text: //===-- LICM.cpp - Loop Invariant Code Motion Pass ------------------------===//
  //
  // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  // See https://llvm.org/LICENSE.txt for license information.
  // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
  //
  //===----------------------------------------------------------------------===//
  //
  // This pass performs loop invariant code motion, attempting to remove as much
  // code from the body of a loop as possible.  It does this by either hoisting
  // code into the preheader block, or by sinking code to the exit blocks if it is
  // safe.  This pass also promotes must-aliased memory locations in the loop to
  // live in registers, thus hoisting and sinking "invariant" loads and stores.
  //
  // Hoisting operations out of loops is a canonicalization transform.  It
  // enables and simplifies subsequent optimizations in the middle-end.
  // Rematerialization of hoisted instructions to reduce register pressure is the
  // responsibility of the back-end, which has more accurate information about
  // register pressure and also handles other optimizations than LICM that
  // increase live-ranges.
  //
  // This pass uses alias analysis for two purposes:
  //
  //  1. Moving loop invariant loads and calls out of loops.  If we can determine
  //     that a load or call inside of a loop never aliases anything stored to,
  //     we can hoist it or sink it like any other instruction.
  //  2. Scalar Promotion of Memory - If there is a store instruction inside of
  //     the loop, we try to move the store to happen AFTER the loop instead of
  //     inside of the loop.  This can only happen if a few conditions are true:
  //       A. The pointer stored through is loop invariant
  //       B. There are no stores or loads in the loop which _may_ alias the
  //          pointer.  There are no calls in the loop which mod/ref the pointer.
  //     If these conditions are true, we can promote the loads and stores in the
  //     loop of the pointer to use a temporary alloca'd variable.  We then use
  //     the SSAUpdater to construct the appropriate SSA form for the value.
  //
  //===----------------------------------------------------------------------===//
  
  #include "llvm/Transforms/Scalar/LICM.h"
  #include "llvm/ADT/SetOperations.h"
  #include "llvm/ADT/Statistic.h"
  #include "llvm/Analysis/AliasAnalysis.h"
  #include "llvm/Analysis/AliasSetTracker.h"
  #include "llvm/Analysis/BasicAliasAnalysis.h"
  #include "llvm/Analysis/BlockFrequencyInfo.h"
  #include "llvm/Analysis/CaptureTracking.h"
  #include "llvm/Analysis/ConstantFolding.h"
  #include "llvm/Analysis/GlobalsModRef.h"
  #include "llvm/Analysis/GuardUtils.h"
  #include "llvm/Analysis/LazyBlockFrequencyInfo.h"
  #include "llvm/Analysis/Loads.h"
  #include "llvm/Analysis/LoopInfo.h"
  #include "llvm/Analysis/LoopIterator.h"
  #include "llvm/Analysis/LoopPass.h"
  #include "llvm/Analysis/MemoryBuiltins.h"
  #include "llvm/Analysis/MemorySSA.h"
  #include "llvm/Analysis/MemorySSAUpdater.h"
  #include "llvm/Analysis/MustExecute.h"
  #include "llvm/Analysis/OptimizationRemarkEmitter.h"
  #include "llvm/Analysis/ScalarEvolution.h"
  #include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
  #include "llvm/Analysis/TargetLibraryInfo.h"
  #include "llvm/Analysis/ValueTracking.h"
  #include "llvm/IR/CFG.h"
  #include "llvm/IR/Constants.h"
  #include "llvm/IR/DataLayout.h"
  #include "llvm/IR/DebugInfoMetadata.h"
  #include "llvm/IR/DerivedTypes.h"
  #include "llvm/IR/Dominators.h"
  #include "llvm/IR/Instructions.h"
  #include "llvm/IR/IntrinsicInst.h"
  #include "llvm/IR/LLVMContext.h"
  #include "llvm/IR/Metadata.h"
  #include "llvm/IR/PatternMatch.h"
  #include "llvm/IR/PredIteratorCache.h"
  #include "llvm/InitializePasses.h"
  #include "llvm/Support/CommandLine.h"
  #include "llvm/Support/Debug.h"
  #include "llvm/Support/raw_ostream.h"
  #include "llvm/Transforms/Scalar.h"
  #include "llvm/Transforms/Scalar/LoopPassManager.h"
  #include "llvm/Transforms/Utils/AssumeBundleBuilder.h"
  #include "llvm/Transforms/Utils/BasicBlockUtils.h"
  #include "llvm/Transforms/Utils/Local.h"
  #include "llvm/Transforms/Utils/LoopUtils.h"
  #include "llvm/Transforms/Utils/SSAUpdater.h"
  #include <algorithm>
  #include <utility>
  using namespace llvm;
  
  #define DEBUG_TYPE "licm"
  
  STATISTIC(NumCreatedBlocks, "Number of blocks created");
  STATISTIC(NumClonedBranches, "Number of branches cloned");
  STATISTIC(NumSunk, "Number of instructions sunk out of loop");
  STATISTIC(NumHoisted, "Number of instructions hoisted out of loop");
  STATISTIC(NumMovedLoads, "Number of load insts hoisted or sunk");
  STATISTIC(NumMovedCalls, "Number of call insts hoisted or sunk");
  STATISTIC(NumPromoted, "Number of memory locations promoted to registers");
  
  /// Memory promotion is enabled by default.
  static cl::opt<bool>
      DisablePromotion("disable-licm-promotion", cl::Hidden, cl::init(false),
                       cl::desc("Disable memory promotion in LICM pass"));
  
  static cl::opt<bool> ControlFlowHoisting(
      "licm-control-flow-hoisting", cl::Hidden, cl::init(false),
      cl::desc("Enable control flow (and PHI) hoisting in LICM"));
  
  static cl::opt<unsigned> HoistSinkColdnessThreshold(
      "licm-coldness-threshold", cl::Hidden, cl::init(4),
      cl::desc("Relative coldness Threshold of hoisting/sinking destination "
               "block for LICM to be considered beneficial"));
  
  static cl::opt<uint32_t> MaxNumUsesTraversed(
      "licm-max-num-uses-traversed", cl::Hidden, cl::init(8),
      cl::desc("Max num uses visited for identifying load "
               "invariance in loop using invariant start (default = 8)"));
  
  // Default value of zero implies we use the regular alias set tracker mechanism
  // instead of the cross product using AA to identify aliasing of the memory
  // location we are interested in.
  static cl::opt<int>
  LICMN2Theshold("licm-n2-threshold", cl::Hidden, cl::init(0),
                 cl::desc("How many instruction to cross product using AA"));
  
  // Experimental option to allow imprecision in LICM in pathological cases, in
  // exchange for faster compile. This is to be removed if MemorySSA starts to
  // address the same issue. This flag applies only when LICM uses MemorySSA
  // instead on AliasSetTracker. LICM calls MemorySSAWalker's
  // getClobberingMemoryAccess, up to the value of the Cap, getting perfect
  // accuracy. Afterwards, LICM will call into MemorySSA's getDefiningAccess,
  // which may not be precise, since optimizeUses is capped. The result is
  // correct, but we may not get as "far up" as possible to get which access is
  // clobbering the one queried.
  cl::opt<unsigned> llvm::SetLicmMssaOptCap(
      "licm-mssa-optimization-cap", cl::init(100), cl::Hidden,
      cl::desc("Enable imprecision in LICM in pathological cases, in exchange "
               "for faster compile. Caps the MemorySSA clobbering calls."));
  
  // Experimentally, memory promotion carries less importance than sinking and
  // hoisting. Limit when we do promotion when using MemorySSA, in order to save
  // compile time.
  cl::opt<unsigned> llvm::SetLicmMssaNoAccForPromotionCap(
      "licm-mssa-max-acc-promotion", cl::init(250), cl::Hidden,
      cl::desc("[LICM & MemorySSA] When MSSA in LICM is disabled, this has no "
               "effect. When MSSA in LICM is enabled, then this is the maximum "
               "number of accesses allowed to be present in a loop in order to "
               "enable memory promotion."));
  
  static bool inSubLoop(BasicBlock *BB, Loop *CurLoop, LoopInfo *LI);
  static bool isNotUsedOrFreeInLoop(const Instruction &I, const Loop *CurLoop,
                                    const LoopSafetyInfo *SafetyInfo,
                                    TargetTransformInfo *TTI, bool &FreeInLoop);
  static void hoist(Instruction &I, const DominatorTree *DT, const Loop *CurLoop,
                    BasicBlock *Dest, ICFLoopSafetyInfo *SafetyInfo,
                    MemorySSAUpdater *MSSAU, ScalarEvolution *SE,
                    OptimizationRemarkEmitter *ORE);
  static bool sink(Instruction &I, LoopInfo *LI, DominatorTree *DT,
                   BlockFrequencyInfo *BFI, const Loop *CurLoop,
                   ICFLoopSafetyInfo *SafetyInfo, MemorySSAUpdater *MSSAU,
                   OptimizationRemarkEmitter *ORE);
  static bool isSafeToExecuteUnconditionally(Instruction &Inst,
                                             const DominatorTree *DT,
                                             const Loop *CurLoop,
                                             const LoopSafetyInfo *SafetyInfo,
                                             OptimizationRemarkEmitter *ORE,
                                             const Instruction *CtxI = nullptr);
  static bool pointerInvalidatedByLoop(MemoryLocation MemLoc,
                                       AliasSetTracker *CurAST, Loop *CurLoop,
                                       AAResults *AA);
  static bool pointerInvalidatedByLoopWithMSSA(MemorySSA *MSSA, MemoryUse *MU,
                                               Loop *CurLoop, Instruction &I,
                                               SinkAndHoistLICMFlags &Flags);
  static bool pointerInvalidatedByBlockWithMSSA(BasicBlock &BB, MemorySSA &MSSA,
                                                MemoryUse &MU);
  static Instruction *cloneInstructionInExitBlock(
      Instruction &I, BasicBlock &ExitBlock, PHINode &PN, const LoopInfo *LI,
      const LoopSafetyInfo *SafetyInfo, MemorySSAUpdater *MSSAU);
  
  static void eraseInstruction(Instruction &I, ICFLoopSafetyInfo &SafetyInfo,
                               AliasSetTracker *AST, MemorySSAUpdater *MSSAU);
  
  static void moveInstructionBefore(Instruction &I, Instruction &Dest,
                                    ICFLoopSafetyInfo &SafetyInfo,
                                    MemorySSAUpdater *MSSAU, ScalarEvolution *SE);
  
  namespace {
  struct LoopInvariantCodeMotion {
    bool runOnLoop(Loop *L, AAResults *AA, LoopInfo *LI, DominatorTree *DT,
                   BlockFrequencyInfo *BFI, TargetLibraryInfo *TLI,
                   TargetTransformInfo *TTI, ScalarEvolution *SE, MemorySSA *MSSA,
                   OptimizationRemarkEmitter *ORE);
  
    LoopInvariantCodeMotion(unsigned LicmMssaOptCap,
                            unsigned LicmMssaNoAccForPromotionCap)
        : LicmMssaOptCap(LicmMssaOptCap),
          LicmMssaNoAccForPromotionCap(LicmMssaNoAccForPromotionCap) {}
  
  private:
    unsigned LicmMssaOptCap;
    unsigned LicmMssaNoAccForPromotionCap;
  
    std::unique_ptr<AliasSetTracker>
    collectAliasInfoForLoop(Loop *L, LoopInfo *LI, AAResults *AA);
    std::unique_ptr<AliasSetTracker>
    collectAliasInfoForLoopWithMSSA(Loop *L, AAResults *AA,
                                    MemorySSAUpdater *MSSAU);
  };
  
  struct LegacyLICMPass : public LoopPass {
    static char ID; // Pass identification, replacement for typeid
    LegacyLICMPass(
        unsigned LicmMssaOptCap = SetLicmMssaOptCap,
        unsigned LicmMssaNoAccForPromotionCap = SetLicmMssaNoAccForPromotionCap)
        : LoopPass(ID), LICM(LicmMssaOptCap, LicmMssaNoAccForPromotionCap) {
      initializeLegacyLICMPassPass(*PassRegistry::getPassRegistry());
    }
  
    bool runOnLoop(Loop *L, LPPassManager &LPM) override {
      if (skipLoop(L))
        return false;
  
      LLVM_DEBUG(dbgs() << "Perform LICM on Loop with header at block "
                        << L->getHeader()->getNameOrAsOperand() << "\n");
  
      auto *SE = getAnalysisIfAvailable<ScalarEvolutionWrapperPass>();
      MemorySSA *MSSA = EnableMSSALoopDependency
                            ? (&getAnalysis<MemorySSAWrapperPass>().getMSSA())
                            : nullptr;
      bool hasProfileData = L->getHeader()->getParent()->hasProfileData();
      BlockFrequencyInfo *BFI =
          hasProfileData ? &getAnalysis<LazyBlockFrequencyInfoPass>().getBFI()
                         : nullptr;
      // For the old PM, we can't use OptimizationRemarkEmitter as an analysis
      // pass. Function analyses need to be preserved across loop transformations
      // but ORE cannot be preserved (see comment before the pass definition).
      OptimizationRemarkEmitter ORE(L->getHeader()->getParent());
      return LICM.runOnLoop(
          L, &getAnalysis<AAResultsWrapperPass>().getAAResults(),
          &getAnalysis<LoopInfoWrapperPass>().getLoopInfo(),
          &getAnalysis<DominatorTreeWrapperPass>().getDomTree(), BFI,
          &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(
              *L->getHeader()->getParent()),
          &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(
              *L->getHeader()->getParent()),
          SE ? &SE->getSE() : nullptr, MSSA, &ORE);
    }
  
