text: //===- llvm/Analysis/LoopAccessAnalysis.h -----------------------*- C++ -*-===//
  //
  // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  // See https://llvm.org/LICENSE.txt for license information.
  // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
  //
  //===----------------------------------------------------------------------===//
  //
  // This file defines the interface for the loop memory dependence framework that
  // was originally developed for the Loop Vectorizer.
  //
  //===----------------------------------------------------------------------===//
  
  #ifndef LLVM_ANALYSIS_LOOPACCESSANALYSIS_H
  #define LLVM_ANALYSIS_LOOPACCESSANALYSIS_H
  
  #include "llvm/ADT/EquivalenceClasses.h"
  #include "llvm/Analysis/LoopAnalysisManager.h"
  #include "llvm/Analysis/ScalarEvolutionExpressions.h"
  #include "llvm/IR/DiagnosticInfo.h"
  #include "llvm/Pass.h"
  
  namespace llvm {
  
  class AAResults;
  class DataLayout;
  class Loop;
  class LoopAccessInfo;
  class raw_ostream;
  class SCEV;
  class SCEVUnionPredicate;
  class Value;
  
  /// Collection of parameters shared beetween the Loop Vectorizer and the
  /// Loop Access Analysis.
  struct VectorizerParams {
    /// Maximum SIMD width.
    static const unsigned MaxVectorWidth;
  
    /// VF as overridden by the user.
    static unsigned VectorizationFactor;
    /// Interleave factor as overridden by the user.
    static unsigned VectorizationInterleave;
    /// True if force-vector-interleave was specified by the user.
    static bool isInterleaveForced();
  
    /// \When performing memory disambiguation checks at runtime do not
    /// make more than this number of comparisons.
    static unsigned RuntimeMemoryCheckThreshold;
  };
  
  /// Checks memory dependences among accesses to the same underlying
  /// object to determine whether there vectorization is legal or not (and at
  /// which vectorization factor).
  ///
  /// Note: This class will compute a conservative dependence for access to
  /// different underlying pointers. Clients, such as the loop vectorizer, will
  /// sometimes deal these potential dependencies by emitting runtime checks.
  ///
  /// We use the ScalarEvolution framework to symbolically evalutate access
  /// functions pairs. Since we currently don't restructure the loop we can rely
  /// on the program order of memory accesses to determine their safety.
  /// At the moment we will only deem accesses as safe for:
  ///  * A negative constant distance assuming program order.
  ///
  ///      Safe: tmp = a[i + 1];     OR     a[i + 1] = x;
  ///            a[i] = tmp;                y = a[i];
  ///
  ///   The latter case is safe because later checks guarantuee that there can't
  ///   be a cycle through a phi node (that is, we check that "x" and "y" is not
  ///   the same variable: a header phi can only be an induction or a reduction, a
  ///   reduction can't have a memory sink, an induction can't have a memory
  ///   source). This is important and must not be violated (or we have to
  ///   resort to checking for cycles through memory).
  ///
  ///  * A positive constant distance assuming program order that is bigger
  ///    than the biggest memory access.
  ///
  ///     tmp = a[i]        OR              b[i] = x
  ///     a[i+2] = tmp                      y = b[i+2];
  ///
  ///     Safe distance: 2 x sizeof(a[0]), and 2 x sizeof(b[0]), respectively.
  ///
  ///  * Zero distances and all accesses have the same size.
  ///
  class MemoryDepChecker {
  public:
    typedef PointerIntPair<Value *, 1, bool> MemAccessInfo;
    typedef SmallVector<MemAccessInfo, 8> MemAccessInfoList;
    /// Set of potential dependent memory accesses.
    typedef EquivalenceClasses<MemAccessInfo> DepCandidates;
  
    /// Type to keep track of the status of the dependence check. The order of
    /// the elements is important and has to be from most permissive to least
    /// permissive.
    enum class VectorizationSafetyStatus {
      // Can vectorize safely without RT checks. All dependences are known to be
      // safe.
      Safe,
      // Can possibly vectorize with RT checks to overcome unknown dependencies.
      PossiblySafeWithRtChecks,
      // Cannot vectorize due to known unsafe dependencies.
      Unsafe,
    };
  
