text: //===-- LICM.cpp - Loop Invariant Code Motion Pass ------------------------===//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  //
  // 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.
  //
  // 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/ADT/Statistic.h"
  #include "llvm/Analysis/AliasAnalysis.h"
  #include "llvm/Analysis/AliasSetTracker.h"
  #include "llvm/Analysis/BasicAliasAnalysis.h"
  #include "llvm/Analysis/CaptureTracking.h"
  #include "llvm/Analysis/ConstantFolding.h"
  #include "llvm/Analysis/GlobalsModRef.h"
  #include "llvm/Analysis/Loads.h"
  #include "llvm/Analysis/LoopInfo.h"
  #include "llvm/Analysis/LoopPass.h"
  #include "llvm/Analysis/MemoryBuiltins.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/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/PredIteratorCache.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/Utils/Local.h"
  #include "llvm/Transforms/Utils/LoopUtils.h"
  #include "llvm/Transforms/Utils/SSAUpdater.h"
  #include <algorithm>
  using namespace llvm;
  
  #define DEBUG_TYPE "licm"
  
  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");
  
  static cl::opt<bool>
      DisablePromotion("disable-licm-promotion", cl::Hidden,
                       cl::desc("Disable memory promotion in LICM pass"));
  
  static bool inSubLoop(BasicBlock *BB, Loop *CurLoop, LoopInfo *LI);
  static bool isNotUsedInLoop(const Instruction &I, const Loop *CurLoop,
                              const LICMSafetyInfo *SafetyInfo);
  static bool hoist(Instruction &I, const DominatorTree *DT, const Loop *CurLoop,
                    const LICMSafetyInfo *SafetyInfo);
  static bool sink(Instruction &I, const LoopInfo *LI, const DominatorTree *DT,
                   const Loop *CurLoop, AliasSetTracker *CurAST,
                   const LICMSafetyInfo *SafetyInfo);
  static bool isGuaranteedToExecute(const Instruction &Inst,
                                    const DominatorTree *DT, const Loop *CurLoop,
                                    const LICMSafetyInfo *SafetyInfo);
  static bool isSafeToExecuteUnconditionally(const Instruction &Inst,
                                             const DominatorTree *DT,
                                             const TargetLibraryInfo *TLI,
                                             const Loop *CurLoop,
                                             const LICMSafetyInfo *SafetyInfo,
                                             const Instruction *CtxI = nullptr);
  static bool pointerInvalidatedByLoop(Value *V, uint64_t Size,
                                       const AAMDNodes &AAInfo,
                                       AliasSetTracker *CurAST);
  static Instruction *
  CloneInstructionInExitBlock(Instruction &I, BasicBlock &ExitBlock, PHINode &PN,
                              const LoopInfo *LI,
                              const LICMSafetyInfo *SafetyInfo);
  static bool canSinkOrHoistInst(Instruction &I, AliasAnalysis *AA,
                                 DominatorTree *DT, TargetLibraryInfo *TLI,
                                 Loop *CurLoop, AliasSetTracker *CurAST,
                                 LICMSafetyInfo *SafetyInfo);
  
  namespace {
  struct LICM : public LoopPass {
    static char ID; // Pass identification, replacement for typeid
    LICM() : LoopPass(ID) {
      initializeLICMPass(*PassRegistry::getPassRegistry());
    }
  
    bool runOnLoop(Loop *L, LPPassManager &LPM) override;
  
    /// This transformation requires natural loop information & requires that
    /// loop preheaders be inserted into the CFG...
    ///
    void getAnalysisUsage(AnalysisUsage &AU) const override {
      AU.setPreservesCFG();
      AU.addRequired<TargetLibraryInfoWrapperPass>();
      getLoopAnalysisUsage(AU);
    }
  
    using llvm::Pass::doFinalization;
  
    bool doFinalization() override {
      assert(LoopToAliasSetMap.empty() && "Didn't free loop alias sets");
      return false;
    }
  
  private:
    AliasAnalysis *AA; // Current AliasAnalysis information
    LoopInfo *LI;      // Current LoopInfo
    DominatorTree *DT; // Dominator Tree for the current Loop.
  
    TargetLibraryInfo *TLI; // TargetLibraryInfo for constant folding.
  
