text: //===- llvm/Analysis/AliasAnalysis.h - Alias Analysis Interface -*- C++ -*-===//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  //
  // This file defines the generic AliasAnalysis interface, which is used as the
  // common interface used by all clients of alias analysis information, and
  // implemented by all alias analysis implementations.  Mod/Ref information is
  // also captured by this interface.
  //
  // Implementations of this interface must implement the various virtual methods,
  // which automatically provides functionality for the entire suite of client
  // APIs.
  //
  // This API identifies memory regions with the Location class. The pointer
  // component specifies the base memory address of the region. The Size specifies
  // the maximum size (in address units) of the memory region, or UnknownSize if
  // the size is not known. The TBAA tag identifies the "type" of the memory
  // reference; see the TypeBasedAliasAnalysis class for details.
  //
  // Some non-obvious details include:
  //  - Pointers that point to two completely different objects in memory never
  //    alias, regardless of the value of the Size component.
  //  - NoAlias doesn't imply inequal pointers. The most obvious example of this
  //    is two pointers to constant memory. Even if they are equal, constant
  //    memory is never stored to, so there will never be any dependencies.
  //    In this and other situations, the pointers may be both NoAlias and
  //    MustAlias at the same time. The current API can only return one result,
  //    though this is rarely a problem in practice.
  //
  //===----------------------------------------------------------------------===//
  
  #ifndef LLVM_ANALYSIS_ALIAS_ANALYSIS_H
  #define LLVM_ANALYSIS_ALIAS_ANALYSIS_H
  
  #include "llvm/Support/CallSite.h"
  #include "llvm/ADT/DenseMap.h"
  
  namespace llvm {
  
  class LoadInst;
  class StoreInst;
  class VAArgInst;
  class TargetData;
  class Pass;
  class AnalysisUsage;
  class MemTransferInst;
  class MemIntrinsic;
  
  class AliasAnalysis {
  protected:
    const TargetData *TD;
  
  private:
    AliasAnalysis *AA;       // Previous Alias Analysis to chain to.
  
  protected:
    /// InitializeAliasAnalysis - Subclasses must call this method to initialize
    /// the AliasAnalysis interface before any other methods are called.  This is
    /// typically called by the run* methods of these subclasses.  This may be
    /// called multiple times.
    ///
    void InitializeAliasAnalysis(Pass *P);
  
    /// getAnalysisUsage - All alias analysis implementations should invoke this
    /// directly (using AliasAnalysis::getAnalysisUsage(AU)).
    virtual void getAnalysisUsage(AnalysisUsage &AU) const;
  
  public:
    static char ID; // Class identification, replacement for typeinfo
    AliasAnalysis() : TD(0), AA(0) {}
    virtual ~AliasAnalysis();  // We want to be subclassed
  
    /// UnknownSize - This is a special value which can be used with the
    /// size arguments in alias queries to indicate that the caller does not
    /// know the sizes of the potential memory references.
    static uint64_t const UnknownSize = ~UINT64_C(0);
  
    /// getTargetData - Return a pointer to the current TargetData object, or
    /// null if no TargetData object is available.
    ///
    const TargetData *getTargetData() const { return TD; }
  
    /// getTypeStoreSize - Return the TargetData store size for the given type,
    /// if known, or a conservative value otherwise.
    ///
    uint64_t getTypeStoreSize(Type *Ty);
  
    //===--------------------------------------------------------------------===//
    /// Alias Queries...
    ///
  
    /// Location - A description of a memory location.
    struct Location {
      /// Ptr - The address of the start of the location.
      const Value *Ptr;
      /// Size - The maximum size of the location, in address-units, or
      /// UnknownSize if the size is not known.  Note that an unknown size does
      /// not mean the pointer aliases the entire virtual address space, because
      /// there are restrictions on stepping out of one object and into another.
      /// See http://llvm.org/docs/LangRef.html#pointeraliasing
      uint64_t Size;
      /// TBAATag - The metadata node which describes the TBAA type of
      /// the location, or null if there is no known unique tag.
      const MDNode *TBAATag;
  
      explicit Location(const Value *P = 0, uint64_t S = UnknownSize,
                        const MDNode *N = 0)
        : Ptr(P), Size(S), TBAATag(N) {}
  