    /// Dependece between memory access instructions.
    struct Dependence {
      /// The type of the dependence.
      enum DepType {
        // No dependence.
        NoDep,
        // We couldn't determine the direction or the distance.
        Unknown,
        // Lexically forward.
        //
        // FIXME: If we only have loop-independent forward dependences (e.g. a
        // read and write of A[i]), LAA will locally deem the dependence "safe"
        // without querying the MemoryDepChecker.  Therefore we can miss
        // enumerating loop-independent forward dependences in
        // getDependences.  Note that as soon as there are different
        // indices used to access the same array, the MemoryDepChecker *is*
        // queried and the dependence list is complete.
        Forward,
        // Forward, but if vectorized, is likely to prevent store-to-load
        // forwarding.
        ForwardButPreventsForwarding,
        // Lexically backward.
        Backward,
        // Backward, but the distance allows a vectorization factor of
        // MaxSafeDepDistBytes.
        BackwardVectorizable,
        // Same, but may prevent store-to-load forwarding.
        BackwardVectorizableButPreventsForwarding
      };
  
      /// String version of the types.
      static const char *DepName[];
  
      /// Index of the source of the dependence in the InstMap vector.
      unsigned Source;
      /// Index of the destination of the dependence in the InstMap vector.
      unsigned Destination;
      /// The type of the dependence.
      DepType Type;
  
      Dependence(unsigned Source, unsigned Destination, DepType Type)
          : Source(Source), Destination(Destination), Type(Type) {}
  
      /// Return the source instruction of the dependence.
      Instruction *getSource(const LoopAccessInfo &LAI) const;
      /// Return the destination instruction of the dependence.
      Instruction *getDestination(const LoopAccessInfo &LAI) const;
  
      /// Dependence types that don't prevent vectorization.
      static VectorizationSafetyStatus isSafeForVectorization(DepType Type);
  
      /// Lexically forward dependence.
      bool isForward() const;
      /// Lexically backward dependence.
      bool isBackward() const;
  
      /// May be a lexically backward dependence type (includes Unknown).
      bool isPossiblyBackward() const;
  
      /// Print the dependence.  \p Instr is used to map the instruction
      /// indices to instructions.
      void print(raw_ostream &OS, unsigned Depth,
                 const SmallVectorImpl<Instruction *> &Instrs) const;
    };
  
    MemoryDepChecker(PredicatedScalarEvolution &PSE, const Loop *L)
        : PSE(PSE), InnermostLoop(L) {}
  
    /// Register the location (instructions are given increasing numbers)
    /// of a write access.
    void addAccess(StoreInst *SI);
  
    /// Register the location (instructions are given increasing numbers)
    /// of a write access.
    void addAccess(LoadInst *LI);
  
    /// Check whether the dependencies between the accesses are safe.
    ///
    /// Only checks sets with elements in \p CheckDeps.
    bool areDepsSafe(DepCandidates &AccessSets, MemAccessInfoList &CheckDeps,
                     const ValueToValueMap &Strides);
  
    /// No memory dependence was encountered that would inhibit
    /// vectorization.
    bool isSafeForVectorization() const {
      return Status == VectorizationSafetyStatus::Safe;
    }
  
    /// Return true if the number of elements that are safe to operate on
    /// simultaneously is not bounded.
    bool isSafeForAnyVectorWidth() const {
      return MaxSafeVectorWidthInBits == UINT_MAX;
    }
  
    /// The maximum number of bytes of a vector register we can vectorize
    /// the accesses safely with.
    uint64_t getMaxSafeDepDistBytes() { return MaxSafeDepDistBytes; }
  
    /// Return the number of elements that are safe to operate on
    /// simultaneously, multiplied by the size of the element in bits.
    uint64_t getMaxSafeVectorWidthInBits() const {
      return MaxSafeVectorWidthInBits;
    }
  
    /// In same cases when the dependency check fails we can still
    /// vectorize the loop with a dynamic array access check.
    bool shouldRetryWithRuntimeCheck() const {
      return FoundNonConstantDistanceDependence &&
             Status == VectorizationSafetyStatus::PossiblySafeWithRtChecks;
    }
  
    /// Returns the memory dependences.  If null is returned we exceeded
    /// the MaxDependences threshold and this information is not
    /// available.
    const SmallVectorImpl<Dependence> *getDependences() const {
      return RecordDependences ? &Dependences : nullptr;
    }
  
    void clearDependences() { Dependences.clear(); }
  
    /// The vector of memory access instructions.  The indices are used as
    /// instruction identifiers in the Dependence class.
    const SmallVectorImpl<Instruction *> &getMemoryInstructions() const {
      return InstMap;
    }
  