    // State that is updated as we process loops.
    bool Changed;            // Set to true when we change anything.
    BasicBlock *Preheader;   // The preheader block of the current loop...
    Loop *CurLoop;           // The current loop we are working on...
    AliasSetTracker *CurAST; // AliasSet information for the current loop...
    DenseMap<Loop *, AliasSetTracker *> LoopToAliasSetMap;
  
    /// cloneBasicBlockAnalysis - Simple Analysis hook. Clone alias set info.
    void cloneBasicBlockAnalysis(BasicBlock *From, BasicBlock *To,
                                 Loop *L) override;
  
    /// deleteAnalysisValue - Simple Analysis hook. Delete value V from alias
    /// set.
    void deleteAnalysisValue(Value *V, Loop *L) override;
  
    /// Simple Analysis hook. Delete loop L from alias set map.
    void deleteAnalysisLoop(Loop *L) override;
  
    AliasSetTracker *collectAliasInfoForLoop(Loop *L);
  };
  }
  
  char LICM::ID = 0;
  INITIALIZE_PASS_BEGIN(LICM, "licm", "Loop Invariant Code Motion", false, false)
  INITIALIZE_PASS_DEPENDENCY(LoopPass)
  INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
  INITIALIZE_PASS_END(LICM, "licm", "Loop Invariant Code Motion", false, false)
  
  Pass *llvm::createLICMPass() { return new LICM(); }
  
  /// 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 LICM::runOnLoop(Loop *L, LPPassManager &LPM) {
    if (skipLoop(L))
      return false;
  
    Changed = false;
  
    // Get our Loop and Alias Analysis information...
    LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
    AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
    DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
  
    TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
  
    assert(L->isLCSSAForm(*DT) && "Loop is not in LCSSA form.");
  
    CurAST = collectAliasInfoForLoop(L);
  
    CurLoop = L;
  
    // Get the preheader block to move instructions into...
    Preheader = L->getLoopPreheader();
  
    // Compute loop safety information.
    LICMSafetyInfo SafetyInfo;
    computeLICMSafetyInfo(&SafetyInfo, CurLoop);
  
    // 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, TLI, CurLoop,
                            CurAST, &SafetyInfo);
    if (Preheader)
      Changed |= hoistRegion(DT->getNode(L->getHeader()), AA, LI, DT, TLI,
                             CurLoop, CurAST, &SafetyInfo);
  
    // Now that all loop invariants have been removed from the loop, promote any
    // memory references to scalars that we can.
    if (!DisablePromotion && (Preheader || L->hasDedicatedExits())) {
      SmallVector<BasicBlock *, 8> ExitBlocks;
      SmallVector<Instruction *, 8> InsertPts;
      PredIteratorCache PIC;
  
      // Loop over all of the alias sets in the tracker object.
      for (AliasSet &AS : *CurAST)
        Changed |=
            promoteLoopAccessesToScalars(AS, ExitBlocks, InsertPts, PIC, LI, DT,
                                         TLI, CurLoop, CurAST, &SafetyInfo);
  
      // 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 (Changed) {
        auto *SEWP = getAnalysisIfAvailable<ScalarEvolutionWrapperPass>();
        formLCSSARecursively(*L, *DT, LI, SEWP ? &SEWP->getSE() : nullptr);
      }
    }
  
    // 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->getParentLoop() || L->getParentLoop()->isLCSSAForm(*DT)) &&
           "Parent loop not left in LCSSA form after LICM!");
  
    // Clear out loops state information for the next iteration
    CurLoop = nullptr;
    Preheader = nullptr;
  
    // If this loop is nested inside of another one, save the alias information
    // for when we process the outer loop.
    if (L->getParentLoop())
      LoopToAliasSetMap[L] = CurAST;
    else
      delete CurAST;
  
    if (Changed)
      if (auto *SEWP = getAnalysisIfAvailable<ScalarEvolutionWrapperPass>())
        SEWP->getSE().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, AliasAnalysis *AA, LoopInfo *LI,
                        DominatorTree *DT, TargetLibraryInfo *TLI, Loop *CurLoop,
                        AliasSetTracker *CurAST, LICMSafetyInfo *SafetyInfo) {
  