      Location getWithNewPtr(const Value *NewPtr) const {
        Location Copy(*this);
        Copy.Ptr = NewPtr;
        return Copy;
      }
  
      Location getWithNewSize(uint64_t NewSize) const {
        Location Copy(*this);
        Copy.Size = NewSize;
        return Copy;
      }
  
      Location getWithoutTBAATag() const {
        Location Copy(*this);
        Copy.TBAATag = 0;
        return Copy;
      }
    };
  
    /// getLocation - Fill in Loc with information about the memory reference by
    /// the given instruction.
    Location getLocation(const LoadInst *LI);
    Location getLocation(const StoreInst *SI);
    Location getLocation(const VAArgInst *VI);
    Location getLocation(const AtomicCmpXchgInst *CXI);
    Location getLocation(const AtomicRMWInst *RMWI);
    static Location getLocationForSource(const MemTransferInst *MTI);
    static Location getLocationForDest(const MemIntrinsic *MI);
  
    /// Alias analysis result - Either we know for sure that it does not alias, we
    /// know for sure it must alias, or we don't know anything: The two pointers
    /// _might_ alias.  This enum is designed so you can do things like:
    ///     if (AA.alias(P1, P2)) { ... }
    /// to check to see if two pointers might alias.
    ///
    /// See docs/AliasAnalysis.html for more information on the specific meanings
    /// of these values.
    ///
    enum AliasResult {
      NoAlias = 0,        ///< No dependencies.
      MayAlias,           ///< Anything goes.
      PartialAlias,       ///< Pointers differ, but pointees overlap.
      MustAlias           ///< Pointers are equal.
    };
  
    /// alias - The main low level interface to the alias analysis implementation.
    /// Returns an AliasResult indicating whether the two pointers are aliased to
    /// each other.  This is the interface that must be implemented by specific
    /// alias analysis implementations.
    virtual AliasResult alias(const Location &LocA, const Location &LocB);
  
    /// alias - A convenience wrapper.
    AliasResult alias(const Value *V1, uint64_t V1Size,
                      const Value *V2, uint64_t V2Size) {
      return alias(Location(V1, V1Size), Location(V2, V2Size));
    }
  
    /// alias - A convenience wrapper.
    AliasResult alias(const Value *V1, const Value *V2) {
      return alias(V1, UnknownSize, V2, UnknownSize);
    }
  
    /// isNoAlias - A trivial helper function to check to see if the specified
    /// pointers are no-alias.
    bool isNoAlias(const Location &LocA, const Location &LocB) {
      return alias(LocA, LocB) == NoAlias;
    }
  
    /// isNoAlias - A convenience wrapper.
    bool isNoAlias(const Value *V1, uint64_t V1Size,
                   const Value *V2, uint64_t V2Size) {
      return isNoAlias(Location(V1, V1Size), Location(V2, V2Size));
    }
    
    /// isMustAlias - A convenience wrapper.
    bool isMustAlias(const Location &LocA, const Location &LocB) {
      return alias(LocA, LocB) == MustAlias;
    }
  
    /// isMustAlias - A convenience wrapper.
    bool isMustAlias(const Value *V1, const Value *V2) {
      return alias(V1, 1, V2, 1) == MustAlias;
    }
    
    /// pointsToConstantMemory - If the specified memory location is
    /// known to be constant, return true. If OrLocal is true and the
    /// specified memory location is known to be "local" (derived from
    /// an alloca), return true. Otherwise return false.
    virtual bool pointsToConstantMemory(const Location &Loc,
                                        bool OrLocal = false);
  
    /// pointsToConstantMemory - A convenient wrapper.
    bool pointsToConstantMemory(const Value *P, bool OrLocal = false) {
      return pointsToConstantMemory(Location(P), OrLocal);
    }
  
    //===--------------------------------------------------------------------===//
    /// Simple mod/ref information...
    ///
  
    /// ModRefResult - Represent the result of a mod/ref query.  Mod and Ref are
    /// bits which may be or'd together.
    ///
    enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 };
  
    /// These values define additional bits used to define the
    /// ModRefBehavior values.
    enum { Nowhere = 0, ArgumentPointees = 4, Anywhere = 8 | ArgumentPointees };
  