    /// Generate a mapping between the memory instructions and their
    /// indices according to program order.
    DenseMap<Instruction *, unsigned> generateInstructionOrderMap() const {
      DenseMap<Instruction *, unsigned> OrderMap;
  
      for (unsigned I = 0; I < InstMap.size(); ++I)
        OrderMap[InstMap[I]] = I;
  
      return OrderMap;
    }
  
    /// Find the set of instructions that read or write via \p Ptr.
    SmallVector<Instruction *, 4> getInstructionsForAccess(Value *Ptr,
                                                           bool isWrite) const;
  
    /// Return the program order indices for the access location (Ptr, IsWrite).
    /// Returns an empty ArrayRef if there are no accesses for the location.
    ArrayRef<unsigned> getOrderForAccess(Value *Ptr, bool IsWrite) const {
      auto I = Accesses.find({Ptr, IsWrite});
      if (I != Accesses.end())
        return I->second;
      return {};
    }
  
  private:
    /// A wrapper around ScalarEvolution, used to add runtime SCEV checks, and
    /// applies dynamic knowledge to simplify SCEV expressions and convert them
    /// to a more usable form. We need this in case assumptions about SCEV
    /// expressions need to be made in order to avoid unknown dependences. For
    /// example we might assume a unit stride for a pointer in order to prove
    /// that a memory access is strided and doesn't wrap.
    PredicatedScalarEvolution &PSE;
    const Loop *InnermostLoop;
  
    /// Maps access locations (ptr, read/write) to program order.
    DenseMap<MemAccessInfo, std::vector<unsigned> > Accesses;
  
    /// Memory access instructions in program order.
    SmallVector<Instruction *, 16> InstMap;
  
    /// The program order index to be used for the next instruction.
    unsigned AccessIdx = 0;
  
    // We can access this many bytes in parallel safely.
    uint64_t MaxSafeDepDistBytes = 0;
  
    /// Number of elements (from consecutive iterations) that are safe to
    /// operate on simultaneously, multiplied by the size of the element in bits.
    /// The size of the element is taken from the memory access that is most
    /// restrictive.
    uint64_t MaxSafeVectorWidthInBits = -1U;
  
    /// If we see a non-constant dependence distance we can still try to
    /// vectorize this loop with runtime checks.
    bool FoundNonConstantDistanceDependence = false;
  
    /// Result of the dependence checks, indicating whether the checked
    /// dependences are safe for vectorization, require RT checks or are known to
    /// be unsafe.
    VectorizationSafetyStatus Status = VectorizationSafetyStatus::Safe;
  
    //// True if Dependences reflects the dependences in the
    //// loop.  If false we exceeded MaxDependences and
    //// Dependences is invalid.
    bool RecordDependences = true;
  
    /// Memory dependences collected during the analysis.  Only valid if
    /// RecordDependences is true.
    SmallVector<Dependence, 8> Dependences;
  
    /// Check whether there is a plausible dependence between the two
    /// accesses.
    ///
    /// Access \p A must happen before \p B in program order. The two indices
    /// identify the index into the program order map.
    ///
    /// This function checks  whether there is a plausible dependence (or the
    /// absence of such can't be proved) between the two accesses. If there is a
    /// plausible dependence but the dependence distance is bigger than one
    /// element access it records this distance in \p MaxSafeDepDistBytes (if this
    /// distance is smaller than any other distance encountered so far).
    /// Otherwise, this function returns true signaling a possible dependence.
    Dependence::DepType isDependent(const MemAccessInfo &A, unsigned AIdx,
                                    const MemAccessInfo &B, unsigned BIdx,
                                    const ValueToValueMap &Strides);
  
    /// Check whether the data dependence could prevent store-load
    /// forwarding.
    ///
    /// \return false if we shouldn't vectorize at all or avoid larger
    /// vectorization factors by limiting MaxSafeDepDistBytes.
    bool couldPreventStoreLoadForward(uint64_t Distance, uint64_t TypeByteSize);
  