    // Verify inputs.
    assert(N != nullptr && AA != nullptr && LI != nullptr && DT != nullptr &&
           CurLoop != nullptr && CurAST != nullptr && SafetyInfo != nullptr &&
           "Unexpected input to sinkRegion");
  
    BasicBlock *BB = N->getBlock();
    // If this subregion is not in the top level loop at all, exit.
    if (!CurLoop->contains(BB))
      return false;
  
    // We are processing blocks in reverse dfo, so process children first.
    bool Changed = false;
    const std::vector<DomTreeNode *> &Children = N->getChildren();
    for (DomTreeNode *Child : Children)
      Changed |= sinkRegion(Child, AA, LI, DT, TLI, CurLoop, CurAST, SafetyInfo);
  
    // 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))
      return Changed;
  
    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)) {
        DEBUG(dbgs() << "LICM deleting dead inst: " << I << '\n');
        ++II;
        CurAST->deleteValue(&I);
        I.eraseFromParent();
        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.
      //
      if (isNotUsedInLoop(I, CurLoop, SafetyInfo) &&
          canSinkOrHoistInst(I, AA, DT, TLI, CurLoop, CurAST, SafetyInfo)) {
        ++II;
        Changed |= sink(I, LI, DT, CurLoop, CurAST, SafetyInfo);
      }
    }
    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 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, AliasAnalysis *AA, LoopInfo *LI,
                         DominatorTree *DT, TargetLibraryInfo *TLI, Loop *CurLoop,
                         AliasSetTracker *CurAST, LICMSafetyInfo *SafetyInfo) {
    // Verify inputs.
    assert(N != nullptr && AA != nullptr && LI != nullptr && DT != nullptr &&
           CurLoop != nullptr && CurAST != nullptr && SafetyInfo != nullptr &&
           "Unexpected input to hoistRegion");
  
    BasicBlock *BB = N->getBlock();
  
    // If this subregion is not in the top level loop at all, exit.
    if (!CurLoop->contains(BB))
      return false;
  
    // Only need to process the contents of this block if it is not part of a
    // subloop (which would already have been processed).
    bool Changed = false;
    if (!inSubLoop(BB, CurLoop, LI))
      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)) {
          DEBUG(dbgs() << "LICM folding inst: " << I << "  --> " << *C << '\n');
          CurAST->copyValue(&I, C);
          CurAST->deleteValue(&I);
          I.replaceAllUsesWith(C);
          I.eraseFromParent();
          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.
        //
        if (CurLoop->hasLoopInvariantOperands(&I) &&
            canSinkOrHoistInst(I, AA, DT, TLI, CurLoop, CurAST, SafetyInfo) &&
            isSafeToExecuteUnconditionally(
                I, DT, TLI, CurLoop, SafetyInfo,
                CurLoop->getLoopPreheader()->getTerminator()))
          Changed |= hoist(I, DT, CurLoop, SafetyInfo);
      }
  
    const std::vector<DomTreeNode *> &Children = N->getChildren();
    for (DomTreeNode *Child : Children)
      Changed |= hoistRegion(Child, AA, LI, DT, TLI, CurLoop, CurAST, SafetyInfo);
    return Changed;
  }
  
  /// Computes loop safety information, checks loop body & header
  /// for the possibility of may throw exception.
  ///
  void llvm::computeLICMSafetyInfo(LICMSafetyInfo *SafetyInfo, Loop *CurLoop) {
    assert(CurLoop != nullptr && "CurLoop cant be null");
    BasicBlock *Header = CurLoop->getHeader();
    // Setting default safety values.
    SafetyInfo->MayThrow = false;
    SafetyInfo->HeaderMayThrow = false;
    // Iterate over header and compute safety info.
    for (BasicBlock::iterator I = Header->begin(), E = Header->end();
         (I != E) && !SafetyInfo->HeaderMayThrow; ++I)
      SafetyInfo->HeaderMayThrow |= I->mayThrow();
  
    SafetyInfo->MayThrow = SafetyInfo->HeaderMayThrow;
    // Iterate over loop instructions and compute safety info.
    for (Loop::block_iterator BB = CurLoop->block_begin(),
                              BBE = CurLoop->block_end();
         (BB != BBE) && !SafetyInfo->MayThrow; ++BB)
      for (BasicBlock::iterator I = (*BB)->begin(), E = (*BB)->end();
           (I != E) && !SafetyInfo->MayThrow; ++I)
        SafetyInfo->MayThrow |= I->mayThrow();
  