    /// ModRefBehavior - Summary of how a function affects memory in the program.
    /// Loads from constant globals are not considered memory accesses for this
    /// interface.  Also, functions may freely modify stack space local to their
    /// invocation without having to report it through these interfaces.
    enum ModRefBehavior {
      /// DoesNotAccessMemory - This function does not perform any non-local loads
      /// or stores to memory.
      ///
      /// This property corresponds to the GCC 'const' attribute.
      /// This property corresponds to the LLVM IR 'readnone' attribute.
      /// This property corresponds to the IntrNoMem LLVM intrinsic flag.
      DoesNotAccessMemory = Nowhere | NoModRef,
  
      /// OnlyReadsArgumentPointees - The only memory references in this function
      /// (if it has any) are non-volatile loads from objects pointed to by its
      /// pointer-typed arguments, with arbitrary offsets.
      ///
      /// This property corresponds to the IntrReadArgMem LLVM intrinsic flag.
      OnlyReadsArgumentPointees = ArgumentPointees | Ref,
  
      /// OnlyAccessesArgumentPointees - The only memory references in this
      /// function (if it has any) are non-volatile loads and stores from objects
      /// pointed to by its pointer-typed arguments, with arbitrary offsets.
      ///
      /// This property corresponds to the IntrReadWriteArgMem LLVM intrinsic flag.
      OnlyAccessesArgumentPointees = ArgumentPointees | ModRef,
  
      /// OnlyReadsMemory - This function does not perform any non-local stores or
      /// volatile loads, but may read from any memory location.
      ///
      /// This property corresponds to the GCC 'pure' attribute.
      /// This property corresponds to the LLVM IR 'readonly' attribute.
      /// This property corresponds to the IntrReadMem LLVM intrinsic flag.
      OnlyReadsMemory = Anywhere | Ref,
  
      /// UnknownModRefBehavior - This indicates that the function could not be
      /// classified into one of the behaviors above.
      UnknownModRefBehavior = Anywhere | ModRef
    };
  
    /// getModRefBehavior - Return the behavior when calling the given call site.
    virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS);
  
    /// getModRefBehavior - Return the behavior when calling the given function.
    /// For use when the call site is not known.
    virtual ModRefBehavior getModRefBehavior(const Function *F);
  
    /// doesNotAccessMemory - If the specified call is known to never read or
    /// write memory, return true.  If the call only reads from known-constant
    /// memory, it is also legal to return true.  Calls that unwind the stack
    /// are legal for this predicate.
    ///
    /// Many optimizations (such as CSE and LICM) can be performed on such calls
    /// without worrying about aliasing properties, and many calls have this
    /// property (e.g. calls to 'sin' and 'cos').
    ///
    /// This property corresponds to the GCC 'const' attribute.
    ///
    bool doesNotAccessMemory(ImmutableCallSite CS) {
      return getModRefBehavior(CS) == DoesNotAccessMemory;
    }
  
    /// doesNotAccessMemory - If the specified function is known to never read or
    /// write memory, return true.  For use when the call site is not known.
    ///
    bool doesNotAccessMemory(const Function *F) {
      return getModRefBehavior(F) == DoesNotAccessMemory;
    }
  
    /// onlyReadsMemory - If the specified call is known to only read from
    /// non-volatile memory (or not access memory at all), return true.  Calls
    /// that unwind the stack are legal for this predicate.
    ///
    /// This property allows many common optimizations to be performed in the
    /// absence of interfering store instructions, such as CSE of strlen calls.
    ///
    /// This property corresponds to the GCC 'pure' attribute.
    ///
    bool onlyReadsMemory(ImmutableCallSite CS) {
      return onlyReadsMemory(getModRefBehavior(CS));
    }
  
    /// onlyReadsMemory - If the specified function is known to only read from
    /// non-volatile memory (or not access memory at all), return true.  For use
    /// when the call site is not known.
    ///
    bool onlyReadsMemory(const Function *F) {
      return onlyReadsMemory(getModRefBehavior(F));
    }
  
    /// onlyReadsMemory - Return true if functions with the specified behavior are
    /// known to only read from non-volatile memory (or not access memory at all).
    ///
    static bool onlyReadsMemory(ModRefBehavior MRB) {
      return !(MRB & Mod);
    }
  