    /// Updates the current safety status with \p S. We can go from Safe to
    /// either PossiblySafeWithRtChecks or Unsafe and from
    /// PossiblySafeWithRtChecks to Unsafe.
    void mergeInStatus(VectorizationSafetyStatus S);
  };
  
  class RuntimePointerChecking;
  /// A grouping of pointers. A single memcheck is required between
  /// two groups.
  struct RuntimeCheckingPtrGroup {
    /// Create a new pointer checking group containing a single
    /// pointer, with index \p Index in RtCheck.
    RuntimeCheckingPtrGroup(unsigned Index, RuntimePointerChecking &RtCheck);
  
    RuntimeCheckingPtrGroup(unsigned Index, const SCEV *Start, const SCEV *End,
                            unsigned AS)
        : High(End), Low(Start), AddressSpace(AS) {
      Members.push_back(Index);
    }
  
    /// Tries to add the pointer recorded in RtCheck at index
    /// \p Index to this pointer checking group. We can only add a pointer
    /// to a checking group if we will still be able to get
    /// the upper and lower bounds of the check. Returns true in case
    /// of success, false otherwise.
    bool addPointer(unsigned Index, RuntimePointerChecking &RtCheck);
    bool addPointer(unsigned Index, const SCEV *Start, const SCEV *End,
                    unsigned AS, ScalarEvolution &SE);
  
    /// The SCEV expression which represents the upper bound of all the
    /// pointers in this group.
    const SCEV *High;
    /// The SCEV expression which represents the lower bound of all the
    /// pointers in this group.
    const SCEV *Low;
    /// Indices of all the pointers that constitute this grouping.
    SmallVector<unsigned, 2> Members;
    /// Address space of the involved pointers.
    unsigned AddressSpace;
  };
  
  /// A memcheck which made up of a pair of grouped pointers.
  typedef std::pair<const RuntimeCheckingPtrGroup *,
                    const RuntimeCheckingPtrGroup *>
      RuntimePointerCheck;
  
  struct PointerDiffInfo {
    const SCEV *SrcStart;
    const SCEV *SinkStart;
    unsigned AccessSize;
  
    PointerDiffInfo(const SCEV *SrcStart, const SCEV *SinkStart,
                    unsigned AccessSize)
        : SrcStart(SrcStart), SinkStart(SinkStart), AccessSize(AccessSize) {}
  };
  
  /// Holds information about the memory runtime legality checks to verify
  /// that a group of pointers do not overlap.
  class RuntimePointerChecking {
    friend struct RuntimeCheckingPtrGroup;
  
  public:
    struct PointerInfo {
      /// Holds the pointer value that we need to check.
      TrackingVH<Value> PointerValue;
      /// Holds the smallest byte address accessed by the pointer throughout all
      /// iterations of the loop.
      const SCEV *Start;
      /// Holds the largest byte address accessed by the pointer throughout all
      /// iterations of the loop, plus 1.
      const SCEV *End;
      /// Holds the information if this pointer is used for writing to memory.
      bool IsWritePtr;
      /// Holds the id of the set of pointers that could be dependent because of a
      /// shared underlying object.
      unsigned DependencySetId;
      /// Holds the id of the disjoint alias set to which this pointer belongs.
      unsigned AliasSetId;
      /// SCEV for the access.
      const SCEV *Expr;
  
      PointerInfo(Value *PointerValue, const SCEV *Start, const SCEV *End,
                  bool IsWritePtr, unsigned DependencySetId, unsigned AliasSetId,
                  const SCEV *Expr)
          : PointerValue(PointerValue), Start(Start), End(End),
            IsWritePtr(IsWritePtr), DependencySetId(DependencySetId),
            AliasSetId(AliasSetId), Expr(Expr) {}
    };
  
    RuntimePointerChecking(MemoryDepChecker &DC, ScalarEvolution *SE)
        : DC(DC), SE(SE) {}
  
    /// Reset the state of the pointer runtime information.
    void reset() {
      Need = false;
      Pointers.clear();
      Checks.clear();
    }
  
    /// Insert a pointer and calculate the start and end SCEVs.
    /// We need \p PSE in order to compute the SCEV expression of the pointer
    /// according to the assumptions that we've made during the analysis.
    /// The method might also version the pointer stride according to \p Strides,
    /// and add new predicates to \p PSE.
    void insert(Loop *Lp, Value *Ptr, const SCEV *PtrExpr, Type *AccessTy,
                bool WritePtr, unsigned DepSetId, unsigned ASId,
                PredicatedScalarEvolution &PSE);
  