    /// This transformation requires natural loop information & requires that
    /// loop preheaders be inserted into the CFG...
    ///
    void getAnalysisUsage(AnalysisUsage &AU) const override {
      AU.addPreserved<DominatorTreeWrapperPass>();
      AU.addPreserved<LoopInfoWrapperPass>();
      AU.addRequired<TargetLibraryInfoWrapperPass>();
      if (EnableMSSALoopDependency) {
        AU.addRequired<MemorySSAWrapperPass>();
        AU.addPreserved<MemorySSAWrapperPass>();
      }
      AU.addRequired<TargetTransformInfoWrapperPass>();
      getLoopAnalysisUsage(AU);
      LazyBlockFrequencyInfoPass::getLazyBFIAnalysisUsage(AU);
      AU.addPreserved<LazyBlockFrequencyInfoPass>();
      AU.addPreserved<LazyBranchProbabilityInfoPass>();
    }
  
  private:
    LoopInvariantCodeMotion LICM;
  };
  } // namespace
  
  PreservedAnalyses LICMPass::run(Loop &L, LoopAnalysisManager &AM,
                                  LoopStandardAnalysisResults &AR, LPMUpdater &) {
    // For the new PM, we also can't use OptimizationRemarkEmitter as an analysis
    // pass.  Function analyses need to be preserved across loop transformations
    // but ORE cannot be preserved (see comment before the pass definition).
    OptimizationRemarkEmitter ORE(L.getHeader()->getParent());
  
    LoopInvariantCodeMotion LICM(LicmMssaOptCap, LicmMssaNoAccForPromotionCap);
    if (!LICM.runOnLoop(&L, &AR.AA, &AR.LI, &AR.DT, AR.BFI, &AR.TLI, &AR.TTI,
                        &AR.SE, AR.MSSA, &ORE))
      return PreservedAnalyses::all();
  
    auto PA = getLoopPassPreservedAnalyses();
  
    PA.preserve<DominatorTreeAnalysis>();
    PA.preserve<LoopAnalysis>();
    if (AR.MSSA)
      PA.preserve<MemorySSAAnalysis>();
  
    return PA;
  }
  
  char LegacyLICMPass::ID = 0;
  INITIALIZE_PASS_BEGIN(LegacyLICMPass, "licm", "Loop Invariant Code Motion",
                        false, false)
  INITIALIZE_PASS_DEPENDENCY(LoopPass)
  INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
  INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
  INITIALIZE_PASS_DEPENDENCY(MemorySSAWrapperPass)
  INITIALIZE_PASS_DEPENDENCY(LazyBFIPass)
  INITIALIZE_PASS_END(LegacyLICMPass, "licm", "Loop Invariant Code Motion", false,
                      false)
  
  Pass *llvm::createLICMPass() { return new LegacyLICMPass(); }
  Pass *llvm::createLICMPass(unsigned LicmMssaOptCap,
                             unsigned LicmMssaNoAccForPromotionCap) {
    return new LegacyLICMPass(LicmMssaOptCap, LicmMssaNoAccForPromotionCap);
  }
  
  llvm::SinkAndHoistLICMFlags::SinkAndHoistLICMFlags(bool IsSink, Loop *L,
                                                     MemorySSA *MSSA)
      : SinkAndHoistLICMFlags(SetLicmMssaOptCap, SetLicmMssaNoAccForPromotionCap,
                              IsSink, L, MSSA) {}
  
  llvm::SinkAndHoistLICMFlags::SinkAndHoistLICMFlags(
      unsigned LicmMssaOptCap, unsigned LicmMssaNoAccForPromotionCap, bool IsSink,
      Loop *L, MemorySSA *MSSA)
      : LicmMssaOptCap(LicmMssaOptCap),
        LicmMssaNoAccForPromotionCap(LicmMssaNoAccForPromotionCap),
        IsSink(IsSink) {
    assert(((L != nullptr) == (MSSA != nullptr)) &&
           "Unexpected values for SinkAndHoistLICMFlags");
    if (!MSSA)
      return;
  
    unsigned AccessCapCount = 0;
    for (auto *BB : L->getBlocks())
      if (const auto *Accesses = MSSA->getBlockAccesses(BB))
        for (const auto &MA : *Accesses) {
          (void)MA;
          ++AccessCapCount;
          if (AccessCapCount > LicmMssaNoAccForPromotionCap) {
            NoOfMemAccTooLarge = true;
            return;
          }
        }
  }
  
  /// Hoist expressions out of the specified loop. Note, alias info for inner
  /// loop is not preserved so it is not a good idea to run LICM multiple
  /// times on one loop.
  bool LoopInvariantCodeMotion::runOnLoop(
      Loop *L, AAResults *AA, LoopInfo *LI, DominatorTree *DT,
      BlockFrequencyInfo *BFI, TargetLibraryInfo *TLI, TargetTransformInfo *TTI,
      ScalarEvolution *SE, MemorySSA *MSSA, OptimizationRemarkEmitter *ORE) {
    bool Changed = false;
  
    assert(L->isLCSSAForm(*DT) && "Loop is not in LCSSA form.");
  
    // If this loop has metadata indicating that LICM is not to be performed then
    // just exit.
    if (hasDisableLICMTransformsHint(L)) {
      return false;
    }
  
    std::unique_ptr<AliasSetTracker> CurAST;
    std::unique_ptr<MemorySSAUpdater> MSSAU;
    std::unique_ptr<SinkAndHoistLICMFlags> Flags;
  
    if (!MSSA) {
      LLVM_DEBUG(dbgs() << "LICM: Using Alias Set Tracker.\n");
      CurAST = collectAliasInfoForLoop(L, LI, AA);
      Flags = std::make_unique<SinkAndHoistLICMFlags>(
          LicmMssaOptCap, LicmMssaNoAccForPromotionCap, /*IsSink=*/true);
    } else {
      LLVM_DEBUG(dbgs() << "LICM: Using MemorySSA.\n");
      MSSAU = std::make_unique<MemorySSAUpdater>(MSSA);
      Flags = std::make_unique<SinkAndHoistLICMFlags>(
          LicmMssaOptCap, LicmMssaNoAccForPromotionCap, /*IsSink=*/true, L, MSSA);
    }
  
    // Get the preheader block to move instructions into...
    BasicBlock *Preheader = L->getLoopPreheader();
  
    // Compute loop safety information.
    ICFLoopSafetyInfo SafetyInfo;
    SafetyInfo.computeLoopSafetyInfo(L);
  
    // We want to visit all of the instructions in this loop... that are not parts
    // of our subloops (they have already had their invariants hoisted out of
    // their loop, into this loop, so there is no need to process the BODIES of
    // the subloops).
    //
    // Traverse the body of the loop in depth first order on the dominator tree so
    // that we are guaranteed to see definitions before we see uses.  This allows
    // us to sink instructions in one pass, without iteration.  After sinking
    // instructions, we perform another pass to hoist them out of the loop.
    if (L->hasDedicatedExits())
      Changed |=
          sinkRegion(DT->getNode(L->getHeader()), AA, LI, DT, BFI, TLI, TTI, L,
                     CurAST.get(), MSSAU.get(), &SafetyInfo, *Flags.get(), ORE);
    Flags->setIsSink(false);
    if (Preheader)
      Changed |= hoistRegion(DT->getNode(L->getHeader()), AA, LI, DT, BFI, TLI, L,
                             CurAST.get(), MSSAU.get(), SE, &SafetyInfo,
                             *Flags.get(), ORE);
  
    // Now that all loop invariants have been removed from the loop, promote any
    // memory references to scalars that we can.
    // Don't sink stores from loops without dedicated block exits. Exits
    // containing indirect branches are not transformed by loop simplify,
    // make sure we catch that. An additional load may be generated in the
    // preheader for SSA updater, so also avoid sinking when no preheader
    // is available.
    if (!DisablePromotion && Preheader && L->hasDedicatedExits() &&
        !Flags->tooManyMemoryAccesses()) {
      // Figure out the loop exits and their insertion points
      SmallVector<BasicBlock *, 8> ExitBlocks;
      L->getUniqueExitBlocks(ExitBlocks);
  
      // We can't insert into a catchswitch.
      bool HasCatchSwitch = llvm::any_of(ExitBlocks, [](BasicBlock *Exit) {
        return isa<CatchSwitchInst>(Exit->getTerminator());
      });
  
      if (!HasCatchSwitch) {
        SmallVector<Instruction *, 8> InsertPts;
        SmallVector<MemoryAccess *, 8> MSSAInsertPts;
        InsertPts.reserve(ExitBlocks.size());
        if (MSSAU)
          MSSAInsertPts.reserve(ExitBlocks.size());
        for (BasicBlock *ExitBlock : ExitBlocks) {
          InsertPts.push_back(&*ExitBlock->getFirstInsertionPt());
          if (MSSAU)
            MSSAInsertPts.push_back(nullptr);
        }
  
        PredIteratorCache PIC;
  
        bool Promoted = false;
  
        // Build an AST using MSSA.
        if (!CurAST.get())
          CurAST = collectAliasInfoForLoopWithMSSA(L, AA, MSSAU.get());
  
        // Loop over all of the alias sets in the tracker object.
        for (AliasSet &AS : *CurAST) {
          // We can promote this alias set if it has a store, if it is a "Must"
          // alias set, if the pointer is loop invariant, and if we are not
          // eliminating any volatile loads or stores.
          if (AS.isForwardingAliasSet() || !AS.isMod() || !AS.isMustAlias() ||
              !L->isLoopInvariant(AS.begin()->getValue()))
            continue;
  
          assert(
              !AS.empty() &&
              "Must alias set should have at least one pointer element in it!");
  
          SmallSetVector<Value *, 8> PointerMustAliases;
          for (const auto &ASI : AS)
            PointerMustAliases.insert(ASI.getValue());
  
          Promoted |= promoteLoopAccessesToScalars(
              PointerMustAliases, ExitBlocks, InsertPts, MSSAInsertPts, PIC, LI,
              DT, TLI, L, CurAST.get(), MSSAU.get(), &SafetyInfo, ORE);
        }
  
        // Once we have promoted values across the loop body we have to
        // recursively reform LCSSA as any nested loop may now have values defined
        // within the loop used in the outer loop.
        // FIXME: This is really heavy handed. It would be a bit better to use an
        // SSAUpdater strategy during promotion that was LCSSA aware and reformed
        // it as it went.
        if (Promoted)
          formLCSSARecursively(*L, *DT, LI, SE);
  
        Changed |= Promoted;
      }
    }
  
    // Check that neither this loop nor its parent have had LCSSA broken. LICM is
    // specifically moving instructions across the loop boundary and so it is
    // especially in need of sanity checking here.
    assert(L->isLCSSAForm(*DT) && "Loop not left in LCSSA form after LICM!");
    assert((L->isOutermost() || L->getParentLoop()->isLCSSAForm(*DT)) &&
           "Parent loop not left in LCSSA form after LICM!");
  
    if (MSSAU.get() && VerifyMemorySSA)
      MSSAU->getMemorySSA()->verifyMemorySSA();
  
    if (Changed && SE)
      SE->forgetLoopDispositions(L);
    return Changed;
  }
  
  /// Walk the specified region of the CFG (defined by all blocks dominated by
  /// the specified block, and that are in the current loop) in reverse depth
  /// first order w.r.t the DominatorTree.  This allows us to visit uses before
  /// definitions, allowing us to sink a loop body in one pass without iteration.
  ///
  bool llvm::sinkRegion(DomTreeNode *N, AAResults *AA, LoopInfo *LI,
                        DominatorTree *DT, BlockFrequencyInfo *BFI,
                        TargetLibraryInfo *TLI, TargetTransformInfo *TTI,
                        Loop *CurLoop, AliasSetTracker *CurAST,
                        MemorySSAUpdater *MSSAU, ICFLoopSafetyInfo *SafetyInfo,
                        SinkAndHoistLICMFlags &Flags,
                        OptimizationRemarkEmitter *ORE) {
  
    // Verify inputs.
    assert(N != nullptr && AA != nullptr && LI != nullptr && DT != nullptr &&
           CurLoop != nullptr && SafetyInfo != nullptr &&
           "Unexpected input to sinkRegion.");
    assert(((CurAST != nullptr) ^ (MSSAU != nullptr)) &&
           "Either AliasSetTracker or MemorySSA should be initialized.");
  
    // We want to visit children before parents. We will enque all the parents
    // before their children in the worklist and process the worklist in reverse
    // order.
    SmallVector<DomTreeNode *, 16> Worklist = collectChildrenInLoop(N, CurLoop);
  
    bool Changed = false;
    for (DomTreeNode *DTN : reverse(Worklist)) {
      BasicBlock *BB = DTN->getBlock();
      // Only need to process the contents of this block if it is not part of a
      // subloop (which would already have been processed).
      if (inSubLoop(BB, CurLoop, LI))
        continue;
  
      for (BasicBlock::iterator II = BB->end(); II != BB->begin();) {
        Instruction &I = *--II;
  
        // If the instruction is dead, we would try to sink it because it isn't
        // used in the loop, instead, just delete it.
        if (isInstructionTriviallyDead(&I, TLI)) {
          LLVM_DEBUG(dbgs() << "LICM deleting dead inst: " << I << '\n');
          salvageKnowledge(&I);
          salvageDebugInfo(I);
          ++II;
          eraseInstruction(I, *SafetyInfo, CurAST, MSSAU);
          Changed = true;
          continue;
        }
  
