getOperand(0);
        }
  
    // Unwrap any lossless ptrtoint cast.
    if (CV) {
      if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV)) {
        Value *Ptr = PTII->getPointerOperand();
        if (PTII->getType() == DL.getIntPtrType(Ptr->getType()))
          CV = Ptr;
      }
    }
    return CV;
  }
  
  /// Given a value comparison instruction,
  /// decode all of the 'cases' that it represents and return the 'default' block.
  BasicBlock *SimplifyCFGOpt::GetValueEqualityComparisonCases(
      Instruction *TI, std::vector<ValueEqualityComparisonCase> &Cases) {
    if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
      Cases.reserve(SI->getNumCases());
      for (auto Case : SI->cases())
        Cases.push_back(ValueEqualityComparisonCase(Case.getCaseValue(),
                                                    Case.getCaseSuccessor()));
      return SI->getDefaultDest();
    }
  
    BranchInst *BI = cast<BranchInst>(TI);
    ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
    BasicBlock *Succ = BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_NE);
    Cases.push_back(ValueEqualityComparisonCase(
        GetConstantInt(ICI->getOperand(1), DL), Succ));
    return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
  }
  
  /// Given a vector of bb/value pairs, remove any entries
  /// in the list that match the specified block.
  static void
  EliminateBlockCases(BasicBlock *BB,
                      std::vector<ValueEqualityComparisonCase> &Cases) {
    llvm::erase_value(Cases, BB);
  }
  
  /// Return true if there are any keys in C1 that exist in C2 as well.
  static bool ValuesOverlap(std::vector<ValueEqualityComparisonCase> &C1,
                            std::vector<ValueEqualityComparisonCase> &C2) {
    std::vector<ValueEqualityComparisonCase> *V1 = &C1, *V2 = &C2;
  
    // Make V1 be smaller than V2.
    if (V1->size() > V2->size())
      std::swap(V1, V2);
  
    if (V1->empty())
      return false;
    if (V1->size() == 1) {
      // Just scan V2.
      ConstantInt *TheVal = (*V1)[0].Value;
      for (unsigned i = 0, e = V2->size(); i != e; ++i)
        if (TheVal == (*V2)[i].Value)
          return true;
    }
  
    // Otherwise, just sort both lists and compare element by element.
    array_pod_sort(V1->begin(), V1->end());
    array_pod_sort(V2->begin(), V2->end());
    unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
    while (i1 != e1 && i2 != e2) {
      if ((*V1)[i1].Value == (*V2)[i2].Value)
        return true;
      if ((*V1)[i1].Value < (*V2)[i2].Value)
        ++i1;
      else
        ++i2;
    }
    return false;
  }
  
  // Set branch weights on SwitchInst. This sets the metadata if there is at
  // least one non-zero weight.
  static void setBranchWeights(SwitchInst *SI, ArrayRef<uint32_t> Weights) {
    // Check that there is at least one non-zero weight. Otherwise, pass
    // nullptr to setMetadata which will erase the existing metadata.
    MDNode *N = nullptr;
    if (llvm::any_of(Weights, [](uint32_t W) { return W != 0; }))
      N = MDBuilder(SI->getParent()->getContext()).createBranchWeights(Weights);
    SI->setMetadata(LLVMContext::MD_prof, N);
  }
  
  // Similar to the above, but for branch and select instructions that take
  // exactly 2 weights.
  static void setBranchWeights(Instruction *I, uint32_t TrueWeight,
                               uint32_t FalseWeight) {
    assert(isa<BranchInst>(I) || isa<SelectInst>(I));
    // Check that there is at least one non-zero weight. Otherwise, pass
    // nullptr to setMetadata which will erase the existing metadata.
    MDNode *N = nullptr;
    if (TrueWeight || FalseWeight)
      N = MDBuilder(I->getParent()->getContext())
              .createBranchWeights(TrueWeight, FalseWeight);
    I->setMetadata(LLVMContext::MD_prof, N);
  }
  
  /// If TI is known to be a terminator instruction and its block is known to
  /// only have a single predecessor block, check to see if that predecessor is
  /// also a value comparison with the same value, and if that comparison
  /// determines the outcome of this comparison. If so, simplify TI. This does a
  /// very limited form of jump threading.
  bool SimplifyCFGOpt::SimplifyEqualityComparisonWithOnlyPredecessor(
      Instruction *TI, BasicBlock *Pred, IRBuilder<> &Builder) {
    Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
    if (!PredVal)
      return false; // Not a value comparison in predecessor.
  
    Value *ThisVal = isValueEqualityComparison(TI);
    assert(ThisVal && "This isn't a value comparison!!");
    if (ThisVal != PredVal)
      return false; // Different predicates.
  
    // TODO: Preserve branch weight metadata, similarly to how
    // FoldValueComparisonIntoPredecessors preserves it.
  
    // Find out information about when control will move from Pred to TI's block.
    std::vector<ValueEqualityComparisonCase> PredCases;
    BasicBlock *PredDef =
        GetValueEqualityComparisonCases(Pred->getTerminator(), PredCases);
    EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
  
    // Find information about how control leaves this block.
    std::vector<ValueEqualityComparisonCase> ThisCases;
    BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
    EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
  
    // If TI's block is the default block from Pred's comparison, potentially
    // simplify TI based on this knowledge.
    if (PredDef == TI->getParent()) {
      // If we are here, we know that the value is none of those cases listed in
      // PredCases.  If there are any cases in ThisCases that are in PredCases, we
      // can simplify TI.
      if (!ValuesOverlap(PredCases, ThisCases))
        return false;
  
      if (isa<BranchInst>(TI)) {
        // Okay, one of the successors of this condbr is dead.  Convert it to a
        // uncond br.
        assert(ThisCases.size() == 1 && "Branch can only have one case!");
        // Insert the new branch.
        Instruction *NI = Builder.CreateBr(ThisDef);
        (void)NI;
  
        // Remove PHI node entries for the dead edge.
        ThisCases[0].Dest->removePredecessor(PredDef);
  
        LLVM_DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
                          << "Through successor TI: " << *TI << "Leaving: " << *NI
                          << "\n");
  
        EraseTerminatorAndDCECond(TI);
  
        if (DTU)
          DTU->applyUpdates(
              {{DominatorTree::Delete, PredDef, ThisCases[0].Dest}});
  
        return true;
      }
  
      SwitchInstProfUpdateWrapper SI = *cast<SwitchInst>(TI);
      // Okay, TI has cases that are statically dead, prune them away.
      SmallPtrSet<Constant *, 16> DeadCases;
      for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
        DeadCases.insert(PredCases[i].Value);
  
      LLVM_DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
                        << "Through successor TI: " << *TI);
  
      SmallDenseMap<BasicBlock *, int, 8> NumPerSuccessorCases;
      for (SwitchInst::CaseIt i = SI->case_end(), e = SI->case_begin(); i != e;) {
        --i;
        auto *Successor = i->getCaseSuccessor();
        if (DTU)
          ++NumPerSuccessorCases[Successor];
        if (DeadCases.count(i->getCaseValue())) {
          Successor->removePredecessor(PredDef);
          SI.removeCase(i);
          if (DTU)
            --NumPerSuccessorCases[Successor];
        }
      }
  
      if (DTU) {
        std::vector<DominatorTree::UpdateType> Updates;
        for (const std::pair<BasicBlock *, int> &I : NumPerSuccessorCases)
          if (I.second == 0)
            Updates.push_back({DominatorTree::Delete, PredDef, I.first});
        DTU->applyUpdates(Updates);
      }
  
      LLVM_DEBUG(dbgs() << "Leaving: " << *TI << "\n");
      return true;
    }
  
    // Otherwise, TI's block must correspond to some matched value.  Find out
    // which value (or set of values) this is.
    ConstantInt *TIV = nullptr;
    BasicBlock *TIBB = TI->getParent();
    for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
      if (PredCases[i].Dest == TIBB) {
        if (TIV)
          return false; // Cannot handle multiple values coming to this block.
        TIV = PredCases[i].Value;
      }
    assert(TIV && "No edge from pred to succ?");
  
    // Okay, we found the one constant that our value can be if we get into TI's
    // BB.  Find out which successor will unconditionally be branched to.
    BasicBlock *TheRealDest = nullptr;
    for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
      if (ThisCases[i].Value == TIV) {
        TheRealDest = ThisCases[i].Dest;
        break;
      }
  
    // If not handled by any explicit cases, it is handled by the default case.
    if (!TheRealDest)
      TheRealDest = ThisDef;
  
    SmallPtrSet<BasicBlock *, 2> RemovedSuccs;
  
    // Remove PHI node entries for dead edges.
    BasicBlock *CheckEdge = TheRealDest;
    for (BasicBlock *Succ : successors(TIBB))
      if (Succ != CheckEdge) {
        if (Succ != TheRealDest)
          RemovedSuccs.insert(Succ);
        Succ->removePredecessor(TIBB);
      } else
        CheckEdge = nullptr;
  
    // Insert the new branch.
    Instruction *NI = Builder.CreateBr(TheRealDest);
    (void)NI;
  
    LLVM_DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
                      << "Through successor TI: " << *TI << "Leaving: " << *NI
                      << "\n");
  
    EraseTerminatorAndDCECond(TI);
    if (DTU) {
      SmallVector<DominatorTree::UpdateType, 2> Updates;
      Updates.reserve(RemovedSuccs.size());
      for (auto *RemovedSucc : RemovedSuccs)
        Updates.push_back({DominatorTree::Delete, TIBB, RemovedSucc});
      DTU->applyUpdates(Updates);
    }
    return true;
  }
  
  namespace {
  
  /// This class implements a stable ordering of constant
  /// integers that does not depend on their address.  This is important for
  /// applications that sort ConstantInt's to ensure uniqueness.
  struct ConstantIntOrdering {
    bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
      return LHS->getValue().ult(RHS->getValue());
    }
  };
  
  } // end anonymous namespace
  
  static int ConstantIntSortPredicate(ConstantInt *const *P1,
                                      ConstantInt *const *P2) {
    const ConstantInt *LHS = *P1;
    const ConstantInt *RHS = *P2;
    if (LHS == RHS)
      return 0;
    return LHS->getValue().ult(RHS->getValue()) ? 1 : -1;
  }
  
  static inline bool HasBranchWeights(const Instruction *I) {
    MDNode *ProfMD = I->getMetadata(LLVMContext::MD_prof);
    if (ProfMD && ProfMD->getOperand(0))
      if (MDString *MDS = dyn_cast<MDString>(ProfMD->getOperand(0)))
        return MDS->getString().equals("branch_weights");
  
    return false;
  }
  
  /// Get Weights of a given terminator, the default weight is at the front
  /// of the vector. If TI is a conditional eq, we need to swap the branch-weight
  /// metadata.
  static void GetBranchWeights(Instruction *TI,
                               SmallVectorImpl<uint64_t> &Weights) {
    MDNode *MD = TI->getMetadata(LLVMContext::MD_prof);
    assert(MD);
    for (unsigned i = 1, e = MD->getNumOperands(); i < e; ++i) {
      ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(i));
      Weights.push_back(CI->getValue().getZExtValue());
    }
  
    // If TI is a conditional eq, the default case is the false case,
    // and the corresponding branch-weight data is at index 2. We swap the
    // default weight to be the first entry.
    if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
      assert(Weights.size() == 2);
      ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
      if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
        std::swap(Weights.front(), Weights.back());
    }
  }
  
  /// Keep halving the weights until all can fit in uint32_t.
  static void FitWeights(MutableArrayRef<uint64_t> Weights) {
    uint64_t Max = *std::max_element(Weights.begin(), Weights.end());
    if (Max > UINT_MAX) {
      unsigned Offset = 32 - countLeadingZeros(Max);
      for (uint64_t &I : Weights)
        I >>= Offset;
    }
  }
  
  static void CloneInstructionsIntoPredecessorBlockAndUpdateSSAUses(
      BasicBlock *BB, BasicBlock *PredBlock, ValueToValueMapTy &VMap) {
    Instruction *PTI = PredBlock->getTerminator();
  
    // If we have bonus instructions, clone them into the predecessor block.
    // Note that there may be multiple predecessor blocks, so we cannot move
    // bonus instructions to a predecessor block.
    for (Instruction &BonusInst : *BB) {
      if (isa<DbgInfoIntrinsic>(BonusInst) || BonusInst.isTerminator())
        continue;
  
      Instruction *NewBonusInst = BonusInst.clone();
  
      if (PTI->getDebugLoc() != NewBonusInst->getDebugLoc()) {
        // Unless the instruction has the same !dbg location as the original
        // branch, drop it. When we fold the bonus instructions we want to make
        // sure we reset their debug locations in order to avoid stepping on
        // dead code caused by folding dead branches.
        NewBonusInst->setDebugLoc(DebugLoc());
      }
  
      RemapInstruction(NewBonusInst, VMap,
                       RF_NoModuleLevelChanges | RF_IgnoreMissingLocals);
      VMap[&BonusInst] = NewBonusInst;
  
      // If we moved a load, we cannot any longer claim any knowledge about
      // its potential value. The previous information might have been valid
      // only given the branch precondition.
      // For an analogous reason, we must also drop all the metadata whose
      // semantics we don't understand. We *can* preserve !annotation, because
      // it is tied to the instruction itself, not the value or position.
      // Similarly strip attributes on call parameters that may cause UB in
      // location the call is moved to.
      NewBonusInst->dropUndefImplyingAttrsAndUnknownMetadata(
          LLVMContext::MD_annotation);
  
      PredBlock->getInstList().insert(PTI->getIterator(), NewBonusInst);
      NewBonusInst->takeName(&BonusInst);
      BonusInst.setName(NewBonusInst->getName() + ".old");
  
      // Update (liveout) uses of bonus instructions,
      // now that the bonus instruction has been cloned into predecessor.
      // Note that we expect to be in a block-closed SSA form for this to work!
      for (Use &U : make_early_inc_range(BonusInst.uses())) {
        auto *UI = cast<Instruction>(U.getUser());
        auto *PN = dyn_cast<PHINode>(UI);
        if (!PN) {
          assert(UI->getParent() == BB && BonusInst.comesBefore(UI) &&
                 "If the user is not a PHI node, then it should be in the same "
                 "block as, and come after, the original bonus instruction.");
          continue; // Keep using the original bonus instruction.
        }
        // Is this the block-closed SSA form PHI node?
        if (PN->getIncomingBlock(U) == BB)
          continue; // Great, keep using the original bonus instruction.
        // The only other alternative is an "use" when coming from
        // the predecessor block - here we should refer to the cloned bonus instr.
        assert(PN->getIncomingBlock(U) == PredBlock &&
               "Not in block-closed SSA form?");
        U.set(NewBonusInst);
      }
    }
  }
  
  bool SimplifyCFGOpt::PerformValueComparisonIntoPredecessorFolding(
      Instruction *TI, Value *&CV, Instruction *PTI, IRBuilder<> &Builder) {
    BasicBlock *BB = TI->getParent();
    BasicBlock *Pred = PTI->getParent();
  
    SmallVector<DominatorTree::UpdateType, 32> Updates;
  
    // Figure out which 'cases' to copy from SI to PSI.
    std::vector<ValueEqualityComparisonCase> BBCases;
    BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
  
    std::vector<ValueEqualityComparisonCase> PredCases;
    BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
  
    // Based on whether the default edge from PTI goes to BB or not, fill in
    // PredCases and PredDefault with the new switch cases we would like to
    // build.
    SmallMapVector<BasicBlock *, int, 8> NewSuccessors;
  
    // Update the branch weight metadata along the way
    SmallVector<uint64_t, 8> Weights;
    bool PredHasWeights = HasBranchWeights(PTI);
    bool SuccHasWeights = HasBranchWeights(TI);
  
    if (PredHasWeights) {
      GetBranchWeights(PTI, Weights);
      // branch-weight metadata is inconsistent here.
      if (Weights.size() != 1 + PredCases.size())
        PredHasWeights = SuccHasWeights = false;
    } else if (SuccHasWeights)
      // If there are no predecessor weights but there are successor weights,
      // populate Weights with 1, which will later be scaled to the sum of
      // successor's weights
      Weights.assign(1 + PredCases.size(), 1);
  
    SmallVector<uint64_t, 8> SuccWeights;
    if (SuccHasWeights) {
      GetBranchWeights(TI, SuccWeights);
      // branch-weight metadata is inconsistent here.
      if (SuccWeights.size() != 1 + BBCases.size())
        PredHasWeights = SuccHasWeights = false;
    } else if (PredHasWeights)
      SuccWeights.assign(1 + BBCases.size(), 1);
  
    if (PredDefault == BB) {
      // If this is the default destination from PTI, only the edges in TI
      // that don't occur in PTI, or that branch to BB will be activated.
      std::set<ConstantInt *, ConstantIntOrdering> PTIHandled;
      for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
        if (PredCases[i].Dest != BB)
          PTIHandled.insert(PredCases[i].Value);
        else {
          // The default destination is BB, we don't need explicit targets.
          std::swap(PredCases[i], PredCases.back());
  
          if (PredHasWeights || SuccHasWeights) {
            // Increase weight for the default case.
            Weights[0] += Weights[i + 1];
            std::swap(Weights[i + 1], Weights.back());
            Weights.pop_back();
          }
  
          PredCases.pop_back();
          --i;
          --e;
        }
  
      // Reconstruct the new switch statement we will be building.
      if (PredDefault != BBDefault) {
        PredDefault->removePredecessor(Pred);
        if (DTU && PredDefault != BB)
          Updates.push_back({DominatorTree::Delete, Pred, PredDefault});
        PredDefault = BBDefault;
        ++NewSuccessors[BBDefault];
      }
  
      unsigned CasesFromPred = Weights.size();
      uint64_t ValidTotalSuccWeight = 0;
      for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
        if (!PTIHandled.count(BBCases[i].Value) && BBCases[i].Dest != BBDefault) {
          PredCases.push_back(BBCases[i]);
          ++NewSuccessors[BBCases[i].Dest];
          if (SuccHasWeights || PredHasWeights) {
            // The default weight is at index 0, so weight for the ith case
            // should be at index i+1. Scale the cases from successor by
            // PredDefaultWeight (Weights[0]).
            Weights.push_back(Weights[0] * SuccWeights[i + 1]);
            ValidTotalSuccWeight += SuccWeights[i + 1];
          }
        }
  
      if (SuccHasWeights || PredHasWeights) {
        ValidTotalSuccWeight += SuccWeights[0];
        // Scale the cases from predecessor by ValidTotalSuccWeight.
        for (unsigned i = 1; i < CasesFromPred; ++i)
          Weights[i] *= ValidTotalSuccWeight;
        // Scale the default weight by SuccDefaultWeight (SuccWeights[0]).
        Weights[0] *= SuccWeights[0];
      }
    } else {
      // If this is not the default destination from PSI, only the edges
      // in SI that occur in PSI with a destination of BB will be
      // activated.
      std::set<ConstantInt *, ConstantIntOrdering> PTIHandled;
      std::map<ConstantInt *, uint64_t> WeightsForHandled;
      for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
        if (PredCases[i].Dest == BB) {
          PTIHandled.insert(PredCases[i].Value);
  
          if (PredHasWeights || SuccHasWeights) {
            WeightsForHandled[PredCases[i].Value] = Weights[i + 1];
            std::swap(Weights[i + 1], Weights.back());
            Weights.pop_back();
          }
  
          std::swap(PredCases[i], PredCases.back());
          PredCases.pop_back();
          --i;
          --e;
        }
  
      // Okay, now we know which constants were sent to BB from the
      // predecessor.  Figure out where they will all go now.
      for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
        if (PTIHandled.count(BBCases[i].Value)) {
          // If this is one we are capable of getting...
          if (PredHasWeights || SuccHasWeights)
            Weights.push_back(WeightsForHandled[BBCases[i].Value]);
          PredCases.push_back(BBCases[i]);
          ++NewSuccessors[BBCases[i].Dest];
          PTIHandled.erase(BBCases[i].Value); // This constant is taken care of
        }
  
      // If there are any constants vectored to BB that TI doesn't handle,
      // they must go to the default destination of TI.
      for (ConstantInt *I : PTIHandled) {
        if (PredHasWeights || SuccHasWeights)
          Weights.push_back(WeightsForHandled[I]);
        PredCases.push_back(ValueEqualityComparisonCase(I, BBDefault));
        ++NewSuccessors[BBDefault];
      }
    }
  
    // Okay, at this point, we know which new successor Pred will get.  Make
    // sure we update the number of entries in the PHI nodes for these
    // successors.
    SmallPtrSet<BasicBlock *, 2> SuccsOfPred;
    if (DTU) {
      SuccsOfPred = {succ_begin(Pred), succ_end(Pred)};
      Updates.reserve(Updates.size() + NewSuccessors.size());
    }
    for (const std::pair<BasicBlock *, int /*Num*/> &NewSuccessor :
         NewSuccessors) {
      for (auto I : seq(0, NewSuccessor.second)) {
        (void)I;
        AddPredecessorToBlock(NewSuccessor.first, Pred, BB);
      }
      if (DTU && !SuccsOfPred.contains(NewSuccessor.first))
        Updates.push_back({DominatorTree::Insert, Pred, NewSuccessor.first});
    }
  
    Builder.SetInsertPoint(PTI);
    // Convert pointer to int before we switch.
    if (CV->getType()->isPointerTy()) {
      CV =
          Builder.CreatePtrToInt(CV, DL.getIntPtrType(CV->getType()), "magicptr");
    }
  
    // Now that the successors are updated, create the new Switch instruction.
    SwitchInst *NewSI = Builder.CreateSwitch(CV, PredDefault, PredCases.size());
    NewSI->setDebugLoc(PTI->getDebugLoc());
    for (ValueEqualityComparisonCase &V : PredCases)
      NewSI->addCase(V.Value, V.Dest);
  
    if (PredHasWeights || SuccHasWeights) {
      // Halve the weights if any of them cannot fit in an uint32_t
      FitWeights(Weights);
  
      SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end());
  
      setBranchWeights(NewSI, MDWeights);
    }
  
    EraseTerminatorAndDCECond(PTI);
  
    // Okay, last check.  If BB is still a successor of PSI, then we must
    // have an infinite loop case.  If so, add an infinitely looping block
    // to handle the case to preserve the behavior of the code.
    BasicBlock *InfLoopBlock = nullptr;
    for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
      if (NewSI->getSuccessor(i) == BB) {
        if (!InfLoopBlock) {
          // Insert it at the end of the function, because it's either code,
          // or it won't matter if it's hot. :)
          InfLoopBlock =
              BasicBlock::Create(BB->getContext(), "infloop", BB->getParent());
          BranchInst::Create(InfLoopBlock, InfLoopBlock);
          if (DTU)
            Updates.push_back(
                {DominatorTree::Insert, InfLoopBlock, InfLoopBlock});
        }
        NewSI->setSuccessor(i, InfLoopBlock);
      }
  
    if (DTU) {
      if (InfLoopBlock)
        Updates.push_back({DominatorTree::Insert, Pred, InfLoopBlock});
  
      Updates.push_back({DominatorTree::Delete, Pred, BB});
  
      DTU->applyUpdates(Updates);
    }
  
    ++NumFoldValueComparisonIntoPredecessors;
    return true;
  }
  
  /// The specified terminator is a value equality comparison instruction
  /// (either a switch or a branch on "X == c").
  /// See if any of the predecessors of the terminator block are value comparisons
  /// on the same value.  If so, and if safe to do so, fold them together.
  bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(Instruction *TI,
                                                           IRBuilder<> &Builder) {
    BasicBlock *BB = TI->getParent();
    Value *CV = isValueEqualityComparison(TI); // CondVal
    assert(CV && "Not a comparison?");
  
    bool Changed = false;
  
    SmallSetVector<BasicBlock *, 16> Preds(pred_begin(BB), pred_end(BB));
    while (!Preds.empty()) {
      BasicBlock *Pred = Preds.pop_back_val();
      Instruction *PTI = Pred->getTerminator();
  
      // Don't try to fold into itself.
      if (Pred == BB)
        continue;
  
      // See if the predecessor is a comparison with the same value.
      Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
      if (PCV != CV)
        continue;
  
      SmallSetVector<BasicBlock *, 4> FailBlocks;
      if (!SafeToMergeTerminators(TI, PTI, &FailBlocks)) {
        for (auto *Succ : FailBlocks) {
          if (!SplitBlockPredecessors(Succ, TI->getParent(), ".fold.split", DTU))
            return false;
        }
      }
  
      PerformValueComparisonIntoPredecessorFolding(TI, CV, PTI, Builder);
      Changed = true;
    }
    return Changed;
  }
  
  // If we would need to insert a select that uses the value of this invoke
  // (comments in HoistThenElseCodeToIf explain why we would need to do this), we
  // can't hoist the invoke, as there is nowhere to put the select in this case.
  static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
                                  Instruction *I1, Instruction *I2) {
    for (BasicBlock *Succ : successors(BB1)) {
      for (const PHINode &PN : Succ->phis()) {
        Value *BB1V = PN.getIncomingValueForBlock(BB1);
        Value *BB2V = PN.getIncomingValueForBlock(BB2);
        if (BB1V != BB2V && (BB1V == I1 || BB2V == I2)) {
          return false;
        }
      }
    }
    return true;
  }
  
  static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I, bool PtrValueMayBeModified = false);
  
  /// Given a conditional branch that goes to BB1 and BB2, hoist any common code
  /// in the two blocks up into the branch block. The caller of this function
  /// guarantees that BI's block dominates BB1 and BB2. If EqTermsOnly is given,
  /// only perform hoisting in case both blocks only contain a terminator. In that
  /// case, only the original BI will be replaced and selects for PHIs are added.
  bool SimplifyCFGOpt::HoistThenElseCodeToIf(BranchInst *BI,
                                             const TargetTransformInfo &TTI,
                                             bool EqTermsOnly) {
    // This does very trivial matching, with limited scanning, to find identical
    // instructions in the two blocks.  In particular, we don't want to get into
    // O(M*N) situations here where M and N are the sizes of BB1 and BB2.  As
    // such, we currently just scan for obviously identical instructions in an
    // identical order.
    BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
    BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
  
    // If either of the blocks has it's address taken, then we can't do this fold,
    // because the code we'd hoist would no longer run when we jump into the block
    // by it's address.
    if (BB1->hasAddressTaken() || BB2->hasAddressTaken())
      return false;
  
    BasicBlock::iterator BB1_Itr = BB1->begin();
    BasicBlock::iterator BB2_Itr = BB2->begin();
  
    Instruction *I1 = &*BB1_Itr++, *I2 = &*BB2_Itr++;
    // Skip debug info if it is not identical.
    DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
    DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
    if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
      while (isa<DbgInfoIntrinsic>(I1))
        I1 = &*BB1_Itr++;
      while (isa<DbgInfoIntrinsic>(I2))
        I2 = &*BB2_Itr++;
    }
    // FIXME: Can we define a safety predicate for CallBr?
    if (isa<PHINode>(I1) || !I1->isIdenticalToWhenDefined(I2) ||
        (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)) ||
        isa<CallBrInst>(I1))
      return false;
  
    BasicBlock *BIParent = BI->getParent();
  
    bool Changed = false;
  
    auto _ = make_scope_exit([&]() {
      if (Changed)
        ++NumHoistCommonCode;
    });
  
    // Check if only hoisting terminators is allowed. This does not add new
    // instructions to the hoist location.
    if (EqTermsOnly) {
      // Skip any debug intrinsics, as they are free to hoist.
      auto *I1NonDbg = &*skipDebugIntrinsics(I1->getIterator());
      auto *I2NonDbg = &*skipDebugIntrinsics(I2->getIterator());
      if (!I1NonDbg->isIdenticalToWhenDefined(I2NonDbg))
        return false;
      if (!I1NonDbg->isTerminator())
        return false;
      // Now we know that we only need to hoist debug instrinsics and the
      // terminator. Let the loop below handle those 2 cases.
    }
  
    do {
      // If we are hoisting the terminator instruction, don't move one (making a
      // broken BB), instead clone it, and remove BI.
      if (I1->isTerminator())
        goto HoistTerminator;
  
      // If we're going to hoist a call, make sure that the two instructions we're
      // commoning/hoisting are both marked with musttail, or neither of them is
      // marked as such. Otherwise, we might end up in a situation where we hoist
      // from a block where the terminator is a `ret` to a block where the terminator
      // is a `br`, and `musttail` calls expect to be followed by a return.
      auto *C1 = dyn_cast<CallInst>(I1);
      auto *C2 = dyn_cast<CallInst>(I2);
      if (C1 && C2)
        if (C1->isMustTailCall() != C2->isMustTailCall())
          return Changed;
  
      if (!TTI.isProfitableToHoist(I1) || !TTI.isProfitableToHoist(I2))
        return Changed;
  
      // If any of the two call sites has nomerge attribute, stop hoisting.
      if (const auto *CB1 = dyn_cast<CallBase>(I1))
        if (CB1->cannotMerge())
          return Changed;
      if (const auto *CB2 = dyn_cast<CallBase>(I2))
        if (CB2->cannotMerge())
          return Changed;
  
      if (isa<DbgInfoIntrinsic>(I1) || isa<DbgInfoIntrinsic>(I2)) {
        assert (isa<DbgInfoIntrinsic>(I1) && isa<DbgInfoIntrinsic>(I2));
        // The debug location is an integral part of a debug info intrinsic
        // and can't be separated from it or replaced.  Instead of attempting
        // to merge locations, simply hoist both copies of the intrinsic.
        BIParent->getInstList().splice(BI->getIterator(),
                                       BB1->getInstList(), I1);
        BIParent->getInstList().splice(BI->getIterator(),
                                       BB2->getInstList(), I2);
        Changed = true;
      } else {
        // For a normal instruction, we just move one to right before the branch,
        // then replace all uses of the other with the first.  Finally, we remove
        // the now redundant second instruction.
        BIParent->getInstList().splice(BI->getIterator(),
                                       BB1->getInstList(), I1);
        if (!I2->use_empty())
          I2->replaceAllUsesWith(I1);
        I1->andIRFlags(I2);
        unsigned KnownIDs[] = {LLVMContext::MD_tbaa,
                               LLVMContext::MD_range,
                               LLVMContext::MD_fpmath,
                               LLVMContext::MD_invariant_load,
                               LLVMContext::MD_nonnull,
                               LLVMContext::MD_invariant_group,
                               LLVMContext::MD_align,
                               LLVMContext::MD_dereferenceable,
                               LLVMContext::MD_dereferenceable_or_null,
                               LLVMContext::MD_mem_parallel_loop_access,
                               LLVMContext::MD_access_group,
                               LLVMContext::MD_preserve_access_index};
        combineMetadata(I1, I2, KnownIDs, true);
  
        // I1 and I2 are being combined into a single instruction.  Its debug
        // location is the merged locations of the original instructions.
        I1->applyMergedLocation(I1->getDebugLoc(), I2->getDebugLoc());
  
        I2->eraseFromParent();
        Changed = true;
      }
      ++NumHoistCommonInstrs;
  
      I1 = &*BB1_Itr++;
      I2 = &*BB2_Itr++;
      // Skip debug info if it is not identical.
      DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
      DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
      if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
        while (isa<DbgInfoIntrinsic>(I1))
          I1 = &*BB1_Itr++;
        while (isa<DbgInfoIntrinsic>(I2))
          I2 = &*BB2_Itr++;
      }
    } while (I1->isIdenticalToWhenDefined(I2));
  
    return true;
  
  HoistTerminator:
    // It may not be possible to hoist an invoke.
    // FIXME: Can we define a safety predicate for CallBr?
    if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
      return Changed;
  
    // TODO: callbr hoisting currently disabled pending further study.
    if (isa<CallBrInst>(I1))
      return Changed;
  
    for (BasicBlock *Succ : successors(BB1)) {
      for (PHINode &PN : Succ->phis()) {
        Value *BB1V = PN.getIncomingValueForBlock(BB1);
        Value *BB2V = PN.getIncomingValueForBlock(BB2);
        if (BB1V == BB2V)
          continue;
  