    /// No run-time memory checking is necessary.
    bool empty() const { return Pointers.empty(); }
  
    /// Generate the checks and store it.  This also performs the grouping
    /// of pointers to reduce the number of memchecks necessary.
    void generateChecks(MemoryDepChecker::DepCandidates &DepCands,
                        bool UseDependencies);
  
    /// Returns the checks that generateChecks created. They can be used to ensure
    /// no read/write accesses overlap across all loop iterations.
    const SmallVectorImpl<RuntimePointerCheck> &getChecks() const {
      return Checks;
    }
  
    // Returns an optional list of (pointer-difference expressions, access size)
    // pairs that can be used to prove that there are no vectorization-preventing
    // dependencies at runtime. There are is a vectorization-preventing dependency
    // if any pointer-difference is <u VF * InterleaveCount * access size. Returns
    // None if pointer-difference checks cannot be used.
    Optional<ArrayRef<PointerDiffInfo>> getDiffChecks() const {
      if (!CanUseDiffCheck)
        return None;
      return {DiffChecks};
    }
  
    /// Decide if we need to add a check between two groups of pointers,
    /// according to needsChecking.
    bool needsChecking(const RuntimeCheckingPtrGroup &M,
                       const RuntimeCheckingPtrGroup &N) const;
  
    /// Returns the number of run-time checks required according to
    /// needsChecking.
    unsigned getNumberOfChecks() const { return Checks.size(); }
  
    /// Print the list run-time memory checks necessary.
    void print(raw_ostream &OS, unsigned Depth = 0) const;
  
    /// Print \p Checks.
    void printChecks(raw_ostream &OS,
                     const SmallVectorImpl<RuntimePointerCheck> &Checks,
                     unsigned Depth = 0) const;
  
    /// This flag indicates if we need to add the runtime check.
    bool Need = false;
  
    /// Information about the pointers that may require checking.
    SmallVector<PointerInfo, 2> Pointers;
  
    /// Holds a partitioning of pointers into "check groups".
    SmallVector<RuntimeCheckingPtrGroup, 2> CheckingGroups;
  
    /// Check if pointers are in the same partition
    ///
    /// \p PtrToPartition contains the partition number for pointers (-1 if the
    /// pointer belongs to multiple partitions).
    static bool
    arePointersInSamePartition(const SmallVectorImpl<int> &PtrToPartition,
                               unsigned PtrIdx1, unsigned PtrIdx2);
  
    /// Decide whether we need to issue a run-time check for pointer at
    /// index \p I and \p J to prove their independence.
    bool needsChecking(unsigned I, unsigned J) const;
  
    /// Return PointerInfo for pointer at index \p PtrIdx.
    const PointerInfo &getPointerInfo(unsigned PtrIdx) const {
      return Pointers[PtrIdx];
    }
  
    ScalarEvolution *getSE() const { return SE; }
  
  private:
    /// Groups pointers such that a single memcheck is required
    /// between two different groups. This will clear the CheckingGroups vector
    /// and re-compute it. We will only group dependecies if \p UseDependencies
    /// is true, otherwise we will create a separate group for each pointer.
    void groupChecks(MemoryDepChecker::DepCandidates &DepCands,
                     bool UseDependencies);
  
    /// Generate the checks and return them.
    SmallVector<RuntimePointerCheck, 4> generateChecks();
  
    /// Try to create add a new (pointer-difference, access size) pair to
    /// DiffCheck for checking groups \p CGI and \p CGJ. If pointer-difference
    /// checks cannot be used for the groups, set CanUseDiffCheck to false.
    void tryToCreateDiffCheck(const RuntimeCheckingPtrGroup &CGI,
                              const RuntimeCheckingPtrGroup &CGJ);
  
    MemoryDepChecker &DC;
  
    /// Holds a pointer to the ScalarEvolution analysis.
    ScalarEvolution *SE;
  
    /// Set of run-time checks required to establish independence of
    /// otherwise may-aliasing pointers in the loop.
    SmallVector<RuntimePointerCheck, 4> Checks;
  
    /// Flag indicating if pointer-difference checks can be used
    bool CanUseDiffCheck = true;
  