    // Compute funclet colors if we might sink/hoist in a function with a funclet
    // personality routine.
    Function *Fn = CurLoop->getHeader()->getParent();
    if (Fn->hasPersonalityFn())
      if (Constant *PersonalityFn = Fn->getPersonalityFn())
        if (isFuncletEHPersonality(classifyEHPersonality(PersonalityFn)))
          SafetyInfo->BlockColors = colorEHFunclets(*Fn);
  }
  
  /// canSinkOrHoistInst - Return true if the hoister and sinker can handle this
  /// instruction.
  ///
  bool canSinkOrHoistInst(Instruction &I, AliasAnalysis *AA, DominatorTree *DT,
                          TargetLibraryInfo *TLI, Loop *CurLoop,
                          AliasSetTracker *CurAST, LICMSafetyInfo *SafetyInfo) {
    // 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 hoist volatile/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->getMetadata(LLVMContext::MD_invariant_load))
        return true;
  
      // Don't hoist loads which have may-aliased stores in loop.
      uint64_t Size = 0;
      if (LI->getType()->isSized())
        Size = I.getModule()->getDataLayout().getTypeStoreSize(LI->getType());
  
      AAMDNodes AAInfo;
      LI->getAAMetadata(AAInfo);
  
      return !pointerInvalidatedByLoop(LI->getOperand(0), Size, AAInfo, CurAST);
    } 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;
  
      // Handle simple cases by querying alias analysis.
      FunctionModRefBehavior Behavior = AA->getModRefBehavior(CI);
      if (Behavior == FMRB_DoesNotAccessMemory)
        return true;
      if (AliasAnalysis::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 (AliasAnalysis::onlyAccessesArgPointees(Behavior)) {
          for (Value *Op : CI->arg_operands())
            if (Op->getType()->isPointerTy() &&
                pointerInvalidatedByLoop(Op, MemoryLocation::UnknownSize,
                                         AAMDNodes(), CurAST))
              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.
        bool FoundMod = false;
        for (AliasSet &AS : *CurAST) {
          if (!AS.isForwardingAliasSet() && AS.isMod()) {
            FoundMod = true;
            break;
          }
        }
        if (!FoundMod)
          return true;
      }
  
      // FIXME: This should use mod/ref information to see if we can hoist or
      // sink the call.
  
      return false;
    }
  
    // Only these instructions are hoistable/sinkable.
    if (!isa<BinaryOperator>(I) && !isa<CastInst>(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))
      return false;
  
    // TODO: Plumb the context instruction through to make hoisting and sinking
    // more powerful. Hoisting of loads already works due to the special casing
    // above.
    return isSafeToExecuteUnconditionally(I, DT, TLI, CurLoop, SafetyInfo,
                                          nullptr);
  }
  
  /// 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 isTriviallyReplacablePHI(const PHINode &PN, const Instruction &I) {
    for (const Value *IncValue : PN.incoming_values())
      if (IncValue != &I)
        return false;
  
    return true;
  }
  
  /// 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.
  ///
  static bool isNotUsedInLoop(const Instruction &I, const Loop *CurLoop,
                              const LICMSafetyInfo *SafetyInfo) {
    const auto &BlockColors = SafetyInfo->BlockColors;
    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;
  
        // A PHI node where all of the incoming values are this instruction are
        // special -- they can just be RAUW'ed with the instruction and thus
        // don't require a use in the predecessor. This is a particular important
        // special case because it is the pattern found in LCSSA form.
        if (isTriviallyReplacablePHI(*PN, I)) {
          if (CurLoop->contains(PN))
            return false;
          else
            continue;
        }
  
        // Otherwise, PHI node uses occur in predecessor blocks if the incoming
        // values. Check for such a use being inside the loop.
        for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
          if (PN->getIncomingValue(i) == &I)
            if (CurLoop->contains(PN->getIncomingBlock(i)))
              return false;
  
        continue;
      }
  
      if (CurLoop->contains(UI))
        return false;
    }
    return true;
  }
  
  static Instruction *
  CloneInstructionInExitBlock(Instruction &I, BasicBlock &ExitBlock, PHINode &PN,
                              const LoopInfo *LI,
                              const LICMSafetyInfo *SafetyInfo) {
    Instruction *New;
    if (auto *CI = dyn_cast<CallInst>(&I)) {
      const auto &BlockColors = SafetyInfo->BlockColors;
  