        // Check for passingValueIsAlwaysUndefined here because we would rather
        // eliminate undefined control flow then converting it to a select.
        if (passingValueIsAlwaysUndefined(BB1V, &PN) ||
            passingValueIsAlwaysUndefined(BB2V, &PN))
          return Changed;
  
        if (isa<ConstantExpr>(BB1V) && !isSafeToSpeculativelyExecute(BB1V))
          return Changed;
        if (isa<ConstantExpr>(BB2V) && !isSafeToSpeculativelyExecute(BB2V))
          return Changed;
      }
    }
  
    // Okay, it is safe to hoist the terminator.
    Instruction *NT = I1->clone();
    BIParent->getInstList().insert(BI->getIterator(), NT);
    if (!NT->getType()->isVoidTy()) {
      I1->replaceAllUsesWith(NT);
      I2->replaceAllUsesWith(NT);
      NT->takeName(I1);
    }
    Changed = true;
    ++NumHoistCommonInstrs;
  
    // Ensure terminator gets a debug location, even an unknown one, in case
    // it involves inlinable calls.
    NT->applyMergedLocation(I1->getDebugLoc(), I2->getDebugLoc());
  
    // PHIs created below will adopt NT's merged DebugLoc.
    IRBuilder<NoFolder> Builder(NT);
  
    // Hoisting one of the terminators from our successor is a great thing.
    // Unfortunately, the successors of the if/else blocks may have PHI nodes in
    // them.  If they do, all PHI entries for BB1/BB2 must agree for all PHI
    // nodes, so we insert select instruction to compute the final result.
    std::map<std::pair<Value *, Value *>, SelectInst *> InsertedSelects;
    for (BasicBlock *Succ : successors(BB1)) {
      for (PHINode &PN : Succ->phis()) {
        Value *BB1V = PN.getIncomingValueForBlock(BB1);
        Value *BB2V = PN.getIncomingValueForBlock(BB2);
        if (BB1V == BB2V)
          continue;
  
        // These values do not agree.  Insert a select instruction before NT
        // that determines the right value.
        SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
        if (!SI) {
          // Propagate fast-math-flags from phi node to its replacement select.
          IRBuilder<>::FastMathFlagGuard FMFGuard(Builder);
          if (isa<FPMathOperator>(PN))
            Builder.setFastMathFlags(PN.getFastMathFlags());
  
          SI = cast<SelectInst>(
              Builder.CreateSelect(BI->getCondition(), BB1V, BB2V,
                                   BB1V->getName() + "." + BB2V->getName(), BI));
        }
  
        // Make the PHI node use the select for all incoming values for BB1/BB2
        for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i)
          if (PN.getIncomingBlock(i) == BB1 || PN.getIncomingBlock(i) == BB2)
            PN.setIncomingValue(i, SI);
      }
    }
  
    SmallVector<DominatorTree::UpdateType, 4> Updates;
  
    // Update any PHI nodes in our new successors.
    for (BasicBlock *Succ : successors(BB1)) {
      AddPredecessorToBlock(Succ, BIParent, BB1);
      if (DTU)
        Updates.push_back({DominatorTree::Insert, BIParent, Succ});
    }
  
    if (DTU)
      for (BasicBlock *Succ : successors(BI))
        Updates.push_back({DominatorTree::Delete, BIParent, Succ});
  
    EraseTerminatorAndDCECond(BI);
    if (DTU)
      DTU->applyUpdates(Updates);
    return Changed;
  }
  
  // Check lifetime markers.
  static bool isLifeTimeMarker(const Instruction *I) {
    if (auto II = dyn_cast<IntrinsicInst>(I)) {
      switch (II->getIntrinsicID()) {
      default:
        break;
      case Intrinsic::lifetime_start:
      case Intrinsic::lifetime_end:
        return true;
      }
    }
    return false;
  }
  
  // TODO: Refine this. This should avoid cases like turning constant memcpy sizes
  // into variables.
  static bool replacingOperandWithVariableIsCheap(const Instruction *I,
                                                  int OpIdx) {
    return !isa<IntrinsicInst>(I);
  }
  
  // All instructions in Insts belong to different blocks that all unconditionally
  // branch to a common successor. Analyze each instruction and return true if it
  // would be possible to sink them into their successor, creating one common
  // instruction instead. For every value that would be required to be provided by
  // PHI node (because an operand varies in each input block), add to PHIOperands.
  static bool canSinkInstructions(
      ArrayRef<Instruction *> Insts,
      DenseMap<Instruction *, SmallVector<Value *, 4>> &PHIOperands) {
    // Prune out obviously bad instructions to move. Each instruction must have
    // exactly zero or one use, and we check later that use is by a single, common
    // PHI instruction in the successor.
    bool HasUse = !Insts.front()->user_empty();
    for (auto *I : Insts) {
      // These instructions may change or break semantics if moved.
      if (isa<PHINode>(I) || I->isEHPad() || isa<AllocaInst>(I) ||
          I->getType()->isTokenTy())
        return false;
  
      // Do not try to sink an instruction in an infinite loop - it can cause
      // this algorithm to infinite loop.
      if (I->getParent()->getSingleSuccessor() == I->getParent())
        return false;
  
      // Conservatively return false if I is an inline-asm instruction. Sinking
      // and merging inline-asm instructions can potentially create arguments
      // that cannot satisfy the inline-asm constraints.
      // If the instruction has nomerge attribute, return false.
      if (const auto *C = dyn_cast<CallBase>(I))
        if (C->isInlineAsm() || C->cannotMerge())
          return false;
  
      // Each instruction must have zero or one use.
      if (HasUse && !I->hasOneUse())
        return false;
      if (!HasUse && !I->user_empty())
        return false;
    }
  
    const Instruction *I0 = Insts.front();
    for (auto *I : Insts)
      if (!I->isSameOperationAs(I0))
        return false;
  
    // All instructions in Insts are known to be the same opcode. If they have a
    // use, check that the only user is a PHI or in the same block as the
    // instruction, because if a user is in the same block as an instruction we're
    // contemplating sinking, it must already be determined to be sinkable.
    if (HasUse) {
      auto *PNUse = dyn_cast<PHINode>(*I0->user_begin());
      auto *Succ = I0->getParent()->getTerminator()->getSuccessor(0);
      if (!all_of(Insts, [&PNUse,&Succ](const Instruction *I) -> bool {
            auto *U = cast<Instruction>(*I->user_begin());
            return (PNUse &&
                    PNUse->getParent() == Succ &&
                    PNUse->getIncomingValueForBlock(I->getParent()) == I) ||
                   U->getParent() == I->getParent();
          }))
        return false;
    }
  
    // Because SROA can't handle speculating stores of selects, try not to sink
    // loads, stores or lifetime markers of allocas when we'd have to create a
    // PHI for the address operand. Also, because it is likely that loads or
    // stores of allocas will disappear when Mem2Reg/SROA is run, don't sink
    // them.
    // This can cause code churn which can have unintended consequences down
    // the line - see https://llvm.org/bugs/show_bug.cgi?id=30244.
    // FIXME: This is a workaround for a deficiency in SROA - see
    // https://llvm.org/bugs/show_bug.cgi?id=30188
    if (isa<StoreInst>(I0) && any_of(Insts, [](const Instruction *I) {
          return isa<AllocaInst>(I->getOperand(1)->stripPointerCasts());
        }))
      return false;
    if (isa<LoadInst>(I0) && any_of(Insts, [](const Instruction *I) {
          return isa<AllocaInst>(I->getOperand(0)->stripPointerCasts());
        }))
      return false;
    if (isLifeTimeMarker(I0) && any_of(Insts, [](const Instruction *I) {
          return isa<AllocaInst>(I->getOperand(1)->stripPointerCasts());
        }))
      return false;
  
    // For calls to be sinkable, they must all be indirect, or have same callee.
    // I.e. if we have two direct calls to different callees, we don't want to
    // turn that into an indirect call. Likewise, if we have an indirect call,
    // and a direct call, we don't actually want to have a single indirect call.
    if (isa<CallBase>(I0)) {
      auto IsIndirectCall = [](const Instruction *I) {
        return cast<CallBase>(I)->isIndirectCall();
      };
      bool HaveIndirectCalls = any_of(Insts, IsIndirectCall);
      bool AllCallsAreIndirect = all_of(Insts, IsIndirectCall);
      if (HaveIndirectCalls) {
        if (!AllCallsAreIndirect)
          return false;
      } else {
        // All callees must be identical.
        Value *Callee = nullptr;
        for (const Instruction *I : Insts) {
          Value *CurrCallee = cast<CallBase>(I)->getCalledOperand();
          if (!Callee)
            Callee = CurrCallee;
          else if (Callee != CurrCallee)
            return false;
        }
      }
    }
  
    for (unsigned OI = 0, OE = I0->getNumOperands(); OI != OE; ++OI) {
      Value *Op = I0->getOperand(OI);
      if (Op->getType()->isTokenTy())
        // Don't touch any operand of token type.
        return false;
  
      auto SameAsI0 = [&I0, OI](const Instruction *I) {
        assert(I->getNumOperands() == I0->getNumOperands());
        return I->getOperand(OI) == I0->getOperand(OI);
      };
      if (!all_of(Insts, SameAsI0)) {
        if ((isa<Constant>(Op) && !replacingOperandWithVariableIsCheap(I0, OI)) ||
            !canReplaceOperandWithVariable(I0, OI))
          // We can't create a PHI from this GEP.
          return false;
        for (auto *I : Insts)
          PHIOperands[I].push_back(I->getOperand(OI));
      }
    }
    return true;
  }
  
  // Assuming canSinkInstructions(Blocks) has returned true, sink the last
  // instruction of every block in Blocks to their common successor, commoning
  // into one instruction.
  static bool sinkLastInstruction(ArrayRef<BasicBlock*> Blocks) {
    auto *BBEnd = Blocks[0]->getTerminator()->getSuccessor(0);
  
    // canSinkInstructions returning true guarantees that every block has at
    // least one non-terminator instruction.
    SmallVector<Instruction*,4> Insts;
    for (auto *BB : Blocks) {
      Instruction *I = BB->getTerminator();
      do {
        I = I->getPrevNode();
      } while (isa<DbgInfoIntrinsic>(I) && I != &BB->front());
      if (!isa<DbgInfoIntrinsic>(I))
        Insts.push_back(I);
    }
  
    // The only checking we need to do now is that all users of all instructions
    // are the same PHI node. canSinkInstructions should have checked this but
    // it is slightly over-aggressive - it gets confused by commutative
    // instructions so double-check it here.
    Instruction *I0 = Insts.front();
    if (!I0->user_empty()) {
      auto *PNUse = dyn_cast<PHINode>(*I0->user_begin());
      if (!all_of(Insts, [&PNUse](const Instruction *I) -> bool {
            auto *U = cast<Instruction>(*I->user_begin());
            return U == PNUse;
          }))
        return false;
    }
  
    // We don't need to do any more checking here; canSinkInstructions should
    // have done it all for us.
    SmallVector<Value*, 4> NewOperands;
    for (unsigned O = 0, E = I0->getNumOperands(); O != E; ++O) {
      // This check is different to that in canSinkInstructions. There, we
      // cared about the global view once simplifycfg (and instcombine) have
      // completed - it takes into account PHIs that become trivially
      // simplifiable.  However here we need a more local view; if an operand
      // differs we create a PHI and rely on instcombine to clean up the very
      // small mess we may make.
      bool NeedPHI = any_of(Insts, [&I0, O](const Instruction *I) {
        return I->getOperand(O) != I0->getOperand(O);
      });
      if (!NeedPHI) {
        NewOperands.push_back(I0->getOperand(O));
        continue;
      }
  
      // Create a new PHI in the successor block and populate it.
      auto *Op = I0->getOperand(O);
      assert(!Op->getType()->isTokenTy() && "Can't PHI tokens!");
      auto *PN = PHINode::Create(Op->getType(), Insts.size(),
                                 Op->getName() + ".sink", &BBEnd->front());
      for (auto *I : Insts)
        PN->addIncoming(I->getOperand(O), I->getParent());
      NewOperands.push_back(PN);
    }
  
    // Arbitrarily use I0 as the new "common" instruction; remap its operands
    // and move it to the start of the successor block.
    for (unsigned O = 0, E = I0->getNumOperands(); O != E; ++O)
      I0->getOperandUse(O).set(NewOperands[O]);
    I0->moveBefore(&*BBEnd->getFirstInsertionPt());
  
    // Update metadata and IR flags, and merge debug locations.
    for (auto *I : Insts)
      if (I != I0) {
        // The debug location for the "common" instruction is the merged locations
        // of all the commoned instructions.  We start with the original location
        // of the "common" instruction and iteratively merge each location in the
        // loop below.
        // This is an N-way merge, which will be inefficient if I0 is a CallInst.
        // However, as N-way merge for CallInst is rare, so we use simplified API
        // instead of using complex API for N-way merge.
        I0->applyMergedLocation(I0->getDebugLoc(), I->getDebugLoc());
        combineMetadataForCSE(I0, I, true);
        I0->andIRFlags(I);
      }
  
    if (!I0->user_empty()) {
      // canSinkLastInstruction checked that all instructions were used by
      // one and only one PHI node. Find that now, RAUW it to our common
      // instruction and nuke it.
      auto *PN = cast<PHINode>(*I0->user_begin());
      PN->replaceAllUsesWith(I0);
      PN->eraseFromParent();
    }
  
    // Finally nuke all instructions apart from the common instruction.
    for (auto *I : Insts)
      if (I != I0)
        I->eraseFromParent();
  
    return true;
  }
  
  namespace {
  
    // LockstepReverseIterator - Iterates through instructions
    // in a set of blocks in reverse order from the first non-terminator.
    // For example (assume all blocks have size n):
    //   LockstepReverseIterator I([B1, B2, B3]);
    //   *I-- = [B1[n], B2[n], B3[n]];
    //   *I-- = [B1[n-1], B2[n-1], B3[n-1]];
    //   *I-- = [B1[n-2], B2[n-2], B3[n-2]];
    //   ...
    class LockstepReverseIterator {
      ArrayRef<BasicBlock*> Blocks;
      SmallVector<Instruction*,4> Insts;
      bool Fail;
  
    public:
      LockstepReverseIterator(ArrayRef<BasicBlock*> Blocks) : Blocks(Blocks) {
        reset();
      }
  
      void reset() {
        Fail = false;
        Insts.clear();
        for (auto *BB : Blocks) {
          Instruction *Inst = BB->getTerminator();
          for (Inst = Inst->getPrevNode(); Inst && isa<DbgInfoIntrinsic>(Inst);)
            Inst = Inst->getPrevNode();
          if (!Inst) {
            // Block wasn't big enough.
            Fail = true;
            return;
          }
          Insts.push_back(Inst);
        }
      }
  
      bool isValid() const {
        return !Fail;
      }
  
      void operator--() {
        if (Fail)
          return;
        for (auto *&Inst : Insts) {
          for (Inst = Inst->getPrevNode(); Inst && isa<DbgInfoIntrinsic>(Inst);)
            Inst = Inst->getPrevNode();
          // Already at beginning of block.
          if (!Inst) {
            Fail = true;
            return;
          }
        }
      }
  
      void operator++() {
        if (Fail)
          return;
        for (auto *&Inst : Insts) {
          for (Inst = Inst->getNextNode(); Inst && isa<DbgInfoIntrinsic>(Inst);)
            Inst = Inst->getNextNode();
          // Already at end of block.
          if (!Inst) {
            Fail = true;
            return;
          }
        }
      }
  
      ArrayRef<Instruction*> operator * () const {
        return Insts;
      }
    };
  
  } // end anonymous namespace
  
  /// Check whether BB's predecessors end with unconditional branches. If it is
  /// true, sink any common code from the predecessors to BB.
  static bool SinkCommonCodeFromPredecessors(BasicBlock *BB,
                                             DomTreeUpdater *DTU) {
    // We support two situations:
    //   (1) all incoming arcs are unconditional
    //   (2) there are non-unconditional incoming arcs
    //
    // (2) is very common in switch defaults and
    // else-if patterns;
    //
    //   if (a) f(1);
    //   else if (b) f(2);
    //
    // produces:
    //
    //       [if]
    //      /    \
    //    [f(1)] [if]
    //      |     | \
    //      |     |  |
    //      |  [f(2)]|
    //       \    | /
    //        [ end ]
    //
    // [end] has two unconditional predecessor arcs and one conditional. The
    // conditional refers to the implicit empty 'else' arc. This conditional
    // arc can also be caused by an empty default block in a switch.
    //
    // In this case, we attempt to sink code from all *unconditional* arcs.
    // If we can sink instructions from these arcs (determined during the scan
    // phase below) we insert a common successor for all unconditional arcs and
    // connect that to [end], to enable sinking:
    //
    //       [if]
    //      /    \
    //    [x(1)] [if]
    //      |     | \
    //      |     |  \
    //      |  [x(2)] |
    //       \   /    |
    //   [sink.split] |
    //         \     /
    //         [ end ]
    //
    SmallVector<BasicBlock*,4> UnconditionalPreds;
    bool HaveNonUnconditionalPredecessors = false;
    for (auto *PredBB : predecessors(BB)) {
      auto *PredBr = dyn_cast<BranchInst>(PredBB->getTerminator());
      if (PredBr && PredBr->isUnconditional())
        UnconditionalPreds.push_back(PredBB);
      else
        HaveNonUnconditionalPredecessors = true;
    }
    if (UnconditionalPreds.size() < 2)
      return false;
  
    // We take a two-step approach to tail sinking. First we scan from the end of
    // each block upwards in lockstep. If the n'th instruction from the end of each
    // block can be sunk, those instructions are added to ValuesToSink and we
    // carry on. If we can sink an instruction but need to PHI-merge some operands
    // (because they're not identical in each instruction) we add these to
    // PHIOperands.
    int ScanIdx = 0;
    SmallPtrSet<Value*,4> InstructionsToSink;
    DenseMap<Instruction*, SmallVector<Value*,4>> PHIOperands;
    LockstepReverseIterator LRI(UnconditionalPreds);
    while (LRI.isValid() &&
           canSinkInstructions(*LRI, PHIOperands)) {
      LLVM_DEBUG(dbgs() << "SINK: instruction can be sunk: " << *(*LRI)[0]
                        << "\n");
      InstructionsToSink.insert((*LRI).begin(), (*LRI).end());
      ++ScanIdx;
      --LRI;
    }
  
    // If no instructions can be sunk, early-return.
    if (ScanIdx == 0)
      return false;
  
    bool followedByDeoptOrUnreachable = IsBlockFollowedByDeoptOrUnreachable(BB);
  
    if (!followedByDeoptOrUnreachable) {
      // Okay, we *could* sink last ScanIdx instructions. But how many can we
      // actually sink before encountering instruction that is unprofitable to
      // sink?
      auto ProfitableToSinkInstruction = [&](LockstepReverseIterator &LRI) {
        unsigned NumPHIdValues = 0;
        for (auto *I : *LRI)
          for (auto *V : PHIOperands[I]) {
            if (!InstructionsToSink.contains(V))
              ++NumPHIdValues;
            // FIXME: this check is overly optimistic. We may end up not sinking
            // said instruction, due to the very same profitability check.
            // See @creating_too_many_phis in sink-common-code.ll.
          }
        LLVM_DEBUG(dbgs() << "SINK: #phid values: " << NumPHIdValues << "\n");
        unsigned NumPHIInsts = NumPHIdValues / UnconditionalPreds.size();
        if ((NumPHIdValues % UnconditionalPreds.size()) != 0)
          NumPHIInsts++;
  
        return NumPHIInsts <= 1;
      };
  
      // We've determined that we are going to sink last ScanIdx instructions,
      // and recorded them in InstructionsToSink. Now, some instructions may be
      // unprofitable to sink. But that determination depends on the instructions
      // that we are going to sink.
  
      // First, forward scan: find the first instruction unprofitable to sink,
      // recording all the ones that are profitable to sink.
      // FIXME: would it be better, after we detect that not all are profitable.
      // to either record the profitable ones, or erase the unprofitable ones?
      // Maybe we need to choose (at runtime) the one that will touch least
      // instrs?
      LRI.reset();
      int Idx = 0;
      SmallPtrSet<Value *, 4> InstructionsProfitableToSink;
      while (Idx < ScanIdx) {
        if (!ProfitableToSinkInstruction(LRI)) {
          // Too many PHIs would be created.
          LLVM_DEBUG(
              dbgs() << "SINK: stopping here, too many PHIs would be created!\n");
          break;
        }
        InstructionsProfitableToSink.insert((*LRI).begin(), (*LRI).end());
        --LRI;
        ++Idx;
      }
  
      // If no instructions can be sunk, early-return.
      if (Idx == 0)
        return false;
  
      // Did we determine that (only) some instructions are unprofitable to sink?
      if (Idx < ScanIdx) {
        // Okay, some instructions are unprofitable.
        ScanIdx = Idx;
        InstructionsToSink = InstructionsProfitableToSink;
  
        // But, that may make other instructions unprofitable, too.
        // So, do a backward scan, do any earlier instructions become
        // unprofitable?
        assert(
            !ProfitableToSinkInstruction(LRI) &&
            "We already know that the last instruction is unprofitable to sink");
        ++LRI;
        --Idx;
        while (Idx >= 0) {
          // If we detect that an instruction becomes unprofitable to sink,
          // all earlier instructions won't be sunk either,
          // so preemptively keep InstructionsProfitableToSink in sync.
          // FIXME: is this the most performant approach?
          for (auto *I : *LRI)
            InstructionsProfitableToSink.erase(I);
          if (!ProfitableToSinkInstruction(LRI)) {
            // Everything starting with this instruction won't be sunk.
            ScanIdx = Idx;
            InstructionsToSink = InstructionsProfitableToSink;
          }
          ++LRI;
          --Idx;
        }
      }
  
      // If no instructions can be sunk, early-return.
      if (ScanIdx == 0)
        return false;
    }
  
    bool Changed = false;
  
    if (HaveNonUnconditionalPredecessors) {
      if (!followedByDeoptOrUnreachable) {
        // It is always legal to sink common instructions from unconditional
        // predecessors. However, if not all predecessors are unconditional,
        // this transformation might be pessimizing. So as a rule of thumb,
        // don't do it unless we'd sink at least one non-speculatable instruction.
        // See https://bugs.llvm.org/show_bug.cgi?id=30244
        LRI.reset();
        int Idx = 0;
        bool Profitable = false;
        while (Idx < ScanIdx) {
          if (!isSafeToSpeculativelyExecute((*LRI)[0])) {
            Profitable = true;
            break;
          }
          --LRI;
          ++Idx;
        }
        if (!Profitable)
          return false;
      }
  
      LLVM_DEBUG(dbgs() << "SINK: Splitting edge\n");
      // We have a conditional edge and we're going to sink some instructions.
      // Insert a new block postdominating all blocks we're going to sink from.
      if (!SplitBlockPredecessors(BB, UnconditionalPreds, ".sink.split", DTU))
        // Edges couldn't be split.
        return false;
      Changed = true;
    }
  
    // Now that we've analyzed all potential sinking candidates, perform the
    // actual sink. We iteratively sink the last non-terminator of the source
    // blocks into their common successor unless doing so would require too
    // many PHI instructions to be generated (currently only one PHI is allowed
    // per sunk instruction).
    //
    // We can use InstructionsToSink to discount values needing PHI-merging that will
    // actually be sunk in a later iteration. This allows us to be more
    // aggressive in what we sink. This does allow a false positive where we
    // sink presuming a later value will also be sunk, but stop half way through
    // and never actually sink it which means we produce more PHIs than intended.
    // This is unlikely in practice though.
    int SinkIdx = 0;
    for (; SinkIdx != ScanIdx; ++SinkIdx) {
      LLVM_DEBUG(dbgs() << "SINK: Sink: "
                        << *UnconditionalPreds[0]->getTerminator()->getPrevNode()
                        << "\n");
  
      // Because we've sunk every instruction in turn, the current instruction to
      // sink is always at index 0.
      LRI.reset();
  
      if (!sinkLastInstruction(UnconditionalPreds)) {
        LLVM_DEBUG(
            dbgs()
            << "SINK: stopping here, failed to actually sink instruction!\n");
        break;
      }
  
      NumSinkCommonInstrs++;
      Changed = true;
    }
    if (SinkIdx != 0)
      ++NumSinkCommonCode;
    return Changed;
  }
  
  namespace {
  
  struct CompatibleSets {
    using SetTy = SmallVector<InvokeInst *, 2>;
  
    SmallVector<SetTy, 1> Sets;
  
    static bool shouldBelongToSameSet(ArrayRef<InvokeInst *> Invokes);
  
    SetTy &getCompatibleSet(InvokeInst *II);
  
    void insert(InvokeInst *II);
  };
  
  CompatibleSets::SetTy &CompatibleSets::getCompatibleSet(InvokeInst *II) {
    // Perform a linear scan over all the existing sets, see if the new `invoke`
    // is compatible with any particular set. Since we know that all the `invokes`
    // within a set are compatible, only check the first `invoke` in each set.
    // WARNING: at worst, this has quadratic complexity.
    for (CompatibleSets::SetTy &Set : Sets) {
      if (CompatibleSets::shouldBelongToSameSet({Set.front(), II}))
        return Set;
    }
  
    // Otherwise, we either had no sets yet, or this invoke forms a new set.
    return Sets.emplace_back();
  }
  
  void CompatibleSets::insert(InvokeInst *II) {
    getCompatibleSet(II).emplace_back(II);
  }
  
  bool CompatibleSets::shouldBelongToSameSet(ArrayRef<InvokeInst *> Invokes) {
    assert(Invokes.size() == 2 && "Always called with exactly two candidates.");
  
    // Can we theoretically merge these `invoke`s?
    auto IsIllegalToMerge = [](InvokeInst *II) {
      return II->cannotMerge() || II->isInlineAsm();
    };
    if (any_of(Invokes, IsIllegalToMerge))
      return false;
  
    // Either both `invoke`s must be   direct,
    // or     both `invoke`s must be indirect.
    auto IsIndirectCall = [](InvokeInst *II) { return II->isIndirectCall(); };
    bool HaveIndirectCalls = any_of(Invokes, IsIndirectCall);
    bool AllCallsAreIndirect = all_of(Invokes, IsIndirectCall);
    if (HaveIndirectCalls) {
      if (!AllCallsAreIndirect)
        return false;
    } else {
      // All callees must be identical.
      Value *Callee = nullptr;
      for (InvokeInst *II : Invokes) {
        Value *CurrCallee = II->getCalledOperand();
        assert(CurrCallee && "There is always a called operand.");
        if (!Callee)
          Callee = CurrCallee;
        else if (Callee != CurrCallee)
          return false;
      }
    }
  
    // Either both `invoke`s must not have a normal destination,
    // or     both `invoke`s must     have a normal destination,
    auto HasNormalDest = [](InvokeInst *II) {
      return !isa<UnreachableInst>(II->getNormalDest()->getFirstNonPHIOrDbg());
    };
    if (any_of(Invokes, HasNormalDest)) {
      // Do not merge `invoke` that does not have a normal destination with one
      // that does have a normal destination, even though doing so would be legal.
      if (!all_of(Invokes, HasNormalDest))
        return false;
  
      // All normal destinations must be identical.
      BasicBlock *NormalBB = nullptr;
      for (InvokeInst *II : Invokes) {
        BasicBlock *CurrNormalBB = II->getNormalDest();
        assert(CurrNormalBB && "There is always a 'continue to' basic block.");
        if (!NormalBB)
          NormalBB = CurrNormalBB;
        else if (NormalBB != CurrNormalBB)
          return false;
      }
  
      // In the normal destination, the incoming values for these two `invoke`s
      // must be compatible.
      SmallPtrSet<Value *, 16> EquivalenceSet(Invokes.begin(), Invokes.end());
      if (!IncomingValuesAreCompatible(
              NormalBB, {Invokes[0]->getParent(), Invokes[1]->getParent()},
              &EquivalenceSet))
        return false;
    }
  
  #ifndef NDEBUG
    // All unwind destinations must be identical.
    // We know that because we have started from said unwind destination.
    BasicBlock *UnwindBB = nullptr;
    for (InvokeInst *II : Invokes) {
      BasicBlock *CurrUnwindBB = II->getUnwindDest();
      assert(CurrUnwindBB && "There is always an 'unwind to' basic block.");
      if (!UnwindBB)
        UnwindBB = CurrUnwindBB;
      else
        assert(UnwindBB == CurrUnwindBB && "Unexpected unwind destination.");
    }
  #endif
  
    // In the unwind destination, the incoming values for these two `invoke`s
    // must be compatible.
    if (!IncomingValuesAreCompatible(
            Invokes.front()->getUnwindDest(),
            {Invokes[0]->getParent(), Invokes[1]->getParent()}))
      return false;
  
    // Ignoring arguments, these `invoke`s must be identical,
    // including operand bundles.
    const InvokeInst *II0 = Invokes.front();
    for (auto *II : Invokes.drop_front())
      if (!II->isSameOperationAs(II0))
        return false;
  
    // Can we theoretically form the data operands for the merged `invoke`?
    auto IsIllegalToMergeArguments = [](auto Ops) {
      Type *Ty = std::get<0>(Ops)->getType();
      assert(Ty == std::get<1>(Ops)->getType() && "Incompatible types?");
      return Ty->isTokenTy() && std::get<0>(Ops) != std::get<1>(Ops);
    };
    assert(Invokes.size() == 2 && "Always called with exactly two candidates.");
    if (any_of(zip(Invokes[0]->data_ops(), Invokes[1]->data_ops()),
               IsIllegalToMergeArguments))
      return false;
  
    return true;
  }
  
  } // namespace
  
  // Merge all invokes in the provided set, all of which are compatible
  // as per the `CompatibleSets::shouldBelongToSameSet()`.
  static void MergeCompatibleInvokesImpl(ArrayRef<InvokeInst *> Invokes,
                                         DomTreeUpdater *DTU) {
    assert(Invokes.size() >= 2 && "Must have at least two invokes to merge.");
  
    SmallVector<DominatorTree::UpdateType, 8> Updates;
    if (DTU)
      Updates.reserve(2 + 3 * Invokes.size());
  
    bool HasNormalDest =
        !isa<UnreachableInst>(Invokes[0]->getNormalDest()->getFirstNonPHIOrDbg());
  
    // Clone one of the invokes into a new basic block.
    // Since they are all compatible, it doesn't matter which invoke is cloned.
    InvokeInst *MergedInvoke = [&Invokes, HasNormalDest]() {
      InvokeInst *II0 = Invokes.front();
      BasicBlock *II0BB = II0->getParent();
      BasicBlock *InsertBeforeBlock =
          II0->getParent()->getIterator()->getNextNode();
      Function *Func = II0BB->getParent();
      LLVMContext &Ctx = II0->getContext();
  
      BasicBlock *MergedInvokeBB = BasicBlock::Create(
          Ctx, II0BB->getName() + ".invoke", Func, InsertBeforeBlock);
  
      auto *MergedInvoke = cast<InvokeInst>(II0->clone());
      // NOTE: all invokes have the same attributes, so no handling needed.
      MergedInvokeBB->getInstList().push_back(MergedInvoke);
  
      if (!HasNormalDest) {
        // This set does not have a normal destination,
        // so just form a new block with unreachable terminator.
        BasicBlock *MergedNormalDest = BasicBlock::Create(
            Ctx, II0BB->getName() + ".cont", Func, InsertBeforeBlock);
        new UnreachableInst(Ctx, MergedNormalDest);
        MergedInvoke->setNormalDest(MergedNormalDest);
      }
  
      // The unwind destination, however, remainds identical for all invokes here.
  
      return MergedInvoke;
    }();
  
    if (DTU) {
      // Predecessor blocks that contained these invokes will now branch to
      // the new block that contains the merged invoke, ...
      for (InvokeInst *II : Invokes)
        Updates.push_back(
            {DominatorTree::Insert, II->getParent(), MergedInvoke->getParent()});
  
      // ... which has the new `unreachable` block as normal destination,
      // or unwinds to the (same for all `invoke`s in this set) `landingpad`,
      for (BasicBlock *SuccBBOfMergedInvoke : successors(MergedInvoke))
        Updates.push_back({DominatorTree::Insert, MergedInvoke->getParent(),
                           SuccBBOfMergedInvoke});
  
      // Since predecessor blocks now unconditionally branch to a new block,
      // they no longer branch to their original successors.
      for (InvokeInst *II : Invokes)
        for (BasicBlock *SuccOfPredBB : successors(II->getParent()))
          Updates.push_back(
              {DominatorTree::Delete, II->getParent(), SuccOfPredBB});
    }
  
    bool IsIndirectCall = Invokes[0]->isIndirectCall();
  