    /// A list of (pointer-difference, access size) pairs that can be used to
    /// prove that there are no vectorization-preventing dependencies.
    SmallVector<PointerDiffInfo> DiffChecks;
  };
  
  /// Drive the analysis of memory accesses in the loop
  ///
  /// This class is responsible for analyzing the memory accesses of a loop.  It
  /// collects the accesses and then its main helper the AccessAnalysis class
  /// finds and categorizes the dependences in buildDependenceSets.
  ///
  /// For memory dependences that can be analyzed at compile time, it determines
  /// whether the dependence is part of cycle inhibiting vectorization.  This work
  /// is delegated to the MemoryDepChecker class.
  ///
  /// For memory dependences that cannot be determined at compile time, it
  /// generates run-time checks to prove independence.  This is done by
  /// AccessAnalysis::canCheckPtrAtRT and the checks are maintained by the
  /// RuntimePointerCheck class.
  ///
  /// If pointers can wrap or can't be expressed as affine AddRec expressions by
  /// ScalarEvolution, we will generate run-time checks by emitting a
  /// SCEVUnionPredicate.
  ///
  /// Checks for both memory dependences and the SCEV predicates contained in the
  /// PSE must be emitted in order for the results of this analysis to be valid.
  class LoopAccessInfo {
  public:
    LoopAccessInfo(Loop *L, ScalarEvolution *SE, const TargetLibraryInfo *TLI,
                   AAResults *AA, DominatorTree *DT, LoopInfo *LI);
  
    /// Return true we can analyze the memory accesses in the loop and there are
    /// no memory dependence cycles.
    bool canVectorizeMemory() const { return CanVecMem; }
  
    /// Return true if there is a convergent operation in the loop. There may
    /// still be reported runtime pointer checks that would be required, but it is
    /// not legal to insert them.
    bool hasConvergentOp() const { return HasConvergentOp; }
  
    const RuntimePointerChecking *getRuntimePointerChecking() const {
      return PtrRtChecking.get();
    }
  
    /// Number of memchecks required to prove independence of otherwise
    /// may-alias pointers.
    unsigned getNumRuntimePointerChecks() const {
      return PtrRtChecking->getNumberOfChecks();
    }
  
    /// Return true if the block BB needs to be predicated in order for the loop
    /// to be vectorized.
    static bool blockNeedsPredication(BasicBlock *BB, Loop *TheLoop,
                                      DominatorTree *DT);
  
    /// Returns true if the value V is uniform within the loop.
    bool isUniform(Value *V) const;
  
    uint64_t getMaxSafeDepDistBytes() const { return MaxSafeDepDistBytes; }
    unsigned getNumStores() const { return NumStores; }
    unsigned getNumLoads() const { return NumLoads;}
  
    /// The diagnostics report generated for the analysis.  E.g. why we
    /// couldn't analyze the loop.
    const OptimizationRemarkAnalysis *getReport() const { return Report.get(); }
  
    /// the Memory Dependence Checker which can determine the
    /// loop-independent and loop-carried dependences between memory accesses.
    const MemoryDepChecker &getDepChecker() const { return *DepChecker; }
  
    /// Return the list of instructions that use \p Ptr to read or write
    /// memory.
    SmallVector<Instruction *, 4> getInstructionsForAccess(Value *Ptr,
                                                           bool isWrite) const {
      return DepChecker->getInstructionsForAccess(Ptr, isWrite);
    }
  
    /// If an access has a symbolic strides, this maps the pointer value to
    /// the stride symbol.
    const ValueToValueMap &getSymbolicStrides() const { return SymbolicStrides; }
  
    /// Pointer has a symbolic stride.
    bool hasStride(Value *V) const { return StrideSet.count(V); }
  
    /// Print the information about the memory accesses in the loop.
    void print(raw_ostream &OS, unsigned Depth = 0) const;
  
    /// If the loop has memory dependence involving an invariant address, i.e. two
    /// stores or a store and a load, then return true, else return false.
    bool hasDependenceInvolvingLoopInvariantAddress() const {
      return HasDependenceInvolvingLoopInvariantAddress;
    }
  
    /// Return the list of stores to invariant addresses.
    const ArrayRef<StoreInst *> getStoresToInvariantAddresses() const {
      return StoresToInvariantAddresses;
    }
  