      // Sinking call-sites need to be handled differently from other
      // instructions.  The cloned call-site needs a funclet bundle operand
      // appropriate for it's 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");
  
    // 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;
  }
  
  /// 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, const LoopInfo *LI, const DominatorTree *DT,
                   const Loop *CurLoop, AliasSetTracker *CurAST,
                   const LICMSafetyInfo *SafetyInfo) {
    DEBUG(dbgs() << "LICM sinking instruction: " << I << "\n");
    bool Changed = false;
    if (isa<LoadInst>(I))
      ++NumMovedLoads;
    else if (isa<CallInst>(I))
      ++NumMovedCalls;
    ++NumSunk;
    Changed = true;
  
  #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.
    while (!I.use_empty()) {
      Value::user_iterator UI = I.user_begin();
      auto *User = cast<Instruction>(*UI);
      if (!DT->isReachableFromEntry(User->getParent())) {
        User->replaceUsesOfWith(&I, UndefValue::get(I.getType()));
        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.
      Use &U = UI.getUse();
      BasicBlock *BB = PN->getIncomingBlock(U);
      if (!DT->isReachableFromEntry(BB)) {
        U = UndefValue::get(I.getType());
        continue;
      }
  
      BasicBlock *ExitBlock = PN->getParent();
      assert(ExitBlockSet.count(ExitBlock) &&
             "The LCSSA PHI is not in an exit block!");
  
      Instruction *New;
      auto It = SunkCopies.find(ExitBlock);
      if (It != SunkCopies.end())
        New = It->second;
      else
        New = SunkCopies[ExitBlock] =
            CloneInstructionInExitBlock(I, *ExitBlock, *PN, LI, SafetyInfo);
  
      PN->replaceAllUsesWith(New);
      PN->eraseFromParent();
    }
  
    CurAST->deleteValue(&I);
    I.eraseFromParent();
    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 bool hoist(Instruction &I, const DominatorTree *DT, const Loop *CurLoop,
                    const LICMSafetyInfo *SafetyInfo) {
    auto *Preheader = CurLoop->getLoopPreheader();
    DEBUG(dbgs() << "LICM hoisting to " << Preheader->getName() << ": " << I
                 << "\n");
  
    // 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.
        !isGuaranteedToExecute(I, DT, CurLoop, SafetyInfo))
      I.dropUnknownNonDebugMetadata();
  
    // Move the new node to the Preheader, before its terminator.
    I.moveBefore(Preheader->getTerminator());
  
    if (isa<LoadInst>(I))
      ++NumMovedLoads;
    else if (isa<CallInst>(I))
      ++NumMovedCalls;
    ++NumHoisted;
    return true;
  }
  
  /// 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(const Instruction &Inst,
                                             const DominatorTree *DT,
                                             const TargetLibraryInfo *TLI,
                                             const Loop *CurLoop,
                                             const LICMSafetyInfo *SafetyInfo,
                                             const Instruction *CtxI) {
    if (isSafeToSpeculativelyExecute(&Inst, CtxI, DT, TLI))
      return true;
  
    return isGuaranteedToExecute(Inst, DT, CurLoop, SafetyInfo);
  }
  
  static bool isGuaranteedToExecute(const Instruction &Inst,
                                    const DominatorTree *DT, const Loop *CurLoop,
                                    const LICMSafetyInfo *SafetyInfo) {
  
    // We have to check to make sure that the instruction dominates all
    // of the exit blocks.  If it doesn't, then there is a path out of the loop
    // which does not execute this instruction, so we can't hoist it.
  