        // Check to see if we can sink this instruction to the exit blocks
        // of the loop.  We can do this if the all users of the instruction are
        // outside of the loop.  In this case, it doesn't even matter if the
        // operands of the instruction are loop invariant.
        //
        bool FreeInLoop = false;
        if (!I.mayHaveSideEffects() &&
            isNotUsedOrFreeInLoop(I, CurLoop, SafetyInfo, TTI, FreeInLoop) &&
            canSinkOrHoistInst(I, AA, DT, CurLoop, CurAST, MSSAU, true, &Flags,
                               ORE)) {
          if (sink(I, LI, DT, BFI, CurLoop, SafetyInfo, MSSAU, ORE)) {
            if (!FreeInLoop) {
              ++II;
              salvageDebugInfo(I);
              eraseInstruction(I, *SafetyInfo, CurAST, MSSAU);
            }
            Changed = true;
          }
        }
      }
    }
    if (MSSAU && VerifyMemorySSA)
      MSSAU->getMemorySSA()->verifyMemorySSA();
    return Changed;
  }
  
  namespace {
  // This is a helper class for hoistRegion to make it able to hoist control flow
  // in order to be able to hoist phis. The way this works is that we initially
  // start hoisting to the loop preheader, and when we see a loop invariant branch
  // we make note of this. When we then come to hoist an instruction that's
  // conditional on such a branch we duplicate the branch and the relevant control
  // flow, then hoist the instruction into the block corresponding to its original
  // block in the duplicated control flow.
  class ControlFlowHoister {
  private:
    // Information about the loop we are hoisting from
    LoopInfo *LI;
    DominatorTree *DT;
    Loop *CurLoop;
    MemorySSAUpdater *MSSAU;
  
    // A map of blocks in the loop to the block their instructions will be hoisted
    // to.
    DenseMap<BasicBlock *, BasicBlock *> HoistDestinationMap;
  
    // The branches that we can hoist, mapped to the block that marks a
    // convergence point of their control flow.
    DenseMap<BranchInst *, BasicBlock *> HoistableBranches;
  
  public:
    ControlFlowHoister(LoopInfo *LI, DominatorTree *DT, Loop *CurLoop,
                       MemorySSAUpdater *MSSAU)
        : LI(LI), DT(DT), CurLoop(CurLoop), MSSAU(MSSAU) {}
  
    void registerPossiblyHoistableBranch(BranchInst *BI) {
      // We can only hoist conditional branches with loop invariant operands.
      if (!ControlFlowHoisting || !BI->isConditional() ||
          !CurLoop->hasLoopInvariantOperands(BI))
        return;
  
      // The branch destinations need to be in the loop, and we don't gain
      // anything by duplicating conditional branches with duplicate successors,
      // as it's essentially the same as an unconditional branch.
      BasicBlock *TrueDest = BI->getSuccessor(0);
      BasicBlock *FalseDest = BI->getSuccessor(1);
      if (!CurLoop->contains(TrueDest) || !CurLoop->contains(FalseDest) ||
          TrueDest == FalseDest)
        return;
  
      // We can hoist BI if one branch destination is the successor of the other,
      // or both have common successor which we check by seeing if the
      // intersection of their successors is non-empty.
      // TODO: This could be expanded to allowing branches where both ends
      // eventually converge to a single block.
      SmallPtrSet<BasicBlock *, 4> TrueDestSucc, FalseDestSucc;
      TrueDestSucc.insert(succ_begin(TrueDest), succ_end(TrueDest));
      FalseDestSucc.insert(succ_begin(FalseDest), succ_end(FalseDest));
      BasicBlock *CommonSucc = nullptr;
      if (TrueDestSucc.count(FalseDest)) {
        CommonSucc = FalseDest;
      } else if (FalseDestSucc.count(TrueDest)) {
        CommonSucc = TrueDest;
      } else {
        set_intersect(TrueDestSucc, FalseDestSucc);
        // If there's one common successor use that.
        if (TrueDestSucc.size() == 1)
          CommonSucc = *TrueDestSucc.begin();
        // If there's more than one pick whichever appears first in the block list
        // (we can't use the value returned by TrueDestSucc.begin() as it's
        // unpredicatable which element gets returned).
        else if (!TrueDestSucc.empty()) {
          Function *F = TrueDest->getParent();
          auto IsSucc = [&](BasicBlock &BB) { return TrueDestSucc.count(&BB); };
          auto It = llvm::find_if(*F, IsSucc);
          assert(It != F->end() && "Could not find successor in function");
          CommonSucc = &*It;
        }
      }
      // The common successor has to be dominated by the branch, as otherwise
      // there will be some other path to the successor that will not be
      // controlled by this branch so any phi we hoist would be controlled by the
      // wrong condition. This also takes care of avoiding hoisting of loop back
      // edges.
      // TODO: In some cases this could be relaxed if the successor is dominated
      // by another block that's been hoisted and we can guarantee that the
      // control flow has been replicated exactly.
      if (CommonSucc && DT->dominates(BI, CommonSucc))
        HoistableBranches[BI] = CommonSucc;
    }
  
    bool canHoistPHI(PHINode *PN) {
      // The phi must have loop invariant operands.
      if (!ControlFlowHoisting || !CurLoop->hasLoopInvariantOperands(PN))
        return false;
      // We can hoist phis if the block they are in is the target of hoistable
      // branches which cover all of the predecessors of the block.
      SmallPtrSet<BasicBlock *, 8> PredecessorBlocks;
      BasicBlock *BB = PN->getParent();
      for (BasicBlock *PredBB : predecessors(BB))
        PredecessorBlocks.insert(PredBB);
      // If we have less predecessor blocks than predecessors then the phi will
      // have more than one incoming value for the same block which we can't
      // handle.
      // TODO: This could be handled be erasing some of the duplicate incoming
      // values.
      if (PredecessorBlocks.size() != pred_size(BB))
        return false;
      for (auto &Pair : HoistableBranches) {
        if (Pair.second == BB) {
          // Which blocks are predecessors via this branch depends on if the
          // branch is triangle-like or diamond-like.
          if (Pair.first->getSuccessor(0) == BB) {
            PredecessorBlocks.erase(Pair.first->getParent());
            PredecessorBlocks.erase(Pair.first->getSuccessor(1));
          } else if (Pair.first->getSuccessor(1) == BB) {
            PredecessorBlocks.erase(Pair.first->getParent());
            PredecessorBlocks.erase(Pair.first->getSuccessor(0));
          } else {
            PredecessorBlocks.erase(Pair.first->getSuccessor(0));
            PredecessorBlocks.erase(Pair.first->getSuccessor(1));
          }
        }
      }
      // PredecessorBlocks will now be empty if for every predecessor of BB we
      // found a hoistable branch source.
      return PredecessorBlocks.empty();
    }
  
    BasicBlock *getOrCreateHoistedBlock(BasicBlock *BB) {
      if (!ControlFlowHoisting)
        return CurLoop->getLoopPreheader();
      // If BB has already been hoisted, return that
      if (HoistDestinationMap.count(BB))
        return HoistDestinationMap[BB];
  
      // Check if this block is conditional based on a pending branch
      auto HasBBAsSuccessor =
          [&](DenseMap<BranchInst *, BasicBlock *>::value_type &Pair) {
            return BB != Pair.second && (Pair.first->getSuccessor(0) == BB ||
                                         Pair.first->getSuccessor(1) == BB);
          };
      auto It = llvm::find_if(HoistableBranches, HasBBAsSuccessor);
  
      // If not involved in a pending branch, hoist to preheader
      BasicBlock *InitialPreheader = CurLoop->getLoopPreheader();
      if (It == HoistableBranches.end()) {
        LLVM_DEBUG(dbgs() << "LICM using "
                          << InitialPreheader->getNameOrAsOperand()
                          << " as hoist destination for "
                          << BB->getNameOrAsOperand() << "\n");
        HoistDestinationMap[BB] = InitialPreheader;
        return InitialPreheader;
      }
      BranchInst *BI = It->first;
      assert(std::find_if(++It, HoistableBranches.end(), HasBBAsSuccessor) ==
                 HoistableBranches.end() &&
             "BB is expected to be the target of at most one branch");
  
      LLVMContext &C = BB->getContext();
      BasicBlock *TrueDest = BI->getSuccessor(0);
      BasicBlock *FalseDest = BI->getSuccessor(1);
      BasicBlock *CommonSucc = HoistableBranches[BI];
      BasicBlock *HoistTarget = getOrCreateHoistedBlock(BI->getParent());
  
      // Create hoisted versions of blocks that currently don't have them
      auto CreateHoistedBlock = [&](BasicBlock *Orig) {
        if (HoistDestinationMap.count(Orig))
          return HoistDestinationMap[Orig];
        BasicBlock *New =
            BasicBlock::Create(C, Orig->getName() + ".licm", Orig->getParent());
        HoistDestinationMap[Orig] = New;
        DT->addNewBlock(New, HoistTarget);
        if (CurLoop->getParentLoop())
          CurLoop->getParentLoop()->addBasicBlockToLoop(New, *LI);
        ++NumCreatedBlocks;
        LLVM_DEBUG(dbgs() << "LICM created " << New->getName()
                          << " as hoist destination for " << Orig->getName()
                          << "\n");
        return New;
      };
      BasicBlock *HoistTrueDest = CreateHoistedBlock(TrueDest);
      BasicBlock *HoistFalseDest = CreateHoistedBlock(FalseDest);
      BasicBlock *HoistCommonSucc = CreateHoistedBlock(CommonSucc);
  
      // Link up these blocks with branches.
      if (!HoistCommonSucc->getTerminator()) {
        // The new common successor we've generated will branch to whatever that
        // hoist target branched to.
        BasicBlock *TargetSucc = HoistTarget->getSingleSuccessor();
        assert(TargetSucc && "Expected hoist target to have a single successor");
        HoistCommonSucc->moveBefore(TargetSucc);
        BranchInst::Create(TargetSucc, HoistCommonSucc);
      }
      if (!HoistTrueDest->getTerminator()) {
        HoistTrueDest->moveBefore(HoistCommonSucc);
        BranchInst::Create(HoistCommonSucc, HoistTrueDest);
      }
      if (!HoistFalseDest->getTerminator()) {
        HoistFalseDest->moveBefore(HoistCommonSucc);
        BranchInst::Create(HoistCommonSucc, HoistFalseDest);
      }
  
      // If BI is being cloned to what was originally the preheader then
      // HoistCommonSucc will now be the new preheader.
      if (HoistTarget == InitialPreheader) {
        // Phis in the loop header now need to use the new preheader.
        InitialPreheader->replaceSuccessorsPhiUsesWith(HoistCommonSucc);
        if (MSSAU)
          MSSAU->wireOldPredecessorsToNewImmediatePredecessor(
              HoistTarget->getSingleSuccessor(), HoistCommonSucc, {HoistTarget});
        // The new preheader dominates the loop header.
        DomTreeNode *PreheaderNode = DT->getNode(HoistCommonSucc);
        DomTreeNode *HeaderNode = DT->getNode(CurLoop->getHeader());
        DT->changeImmediateDominator(HeaderNode, PreheaderNode);
        // The preheader hoist destination is now the new preheader, with the
        // exception of the hoist destination of this branch.
        for (auto &Pair : HoistDestinationMap)
          if (Pair.second == InitialPreheader && Pair.first != BI->getParent())
            Pair.second = HoistCommonSucc;
      }
  
      // Now finally clone BI.
      ReplaceInstWithInst(
          HoistTarget->getTerminator(),
          BranchInst::Create(HoistTrueDest, HoistFalseDest, BI->getCondition()));
      ++NumClonedBranches;
  
      assert(CurLoop->getLoopPreheader() &&
             "Hoisting blocks should not have destroyed preheader");
      return HoistDestinationMap[BB];
    }
  };
  } // namespace
  
  // Hoisting/sinking instruction out of a loop isn't always beneficial. It's only
  // only worthwhile if the destination block is actually colder than current
  // block.
  static bool worthSinkOrHoistInst(Instruction &I, BasicBlock *DstBlock,
                                   OptimizationRemarkEmitter *ORE,
                                   BlockFrequencyInfo *BFI) {
    // Check block frequency only when runtime profile is available
    // to avoid pathological cases. With static profile, lean towards
    // hosting because it helps canonicalize the loop for vectorizer.
    if (!DstBlock->getParent()->hasProfileData())
      return true;
  
    if (!HoistSinkColdnessThreshold || !BFI)
      return true;
  
    BasicBlock *SrcBlock = I.getParent();
    if (BFI->getBlockFreq(DstBlock).getFrequency() / HoistSinkColdnessThreshold >
        BFI->getBlockFreq(SrcBlock).getFrequency()) {
      ORE->emit([&]() {
        return OptimizationRemarkMissed(DEBUG_TYPE, "SinkHoistInst", &I)
               << "failed to sink or hoist instruction because containing block "
                  "has lower frequency than destination block";
      });
      return false;
    }
  
    return true;
  }
  
  /// Walk the specified region of the CFG (defined by all blocks dominated by
  /// the specified block, and that are in the current loop) in depth first
  /// order w.r.t the DominatorTree.  This allows us to visit definitions before
  /// uses, allowing us to hoist a loop body in one pass without iteration.
  ///
  bool llvm::hoistRegion(DomTreeNode *N, AAResults *AA, LoopInfo *LI,
                         DominatorTree *DT, BlockFrequencyInfo *BFI,
                         TargetLibraryInfo *TLI, Loop *CurLoop,
                         AliasSetTracker *CurAST, MemorySSAUpdater *MSSAU,
                         ScalarEvolution *SE, ICFLoopSafetyInfo *SafetyInfo,
                         SinkAndHoistLICMFlags &Flags,
                         OptimizationRemarkEmitter *ORE) {
    // Verify inputs.
    assert(N != nullptr && AA != nullptr && LI != nullptr && DT != nullptr &&
           CurLoop != nullptr && SafetyInfo != nullptr &&
           "Unexpected input to hoistRegion.");
    assert(((CurAST != nullptr) ^ (MSSAU != nullptr)) &&
           "Either AliasSetTracker or MemorySSA should be initialized.");
  