    /// Used to add runtime SCEV checks. Simplifies SCEV expressions and converts
    /// them to a more usable form.  All SCEV expressions during the analysis
    /// should be re-written (and therefore simplified) according to PSE.
    /// A user of LoopAccessAnalysis will need to emit the runtime checks
    /// associated with this predicate.
    const PredicatedScalarEvolution &getPSE() const { return *PSE; }
  
  private:
    /// Analyze the loop.
    void analyzeLoop(AAResults *AA, LoopInfo *LI,
                     const TargetLibraryInfo *TLI, DominatorTree *DT);
  
    /// Check if the structure of the loop allows it to be analyzed by this
    /// pass.
    bool canAnalyzeLoop();
  
    /// Save the analysis remark.
    ///
    /// LAA does not directly emits the remarks.  Instead it stores it which the
    /// client can retrieve and presents as its own analysis
    /// (e.g. -Rpass-analysis=loop-vectorize).
    OptimizationRemarkAnalysis &recordAnalysis(StringRef RemarkName,
                                               Instruction *Instr = nullptr);
  
    /// Collect memory access with loop invariant strides.
    ///
    /// Looks for accesses like "a[i * StrideA]" where "StrideA" is loop
    /// invariant.
    void collectStridedAccess(Value *LoadOrStoreInst);
  
    // Emits the first unsafe memory dependence in a loop.
    // Emits nothing if there are no unsafe dependences
    // or if the dependences were not recorded.
    void emitUnsafeDependenceRemark();
  
    std::unique_ptr<PredicatedScalarEvolution> PSE;
  
    /// We need to check that all of the pointers in this list are disjoint
    /// at runtime. Using std::unique_ptr to make using move ctor simpler.
    std::unique_ptr<RuntimePointerChecking> PtrRtChecking;
  
    /// the Memory Dependence Checker which can determine the
    /// loop-independent and loop-carried dependences between memory accesses.
    std::unique_ptr<MemoryDepChecker> DepChecker;
  
    Loop *TheLoop;
  
    unsigned NumLoads = 0;
    unsigned NumStores = 0;
  
    uint64_t MaxSafeDepDistBytes = -1;
  
    /// Cache the result of analyzeLoop.
    bool CanVecMem = false;
    bool HasConvergentOp = false;
  
    /// Indicator that there are non vectorizable stores to a uniform address.
    bool HasDependenceInvolvingLoopInvariantAddress = false;
  
    /// List of stores to invariant addresses.
    SmallVector<StoreInst *> StoresToInvariantAddresses;
  
    /// The diagnostics report generated for the analysis.  E.g. why we
    /// couldn't analyze the loop.
    std::unique_ptr<OptimizationRemarkAnalysis> Report;
  
    /// If an access has a symbolic strides, this maps the pointer value to
    /// the stride symbol.
    ValueToValueMap SymbolicStrides;
  
    /// Set of symbolic strides values.
    SmallPtrSet<Value *, 8> StrideSet;
  };
  
  Value *stripIntegerCast(Value *V);
  
  /// Return the SCEV corresponding to a pointer with the symbolic stride
  /// replaced with constant one, assuming the SCEV predicate associated with
  /// \p PSE is true.
  ///
  /// If necessary this method will version the stride of the pointer according
  /// to \p PtrToStride and therefore add further predicates to \p PSE.
  ///
  /// \p PtrToStride provides the mapping between the pointer value and its
  /// stride as collected by LoopVectorizationLegality::collectStridedAccess.
  const SCEV *replaceSymbolicStrideSCEV(PredicatedScalarEvolution &PSE,
                                        const ValueToValueMap &PtrToStride,
                                        Value *Ptr);
  
  /// If the pointer has a constant stride return it in units of the access type
  /// size.  Otherwise return zero.
  ///
  /// Ensure that it does not wrap in the address space, assuming the predicate
  /// associated with \p PSE is true.
  ///
  /// If necessary this method will version the stride of the pointer according
  /// to \p PtrToStride and therefore add further predicates to \p PSE.
  /// The \p Assume parameter indicates if we are allowed to make additional
  /// run-time assumptions.
  int64_t getPtrStride(PredicatedScalarEvolution &PSE, Type *AccessTy, Value *Ptr,
                       const Loop *Lp,
                       const ValueToValueMap &StridesMap = ValueToValueMap(),
                       bool Assume = false, bool ShouldCheckWrap = true);
  