    // If the instruction is in the header block for the loop (which is very
    // common), it is always guaranteed to dominate the exit blocks.  Since this
    // is a common case, and can save some work, check it now.
    if (Inst.getParent() == CurLoop->getHeader())
      // If there's a throw in the header block, we can't guarantee we'll reach
      // Inst.
      return !SafetyInfo->HeaderMayThrow;
  
    // Somewhere in this loop there is an instruction which may throw and make us
    // exit the loop.
    if (SafetyInfo->MayThrow)
      return false;
  
    // Get the exit blocks for the current loop.
    SmallVector<BasicBlock *, 8> ExitBlocks;
    CurLoop->getExitBlocks(ExitBlocks);
  
    // Verify that the block dominates each of the exit blocks of the loop.
    for (BasicBlock *ExitBlock : ExitBlocks)
      if (!DT->dominates(Inst.getParent(), ExitBlock))
        return false;
  
    // As a degenerate case, if the loop is statically infinite then we haven't
    // proven anything since there are no exit blocks.
    if (ExitBlocks.empty())
      return false;
  
    return true;
  }
  
  namespace {
  class LoopPromoter : public LoadAndStorePromoter {
    Value *SomePtr; // Designated pointer to store to.
    SmallPtrSetImpl<Value *> &PointerMustAliases;
    SmallVectorImpl<BasicBlock *> &LoopExitBlocks;
    SmallVectorImpl<Instruction *> &LoopInsertPts;
    PredIteratorCache &PredCache;
    AliasSetTracker &AST;
    LoopInfo &LI;
    DebugLoc DL;
    int Alignment;
    AAMDNodes AATags;
  
    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,
                 SmallPtrSetImpl<Value *> &PMA,
                 SmallVectorImpl<BasicBlock *> &LEB,
                 SmallVectorImpl<Instruction *> &LIP, PredIteratorCache &PIC,
                 AliasSetTracker &ast, LoopInfo &li, DebugLoc dl, int alignment,
                 const AAMDNodes &AATags)
        : LoadAndStorePromoter(Insts, S), SomePtr(SP), PointerMustAliases(PMA),
          LoopExitBlocks(LEB), LoopInsertPts(LIP), PredCache(PIC), AST(ast),
          LI(li), DL(dl), Alignment(alignment), AATags(AATags) {}
  
    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() const 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);
        NewSI->setAlignment(Alignment);
        NewSI->setDebugLoc(DL);
        if (AATags)
          NewSI->setAAMetadata(AATags);
      }
    }
  
    void replaceLoadWithValue(LoadInst *LI, Value *V) const override {
      // Update alias analysis.
      AST.copyValue(LI, V);
    }
    void instructionDeleted(Instruction *I) const override { AST.deleteValue(I); }
  };
  } // end anon 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(
      AliasSet &AS, SmallVectorImpl<BasicBlock *> &ExitBlocks,
      SmallVectorImpl<Instruction *> &InsertPts, PredIteratorCache &PIC,
      LoopInfo *LI, DominatorTree *DT, const TargetLibraryInfo *TLI,
      Loop *CurLoop, AliasSetTracker *CurAST, LICMSafetyInfo *SafetyInfo) {
    // Verify inputs.
    assert(LI != nullptr && DT != nullptr && CurLoop != nullptr &&
           CurAST != nullptr && SafetyInfo != nullptr &&
           "Unexpected Input to promoteLoopAccessesToScalars");
  
    // 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() ||
        AS.isVolatile() || !CurLoop->isLoopInvariant(AS.begin()->getValue()))
      return false;
  
    assert(!AS.empty() &&
           "Must alias set should have at least one pointer element in it!");
  
    Value *SomePtr = AS.begin()->getValue();
    BasicBlock *Preheader = CurLoop->getLoopPreheader();
  
    // It isn't 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:
    // 1) The memory may not be dereferenceable on entry to the loop.  In this
    //    case, we can't insert the required load in the preheader.
    // 2) The memory model does not allow us to insert a store along any dynamic
    //    path which did not originally have one.
    //
    // It is safe to promote P if all uses are direct load/stores and if at
    // least one is guaranteed to be executed.
    bool GuaranteedToExecute = false;
  
    // It is also safe to promote P if we can prove that speculating a load into
    // the preheader is safe (i.e. proving dereferenceability on all
    // paths through the loop), and that the memory can be proven thread local
    // (so that the memory model requirement doesn't apply.)  We first establish
    // the former, and then run a capture analysis below to establish the later.
    // We can use any access within the alias set to prove dereferenceability
    // since they're all must alias.
    bool CanSpeculateLoad = false;
  