    ControlFlowHoister CFH(LI, DT, CurLoop, MSSAU);
  
    // Keep track of instructions that have been hoisted, as they may need to be
    // re-hoisted if they end up not dominating all of their uses.
    SmallVector<Instruction *, 16> HoistedInstructions;
  
    // For PHI hoisting to work we need to hoist blocks before their successors.
    // We can do this by iterating through the blocks in the loop in reverse
    // post-order.
    LoopBlocksRPO Worklist(CurLoop);
    Worklist.perform(LI);
    bool Changed = false;
    for (BasicBlock *BB : Worklist) {
      // Only need to process the contents of this block if it is not part of a
      // subloop (which would already have been processed).
      if (inSubLoop(BB, CurLoop, LI))
        continue;
  
      for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E;) {
        Instruction &I = *II++;
        // Try constant folding this instruction.  If all the operands are
        // constants, it is technically hoistable, but it would be better to
        // just fold it.
        if (Constant *C = ConstantFoldInstruction(
                &I, I.getModule()->getDataLayout(), TLI)) {
          LLVM_DEBUG(dbgs() << "LICM folding inst: " << I << "  --> " << *C
                            << '\n');
          if (CurAST)
            CurAST->copyValue(&I, C);
          // FIXME MSSA: Such replacements may make accesses unoptimized (D51960).
          I.replaceAllUsesWith(C);
          if (isInstructionTriviallyDead(&I, TLI))
            eraseInstruction(I, *SafetyInfo, CurAST, MSSAU);
          Changed = true;
          continue;
        }
  
        // Try hoisting the instruction out to the preheader.  We can only do
        // this if all of the operands of the instruction are loop invariant and
        // if it is safe to hoist the instruction. We also check block frequency
        // to make sure instruction only gets hoisted into colder blocks.
        // TODO: It may be safe to hoist if we are hoisting to a conditional block
        // and we have accurately duplicated the control flow from the loop header
        // to that block.
        if (CurLoop->hasLoopInvariantOperands(&I) &&
            canSinkOrHoistInst(I, AA, DT, CurLoop, CurAST, MSSAU, true, &Flags,
                               ORE) &&
            worthSinkOrHoistInst(I, CurLoop->getLoopPreheader(), ORE, BFI) &&
            isSafeToExecuteUnconditionally(
                I, DT, CurLoop, SafetyInfo, ORE,
                CurLoop->getLoopPreheader()->getTerminator())) {
          hoist(I, DT, CurLoop, CFH.getOrCreateHoistedBlock(BB), SafetyInfo,
                MSSAU, SE, ORE);
          HoistedInstructions.push_back(&I);
          Changed = true;
          continue;
        }
  
        // Attempt to remove floating point division out of the loop by
        // converting it to a reciprocal multiplication.
        if (I.getOpcode() == Instruction::FDiv && I.hasAllowReciprocal() &&
            CurLoop->isLoopInvariant(I.getOperand(1))) {
          auto Divisor = I.getOperand(1);
          auto One = llvm::ConstantFP::get(Divisor->getType(), 1.0);
          auto ReciprocalDivisor = BinaryOperator::CreateFDiv(One, Divisor);
          ReciprocalDivisor->setFastMathFlags(I.getFastMathFlags());
          SafetyInfo->insertInstructionTo(ReciprocalDivisor, I.getParent());
          ReciprocalDivisor->insertBefore(&I);
  
          auto Product =
              BinaryOperator::CreateFMul(I.getOperand(0), ReciprocalDivisor);
          Product->setFastMathFlags(I.getFastMathFlags());
          SafetyInfo->insertInstructionTo(Product, I.getParent());
          Product->insertAfter(&I);
          I.replaceAllUsesWith(Product);
          eraseInstruction(I, *SafetyInfo, CurAST, MSSAU);
  
          hoist(*ReciprocalDivisor, DT, CurLoop, CFH.getOrCreateHoistedBlock(BB),
                SafetyInfo, MSSAU, SE, ORE);
          HoistedInstructions.push_back(ReciprocalDivisor);
          Changed = true;
          continue;
        }
  
        auto IsInvariantStart = [&](Instruction &I) {
          using namespace PatternMatch;
          return I.use_empty() &&
                 match(&I, m_Intrinsic<Intrinsic::invariant_start>());
        };
        auto MustExecuteWithoutWritesBefore = [&](Instruction &I) {
          return SafetyInfo->isGuaranteedToExecute(I, DT, CurLoop) &&
                 SafetyInfo->doesNotWriteMemoryBefore(I, CurLoop);
        };
        if ((IsInvariantStart(I) || isGuard(&I)) &&
            CurLoop->hasLoopInvariantOperands(&I) &&
            MustExecuteWithoutWritesBefore(I)) {
          hoist(I, DT, CurLoop, CFH.getOrCreateHoistedBlock(BB), SafetyInfo,
                MSSAU, SE, ORE);
          HoistedInstructions.push_back(&I);
          Changed = true;
          continue;
        }
  
        if (PHINode *PN = dyn_cast<PHINode>(&I)) {
          if (CFH.canHoistPHI(PN)) {
            // Redirect incoming blocks first to ensure that we create hoisted
            // versions of those blocks before we hoist the phi.
            for (unsigned int i = 0; i < PN->getNumIncomingValues(); ++i)
              PN->setIncomingBlock(
                  i, CFH.getOrCreateHoistedBlock(PN->getIncomingBlock(i)));
            hoist(*PN, DT, CurLoop, CFH.getOrCreateHoistedBlock(BB), SafetyInfo,
                  MSSAU, SE, ORE);
            assert(DT->dominates(PN, BB) && "Conditional PHIs not expected");
            Changed = true;
            continue;
          }
        }
  
        // Remember possibly hoistable branches so we can actually hoist them
        // later if needed.
        if (BranchInst *BI = dyn_cast<BranchInst>(&I))
          CFH.registerPossiblyHoistableBranch(BI);
      }
    }
  
    // If we hoisted instructions to a conditional block they may not dominate
    // their uses that weren't hoisted (such as phis where some operands are not
    // loop invariant). If so make them unconditional by moving them to their
    // immediate dominator. We iterate through the instructions in reverse order
    // which ensures that when we rehoist an instruction we rehoist its operands,
    // and also keep track of where in the block we are rehoisting to to make sure
    // that we rehoist instructions before the instructions that use them.
    Instruction *HoistPoint = nullptr;
    if (ControlFlowHoisting) {
      for (Instruction *I : reverse(HoistedInstructions)) {
        if (!llvm::all_of(I->uses(),
                          [&](Use &U) { return DT->dominates(I, U); })) {
          BasicBlock *Dominator =
              DT->getNode(I->getParent())->getIDom()->getBlock();
          if (!HoistPoint || !DT->dominates(HoistPoint->getParent(), Dominator)) {
            if (HoistPoint)
              assert(DT->dominates(Dominator, HoistPoint->getParent()) &&
                     "New hoist point expected to dominate old hoist point");
            HoistPoint = Dominator->getTerminator();
          }
          LLVM_DEBUG(dbgs() << "LICM rehoisting to "
                            << HoistPoint->getParent()->getNameOrAsOperand()
                            << ": " << *I << "\n");
          moveInstructionBefore(*I, *HoistPoint, *SafetyInfo, MSSAU, SE);
          HoistPoint = I;
          Changed = true;
        }
      }
    }
    if (MSSAU && VerifyMemorySSA)
      MSSAU->getMemorySSA()->verifyMemorySSA();
  
      // Now that we've finished hoisting make sure that LI and DT are still
      // valid.
  #ifdef EXPENSIVE_CHECKS
    if (Changed) {
      assert(DT->verify(DominatorTree::VerificationLevel::Fast) &&
             "Dominator tree verification failed");
      LI->verify(*DT);
    }
  #endif
  
    return Changed;
  }
  
  // Return true if LI is invariant within scope of the loop. LI is invariant if
  // CurLoop is dominated by an invariant.start representing the same memory
  // location and size as the memory location LI loads from, and also the
  // invariant.start has no uses.
  static bool isLoadInvariantInLoop(LoadInst *LI, DominatorTree *DT,
                                    Loop *CurLoop) {
    Value *Addr = LI->getOperand(0);
    const DataLayout &DL = LI->getModule()->getDataLayout();
    const TypeSize LocSizeInBits = DL.getTypeSizeInBits(LI->getType());
  
    // It is not currently possible for clang to generate an invariant.start
    // intrinsic with scalable vector types because we don't support thread local
    // sizeless types and we don't permit sizeless types in structs or classes.
    // Furthermore, even if support is added for this in future the intrinsic
    // itself is defined to have a size of -1 for variable sized objects. This
    // makes it impossible to verify if the intrinsic envelops our region of
    // interest. For example, both <vscale x 32 x i8> and <vscale x 16 x i8>
    // types would have a -1 parameter, but the former is clearly double the size
    // of the latter.
    if (LocSizeInBits.isScalable())
      return false;
  
    // if the type is i8 addrspace(x)*, we know this is the type of
    // llvm.invariant.start operand
    auto *PtrInt8Ty = PointerType::get(Type::getInt8Ty(LI->getContext()),
                                       LI->getPointerAddressSpace());
    unsigned BitcastsVisited = 0;
    // Look through bitcasts until we reach the i8* type (this is invariant.start
    // operand type).
    while (Addr->getType() != PtrInt8Ty) {
      auto *BC = dyn_cast<BitCastInst>(Addr);
      // Avoid traversing high number of bitcast uses.
      if (++BitcastsVisited > MaxNumUsesTraversed || !BC)
        return false;
      Addr = BC->getOperand(0);
    }
  
    unsigned UsesVisited = 0;
    // Traverse all uses of the load operand value, to see if invariant.start is
    // one of the uses, and whether it dominates the load instruction.
    for (auto *U : Addr->users()) {
      // Avoid traversing for Load operand with high number of users.
      if (++UsesVisited > MaxNumUsesTraversed)
        return false;
      IntrinsicInst *II = dyn_cast<IntrinsicInst>(U);
      // If there are escaping uses of invariant.start instruction, the load maybe
      // non-invariant.
      if (!II || II->getIntrinsicID() != Intrinsic::invariant_start ||
          !II->use_empty())
        continue;
      ConstantInt *InvariantSize = cast<ConstantInt>(II->getArgOperand(0));
      // The intrinsic supports having a -1 argument for variable sized objects
      // so we should check for that here.
      if (InvariantSize->isNegative())
        continue;
      uint64_t InvariantSizeInBits = InvariantSize->getSExtValue() * 8;
      // Confirm the invariant.start location size contains the load operand size
      // in bits. Also, the invariant.start should dominate the load, and we
      // should not hoist the load out of a loop that contains this dominating
      // invariant.start.
      if (LocSizeInBits.getFixedSize() <= InvariantSizeInBits &&
          DT->properlyDominates(II->getParent(), CurLoop->getHeader()))
        return true;
    }
  
    return false;
  }
  
  namespace {
  /// Return true if-and-only-if we know how to (mechanically) both hoist and
  /// sink a given instruction out of a loop.  Does not address legality
  /// concerns such as aliasing or speculation safety.
  bool isHoistableAndSinkableInst(Instruction &I) {
    // Only these instructions are hoistable/sinkable.
    return (isa<LoadInst>(I) || isa<StoreInst>(I) || isa<CallInst>(I) ||
            isa<FenceInst>(I) || isa<CastInst>(I) || isa<UnaryOperator>(I) ||
            isa<BinaryOperator>(I) || isa<SelectInst>(I) ||
            isa<GetElementPtrInst>(I) || isa<CmpInst>(I) ||
            isa<InsertElementInst>(I) || isa<ExtractElementInst>(I) ||
            isa<ShuffleVectorInst>(I) || isa<ExtractValueInst>(I) ||
            isa<InsertValueInst>(I) || isa<FreezeInst>(I));
  }
  /// Return true if all of the alias sets within this AST are known not to
  /// contain a Mod, or if MSSA knows thare are no MemoryDefs in the loop.
  bool isReadOnly(AliasSetTracker *CurAST, const MemorySSAUpdater *MSSAU,
                  const Loop *L) {
    if (CurAST) {
      for (AliasSet &AS : *CurAST) {
        if (!AS.isForwardingAliasSet() && AS.isMod()) {
          return false;
        }
      }
      return true;
    } else { /*MSSAU*/
      for (auto *BB : L->getBlocks())
        if (MSSAU->getMemorySSA()->getBlockDefs(BB))
          return false;
      return true;
    }
  }
  
  /// Return true if I is the only Instruction with a MemoryAccess in L.
  bool isOnlyMemoryAccess(const Instruction *I, const Loop *L,
                          const MemorySSAUpdater *MSSAU) {
    for (auto *BB : L->getBlocks())
      if (auto *Accs = MSSAU->getMemorySSA()->getBlockAccesses(BB)) {
        int NotAPhi = 0;
        for (const auto &Acc : *Accs) {
          if (isa<MemoryPhi>(&Acc))
            continue;
          const auto *MUD = cast<MemoryUseOrDef>(&Acc);
          if (MUD->getMemoryInst() != I || NotAPhi++ == 1)
            return false;
        }
      }
    return true;
  }
  }
  
  bool llvm::canSinkOrHoistInst(Instruction &I, AAResults *AA, DominatorTree *DT,
                                Loop *CurLoop, AliasSetTracker *CurAST,
                                MemorySSAUpdater *MSSAU,
                                bool TargetExecutesOncePerLoop,
                                SinkAndHoistLICMFlags *Flags,
                                OptimizationRemarkEmitter *ORE) {
    assert(((CurAST != nullptr) ^ (MSSAU != nullptr)) &&
           "Either AliasSetTracker or MemorySSA should be initialized.");
  
    // If we don't understand the instruction, bail early.
    if (!isHoistableAndSinkableInst(I))
      return false;
  
    MemorySSA *MSSA = MSSAU ? MSSAU->getMemorySSA() : nullptr;
    if (MSSA)
      assert(Flags != nullptr && "Flags cannot be null.");
  
    // Loads have extra constraints we have to verify before we can hoist them.
    if (LoadInst *LI = dyn_cast<LoadInst>(&I)) {
      if (!LI->isUnordered())
        return false; // Don't sink/hoist volatile or ordered atomic loads!
  