    /// onlyAccessesArgPointees - Return true if functions with the specified
    /// behavior are known to read and write at most from objects pointed to by
    /// their pointer-typed arguments (with arbitrary offsets).
    ///
    static bool onlyAccessesArgPointees(ModRefBehavior MRB) {
      return !(MRB & Anywhere & ~ArgumentPointees);
    }
  
    /// doesAccessArgPointees - Return true if functions with the specified
    /// behavior are known to potentially read or write from objects pointed
    /// to be their pointer-typed arguments (with arbitrary offsets).
    ///
    static bool doesAccessArgPointees(ModRefBehavior MRB) {
      return (MRB & ModRef) && (MRB & ArgumentPointees);
    }
  
    /// getModRefInfo - Return information about whether or not an instruction may
    /// read or write the specified memory location.  An instruction
    /// that doesn't read or write memory may be trivially LICM'd for example.
    ModRefResult getModRefInfo(const Instruction *I,
                               const Location &Loc) {
      switch (I->getOpcode()) {
      case Instruction::VAArg:  return getModRefInfo((const VAArgInst*)I, Loc);
      case Instruction::Load:   return getModRefInfo((const LoadInst*)I,  Loc);
      case Instruction::Store:  return getModRefInfo((const StoreInst*)I, Loc);
      case Instruction::Fence:  return getModRefInfo((const FenceInst*)I, Loc);
      case Instruction::AtomicCmpXchg:
        return getModRefInfo((const AtomicCmpXchgInst*)I, Loc);
      case Instruction::AtomicRMW:
        return getModRefInfo((const AtomicRMWInst*)I, Loc);
      case Instruction::Call:   return getModRefInfo((const CallInst*)I,  Loc);
      case Instruction::Invoke: return getModRefInfo((const InvokeInst*)I,Loc);
      default:                  return NoModRef;
      }
    }
  
    /// getModRefInfo - A convenience wrapper.
    ModRefResult getModRefInfo(const Instruction *I,
                               const Value *P, uint64_t Size) {
      return getModRefInfo(I, Location(P, Size));
    }
  
    /// getModRefInfo (for call sites) - Return whether information about whether
    /// a particular call site modifies or reads the specified memory location.
    virtual ModRefResult getModRefInfo(ImmutableCallSite CS,
                                       const Location &Loc);
  
    /// getModRefInfo (for call sites) - A convenience wrapper.
    ModRefResult getModRefInfo(ImmutableCallSite CS,
                               const Value *P, uint64_t Size) {
      return getModRefInfo(CS, Location(P, Size));
    }
  
    /// getModRefInfo (for calls) - Return whether information about whether
    /// a particular call modifies or reads the specified memory location.
    ModRefResult getModRefInfo(const CallInst *C, const Location &Loc) {
      return getModRefInfo(ImmutableCallSite(C), Loc);
    }
  
    /// getModRefInfo (for calls) - A convenience wrapper.
    ModRefResult getModRefInfo(const CallInst *C, const Value *P, uint64_t Size) {
      return getModRefInfo(C, Location(P, Size));
    }
  
    /// getModRefInfo (for invokes) - Return whether information about whether
    /// a particular invoke modifies or reads the specified memory location.
    ModRefResult getModRefInfo(const InvokeInst *I,
                               const Location &Loc) {
      return getModRefInfo(ImmutableCallSite(I), Loc);
    }
  
    /// getModRefInfo (for invokes) - A convenience wrapper.
    ModRefResult getModRefInfo(const InvokeInst *I,
                               const Value *P, uint64_t Size) {
      return getModRefInfo(I, Location(P, Size));
    }
  
    /// getModRefInfo (for loads) - Return whether information about whether
    /// a particular load modifies or reads the specified memory location.
    ModRefResult getModRefInfo(const LoadInst *L, const Location &Loc);
  
    /// getModRefInfo (for loads) - A convenience wrapper.
    ModRefResult getModRefInfo(const LoadInst *L, const Value *P, uint64_t Size) {
      return getModRefInfo(L, Location(P, Size));
    }
  
    /// getModRefInfo (for stores) - Return whether information about whether
    /// a particular store modifies or reads the specified memory location.
    ModRefResult getModRefInfo(const StoreInst *S, const Location &Loc);
  