    // Form the merged operands for the merged invoke.
    for (Use &U : MergedInvoke->operands()) {
      // Only PHI together the indirect callees and data operands.
      if (MergedInvoke->isCallee(&U)) {
        if (!IsIndirectCall)
          continue;
      } else if (!MergedInvoke->isDataOperand(&U))
        continue;
  
      // Don't create trivial PHI's with all-identical incoming values.
      bool NeedPHI = any_of(Invokes, [&U](InvokeInst *II) {
        return II->getOperand(U.getOperandNo()) != U.get();
      });
      if (!NeedPHI)
        continue;
  
      // Form a PHI out of all the data ops under this index.
      PHINode *PN = PHINode::Create(
          U->getType(), /*NumReservedValues=*/Invokes.size(), "", MergedInvoke);
      for (InvokeInst *II : Invokes)
        PN->addIncoming(II->getOperand(U.getOperandNo()), II->getParent());
  
      U.set(PN);
    }
  
    // We've ensured that each PHI node has compatible (identical) incoming values
    // when coming from each of the `invoke`s in the current merge set,
    // so update the PHI nodes accordingly.
    for (BasicBlock *Succ : successors(MergedInvoke))
      AddPredecessorToBlock(Succ, /*NewPred=*/MergedInvoke->getParent(),
                            /*ExistPred=*/Invokes.front()->getParent());
  
    // And finally, replace the original `invoke`s with an unconditional branch
    // to the block with the merged `invoke`. Also, give that merged `invoke`
    // the merged debugloc of all the original `invoke`s.
    const DILocation *MergedDebugLoc = nullptr;
    for (InvokeInst *II : Invokes) {
      // Compute the debug location common to all the original `invoke`s.
      if (!MergedDebugLoc)
        MergedDebugLoc = II->getDebugLoc();
      else
        MergedDebugLoc =
            DILocation::getMergedLocation(MergedDebugLoc, II->getDebugLoc());
  
      // And replace the old `invoke` with an unconditionally branch
      // to the block with the merged `invoke`.
      for (BasicBlock *OrigSuccBB : successors(II->getParent()))
        OrigSuccBB->removePredecessor(II->getParent());
      BranchInst::Create(MergedInvoke->getParent(), II->getParent());
      II->replaceAllUsesWith(MergedInvoke);
      II->eraseFromParent();
      ++NumInvokesMerged;
    }
    MergedInvoke->setDebugLoc(MergedDebugLoc);
    ++NumInvokeSetsFormed;
  
    if (DTU)
      DTU->applyUpdates(Updates);
  }
  
  /// If this block is a `landingpad` exception handling block, categorize all
  /// the predecessor `invoke`s into sets, with all `invoke`s in each set
  /// being "mergeable" together, and then merge invokes in each set together.
  ///
  /// This is a weird mix of hoisting and sinking. Visually, it goes from:
  ///          [...]        [...]
  ///            |            |
  ///        [invoke0]    [invoke1]
  ///           / \          / \
  ///     [cont0] [landingpad] [cont1]
  /// to:
  ///      [...] [...]
  ///          \ /
  ///       [invoke]
  ///          / \
  ///     [cont] [landingpad]
  ///
  /// But of course we can only do that if the invokes share the `landingpad`,
  /// edges invoke0->cont0 and invoke1->cont1 are "compatible",
  /// and the invoked functions are "compatible".
  static bool MergeCompatibleInvokes(BasicBlock *BB, DomTreeUpdater *DTU) {
    if (!EnableMergeCompatibleInvokes)
      return false;
  
    bool Changed = false;
  
    // FIXME: generalize to all exception handling blocks?
    if (!BB->isLandingPad())
      return Changed;
  
    CompatibleSets Grouper;
  
    // Record all the predecessors of this `landingpad`. As per verifier,
    // the only allowed predecessor is the unwind edge of an `invoke`.
    // We want to group "compatible" `invokes` into the same set to be merged.
    for (BasicBlock *PredBB : predecessors(BB))
      Grouper.insert(cast<InvokeInst>(PredBB->getTerminator()));
  
    // And now, merge `invoke`s that were grouped togeter.
    for (ArrayRef<InvokeInst *> Invokes : Grouper.Sets) {
      if (Invokes.size() < 2)
        continue;
      Changed = true;
      MergeCompatibleInvokesImpl(Invokes, DTU);
    }
  
    return Changed;
  }
  
  /// Determine if we can hoist sink a sole store instruction out of a
  /// conditional block.
  ///
  /// We are looking for code like the following:
  ///   BrBB:
  ///     store i32 %add, i32* %arrayidx2
  ///     ... // No other stores or function calls (we could be calling a memory
  ///     ... // function).
  ///     %cmp = icmp ult %x, %y
  ///     br i1 %cmp, label %EndBB, label %ThenBB
  ///   ThenBB:
  ///     store i32 %add5, i32* %arrayidx2
  ///     br label EndBB
  ///   EndBB:
  ///     ...
  ///   We are going to transform this into:
  ///   BrBB:
  ///     store i32 %add, i32* %arrayidx2
  ///     ... //
  ///     %cmp = icmp ult %x, %y
  ///     %add.add5 = select i1 %cmp, i32 %add, %add5
  ///     store i32 %add.add5, i32* %arrayidx2
  ///     ...
  ///
  /// \return The pointer to the value of the previous store if the store can be
  ///         hoisted into the predecessor block. 0 otherwise.
  static Value *isSafeToSpeculateStore(Instruction *I, BasicBlock *BrBB,
                                       BasicBlock *StoreBB, BasicBlock *EndBB) {
    StoreInst *StoreToHoist = dyn_cast<StoreInst>(I);
    if (!StoreToHoist)
      return nullptr;
  
    // Volatile or atomic.
    if (!StoreToHoist->isSimple())
      return nullptr;
  
    Value *StorePtr = StoreToHoist->getPointerOperand();
    Type *StoreTy = StoreToHoist->getValueOperand()->getType();
  
    // Look for a store to the same pointer in BrBB.
    unsigned MaxNumInstToLookAt = 9;
    // Skip pseudo probe intrinsic calls which are not really killing any memory
    // accesses.
    for (Instruction &CurI : reverse(BrBB->instructionsWithoutDebug(true))) {
      if (!MaxNumInstToLookAt)
        break;
      --MaxNumInstToLookAt;
  
      // Could be calling an instruction that affects memory like free().
      if (CurI.mayWriteToMemory() && !isa<StoreInst>(CurI))
        return nullptr;
  
      if (auto *SI = dyn_cast<StoreInst>(&CurI)) {
        // Found the previous store to same location and type. Make sure it is
        // simple, to avoid introducing a spurious non-atomic write after an
        // atomic write.
        if (SI->getPointerOperand() == StorePtr &&
            SI->getValueOperand()->getType() == StoreTy && SI->isSimple())
          // Found the previous store, return its value operand.
          return SI->getValueOperand();
        return nullptr; // Unknown store.
      }
  
      if (auto *LI = dyn_cast<LoadInst>(&CurI)) {
        if (LI->getPointerOperand() == StorePtr && LI->getType() == StoreTy &&
            LI->isSimple()) {
          // Local objects (created by an `alloca` instruction) are always
          // writable, so once we are past a read from a location it is valid to
          // also write to that same location.
          // If the address of the local object never escapes the function, that
          // means it's never concurrently read or written, hence moving the store
          // from under the condition will not introduce a data race.
          auto *AI = dyn_cast<AllocaInst>(getUnderlyingObject(StorePtr));
          if (AI && !PointerMayBeCaptured(AI, false, true))
            // Found a previous load, return it.
            return LI;
        }
        // The load didn't work out, but we may still find a store.
      }
    }
  
    return nullptr;
  }
  
  /// Estimate the cost of the insertion(s) and check that the PHI nodes can be
  /// converted to selects.
  static bool validateAndCostRequiredSelects(BasicBlock *BB, BasicBlock *ThenBB,
                                             BasicBlock *EndBB,
                                             unsigned &SpeculatedInstructions,
                                             InstructionCost &Cost,
                                             const TargetTransformInfo &TTI) {
    TargetTransformInfo::TargetCostKind CostKind =
      BB->getParent()->hasMinSize()
      ? TargetTransformInfo::TCK_CodeSize
      : TargetTransformInfo::TCK_SizeAndLatency;
  
    bool HaveRewritablePHIs = false;
    for (PHINode &PN : EndBB->phis()) {
      Value *OrigV = PN.getIncomingValueForBlock(BB);
      Value *ThenV = PN.getIncomingValueForBlock(ThenBB);
  
      // FIXME: Try to remove some of the duplication with HoistThenElseCodeToIf.
      // Skip PHIs which are trivial.
      if (ThenV == OrigV)
        continue;
  
      Cost += TTI.getCmpSelInstrCost(Instruction::Select, PN.getType(), nullptr,
                                     CmpInst::BAD_ICMP_PREDICATE, CostKind);
  
      // Don't convert to selects if we could remove undefined behavior instead.
      if (passingValueIsAlwaysUndefined(OrigV, &PN) ||
          passingValueIsAlwaysUndefined(ThenV, &PN))
        return false;
  
      HaveRewritablePHIs = true;
      ConstantExpr *OrigCE = dyn_cast<ConstantExpr>(OrigV);
      ConstantExpr *ThenCE = dyn_cast<ConstantExpr>(ThenV);
      if (!OrigCE && !ThenCE)
        continue; // Known safe and cheap.
  
      if ((ThenCE && !isSafeToSpeculativelyExecute(ThenCE)) ||
          (OrigCE && !isSafeToSpeculativelyExecute(OrigCE)))
        return false;
      InstructionCost OrigCost = OrigCE ? computeSpeculationCost(OrigCE, TTI) : 0;
      InstructionCost ThenCost = ThenCE ? computeSpeculationCost(ThenCE, TTI) : 0;
      InstructionCost MaxCost =
          2 * PHINodeFoldingThreshold * TargetTransformInfo::TCC_Basic;
      if (OrigCost + ThenCost > MaxCost)
        return false;
  
      // Account for the cost of an unfolded ConstantExpr which could end up
      // getting expanded into Instructions.
      // FIXME: This doesn't account for how many operations are combined in the
      // constant expression.
      ++SpeculatedInstructions;
      if (SpeculatedInstructions > 1)
        return false;
    }
  
    return HaveRewritablePHIs;
  }
  
  /// Speculate a conditional basic block flattening the CFG.
  ///
  /// Note that this is a very risky transform currently. Speculating
  /// instructions like this is most often not desirable. Instead, there is an MI
  /// pass which can do it with full awareness of the resource constraints.
  /// However, some cases are "obvious" and we should do directly. An example of
  /// this is speculating a single, reasonably cheap instruction.
  ///
  /// There is only one distinct advantage to flattening the CFG at the IR level:
  /// it makes very common but simplistic optimizations such as are common in
  /// instcombine and the DAG combiner more powerful by removing CFG edges and
  /// modeling their effects with easier to reason about SSA value graphs.
  ///
  ///
  /// An illustration of this transform is turning this IR:
  /// \code
  ///   BB:
  ///     %cmp = icmp ult %x, %y
  ///     br i1 %cmp, label %EndBB, label %ThenBB
  ///   ThenBB:
  ///     %sub = sub %x, %y
  ///     br label BB2
  ///   EndBB:
  ///     %phi = phi [ %sub, %ThenBB ], [ 0, %EndBB ]
  ///     ...
  /// \endcode
  ///
  /// Into this IR:
  /// \code
  ///   BB:
  ///     %cmp = icmp ult %x, %y
  ///     %sub = sub %x, %y
  ///     %cond = select i1 %cmp, 0, %sub
  ///     ...
  /// \endcode
  ///
  /// \returns true if the conditional block is removed.
  bool SimplifyCFGOpt::SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB,
                                              const TargetTransformInfo &TTI) {
    // Be conservative for now. FP select instruction can often be expensive.
    Value *BrCond = BI->getCondition();
    if (isa<FCmpInst>(BrCond))
      return false;
  
    BasicBlock *BB = BI->getParent();
    BasicBlock *EndBB = ThenBB->getTerminator()->getSuccessor(0);
    InstructionCost Budget =
        PHINodeFoldingThreshold * TargetTransformInfo::TCC_Basic;
  
    // If ThenBB is actually on the false edge of the conditional branch, remember
    // to swap the select operands later.
    bool Invert = false;
    if (ThenBB != BI->getSuccessor(0)) {
      assert(ThenBB == BI->getSuccessor(1) && "No edge from 'if' block?");
      Invert = true;
    }
    assert(EndBB == BI->getSuccessor(!Invert) && "No edge from to end block");
  
    // If the branch is non-unpredictable, and is predicted to *not* branch to
    // the `then` block, then avoid speculating it.
    if (!BI->getMetadata(LLVMContext::MD_unpredictable)) {
      uint64_t TWeight, FWeight;
      if (BI->extractProfMetadata(TWeight, FWeight) && (TWeight + FWeight) != 0) {
        uint64_t EndWeight = Invert ? TWeight : FWeight;
        BranchProbability BIEndProb =
            BranchProbability::getBranchProbability(EndWeight, TWeight + FWeight);
        BranchProbability Likely = TTI.getPredictableBranchThreshold();
        if (BIEndProb >= Likely)
          return false;
      }
    }
  
    // Keep a count of how many times instructions are used within ThenBB when
    // they are candidates for sinking into ThenBB. Specifically:
    // - They are defined in BB, and
    // - They have no side effects, and
    // - All of their uses are in ThenBB.
    SmallDenseMap<Instruction *, unsigned, 4> SinkCandidateUseCounts;
  
    SmallVector<Instruction *, 4> SpeculatedDbgIntrinsics;
  
    unsigned SpeculatedInstructions = 0;
    Value *SpeculatedStoreValue = nullptr;
    StoreInst *SpeculatedStore = nullptr;
    for (BasicBlock::iterator BBI = ThenBB->begin(),
                              BBE = std::prev(ThenBB->end());
         BBI != BBE; ++BBI) {
      Instruction *I = &*BBI;
      // Skip debug info.
      if (isa<DbgInfoIntrinsic>(I)) {
        SpeculatedDbgIntrinsics.push_back(I);
        continue;
      }
  
      // Skip pseudo probes. The consequence is we lose track of the branch
      // probability for ThenBB, which is fine since the optimization here takes
      // place regardless of the branch probability.
      if (isa<PseudoProbeInst>(I)) {
        // The probe should be deleted so that it will not be over-counted when
        // the samples collected on the non-conditional path are counted towards
        // the conditional path. We leave it for the counts inference algorithm to
        // figure out a proper count for an unknown probe.
        SpeculatedDbgIntrinsics.push_back(I);
        continue;
      }
  
      // Only speculatively execute a single instruction (not counting the
      // terminator) for now.
      ++SpeculatedInstructions;
      if (SpeculatedInstructions > 1)
        return false;
  
      // Don't hoist the instruction if it's unsafe or expensive.
      if (!isSafeToSpeculativelyExecute(I) &&
          !(HoistCondStores && (SpeculatedStoreValue = isSafeToSpeculateStore(
                                    I, BB, ThenBB, EndBB))))
        return false;
      if (!SpeculatedStoreValue &&
          computeSpeculationCost(I, TTI) >
              PHINodeFoldingThreshold * TargetTransformInfo::TCC_Basic)
        return false;
  
      // Store the store speculation candidate.
      if (SpeculatedStoreValue)
        SpeculatedStore = cast<StoreInst>(I);
  
      // Do not hoist the instruction if any of its operands are defined but not
      // used in BB. The transformation will prevent the operand from
      // being sunk into the use block.
      for (Use &Op : I->operands()) {
        Instruction *OpI = dyn_cast<Instruction>(Op);
        if (!OpI || OpI->getParent() != BB || OpI->mayHaveSideEffects())
          continue; // Not a candidate for sinking.
  
        ++SinkCandidateUseCounts[OpI];
      }
    }
  
    // Consider any sink candidates which are only used in ThenBB as costs for
    // speculation. Note, while we iterate over a DenseMap here, we are summing
    // and so iteration order isn't significant.
    for (SmallDenseMap<Instruction *, unsigned, 4>::iterator
             I = SinkCandidateUseCounts.begin(),
             E = SinkCandidateUseCounts.end();
         I != E; ++I)
      if (I->first->hasNUses(I->second)) {
        ++SpeculatedInstructions;
        if (SpeculatedInstructions > 1)
          return false;
      }
  
    // Check that we can insert the selects and that it's not too expensive to do
    // so.
    bool Convert = SpeculatedStore != nullptr;
    InstructionCost Cost = 0;
    Convert |= validateAndCostRequiredSelects(BB, ThenBB, EndBB,
                                              SpeculatedInstructions,
                                              Cost, TTI);
    if (!Convert || Cost > Budget)
      return false;
  
    // If we get here, we can hoist the instruction and if-convert.
    LLVM_DEBUG(dbgs() << "SPECULATIVELY EXECUTING BB" << *ThenBB << "\n";);
  
    // Insert a select of the value of the speculated store.
    if (SpeculatedStoreValue) {
      IRBuilder<NoFolder> Builder(BI);
      Value *TrueV = SpeculatedStore->getValueOperand();
      Value *FalseV = SpeculatedStoreValue;
      if (Invert)
        std::swap(TrueV, FalseV);
      Value *S = Builder.CreateSelect(
          BrCond, TrueV, FalseV, "spec.store.select", BI);
      SpeculatedStore->setOperand(0, S);
      SpeculatedStore->applyMergedLocation(BI->getDebugLoc(),
                                           SpeculatedStore->getDebugLoc());
    }
  
    // Metadata can be dependent on the condition we are hoisting above.
    // Conservatively strip all metadata on the instruction. Drop the debug loc
    // to avoid making it appear as if the condition is a constant, which would
    // be misleading while debugging.
    // Similarly strip attributes that maybe dependent on condition we are
    // hoisting above.
    for (auto &I : *ThenBB) {
      if (!SpeculatedStoreValue || &I != SpeculatedStore)
        I.setDebugLoc(DebugLoc());
      I.dropUndefImplyingAttrsAndUnknownMetadata();
    }
  
    // Hoist the instructions.
    BB->getInstList().splice(BI->getIterator(), ThenBB->getInstList(),
                             ThenBB->begin(), std::prev(ThenBB->end()));
  
    // Insert selects and rewrite the PHI operands.
    IRBuilder<NoFolder> Builder(BI);
    for (PHINode &PN : EndBB->phis()) {
      unsigned OrigI = PN.getBasicBlockIndex(BB);
      unsigned ThenI = PN.getBasicBlockIndex(ThenBB);
      Value *OrigV = PN.getIncomingValue(OrigI);
      Value *ThenV = PN.getIncomingValue(ThenI);
  
      // Skip PHIs which are trivial.
      if (OrigV == ThenV)
        continue;
  
      // Create a select whose true value is the speculatively executed value and
      // false value is the pre-existing value. Swap them if the branch
      // destinations were inverted.
      Value *TrueV = ThenV, *FalseV = OrigV;
      if (Invert)
        std::swap(TrueV, FalseV);
      Value *V = Builder.CreateSelect(BrCond, TrueV, FalseV, "spec.select", BI);
      PN.setIncomingValue(OrigI, V);
      PN.setIncomingValue(ThenI, V);
    }
  
    // Remove speculated dbg intrinsics.
    // FIXME: Is it possible to do this in a more elegant way? Moving/merging the
    // dbg value for the different flows and inserting it after the select.
    for (Instruction *I : SpeculatedDbgIntrinsics)
      I->eraseFromParent();
  
    ++NumSpeculations;
    return true;
  }
  
  /// Return true if we can thread a branch across this block.
  static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
    int Size = 0;
  
    SmallPtrSet<const Value *, 32> EphValues;
    auto IsEphemeral = [&](const Instruction *I) {
      if (isa<AssumeInst>(I))
        return true;
      return !I->mayHaveSideEffects() && !I->isTerminator() &&
             all_of(I->users(),
                    [&](const User *U) { return EphValues.count(U); });
    };
  
    // Walk the loop in reverse so that we can identify ephemeral values properly
    // (values only feeding assumes).
    for (Instruction &I : reverse(BB->instructionsWithoutDebug(false))) {
      // Can't fold blocks that contain noduplicate or convergent calls.
      if (CallInst *CI = dyn_cast<CallInst>(&I))
        if (CI->cannotDuplicate() || CI->isConvergent())
          return false;
  
      // Ignore ephemeral values which are deleted during codegen.
      if (IsEphemeral(&I))
        EphValues.insert(&I);
      // We will delete Phis while threading, so Phis should not be accounted in
      // block's size.
      else if (!isa<PHINode>(I)) {
        if (Size++ > MaxSmallBlockSize)
          return false; // Don't clone large BB's.
      }
  
      // We can only support instructions that do not define values that are
      // live outside of the current basic block.
      for (User *U : I.users()) {
        Instruction *UI = cast<Instruction>(U);
        if (UI->getParent() != BB || isa<PHINode>(UI))
          return false;
      }
  
      // Looks ok, continue checking.
    }
  
    return true;
  }
  
  /// If we have a conditional branch on a PHI node value that is defined in the
  /// same block as the branch and if any PHI entries are constants, thread edges
  /// corresponding to that entry to be branches to their ultimate destination.
  static Optional<bool> FoldCondBranchOnPHIImpl(BranchInst *BI,
                                                DomTreeUpdater *DTU,
                                                const DataLayout &DL,
                                                AssumptionCache *AC) {
    BasicBlock *BB = BI->getParent();
    PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
    // NOTE: we currently cannot transform this case if the PHI node is used
    // outside of the block.
    if (!PN || PN->getParent() != BB || !PN->hasOneUse())
      return false;
  
    // Degenerate case of a single entry PHI.
    if (PN->getNumIncomingValues() == 1) {
      FoldSingleEntryPHINodes(PN->getParent());
      return true;
    }
  
    // Now we know that this block has multiple preds and two succs.
    if (!BlockIsSimpleEnoughToThreadThrough(BB))
      return false;
  
    // Okay, this is a simple enough basic block.  See if any phi values are
    // constants.
    for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
      ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i));
      if (!CB || !CB->getType()->isIntegerTy(1))
        continue;
  
      // Okay, we now know that all edges from PredBB should be revectored to
      // branch to RealDest.
      BasicBlock *PredBB = PN->getIncomingBlock(i);
      BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
  
      if (RealDest == BB)
        continue; // Skip self loops.
      // Skip if the predecessor's terminator is an indirect branch.
      if (isa<IndirectBrInst>(PredBB->getTerminator()))
        continue;
  
      SmallVector<DominatorTree::UpdateType, 3> Updates;
  
      // The dest block might have PHI nodes, other predecessors and other
      // difficult cases.  Instead of being smart about this, just insert a new
      // block that jumps to the destination block, effectively splitting
      // the edge we are about to create.
      BasicBlock *EdgeBB =
          BasicBlock::Create(BB->getContext(), RealDest->getName() + ".critedge",
                             RealDest->getParent(), RealDest);
      BranchInst *CritEdgeBranch = BranchInst::Create(RealDest, EdgeBB);
      if (DTU)
        Updates.push_back({DominatorTree::Insert, EdgeBB, RealDest});
      CritEdgeBranch->setDebugLoc(BI->getDebugLoc());
  
      // Update PHI nodes.
      AddPredecessorToBlock(RealDest, EdgeBB, BB);
  
      // BB may have instructions that are being threaded over.  Clone these
      // instructions into EdgeBB.  We know that there will be no uses of the
      // cloned instructions outside of EdgeBB.
      BasicBlock::iterator InsertPt = EdgeBB->begin();
      DenseMap<Value *, Value *> TranslateMap; // Track translated values.
      for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
        if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
          TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
          continue;
        }
        // Clone the instruction.
        Instruction *N = BBI->clone();
        if (BBI->hasName())
          N->setName(BBI->getName() + ".c");
  
        // Update operands due to translation.
        for (Use &Op : N->operands()) {
          DenseMap<Value *, Value *>::iterator PI = TranslateMap.find(Op);
          if (PI != TranslateMap.end())
            Op = PI->second;
        }
  
        // Check for trivial simplification.
        if (Value *V = SimplifyInstruction(N, {DL, nullptr, nullptr, AC})) {
          if (!BBI->use_empty())
            TranslateMap[&*BBI] = V;
          if (!N->mayHaveSideEffects()) {
            N->deleteValue(); // Instruction folded away, don't need actual inst
            N = nullptr;
          }
        } else {
          if (!BBI->use_empty())
            TranslateMap[&*BBI] = N;
        }
        if (N) {
          // Insert the new instruction into its new home.
          EdgeBB->getInstList().insert(InsertPt, N);
  
          // Register the new instruction with the assumption cache if necessary.
          if (auto *Assume = dyn_cast<AssumeInst>(N))
            if (AC)
              AC->registerAssumption(Assume);
        }
      }
  
      // Loop over all of the edges from PredBB to BB, changing them to branch
      // to EdgeBB instead.
      Instruction *PredBBTI = PredBB->getTerminator();
      for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
        if (PredBBTI->getSuccessor(i) == BB) {
          BB->removePredecessor(PredBB);
          PredBBTI->setSuccessor(i, EdgeBB);
        }
  
      if (DTU) {
        Updates.push_back({DominatorTree::Insert, PredBB, EdgeBB});
        Updates.push_back({DominatorTree::Delete, PredBB, BB});
  
        DTU->applyUpdates(Updates);
      }
  
      // Signal repeat, simplifying any other constants.
      return None;
    }
  
    return false;
  }
  
  static bool FoldCondBranchOnPHI(BranchInst *BI, DomTreeUpdater *DTU,
                                  const DataLayout &DL, AssumptionCache *AC) {
    Optional<bool> Result;
    bool EverChanged = false;
    do {
      // Note that None means "we changed things, but recurse further."
      Result = FoldCondBranchOnPHIImpl(BI, DTU, DL, AC);
      EverChanged |= Result == None || *Result;
    } while (Result == None);
    return EverChanged;
  }
  
  /// Given a BB that starts with the specified two-entry PHI node,
  /// see if we can eliminate it.
  static bool FoldTwoEntryPHINode(PHINode *PN, const TargetTransformInfo &TTI,
                                  DomTreeUpdater *DTU, const DataLayout &DL) {
    // Ok, this is a two entry PHI node.  Check to see if this is a simple "if
    // statement", which has a very simple dominance structure.  Basically, we
    // are trying to find the condition that is being branched on, which
    // subsequently causes this merge to happen.  We really want control
    // dependence information for this check, but simplifycfg can't keep it up
    // to date, and this catches most of the cases we care about anyway.
    BasicBlock *BB = PN->getParent();
  
    BasicBlock *IfTrue, *IfFalse;
    BranchInst *DomBI = GetIfCondition(BB, IfTrue, IfFalse);
    if (!DomBI)
      return false;
    Value *IfCond = DomBI->getCondition();
    // Don't bother if the branch will be constant folded trivially.
    if (isa<ConstantInt>(IfCond))
      return false;
  
    BasicBlock *DomBlock = DomBI->getParent();
    SmallVector<BasicBlock *, 2> IfBlocks;
    llvm::copy_if(
        PN->blocks(), std::back_inserter(IfBlocks), [](BasicBlock *IfBlock) {
          return cast<BranchInst>(IfBlock->getTerminator())->isUnconditional();
        });
    assert((IfBlocks.size() == 1 || IfBlocks.size() == 2) &&
           "Will have either one or two blocks to speculate.");
  
    // If the branch is non-unpredictable, see if we either predictably jump to
    // the merge bb (if we have only a single 'then' block), or if we predictably
    // jump to one specific 'then' block (if we have two of them).
    // It isn't beneficial to speculatively execute the code
    // from the block that we know is predictably not entered.
    if (!DomBI->getMetadata(LLVMContext::MD_unpredictable)) {
      uint64_t TWeight, FWeight;
      if (DomBI->extractProfMetadata(TWeight, FWeight) &&
          (TWeight + FWeight) != 0) {
        BranchProbability BITrueProb =
            BranchProbability::getBranchProbability(TWeight, TWeight + FWeight);
        BranchProbability Likely = TTI.getPredictableBranchThreshold();
        BranchProbability BIFalseProb = BITrueProb.getCompl();
        if (IfBlocks.size() == 1) {
          BranchProbability BIBBProb =
              DomBI->getSuccessor(0) == BB ? BITrueProb : BIFalseProb;
          if (BIBBProb >= Likely)
            return false;
        } else {
          if (BITrueProb >= Likely || BIFalseProb >= Likely)
            return false;
        }
      }
    }
  
    // Don't try to fold an unreachable block. For example, the phi node itself
    // can't be the candidate if-condition for a select that we want to form.
    if (auto *IfCondPhiInst = dyn_cast<PHINode>(IfCond))
      if (IfCondPhiInst->getParent() == BB)
        return false;
  
    // Okay, we found that we can merge this two-entry phi node into a select.
    // Doing so would require us to fold *all* two entry phi nodes in this block.
    // At some point this becomes non-profitable (particularly if the target
    // doesn't support cmov's).  Only do this transformation if there are two or
    // fewer PHI nodes in this block.
    unsigned NumPhis = 0;
    for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
      if (NumPhis > 2)
        return false;
  
    // Loop over the PHI's seeing if we can promote them all to select
    // instructions.  While we are at it, keep track of the instructions
    // that need to be moved to the dominating block.
    SmallPtrSet<Instruction *, 4> AggressiveInsts;
    InstructionCost Cost = 0;
    InstructionCost Budget =
        TwoEntryPHINodeFoldingThreshold * TargetTransformInfo::TCC_Basic;
  
    bool Changed = false;
    for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) {
      PHINode *PN = cast<PHINode>(II++);
      if (Value *V = SimplifyInstruction(PN, {DL, PN})) {
        PN->replaceAllUsesWith(V);
        PN->eraseFromParent();
        Changed = true;
        continue;
      }
  
      if (!dominatesMergePoint(PN->getIncomingValue(0), BB, AggressiveInsts,
                               Cost, Budget, TTI) ||
          !dominatesMergePoint(PN->getIncomingValue(1), BB, AggressiveInsts,
                               Cost, Budget, TTI))
        return Changed;
    }
  
    // If we folded the first phi, PN dangles at this point.  Refresh it.  If
    // we ran out of PHIs then we simplified them all.
    PN = dyn_cast<PHINode>(BB->begin());
    if (!PN)
      return true;
  
    // Return true if at least one of these is a 'not', and another is either
    // a 'not' too, or a constant.
    auto CanHoistNotFromBothValues = [](Value *V0, Value *V1) {
      if (!match(V0, m_Not(m_Value())))
        std::swap(V0, V1);
      auto Invertible = m_CombineOr(m_Not(m_Value()), m_AnyIntegralConstant());
      return match(V0, m_Not(m_Value())) && match(V1, Invertible);
    };
  
    // Don't fold i1 branches on PHIs which contain binary operators or
    // (possibly inverted) select form of or/ands,  unless one of
    // the incoming values is an 'not' and another one is freely invertible.
    // These can often be turned into switches and other things.
    auto IsBinOpOrAnd = [](Value *V) {
      return match(
          V, m_CombineOr(
                 m_BinOp(),
                 m_CombineOr(m_Select(m_Value(), m_ImmConstant(), m_Value()),
                             m_Select(m_Value(), m_Value(), m_ImmConstant()))));
    };
    if (PN->getType()->isIntegerTy(1) &&
        (IsBinOpOrAnd(PN->getIncomingValue(0)) ||
         IsBinOpOrAnd(PN->getIncomingValue(1)) || IsBinOpOrAnd(IfCond)) &&
        !CanHoistNotFromBothValues(PN->getIncomingValue(0),
                                   PN->getIncomingValue(1)))
      return Changed;
  
    // If all PHI nodes are promotable, check to make sure that all instructions
    // in the predecessor blocks can be promoted as well. If not, we won't be able
    // to get rid of the control flow, so it's not worth promoting to select
    // instructions.
    for (BasicBlock *IfBlock : IfBlocks)
      for (BasicBlock::iterator I = IfBlock->begin(); !I->isTerminator(); ++I)
        if (!AggressiveInsts.count(&*I) && !I->isDebugOrPseudoInst()) {
          // This is not an aggressive instruction that we can promote.
          // Because of this, we won't be able to get rid of the control flow, so
          // the xform is not worth it.
          return Changed;
        }
  
    // If either of the blocks has it's address taken, we can't do this fold.
    if (any_of(IfBlocks,
               [](BasicBlock *IfBlock) { return IfBlock->hasAddressTaken(); }))
      return Changed;
  
    LLVM_DEBUG(dbgs() << "FOUND IF CONDITION!  " << *IfCond
                      << "  T: " << IfTrue->getName()
                      << "  F: " << IfFalse->getName() << "\n");
  
    // If we can still promote the PHI nodes after this gauntlet of tests,
    // do all of the PHI's now.
  