    SmallVector<Instruction *, 64> LoopUses;
    SmallPtrSet<Value *, 4> PointerMustAliases;
  
    // We start with an alignment of one and try to find instructions that allow
    // us to prove better alignment.
    unsigned Alignment = 1;
    AAMDNodes AATags;
    bool HasDedicatedExits = CurLoop->hasDedicatedExits();
  
    // 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 (!HasDedicatedExits || !Preheader)
      return false;
  
    const DataLayout &MDL = Preheader->getModule()->getDataLayout();
  
    // 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.
    bool Changed = false;
    for (AliasSet::iterator ASI = AS.begin(), E = AS.end(); ASI != E; ++ASI) {
      Value *ASIV = ASI->getValue();
      PointerMustAliases.insert(ASIV);
  
      // 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 Changed;
  
      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 (const LoadInst *Load = dyn_cast<LoadInst>(UI)) {
          assert(!Load->isVolatile() && "AST broken");
          if (!Load->isSimple())
            return Changed;
  
          if (!GuaranteedToExecute && !CanSpeculateLoad)
            CanSpeculateLoad = isSafeToExecuteUnconditionally(
                *Load, DT, TLI, CurLoop, SafetyInfo, Preheader->getTerminator());
        } 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;
          assert(!Store->isVolatile() && "AST broken");
          if (!Store->isSimple())
            return Changed;
  
          // Note that we only check GuaranteedToExecute inside the store case
          // so that we do not introduce stores where they did not exist before
          // (which would break the LLVM concurrency model).
  
          // If the alignment of this instruction allows us to specify a more
          // restrictive (and performant) alignment and if we are sure this
          // instruction will be executed, update the alignment.
          // Larger is better, with the exception of 0 being the best alignment.
          unsigned InstAlignment = Store->getAlignment();
          if ((InstAlignment > Alignment || InstAlignment == 0) && Alignment != 0)
            if (isGuaranteedToExecute(*UI, DT, CurLoop, SafetyInfo)) {
              GuaranteedToExecute = true;
              Alignment = InstAlignment;
            }
  
          if (!GuaranteedToExecute)
            GuaranteedToExecute =
                isGuaranteedToExecute(*UI, DT, CurLoop, SafetyInfo);
  
          if (!GuaranteedToExecute && !CanSpeculateLoad) {
            CanSpeculateLoad = isDereferenceableAndAlignedPointer(
                Store->getPointerOperand(), Store->getAlignment(), MDL,
                Preheader->getTerminator(), DT, TLI);
          }
        } else
          return Changed; // 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);
      }
    }
  
    // Check legality per comment above. Otherwise, we can't promote.
    bool PromotionIsLegal = GuaranteedToExecute;
    if (!PromotionIsLegal && CanSpeculateLoad) {
      // If this is a thread local location, then we can insert stores along
      // paths which originally didn't have them without violating the memory
      // model.
      Value *Object = GetUnderlyingObject(SomePtr, MDL);
      PromotionIsLegal =
          isAllocLikeFn(Object, TLI) && !PointerMayBeCaptured(Object, true, true);
    }
    if (!PromotionIsLegal)
      return Changed;
  
    // Figure out the loop exits and their insertion points, if this is the
    // first promotion.
    if (ExitBlocks.empty()) {
      CurLoop->getUniqueExitBlocks(ExitBlocks);
      InsertPts.clear();
      InsertPts.reserve(ExitBlocks.size());
      for (BasicBlock *ExitBlock : ExitBlocks)
        InsertPts.push_back(&*ExitBlock->getFirstInsertionPt());
    }
  
    // Can't insert into a catchswitch.
    for (BasicBlock *ExitBlock : ExitBlocks)
      if (isa<CatchSwitchInst>(ExitBlock->getTerminator()))
        return Changed;
  
    // Otherwise, this is safe to promote, lets do it!
    DEBUG(dbgs() << "LICM: Promoting value stored to in loop: " << *SomePtr
                 << '\n');
    Changed = true;
    ++NumPromoted;
  
    // Grab a debug location for the inserted loads/stores; given that the
    // inserted loads/stores have little relation to the original loads/stores,
    // this code just arbitrarily picks a location from one, since any debug
    // location is better than none.
    DebugLoc DL = LoopUses[0]->getDebugLoc();
  