  /// Returns the distance between the pointers \p PtrA and \p PtrB iff they are
  /// compatible and it is possible to calculate the distance between them. This
  /// is a simple API that does not depend on the analysis pass.
  /// \param StrictCheck Ensure that the calculated distance matches the
  /// type-based one after all the bitcasts removal in the provided pointers.
  Optional<int> getPointersDiff(Type *ElemTyA, Value *PtrA, Type *ElemTyB,
                                Value *PtrB, const DataLayout &DL,
                                ScalarEvolution &SE, bool StrictCheck = false,
                                bool CheckType = true);
  
  /// Attempt to sort the pointers in \p VL and return the sorted indices
  /// in \p SortedIndices, if reordering is required.
  ///
  /// Returns 'true' if sorting is legal, otherwise returns 'false'.
  ///
  /// For example, for a given \p VL of memory accesses in program order, a[i+4],
  /// a[i+0], a[i+1] and a[i+7], this function will sort the \p VL and save the
  /// sorted indices in \p SortedIndices as a[i+0], a[i+1], a[i+4], a[i+7] and
  /// saves the mask for actual memory accesses in program order in
  /// \p SortedIndices as <1,2,0,3>
  bool sortPtrAccesses(ArrayRef<Value *> VL, Type *ElemTy, const DataLayout &DL,
                       ScalarEvolution &SE,
                       SmallVectorImpl<unsigned> &SortedIndices);
  
  /// Returns true if the memory operations \p A and \p B are consecutive.
  /// This is a simple API that does not depend on the analysis pass.
  bool isConsecutiveAccess(Value *A, Value *B, const DataLayout &DL,
                           ScalarEvolution &SE, bool CheckType = true);
  
  /// This analysis provides dependence information for the memory accesses
  /// of a loop.
  ///
  /// It runs the analysis for a loop on demand.  This can be initiated by
  /// querying the loop access info via LAA::getInfo.  getInfo return a
  /// LoopAccessInfo object.  See this class for the specifics of what information
  /// is provided.
  class LoopAccessLegacyAnalysis : public FunctionPass {
  public:
    static char ID;
  
    LoopAccessLegacyAnalysis();
  
    bool runOnFunction(Function &F) override;
  
    void getAnalysisUsage(AnalysisUsage &AU) const override;
  
    /// Query the result of the loop access information for the loop \p L.
    ///
    /// If there is no cached result available run the analysis.
    const LoopAccessInfo &getInfo(Loop *L);
  
    void releaseMemory() override {
      // Invalidate the cache when the pass is freed.
      LoopAccessInfoMap.clear();
    }
  
    /// Print the result of the analysis when invoked with -analyze.
    void print(raw_ostream &OS, const Module *M = nullptr) const override;
  
  private:
    /// The cache.
    DenseMap<Loop *, std::unique_ptr<LoopAccessInfo>> LoopAccessInfoMap;
  
    // The used analysis passes.
    ScalarEvolution *SE = nullptr;
    const TargetLibraryInfo *TLI = nullptr;
    AAResults *AA = nullptr;
    DominatorTree *DT = nullptr;
    LoopInfo *LI = nullptr;
  };
  
  /// This analysis provides dependence information for the memory
  /// accesses of a loop.
  ///
  /// It runs the analysis for a loop on demand.  This can be initiated by
  /// querying the loop access info via AM.getResult<LoopAccessAnalysis>.
  /// getResult return a LoopAccessInfo object.  See this class for the
  /// specifics of what information is provided.
  class LoopAccessAnalysis
      : public AnalysisInfoMixin<LoopAccessAnalysis> {
    friend AnalysisInfoMixin<LoopAccessAnalysis>;
    static AnalysisKey Key;
  
  public:
    typedef LoopAccessInfo Result;
  
    Result run(Loop &L, LoopAnalysisManager &AM, LoopStandardAnalysisResults &AR);
  };
  
  inline Instruction *MemoryDepChecker::Dependence::getSource(
      const LoopAccessInfo &LAI) const {
    return LAI.getDepChecker().getMemoryInstructions()[Source];
  }
  
  inline Instruction *MemoryDepChecker::Dependence::getDestination(
      const LoopAccessInfo &LAI) const {
    return LAI.getDepChecker().getMemoryInstructions()[Destination];
  }
  
  } // End llvm namespace
  
  #endif
  