    // Move all 'aggressive' instructions, which are defined in the
    // conditional parts of the if's up to the dominating block.
    for (BasicBlock *IfBlock : IfBlocks)
        hoistAllInstructionsInto(DomBlock, DomBI, IfBlock);
  
    IRBuilder<NoFolder> Builder(DomBI);
    // Propagate fast-math-flags from phi nodes to replacement selects.
    IRBuilder<>::FastMathFlagGuard FMFGuard(Builder);
    while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
      if (isa<FPMathOperator>(PN))
        Builder.setFastMathFlags(PN->getFastMathFlags());
  
      // Change the PHI node into a select instruction.
      Value *TrueVal = PN->getIncomingValueForBlock(IfTrue);
      Value *FalseVal = PN->getIncomingValueForBlock(IfFalse);
  
      Value *Sel = Builder.CreateSelect(IfCond, TrueVal, FalseVal, "", DomBI);
      PN->replaceAllUsesWith(Sel);
      Sel->takeName(PN);
      PN->eraseFromParent();
    }
  
    // At this point, all IfBlocks are empty, so our if statement
    // has been flattened.  Change DomBlock to jump directly to our new block to
    // avoid other simplifycfg's kicking in on the diamond.
    Builder.CreateBr(BB);
  
    SmallVector<DominatorTree::UpdateType, 3> Updates;
    if (DTU) {
      Updates.push_back({DominatorTree::Insert, DomBlock, BB});
      for (auto *Successor : successors(DomBlock))
        Updates.push_back({DominatorTree::Delete, DomBlock, Successor});
    }
  
    DomBI->eraseFromParent();
    if (DTU)
      DTU->applyUpdates(Updates);
  
    return true;
  }
  
  static Value *createLogicalOp(IRBuilderBase &Builder,
                                Instruction::BinaryOps Opc, Value *LHS,
                                Value *RHS, const Twine &Name = "") {
    // Try to relax logical op to binary op.
    if (impliesPoison(RHS, LHS))
      return Builder.CreateBinOp(Opc, LHS, RHS, Name);
    if (Opc == Instruction::And)
      return Builder.CreateLogicalAnd(LHS, RHS, Name);
    if (Opc == Instruction::Or)
      return Builder.CreateLogicalOr(LHS, RHS, Name);
    llvm_unreachable("Invalid logical opcode");
  }
  
  /// Return true if either PBI or BI has branch weight available, and store
  /// the weights in {Pred|Succ}{True|False}Weight. If one of PBI and BI does
  /// not have branch weight, use 1:1 as its weight.
  static bool extractPredSuccWeights(BranchInst *PBI, BranchInst *BI,
                                     uint64_t &PredTrueWeight,
                                     uint64_t &PredFalseWeight,
                                     uint64_t &SuccTrueWeight,
                                     uint64_t &SuccFalseWeight) {
    bool PredHasWeights =
        PBI->extractProfMetadata(PredTrueWeight, PredFalseWeight);
    bool SuccHasWeights =
        BI->extractProfMetadata(SuccTrueWeight, SuccFalseWeight);
    if (PredHasWeights || SuccHasWeights) {
      if (!PredHasWeights)
        PredTrueWeight = PredFalseWeight = 1;
      if (!SuccHasWeights)
        SuccTrueWeight = SuccFalseWeight = 1;
      return true;
    } else {
      return false;
    }
  }
  
  /// Determine if the two branches share a common destination and deduce a glue
  /// that joins the branches' conditions to arrive at the common destination if
  /// that would be profitable.
  static Optional<std::pair<Instruction::BinaryOps, bool>>
  shouldFoldCondBranchesToCommonDestination(BranchInst *BI, BranchInst *PBI,
                                            const TargetTransformInfo *TTI) {
    assert(BI && PBI && BI->isConditional() && PBI->isConditional() &&
           "Both blocks must end with a conditional branches.");
    assert(is_contained(predecessors(BI->getParent()), PBI->getParent()) &&
           "PredBB must be a predecessor of BB.");
  
    // We have the potential to fold the conditions together, but if the
    // predecessor branch is predictable, we may not want to merge them.
    uint64_t PTWeight, PFWeight;
    BranchProbability PBITrueProb, Likely;
    if (TTI && !PBI->getMetadata(LLVMContext::MD_unpredictable) &&
        PBI->extractProfMetadata(PTWeight, PFWeight) &&
        (PTWeight + PFWeight) != 0) {
      PBITrueProb =
          BranchProbability::getBranchProbability(PTWeight, PTWeight + PFWeight);
      Likely = TTI->getPredictableBranchThreshold();
    }
  
    if (PBI->getSuccessor(0) == BI->getSuccessor(0)) {
      // Speculate the 2nd condition unless the 1st is probably true.
      if (PBITrueProb.isUnknown() || PBITrueProb < Likely)
        return {{Instruction::Or, false}};
    } else if (PBI->getSuccessor(1) == BI->getSuccessor(1)) {
      // Speculate the 2nd condition unless the 1st is probably false.
      if (PBITrueProb.isUnknown() || PBITrueProb.getCompl() < Likely)
        return {{Instruction::And, false}};
    } else if (PBI->getSuccessor(0) == BI->getSuccessor(1)) {
      // Speculate the 2nd condition unless the 1st is probably true.
      if (PBITrueProb.isUnknown() || PBITrueProb < Likely)
        return {{Instruction::And, true}};
    } else if (PBI->getSuccessor(1) == BI->getSuccessor(0)) {
      // Speculate the 2nd condition unless the 1st is probably false.
      if (PBITrueProb.isUnknown() || PBITrueProb.getCompl() < Likely)
        return {{Instruction::Or, true}};
    }
    return None;
  }
  
  static bool performBranchToCommonDestFolding(BranchInst *BI, BranchInst *PBI,
                                               DomTreeUpdater *DTU,
                                               MemorySSAUpdater *MSSAU,
                                               const TargetTransformInfo *TTI) {
    BasicBlock *BB = BI->getParent();
    BasicBlock *PredBlock = PBI->getParent();
  
    // Determine if the two branches share a common destination.
    Instruction::BinaryOps Opc;
    bool InvertPredCond;
    std::tie(Opc, InvertPredCond) =
        *shouldFoldCondBranchesToCommonDestination(BI, PBI, TTI);
  
    LLVM_DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB);
  
    IRBuilder<> Builder(PBI);
    // The builder is used to create instructions to eliminate the branch in BB.
    // If BB's terminator has !annotation metadata, add it to the new
    // instructions.
    Builder.CollectMetadataToCopy(BB->getTerminator(),
                                  {LLVMContext::MD_annotation});
  
    // If we need to invert the condition in the pred block to match, do so now.
    if (InvertPredCond) {
      Value *NewCond = PBI->getCondition();
      if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) {
        CmpInst *CI = cast<CmpInst>(NewCond);
        CI->setPredicate(CI->getInversePredicate());
      } else {
        NewCond =
            Builder.CreateNot(NewCond, PBI->getCondition()->getName() + ".not");
      }
  
      PBI->setCondition(NewCond);
      PBI->swapSuccessors();
    }
  
    BasicBlock *UniqueSucc =
        PBI->getSuccessor(0) == BB ? BI->getSuccessor(0) : BI->getSuccessor(1);
  
    // Before cloning instructions, notify the successor basic block that it
    // is about to have a new predecessor. This will update PHI nodes,
    // which will allow us to update live-out uses of bonus instructions.
    AddPredecessorToBlock(UniqueSucc, PredBlock, BB, MSSAU);
  
    // Try to update branch weights.
    uint64_t PredTrueWeight, PredFalseWeight, SuccTrueWeight, SuccFalseWeight;
    if (extractPredSuccWeights(PBI, BI, PredTrueWeight, PredFalseWeight,
                               SuccTrueWeight, SuccFalseWeight)) {
      SmallVector<uint64_t, 8> NewWeights;
  
      if (PBI->getSuccessor(0) == BB) {
        // PBI: br i1 %x, BB, FalseDest
        // BI:  br i1 %y, UniqueSucc, FalseDest
        // TrueWeight is TrueWeight for PBI * TrueWeight for BI.
        NewWeights.push_back(PredTrueWeight * SuccTrueWeight);
        // FalseWeight is FalseWeight for PBI * TotalWeight for BI +
        //               TrueWeight for PBI * FalseWeight for BI.
        // We assume that total weights of a BranchInst can fit into 32 bits.
        // Therefore, we will not have overflow using 64-bit arithmetic.
        NewWeights.push_back(PredFalseWeight *
                                 (SuccFalseWeight + SuccTrueWeight) +
                             PredTrueWeight * SuccFalseWeight);
      } else {
        // PBI: br i1 %x, TrueDest, BB
        // BI:  br i1 %y, TrueDest, UniqueSucc
        // TrueWeight is TrueWeight for PBI * TotalWeight for BI +
        //              FalseWeight for PBI * TrueWeight for BI.
        NewWeights.push_back(PredTrueWeight * (SuccFalseWeight + SuccTrueWeight) +
                             PredFalseWeight * SuccTrueWeight);
        // FalseWeight is FalseWeight for PBI * FalseWeight for BI.
        NewWeights.push_back(PredFalseWeight * SuccFalseWeight);
      }
  
      // Halve the weights if any of them cannot fit in an uint32_t
      FitWeights(NewWeights);
  
      SmallVector<uint32_t, 8> MDWeights(NewWeights.begin(), NewWeights.end());
      setBranchWeights(PBI, MDWeights[0], MDWeights[1]);
  
      // TODO: If BB is reachable from all paths through PredBlock, then we
      // could replace PBI's branch probabilities with BI's.
    } else
      PBI->setMetadata(LLVMContext::MD_prof, nullptr);
  
    // Now, update the CFG.
    PBI->setSuccessor(PBI->getSuccessor(0) != BB, UniqueSucc);
  
    if (DTU)
      DTU->applyUpdates({{DominatorTree::Insert, PredBlock, UniqueSucc},
                         {DominatorTree::Delete, PredBlock, BB}});
  
    // If BI was a loop latch, it may have had associated loop metadata.
    // We need to copy it to the new latch, that is, PBI.
    if (MDNode *LoopMD = BI->getMetadata(LLVMContext::MD_loop))
      PBI->setMetadata(LLVMContext::MD_loop, LoopMD);
  
    ValueToValueMapTy VMap; // maps original values to cloned values
    CloneInstructionsIntoPredecessorBlockAndUpdateSSAUses(BB, PredBlock, VMap);
  
    // Now that the Cond was cloned into the predecessor basic block,
    // or/and the two conditions together.
    Value *BICond = VMap[BI->getCondition()];
    PBI->setCondition(
        createLogicalOp(Builder, Opc, PBI->getCondition(), BICond, "or.cond"));
  
    // Copy any debug value intrinsics into the end of PredBlock.
    for (Instruction &I : *BB) {
      if (isa<DbgInfoIntrinsic>(I)) {
        Instruction *NewI = I.clone();
        RemapInstruction(NewI, VMap,
                         RF_NoModuleLevelChanges | RF_IgnoreMissingLocals);
        NewI->insertBefore(PBI);
      }
    }
  
    ++NumFoldBranchToCommonDest;
    return true;
  }
  
  /// Return if an instruction's type or any of its operands' types are a vector
  /// type.
  static bool isVectorOp(Instruction &I) {
    return I.getType()->isVectorTy() || any_of(I.operands(), [](Use &U) {
             return U->getType()->isVectorTy();
           });
  }
  
  /// If this basic block is simple enough, and if a predecessor branches to us
  /// and one of our successors, fold the block into the predecessor and use
  /// logical operations to pick the right destination.
  bool llvm::FoldBranchToCommonDest(BranchInst *BI, DomTreeUpdater *DTU,
                                    MemorySSAUpdater *MSSAU,
                                    const TargetTransformInfo *TTI,
                                    unsigned BonusInstThreshold) {
    // If this block ends with an unconditional branch,
    // let SpeculativelyExecuteBB() deal with it.
    if (!BI->isConditional())
      return false;
  
    BasicBlock *BB = BI->getParent();
    TargetTransformInfo::TargetCostKind CostKind =
      BB->getParent()->hasMinSize() ? TargetTransformInfo::TCK_CodeSize
                                    : TargetTransformInfo::TCK_SizeAndLatency;
  
    Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
  
    if (!Cond || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
        Cond->getParent() != BB || !Cond->hasOneUse())
      return false;
  
    // Cond is known to be a compare or binary operator.  Check to make sure that
    // neither operand is a potentially-trapping constant expression.
    if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
      if (CE->canTrap())
        return false;
    if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
      if (CE->canTrap())
        return false;
  
    // Finally, don't infinitely unroll conditional loops.
    if (is_contained(successors(BB), BB))
      return false;
  
    // With which predecessors will we want to deal with?
    SmallVector<BasicBlock *, 8> Preds;
    for (BasicBlock *PredBlock : predecessors(BB)) {
      BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
  
      // Check that we have two conditional branches.  If there is a PHI node in
      // the common successor, verify that the same value flows in from both
      // blocks.
      if (!PBI || PBI->isUnconditional() || !SafeToMergeTerminators(BI, PBI))
        continue;
  
      // Determine if the two branches share a common destination.
      Instruction::BinaryOps Opc;
      bool InvertPredCond;
      if (auto Recipe = shouldFoldCondBranchesToCommonDestination(BI, PBI, TTI))
        std::tie(Opc, InvertPredCond) = *Recipe;
      else
        continue;
  
      // Check the cost of inserting the necessary logic before performing the
      // transformation.
      if (TTI) {
        Type *Ty = BI->getCondition()->getType();
        InstructionCost Cost = TTI->getArithmeticInstrCost(Opc, Ty, CostKind);
        if (InvertPredCond && (!PBI->getCondition()->hasOneUse() ||
            !isa<CmpInst>(PBI->getCondition())))
          Cost += TTI->getArithmeticInstrCost(Instruction::Xor, Ty, CostKind);
  
        if (Cost > BranchFoldThreshold)
          continue;
      }
  
      // Ok, we do want to deal with this predecessor. Record it.
      Preds.emplace_back(PredBlock);
    }
  
    // If there aren't any predecessors into which we can fold,
    // don't bother checking the cost.
    if (Preds.empty())
      return false;
  
    // Only allow this transformation if computing the condition doesn't involve
    // too many instructions and these involved instructions can be executed
    // unconditionally. We denote all involved instructions except the condition
    // as "bonus instructions", and only allow this transformation when the
    // number of the bonus instructions we'll need to create when cloning into
    // each predecessor does not exceed a certain threshold.
    unsigned NumBonusInsts = 0;
    bool SawVectorOp = false;
    const unsigned PredCount = Preds.size();
    for (Instruction &I : *BB) {
      // Don't check the branch condition comparison itself.
      if (&I == Cond)
        continue;
      // Ignore dbg intrinsics, and the terminator.
      if (isa<DbgInfoIntrinsic>(I) || isa<BranchInst>(I))
        continue;
      // I must be safe to execute unconditionally.
      if (!isSafeToSpeculativelyExecute(&I))
        return false;
      SawVectorOp |= isVectorOp(I);
  
      // Account for the cost of duplicating this instruction into each
      // predecessor. Ignore free instructions.
      if (!TTI ||
          TTI->getUserCost(&I, CostKind) != TargetTransformInfo::TCC_Free) {
        NumBonusInsts += PredCount;
  
        // Early exits once we reach the limit.
        if (NumBonusInsts >
            BonusInstThreshold * BranchFoldToCommonDestVectorMultiplier)
          return false;
      }
  
      auto IsBCSSAUse = [BB, &I](Use &U) {
        auto *UI = cast<Instruction>(U.getUser());
        if (auto *PN = dyn_cast<PHINode>(UI))
          return PN->getIncomingBlock(U) == BB;
        return UI->getParent() == BB && I.comesBefore(UI);
      };
  
      // Does this instruction require rewriting of uses?
      if (!all_of(I.uses(), IsBCSSAUse))
        return false;
    }
    if (NumBonusInsts >
        BonusInstThreshold *
            (SawVectorOp ? BranchFoldToCommonDestVectorMultiplier : 1))
      return false;
  
    // Ok, we have the budget. Perform the transformation.
    for (BasicBlock *PredBlock : Preds) {
      auto *PBI = cast<BranchInst>(PredBlock->getTerminator());
      return performBranchToCommonDestFolding(BI, PBI, DTU, MSSAU, TTI);
    }
    return false;
  }
  
  // If there is only one store in BB1 and BB2, return it, otherwise return
  // nullptr.
  static StoreInst *findUniqueStoreInBlocks(BasicBlock *BB1, BasicBlock *BB2) {
    StoreInst *S = nullptr;
    for (auto *BB : {BB1, BB2}) {
      if (!BB)
        continue;
      for (auto &I : *BB)
        if (auto *SI = dyn_cast<StoreInst>(&I)) {
          if (S)
            // Multiple stores seen.
            return nullptr;
          else
            S = SI;
        }
    }
    return S;
  }
  
  static Value *ensureValueAvailableInSuccessor(Value *V, BasicBlock *BB,
                                                Value *AlternativeV = nullptr) {
    // PHI is going to be a PHI node that allows the value V that is defined in
    // BB to be referenced in BB's only successor.
    //
    // If AlternativeV is nullptr, the only value we care about in PHI is V. It
    // doesn't matter to us what the other operand is (it'll never get used). We
    // could just create a new PHI with an undef incoming value, but that could
    // increase register pressure if EarlyCSE/InstCombine can't fold it with some
    // other PHI. So here we directly look for some PHI in BB's successor with V
    // as an incoming operand. If we find one, we use it, else we create a new
    // one.
    //
    // If AlternativeV is not nullptr, we care about both incoming values in PHI.
    // PHI must be exactly: phi <ty> [ %BB, %V ], [ %OtherBB, %AlternativeV]
    // where OtherBB is the single other predecessor of BB's only successor.
    PHINode *PHI = nullptr;
    BasicBlock *Succ = BB->getSingleSuccessor();
  
    for (auto I = Succ->begin(); isa<PHINode>(I); ++I)
      if (cast<PHINode>(I)->getIncomingValueForBlock(BB) == V) {
        PHI = cast<PHINode>(I);
        if (!AlternativeV)
          break;
  
        assert(Succ->hasNPredecessors(2));
        auto PredI = pred_begin(Succ);
        BasicBlock *OtherPredBB = *PredI == BB ? *++PredI : *PredI;
        if (PHI->getIncomingValueForBlock(OtherPredBB) == AlternativeV)
          break;
        PHI = nullptr;
      }
    if (PHI)
      return PHI;
  
    // If V is not an instruction defined in BB, just return it.
    if (!AlternativeV &&
        (!isa<Instruction>(V) || cast<Instruction>(V)->getParent() != BB))
      return V;
  
    PHI = PHINode::Create(V->getType(), 2, "simplifycfg.merge", &Succ->front());
    PHI->addIncoming(V, BB);
    for (BasicBlock *PredBB : predecessors(Succ))
      if (PredBB != BB)
        PHI->addIncoming(
            AlternativeV ? AlternativeV : UndefValue::get(V->getType()), PredBB);
    return PHI;
  }
  
  static bool mergeConditionalStoreToAddress(
      BasicBlock *PTB, BasicBlock *PFB, BasicBlock *QTB, BasicBlock *QFB,
      BasicBlock *PostBB, Value *Address, bool InvertPCond, bool InvertQCond,
      DomTreeUpdater *DTU, const DataLayout &DL, const TargetTransformInfo &TTI) {
    // For every pointer, there must be exactly two stores, one coming from
    // PTB or PFB, and the other from QTB or QFB. We don't support more than one
    // store (to any address) in PTB,PFB or QTB,QFB.
    // FIXME: We could relax this restriction with a bit more work and performance
    // testing.
    StoreInst *PStore = findUniqueStoreInBlocks(PTB, PFB);
    StoreInst *QStore = findUniqueStoreInBlocks(QTB, QFB);
    if (!PStore || !QStore)
      return false;
  
    // Now check the stores are compatible.
    if (!QStore->isUnordered() || !PStore->isUnordered() ||
        PStore->getValueOperand()->getType() !=
            QStore->getValueOperand()->getType())
      return false;
  
    // Check that sinking the store won't cause program behavior changes. Sinking
    // the store out of the Q blocks won't change any behavior as we're sinking
    // from a block to its unconditional successor. But we're moving a store from
    // the P blocks down through the middle block (QBI) and past both QFB and QTB.
    // So we need to check that there are no aliasing loads or stores in
    // QBI, QTB and QFB. We also need to check there are no conflicting memory
    // operations between PStore and the end of its parent block.
    //
    // The ideal way to do this is to query AliasAnalysis, but we don't
    // preserve AA currently so that is dangerous. Be super safe and just
    // check there are no other memory operations at all.
    for (auto &I : *QFB->getSinglePredecessor())
      if (I.mayReadOrWriteMemory())
        return false;
    for (auto &I : *QFB)
      if (&I != QStore && I.mayReadOrWriteMemory())
        return false;
    if (QTB)
      for (auto &I : *QTB)
        if (&I != QStore && I.mayReadOrWriteMemory())
          return false;
    for (auto I = BasicBlock::iterator(PStore), E = PStore->getParent()->end();
         I != E; ++I)
      if (&*I != PStore && I->mayReadOrWriteMemory())
        return false;
  
    // If we're not in aggressive mode, we only optimize if we have some
    // confidence that by optimizing we'll allow P and/or Q to be if-converted.
    auto IsWorthwhile = [&](BasicBlock *BB, ArrayRef<StoreInst *> FreeStores) {
      if (!BB)
        return true;
      // Heuristic: if the block can be if-converted/phi-folded and the
      // instructions inside are all cheap (arithmetic/GEPs), it's worthwhile to
      // thread this store.
      InstructionCost Cost = 0;
      InstructionCost Budget =
          PHINodeFoldingThreshold * TargetTransformInfo::TCC_Basic;
      for (auto &I : BB->instructionsWithoutDebug(false)) {
        // Consider terminator instruction to be free.
        if (I.isTerminator())
          continue;
        // If this is one the stores that we want to speculate out of this BB,
        // then don't count it's cost, consider it to be free.
        if (auto *S = dyn_cast<StoreInst>(&I))
          if (llvm::find(FreeStores, S))
            continue;
        // Else, we have a white-list of instructions that we are ak speculating.
        if (!isa<BinaryOperator>(I) && !isa<GetElementPtrInst>(I))
          return false; // Not in white-list - not worthwhile folding.
        // And finally, if this is a non-free instruction that we are okay
        // speculating, ensure that we consider the speculation budget.
        Cost += TTI.getUserCost(&I, TargetTransformInfo::TCK_SizeAndLatency);
        if (Cost > Budget)
          return false; // Eagerly refuse to fold as soon as we're out of budget.
      }
      assert(Cost <= Budget &&
             "When we run out of budget we will eagerly return from within the "
             "per-instruction loop.");
      return true;
    };
  
    const std::array<StoreInst *, 2> FreeStores = {PStore, QStore};
    if (!MergeCondStoresAggressively &&
        (!IsWorthwhile(PTB, FreeStores) || !IsWorthwhile(PFB, FreeStores) ||
         !IsWorthwhile(QTB, FreeStores) || !IsWorthwhile(QFB, FreeStores)))
      return false;
  
    // If PostBB has more than two predecessors, we need to split it so we can
    // sink the store.
    if (std::next(pred_begin(PostBB), 2) != pred_end(PostBB)) {
      // We know that QFB's only successor is PostBB. And QFB has a single
      // predecessor. If QTB exists, then its only successor is also PostBB.
      // If QTB does not exist, then QFB's only predecessor has a conditional
      // branch to QFB and PostBB.
      BasicBlock *TruePred = QTB ? QTB : QFB->getSinglePredecessor();
      BasicBlock *NewBB =
          SplitBlockPredecessors(PostBB, {QFB, TruePred}, "condstore.split", DTU);
      if (!NewBB)
        return false;
      PostBB = NewBB;
    }
  
    // OK, we're going to sink the stores to PostBB. The store has to be
    // conditional though, so first create the predicate.
    Value *PCond = cast<BranchInst>(PFB->getSinglePredecessor()->getTerminator())
                       ->getCondition();
    Value *QCond = cast<BranchInst>(QFB->getSinglePredecessor()->getTerminator())
                       ->getCondition();
  
    Value *PPHI = ensureValueAvailableInSuccessor(PStore->getValueOperand(),
                                                  PStore->getParent());
    Value *QPHI = ensureValueAvailableInSuccessor(QStore->getValueOperand(),
                                                  QStore->getParent(), PPHI);
  
    IRBuilder<> QB(&*PostBB->getFirstInsertionPt());
  
    Value *PPred = PStore->getParent() == PTB ? PCond : QB.CreateNot(PCond);
    Value *QPred = QStore->getParent() == QTB ? QCond : QB.CreateNot(QCond);
  
    if (InvertPCond)
      PPred = QB.CreateNot(PPred);
    if (InvertQCond)
      QPred = QB.CreateNot(QPred);
    Value *CombinedPred = QB.CreateOr(PPred, QPred);
  
    auto *T = SplitBlockAndInsertIfThen(CombinedPred, &*QB.GetInsertPoint(),
                                        /*Unreachable=*/false,
                                        /*BranchWeights=*/nullptr, DTU);
    QB.SetInsertPoint(T);
    StoreInst *SI = cast<StoreInst>(QB.CreateStore(QPHI, Address));
    SI->setAAMetadata(PStore->getAAMetadata().merge(QStore->getAAMetadata()));
    // Choose the minimum alignment. If we could prove both stores execute, we
    // could use biggest one.  In this case, though, we only know that one of the
    // stores executes.  And we don't know it's safe to take the alignment from a
    // store that doesn't execute.
    SI->setAlignment(std::min(PStore->getAlign(), QStore->getAlign()));
  
    QStore->eraseFromParent();
    PStore->eraseFromParent();
  
    return true;
  }
  
  static bool mergeConditionalStores(BranchInst *PBI, BranchInst *QBI,
                                     DomTreeUpdater *DTU, const DataLayout &DL,
                                     const TargetTransformInfo &TTI) {
    // The intention here is to find diamonds or triangles (see below) where each
    // conditional block contains a store to the same address. Both of these
    // stores are conditional, so they can't be unconditionally sunk. But it may
    // be profitable to speculatively sink the stores into one merged store at the
    // end, and predicate the merged store on the union of the two conditions of
    // PBI and QBI.
    //
    // This can reduce the number of stores executed if both of the conditions are
    // true, and can allow the blocks to become small enough to be if-converted.
    // This optimization will also chain, so that ladders of test-and-set
    // sequences can be if-converted away.
    //
    // We only deal with simple diamonds or triangles:
    //
    //     PBI       or      PBI        or a combination of the two
    //    /   \               | \
    //   PTB  PFB             |  PFB
    //    \   /               | /
    //     QBI                QBI
    //    /  \                | \
    //   QTB  QFB             |  QFB
    //    \  /                | /
    //    PostBB            PostBB
    //
    // We model triangles as a type of diamond with a nullptr "true" block.
    // Triangles are canonicalized so that the fallthrough edge is represented by
    // a true condition, as in the diagram above.
    BasicBlock *PTB = PBI->getSuccessor(0);
    BasicBlock *PFB = PBI->getSuccessor(1);
    BasicBlock *QTB = QBI->getSuccessor(0);
    BasicBlock *QFB = QBI->getSuccessor(1);
    BasicBlock *PostBB = QFB->getSingleSuccessor();
  
    // Make sure we have a good guess for PostBB. If QTB's only successor is
    // QFB, then QFB is a better PostBB.
    if (QTB->getSingleSuccessor() == QFB)
      PostBB = QFB;
  
    // If we couldn't find a good PostBB, stop.
    if (!PostBB)
      return false;
  
    bool InvertPCond = false, InvertQCond = false;
    // Canonicalize fallthroughs to the true branches.
    if (PFB == QBI->getParent()) {
      std::swap(PFB, PTB);
      InvertPCond = true;
    }
    if (QFB == PostBB) {
      std::swap(QFB, QTB);
      InvertQCond = true;
    }
  
    // From this point on we can assume PTB or QTB may be fallthroughs but PFB
    // and QFB may not. Model fallthroughs as a nullptr block.
    if (PTB == QBI->getParent())
      PTB = nullptr;
    if (QTB == PostBB)
      QTB = nullptr;
  
    // Legality bailouts. We must have at least the non-fallthrough blocks and
    // the post-dominating block, and the non-fallthroughs must only have one
    // predecessor.
    auto HasOnePredAndOneSucc = [](BasicBlock *BB, BasicBlock *P, BasicBlock *S) {
      return BB->getSinglePredecessor() == P && BB->getSingleSuccessor() == S;
    };
    if (!HasOnePredAndOneSucc(PFB, PBI->getParent(), QBI->getParent()) ||
        !HasOnePredAndOneSucc(QFB, QBI->getParent(), PostBB))
      return false;
    if ((PTB && !HasOnePredAndOneSucc(PTB, PBI->getParent(), QBI->getParent())) ||
        (QTB && !HasOnePredAndOneSucc(QTB, QBI->getParent(), PostBB)))
      return false;
    if (!QBI->getParent()->hasNUses(2))
      return false;
  
    // OK, this is a sequence of two diamonds or triangles.
    // Check if there are stores in PTB or PFB that are repeated in QTB or QFB.
    SmallPtrSet<Value *, 4> PStoreAddresses, QStoreAddresses;
    for (auto *BB : {PTB, PFB}) {
      if (!BB)
        continue;
      for (auto &I : *BB)
        if (StoreInst *SI = dyn_cast<StoreInst>(&I))
          PStoreAddresses.insert(SI->getPointerOperand());
    }
    for (auto *BB : {QTB, QFB}) {
      if (!BB)
        continue;
      for (auto &I : *BB)
        if (StoreInst *SI = dyn_cast<StoreInst>(&I))
          QStoreAddresses.insert(SI->getPointerOperand());
    }
  
    set_intersect(PStoreAddresses, QStoreAddresses);
    // set_intersect mutates PStoreAddresses in place. Rename it here to make it
    // clear what it contains.
    auto &CommonAddresses = PStoreAddresses;
  
    bool Changed = false;
    for (auto *Address : CommonAddresses)
      Changed |=
          mergeConditionalStoreToAddress(PTB, PFB, QTB, QFB, PostBB, Address,
                                         InvertPCond, InvertQCond, DTU, DL, TTI);
    return Changed;
  }
  
  /// If the previous block ended with a widenable branch, determine if reusing
  /// the target block is profitable and legal.  This will have the effect of
  /// "widening" PBI, but doesn't require us to reason about hosting safety.
  static bool tryWidenCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI,
                                             DomTreeUpdater *DTU) {
    // TODO: This can be generalized in two important ways:
    // 1) We can allow phi nodes in IfFalseBB and simply reuse all the input
    //    values from the PBI edge.
    // 2) We can sink side effecting instructions into BI's fallthrough
    //    successor provided they doesn't contribute to computation of
    //    BI's condition.
    Value *CondWB, *WC;
    BasicBlock *IfTrueBB, *IfFalseBB;
    if (!parseWidenableBranch(PBI, CondWB, WC, IfTrueBB, IfFalseBB) ||
        IfTrueBB != BI->getParent() || !BI->getParent()->getSinglePredecessor())
      return false;
    if (!IfFalseBB->phis().empty())
      return false; // TODO
    // Use lambda to lazily compute expensive condition after cheap ones.
    auto NoSideEffects = [](BasicBlock &BB) {
      return llvm::none_of(BB, [](const Instruction &I) {
          return I.mayWriteToMemory() || I.mayHaveSideEffects();
        });
    };
    if (BI->getSuccessor(1) != IfFalseBB && // no inf looping
        BI->getSuccessor(1)->getTerminatingDeoptimizeCall() && // profitability
        NoSideEffects(*BI->getParent())) {
      auto *OldSuccessor = BI->getSuccessor(1);
      OldSuccessor->removePredecessor(BI->getParent());
      BI->setSuccessor(1, IfFalseBB);
      if (DTU)
        DTU->applyUpdates(
            {{DominatorTree::Insert, BI->getParent(), IfFalseBB},
             {DominatorTree::Delete, BI->getParent(), OldSuccessor}});
      return true;
    }
    if (BI->getSuccessor(0) != IfFalseBB && // no inf looping
        BI->getSuccessor(0)->getTerminatingDeoptimizeCall() && // profitability
        NoSideEffects(*BI->getParent())) {
      auto *OldSuccessor = BI->getSuccessor(0);
      OldSuccessor->removePredecessor(BI->getParent());
      BI->setSuccessor(0, IfFalseBB);
      if (DTU)
        DTU->applyUpdates(
            {{DominatorTree::Insert, BI->getParent(), IfFalseBB},
             {DominatorTree::Delete, BI->getParent(), OldSuccessor}});
      return true;
    }
    return false;
  }
  
  /// If we have a conditional branch as a predecessor of another block,
  /// this function tries to simplify it.  We know
  /// that PBI and BI are both conditional branches, and BI is in one of the
  /// successor blocks of PBI - PBI branches to BI.
  static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI,
                                             DomTreeUpdater *DTU,
                                             const DataLayout &DL,
                                             const TargetTransformInfo &TTI) {
    assert(PBI->isConditional() && BI->isConditional());
    BasicBlock *BB = BI->getParent();
  
    // If this block ends with a branch instruction, and if there is a
    // predecessor that ends on a branch of the same condition, make
    // this conditional branch redundant.
    if (PBI->getCondition() == BI->getCondition() &&
        PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
      // Okay, the outcome of this conditional branch is statically
      // knowable.  If this block had a single pred, handle specially.
      if (BB->getSinglePredecessor()) {
        // Turn this into a branch on constant.
        bool CondIsTrue = PBI->getSuccessor(0) == BB;
        BI->setCondition(
            ConstantInt::get(Type::getInt1Ty(BB->getContext()), CondIsTrue));
        return true; // Nuke the branch on constant.
      }
  
      // Otherwise, if there are multiple predecessors, insert a PHI that merges
      // in the constant and simplify the block result.  Subsequent passes of
      // simplifycfg will thread the block.
      if (BlockIsSimpleEnoughToThreadThrough(BB)) {
        pred_iterator PB = pred_begin(BB), PE = pred_end(BB);
        PHINode *NewPN = PHINode::Create(
            Type::getInt1Ty(BB->getContext()), std::distance(PB, PE),
            BI->getCondition()->getName() + ".pr", &BB->front());
        // Okay, we're going to insert the PHI node.  Since PBI is not the only
        // predecessor, compute the PHI'd conditional value for all of the preds.
        // Any predecessor where the condition is not computable we keep symbolic.
        for (pred_iterator PI = PB; PI != PE; ++PI) {
          BasicBlock *P = *PI;
          if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) && PBI != BI &&
              PBI->isConditional() && PBI->getCondition() == BI->getCondition() &&
              PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
            bool CondIsTrue = PBI->getSuccessor(0) == BB;
            NewPN->addIncoming(
                ConstantInt::get(Type::getInt1Ty(BB->getContext()), CondIsTrue),
                P);
          } else {
            NewPN->addIncoming(BI->getCondition(), P);
          }
        }
  
        BI->setCondition(NewPN);
        return true;
      }
    }
  
    // If the previous block ended with a widenable branch, determine if reusing
    // the target block is profitable and legal.  This will have the effect of
    // "widening" PBI, but doesn't require us to reason about hosting safety.
    if (tryWidenCondBranchToCondBranch(PBI, BI, DTU))
      return true;
  
    if (auto *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
      if (CE->canTrap())
        return false;
  
    // If both branches are conditional and both contain stores to the same
    // address, remove the stores from the conditionals and create a conditional
    // merged store at the end.
    if (MergeCondStores && mergeConditionalStores(PBI, BI, DTU, DL, TTI))
      return true;
  
    // If this is a conditional branch in an empty block, and if any
    // predecessors are a conditional branch to one of our destinations,
    // fold the conditions into logical ops and one cond br.
  