    // 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, PIC, *CurAST, *LI, DL, Alignment, AATags);
  
    // 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, SomePtr->getName() + ".promoted", Preheader->getTerminator());
    PreheaderLoad->setAlignment(Alignment);
    PreheaderLoad->setDebugLoc(DL);
    if (AATags)
      PreheaderLoad->setAAMetadata(AATags);
    SSA.AddAvailableValue(Preheader, PreheaderLoad);
  
    // Rewrite all the loads in the loop and remember all the definitions from
    // stores in the loop.
    Promoter.run(LoopUses);
  
    // If the SSAUpdater didn't use the load in the preheader, just zap it now.
    if (PreheaderLoad->use_empty())
      PreheaderLoad->eraseFromParent();
  
    return Changed;
  }
  
  /// Returns an owning pointer to an alias set which incorporates aliasing info
  /// from L and all subloops of L.
  AliasSetTracker *LICM::collectAliasInfoForLoop(Loop *L) {
    AliasSetTracker *CurAST = nullptr;
    SmallVector<Loop *, 4> RecomputeLoops;
    for (Loop *InnerL : L->getSubLoops()) {
      auto MapI = LoopToAliasSetMap.find(InnerL);
      // If the AST for this inner loop is missing it may have been merged into
      // some other loop's AST and then that loop unrolled, and so we need to
      // recompute it.
      if (MapI == LoopToAliasSetMap.end()) {
        RecomputeLoops.push_back(InnerL);
        continue;
      }
      AliasSetTracker *InnerAST = MapI->second;
  
      if (CurAST != nullptr) {
        // What if InnerLoop was modified by other passes ?
        CurAST->add(*InnerAST);
  
        // Once we've incorporated the inner loop's AST into ours, we don't need
        // the subloop's anymore.
        delete InnerAST;
      } else {
        CurAST = InnerAST;
      }
      LoopToAliasSetMap.erase(MapI);
    }
    if (CurAST == nullptr)
      CurAST = new AliasSetTracker(*AA);
  
    auto mergeLoop = [&](Loop *L) {
      // Loop over the body of this loop, looking for calls, invokes, and stores.
      // Because subloops have already been incorporated into AST, we skip blocks
      // in subloops.
      for (BasicBlock *BB : L->blocks())
        if (LI->getLoopFor(BB) == L) // Ignore blocks in subloops.
          CurAST->add(*BB);          // Incorporate the specified basic block
    };
  
    // Add everything from the sub loops that are no longer directly available.
    for (Loop *InnerL : RecomputeLoops)
      mergeLoop(InnerL);
  
    // And merge in this loop.
    mergeLoop(L);
  
    return CurAST;
  }
  
  /// Simple analysis hook. Clone alias set info.
  ///
  void LICM::cloneBasicBlockAnalysis(BasicBlock *From, BasicBlock *To, Loop *L) {
    AliasSetTracker *AST = LoopToAliasSetMap.lookup(L);
    if (!AST)
      return;
  
    AST->copyValue(From, To);
  }
  
  /// Simple Analysis hook. Delete value V from alias set
  ///
  void LICM::deleteAnalysisValue(Value *V, Loop *L) {
    AliasSetTracker *AST = LoopToAliasSetMap.lookup(L);
    if (!AST)
      return;
  
    AST->deleteValue(V);
  }
  
  /// Simple Analysis hook. Delete value L from alias set map.
  ///
  void LICM::deleteAnalysisLoop(Loop *L) {
    AliasSetTracker *AST = LoopToAliasSetMap.lookup(L);
    if (!AST)
      return;
  
    delete AST;
    LoopToAliasSetMap.erase(L);
  }
  
  /// Return true if the body of this loop may store into the memory
  /// location pointed to by V.
  ///
  static bool pointerInvalidatedByLoop(Value *V, uint64_t Size,
                                       const AAMDNodes &AAInfo,
                                       AliasSetTracker *CurAST) {
    // Check to see if any of the basic blocks in CurLoop invalidate *V.
    return CurAST->getAliasSetForPointer(V, Size, AAInfo).isMod();
  }
  
  /// 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;
  }
  