      // Loads from constant memory are always safe to move, even if they end up
      // in the same alias set as something that ends up being modified.
      if (AA->pointsToConstantMemory(LI->getOperand(0)))
        return true;
      if (LI->hasMetadata(LLVMContext::MD_invariant_load))
        return true;
  
      if (LI->isAtomic() && !TargetExecutesOncePerLoop)
        return false; // Don't risk duplicating unordered loads
  
      // This checks for an invariant.start dominating the load.
      if (isLoadInvariantInLoop(LI, DT, CurLoop))
        return true;
  
      bool Invalidated;
      if (CurAST)
        Invalidated = pointerInvalidatedByLoop(MemoryLocation::get(LI), CurAST,
                                               CurLoop, AA);
      else
        Invalidated = pointerInvalidatedByLoopWithMSSA(
            MSSA, cast<MemoryUse>(MSSA->getMemoryAccess(LI)), CurLoop, I, *Flags);
      // Check loop-invariant address because this may also be a sinkable load
      // whose address is not necessarily loop-invariant.
      if (ORE && Invalidated && CurLoop->isLoopInvariant(LI->getPointerOperand()))
        ORE->emit([&]() {
          return OptimizationRemarkMissed(
                     DEBUG_TYPE, "LoadWithLoopInvariantAddressInvalidated", LI)
                 << "failed to move load with loop-invariant address "
                    "because the loop may invalidate its value";
        });
  
      return !Invalidated;
    } else if (CallInst *CI = dyn_cast<CallInst>(&I)) {
      // Don't sink or hoist dbg info; it's legal, but not useful.
      if (isa<DbgInfoIntrinsic>(I))
        return false;
  
      // Don't sink calls which can throw.
      if (CI->mayThrow())
        return false;
  
      // Convergent attribute has been used on operations that involve
      // inter-thread communication which results are implicitly affected by the
      // enclosing control flows. It is not safe to hoist or sink such operations
      // across control flow.
      if (CI->isConvergent())
        return false;
  
      using namespace PatternMatch;
      if (match(CI, m_Intrinsic<Intrinsic::assume>()))
        // Assumes don't actually alias anything or throw
        return true;
  
      if (match(CI, m_Intrinsic<Intrinsic::experimental_widenable_condition>()))
        // Widenable conditions don't actually alias anything or throw
        return true;
  
      // Handle simple cases by querying alias analysis.
      FunctionModRefBehavior Behavior = AA->getModRefBehavior(CI);
      if (Behavior == FMRB_DoesNotAccessMemory)
        return true;
      if (AAResults::onlyReadsMemory(Behavior)) {
        // A readonly argmemonly function only reads from memory pointed to by
        // it's arguments with arbitrary offsets.  If we can prove there are no
        // writes to this memory in the loop, we can hoist or sink.
        if (AAResults::onlyAccessesArgPointees(Behavior)) {
          // TODO: expand to writeable arguments
          for (Value *Op : CI->arg_operands())
            if (Op->getType()->isPointerTy()) {
              bool Invalidated;
              if (CurAST)
                Invalidated = pointerInvalidatedByLoop(
                    MemoryLocation::getBeforeOrAfter(Op), CurAST, CurLoop, AA);
              else
                Invalidated = pointerInvalidatedByLoopWithMSSA(
                    MSSA, cast<MemoryUse>(MSSA->getMemoryAccess(CI)), CurLoop, I,
                    *Flags);
              if (Invalidated)
                return false;
            }
          return true;
        }
  
        // If this call only reads from memory and there are no writes to memory
        // in the loop, we can hoist or sink the call as appropriate.
        if (isReadOnly(CurAST, MSSAU, CurLoop))
          return true;
      }
  
      // FIXME: This should use mod/ref information to see if we can hoist or
      // sink the call.
  
      return false;
    } else if (auto *FI = dyn_cast<FenceInst>(&I)) {
      // Fences alias (most) everything to provide ordering.  For the moment,
      // just give up if there are any other memory operations in the loop.
      if (CurAST) {
        auto Begin = CurAST->begin();
        assert(Begin != CurAST->end() && "must contain FI");
        if (std::next(Begin) != CurAST->end())
          // constant memory for instance, TODO: handle better
          return false;
        auto *UniqueI = Begin->getUniqueInstruction();
        if (!UniqueI)
          // other memory op, give up
          return false;
        (void)FI; // suppress unused variable warning
        assert(UniqueI == FI && "AS must contain FI");
        return true;
      } else // MSSAU
        return isOnlyMemoryAccess(FI, CurLoop, MSSAU);
    } else if (auto *SI = dyn_cast<StoreInst>(&I)) {
      if (!SI->isUnordered())
        return false; // Don't sink/hoist volatile or ordered atomic store!
  
      // We can only hoist a store that we can prove writes a value which is not
      // read or overwritten within the loop.  For those cases, we fallback to
      // load store promotion instead.  TODO: We can extend this to cases where
      // there is exactly one write to the location and that write dominates an
      // arbitrary number of reads in the loop.
      if (CurAST) {
        auto &AS = CurAST->getAliasSetFor(MemoryLocation::get(SI));
  
        if (AS.isRef() || !AS.isMustAlias())
          // Quick exit test, handled by the full path below as well.
          return false;
        auto *UniqueI = AS.getUniqueInstruction();
        if (!UniqueI)
          // other memory op, give up
          return false;
        assert(UniqueI == SI && "AS must contain SI");
        return true;
      } else { // MSSAU
        if (isOnlyMemoryAccess(SI, CurLoop, MSSAU))
          return true;
        // If there are more accesses than the Promotion cap or no "quota" to
        // check clobber, then give up as we're not walking a list that long.
        if (Flags->tooManyMemoryAccesses() || Flags->tooManyClobberingCalls())
          return false;
        // If there are interfering Uses (i.e. their defining access is in the
        // loop), or ordered loads (stored as Defs!), don't move this store.
        // Could do better here, but this is conservatively correct.
        // TODO: Cache set of Uses on the first walk in runOnLoop, update when
        // moving accesses. Can also extend to dominating uses.
        auto *SIMD = MSSA->getMemoryAccess(SI);
        for (auto *BB : CurLoop->getBlocks())
          if (auto *Accesses = MSSA->getBlockAccesses(BB)) {
            for (const auto &MA : *Accesses)
              if (const auto *MU = dyn_cast<MemoryUse>(&MA)) {
                auto *MD = MU->getDefiningAccess();
                if (!MSSA->isLiveOnEntryDef(MD) &&
                    CurLoop->contains(MD->getBlock()))
                  return false;
                // Disable hoisting past potentially interfering loads. Optimized
                // Uses may point to an access outside the loop, as getClobbering
                // checks the previous iteration when walking the backedge.
                // FIXME: More precise: no Uses that alias SI.
                if (!Flags->getIsSink() && !MSSA->dominates(SIMD, MU))
                  return false;
              } else if (const auto *MD = dyn_cast<MemoryDef>(&MA)) {
                if (auto *LI = dyn_cast<LoadInst>(MD->getMemoryInst())) {
                  (void)LI; // Silence warning.
                  assert(!LI->isUnordered() && "Expected unordered load");
                  return false;
                }
                // Any call, while it may not be clobbering SI, it may be a use.
                if (auto *CI = dyn_cast<CallInst>(MD->getMemoryInst())) {
                  // Check if the call may read from the memory locattion written
                  // to by SI. Check CI's attributes and arguments; the number of
                  // such checks performed is limited above by NoOfMemAccTooLarge.
                  ModRefInfo MRI = AA->getModRefInfo(CI, MemoryLocation::get(SI));
                  if (isModOrRefSet(MRI))
                    return false;
                }
              }
          }
        auto *Source = MSSA->getSkipSelfWalker()->getClobberingMemoryAccess(SI);
        Flags->incrementClobberingCalls();
        // If there are no clobbering Defs in the loop, store is safe to hoist.
        return MSSA->isLiveOnEntryDef(Source) ||
               !CurLoop->contains(Source->getBlock());
      }
    }
  
    assert(!I.mayReadOrWriteMemory() && "unhandled aliasing");
  
    // We've established mechanical ability and aliasing, it's up to the caller
    // to check fault safety
    return true;
  }
  
  /// Returns true if a PHINode is a trivially replaceable with an
  /// Instruction.
  /// This is true when all incoming values are that instruction.
  /// This pattern occurs most often with LCSSA PHI nodes.
  ///
  static bool isTriviallyReplaceablePHI(const PHINode &PN, const Instruction &I) {
    for (const Value *IncValue : PN.incoming_values())
      if (IncValue != &I)
        return false;
  
    return true;
  }
  
  /// Return true if the instruction is free in the loop.
  static bool isFreeInLoop(const Instruction &I, const Loop *CurLoop,
                           const TargetTransformInfo *TTI) {
  
    if (const GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(&I)) {
      if (TTI->getUserCost(GEP, TargetTransformInfo::TCK_SizeAndLatency) !=
          TargetTransformInfo::TCC_Free)
        return false;
      // For a GEP, we cannot simply use getUserCost because currently it
      // optimistically assume that a GEP will fold into addressing mode
      // regardless of its users.
      const BasicBlock *BB = GEP->getParent();
      for (const User *U : GEP->users()) {
        const Instruction *UI = cast<Instruction>(U);
        if (CurLoop->contains(UI) &&
            (BB != UI->getParent() ||
             (!isa<StoreInst>(UI) && !isa<LoadInst>(UI))))
          return false;
      }
      return true;
    } else
      return TTI->getUserCost(&I, TargetTransformInfo::TCK_SizeAndLatency) ==
             TargetTransformInfo::TCC_Free;
  }
  
  /// Return true if the only users of this instruction are outside of
  /// the loop. If this is true, we can sink the instruction to the exit
  /// blocks of the loop.
  ///
  /// We also return true if the instruction could be folded away in lowering.
  /// (e.g.,  a GEP can be folded into a load as an addressing mode in the loop).
  static bool isNotUsedOrFreeInLoop(const Instruction &I, const Loop *CurLoop,
                                    const LoopSafetyInfo *SafetyInfo,
                                    TargetTransformInfo *TTI, bool &FreeInLoop) {
    const auto &BlockColors = SafetyInfo->getBlockColors();
    bool IsFree = isFreeInLoop(I, CurLoop, TTI);
    for (const User *U : I.users()) {
      const Instruction *UI = cast<Instruction>(U);
      if (const PHINode *PN = dyn_cast<PHINode>(UI)) {
        const BasicBlock *BB = PN->getParent();
        // We cannot sink uses in catchswitches.
        if (isa<CatchSwitchInst>(BB->getTerminator()))
          return false;
  
        // We need to sink a callsite to a unique funclet.  Avoid sinking if the
        // phi use is too muddled.
        if (isa<CallInst>(I))
          if (!BlockColors.empty() &&
              BlockColors.find(const_cast<BasicBlock *>(BB))->second.size() != 1)
            return false;
      }
  
      if (CurLoop->contains(UI)) {
        if (IsFree) {
          FreeInLoop = true;
          continue;
        }
        return false;
      }
    }
    return true;
  }
  
  static Instruction *cloneInstructionInExitBlock(
      Instruction &I, BasicBlock &ExitBlock, PHINode &PN, const LoopInfo *LI,
      const LoopSafetyInfo *SafetyInfo, MemorySSAUpdater *MSSAU) {
    Instruction *New;
    if (auto *CI = dyn_cast<CallInst>(&I)) {
      const auto &BlockColors = SafetyInfo->getBlockColors();
  
      // Sinking call-sites need to be handled differently from other
      // instructions.  The cloned call-site needs a funclet bundle operand
      // appropriate for its location in the CFG.
      SmallVector<OperandBundleDef, 1> OpBundles;
      for (unsigned BundleIdx = 0, BundleEnd = CI->getNumOperandBundles();
           BundleIdx != BundleEnd; ++BundleIdx) {
        OperandBundleUse Bundle = CI->getOperandBundleAt(BundleIdx);
        if (Bundle.getTagID() == LLVMContext::OB_funclet)
          continue;
  