    // Ignore dbg intrinsics.
    if (&*BB->instructionsWithoutDebug(false).begin() != BI)
      return false;
  
    int PBIOp, BIOp;
    if (PBI->getSuccessor(0) == BI->getSuccessor(0)) {
      PBIOp = 0;
      BIOp = 0;
    } else if (PBI->getSuccessor(0) == BI->getSuccessor(1)) {
      PBIOp = 0;
      BIOp = 1;
    } else if (PBI->getSuccessor(1) == BI->getSuccessor(0)) {
      PBIOp = 1;
      BIOp = 0;
    } else if (PBI->getSuccessor(1) == BI->getSuccessor(1)) {
      PBIOp = 1;
      BIOp = 1;
    } else {
      return false;
    }
  
    // Check to make sure that the other destination of this branch
    // isn't BB itself.  If so, this is an infinite loop that will
    // keep getting unwound.
    if (PBI->getSuccessor(PBIOp) == BB)
      return false;
  
    // Do not perform this transformation if it would require
    // insertion of a large number of select instructions. For targets
    // without predication/cmovs, this is a big pessimization.
  
    // Also do not perform this transformation if any phi node in the common
    // destination block can trap when reached by BB or PBB (PR17073). In that
    // case, it would be unsafe to hoist the operation into a select instruction.
  
    BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
    BasicBlock *RemovedDest = PBI->getSuccessor(PBIOp ^ 1);
    unsigned NumPhis = 0;
    for (BasicBlock::iterator II = CommonDest->begin(); isa<PHINode>(II);
         ++II, ++NumPhis) {
      if (NumPhis > 2) // Disable this xform.
        return false;
  
      PHINode *PN = cast<PHINode>(II);
      Value *BIV = PN->getIncomingValueForBlock(BB);
      if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BIV))
        if (CE->canTrap())
          return false;
  
      unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
      Value *PBIV = PN->getIncomingValue(PBBIdx);
      if (ConstantExpr *CE = dyn_cast<ConstantExpr>(PBIV))
        if (CE->canTrap())
          return false;
    }
  
    // Finally, if everything is ok, fold the branches to logical ops.
    BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
  
    LLVM_DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent()
                      << "AND: " << *BI->getParent());
  
    SmallVector<DominatorTree::UpdateType, 5> Updates;
  
    // If OtherDest *is* BB, then BB is a basic block with a single conditional
    // branch in it, where one edge (OtherDest) goes back to itself but the other
    // exits.  We don't *know* that the program avoids the infinite loop
    // (even though that seems likely).  If we do this xform naively, we'll end up
    // recursively unpeeling the loop.  Since we know that (after the xform is
    // done) that the block *is* infinite if reached, we just make it an obviously
    // infinite loop with no cond branch.
    if (OtherDest == BB) {
      // Insert it at the end of the function, because it's either code,
      // or it won't matter if it's hot. :)
      BasicBlock *InfLoopBlock =
          BasicBlock::Create(BB->getContext(), "infloop", BB->getParent());
      BranchInst::Create(InfLoopBlock, InfLoopBlock);
      if (DTU)
        Updates.push_back({DominatorTree::Insert, InfLoopBlock, InfLoopBlock});
      OtherDest = InfLoopBlock;
    }
  
    LLVM_DEBUG(dbgs() << *PBI->getParent()->getParent());
  
    // BI may have other predecessors.  Because of this, we leave
    // it alone, but modify PBI.
  
    // Make sure we get to CommonDest on True&True directions.
    Value *PBICond = PBI->getCondition();
    IRBuilder<NoFolder> Builder(PBI);
    if (PBIOp)
      PBICond = Builder.CreateNot(PBICond, PBICond->getName() + ".not");
  
    Value *BICond = BI->getCondition();
    if (BIOp)
      BICond = Builder.CreateNot(BICond, BICond->getName() + ".not");
  
    // Merge the conditions.
    Value *Cond =
        createLogicalOp(Builder, Instruction::Or, PBICond, BICond, "brmerge");
  
    // Modify PBI to branch on the new condition to the new dests.
    PBI->setCondition(Cond);
    PBI->setSuccessor(0, CommonDest);
    PBI->setSuccessor(1, OtherDest);
  
    if (DTU) {
      Updates.push_back({DominatorTree::Insert, PBI->getParent(), OtherDest});
      Updates.push_back({DominatorTree::Delete, PBI->getParent(), RemovedDest});
  
      DTU->applyUpdates(Updates);
    }
  
    // Update branch weight for PBI.
    uint64_t PredTrueWeight, PredFalseWeight, SuccTrueWeight, SuccFalseWeight;
    uint64_t PredCommon, PredOther, SuccCommon, SuccOther;
    bool HasWeights =
        extractPredSuccWeights(PBI, BI, PredTrueWeight, PredFalseWeight,
                               SuccTrueWeight, SuccFalseWeight);
    if (HasWeights) {
      PredCommon = PBIOp ? PredFalseWeight : PredTrueWeight;
      PredOther = PBIOp ? PredTrueWeight : PredFalseWeight;
      SuccCommon = BIOp ? SuccFalseWeight : SuccTrueWeight;
      SuccOther = BIOp ? SuccTrueWeight : SuccFalseWeight;
      // The weight to CommonDest should be PredCommon * SuccTotal +
      //                                    PredOther * SuccCommon.
      // The weight to OtherDest should be PredOther * SuccOther.
      uint64_t NewWeights[2] = {PredCommon * (SuccCommon + SuccOther) +
                                    PredOther * SuccCommon,
                                PredOther * SuccOther};
      // Halve the weights if any of them cannot fit in an uint32_t
      FitWeights(NewWeights);
  
      setBranchWeights(PBI, NewWeights[0], NewWeights[1]);
    }
  
    // OtherDest may have phi nodes.  If so, add an entry from PBI's
    // block that are identical to the entries for BI's block.
    AddPredecessorToBlock(OtherDest, PBI->getParent(), BB);
  
    // We know that the CommonDest already had an edge from PBI to
    // it.  If it has PHIs though, the PHIs may have different
    // entries for BB and PBI's BB.  If so, insert a select to make
    // them agree.
    for (PHINode &PN : CommonDest->phis()) {
      Value *BIV = PN.getIncomingValueForBlock(BB);
      unsigned PBBIdx = PN.getBasicBlockIndex(PBI->getParent());
      Value *PBIV = PN.getIncomingValue(PBBIdx);
      if (BIV != PBIV) {
        // Insert a select in PBI to pick the right value.
        SelectInst *NV = cast<SelectInst>(
            Builder.CreateSelect(PBICond, PBIV, BIV, PBIV->getName() + ".mux"));
        PN.setIncomingValue(PBBIdx, NV);
        // Although the select has the same condition as PBI, the original branch
        // weights for PBI do not apply to the new select because the select's
        // 'logical' edges are incoming edges of the phi that is eliminated, not
        // the outgoing edges of PBI.
        if (HasWeights) {
          uint64_t PredCommon = PBIOp ? PredFalseWeight : PredTrueWeight;
          uint64_t PredOther = PBIOp ? PredTrueWeight : PredFalseWeight;
          uint64_t SuccCommon = BIOp ? SuccFalseWeight : SuccTrueWeight;
          uint64_t SuccOther = BIOp ? SuccTrueWeight : SuccFalseWeight;
          // The weight to PredCommonDest should be PredCommon * SuccTotal.
          // The weight to PredOtherDest should be PredOther * SuccCommon.
          uint64_t NewWeights[2] = {PredCommon * (SuccCommon + SuccOther),
                                    PredOther * SuccCommon};
  
          FitWeights(NewWeights);
  
          setBranchWeights(NV, NewWeights[0], NewWeights[1]);
        }
      }
    }
  
    LLVM_DEBUG(dbgs() << "INTO: " << *PBI->getParent());
    LLVM_DEBUG(dbgs() << *PBI->getParent()->getParent());
  
    // This basic block is probably dead.  We know it has at least
    // one fewer predecessor.
    return true;
  }
  
  // Simplifies a terminator by replacing it with a branch to TrueBB if Cond is
  // true or to FalseBB if Cond is false.
  // Takes care of updating the successors and removing the old terminator.
  // Also makes sure not to introduce new successors by assuming that edges to
  // non-successor TrueBBs and FalseBBs aren't reachable.
  bool SimplifyCFGOpt::SimplifyTerminatorOnSelect(Instruction *OldTerm,
                                                  Value *Cond, BasicBlock *TrueBB,
                                                  BasicBlock *FalseBB,
                                                  uint32_t TrueWeight,
                                                  uint32_t FalseWeight) {
    auto *BB = OldTerm->getParent();
    // Remove any superfluous successor edges from the CFG.
    // First, figure out which successors to preserve.
    // If TrueBB and FalseBB are equal, only try to preserve one copy of that
    // successor.
    BasicBlock *KeepEdge1 = TrueBB;
    BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : nullptr;
  
    SmallSetVector<BasicBlock *, 2> RemovedSuccessors;
  
    // Then remove the rest.
    for (BasicBlock *Succ : successors(OldTerm)) {
      // Make sure only to keep exactly one copy of each edge.
      if (Succ == KeepEdge1)
        KeepEdge1 = nullptr;
      else if (Succ == KeepEdge2)
        KeepEdge2 = nullptr;
      else {
        Succ->removePredecessor(BB,
                                /*KeepOneInputPHIs=*/true);
  
        if (Succ != TrueBB && Succ != FalseBB)
          RemovedSuccessors.insert(Succ);
      }
    }
  
    IRBuilder<> Builder(OldTerm);
    Builder.SetCurrentDebugLocation(OldTerm->getDebugLoc());
  
    // Insert an appropriate new terminator.
    if (!KeepEdge1 && !KeepEdge2) {
      if (TrueBB == FalseBB) {
        // We were only looking for one successor, and it was present.
        // Create an unconditional branch to it.
        Builder.CreateBr(TrueBB);
      } else {
        // We found both of the successors we were looking for.
        // Create a conditional branch sharing the condition of the select.
        BranchInst *NewBI = Builder.CreateCondBr(Cond, TrueBB, FalseBB);
        if (TrueWeight != FalseWeight)
          setBranchWeights(NewBI, TrueWeight, FalseWeight);
      }
    } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) {
      // Neither of the selected blocks were successors, so this
      // terminator must be unreachable.
      new UnreachableInst(OldTerm->getContext(), OldTerm);
    } else {
      // One of the selected values was a successor, but the other wasn't.
      // Insert an unconditional branch to the one that was found;
      // the edge to the one that wasn't must be unreachable.
      if (!KeepEdge1) {
        // Only TrueBB was found.
        Builder.CreateBr(TrueBB);
      } else {
        // Only FalseBB was found.
        Builder.CreateBr(FalseBB);
      }
    }
  
    EraseTerminatorAndDCECond(OldTerm);
  
    if (DTU) {
      SmallVector<DominatorTree::UpdateType, 2> Updates;
      Updates.reserve(RemovedSuccessors.size());
      for (auto *RemovedSuccessor : RemovedSuccessors)
        Updates.push_back({DominatorTree::Delete, BB, RemovedSuccessor});
      DTU->applyUpdates(Updates);
    }
  
    return true;
  }
  
  // Replaces
  //   (switch (select cond, X, Y)) on constant X, Y
  // with a branch - conditional if X and Y lead to distinct BBs,
  // unconditional otherwise.
  bool SimplifyCFGOpt::SimplifySwitchOnSelect(SwitchInst *SI,
                                              SelectInst *Select) {
    // Check for constant integer values in the select.
    ConstantInt *TrueVal = dyn_cast<ConstantInt>(Select->getTrueValue());
    ConstantInt *FalseVal = dyn_cast<ConstantInt>(Select->getFalseValue());
    if (!TrueVal || !FalseVal)
      return false;
  
    // Find the relevant condition and destinations.
    Value *Condition = Select->getCondition();
    BasicBlock *TrueBB = SI->findCaseValue(TrueVal)->getCaseSuccessor();
    BasicBlock *FalseBB = SI->findCaseValue(FalseVal)->getCaseSuccessor();
  
    // Get weight for TrueBB and FalseBB.
    uint32_t TrueWeight = 0, FalseWeight = 0;
    SmallVector<uint64_t, 8> Weights;
    bool HasWeights = HasBranchWeights(SI);
    if (HasWeights) {
      GetBranchWeights(SI, Weights);
      if (Weights.size() == 1 + SI->getNumCases()) {
        TrueWeight =
            (uint32_t)Weights[SI->findCaseValue(TrueVal)->getSuccessorIndex()];
        FalseWeight =
            (uint32_t)Weights[SI->findCaseValue(FalseVal)->getSuccessorIndex()];
      }
    }
  
    // Perform the actual simplification.
    return SimplifyTerminatorOnSelect(SI, Condition, TrueBB, FalseBB, TrueWeight,
                                      FalseWeight);
  }
  
  // Replaces
  //   (indirectbr (select cond, blockaddress(@fn, BlockA),
  //                             blockaddress(@fn, BlockB)))
  // with
  //   (br cond, BlockA, BlockB).
  bool SimplifyCFGOpt::SimplifyIndirectBrOnSelect(IndirectBrInst *IBI,
                                                  SelectInst *SI) {
    // Check that both operands of the select are block addresses.
    BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue());
    BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue());
    if (!TBA || !FBA)
      return false;
  
    // Extract the actual blocks.
    BasicBlock *TrueBB = TBA->getBasicBlock();
    BasicBlock *FalseBB = FBA->getBasicBlock();
  
    // Perform the actual simplification.
    return SimplifyTerminatorOnSelect(IBI, SI->getCondition(), TrueBB, FalseBB, 0,
                                      0);
  }
  
  /// This is called when we find an icmp instruction
  /// (a seteq/setne with a constant) as the only instruction in a
  /// block that ends with an uncond branch.  We are looking for a very specific
  /// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified.  In
  /// this case, we merge the first two "or's of icmp" into a switch, but then the
  /// default value goes to an uncond block with a seteq in it, we get something
  /// like:
  ///
  ///   switch i8 %A, label %DEFAULT [ i8 1, label %end    i8 2, label %end ]
  /// DEFAULT:
  ///   %tmp = icmp eq i8 %A, 92
  ///   br label %end
  /// end:
  ///   ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ]
  ///
  /// We prefer to split the edge to 'end' so that there is a true/false entry to
  /// the PHI, merging the third icmp into the switch.
  bool SimplifyCFGOpt::tryToSimplifyUncondBranchWithICmpInIt(
      ICmpInst *ICI, IRBuilder<> &Builder) {
    BasicBlock *BB = ICI->getParent();
  
    // If the block has any PHIs in it or the icmp has multiple uses, it is too
    // complex.
    if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse())
      return false;
  
    Value *V = ICI->getOperand(0);
    ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1));
  
    // The pattern we're looking for is where our only predecessor is a switch on
    // 'V' and this block is the default case for the switch.  In this case we can
    // fold the compared value into the switch to simplify things.
    BasicBlock *Pred = BB->getSinglePredecessor();
    if (!Pred || !isa<SwitchInst>(Pred->getTerminator()))
      return false;
  
    SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator());
    if (SI->getCondition() != V)
      return false;
  
    // If BB is reachable on a non-default case, then we simply know the value of
    // V in this block.  Substitute it and constant fold the icmp instruction
    // away.
    if (SI->getDefaultDest() != BB) {
      ConstantInt *VVal = SI->findCaseDest(BB);
      assert(VVal && "Should have a unique destination value");
      ICI->setOperand(0, VVal);
  
      if (Value *V = SimplifyInstruction(ICI, {DL, ICI})) {
        ICI->replaceAllUsesWith(V);
        ICI->eraseFromParent();
      }
      // BB is now empty, so it is likely to simplify away.
      return requestResimplify();
    }
  
    // Ok, the block is reachable from the default dest.  If the constant we're
    // comparing exists in one of the other edges, then we can constant fold ICI
    // and zap it.
    if (SI->findCaseValue(Cst) != SI->case_default()) {
      Value *V;
      if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
        V = ConstantInt::getFalse(BB->getContext());
      else
        V = ConstantInt::getTrue(BB->getContext());
  
      ICI->replaceAllUsesWith(V);
      ICI->eraseFromParent();
      // BB is now empty, so it is likely to simplify away.
      return requestResimplify();
    }
  
    // The use of the icmp has to be in the 'end' block, by the only PHI node in
    // the block.
    BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0);
    PHINode *PHIUse = dyn_cast<PHINode>(ICI->user_back());
    if (PHIUse == nullptr || PHIUse != &SuccBlock->front() ||
        isa<PHINode>(++BasicBlock::iterator(PHIUse)))
      return false;
  
    // If the icmp is a SETEQ, then the default dest gets false, the new edge gets
    // true in the PHI.
    Constant *DefaultCst = ConstantInt::getTrue(BB->getContext());
    Constant *NewCst = ConstantInt::getFalse(BB->getContext());
  
    if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
      std::swap(DefaultCst, NewCst);
  
    // Replace ICI (which is used by the PHI for the default value) with true or
    // false depending on if it is EQ or NE.
    ICI->replaceAllUsesWith(DefaultCst);
    ICI->eraseFromParent();
  
    SmallVector<DominatorTree::UpdateType, 2> Updates;
  
    // Okay, the switch goes to this block on a default value.  Add an edge from
    // the switch to the merge point on the compared value.
    BasicBlock *NewBB =
        BasicBlock::Create(BB->getContext(), "switch.edge", BB->getParent(), BB);
    {
      SwitchInstProfUpdateWrapper SIW(*SI);
      auto W0 = SIW.getSuccessorWeight(0);
      SwitchInstProfUpdateWrapper::CaseWeightOpt NewW;
      if (W0) {
        NewW = ((uint64_t(*W0) + 1) >> 1);
        SIW.setSuccessorWeight(0, *NewW);
      }
      SIW.addCase(Cst, NewBB, NewW);
      if (DTU)
        Updates.push_back({DominatorTree::Insert, Pred, NewBB});
    }
  
    // NewBB branches to the phi block, add the uncond branch and the phi entry.
    Builder.SetInsertPoint(NewBB);
    Builder.SetCurrentDebugLocation(SI->getDebugLoc());
    Builder.CreateBr(SuccBlock);
    PHIUse->addIncoming(NewCst, NewBB);
    if (DTU) {
      Updates.push_back({DominatorTree::Insert, NewBB, SuccBlock});
      DTU->applyUpdates(Updates);
    }
    return true;
  }
  
  /// The specified branch is a conditional branch.
  /// Check to see if it is branching on an or/and chain of icmp instructions, and
  /// fold it into a switch instruction if so.
  bool SimplifyCFGOpt::SimplifyBranchOnICmpChain(BranchInst *BI,
                                                 IRBuilder<> &Builder,
                                                 const DataLayout &DL) {
    Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
    if (!Cond)
      return false;
  
    // Change br (X == 0 | X == 1), T, F into a switch instruction.
    // If this is a bunch of seteq's or'd together, or if it's a bunch of
    // 'setne's and'ed together, collect them.
  
    // Try to gather values from a chain of and/or to be turned into a switch
    ConstantComparesGatherer ConstantCompare(Cond, DL);
    // Unpack the result
    SmallVectorImpl<ConstantInt *> &Values = ConstantCompare.Vals;
    Value *CompVal = ConstantCompare.CompValue;
    unsigned UsedICmps = ConstantCompare.UsedICmps;
    Value *ExtraCase = ConstantCompare.Extra;
  
    // If we didn't have a multiply compared value, fail.
    if (!CompVal)
      return false;
  
    // Avoid turning single icmps into a switch.
    if (UsedICmps <= 1)
      return false;
  
    bool TrueWhenEqual = match(Cond, m_LogicalOr(m_Value(), m_Value()));
  
    // There might be duplicate constants in the list, which the switch
    // instruction can't handle, remove them now.
    array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate);
    Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
  
    // If Extra was used, we require at least two switch values to do the
    // transformation.  A switch with one value is just a conditional branch.
    if (ExtraCase && Values.size() < 2)
      return false;
  
    // TODO: Preserve branch weight metadata, similarly to how
    // FoldValueComparisonIntoPredecessors preserves it.
  
    // Figure out which block is which destination.
    BasicBlock *DefaultBB = BI->getSuccessor(1);
    BasicBlock *EdgeBB = BI->getSuccessor(0);
    if (!TrueWhenEqual)
      std::swap(DefaultBB, EdgeBB);
  
    BasicBlock *BB = BI->getParent();
  
    LLVM_DEBUG(dbgs() << "Converting 'icmp' chain with " << Values.size()
                      << " cases into SWITCH.  BB is:\n"
                      << *BB);
  
    SmallVector<DominatorTree::UpdateType, 2> Updates;
  
    // If there are any extra values that couldn't be folded into the switch
    // then we evaluate them with an explicit branch first. Split the block
    // right before the condbr to handle it.
    if (ExtraCase) {
      BasicBlock *NewBB = SplitBlock(BB, BI, DTU, /*LI=*/nullptr,
                                     /*MSSAU=*/nullptr, "switch.early.test");
  
      // Remove the uncond branch added to the old block.
      Instruction *OldTI = BB->getTerminator();
      Builder.SetInsertPoint(OldTI);
  
      // There can be an unintended UB if extra values are Poison. Before the
      // transformation, extra values may not be evaluated according to the
      // condition, and it will not raise UB. But after transformation, we are
      // evaluating extra values before checking the condition, and it will raise
      // UB. It can be solved by adding freeze instruction to extra values.
      AssumptionCache *AC = Options.AC;
  
      if (!isGuaranteedNotToBeUndefOrPoison(ExtraCase, AC, BI, nullptr))
        ExtraCase = Builder.CreateFreeze(ExtraCase);
  
      if (TrueWhenEqual)
        Builder.CreateCondBr(ExtraCase, EdgeBB, NewBB);
      else
        Builder.CreateCondBr(ExtraCase, NewBB, EdgeBB);
  
      OldTI->eraseFromParent();
  
      if (DTU)
        Updates.push_back({DominatorTree::Insert, BB, EdgeBB});
  
      // If there are PHI nodes in EdgeBB, then we need to add a new entry to them
      // for the edge we just added.
      AddPredecessorToBlock(EdgeBB, BB, NewBB);
  
      LLVM_DEBUG(dbgs() << "  ** 'icmp' chain unhandled condition: " << *ExtraCase
                        << "\nEXTRABB = " << *BB);
      BB = NewBB;
    }
  
    Builder.SetInsertPoint(BI);
    // Convert pointer to int before we switch.
    if (CompVal->getType()->isPointerTy()) {
      CompVal = Builder.CreatePtrToInt(
          CompVal, DL.getIntPtrType(CompVal->getType()), "magicptr");
    }
  
    // Create the new switch instruction now.
    SwitchInst *New = Builder.CreateSwitch(CompVal, DefaultBB, Values.size());
  
    // Add all of the 'cases' to the switch instruction.
    for (unsigned i = 0, e = Values.size(); i != e; ++i)
      New->addCase(Values[i], EdgeBB);
  
    // We added edges from PI to the EdgeBB.  As such, if there were any
    // PHI nodes in EdgeBB, they need entries to be added corresponding to
    // the number of edges added.
    for (BasicBlock::iterator BBI = EdgeBB->begin(); isa<PHINode>(BBI); ++BBI) {
      PHINode *PN = cast<PHINode>(BBI);
      Value *InVal = PN->getIncomingValueForBlock(BB);
      for (unsigned i = 0, e = Values.size() - 1; i != e; ++i)
        PN->addIncoming(InVal, BB);
    }
  
    // Erase the old branch instruction.
    EraseTerminatorAndDCECond(BI);
    if (DTU)
      DTU->applyUpdates(Updates);
  
    LLVM_DEBUG(dbgs() << "  ** 'icmp' chain result is:\n" << *BB << '\n');
    return true;
  }
  
  bool SimplifyCFGOpt::simplifyResume(ResumeInst *RI, IRBuilder<> &Builder) {
    if (isa<PHINode>(RI->getValue()))
      return simplifyCommonResume(RI);
    else if (isa<LandingPadInst>(RI->getParent()->getFirstNonPHI()) &&
             RI->getValue() == RI->getParent()->getFirstNonPHI())
      // The resume must unwind the exception that caused control to branch here.
      return simplifySingleResume(RI);
  
    return false;
  }
  
  // Check if cleanup block is empty
  static bool isCleanupBlockEmpty(iterator_range<BasicBlock::iterator> R) {
    for (Instruction &I : R) {
      auto *II = dyn_cast<IntrinsicInst>(&I);
      if (!II)
        return false;
  
      Intrinsic::ID IntrinsicID = II->getIntrinsicID();
      switch (IntrinsicID) {
      case Intrinsic::dbg_declare:
      case Intrinsic::dbg_value:
      case Intrinsic::dbg_label:
      case Intrinsic::lifetime_end:
        break;
      default:
        return false;
      }
    }
    return true;
  }
  
  // Simplify resume that is shared by several landing pads (phi of landing pad).
  bool SimplifyCFGOpt::simplifyCommonResume(ResumeInst *RI) {
    BasicBlock *BB = RI->getParent();
  
    // Check that there are no other instructions except for debug and lifetime
    // intrinsics between the phi's and resume instruction.
    if (!isCleanupBlockEmpty(
            make_range(RI->getParent()->getFirstNonPHI(), BB->getTerminator())))
      return false;
  
    SmallSetVector<BasicBlock *, 4> TrivialUnwindBlocks;
    auto *PhiLPInst = cast<PHINode>(RI->getValue());
  
    // Check incoming blocks to see if any of them are trivial.
    for (unsigned Idx = 0, End = PhiLPInst->getNumIncomingValues(); Idx != End;
         Idx++) {
      auto *IncomingBB = PhiLPInst->getIncomingBlock(Idx);
      auto *IncomingValue = PhiLPInst->getIncomingValue(Idx);
  
      // If the block has other successors, we can not delete it because
      // it has other dependents.
      if (IncomingBB->getUniqueSuccessor() != BB)
        continue;
  
      auto *LandingPad = dyn_cast<LandingPadInst>(IncomingBB->getFirstNonPHI());
      // Not the landing pad that caused the control to branch here.
      if (IncomingValue != LandingPad)
        continue;
  
      if (isCleanupBlockEmpty(
              make_range(LandingPad->getNextNode(), IncomingBB->getTerminator())))
        TrivialUnwindBlocks.insert(IncomingBB);
    }
  
    // If no trivial unwind blocks, don't do any simplifications.
    if (TrivialUnwindBlocks.empty())
      return false;
  
    // Turn all invokes that unwind here into calls.
    for (auto *TrivialBB : TrivialUnwindBlocks) {
      // Blocks that will be simplified should be removed from the phi node.
      // Note there could be multiple edges to the resume block, and we need
      // to remove them all.
      while (PhiLPInst->getBasicBlockIndex(TrivialBB) != -1)
        BB->removePredecessor(TrivialBB, true);
  
      for (BasicBlock *Pred :
           llvm::make_early_inc_range(predecessors(TrivialBB))) {
        removeUnwindEdge(Pred, DTU);
        ++NumInvokes;
      }
  
      // In each SimplifyCFG run, only the current processed block can be erased.
      // Otherwise, it will break the iteration of SimplifyCFG pass. So instead
      // of erasing TrivialBB, we only remove the branch to the common resume
      // block so that we can later erase the resume block since it has no
      // predecessors.
      TrivialBB->getTerminator()->eraseFromParent();
      new UnreachableInst(RI->getContext(), TrivialBB);
      if (DTU)
        DTU->applyUpdates({{DominatorTree::Delete, TrivialBB, BB}});
    }
  
    // Delete the resume block if all its predecessors have been removed.
    if (pred_empty(BB))
      DeleteDeadBlock(BB, DTU);
  
    return !TrivialUnwindBlocks.empty();
  }
  
  // Simplify resume that is only used by a single (non-phi) landing pad.
  bool SimplifyCFGOpt::simplifySingleResume(ResumeInst *RI) {
    BasicBlock *BB = RI->getParent();
    auto *LPInst = cast<LandingPadInst>(BB->getFirstNonPHI());
    assert(RI->getValue() == LPInst &&
           "Resume must unwind the exception that caused control to here");
  
    // Check that there are no other instructions except for debug intrinsics.
    if (!isCleanupBlockEmpty(
            make_range<Instruction *>(LPInst->getNextNode(), RI)))
      return false;
  
    // Turn all invokes that unwind here into calls and delete the basic block.
    for (BasicBlock *Pred : llvm::make_early_inc_range(predecessors(BB))) {
      removeUnwindEdge(Pred, DTU);
      ++NumInvokes;
    }
  
    // The landingpad is now unreachable.  Zap it.
    DeleteDeadBlock(BB, DTU);
    return true;
  }
  
  static bool removeEmptyCleanup(CleanupReturnInst *RI, DomTreeUpdater *DTU) {
    // If this is a trivial cleanup pad that executes no instructions, it can be
    // eliminated.  If the cleanup pad continues to the caller, any predecessor
    // that is an EH pad will be updated to continue to the caller and any
    // predecessor that terminates with an invoke instruction will have its invoke
    // instruction converted to a call instruction.  If the cleanup pad being
    // simplified does not continue to the caller, each predecessor will be
    // updated to continue to the unwind destination of the cleanup pad being
    // simplified.
    BasicBlock *BB = RI->getParent();
    CleanupPadInst *CPInst = RI->getCleanupPad();
    if (CPInst->getParent() != BB)
      // This isn't an empty cleanup.
      return false;
  
    // We cannot kill the pad if it has multiple uses.  This typically arises
    // from unreachable basic blocks.
    if (!CPInst->hasOneUse())
      return false;
  
    // Check that there are no other instructions except for benign intrinsics.
    if (!isCleanupBlockEmpty(
            make_range<Instruction *>(CPInst->getNextNode(), RI)))
      return false;
  
    // If the cleanup return we are simplifying unwinds to the caller, this will
    // set UnwindDest to nullptr.
    BasicBlock *UnwindDest = RI->getUnwindDest();
    Instruction *DestEHPad = UnwindDest ? UnwindDest->getFirstNonPHI() : nullptr;
  
    // We're about to remove BB from the control flow.  Before we do, sink any
    // PHINodes into the unwind destination.  Doing this before changing the
    // control flow avoids some potentially slow checks, since we can currently
    // be certain that UnwindDest and BB have no common predecessors (since they
    // are both EH pads).
    if (UnwindDest) {
      // First, go through the PHI nodes in UnwindDest and update any nodes that
      // reference the block we are removing
      for (PHINode &DestPN : UnwindDest->phis()) {
        int Idx = DestPN.getBasicBlockIndex(BB);
        // Since BB unwinds to UnwindDest, it has to be in the PHI node.
        assert(Idx != -1);
        // This PHI node has an incoming value that corresponds to a control
        // path through the cleanup pad we are removing.  If the incoming
        // value is in the cleanup pad, it must be a PHINode (because we
        // verified above that the block is otherwise empty).  Otherwise, the
        // value is either a constant or a value that dominates the cleanup
        // pad being removed.
        //
        // Because BB and UnwindDest are both EH pads, all of their
        // predecessors must unwind to these blocks, and since no instruction
        // can have multiple unwind destinations, there will be no overlap in
        // incoming blocks between SrcPN and DestPN.
        Value *SrcVal = DestPN.getIncomingValue(Idx);
        PHINode *SrcPN = dyn_cast<PHINode>(SrcVal);
  
        bool NeedPHITranslation = SrcPN && SrcPN->getParent() == BB;
        for (auto *Pred : predecessors(BB)) {
          Value *Incoming =
              NeedPHITranslation ? SrcPN->getIncomingValueForBlock(Pred) : SrcVal;
          DestPN.addIncoming(Incoming, Pred);
        }
      }
  
      // Sink any remaining PHI nodes directly into UnwindDest.
      Instruction *InsertPt = DestEHPad;
      for (PHINode &PN : make_early_inc_range(BB->phis())) {
        if (PN.use_empty() || !PN.isUsedOutsideOfBlock(BB))
          // If the PHI node has no uses or all of its uses are in this basic
          // block (meaning they are debug or lifetime intrinsics), just leave
          // it.  It will be erased when we erase BB below.
          continue;
  
        // Otherwise, sink this PHI node into UnwindDest.
        // Any predecessors to UnwindDest which are not already represented
        // must be back edges which inherit the value from the path through
        // BB.  In this case, the PHI value must reference itself.
        for (auto *pred : predecessors(UnwindDest))
          if (pred != BB)
            PN.addIncoming(&PN, pred);
        PN.moveBefore(InsertPt);
        // Also, add a dummy incoming value for the original BB itself,
        // so that the PHI is well-formed until we drop said predecessor.
        PN.addIncoming(UndefValue::get(PN.getType()), BB);
      }
    }
  
    std::vector<DominatorTree::UpdateType> Updates;
  
    // We use make_early_inc_range here because we will remove all predecessors.
    for (BasicBlock *PredBB : llvm::make_early_inc_range(predecessors(BB))) {
      if (UnwindDest == nullptr) {
        if (DTU) {
          DTU->applyUpdates(Updates);
          Updates.clear();
        }
        removeUnwindEdge(PredBB, DTU);
        ++NumInvokes;
      } else {
        BB->removePredecessor(PredBB);
        Instruction *TI = PredBB->getTerminator();
        TI->replaceUsesOfWith(BB, UnwindDest);
        if (DTU) {
          Updates.push_back({DominatorTree::Insert, PredBB, UnwindDest});
          Updates.push_back({DominatorTree::Delete, PredBB, BB});
        }
      }
    }
  
    if (DTU)
      DTU->applyUpdates(Updates);
  
    DeleteDeadBlock(BB, DTU);
  
    return true;
  }
  
  // Try to merge two cleanuppads together.
  static bool mergeCleanupPad(CleanupReturnInst *RI) {
    // Skip any cleanuprets which unwind to caller, there is nothing to merge
    // with.
    BasicBlock *UnwindDest = RI->getUnwindDest();
    if (!UnwindDest)
      return false;
  
    // This cleanupret isn't the only predecessor of this cleanuppad, it wouldn't
    // be safe to merge without code duplication.
    if (UnwindDest->getSinglePredecessor() != RI->getParent())
      return false;
  
    // Verify that our cleanuppad's unwind destination is another cleanuppad.
    auto *SuccessorCleanupPad = dyn_cast<CleanupPadInst>(&UnwindDest->front());
    if (!SuccessorCleanupPad)
      return false;
  
    CleanupPadInst *PredecessorCleanupPad = RI->getCleanupPad();
    // Replace any uses of the successor cleanupad with the predecessor pad
    // The only cleanuppad uses should be this cleanupret, it's cleanupret and
    // funclet bundle operands.
    SuccessorCleanupPad->replaceAllUsesWith(PredecessorCleanupPad);
    // Remove the old cleanuppad.
    SuccessorCleanupPad->eraseFromParent();
    // Now, we simply replace the cleanupret with a branch to the unwind
    // destination.
    BranchInst::Create(UnwindDest, RI->getParent());
    RI->eraseFromParent();
  
    return true;
  }
  
  bool SimplifyCFGOpt::simplifyCleanupReturn(CleanupReturnInst *RI) {
    // It is possible to transiantly have an undef cleanuppad operand because we
    // have deleted some, but not all, dead blocks.
    // Eventually, this block will be deleted.
    if (isa<UndefValue>(RI->getOperand(0)))
      return false;
  
    if (mergeCleanupPad(RI))
      return true;
  
    if (removeEmptyCleanup(RI, DTU))
      return true;
  
    return false;
  }
  
  // WARNING: keep in sync with InstCombinerImpl::visitUnreachableInst()!
  bool SimplifyCFGOpt::simplifyUnreachable(UnreachableInst *UI) {
    BasicBlock *BB = UI->getParent();
  
    bool Changed = false;
  
    // If there are any instructions immediately before the unreachable that can
    // be removed, do so.
    while (UI->getIterator() != BB->begin()) {
      BasicBlock::iterator BBI = UI->getIterator();
      --BBI;
  
      if (!isGuaranteedToTransferExecutionToSuccessor(&*BBI))
        break; // Can not drop any more instructions. We're done here.
      // Otherwise, this instruction can be freely erased,
      // even if it is not side-effect free.
  
      // Note that deleting EH's here is in fact okay, although it involves a bit
      // of subtle reasoning. If this inst is an EH, all the predecessors of this
      // block will be the unwind edges of Invoke/CatchSwitch/CleanupReturn,
      // and we can therefore guarantee this block will be erased.
  
      // Delete this instruction (any uses are guaranteed to be dead)
      BBI->replaceAllUsesWith(PoisonValue::get(BBI->getType()));
      BBI->eraseFromParent();
      Changed = true;
    }
  
    // If the unreachable instruction is the first in the block, take a gander
    // at all of the predecessors of this instruction, and simplify them.
    if (&BB->front() != UI)
      return Changed;
  
    std::vector<DominatorTree::UpdateType> Updates;
  
    SmallSetVector<BasicBlock *, 8> Preds(pred_begin(BB), pred_end(BB));
    for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
      auto *Predecessor = Preds[i];
      Instruction *TI = Predecessor->getTerminator();
      IRBuilder<> Builder(TI);
      if (auto *BI = dyn_cast<BranchInst>(TI)) {
        // We could either have a proper unconditional branch,
        // or a degenerate conditional branch with matching destinations.
        if (all_of(BI->successors(),
                   [BB](auto *Successor) { return Successor == BB; })) {
          new UnreachableInst(TI->getContext(), TI);
          TI->eraseFromParent();
          Changed = true;
        } else {
          assert(BI->isConditional() && "Can't get here with an uncond branch.");
          Value* Cond = BI->getCondition();
          assert(BI->getSuccessor(0) != BI->getSuccessor(1) &&
                 "The destinations are guaranteed to be different here.");
          if (BI->getSuccessor(0) == BB) {
            Builder.CreateAssumption(Builder.CreateNot(Cond));
            Builder.CreateBr(BI->getSuccessor(1));
          } else {
            assert(BI->getSuccessor(1) == BB && "Incorrect CFG");
            Builder.CreateAssumption(Cond);
            Builder.CreateBr(BI->getSuccessor(0));
          }
          EraseTerminatorAndDCECond(BI);
          Changed = true;
        }
        if (DTU)
          Updates.push_back({DominatorTree::Delete, Predecessor, BB});
      } else if (auto *SI = dyn_cast<SwitchInst>(TI)) {
        SwitchInstProfUpdateWrapper SU(*SI);
        for (auto i = SU->case_begin(), e = SU->case_end(); i != e;) {
          if (i->getCaseSuccessor() != BB) {
            ++i;
            continue;
          }
          BB->removePredecessor(SU->getParent());
          i = SU.removeCase(i);
          e = SU->case_end();
          Changed = true;
        }
        // Note that the default destination can't be removed!
        if (DTU && SI->getDefaultDest() != BB)
          Updates.push_back({DominatorTree::Delete, Predecessor, BB});
      } else if (auto *II = dyn_cast<InvokeInst>(TI)) {
        if (II->getUnwindDest() == BB) {
          if (DTU) {
            DTU->applyUpdates(Updates);
            Updates.clear();
          }
          removeUnwindEdge(TI->getParent(), DTU);
          Changed = true;
        }
      } else if (auto *CSI = dyn_cast<CatchSwitchInst>(TI)) {
        if (CSI->getUnwindDest() == BB) {
          if (DTU) {
            DTU->applyUpdates(Updates);
            Updates.clear();
          }
          removeUnwindEdge(TI->getParent(), DTU);
          Changed = true;
          continue;
        }
  
        for (CatchSwitchInst::handler_iterator I = CSI->handler_begin(),
                                               E = CSI->handler_end();
             I != E; ++I) {
          if (*I == BB) {
            CSI->removeHandler(I);
            --I;
            --E;
            Changed = true;
          }
        }
        if (DTU)
          Updates.push_back({DominatorTree::Delete, Predecessor, BB});
        if (CSI->getNumHandlers() == 0) {
          if (CSI->hasUnwindDest()) {
            // Redirect all predecessors of the block containing CatchSwitchInst
            // to instead branch to the CatchSwitchInst's unwind destination.
            if (DTU) {
              for (auto *PredecessorOfPredecessor : predecessors(Predecessor)) {
                Updates.push_back({DominatorTree::Insert,
                                   PredecessorOfPredecessor,
                                   CSI->getUnwindDest()});
                Updates.push_back({DominatorTree::Delete,
                                   PredecessorOfPredecessor, Predecessor});
              }
            }
            Predecessor->replaceAllUsesWith(CSI->getUnwindDest());
          } else {
            // Rewrite all preds to unwind to caller (or from invoke to call).
            if (DTU) {
              DTU->applyUpdates(Updates);
              Updates.clear();
            }
            SmallVector<BasicBlock *, 8> EHPreds(predecessors(Predecessor));
            for (BasicBlock *EHPred : EHPreds)
              removeUnwindEdge(EHPred, DTU);
          }
          // The catchswitch is no longer reachable.
          new UnreachableInst(CSI->getContext(), CSI);
          CSI->eraseFromParent();
          Changed = true;
        }
      } else if (auto *CRI = dyn_cast<CleanupReturnInst>(TI)) {
        (void)CRI;
        assert(CRI->hasUnwindDest() && CRI->getUnwindDest() == BB &&
               "Expected to always have an unwind to BB.");
        if (DTU)
          Updates.push_back({DominatorTree::Delete, Predecessor, BB});
        new UnreachableInst(TI->getContext(), TI);
        TI->eraseFromParent();
        Changed = true;
      }
    }
  
    if (DTU)
      DTU->applyUpdates(Updates);
  
    // If this block is now dead, remove it.
    if (pred_empty(BB) && BB != &BB->getParent()->getEntryBlock()) {
      DeleteDeadBlock(BB, DTU);
      return true;
    }
  
    return Changed;
  }
  
  static bool CasesAreContiguous(SmallVectorImpl<ConstantInt *> &Cases) {
    assert(Cases.size() >= 1);
  
    array_pod_sort(Cases.begin(), Cases.end(), ConstantIntSortPredicate);
    for (size_t I = 1, E = Cases.size(); I != E; ++I) {
      if (Cases[I - 1]->getValue() != Cases[I]->getValue() + 1)
        return false;
    }
    return true;
  }
  
  static void createUnreachableSwitchDefault(SwitchInst *Switch,
                                             DomTreeUpdater *DTU) {
    LLVM_DEBUG(dbgs() << "SimplifyCFG: switch default is dead.\n");
    auto *BB = Switch->getParent();
    auto *OrigDefaultBlock = Switch->getDefaultDest();
    OrigDefaultBlock->removePredecessor(BB);
    BasicBlock *NewDefaultBlock = BasicBlock::Create(
        BB->getContext(), BB->getName() + ".unreachabledefault", BB->getParent(),
        OrigDefaultBlock);
    new UnreachableInst(Switch->getContext(), NewDefaultBlock);
    Switch->setDefaultDest(&*NewDefaultBlock);
    if (DTU) {
      SmallVector<DominatorTree::UpdateType, 2> Updates;
      Updates.push_back({DominatorTree::Insert, BB, &*NewDefaultBlock});
      if (!is_contained(successors(BB), OrigDefaultBlock))
        Updates.push_back({DominatorTree::Delete, BB, &*OrigDefaultBlock});
      DTU->applyUpdates(Updates);
    }
  }
  
  /// Turn a switch with two reachable destinations into an integer range
  /// comparison and branch.
  bool SimplifyCFGOpt::TurnSwitchRangeIntoICmp(SwitchInst *SI,
                                               IRBuilder<> &Builder) {
    assert(SI->getNumCases() > 1 && "Degenerate switch?");
  
    bool HasDefault =
        !isa<UnreachableInst>(SI->getDefaultDest()->getFirstNonPHIOrDbg());
  
    auto *BB = SI->getParent();
  
    // Partition the cases into two sets with different destinations.
    BasicBlock *DestA = HasDefault ? SI->getDefaultDest() : nullptr;
    BasicBlock *DestB = nullptr;
    SmallVector<ConstantInt *, 16> CasesA;
    SmallVector<ConstantInt *, 16> CasesB;
  
    for (auto Case : SI->cases()) {
      BasicBlock *Dest = Case.getCaseSuccessor();
      if (!DestA)
        DestA = Dest;
      if (Dest == DestA) {
        CasesA.push_back(Case.getCaseValue());
        continue;
      }
      if (!DestB)
        DestB = Dest;
      if (Dest == DestB) {
        CasesB.push_back(Case.getCaseValue());
        continue;
      }
      return false; // More than two destinations.
    }
  
    assert(DestA && DestB &&
           "Single-destination switch should have been folded.");
    assert(DestA != DestB);
    assert(DestB != SI->getDefaultDest());
    assert(!CasesB.empty() && "There must be non-default cases.");
    assert(!CasesA.empty() || HasDefault);
  
    // Figure out if one of the sets of cases form a contiguous range.
    SmallVectorImpl<ConstantInt *> *ContiguousCases = nullptr;
    BasicBlock *ContiguousDest = nullptr;
    BasicBlock *OtherDest = nullptr;
    if (!CasesA.empty() && CasesAreContiguous(CasesA)) {
      ContiguousCases = &CasesA;
      ContiguousDest = DestA;
      OtherDest = DestB;
    } else if (CasesAreContiguous(CasesB)) {
      ContiguousCases = &CasesB;
      ContiguousDest = DestB;
      OtherDest = DestA;
    } else
      return false;
  
    // Start building the compare and branch.
  
    Constant *Offset = ConstantExpr::getNeg(ContiguousCases->back());
    Constant *NumCases =
        ConstantInt::get(Offset->getType(), ContiguousCases->size());
  
    Value *Sub = SI->getCondition();
    if (!Offset->isNullValue())
      Sub = Builder.CreateAdd(Sub, Offset, Sub->getName() + ".off");
  
    Value *Cmp;
    // If NumCases overflowed, then all possible values jump to the successor.
    if (NumCases->isNullValue() && !ContiguousCases->empty())
      Cmp = ConstantInt::getTrue(SI->getContext());
    else
      Cmp = Builder.CreateICmpULT(Sub, NumCases, "switch");
    BranchInst *NewBI = Builder.CreateCondBr(Cmp, ContiguousDest, OtherDest);
  
    // Update weight for the newly-created conditional branch.
    if (HasBranchWeights(SI)) {
      SmallVector<uint64_t, 8> Weights;
      GetBranchWeights(SI, Weights);
      if (Weights.size() == 1 + SI->getNumCases()) {
        uint64_t TrueWeight = 0;
        uint64_t FalseWeight = 0;
        for (size_t I = 0, E = Weights.size(); I != E; ++I) {
          if (SI->getSuccessor(I) == ContiguousDest)
            TrueWeight += Weights[I];
          else
            FalseWeight += Weights[I];
        }
        while (TrueWeight > UINT32_MAX || FalseWeight > UINT32_MAX) {
          TrueWeight /= 2;
          FalseWeight /= 2;
        }
        setBranchWeights(NewBI, TrueWeight, FalseWeight);
      }
    }
  
    // Prune obsolete incoming values off the successors' PHI nodes.
    for (auto BBI = ContiguousDest->begin(); isa<PHINode>(BBI); ++BBI) {
      unsigned PreviousEdges = ContiguousCases->size();
      if (ContiguousDest == SI->getDefaultDest())
        ++PreviousEdges;
      for (unsigned I = 0, E = PreviousEdges - 1; I != E; ++I)
        cast<PHINode>(BBI)->removeIncomingValue(SI->getParent());
    }
    for (auto BBI = OtherDest->begin(); isa<PHINode>(BBI); ++BBI) {
      unsigned PreviousEdges = SI->getNumCases() - ContiguousCases->size();
      if (OtherDest == SI->getDefaultDest())
        ++PreviousEdges;
      for (unsigned I = 0, E = PreviousEdges - 1; I != E; ++I)
        cast<PHINode>(BBI)->removeIncomingValue(SI->getParent());
    }
  
    // Clean up the default block - it may have phis or other instructions before
    // the unreachable terminator.
    if (!HasDefault)
      createUnreachableSwitchDefault(SI, DTU);
  
    auto *UnreachableDefault = SI->getDefaultDest();
  
    // Drop the switch.
    SI->eraseFromParent();
  
    if (!HasDefault && DTU)
      DTU->applyUpdates({{DominatorTree::Delete, BB, UnreachableDefault}});
  
    return true;
  }
  
  /// Compute masked bits for the condition of a switch
  /// and use it to remove dead cases.
  static bool eliminateDeadSwitchCases(SwitchInst *SI, DomTreeUpdater *DTU,
                                       AssumptionCache *AC,
                                       const DataLayout &DL) {
    Value *Cond = SI->getCondition();
    KnownBits Known = computeKnownBits(Cond, DL, 0, AC, SI);
  
    // We can also eliminate cases by determining that their values are outside of
    // the limited range of the condition based on how many significant (non-sign)
    // bits are in the condition value.
    unsigned MaxSignificantBitsInCond =
        ComputeMaxSignificantBits(Cond, DL, 0, AC, SI);
  
    // Gather dead cases.
    SmallVector<ConstantInt *, 8> DeadCases;
    SmallDenseMap<BasicBlock *, int, 8> NumPerSuccessorCases;
    SmallVector<BasicBlock *, 8> UniqueSuccessors;
    for (auto &Case : SI->cases()) {
      auto *Successor = Case.getCaseSuccessor();
      if (DTU) {
        if (!NumPerSuccessorCases.count(Successor))
          UniqueSuccessors.push_back(Successor);
        ++NumPerSuccessorCases[Successor];
      }
      const APInt &CaseVal = Case.getCaseValue()->getValue();
      if (Known.Zero.intersects(CaseVal) || !Known.One.isSubsetOf(CaseVal) ||
          (CaseVal.getMinSignedBits() > MaxSignificantBitsInCond)) {
        DeadCases.push_back(Case.getCaseValue());
        if (DTU)
          --NumPerSuccessorCases[Successor];
        LLVM_DEBUG(dbgs() << "SimplifyCFG: switch case " << CaseVal
                          << " is dead.\n");
      }
    }
  
    // If we can prove that the cases must cover all possible values, the
    // default destination becomes dead and we can remove it.  If we know some
    // of the bits in the value, we can use that to more precisely compute the
    // number of possible unique case values.
    bool HasDefault =
        !isa<UnreachableInst>(SI->getDefaultDest()->getFirstNonPHIOrDbg());
    const unsigned NumUnknownBits =
        Known.getBitWidth() - (Known.Zero | Known.One).countPopulation();
    assert(NumUnknownBits <= Known.getBitWidth());
    if (HasDefault && DeadCases.empty() &&
        NumUnknownBits < 64 /* avoid overflow */ &&
        SI->getNumCases() == (1ULL << NumUnknownBits)) {
      createUnreachableSwitchDefault(SI, DTU);
      return true;
    }
  
    if (DeadCases.empty())
      return false;
  
    SwitchInstProfUpdateWrapper SIW(*SI);
    for (ConstantInt *DeadCase : DeadCases) {
      SwitchInst::CaseIt CaseI = SI->findCaseValue(DeadCase);
      assert(CaseI != SI->case_default() &&
             "Case was not found. Probably mistake in DeadCases forming.");
      // Prune unused values from PHI nodes.
      CaseI->getCaseSuccessor()->removePredecessor(SI->getParent());
      SIW.removeCase(CaseI);
    }
  
    if (DTU) {
      std::vector<DominatorTree::UpdateType> Updates;
      for (auto *Successor : UniqueSuccessors)
        if (NumPerSuccessorCases[Successor] == 0)
          Updates.push_back({DominatorTree::Delete, SI->getParent(), Successor});
      DTU->applyUpdates(Updates);
    }
  
    return true;
  }
  
  /// If BB would be eligible for simplification by
  /// TryToSimplifyUncondBranchFromEmptyBlock (i.e. it is empty and terminated
  /// by an unconditional branch), look at the phi node for BB in the successor
  /// block and see if the incoming value is equal to CaseValue. If so, return
  /// the phi node, and set PhiIndex to BB's index in the phi node.
  static PHINode *FindPHIForConditionForwarding(ConstantInt *CaseValue,
                                                BasicBlock *BB, int *PhiIndex) {
    if (BB->getFirstNonPHIOrDbg() != BB->getTerminator())
      return nullptr; // BB must be empty to be a candidate for simplification.
    if (!BB->getSinglePredecessor())
      return nullptr; // BB must be dominated by the switch.
  
    BranchInst *Branch = dyn_cast<BranchInst>(BB->getTerminator());
    if (!Branch || !Branch->isUnconditional())
      return nullptr; // Terminator must be unconditional branch.
  
    BasicBlock *Succ = Branch->getSuccessor(0);
  
    for (PHINode &PHI : Succ->phis()) {
      int Idx = PHI.getBasicBlockIndex(BB);
      assert(Idx >= 0 && "PHI has no entry for predecessor?");
  
      Value *InValue = PHI.getIncomingValue(Idx);
      if (InValue != CaseValue)
        continue;
  
      *PhiIndex = Idx;
      return &PHI;
    }
  
    return nullptr;
  }
  
  /// Try to forward the condition of a switch instruction to a phi node
  /// dominated by the switch, if that would mean that some of the destination
  /// blocks of the switch can be folded away. Return true if a change is made.
  static bool ForwardSwitchConditionToPHI(SwitchInst *SI) {
    using ForwardingNodesMap = DenseMap<PHINode *, SmallVector<int, 4>>;
  
    ForwardingNodesMap ForwardingNodes;
    BasicBlock *SwitchBlock = SI->getParent();
    bool Changed = false;
    for (auto &Case : SI->cases()) {
      ConstantInt *CaseValue = Case.getCaseValue();
      BasicBlock *CaseDest = Case.getCaseSuccessor();
  
      // Replace phi operands in successor blocks that are using the constant case
      // value rather than the switch condition variable:
      //   switchbb:
      //   switch i32 %x, label %default [
      //     i32 17, label %succ
      //   ...
      //   succ:
      //     %r = phi i32 ... [ 17, %switchbb ] ...
      // -->
      //     %r = phi i32 ... [ %x, %switchbb ] ...
  
      for (PHINode &Phi : CaseDest->phis()) {
        // This only works if there is exactly 1 incoming edge from the switch to
        // a phi. If there is >1, that means multiple cases of the switch map to 1
        // value in the phi, and that phi value is not the switch condition. Thus,
        // this transform would not make sense (the phi would be invalid because
        // a phi can't have different incoming values from the same block).
        int SwitchBBIdx = Phi.getBasicBlockIndex(SwitchBlock);
        if (Phi.getIncomingValue(SwitchBBIdx) == CaseValue &&
            count(Phi.blocks(), SwitchBlock) == 1) {
          Phi.setIncomingValue(SwitchBBIdx, SI->getCondition());
          Changed = true;
        }
      }
  
      // Collect phi nodes that are indirectly using this switch's case constants.
      int PhiIdx;
      if (auto *Phi = FindPHIForConditionForwarding(CaseValue, CaseDest, &PhiIdx))
        ForwardingNodes[Phi].push_back(PhiIdx);
    }
  
    for (auto &ForwardingNode : ForwardingNodes) {
      PHINode *Phi = ForwardingNode.first;
      SmallVectorImpl<int> &Indexes = ForwardingNode.second;
      if (Indexes.size() < 2)
        continue;
  
      for (int Index : Indexes)
        Phi->setIncomingValue(Index, SI->getCondition());
      Changed = true;
    }
  
    return Changed;
  }
  
  /// Return true if the backend will be able to handle
  /// initializing an array of constants like C.
  static bool ValidLookupTableConstant(Constant *C, const TargetTransformInfo &TTI) {
    if (C->isThreadDependent())
      return false;
    if (C->isDLLImportDependent())
      return false;
  
    if (!isa<ConstantFP>(C) && !isa<ConstantInt>(C) &&
        !isa<ConstantPointerNull>(C) && !isa<GlobalValue>(C) &&
        !isa<UndefValue>(C) && !isa<ConstantExpr>(C))
      return false;
  
    if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) {
      // Pointer casts and in-bounds GEPs will not prohibit the backend from
      // materializing the array of constants.
      Constant *StrippedC = cast<Constant>(CE->stripInBoundsConstantOffsets());
      if (StrippedC == C || !ValidLookupTableConstant(StrippedC, TTI))
        return false;
    }
  
    if (!TTI.shouldBuildLookupTablesForConstant(C))
      return false;
  
    return true;
  }
  
  /// If V is a Constant, return it. Otherwise, try to look up
  /// its constant value in ConstantPool, returning 0 if it's not there.
  static Constant *
  LookupConstant(Value *V,
                 const SmallDenseMap<Value *, Constant *> &ConstantPool) {
    if (Constant *C = dyn_cast<Constant>(V))
      return C;
    return ConstantPool.lookup(V);
  }
  
  /// Try to fold instruction I into a constant. This works for
  /// simple instructions such as binary operations where both operands are
  /// constant or can be replaced by constants from the ConstantPool. Returns the
  /// resulting constant on success, 0 otherwise.
  static Constant *
  ConstantFold(Instruction *I, const DataLayout &DL,
               const SmallDenseMap<Value *, Constant *> &ConstantPool) {
    if (SelectInst *Select = dyn_cast<SelectInst>(I)) {
      Constant *A = LookupConstant(Select->getCondition(), ConstantPool);
      if (!A)
        return nullptr;
      if (A->isAllOnesValue())
        return LookupConstant(Select->getTrueValue(), ConstantPool);
      if (A->isNullValue())
        return LookupConstant(Select->getFalseValue(), ConstantPool);
      return nullptr;
    }
  
    SmallVector<Constant *, 4> COps;
    for (unsigned N = 0, E = I->getNumOperands(); N != E; ++N) {
      if (Constant *A = LookupConstant(I->getOperand(N), ConstantPool))
        COps.push_back(A);
      else
        return nullptr;
    }
  
    if (CmpInst *Cmp = dyn_cast<CmpInst>(I)) {
      return ConstantFoldCompareInstOperands(Cmp->getPredicate(), COps[0],
                                             COps[1], DL);
    }
  
    return ConstantFoldInstOperands(I, COps, DL);
  }
  
  /// Try to determine the resulting constant values in phi nodes
  /// at the common destination basic block, *CommonDest, for one of the case
  /// destionations CaseDest corresponding to value CaseVal (0 for the default
  /// case), of a switch instruction SI.
  static bool
  GetCaseResults(SwitchInst *SI, ConstantInt *CaseVal, BasicBlock *CaseDest,
                 BasicBlock **CommonDest,
                 SmallVectorImpl<std::pair<PHINode *, Constant *>> &Res,
                 const DataLayout &DL, const TargetTransformInfo &TTI) {
    // The block from which we enter the common destination.
    BasicBlock *Pred = SI->getParent();
  
    // If CaseDest is empty except for some side-effect free instructions through
    // which we can constant-propagate the CaseVal, continue to its successor.
    SmallDenseMap<Value *, Constant *> ConstantPool;
    ConstantPool.insert(std::make_pair(SI->getCondition(), CaseVal));
    for (Instruction &I : CaseDest->instructionsWithoutDebug(false)) {
      if (I.isTerminator()) {
        // If the terminator is a simple branch, continue to the next block.
        if (I.getNumSuccessors() != 1 || I.isExceptionalTerminator())
          return false;
        Pred = CaseDest;
        CaseDest = I.getSuccessor(0);
      } else if (Constant *C = ConstantFold(&I, DL, ConstantPool)) {
        // Instruction is side-effect free and constant.
  