        OpBundles.emplace_back(Bundle);
      }
  
      if (!BlockColors.empty()) {
        const ColorVector &CV = BlockColors.find(&ExitBlock)->second;
        assert(CV.size() == 1 && "non-unique color for exit block!");
        BasicBlock *BBColor = CV.front();
        Instruction *EHPad = BBColor->getFirstNonPHI();
        if (EHPad->isEHPad())
          OpBundles.emplace_back("funclet", EHPad);
      }
  
      New = CallInst::Create(CI, OpBundles);
    } else {
      New = I.clone();
    }
  
    ExitBlock.getInstList().insert(ExitBlock.getFirstInsertionPt(), New);
    if (!I.getName().empty())
      New->setName(I.getName() + ".le");
  
    if (MSSAU && MSSAU->getMemorySSA()->getMemoryAccess(&I)) {
      // Create a new MemoryAccess and let MemorySSA set its defining access.
      MemoryAccess *NewMemAcc = MSSAU->createMemoryAccessInBB(
          New, nullptr, New->getParent(), MemorySSA::Beginning);
      if (NewMemAcc) {
        if (auto *MemDef = dyn_cast<MemoryDef>(NewMemAcc))
          MSSAU->insertDef(MemDef, /*RenameUses=*/true);
        else {
          auto *MemUse = cast<MemoryUse>(NewMemAcc);
          MSSAU->insertUse(MemUse, /*RenameUses=*/true);
        }
      }
    }
  
    // Build LCSSA PHI nodes for any in-loop operands. Note that this is
    // particularly cheap because we can rip off the PHI node that we're
    // replacing for the number and blocks of the predecessors.
    // OPT: If this shows up in a profile, we can instead finish sinking all
    // invariant instructions, and then walk their operands to re-establish
    // LCSSA. That will eliminate creating PHI nodes just to nuke them when
    // sinking bottom-up.
    for (User::op_iterator OI = New->op_begin(), OE = New->op_end(); OI != OE;
         ++OI)
      if (Instruction *OInst = dyn_cast<Instruction>(*OI))
        if (Loop *OLoop = LI->getLoopFor(OInst->getParent()))
          if (!OLoop->contains(&PN)) {
            PHINode *OpPN =
                PHINode::Create(OInst->getType(), PN.getNumIncomingValues(),
                                OInst->getName() + ".lcssa", &ExitBlock.front());
            for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i)
              OpPN->addIncoming(OInst, PN.getIncomingBlock(i));
            *OI = OpPN;
          }
    return New;
  }
  
  static void eraseInstruction(Instruction &I, ICFLoopSafetyInfo &SafetyInfo,
                               AliasSetTracker *AST, MemorySSAUpdater *MSSAU) {
    if (AST)
      AST->deleteValue(&I);
    if (MSSAU)
      MSSAU->removeMemoryAccess(&I);
    SafetyInfo.removeInstruction(&I);
    I.eraseFromParent();
  }
  
  static void moveInstructionBefore(Instruction &I, Instruction &Dest,
                                    ICFLoopSafetyInfo &SafetyInfo,
                                    MemorySSAUpdater *MSSAU,
                                    ScalarEvolution *SE) {
    SafetyInfo.removeInstruction(&I);
    SafetyInfo.insertInstructionTo(&I, Dest.getParent());
    I.moveBefore(&Dest);
    if (MSSAU)
      if (MemoryUseOrDef *OldMemAcc = cast_or_null<MemoryUseOrDef>(
              MSSAU->getMemorySSA()->getMemoryAccess(&I)))
        MSSAU->moveToPlace(OldMemAcc, Dest.getParent(),
                           MemorySSA::BeforeTerminator);
    if (SE)
      SE->forgetValue(&I);
  }
  
  static Instruction *sinkThroughTriviallyReplaceablePHI(
      PHINode *TPN, Instruction *I, LoopInfo *LI,
      SmallDenseMap<BasicBlock *, Instruction *, 32> &SunkCopies,
      const LoopSafetyInfo *SafetyInfo, const Loop *CurLoop,
      MemorySSAUpdater *MSSAU) {
    assert(isTriviallyReplaceablePHI(*TPN, *I) &&
           "Expect only trivially replaceable PHI");
    BasicBlock *ExitBlock = TPN->getParent();
    Instruction *New;
    auto It = SunkCopies.find(ExitBlock);
    if (It != SunkCopies.end())
      New = It->second;
    else
      New = SunkCopies[ExitBlock] = cloneInstructionInExitBlock(
          *I, *ExitBlock, *TPN, LI, SafetyInfo, MSSAU);
    return New;
  }
  
  static bool canSplitPredecessors(PHINode *PN, LoopSafetyInfo *SafetyInfo) {
    BasicBlock *BB = PN->getParent();
    if (!BB->canSplitPredecessors())
      return false;
    // It's not impossible to split EHPad blocks, but if BlockColors already exist
    // it require updating BlockColors for all offspring blocks accordingly. By
    // skipping such corner case, we can make updating BlockColors after splitting
    // predecessor fairly simple.
    if (!SafetyInfo->getBlockColors().empty() && BB->getFirstNonPHI()->isEHPad())
      return false;
    for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
      BasicBlock *BBPred = *PI;
      if (isa<IndirectBrInst>(BBPred->getTerminator()) ||
          isa<CallBrInst>(BBPred->getTerminator()))
        return false;
    }
    return true;
  }
  
  static void splitPredecessorsOfLoopExit(PHINode *PN, DominatorTree *DT,
                                          LoopInfo *LI, const Loop *CurLoop,
                                          LoopSafetyInfo *SafetyInfo,
                                          MemorySSAUpdater *MSSAU) {
  #ifndef NDEBUG
    SmallVector<BasicBlock *, 32> ExitBlocks;
    CurLoop->getUniqueExitBlocks(ExitBlocks);
    SmallPtrSet<BasicBlock *, 32> ExitBlockSet(ExitBlocks.begin(),
                                               ExitBlocks.end());
  #endif
    BasicBlock *ExitBB = PN->getParent();
    assert(ExitBlockSet.count(ExitBB) && "Expect the PHI is in an exit block.");
  
    // Split predecessors of the loop exit to make instructions in the loop are
    // exposed to exit blocks through trivially replaceable PHIs while keeping the
    // loop in the canonical form where each predecessor of each exit block should
    // be contained within the loop. For example, this will convert the loop below
    // from
    //
    // LB1:
    //   %v1 =
    //   br %LE, %LB2
    // LB2:
    //   %v2 =
    //   br %LE, %LB1
    // LE:
    //   %p = phi [%v1, %LB1], [%v2, %LB2] <-- non-trivially replaceable
    //
    // to
    //
    // LB1:
    //   %v1 =
    //   br %LE.split, %LB2
    // LB2:
    //   %v2 =
    //   br %LE.split2, %LB1
    // LE.split:
    //   %p1 = phi [%v1, %LB1]  <-- trivially replaceable
    //   br %LE
    // LE.split2:
    //   %p2 = phi [%v2, %LB2]  <-- trivially replaceable
    //   br %LE
    // LE:
    //   %p = phi [%p1, %LE.split], [%p2, %LE.split2]
    //
    const auto &BlockColors = SafetyInfo->getBlockColors();
    SmallSetVector<BasicBlock *, 8> PredBBs(pred_begin(ExitBB), pred_end(ExitBB));
    while (!PredBBs.empty()) {
      BasicBlock *PredBB = *PredBBs.begin();
      assert(CurLoop->contains(PredBB) &&
             "Expect all predecessors are in the loop");
      if (PN->getBasicBlockIndex(PredBB) >= 0) {
        BasicBlock *NewPred = SplitBlockPredecessors(
            ExitBB, PredBB, ".split.loop.exit", DT, LI, MSSAU, true);
        // Since we do not allow splitting EH-block with BlockColors in
        // canSplitPredecessors(), we can simply assign predecessor's color to
        // the new block.
        if (!BlockColors.empty())
          // Grab a reference to the ColorVector to be inserted before getting the
          // reference to the vector we are copying because inserting the new
          // element in BlockColors might cause the map to be reallocated.
          SafetyInfo->copyColors(NewPred, PredBB);
      }
      PredBBs.remove(PredBB);
    }
  }
  
  /// When an instruction is found to only be used outside of the loop, this
  /// function moves it to the exit blocks and patches up SSA form as needed.
  /// This method is guaranteed to remove the original instruction from its
  /// position, and may either delete it or move it to outside of the loop.
  ///
  static bool sink(Instruction &I, LoopInfo *LI, DominatorTree *DT,
                   BlockFrequencyInfo *BFI, const Loop *CurLoop,
                   ICFLoopSafetyInfo *SafetyInfo, MemorySSAUpdater *MSSAU,
                   OptimizationRemarkEmitter *ORE) {
    LLVM_DEBUG(dbgs() << "LICM sinking instruction: " << I << "\n");
    ORE->emit([&]() {
      return OptimizationRemark(DEBUG_TYPE, "InstSunk", &I)
             << "sinking " << ore::NV("Inst", &I);
    });
    bool Changed = false;
    if (isa<LoadInst>(I))
      ++NumMovedLoads;
    else if (isa<CallInst>(I))
      ++NumMovedCalls;
    ++NumSunk;
  
    // Iterate over users to be ready for actual sinking. Replace users via
    // unreachable blocks with undef and make all user PHIs trivially replaceable.
    SmallPtrSet<Instruction *, 8> VisitedUsers;
    for (Value::user_iterator UI = I.user_begin(), UE = I.user_end(); UI != UE;) {
      auto *User = cast<Instruction>(*UI);
      Use &U = UI.getUse();
      ++UI;
  
      if (VisitedUsers.count(User) || CurLoop->contains(User))
        continue;
  
      if (!DT->isReachableFromEntry(User->getParent())) {
        U = UndefValue::get(I.getType());
        Changed = true;
        continue;
      }
  
      // The user must be a PHI node.
      PHINode *PN = cast<PHINode>(User);
  
      // Surprisingly, instructions can be used outside of loops without any
      // exits.  This can only happen in PHI nodes if the incoming block is
      // unreachable.
      BasicBlock *BB = PN->getIncomingBlock(U);
      if (!DT->isReachableFromEntry(BB)) {
        U = UndefValue::get(I.getType());
        Changed = true;
        continue;
      }
  
      VisitedUsers.insert(PN);
      if (isTriviallyReplaceablePHI(*PN, I))
        continue;
  
      if (!canSplitPredecessors(PN, SafetyInfo))
        return Changed;
  
      // Split predecessors of the PHI so that we can make users trivially
      // replaceable.
      splitPredecessorsOfLoopExit(PN, DT, LI, CurLoop, SafetyInfo, MSSAU);
  
      // Should rebuild the iterators, as they may be invalidated by
      // splitPredecessorsOfLoopExit().
      UI = I.user_begin();
      UE = I.user_end();
    }
  
    if (VisitedUsers.empty())
      return Changed;
  
  #ifndef NDEBUG
    SmallVector<BasicBlock *, 32> ExitBlocks;
    CurLoop->getUniqueExitBlocks(ExitBlocks);
    SmallPtrSet<BasicBlock *, 32> ExitBlockSet(ExitBlocks.begin(),
                                               ExitBlocks.end());
  #endif
  
    // Clones of this instruction. Don't create more than one per exit block!
    SmallDenseMap<BasicBlock *, Instruction *, 32> SunkCopies;
  
    // If this instruction is only used outside of the loop, then all users are
    // PHI nodes in exit blocks due to LCSSA form. Just RAUW them with clones of
    // the instruction.
    // First check if I is worth sinking for all uses. Sink only when it is worth
    // across all uses.
    SmallSetVector<User*, 8> Users(I.user_begin(), I.user_end());
    SmallVector<PHINode *, 8> ExitPNs;
    for (auto *UI : Users) {
      auto *User = cast<Instruction>(UI);
  
      if (CurLoop->contains(User))
        continue;
  
      PHINode *PN = cast<PHINode>(User);
      assert(ExitBlockSet.count(PN->getParent()) &&
             "The LCSSA PHI is not in an exit block!");
      if (!worthSinkOrHoistInst(I, PN->getParent(), ORE, BFI)) {
        return Changed;
      }
  
      ExitPNs.push_back(PN);
    }
  
    for (auto *PN : ExitPNs) {
  
      // The PHI must be trivially replaceable.
      Instruction *New = sinkThroughTriviallyReplaceablePHI(
          PN, &I, LI, SunkCopies, SafetyInfo, CurLoop, MSSAU);
      PN->replaceAllUsesWith(New);
      eraseInstruction(*PN, *SafetyInfo, nullptr, nullptr);
      Changed = true;
    }
    return Changed;
  }
  
  /// When an instruction is found to only use loop invariant operands that
  /// is safe to hoist, this instruction is called to do the dirty work.
  ///
  static void hoist(Instruction &I, const DominatorTree *DT, const Loop *CurLoop,
                    BasicBlock *Dest, ICFLoopSafetyInfo *SafetyInfo,
                    MemorySSAUpdater *MSSAU, ScalarEvolution *SE,
                    OptimizationRemarkEmitter *ORE) {
    LLVM_DEBUG(dbgs() << "LICM hoisting to " << Dest->getNameOrAsOperand() << ": "
                      << I << "\n");
    ORE->emit([&]() {
      return OptimizationRemark(DEBUG_TYPE, "Hoisted", &I) << "hoisting "
                                                           << ore::NV("Inst", &I);
    });
  