        // If the instruction has uses outside this block or a phi node slot for
        // the block, it is not safe to bypass the instruction since it would then
        // no longer dominate all its uses.
        for (auto &Use : I.uses()) {
          User *User = Use.getUser();
          if (Instruction *I = dyn_cast<Instruction>(User))
            if (I->getParent() == CaseDest)
              continue;
          if (PHINode *Phi = dyn_cast<PHINode>(User))
            if (Phi->getIncomingBlock(Use) == CaseDest)
              continue;
          return false;
        }
  
        ConstantPool.insert(std::make_pair(&I, C));
      } else {
        break;
      }
    }
  
    // If we did not have a CommonDest before, use the current one.
    if (!*CommonDest)
      *CommonDest = CaseDest;
    // If the destination isn't the common one, abort.
    if (CaseDest != *CommonDest)
      return false;
  
    // Get the values for this case from phi nodes in the destination block.
    for (PHINode &PHI : (*CommonDest)->phis()) {
      int Idx = PHI.getBasicBlockIndex(Pred);
      if (Idx == -1)
        continue;
  
      Constant *ConstVal =
          LookupConstant(PHI.getIncomingValue(Idx), ConstantPool);
      if (!ConstVal)
        return false;
  
      // Be conservative about which kinds of constants we support.
      if (!ValidLookupTableConstant(ConstVal, TTI))
        return false;
  
      Res.push_back(std::make_pair(&PHI, ConstVal));
    }
  
    return Res.size() > 0;
  }
  
  // Helper function used to add CaseVal to the list of cases that generate
  // Result. Returns the updated number of cases that generate this result.
  static uintptr_t MapCaseToResult(ConstantInt *CaseVal,
                                   SwitchCaseResultVectorTy &UniqueResults,
                                   Constant *Result) {
    for (auto &I : UniqueResults) {
      if (I.first == Result) {
        I.second.push_back(CaseVal);
        return I.second.size();
      }
    }
    UniqueResults.push_back(
        std::make_pair(Result, SmallVector<ConstantInt *, 4>(1, CaseVal)));
    return 1;
  }
  
  // Helper function that initializes a map containing
  // results for the PHI node of the common destination block for a switch
  // instruction. Returns false if multiple PHI nodes have been found or if
  // there is not a common destination block for the switch.
  static bool
  InitializeUniqueCases(SwitchInst *SI, PHINode *&PHI, BasicBlock *&CommonDest,
                        SwitchCaseResultVectorTy &UniqueResults,
                        Constant *&DefaultResult, const DataLayout &DL,
                        const TargetTransformInfo &TTI,
                        uintptr_t MaxUniqueResults, uintptr_t MaxCasesPerResult) {
    for (auto &I : SI->cases()) {
      ConstantInt *CaseVal = I.getCaseValue();
  
      // Resulting value at phi nodes for this case value.
      SwitchCaseResultsTy Results;
      if (!GetCaseResults(SI, CaseVal, I.getCaseSuccessor(), &CommonDest, Results,
                          DL, TTI))
        return false;
  
      // Only one value per case is permitted.
      if (Results.size() > 1)
        return false;
  
      // Add the case->result mapping to UniqueResults.
      const uintptr_t NumCasesForResult =
          MapCaseToResult(CaseVal, UniqueResults, Results.begin()->second);
  
      // Early out if there are too many cases for this result.
      if (NumCasesForResult > MaxCasesPerResult)
        return false;
  
      // Early out if there are too many unique results.
      if (UniqueResults.size() > MaxUniqueResults)
        return false;
  
      // Check the PHI consistency.
      if (!PHI)
        PHI = Results[0].first;
      else if (PHI != Results[0].first)
        return false;
    }
    // Find the default result value.
    SmallVector<std::pair<PHINode *, Constant *>, 1> DefaultResults;
    BasicBlock *DefaultDest = SI->getDefaultDest();
    GetCaseResults(SI, nullptr, SI->getDefaultDest(), &CommonDest, DefaultResults,
                   DL, TTI);
    // If the default value is not found abort unless the default destination
    // is unreachable.
    DefaultResult =
        DefaultResults.size() == 1 ? DefaultResults.begin()->second : nullptr;
    if ((!DefaultResult &&
         !isa<UnreachableInst>(DefaultDest->getFirstNonPHIOrDbg())))
      return false;
  
    return true;
  }
  
  // Helper function that checks if it is possible to transform a switch with only
  // two cases (or two cases + default) that produces a result into a select.
  // Example:
  // switch (a) {
  //   case 10:                %0 = icmp eq i32 %a, 10
  //     return 10;            %1 = select i1 %0, i32 10, i32 4
  //   case 20:        ---->   %2 = icmp eq i32 %a, 20
  //     return 2;             %3 = select i1 %2, i32 2, i32 %1
  //   default:
  //     return 4;
  // }
  static Value *ConvertTwoCaseSwitch(const SwitchCaseResultVectorTy &ResultVector,
                                     Constant *DefaultResult, Value *Condition,
                                     IRBuilder<> &Builder) {
    // If we are selecting between only two cases transform into a simple
    // select or a two-way select if default is possible.
    if (ResultVector.size() == 2 && ResultVector[0].second.size() == 1 &&
        ResultVector[1].second.size() == 1) {
      ConstantInt *const FirstCase = ResultVector[0].second[0];
      ConstantInt *const SecondCase = ResultVector[1].second[0];
  
      bool DefaultCanTrigger = DefaultResult;
      Value *SelectValue = ResultVector[1].first;
      if (DefaultCanTrigger) {
        Value *const ValueCompare =
            Builder.CreateICmpEQ(Condition, SecondCase, "switch.selectcmp");
        SelectValue = Builder.CreateSelect(ValueCompare, ResultVector[1].first,
                                           DefaultResult, "switch.select");
      }
      Value *const ValueCompare =
          Builder.CreateICmpEQ(Condition, FirstCase, "switch.selectcmp");
      return Builder.CreateSelect(ValueCompare, ResultVector[0].first,
                                  SelectValue, "switch.select");
    }
  
    // Handle the degenerate case where two cases have the same value.
    if (ResultVector.size() == 1 && ResultVector[0].second.size() == 2 &&
        DefaultResult) {
      Value *Cmp1 = Builder.CreateICmpEQ(
          Condition, ResultVector[0].second[0], "switch.selectcmp.case1");
      Value *Cmp2 = Builder.CreateICmpEQ(
          Condition, ResultVector[0].second[1], "switch.selectcmp.case2");
      Value *Cmp = Builder.CreateOr(Cmp1, Cmp2, "switch.selectcmp");
      return Builder.CreateSelect(Cmp, ResultVector[0].first, DefaultResult);
    }
  
    return nullptr;
  }
  
  // Helper function to cleanup a switch instruction that has been converted into
  // a select, fixing up PHI nodes and basic blocks.
  static void RemoveSwitchAfterSelectConversion(SwitchInst *SI, PHINode *PHI,
                                                Value *SelectValue,
                                                IRBuilder<> &Builder,
                                                DomTreeUpdater *DTU) {
    std::vector<DominatorTree::UpdateType> Updates;
  
    BasicBlock *SelectBB = SI->getParent();
    BasicBlock *DestBB = PHI->getParent();
  
    if (DTU && !is_contained(predecessors(DestBB), SelectBB))
      Updates.push_back({DominatorTree::Insert, SelectBB, DestBB});
    Builder.CreateBr(DestBB);
  
    // Remove the switch.
  
    while (PHI->getBasicBlockIndex(SelectBB) >= 0)
      PHI->removeIncomingValue(SelectBB);
    PHI->addIncoming(SelectValue, SelectBB);
  
    SmallPtrSet<BasicBlock *, 4> RemovedSuccessors;
    for (unsigned i = 0, e = SI->getNumSuccessors(); i < e; ++i) {
      BasicBlock *Succ = SI->getSuccessor(i);
  
      if (Succ == DestBB)
        continue;
      Succ->removePredecessor(SelectBB);
      if (DTU && RemovedSuccessors.insert(Succ).second)
        Updates.push_back({DominatorTree::Delete, SelectBB, Succ});
    }
    SI->eraseFromParent();
    if (DTU)
      DTU->applyUpdates(Updates);
  }
  
  /// If the switch is only used to initialize one or more
  /// phi nodes in a common successor block with only two different
  /// constant values, replace the switch with select.
  static bool switchToSelect(SwitchInst *SI, IRBuilder<> &Builder,
                             DomTreeUpdater *DTU, const DataLayout &DL,
                             const TargetTransformInfo &TTI) {
    Value *const Cond = SI->getCondition();
    PHINode *PHI = nullptr;
    BasicBlock *CommonDest = nullptr;
    Constant *DefaultResult;
    SwitchCaseResultVectorTy UniqueResults;
    // Collect all the cases that will deliver the same value from the switch.
    if (!InitializeUniqueCases(SI, PHI, CommonDest, UniqueResults, DefaultResult,
                               DL, TTI, /*MaxUniqueResults*/2,
                               /*MaxCasesPerResult*/2))
      return false;
    assert(PHI != nullptr && "PHI for value select not found");
  
    Builder.SetInsertPoint(SI);
    Value *SelectValue =
        ConvertTwoCaseSwitch(UniqueResults, DefaultResult, Cond, Builder);
    if (SelectValue) {
      RemoveSwitchAfterSelectConversion(SI, PHI, SelectValue, Builder, DTU);
      return true;
    }
    // The switch couldn't be converted into a select.
    return false;
  }
  
  namespace {
  
  /// This class represents a lookup table that can be used to replace a switch.
  class SwitchLookupTable {
  public:
    /// Create a lookup table to use as a switch replacement with the contents
    /// of Values, using DefaultValue to fill any holes in the table.
    SwitchLookupTable(
        Module &M, uint64_t TableSize, ConstantInt *Offset,
        const SmallVectorImpl<std::pair<ConstantInt *, Constant *>> &Values,
        Constant *DefaultValue, const DataLayout &DL, const StringRef &FuncName);
  
    /// Build instructions with Builder to retrieve the value at
    /// the position given by Index in the lookup table.
    Value *BuildLookup(Value *Index, IRBuilder<> &Builder);
  
    /// Return true if a table with TableSize elements of
    /// type ElementType would fit in a target-legal register.
    static bool WouldFitInRegister(const DataLayout &DL, uint64_t TableSize,
                                   Type *ElementType);
  
  private:
    // Depending on the contents of the table, it can be represented in
    // different ways.
    enum {
      // For tables where each element contains the same value, we just have to
      // store that single value and return it for each lookup.
      SingleValueKind,
  
      // For tables where there is a linear relationship between table index
      // and values. We calculate the result with a simple multiplication
      // and addition instead of a table lookup.
      LinearMapKind,
  
      // For small tables with integer elements, we can pack them into a bitmap
      // that fits into a target-legal register. Values are retrieved by
      // shift and mask operations.
      BitMapKind,
  
      // The table is stored as an array of values. Values are retrieved by load
      // instructions from the table.
      ArrayKind
    } Kind;
  
    // For SingleValueKind, this is the single value.
    Constant *SingleValue = nullptr;
  
    // For BitMapKind, this is the bitmap.
    ConstantInt *BitMap = nullptr;
    IntegerType *BitMapElementTy = nullptr;
  
    // For LinearMapKind, these are the constants used to derive the value.
    ConstantInt *LinearOffset = nullptr;
    ConstantInt *LinearMultiplier = nullptr;
  
    // For ArrayKind, this is the array.
    GlobalVariable *Array = nullptr;
  };
  
  } // end anonymous namespace
  
  SwitchLookupTable::SwitchLookupTable(
      Module &M, uint64_t TableSize, ConstantInt *Offset,
      const SmallVectorImpl<std::pair<ConstantInt *, Constant *>> &Values,
      Constant *DefaultValue, const DataLayout &DL, const StringRef &FuncName) {
    assert(Values.size() && "Can't build lookup table without values!");
    assert(TableSize >= Values.size() && "Can't fit values in table!");
  
    // If all values in the table are equal, this is that value.
    SingleValue = Values.begin()->second;
  
    Type *ValueType = Values.begin()->second->getType();
  
    // Build up the table contents.
    SmallVector<Constant *, 64> TableContents(TableSize);
    for (size_t I = 0, E = Values.size(); I != E; ++I) {
      ConstantInt *CaseVal = Values[I].first;
      Constant *CaseRes = Values[I].second;
      assert(CaseRes->getType() == ValueType);
  
      uint64_t Idx = (CaseVal->getValue() - Offset->getValue()).getLimitedValue();
      TableContents[Idx] = CaseRes;
  
      if (CaseRes != SingleValue)
        SingleValue = nullptr;
    }
  
    // Fill in any holes in the table with the default result.
    if (Values.size() < TableSize) {
      assert(DefaultValue &&
             "Need a default value to fill the lookup table holes.");
      assert(DefaultValue->getType() == ValueType);
      for (uint64_t I = 0; I < TableSize; ++I) {
        if (!TableContents[I])
          TableContents[I] = DefaultValue;
      }
  
      if (DefaultValue != SingleValue)
        SingleValue = nullptr;
    }
  
    // If each element in the table contains the same value, we only need to store
    // that single value.
    if (SingleValue) {
      Kind = SingleValueKind;
      return;
    }
  
    // Check if we can derive the value with a linear transformation from the
    // table index.
    if (isa<IntegerType>(ValueType)) {
      bool LinearMappingPossible = true;
      APInt PrevVal;
      APInt DistToPrev;
      assert(TableSize >= 2 && "Should be a SingleValue table.");
      // Check if there is the same distance between two consecutive values.
      for (uint64_t I = 0; I < TableSize; ++I) {
        ConstantInt *ConstVal = dyn_cast<ConstantInt>(TableContents[I]);
        if (!ConstVal) {
          // This is an undef. We could deal with it, but undefs in lookup tables
          // are very seldom. It's probably not worth the additional complexity.
          LinearMappingPossible = false;
          break;
        }
        const APInt &Val = ConstVal->getValue();
        if (I != 0) {
          APInt Dist = Val - PrevVal;
          if (I == 1) {
            DistToPrev = Dist;
          } else if (Dist != DistToPrev) {
            LinearMappingPossible = false;
            break;
          }
        }
        PrevVal = Val;
      }
      if (LinearMappingPossible) {
        LinearOffset = cast<ConstantInt>(TableContents[0]);
        LinearMultiplier = ConstantInt::get(M.getContext(), DistToPrev);
        Kind = LinearMapKind;
        ++NumLinearMaps;
        return;
      }
    }
  
    // If the type is integer and the table fits in a register, build a bitmap.
    if (WouldFitInRegister(DL, TableSize, ValueType)) {
      IntegerType *IT = cast<IntegerType>(ValueType);
      APInt TableInt(TableSize * IT->getBitWidth(), 0);
      for (uint64_t I = TableSize; I > 0; --I) {
        TableInt <<= IT->getBitWidth();
        // Insert values into the bitmap. Undef values are set to zero.
        if (!isa<UndefValue>(TableContents[I - 1])) {
          ConstantInt *Val = cast<ConstantInt>(TableContents[I - 1]);
          TableInt |= Val->getValue().zext(TableInt.getBitWidth());
        }
      }
      BitMap = ConstantInt::get(M.getContext(), TableInt);
      BitMapElementTy = IT;
      Kind = BitMapKind;
      ++NumBitMaps;
      return;
    }
  
    // Store the table in an array.
    ArrayType *ArrayTy = ArrayType::get(ValueType, TableSize);
    Constant *Initializer = ConstantArray::get(ArrayTy, TableContents);
  
    Array = new GlobalVariable(M, ArrayTy, /*isConstant=*/true,
                               GlobalVariable::PrivateLinkage, Initializer,
                               "switch.table." + FuncName);
    Array->setUnnamedAddr(GlobalValue::UnnamedAddr::Global);
    // Set the alignment to that of an array items. We will be only loading one
    // value out of it.
    Array->setAlignment(Align(DL.getPrefTypeAlignment(ValueType)));
    Kind = ArrayKind;
  }
  
  Value *SwitchLookupTable::BuildLookup(Value *Index, IRBuilder<> &Builder) {
    switch (Kind) {
    case SingleValueKind:
      return SingleValue;
    case LinearMapKind: {
      // Derive the result value from the input value.
      Value *Result = Builder.CreateIntCast(Index, LinearMultiplier->getType(),
                                            false, "switch.idx.cast");
      if (!LinearMultiplier->isOne())
        Result = Builder.CreateMul(Result, LinearMultiplier, "switch.idx.mult");
      if (!LinearOffset->isZero())
        Result = Builder.CreateAdd(Result, LinearOffset, "switch.offset");
      return Result;
    }
    case BitMapKind: {
      // Type of the bitmap (e.g. i59).
      IntegerType *MapTy = BitMap->getType();
  
      // Cast Index to the same type as the bitmap.
      // Note: The Index is <= the number of elements in the table, so
      // truncating it to the width of the bitmask is safe.
      Value *ShiftAmt = Builder.CreateZExtOrTrunc(Index, MapTy, "switch.cast");
  
      // Multiply the shift amount by the element width.
      ShiftAmt = Builder.CreateMul(
          ShiftAmt, ConstantInt::get(MapTy, BitMapElementTy->getBitWidth()),
          "switch.shiftamt");
  
      // Shift down.
      Value *DownShifted =
          Builder.CreateLShr(BitMap, ShiftAmt, "switch.downshift");
      // Mask off.
      return Builder.CreateTrunc(DownShifted, BitMapElementTy, "switch.masked");
    }
    case ArrayKind: {
      // Make sure the table index will not overflow when treated as signed.
      IntegerType *IT = cast<IntegerType>(Index->getType());
      uint64_t TableSize =
          Array->getInitializer()->getType()->getArrayNumElements();
      if (TableSize > (1ULL << (IT->getBitWidth() - 1)))
        Index = Builder.CreateZExt(
            Index, IntegerType::get(IT->getContext(), IT->getBitWidth() + 1),
            "switch.tableidx.zext");
  
      Value *GEPIndices[] = {Builder.getInt32(0), Index};
      Value *GEP = Builder.CreateInBoundsGEP(Array->getValueType(), Array,
                                             GEPIndices, "switch.gep");
      return Builder.CreateLoad(
          cast<ArrayType>(Array->getValueType())->getElementType(), GEP,
          "switch.load");
    }
    }
    llvm_unreachable("Unknown lookup table kind!");
  }
  
  bool SwitchLookupTable::WouldFitInRegister(const DataLayout &DL,
                                             uint64_t TableSize,
                                             Type *ElementType) {
    auto *IT = dyn_cast<IntegerType>(ElementType);
    if (!IT)
      return false;
    // FIXME: If the type is wider than it needs to be, e.g. i8 but all values
    // are <= 15, we could try to narrow the type.
  
    // Avoid overflow, fitsInLegalInteger uses unsigned int for the width.
    if (TableSize >= UINT_MAX / IT->getBitWidth())
      return false;
    return DL.fitsInLegalInteger(TableSize * IT->getBitWidth());
  }
  
  static bool isTypeLegalForLookupTable(Type *Ty, const TargetTransformInfo &TTI,
                                        const DataLayout &DL) {
    // Allow any legal type.
    if (TTI.isTypeLegal(Ty))
      return true;
  
    auto *IT = dyn_cast<IntegerType>(Ty);
    if (!IT)
      return false;
  
    // Also allow power of 2 integer types that have at least 8 bits and fit in
    // a register. These types are common in frontend languages and targets
    // usually support loads of these types.
    // TODO: We could relax this to any integer that fits in a register and rely
    // on ABI alignment and padding in the table to allow the load to be widened.
    // Or we could widen the constants and truncate the load.
    unsigned BitWidth = IT->getBitWidth();
    return BitWidth >= 8 && isPowerOf2_32(BitWidth) &&
           DL.fitsInLegalInteger(IT->getBitWidth());
  }
  
  /// Determine whether a lookup table should be built for this switch, based on
  /// the number of cases, size of the table, and the types of the results.
  // TODO: We could support larger than legal types by limiting based on the
  // number of loads required and/or table size. If the constants are small we
  // could use smaller table entries and extend after the load.
  static bool
  ShouldBuildLookupTable(SwitchInst *SI, uint64_t TableSize,
                         const TargetTransformInfo &TTI, const DataLayout &DL,
                         const SmallDenseMap<PHINode *, Type *> &ResultTypes) {
    if (SI->getNumCases() > TableSize || TableSize >= UINT64_MAX / 10)
      return false; // TableSize overflowed, or mul below might overflow.
  
    bool AllTablesFitInRegister = true;
    bool HasIllegalType = false;
    for (const auto &I : ResultTypes) {
      Type *Ty = I.second;
  
      // Saturate this flag to true.
      HasIllegalType = HasIllegalType || !isTypeLegalForLookupTable(Ty, TTI, DL);
  
      // Saturate this flag to false.
      AllTablesFitInRegister =
          AllTablesFitInRegister &&
          SwitchLookupTable::WouldFitInRegister(DL, TableSize, Ty);
  
      // If both flags saturate, we're done. NOTE: This *only* works with
      // saturating flags, and all flags have to saturate first due to the
      // non-deterministic behavior of iterating over a dense map.
      if (HasIllegalType && !AllTablesFitInRegister)
        break;
    }
  
    // If each table would fit in a register, we should build it anyway.
    if (AllTablesFitInRegister)
      return true;
  
    // Don't build a table that doesn't fit in-register if it has illegal types.
    if (HasIllegalType)
      return false;
  
    // The table density should be at least 40%. This is the same criterion as for
    // jump tables, see SelectionDAGBuilder::handleJTSwitchCase.
    // FIXME: Find the best cut-off.
    return SI->getNumCases() * 10 >= TableSize * 4;
  }
  
  /// Try to reuse the switch table index compare. Following pattern:
  /// \code
  ///     if (idx < tablesize)
  ///        r = table[idx]; // table does not contain default_value
  ///     else
  ///        r = default_value;
  ///     if (r != default_value)
  ///        ...
  /// \endcode
  /// Is optimized to:
  /// \code
  ///     cond = idx < tablesize;
  ///     if (cond)
  ///        r = table[idx];
  ///     else
  ///        r = default_value;
  ///     if (cond)
  ///        ...
  /// \endcode
  /// Jump threading will then eliminate the second if(cond).
  static void reuseTableCompare(
      User *PhiUser, BasicBlock *PhiBlock, BranchInst *RangeCheckBranch,
      Constant *DefaultValue,
      const SmallVectorImpl<std::pair<ConstantInt *, Constant *>> &Values) {
    ICmpInst *CmpInst = dyn_cast<ICmpInst>(PhiUser);
    if (!CmpInst)
      return;
  
    // We require that the compare is in the same block as the phi so that jump
    // threading can do its work afterwards.
    if (CmpInst->getParent() != PhiBlock)
      return;
  
    Constant *CmpOp1 = dyn_cast<Constant>(CmpInst->getOperand(1));
    if (!CmpOp1)
      return;
  
    Value *RangeCmp = RangeCheckBranch->getCondition();
    Constant *TrueConst = ConstantInt::getTrue(RangeCmp->getType());
    Constant *FalseConst = ConstantInt::getFalse(RangeCmp->getType());
  
    // Check if the compare with the default value is constant true or false.
    Constant *DefaultConst = ConstantExpr::getICmp(CmpInst->getPredicate(),
                                                   DefaultValue, CmpOp1, true);
    if (DefaultConst != TrueConst && DefaultConst != FalseConst)
      return;
  
    // Check if the compare with the case values is distinct from the default
    // compare result.
    for (auto ValuePair : Values) {
      Constant *CaseConst = ConstantExpr::getICmp(CmpInst->getPredicate(),
                                                  ValuePair.second, CmpOp1, true);
      if (!CaseConst || CaseConst == DefaultConst ||
          (CaseConst != TrueConst && CaseConst != FalseConst))
        return;
    }
  
    // Check if the branch instruction dominates the phi node. It's a simple
    // dominance check, but sufficient for our needs.
    // Although this check is invariant in the calling loops, it's better to do it
    // at this late stage. Practically we do it at most once for a switch.
    BasicBlock *BranchBlock = RangeCheckBranch->getParent();
    for (BasicBlock *Pred : predecessors(PhiBlock)) {
      if (Pred != BranchBlock && Pred->getUniquePredecessor() != BranchBlock)
        return;
    }
  
    if (DefaultConst == FalseConst) {
      // The compare yields the same result. We can replace it.
      CmpInst->replaceAllUsesWith(RangeCmp);
      ++NumTableCmpReuses;
    } else {
      // The compare yields the same result, just inverted. We can replace it.
      Value *InvertedTableCmp = BinaryOperator::CreateXor(
          RangeCmp, ConstantInt::get(RangeCmp->getType(), 1), "inverted.cmp",
          RangeCheckBranch);
      CmpInst->replaceAllUsesWith(InvertedTableCmp);
      ++NumTableCmpReuses;
    }
  }
  
  /// If the switch is only used to initialize one or more phi nodes in a common
  /// successor block with different constant values, replace the switch with
  /// lookup tables.
  static bool SwitchToLookupTable(SwitchInst *SI, IRBuilder<> &Builder,
                                  DomTreeUpdater *DTU, const DataLayout &DL,
                                  const TargetTransformInfo &TTI) {
    assert(SI->getNumCases() > 1 && "Degenerate switch?");
  
    BasicBlock *BB = SI->getParent();
    Function *Fn = BB->getParent();
    // Only build lookup table when we have a target that supports it or the
    // attribute is not set.
    if (!TTI.shouldBuildLookupTables() ||
        (Fn->getFnAttribute("no-jump-tables").getValueAsBool()))
      return false;
  
    // FIXME: If the switch is too sparse for a lookup table, perhaps we could
    // split off a dense part and build a lookup table for that.
  
    // FIXME: This creates arrays of GEPs to constant strings, which means each
    // GEP needs a runtime relocation in PIC code. We should just build one big
    // string and lookup indices into that.
  
    // Ignore switches with less than three cases. Lookup tables will not make
    // them faster, so we don't analyze them.
    if (SI->getNumCases() < 3)
      return false;
  
    // Figure out the corresponding result for each case value and phi node in the
    // common destination, as well as the min and max case values.
    assert(!SI->cases().empty());
    SwitchInst::CaseIt CI = SI->case_begin();
    ConstantInt *MinCaseVal = CI->getCaseValue();
    ConstantInt *MaxCaseVal = CI->getCaseValue();
  
    BasicBlock *CommonDest = nullptr;
  
    using ResultListTy = SmallVector<std::pair<ConstantInt *, Constant *>, 4>;
    SmallDenseMap<PHINode *, ResultListTy> ResultLists;
  
    SmallDenseMap<PHINode *, Constant *> DefaultResults;
    SmallDenseMap<PHINode *, Type *> ResultTypes;
    SmallVector<PHINode *, 4> PHIs;
  
    for (SwitchInst::CaseIt E = SI->case_end(); CI != E; ++CI) {
      ConstantInt *CaseVal = CI->getCaseValue();
      if (CaseVal->getValue().slt(MinCaseVal->getValue()))
        MinCaseVal = CaseVal;
      if (CaseVal->getValue().sgt(MaxCaseVal->getValue()))
        MaxCaseVal = CaseVal;
  
      // Resulting value at phi nodes for this case value.
      using ResultsTy = SmallVector<std::pair<PHINode *, Constant *>, 4>;
      ResultsTy Results;
      if (!GetCaseResults(SI, CaseVal, CI->getCaseSuccessor(), &CommonDest,
                          Results, DL, TTI))
        return false;
  
      // Append the result from this case to the list for each phi.
      for (const auto &I : Results) {
        PHINode *PHI = I.first;
        Constant *Value = I.second;
        if (!ResultLists.count(PHI))
          PHIs.push_back(PHI);
        ResultLists[PHI].push_back(std::make_pair(CaseVal, Value));
      }
    }
  
    // Keep track of the result types.
    for (PHINode *PHI : PHIs) {
      ResultTypes[PHI] = ResultLists[PHI][0].second->getType();
    }
  
    uint64_t NumResults = ResultLists[PHIs[0]].size();
    APInt RangeSpread = MaxCaseVal->getValue() - MinCaseVal->getValue();
    uint64_t TableSize = RangeSpread.getLimitedValue() + 1;
    bool TableHasHoles = (NumResults < TableSize);
  
    // If the table has holes, we need a constant result for the default case
    // or a bitmask that fits in a register.
    SmallVector<std::pair<PHINode *, Constant *>, 4> DefaultResultsList;
    bool HasDefaultResults =
        GetCaseResults(SI, nullptr, SI->getDefaultDest(), &CommonDest,
                       DefaultResultsList, DL, TTI);
  
    bool NeedMask = (TableHasHoles && !HasDefaultResults);
    if (NeedMask) {
      // As an extra penalty for the validity test we require more cases.
      if (SI->getNumCases() < 4) // FIXME: Find best threshold value (benchmark).
        return false;
      if (!DL.fitsInLegalInteger(TableSize))
        return false;
    }
  
    for (const auto &I : DefaultResultsList) {
      PHINode *PHI = I.first;
      Constant *Result = I.second;
      DefaultResults[PHI] = Result;
    }
  
    if (!ShouldBuildLookupTable(SI, TableSize, TTI, DL, ResultTypes))
      return false;
  
    std::vector<DominatorTree::UpdateType> Updates;
  
    // Create the BB that does the lookups.
    Module &Mod = *CommonDest->getParent()->getParent();
    BasicBlock *LookupBB = BasicBlock::Create(
        Mod.getContext(), "switch.lookup", CommonDest->getParent(), CommonDest);
  
    // Compute the table index value.
    Builder.SetInsertPoint(SI);
    Value *TableIndex;
    if (MinCaseVal->isNullValue())
      TableIndex = SI->getCondition();
    else
      TableIndex = Builder.CreateSub(SI->getCondition(), MinCaseVal,
                                     "switch.tableidx");
  
    // Compute the maximum table size representable by the integer type we are
    // switching upon.
    unsigned CaseSize = MinCaseVal->getType()->getPrimitiveSizeInBits();
    uint64_t MaxTableSize = CaseSize > 63 ? UINT64_MAX : 1ULL << CaseSize;
    assert(MaxTableSize >= TableSize &&
           "It is impossible for a switch to have more entries than the max "
           "representable value of its input integer type's size.");
  
    // If the default destination is unreachable, or if the lookup table covers
    // all values of the conditional variable, branch directly to the lookup table
    // BB. Otherwise, check that the condition is within the case range.
    const bool DefaultIsReachable =
        !isa<UnreachableInst>(SI->getDefaultDest()->getFirstNonPHIOrDbg());
    const bool GeneratingCoveredLookupTable = (MaxTableSize == TableSize);
    BranchInst *RangeCheckBranch = nullptr;
  
    if (!DefaultIsReachable || GeneratingCoveredLookupTable) {
      Builder.CreateBr(LookupBB);
      if (DTU)
        Updates.push_back({DominatorTree::Insert, BB, LookupBB});
      // Note: We call removeProdecessor later since we need to be able to get the
      // PHI value for the default case in case we're using a bit mask.
    } else {
      Value *Cmp = Builder.CreateICmpULT(
          TableIndex, ConstantInt::get(MinCaseVal->getType(), TableSize));
      RangeCheckBranch =
          Builder.CreateCondBr(Cmp, LookupBB, SI->getDefaultDest());
      if (DTU)
        Updates.push_back({DominatorTree::Insert, BB, LookupBB});
    }
  
    // Populate the BB that does the lookups.
    Builder.SetInsertPoint(LookupBB);
  
    if (NeedMask) {
      // Before doing the lookup, we do the hole check. The LookupBB is therefore
      // re-purposed to do the hole check, and we create a new LookupBB.
      BasicBlock *MaskBB = LookupBB;
      MaskBB->setName("switch.hole_check");
      LookupBB = BasicBlock::Create(Mod.getContext(), "switch.lookup",
                                    CommonDest->getParent(), CommonDest);
  
      // Make the mask's bitwidth at least 8-bit and a power-of-2 to avoid
      // unnecessary illegal types.
      uint64_t TableSizePowOf2 = NextPowerOf2(std::max(7ULL, TableSize - 1ULL));
      APInt MaskInt(TableSizePowOf2, 0);
      APInt One(TableSizePowOf2, 1);
      // Build bitmask; fill in a 1 bit for every case.
      const ResultListTy &ResultList = ResultLists[PHIs[0]];
      for (size_t I = 0, E = ResultList.size(); I != E; ++I) {
        uint64_t Idx = (ResultList[I].first->getValue() - MinCaseVal->getValue())
                           .getLimitedValue();
        MaskInt |= One << Idx;
      }
      ConstantInt *TableMask = ConstantInt::get(Mod.getContext(), MaskInt);
  
      // Get the TableIndex'th bit of the bitmask.
      // If this bit is 0 (meaning hole) jump to the default destination,
      // else continue with table lookup.
      IntegerType *MapTy = TableMask->getType();
      Value *MaskIndex =
          Builder.CreateZExtOrTrunc(TableIndex, MapTy, "switch.maskindex");
      Value *Shifted = Builder.CreateLShr(TableMask, MaskIndex, "switch.shifted");
      Value *LoBit = Builder.CreateTrunc(
          Shifted, Type::getInt1Ty(Mod.getContext()), "switch.lobit");
      Builder.CreateCondBr(LoBit, LookupBB, SI->getDefaultDest());
      if (DTU) {
        Updates.push_back({DominatorTree::Insert, MaskBB, LookupBB});
        Updates.push_back({DominatorTree::Insert, MaskBB, SI->getDefaultDest()});
      }
      Builder.SetInsertPoint(LookupBB);
      AddPredecessorToBlock(SI->getDefaultDest(), MaskBB, BB);
    }
  
    if (!DefaultIsReachable || GeneratingCoveredLookupTable) {
      // We cached PHINodes in PHIs. To avoid accessing deleted PHINodes later,
      // do not delete PHINodes here.
      SI->getDefaultDest()->removePredecessor(BB,
                                              /*KeepOneInputPHIs=*/true);
      if (DTU)
        Updates.push_back({DominatorTree::Delete, BB, SI->getDefaultDest()});
    }
  
    for (PHINode *PHI : PHIs) {
      const ResultListTy &ResultList = ResultLists[PHI];
  
      // If using a bitmask, use any value to fill the lookup table holes.
      Constant *DV = NeedMask ? ResultLists[PHI][0].second : DefaultResults[PHI];
      StringRef FuncName = Fn->getName();
      SwitchLookupTable Table(Mod, TableSize, MinCaseVal, ResultList, DV, DL,
                              FuncName);
  
      Value *Result = Table.BuildLookup(TableIndex, Builder);
  
      // Do a small peephole optimization: re-use the switch table compare if
      // possible.
      if (!TableHasHoles && HasDefaultResults && RangeCheckBranch) {
        BasicBlock *PhiBlock = PHI->getParent();
        // Search for compare instructions which use the phi.
        for (auto *User : PHI->users()) {
          reuseTableCompare(User, PhiBlock, RangeCheckBranch, DV, ResultList);
        }
      }
  
      PHI->addIncoming(Result, LookupBB);
    }
  
    Builder.CreateBr(CommonDest);
    if (DTU)
      Updates.push_back({DominatorTree::Insert, LookupBB, CommonDest});
  
    // Remove the switch.
    SmallPtrSet<BasicBlock *, 8> RemovedSuccessors;
    for (unsigned i = 0, e = SI->getNumSuccessors(); i < e; ++i) {
      BasicBlock *Succ = SI->getSuccessor(i);
  
      if (Succ == SI->getDefaultDest())
        continue;
      Succ->removePredecessor(BB);
      if (DTU && RemovedSuccessors.insert(Succ).second)
        Updates.push_back({DominatorTree::Delete, BB, Succ});
    }
    SI->eraseFromParent();
  
    if (DTU)
      DTU->applyUpdates(Updates);
  
    ++NumLookupTables;
    if (NeedMask)
      ++NumLookupTablesHoles;
    return true;
  }
  
  static bool isSwitchDense(ArrayRef<int64_t> Values) {
    // See also SelectionDAGBuilder::isDense(), which this function was based on.
    uint64_t Diff = (uint64_t)Values.back() - (uint64_t)Values.front();
    uint64_t Range = Diff + 1;
    uint64_t NumCases = Values.size();
    // 40% is the default density for building a jump table in optsize/minsize mode.
    uint64_t MinDensity = 40;
  
    return NumCases * 100 >= Range * MinDensity;
  }
  
  /// Try to transform a switch that has "holes" in it to a contiguous sequence
  /// of cases.
  ///
  /// A switch such as: switch(i) {case 5: case 9: case 13: case 17:} can be
  /// range-reduced to: switch ((i-5) / 4) {case 0: case 1: case 2: case 3:}.
  ///
  /// This converts a sparse switch into a dense switch which allows better
  /// lowering and could also allow transforming into a lookup table.
  static bool ReduceSwitchRange(SwitchInst *SI, IRBuilder<> &Builder,
                                const DataLayout &DL,
                                const TargetTransformInfo &TTI) {
    auto *CondTy = cast<IntegerType>(SI->getCondition()->getType());
    if (CondTy->getIntegerBitWidth() > 64 ||
        !DL.fitsInLegalInteger(CondTy->getIntegerBitWidth()))
      return false;
    // Only bother with this optimization if there are more than 3 switch cases;
    // SDAG will only bother creating jump tables for 4 or more cases.
    if (SI->getNumCases() < 4)
      return false;
  
    // This transform is agnostic to the signedness of the input or case values. We
    // can treat the case values as signed or unsigned. We can optimize more common
    // cases such as a sequence crossing zero {-4,0,4,8} if we interpret case values
    // as signed.
    SmallVector<int64_t,4> Values;
    for (auto &C : SI->cases())
      Values.push_back(C.getCaseValue()->getValue().getSExtValue());
    llvm::sort(Values);
  
    // If the switch is already dense, there's nothing useful to do here.
    if (isSwitchDense(Values))
      return false;
  
    // First, transform the values such that they start at zero and ascend.
    int64_t Base = Values[0];
    for (auto &V : Values)
      V -= (uint64_t)(Base);
  
    // Now we have signed numbers that have been shifted so that, given enough
    // precision, there are no negative values. Since the rest of the transform
    // is bitwise only, we switch now to an unsigned representation.
  
    // This transform can be done speculatively because it is so cheap - it
    // results in a single rotate operation being inserted.
    // FIXME: It's possible that optimizing a switch on powers of two might also
    // be beneficial - flag values are often powers of two and we could use a CLZ
    // as the key function.
  
    // countTrailingZeros(0) returns 64. As Values is guaranteed to have more than
    // one element and LLVM disallows duplicate cases, Shift is guaranteed to be
    // less than 64.
    unsigned Shift = 64;
    for (auto &V : Values)
      Shift = std::min(Shift, countTrailingZeros((uint64_t)V));
    assert(Shift < 64);
    if (Shift > 0)
      for (auto &V : Values)
        V = (int64_t)((uint64_t)V >> Shift);
  
    if (!isSwitchDense(Values))
      // Transform didn't create a dense switch.
      return false;
  
    // The obvious transform is to shift the switch condition right and emit a
    // check that the condition actually cleanly divided by GCD, i.e.
    //   C & (1 << Shift - 1) == 0
    // inserting a new CFG edge to handle the case where it didn't divide cleanly.
    //
    // A cheaper way of doing this is a simple ROTR(C, Shift). This performs the
    // shift and puts the shifted-off bits in the uppermost bits. If any of these
    // are nonzero then the switch condition will be very large and will hit the
    // default case.
  
    auto *Ty = cast<IntegerType>(SI->getCondition()->getType());
    Builder.SetInsertPoint(SI);
    auto *ShiftC = ConstantInt::get(Ty, Shift);
    auto *Sub = Builder.CreateSub(SI->getCondition(), ConstantInt::get(Ty, Base));
    auto *LShr = Builder.CreateLShr(Sub, ShiftC);
    auto *Shl = Builder.CreateShl(Sub, Ty->getBitWidth() - Shift);
    auto *Rot = Builder.CreateOr(LShr, Shl);
    SI->replaceUsesOfWith(SI->getCondition(), Rot);
  
    for (auto Case : SI->cases()) {
      auto *Orig = Case.getCaseValue();
      auto Sub = Orig->getValue() - APInt(Ty->getBitWidth(), Base);
      Case.setValue(
          cast<ConstantInt>(ConstantInt::get(Ty, Sub.lshr(ShiftC->getValue()))));
    }
    return true;
  }
  
  bool SimplifyCFGOpt::simplifySwitch(SwitchInst *SI, IRBuilder<> &Builder) {
    BasicBlock *BB = SI->getParent();
  
    if (isValueEqualityComparison(SI)) {
      // If we only have one predecessor, and if it is a branch on this value,
      // see if that predecessor totally determines the outcome of this switch.
      if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
        if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred, Builder))
          return requestResimplify();
  
      Value *Cond = SI->getCondition();
      if (SelectInst *Select = dyn_cast<SelectInst>(Cond))
        if (SimplifySwitchOnSelect(SI, Select))
          return requestResimplify();
  
      // If the block only contains the switch, see if we can fold the block
      // away into any preds.
      if (SI == &*BB->instructionsWithoutDebug(false).begin())
        if (FoldValueComparisonIntoPredecessors(SI, Builder))
          return requestResimplify();
    }
  
    // Try to transform the switch into an icmp and a branch.
    // The conversion from switch to comparison may lose information on
    // impossible switch values, so disable it early in the pipeline.
    if (Options.ConvertSwitchRangeToICmp && TurnSwitchRangeIntoICmp(SI, Builder))
      return requestResimplify();
  
    // Remove unreachable cases.
    if (eliminateDeadSwitchCases(SI, DTU, Options.AC, DL))
      return requestResimplify();
  
    if (switchToSelect(SI, Builder, DTU, DL, TTI))
      return requestResimplify();
  
    if (Options.ForwardSwitchCondToPhi && ForwardSwitchConditionToPHI(SI))
      return requestResimplify();
  
    // The conversion from switch to lookup tables results in difficult-to-analyze
    // code and makes pruning branches much harder. This is a problem if the
    // switch expression itself can still be restricted as a result of inlining or
    // CVP. Therefore, only apply this transformation during late stages of the
    // optimisation pipeline.
    if (Options.ConvertSwitchToLookupTable &&
        SwitchToLookupTable(SI, Builder, DTU, DL, TTI))
      return requestResimplify();
  
    if (ReduceSwitchRange(SI, Builder, DL, TTI))
      return requestResimplify();
  
    return false;
  }
  
  bool SimplifyCFGOpt::simplifyIndirectBr(IndirectBrInst *IBI) {
    BasicBlock *BB = IBI->getParent();
    bool Changed = false;
  
    // Eliminate redundant destinations.
    SmallPtrSet<Value *, 8> Succs;
    SmallSetVector<BasicBlock *, 8> RemovedSuccs;
    for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
      BasicBlock *Dest = IBI->getDestination(i);
      if (!Dest->hasAddressTaken() || !Succs.insert(Dest).second) {
        if (!Dest->hasAddressTaken())
          RemovedSuccs.insert(Dest);
        Dest->removePredecessor(BB);
        IBI->removeDestination(i);
        --i;
        --e;
        Changed = true;
      }
    }
  
    if (DTU) {
      std::vector<DominatorTree::UpdateType> Updates;
      Updates.reserve(RemovedSuccs.size());
      for (auto *RemovedSucc : RemovedSuccs)
        Updates.push_back({DominatorTree::Delete, BB, RemovedSucc});
      DTU->applyUpdates(Updates);
    }
  
    if (IBI->getNumDestinations() == 0) {
      // If the indirectbr has no successors, change it to unreachable.
      new UnreachableInst(IBI->getContext(), IBI);
      EraseTerminatorAndDCECond(IBI);
      return true;
    }
  
    if (IBI->getNumDestinations() == 1) {
      // If the indirectbr has one successor, change it to a direct branch.
      BranchInst::Create(IBI->getDestination(0), IBI);
      EraseTerminatorAndDCECond(IBI);
      return true;
    }
  
    if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) {
      if (SimplifyIndirectBrOnSelect(IBI, SI))
        return requestResimplify();
    }
    return Changed;
  }
  
  /// Given an block with only a single landing pad and a unconditional branch
  /// try to find another basic block which this one can be merged with.  This
  /// handles cases where we have multiple invokes with unique landing pads, but
  /// a shared handler.
  ///
  /// We specifically choose to not worry about merging non-empty blocks
  /// here.  That is a PRE/scheduling problem and is best solved elsewhere.  In
  /// practice, the optimizer produces empty landing pad blocks quite frequently
  /// when dealing with exception dense code.  (see: instcombine, gvn, if-else
  /// sinking in this file)
  ///
  /// This is primarily a code size optimization.  We need to avoid performing
  /// any transform which might inhibit optimization (such as our ability to
  /// specialize a particular handler via tail commoning).  We do this by not
  /// merging any blocks which require us to introduce a phi.  Since the same
  /// values are flowing through both blocks, we don't lose any ability to
  /// specialize.  If anything, we make such specialization more likely.
  ///
  /// TODO - This transformation could remove entries from a phi in the target
  /// block when the inputs in the phi are the same for the two blocks being
  /// merged.  In some cases, this could result in removal of the PHI entirely.
  static bool TryToMergeLandingPad(LandingPadInst *LPad, BranchInst *BI,
                                   BasicBlock *BB, DomTreeUpdater *DTU) {
    auto Succ = BB->getUniqueSuccessor();
    assert(Succ);
    // If there's a phi in the successor block, we'd likely have to introduce
    // a phi into the merged landing pad block.
    if (isa<PHINode>(*Succ->begin()))
      return false;
  
    for (BasicBlock *OtherPred : predecessors(Succ)) {
      if (BB == OtherPred)
        continue;
      BasicBlock::iterator I = OtherPred->begin();
      LandingPadInst *LPad2 = dyn_cast<LandingPadInst>(I);
      if (!LPad2 || !LPad2->isIdenticalTo(LPad))
        continue;
      for (++I; isa<DbgInfoIntrinsic>(I); ++I)
        ;
      BranchInst *BI2 = dyn_cast<BranchInst>(I);
      if (!BI2 || !BI2->isIdenticalTo(BI))
        continue;
  
      std::vector<DominatorTree::UpdateType> Updates;
  
      // We've found an identical block.  Update our predecessors to take that
      // path instead and make ourselves dead.
      SmallSetVector<BasicBlock *, 16> UniquePreds(pred_begin(BB), pred_end(BB));
      for (BasicBlock *Pred : UniquePreds) {
        InvokeInst *II = cast<InvokeInst>(Pred->getTerminator());
        assert(II->getNormalDest() != BB && II->getUnwindDest() == BB &&
               "unexpected successor");
        II->setUnwindDest(OtherPred);
        if (DTU) {
          Updates.push_back({DominatorTree::Insert, Pred, OtherPred});
          Updates.push_back({DominatorTree::Delete, Pred, BB});
        }
      }
  
      // The debug info in OtherPred doesn't cover the merged control flow that
      // used to go through BB.  We need to delete it or update it.
      for (Instruction &Inst : llvm::make_early_inc_range(*OtherPred))
        if (isa<DbgInfoIntrinsic>(Inst))
          Inst.eraseFromParent();
  
      SmallSetVector<BasicBlock *, 16> UniqueSuccs(succ_begin(BB), succ_end(BB));
      for (BasicBlock *Succ : UniqueSuccs) {
        Succ->removePredecessor(BB);
        if (DTU)
          Updates.push_back({DominatorTree::Delete, BB, Succ});
      }
  
      IRBuilder<> Builder(BI);
      Builder.CreateUnreachable();
      BI->eraseFromParent();
      if (DTU)
        DTU->applyUpdates(Updates);
      return true;
    }
    return false;
  }
  
  bool SimplifyCFGOpt::simplifyBranch(BranchInst *Branch, IRBuilder<> &Builder) {
    return Branch->isUnconditional() ? simplifyUncondBranch(Branch, Builder)
                                     : simplifyCondBranch(Branch, Builder);
  }
  
  bool SimplifyCFGOpt::simplifyUncondBranch(BranchInst *BI,
                                            IRBuilder<> &Builder) {
    BasicBlock *BB = BI->getParent();
    BasicBlock *Succ = BI->getSuccessor(0);
  
    // If the Terminator is the only non-phi instruction, simplify the block.
    // If LoopHeader is provided, check if the block or its successor is a loop
    // header. (This is for early invocations before loop simplify and
    // vectorization to keep canonical loop forms for nested loops. These blocks
    // can be eliminated when the pass is invoked later in the back-end.)
    // Note that if BB has only one predecessor then we do not introduce new
    // backedge, so we can eliminate BB.
    bool NeedCanonicalLoop =
        Options.NeedCanonicalLoop &&
        (!LoopHeaders.empty() && BB->hasNPredecessorsOrMore(2) &&
         (is_contained(LoopHeaders, BB) || is_contained(LoopHeaders, Succ)));
    BasicBlock::iterator I = BB->getFirstNonPHIOrDbg(true)->getIterator();
    if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() &&
        !NeedCanonicalLoop && TryToSimplifyUncondBranchFromEmptyBlock(BB, DTU))
      return true;
  
    // If the only instruction in the block is a seteq/setne comparison against a
    // constant, try to simplify the block.
    if (ICmpInst *ICI = dyn_cast<ICmpInst>(I))
      if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) {
        for (++I; isa<DbgInfoIntrinsic>(I); ++I)
          ;
        if (I->isTerminator() &&
            tryToSimplifyUncondBranchWithICmpInIt(ICI, Builder))
          return true;
      }
  
    // See if we can merge an empty landing pad block with another which is
    // equivalent.
    if (LandingPadInst *LPad = dyn_cast<LandingPadInst>(I)) {
      for (++I; isa<DbgInfoIntrinsic>(I); ++I)
        ;
      if (I->isTerminator() && TryToMergeLandingPad(LPad, BI, BB, DTU))
        return true;
    }
  
    // If this basic block is ONLY a compare and a branch, and if a predecessor
    // branches to us and our successor, fold the comparison into the
    // predecessor and use logical operations to update the incoming value
    // for PHI nodes in common successor.
    if (FoldBranchToCommonDest(BI, DTU, /*MSSAU=*/nullptr, &TTI,
                               Options.BonusInstThreshold))
      return requestResimplify();
    return false;
  }
  
  static BasicBlock *allPredecessorsComeFromSameSource(BasicBlock *BB) {
    BasicBlock *PredPred = nullptr;
    for (auto *P : predecessors(BB)) {
      BasicBlock *PPred = P->getSinglePredecessor();
      if (!PPred || (PredPred && PredPred != PPred))
        return nullptr;
      PredPred = PPred;
    }
    return PredPred;
  }
  
  bool SimplifyCFGOpt::simplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) {
    assert(
        !isa<ConstantInt>(BI->getCondition()) &&
        BI->getSuccessor(0) != BI->getSuccessor(1) &&
        "Tautological conditional branch should have been eliminated already.");
  
    BasicBlock *BB = BI->getParent();
    if (!Options.SimplifyCondBranch)
      return false;
  
    // Conditional branch
    if (isValueEqualityComparison(BI)) {
      // If we only have one predecessor, and if it is a branch on this value,
      // see if that predecessor totally determines the outcome of this
      // switch.
      if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
        if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred, Builder))
          return requestResimplify();
  
      // This block must be empty, except for the setcond inst, if it exists.
      // Ignore dbg and pseudo intrinsics.
      auto I = BB->instructionsWithoutDebug(true).begin();
      if (&*I == BI) {
        if (FoldValueComparisonIntoPredecessors(BI, Builder))
          return requestResimplify();
      } else if (&*I == cast<Instruction>(BI->getCondition())) {
        ++I;
        if (&*I == BI && FoldValueComparisonIntoPredecessors(BI, Builder))
          return requestResimplify();
      }
    }
  
    // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction.
    if (SimplifyBranchOnICmpChain(BI, Builder, DL))
      return true;
  
    // If this basic block has dominating predecessor blocks and the dominating
    // blocks' conditions imply BI's condition, we know the direction of BI.
    Optional<bool> Imp = isImpliedByDomCondition(BI->getCondition(), BI, DL);
    if (Imp) {
      // Turn this into a branch on constant.
      auto *OldCond = BI->getCondition();
      ConstantInt *TorF = *Imp ? ConstantInt::getTrue(BB->getContext())
                               : ConstantInt::getFalse(BB->getContext());
      BI->setCondition(TorF);
      RecursivelyDeleteTriviallyDeadInstructions(OldCond);
      return requestResimplify();
    }
  
    // If this basic block is ONLY a compare and a branch, and if a predecessor
    // branches to us and one of our successors, fold the comparison into the
    // predecessor and use logical operations to pick the right destination.
    if (FoldBranchToCommonDest(BI, DTU, /*MSSAU=*/nullptr, &TTI,
                               Options.BonusInstThreshold))
      return requestResimplify();
  
    // We have a conditional branch to two blocks that are only reachable
    // from BI.  We know that the condbr dominates the two blocks, so see if
    // there is any identical code in the "then" and "else" blocks.  If so, we
    // can hoist it up to the branching block.
    if (BI->getSuccessor(0)->getSinglePredecessor()) {
      if (BI->getSuccessor(1)->getSinglePredecessor()) {
        if (HoistCommon &&
            HoistThenElseCodeToIf(BI, TTI, !Options.HoistCommonInsts))
          return requestResimplify();
      } else {
        // If Successor #1 has multiple preds, we may be able to conditionally
        // execute Successor #0 if it branches to Successor #1.
        Instruction *Succ0TI = BI->getSuccessor(0)->getTerminator();
        if (Succ0TI->getNumSuccessors() == 1 &&
            Succ0TI->getSuccessor(0) == BI->getSuccessor(1))
          if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0), TTI))
            return requestResimplify();
      }
    } else if (BI->getSuccessor(1)->getSinglePredecessor()) {
      // If Successor #0 has multiple preds, we may be able to conditionally
      // execute Successor #1 if it branches to Successor #0.
      Instruction *Succ1TI = BI->getSuccessor(1)->getTerminator();
      if (Succ1TI->getNumSuccessors() == 1 &&
          Succ1TI->getSuccessor(0) == BI->getSuccessor(0))
        if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1), TTI))
          return requestResimplify();
    }
  
    // If this is a branch on a phi node in the current block, thread control
    // through this block if any PHI node entries are constants.
    if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
      if (PN->getParent() == BI->getParent())
        if (FoldCondBranchOnPHI(BI, DTU, DL, Options.AC))
          return requestResimplify();
  
    // Scan predecessor blocks for conditional branches.
    for (BasicBlock *Pred : predecessors(BB))
      if (BranchInst *PBI = dyn_cast<BranchInst>(Pred->getTerminator()))
        if (PBI != BI && PBI->isConditional())
          if (SimplifyCondBranchToCondBranch(PBI, BI, DTU, DL, TTI))
            return requestResimplify();
  
    // Look for diamond patterns.
    if (MergeCondStores)
      if (BasicBlock *PrevBB = allPredecessorsComeFromSameSource(BB))
        if (BranchInst *PBI = dyn_cast<BranchInst>(PrevBB->getTerminator()))
          if (PBI != BI && PBI->isConditional())
            if (mergeConditionalStores(PBI, BI, DTU, DL, TTI))
              return requestResimplify();
  
    return false;
  }
  
  /// Check if passing a value to an instruction will cause undefined behavior.
  static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I, bool PtrValueMayBeModified) {
    Constant *C = dyn_cast<Constant>(V);
    if (!C)
      return false;
  
    if (I->use_empty())
      return false;
  
    if (C->isNullValue() || isa<UndefValue>(C)) {
      // Only look at the first use, avoid hurting compile time with long uselists
      auto *Use = cast<Instruction>(*I->user_begin());
      // Bail out if Use is not in the same BB as I or Use == I or Use comes
      // before I in the block. The latter two can be the case if Use is a PHI
      // node.
      if (Use->getParent() != I->getParent() || Use == I || Use->comesBefore(I))
        return false;
  
      // Now make sure that there are no instructions in between that can alter
      // control flow (eg. calls)
      auto InstrRange =
          make_range(std::next(I->getIterator()), Use->getIterator());
      if (any_of(InstrRange, [](Instruction &I) {
            return !isGuaranteedToTransferExecutionToSuccessor(&I);
          }))
        return false;
  
      // Look through GEPs. A load from a GEP derived from NULL is still undefined
      if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Use))
        if (GEP->getPointerOperand() == I) {
          if (!GEP->isInBounds() || !GEP->hasAllZeroIndices())
            PtrValueMayBeModified = true;
          return passingValueIsAlwaysUndefined(V, GEP, PtrValueMayBeModified);
        }
  
      // Look through bitcasts.
      if (BitCastInst *BC = dyn_cast<BitCastInst>(Use))
        return passingValueIsAlwaysUndefined(V, BC, PtrValueMayBeModified);
  
      // Load from null is undefined.
      if (LoadInst *LI = dyn_cast<LoadInst>(Use))
        if (!LI->isVolatile())
          return !NullPointerIsDefined(LI->getFunction(),
                                       LI->getPointerAddressSpace());
  
      // Store to null is undefined.
      if (StoreInst *SI = dyn_cast<StoreInst>(Use))
        if (!SI->isVolatile())
          return (!NullPointerIsDefined(SI->getFunction(),
                                        SI->getPointerAddressSpace())) &&
                 SI->getPointerOperand() == I;
  
      if (auto *CB = dyn_cast<CallBase>(Use)) {
        if (C->isNullValue() && NullPointerIsDefined(CB->getFunction()))
          return false;
        // A call to null is undefined.
        if (CB->getCalledOperand() == I)
          return true;
  
        if (C->isNullValue()) {
          for (const llvm::Use &Arg : CB->args())
            if (Arg == I) {
              unsigned ArgIdx = CB->getArgOperandNo(&Arg);
              if (CB->isPassingUndefUB(ArgIdx) &&
                  CB->paramHasAttr(ArgIdx, Attribute::NonNull)) {
                // Passing null to a nonnnull+noundef argument is undefined.
                return !PtrValueMayBeModified;
              }
            }
        } else if (isa<UndefValue>(C)) {
          // Passing undef to a noundef argument is undefined.
          for (const llvm::Use &Arg : CB->args())
            if (Arg == I) {
              unsigned ArgIdx = CB->getArgOperandNo(&Arg);
              if (CB->isPassingUndefUB(ArgIdx)) {
                // Passing undef to a noundef argument is undefined.
                return true;
              }
            }
        }
      }
    }
    return false;
  }
  
  /// If BB has an incoming value that will always trigger undefined behavior
  /// (eg. null pointer dereference), remove the branch leading here.
  static bool removeUndefIntroducingPredecessor(BasicBlock *BB,
                                                DomTreeUpdater *DTU) {
    for (PHINode &PHI : BB->phis())
      for (unsigned i = 0, e = PHI.getNumIncomingValues(); i != e; ++i)
        if (passingValueIsAlwaysUndefined(PHI.getIncomingValue(i), &PHI)) {
          BasicBlock *Predecessor = PHI.getIncomingBlock(i);
          Instruction *T = Predecessor->getTerminator();
          IRBuilder<> Builder(T);
          if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
            BB->removePredecessor(Predecessor);
            // Turn uncoditional branches into unreachables and remove the dead
            // destination from conditional branches.
            if (BI->isUnconditional())
              Builder.CreateUnreachable();
            else {
              // Preserve guarding condition in assume, because it might not be
              // inferrable from any dominating condition.
              Value *Cond = BI->getCondition();
              if (BI->getSuccessor(0) == BB)
                Builder.CreateAssumption(Builder.CreateNot(Cond));
              else
                Builder.CreateAssumption(Cond);
              Builder.CreateBr(BI->getSuccessor(0) == BB ? BI->getSuccessor(1)
                                                         : BI->getSuccessor(0));
            }
            BI->eraseFromParent();
            if (DTU)
              DTU->applyUpdates({{DominatorTree::Delete, Predecessor, BB}});
            return true;
          } else if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) {
            // Redirect all branches leading to UB into
            // a newly created unreachable block.
            BasicBlock *Unreachable = BasicBlock::Create(
                Predecessor->getContext(), "unreachable", BB->getParent(), BB);
            Builder.SetInsertPoint(Unreachable);
            // The new block contains only one instruction: Unreachable
            Builder.CreateUnreachable();
            for (auto &Case : SI->cases())
              if (Case.getCaseSuccessor() == BB) {
                BB->removePredecessor(Predecessor);
                Case.setSuccessor(Unreachable);
              }
            if (SI->getDefaultDest() == BB) {
              BB->removePredecessor(Predecessor);
              SI->setDefaultDest(Unreachable);
            }
  
            if (DTU)
              DTU->applyUpdates(
                  { { DominatorTree::Insert, Predecessor, Unreachable },
                    { DominatorTree::Delete, Predecessor, BB } });
            return true;
          }
        }
  
    return false;
  }
  
  bool SimplifyCFGOpt::simplifyOnce(BasicBlock *BB) {
    bool Changed = false;
  
    assert(BB && BB->getParent() && "Block not embedded in function!");
    assert(BB->getTerminator() && "Degenerate basic block encountered!");
  
    // Remove basic blocks that have no predecessors (except the entry block)...
    // or that just have themself as a predecessor.  These are unreachable.
    if ((pred_empty(BB) && BB != &BB->getParent()->getEntryBlock()) ||
        BB->getSinglePredecessor() == BB) {
      LLVM_DEBUG(dbgs() << "Removing BB: \n" << *BB);
      DeleteDeadBlock(BB, DTU);
      return true;
    }
  
    // Check to see if we can constant propagate this terminator instruction
    // away...
    Changed |= ConstantFoldTerminator(BB, /*DeleteDeadConditions=*/true,
                                      /*TLI=*/nullptr, DTU);
  
    // Check for and eliminate duplicate PHI nodes in this block.
    Changed |= EliminateDuplicatePHINodes(BB);
  
    // Check for and remove branches that will always cause undefined behavior.
    if (removeUndefIntroducingPredecessor(BB, DTU))
      return requestResimplify();
  
    // Merge basic blocks into their predecessor if there is only one distinct
    // pred, and if there is only one distinct successor of the predecessor, and
    // if there are no PHI nodes.
    if (MergeBlockIntoPredecessor(BB, DTU))
      return true;
  
    if (SinkCommon && Options.SinkCommonInsts)
      if (SinkCommonCodeFromPredecessors(BB, DTU) ||
          MergeCompatibleInvokes(BB, DTU)) {
        // SinkCommonCodeFromPredecessors() does not automatically CSE PHI's,
        // so we may now how duplicate PHI's.
        // Let's rerun EliminateDuplicatePHINodes() first,
        // before FoldTwoEntryPHINode() potentially converts them into select's,
        // after which we'd need a whole EarlyCSE pass run to cleanup them.
        return true;
      }
  
    IRBuilder<> Builder(BB);
  
    if (Options.FoldTwoEntryPHINode) {
      // If there is a trivial two-entry PHI node in this basic block, and we can
      // eliminate it, do so now.
      if (auto *PN = dyn_cast<PHINode>(BB->begin()))
        if (PN->getNumIncomingValues() == 2)
          if (FoldTwoEntryPHINode(PN, TTI, DTU, DL))
            return true;
    }
  
    Instruction *Terminator = BB->getTerminator();
    Builder.SetInsertPoint(Terminator);
    switch (Terminator->getOpcode()) {
    case Instruction::Br:
      Changed |= simplifyBranch(cast<BranchInst>(Terminator), Builder);
      break;
    case Instruction::Resume:
      Changed |= simplifyResume(cast<ResumeInst>(Terminator), Builder);
      break;
    case Instruction::CleanupRet:
      Changed |= simplifyCleanupReturn(cast<CleanupReturnInst>(Terminator));
      break;
    case Instruction::Switch:
      Changed |= simplifySwitch(cast<SwitchInst>(Terminator), Builder);
      break;
    case Instruction::Unreachable:
      Changed |= simplifyUnreachable(cast<UnreachableInst>(Terminator));
      break;
    case Instruction::IndirectBr:
      Changed |= simplifyIndirectBr(cast<IndirectBrInst>(Terminator));
      break;
    }
  
    return Changed;
  }
  
  bool SimplifyCFGOpt::run(BasicBlock *BB) {
    bool Changed = false;
  
    // Repeated simplify BB as long as resimplification is requested.
    do {
      Resimplify = false;
  
      // Perform one round of simplifcation. Resimplify flag will be set if
      // another iteration is requested.
      Changed |= simplifyOnce(BB);
    } while (Resimplify);
  
    return Changed;
  }
  
  bool llvm::simplifyCFG(BasicBlock *BB, const TargetTransformInfo &TTI,
                         DomTreeUpdater *DTU, const SimplifyCFGOptions &Options,
                         ArrayRef<WeakVH> LoopHeaders) {
    return SimplifyCFGOpt(TTI, DTU, BB->getModule()->getDataLayout(), LoopHeaders,
                          Options)
        .run(BB);
  }
  