    // Metadata can be dependent on conditions we are hoisting above.
    // Conservatively strip all metadata on the instruction unless we were
    // guaranteed to execute I if we entered the loop, in which case the metadata
    // is valid in the loop preheader.
    if (I.hasMetadataOtherThanDebugLoc() &&
        // The check on hasMetadataOtherThanDebugLoc is to prevent us from burning
        // time in isGuaranteedToExecute if we don't actually have anything to
        // drop.  It is a compile time optimization, not required for correctness.
        !SafetyInfo->isGuaranteedToExecute(I, DT, CurLoop))
      I.dropUnknownNonDebugMetadata();
  
    if (isa<PHINode>(I))
      // Move the new node to the end of the phi list in the destination block.
      moveInstructionBefore(I, *Dest->getFirstNonPHI(), *SafetyInfo, MSSAU, SE);
    else
      // Move the new node to the destination block, before its terminator.
      moveInstructionBefore(I, *Dest->getTerminator(), *SafetyInfo, MSSAU, SE);
  
    I.updateLocationAfterHoist();
  
    if (isa<LoadInst>(I))
      ++NumMovedLoads;
    else if (isa<CallInst>(I))
      ++NumMovedCalls;
    ++NumHoisted;
  }
  
  /// Only sink or hoist an instruction if it is not a trapping instruction,
  /// or if the instruction is known not to trap when moved to the preheader.
  /// or if it is a trapping instruction and is guaranteed to execute.
  static bool isSafeToExecuteUnconditionally(Instruction &Inst,
                                             const DominatorTree *DT,
                                             const Loop *CurLoop,
                                             const LoopSafetyInfo *SafetyInfo,
                                             OptimizationRemarkEmitter *ORE,
                                             const Instruction *CtxI) {
    if (isSafeToSpeculativelyExecute(&Inst, CtxI, DT))
      return true;
  
    bool GuaranteedToExecute =
        SafetyInfo->isGuaranteedToExecute(Inst, DT, CurLoop);
  
    if (!GuaranteedToExecute) {
      auto *LI = dyn_cast<LoadInst>(&Inst);
      if (LI && CurLoop->isLoopInvariant(LI->getPointerOperand()))
        ORE->emit([&]() {
          return OptimizationRemarkMissed(
                     DEBUG_TYPE, "LoadWithLoopInvariantAddressCondExecuted", LI)
                 << "failed to hoist load with loop-invariant address "
                    "because load is conditionally executed";
        });
    }
  
    return GuaranteedToExecute;
  }
  
  namespace {
  class LoopPromoter : public LoadAndStorePromoter {
    Value *SomePtr; // Designated pointer to store to.
    const SmallSetVector<Value *, 8> &PointerMustAliases;
    SmallVectorImpl<BasicBlock *> &LoopExitBlocks;
    SmallVectorImpl<Instruction *> &LoopInsertPts;
    SmallVectorImpl<MemoryAccess *> &MSSAInsertPts;
    PredIteratorCache &PredCache;
    AliasSetTracker *AST;
    MemorySSAUpdater *MSSAU;
    LoopInfo &LI;
    DebugLoc DL;
    int Alignment;
    bool UnorderedAtomic;
    AAMDNodes AATags;
    ICFLoopSafetyInfo &SafetyInfo;
  
    Value *maybeInsertLCSSAPHI(Value *V, BasicBlock *BB) const {
      if (Instruction *I = dyn_cast<Instruction>(V))
        if (Loop *L = LI.getLoopFor(I->getParent()))
          if (!L->contains(BB)) {
            // We need to create an LCSSA PHI node for the incoming value and
            // store that.
            PHINode *PN = PHINode::Create(I->getType(), PredCache.size(BB),
                                          I->getName() + ".lcssa", &BB->front());
            for (BasicBlock *Pred : PredCache.get(BB))
              PN->addIncoming(I, Pred);
            return PN;
          }
      return V;
    }
  
  public:
    LoopPromoter(Value *SP, ArrayRef<const Instruction *> Insts, SSAUpdater &S,
                 const SmallSetVector<Value *, 8> &PMA,
                 SmallVectorImpl<BasicBlock *> &LEB,
                 SmallVectorImpl<Instruction *> &LIP,
                 SmallVectorImpl<MemoryAccess *> &MSSAIP, PredIteratorCache &PIC,
                 AliasSetTracker *ast, MemorySSAUpdater *MSSAU, LoopInfo &li,
                 DebugLoc dl, int alignment, bool UnorderedAtomic,
                 const AAMDNodes &AATags, ICFLoopSafetyInfo &SafetyInfo)
        : LoadAndStorePromoter(Insts, S), SomePtr(SP), PointerMustAliases(PMA),
          LoopExitBlocks(LEB), LoopInsertPts(LIP), MSSAInsertPts(MSSAIP),
          PredCache(PIC), AST(ast), MSSAU(MSSAU), LI(li), DL(std::move(dl)),
          Alignment(alignment), UnorderedAtomic(UnorderedAtomic), AATags(AATags),
          SafetyInfo(SafetyInfo) {}
  
    bool isInstInList(Instruction *I,
                      const SmallVectorImpl<Instruction *> &) const override {
      Value *Ptr;
      if (LoadInst *LI = dyn_cast<LoadInst>(I))
        Ptr = LI->getOperand(0);
      else
        Ptr = cast<StoreInst>(I)->getPointerOperand();
      return PointerMustAliases.count(Ptr);
    }
  
    void doExtraRewritesBeforeFinalDeletion() override {
      // Insert stores after in the loop exit blocks.  Each exit block gets a
      // store of the live-out values that feed them.  Since we've already told
      // the SSA updater about the defs in the loop and the preheader
      // definition, it is all set and we can start using it.
      for (unsigned i = 0, e = LoopExitBlocks.size(); i != e; ++i) {
        BasicBlock *ExitBlock = LoopExitBlocks[i];
        Value *LiveInValue = SSA.GetValueInMiddleOfBlock(ExitBlock);
        LiveInValue = maybeInsertLCSSAPHI(LiveInValue, ExitBlock);
        Value *Ptr = maybeInsertLCSSAPHI(SomePtr, ExitBlock);
        Instruction *InsertPos = LoopInsertPts[i];
        StoreInst *NewSI = new StoreInst(LiveInValue, Ptr, InsertPos);
        if (UnorderedAtomic)
          NewSI->setOrdering(AtomicOrdering::Unordered);
        NewSI->setAlignment(Align(Alignment));
        NewSI->setDebugLoc(DL);
        if (AATags)
          NewSI->setAAMetadata(AATags);
  
        if (MSSAU) {
          MemoryAccess *MSSAInsertPoint = MSSAInsertPts[i];
          MemoryAccess *NewMemAcc;
          if (!MSSAInsertPoint) {
            NewMemAcc = MSSAU->createMemoryAccessInBB(
                NewSI, nullptr, NewSI->getParent(), MemorySSA::Beginning);
          } else {
            NewMemAcc =
                MSSAU->createMemoryAccessAfter(NewSI, nullptr, MSSAInsertPoint);
          }
          MSSAInsertPts[i] = NewMemAcc;
          MSSAU->insertDef(cast<MemoryDef>(NewMemAcc), true);
          // FIXME: true for safety, false may still be correct.
        }
      }
    }
  
    void replaceLoadWithValue(LoadInst *LI, Value *V) const override {
      // Update alias analysis.
      if (AST)
        AST->copyValue(LI, V);
    }
    void instructionDeleted(Instruction *I) const override {
      SafetyInfo.removeInstruction(I);
      if (AST)
        AST->deleteValue(I);
      if (MSSAU)
        MSSAU->removeMemoryAccess(I);
    }
  };
  
  
  /// Return true iff we can prove that a caller of this function can not inspect
  /// the contents of the provided object in a well defined program.
  bool isKnownNonEscaping(Value *Object, const TargetLibraryInfo *TLI) {
    if (isa<AllocaInst>(Object))
      // Since the alloca goes out of scope, we know the caller can't retain a
      // reference to it and be well defined.  Thus, we don't need to check for
      // capture.
      return true;
  
    // For all other objects we need to know that the caller can't possibly
    // have gotten a reference to the object.  There are two components of
    // that:
    //   1) Object can't be escaped by this function.  This is what
    //      PointerMayBeCaptured checks.
    //   2) Object can't have been captured at definition site.  For this, we
    //      need to know the return value is noalias.  At the moment, we use a
    //      weaker condition and handle only AllocLikeFunctions (which are
    //      known to be noalias).  TODO
    return isAllocLikeFn(Object, TLI) &&
      !PointerMayBeCaptured(Object, true, true);
  }
  
  } // namespace
  
  /// Try to promote memory values to scalars by sinking stores out of the
  /// loop and moving loads to before the loop.  We do this by looping over
  /// the stores in the loop, looking for stores to Must pointers which are
  /// loop invariant.
  ///
  bool llvm::promoteLoopAccessesToScalars(
      const SmallSetVector<Value *, 8> &PointerMustAliases,
      SmallVectorImpl<BasicBlock *> &ExitBlocks,
      SmallVectorImpl<Instruction *> &InsertPts,
      SmallVectorImpl<MemoryAccess *> &MSSAInsertPts, PredIteratorCache &PIC,
      LoopInfo *LI, DominatorTree *DT, const TargetLibraryInfo *TLI,
      Loop *CurLoop, AliasSetTracker *CurAST, MemorySSAUpdater *MSSAU,
      ICFLoopSafetyInfo *SafetyInfo, OptimizationRemarkEmitter *ORE) {
    // Verify inputs.
    assert(LI != nullptr && DT != nullptr && CurLoop != nullptr &&
           SafetyInfo != nullptr &&
           "Unexpected Input to promoteLoopAccessesToScalars");
  
    Value *SomePtr = *PointerMustAliases.begin();
    BasicBlock *Preheader = CurLoop->getLoopPreheader();
  
    // It is not safe to promote a load/store from the loop if the load/store is
    // conditional.  For example, turning:
    //
    //    for () { if (c) *P += 1; }
    //
    // into:
    //
    //    tmp = *P;  for () { if (c) tmp +=1; } *P = tmp;
    //
    // is not safe, because *P may only be valid to access if 'c' is true.
    //
    // The safety property divides into two parts:
    // p1) The memory may not be dereferenceable on entry to the loop.  In this
    //    case, we can't insert the required load in the preheader.
    // p2) The memory model does not allow us to insert a store along any dynamic
    //    path which did not originally have one.
    //
    // If at least one store is guaranteed to execute, both properties are
    // satisfied, and promotion is legal.
    //
    // This, however, is not a necessary condition. Even if no store/load is
    // guaranteed to execute, we can still establish these properties.
    // We can establish (p1) by proving that hoisting the load into the preheader
    // is safe (i.e. proving dereferenceability on all paths through the loop). We
    // can use any access within the alias set to prove dereferenceability,
    // since they're all must alias.
    //
    // There are two ways establish (p2):
    // a) Prove the location is thread-local. In this case the memory model
    // requirement does not apply, and stores are safe to insert.
    // b) Prove a store dominates every exit block. In this case, if an exit
    // blocks is reached, the original dynamic path would have taken us through
    // the store, so inserting a store into the exit block is safe. Note that this
    // is different from the store being guaranteed to execute. For instance,
    // if an exception is thrown on the first iteration of the loop, the original
    // store is never executed, but the exit blocks are not executed either.
  
    bool DereferenceableInPH = false;
    bool SafeToInsertStore = false;
  
    SmallVector<Instruction *, 64> LoopUses;
  
    // We start with an alignment of one and try to find instructions that allow
    // us to prove better alignment.
    Align Alignment;
    // Keep track of which types of access we see
    bool SawUnorderedAtomic = false;
    bool SawNotAtomic = false;
    AAMDNodes AATags;
  
    const DataLayout &MDL = Preheader->getModule()->getDataLayout();
  
    bool IsKnownThreadLocalObject = false;
    if (SafetyInfo->anyBlockMayThrow()) {
      // If a loop can throw, we have to insert a store along each unwind edge.
      // That said, we can't actually make the unwind edge explicit. Therefore,
      // we have to prove that the store is dead along the unwind edge.  We do
      // this by proving that the caller can't have a reference to the object
      // after return and thus can't possibly load from the object.
      Value *Object = getUnderlyingObject(SomePtr);
      if (!isKnownNonEscaping(Object, TLI))
        return false;
      // Subtlety: Alloca's aren't visible to callers, but *are* potentially
      // visible to other threads if captured and used during their lifetimes.
      IsKnownThreadLocalObject = !isa<AllocaInst>(Object);
    }
  
    // Check that all of the pointers in the alias set have the same type.  We
    // cannot (yet) promote a memory location that is loaded and stored in
    // different sizes.  While we are at it, collect alignment and AA info.
    for (Value *ASIV : PointerMustAliases) {
      // Check that all of the pointers in the alias set have the same type.  We
      // cannot (yet) promote a memory location that is loaded and stored in
      // different sizes.
      if (SomePtr->getType() != ASIV->getType())
        return false;
  
      for (User *U : ASIV->users()) {
        // Ignore instructions that are outside the loop.
        Instruction *UI = dyn_cast<Instruction>(U);
        if (!UI || !CurLoop->contains(UI))
          continue;
  
        // If there is an non-load/store instruction in the loop, we can't promote
        // it.
        if (LoadInst *Load = dyn_cast<LoadInst>(UI)) {
          if (!Load->isUnordered())
            return false;
  
          SawUnorderedAtomic |= Load->isAtomic();
          SawNotAtomic |= !Load->isAtomic();
  
          Align InstAlignment = Load->getAlign();
  
          // Note that proving a load safe to speculate requires proving
          // sufficient alignment at the target location.  Proving it guaranteed
          // to execute does as well.  Thus we can increase our guaranteed
          // alignment as well. 
          if (!DereferenceableInPH || (InstAlignment > Alignment))
            if (isSafeToExecuteUnconditionally(*Load, DT, CurLoop, SafetyInfo,
                                               ORE, Preheader->getTerminator())) {
              DereferenceableInPH = true;
              Alignment = std::max(Alignment, InstAlignment);
            }
        } else if (const StoreInst *Store = dyn_cast<StoreInst>(UI)) {
          // Stores *of* the pointer are not interesting, only stores *to* the
          // pointer.
          if (UI->getOperand(1) != ASIV)
            continue;
          if (!Store->isUnordered())
            return false;
  
          SawUnorderedAtomic |= Store->isAtomic();
          SawNotAtomic |= !Store->isAtomic();
  
          // If the store is guaranteed to execute, both properties are satisfied.
          // We may want to check if a store is guaranteed to execute even if we
          // already know that promotion is safe, since it may have higher
          // alignment than any other guaranteed stores, in which case we can
          // raise the alignment on the promoted store.
          Align InstAlignment = Store->getAlign();
  
          if (!DereferenceableInPH || !SafeToInsertStore ||
              (InstAlignment > Alignment)) {
            if (SafetyInfo->isGuaranteedToExecute(*UI, DT, CurLoop)) {
              DereferenceableInPH = true;
              SafeToInsertStore = true;
              Alignment = std::max(Alignment, InstAlignment);
            }
          }
  
          // If a store dominates all exit blocks, it is safe to sink.
          // As explained above, if an exit block was executed, a dominating
          // store must have been executed at least once, so we are not
          // introducing stores on paths that did not have them.
          // Note that this only looks at explicit exit blocks. If we ever
          // start sinking stores into unwind edges (see above), this will break.
          if (!SafeToInsertStore)
            SafeToInsertStore = llvm::all_of(ExitBlocks, [&](BasicBlock *Exit) {
              return DT->dominates(Store->getParent(), Exit);
            });
  
          // If the store is not guaranteed to execute, we may still get
          // deref info through it.
          if (!DereferenceableInPH) {
            DereferenceableInPH = isDereferenceableAndAlignedPointer(
                Store->getPointerOperand(), Store->getValueOperand()->getType(),
                Store->getAlign(), MDL, Preheader->getTerminator(), DT);
          }
        } else
          return false; // Not a load or store.
  
        // Merge the AA tags.
        if (LoopUses.empty()) {
          // On the first load/store, just take its AA tags.
          UI->getAAMetadata(AATags);
        } else if (AATags) {
          UI->getAAMetadata(AATags, /* Merge = */ true);
        }
  
        LoopUses.push_back(UI);
      }
    }
  
    // If we found both an unordered atomic instruction and a non-atomic memory
    // access, bail.  We can't blindly promote non-atomic to atomic since we
    // might not be able to lower the result.  We can't downgrade since that
    // would violate memory model.  Also, align 0 is an error for atomics.
    if (SawUnorderedAtomic && SawNotAtomic)
      return false;
  
    // If we're inserting an atomic load in the preheader, we must be able to
    // lower it.  We're only guaranteed to be able to lower naturally aligned
    // atomics.
    auto *SomePtrElemType = SomePtr->getType()->getPointerElementType();
    if (SawUnorderedAtomic &&
        Alignment < MDL.getTypeStoreSize(SomePtrElemType))
      return false;
  
    // If we couldn't prove we can hoist the load, bail.
    if (!DereferenceableInPH)
      return false;
  
    // We know we can hoist the load, but don't have a guaranteed store.
    // Check whether the location is thread-local. If it is, then we can insert
    // stores along paths which originally didn't have them without violating the
    // memory model.
    if (!SafeToInsertStore) {
      if (IsKnownThreadLocalObject)
        SafeToInsertStore = true;
      else {
        Value *Object = getUnderlyingObject(SomePtr);
        SafeToInsertStore =
            (isAllocLikeFn(Object, TLI) || isa<AllocaInst>(Object)) &&
            !PointerMayBeCaptured(Object, true, true);
      }
    }
  
    // If we've still failed to prove we can sink the store, give up.
    if (!SafeToInsertStore)
      return false;
  
    // Otherwise, this is safe to promote, lets do it!
    LLVM_DEBUG(dbgs() << "LICM: Promoting value stored to in loop: " << *SomePtr
                      << '\n');
    ORE->emit([&]() {
      return OptimizationRemark(DEBUG_TYPE, "PromoteLoopAccessesToScalar",
                                LoopUses[0])
             << "Moving accesses to memory location out of the loop";
    });
    ++NumPromoted;
  
    // Look at all the loop uses, and try to merge their locations.
    std::vector<const DILocation *> LoopUsesLocs;
    for (auto U : LoopUses)
      LoopUsesLocs.push_back(U->getDebugLoc().get());
    auto DL = DebugLoc(DILocation::getMergedLocations(LoopUsesLocs));
  
    // We use the SSAUpdater interface to insert phi nodes as required.
    SmallVector<PHINode *, 16> NewPHIs;
    SSAUpdater SSA(&NewPHIs);
    LoopPromoter Promoter(SomePtr, LoopUses, SSA, PointerMustAliases, ExitBlocks,
                          InsertPts, MSSAInsertPts, PIC, CurAST, MSSAU, *LI, DL,
                          Alignment.value(), SawUnorderedAtomic, AATags,
                          *SafetyInfo);
  
    // Set up the preheader to have a definition of the value.  It is the live-out
    // value from the preheader that uses in the loop will use.
    LoadInst *PreheaderLoad = new LoadInst(
        SomePtr->getType()->getPointerElementType(), SomePtr,
        SomePtr->getName() + ".promoted", Preheader->getTerminator());
    if (SawUnorderedAtomic)
      PreheaderLoad->setOrdering(AtomicOrdering::Unordered);
    PreheaderLoad->setAlignment(Alignment);
    PreheaderLoad->setDebugLoc(DebugLoc());
    if (AATags)
      PreheaderLoad->setAAMetadata(AATags);
    SSA.AddAvailableValue(Preheader, PreheaderLoad);
  
    if (MSSAU) {
      MemoryAccess *PreheaderLoadMemoryAccess = MSSAU->createMemoryAccessInBB(
          PreheaderLoad, nullptr, PreheaderLoad->getParent(), MemorySSA::End);
      MemoryUse *NewMemUse = cast<MemoryUse>(PreheaderLoadMemoryAccess);
      MSSAU->insertUse(NewMemUse, /*RenameUses=*/true);
    }
  
    if (MSSAU && VerifyMemorySSA)
      MSSAU->getMemorySSA()->verifyMemorySSA();
    // Rewrite all the loads in the loop and remember all the definitions from
    // stores in the loop.
    Promoter.run(LoopUses);
  
    if (MSSAU && VerifyMemorySSA)
      MSSAU->getMemorySSA()->verifyMemorySSA();
    // If the SSAUpdater didn't use the load in the preheader, just zap it now.
    if (PreheaderLoad->use_empty())
      eraseInstruction(*PreheaderLoad, *SafetyInfo, CurAST, MSSAU);
  
    return true;
  }
  
  /// Returns an owning pointer to an alias set which incorporates aliasing info
  /// from L and all subloops of L.
  std::unique_ptr<AliasSetTracker>
  LoopInvariantCodeMotion::collectAliasInfoForLoop(Loop *L, LoopInfo *LI,
                                                   AAResults *AA) {
    auto CurAST = std::make_unique<AliasSetTracker>(*AA);
  
    // Add everything from all the sub loops.
    for (Loop *InnerL : L->getSubLoops())
      for (BasicBlock *BB : InnerL->blocks())
        CurAST->add(*BB);
  
    // And merge in this loop (without anything from inner loops).
    for (BasicBlock *BB : L->blocks())
      if (LI->getLoopFor(BB) == L)
        CurAST->add(*BB);
  
    return CurAST;
  }
  
  std::unique_ptr<AliasSetTracker>
  LoopInvariantCodeMotion::collectAliasInfoForLoopWithMSSA(
      Loop *L, AAResults *AA, MemorySSAUpdater *MSSAU) {
    auto *MSSA = MSSAU->getMemorySSA();
    auto CurAST = std::make_unique<AliasSetTracker>(*AA, MSSA, L);
    CurAST->addAllInstructionsInLoopUsingMSSA();
    return CurAST;
  }
  
  static bool pointerInvalidatedByLoop(MemoryLocation MemLoc,
                                       AliasSetTracker *CurAST, Loop *CurLoop,
                                       AAResults *AA) {
    // First check to see if any of the basic blocks in CurLoop invalidate *V.
    bool isInvalidatedAccordingToAST = CurAST->getAliasSetFor(MemLoc).isMod();
  
    if (!isInvalidatedAccordingToAST || !LICMN2Theshold)
      return isInvalidatedAccordingToAST;
  
    // Check with a diagnostic analysis if we can refine the information above.
    // This is to identify the limitations of using the AST.
    // The alias set mechanism used by LICM has a major weakness in that it
    // combines all things which may alias into a single set *before* asking
    // modref questions. As a result, a single readonly call within a loop will
    // collapse all loads and stores into a single alias set and report
    // invalidation if the loop contains any store. For example, readonly calls
    // with deopt states have this form and create a general alias set with all
    // loads and stores.  In order to get any LICM in loops containing possible
    // deopt states we need a more precise invalidation of checking the mod ref
    // info of each instruction within the loop and LI. This has a complexity of
    // O(N^2), so currently, it is used only as a diagnostic tool since the
    // default value of LICMN2Threshold is zero.
  
    // Don't look at nested loops.
    if (CurLoop->begin() != CurLoop->end())
      return true;
  
    int N = 0;
    for (BasicBlock *BB : CurLoop->getBlocks())
      for (Instruction &I : *BB) {
        if (N >= LICMN2Theshold) {
          LLVM_DEBUG(dbgs() << "Alasing N2 threshold exhausted for "
                            << *(MemLoc.Ptr) << "\n");
          return true;
        }
        N++;
        auto Res = AA->getModRefInfo(&I, MemLoc);
        if (isModSet(Res)) {
          LLVM_DEBUG(dbgs() << "Aliasing failed on " << I << " for "
                            << *(MemLoc.Ptr) << "\n");
          return true;
        }
      }
    LLVM_DEBUG(dbgs() << "Aliasing okay for " << *(MemLoc.Ptr) << "\n");
    return false;
  }
  
  bool pointerInvalidatedByLoopWithMSSA(MemorySSA *MSSA, MemoryUse *MU,
                                        Loop *CurLoop, Instruction &I,
                                        SinkAndHoistLICMFlags &Flags) {
    // For hoisting, use the walker to determine safety
    if (!Flags.getIsSink()) {
      MemoryAccess *Source;
      // See declaration of SetLicmMssaOptCap for usage details.
      if (Flags.tooManyClobberingCalls())
        Source = MU->getDefiningAccess();
      else {
        Source = MSSA->getSkipSelfWalker()->getClobberingMemoryAccess(MU);
        Flags.incrementClobberingCalls();
      }
      return !MSSA->isLiveOnEntryDef(Source) &&
             CurLoop->contains(Source->getBlock());
    }
  
    // For sinking, we'd need to check all Defs below this use. The getClobbering
    // call will look on the backedge of the loop, but will check aliasing with
    // the instructions on the previous iteration.
    // For example:
    // for (i ... )
    //   load a[i] ( Use (LoE)
    //   store a[i] ( 1 = Def (2), with 2 = Phi for the loop.
    //   i++;
    // The load sees no clobbering inside the loop, as the backedge alias check
    // does phi translation, and will check aliasing against store a[i-1].
    // However sinking the load outside the loop, below the store is incorrect.
  
    // For now, only sink if there are no Defs in the loop, and the existing ones
    // precede the use and are in the same block.
    // FIXME: Increase precision: Safe to sink if Use post dominates the Def;
    // needs PostDominatorTreeAnalysis.
    // FIXME: More precise: no Defs that alias this Use.
    if (Flags.tooManyMemoryAccesses())
      return true;
    for (auto *BB : CurLoop->getBlocks())
      if (pointerInvalidatedByBlockWithMSSA(*BB, *MSSA, *MU))
        return true;
    // When sinking, the source block may not be part of the loop so check it.
    if (!CurLoop->contains(&I))
      return pointerInvalidatedByBlockWithMSSA(*I.getParent(), *MSSA, *MU);
  
    return false;
  }
  
  bool pointerInvalidatedByBlockWithMSSA(BasicBlock &BB, MemorySSA &MSSA,
                                         MemoryUse &MU) {
    if (const auto *Accesses = MSSA.getBlockDefs(&BB))
      for (const auto &MA : *Accesses)
        if (const auto *MD = dyn_cast<MemoryDef>(&MA))
          if (MU.getBlock() != MD->getBlock() || !MSSA.locallyDominates(MD, &MU))
            return true;
    return false;
  }
  
  /// Little predicate that returns true if the specified basic block is in
  /// a subloop of the current one, not the current one itself.
  ///
  static bool inSubLoop(BasicBlock *BB, Loop *CurLoop, LoopInfo *LI) {
    assert(CurLoop->contains(BB) && "Only valid if BB is IN the loop");
    return LI->getLoopFor(BB) != CurLoop;
  }
  