    /// getModRefInfo (for stores) - A convenience wrapper.
    ModRefResult getModRefInfo(const StoreInst *S, const Value *P, uint64_t Size){
      return getModRefInfo(S, Location(P, Size));
    }
  
    /// getModRefInfo (for fences) - Return whether information about whether
    /// a particular store modifies or reads the specified memory location.
    ModRefResult getModRefInfo(const FenceInst *S, const Location &Loc) {
      // Conservatively correct.  (We could possibly be a bit smarter if
      // Loc is a alloca that doesn't escape.)
      return ModRef;
    }
  
    /// getModRefInfo (for fences) - A convenience wrapper.
    ModRefResult getModRefInfo(const FenceInst *S, const Value *P, uint64_t Size){
      return getModRefInfo(S, Location(P, Size));
    }
  
    /// getModRefInfo (for cmpxchges) - Return whether information about whether
    /// a particular cmpxchg modifies or reads the specified memory location.
    ModRefResult getModRefInfo(const AtomicCmpXchgInst *CX, const Location &Loc);
  
    /// getModRefInfo (for cmpxchges) - A convenience wrapper.
    ModRefResult getModRefInfo(const AtomicCmpXchgInst *CX,
                               const Value *P, unsigned Size) {
      return getModRefInfo(CX, Location(P, Size));
    }
  
    /// getModRefInfo (for atomicrmws) - Return whether information about whether
    /// a particular atomicrmw modifies or reads the specified memory location.
    ModRefResult getModRefInfo(const AtomicRMWInst *RMW, const Location &Loc);
  
    /// getModRefInfo (for atomicrmws) - A convenience wrapper.
    ModRefResult getModRefInfo(const AtomicRMWInst *RMW,
                               const Value *P, unsigned Size) {
      return getModRefInfo(RMW, Location(P, Size));
    }
  
    /// getModRefInfo (for va_args) - Return whether information about whether
    /// a particular va_arg modifies or reads the specified memory location.
    ModRefResult getModRefInfo(const VAArgInst* I, const Location &Loc);
  
    /// getModRefInfo (for va_args) - A convenience wrapper.
    ModRefResult getModRefInfo(const VAArgInst* I, const Value* P, uint64_t Size){
      return getModRefInfo(I, Location(P, Size));
    }
  
    /// getModRefInfo - Return information about whether two call sites may refer
    /// to the same set of memory locations.  See 
    ///   http://llvm.org/docs/AliasAnalysis.html#ModRefInfo
    /// for details.
    virtual ModRefResult getModRefInfo(ImmutableCallSite CS1,
                                       ImmutableCallSite CS2);
  
    //===--------------------------------------------------------------------===//
    /// Higher level methods for querying mod/ref information.
    ///
  
    /// canBasicBlockModify - Return true if it is possible for execution of the
    /// specified basic block to modify the value pointed to by Ptr.
    bool canBasicBlockModify(const BasicBlock &BB, const Location &Loc);
  
    /// canBasicBlockModify - A convenience wrapper.
    bool canBasicBlockModify(const BasicBlock &BB, const Value *P, uint64_t Size){
      return canBasicBlockModify(BB, Location(P, Size));
    }
  
    /// canInstructionRangeModify - Return true if it is possible for the
    /// execution of the specified instructions to modify the value pointed to by
    /// Ptr.  The instructions to consider are all of the instructions in the
    /// range of [I1,I2] INCLUSIVE.  I1 and I2 must be in the same basic block.
    bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2,
                                   const Location &Loc);
  
    /// canInstructionRangeModify - A convenience wrapper.
    bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2,
                                   const Value *Ptr, uint64_t Size) {
      return canInstructionRangeModify(I1, I2, Location(Ptr, Size));
    }
  
    //===--------------------------------------------------------------------===//
    /// Methods that clients should call when they transform the program to allow
    /// alias analyses to update their internal data structures.  Note that these
    /// methods may be called on any instruction, regardless of whether or not
    /// they have pointer-analysis implications.
    ///
  
    /// deleteValue - This method should be called whenever an LLVM Value is
    /// deleted from the program, for example when an instruction is found to be
    /// redundant and is eliminated.
    ///
    virtual void deleteValue(Value *V);
  
    /// copyValue - This method should be used whenever a preexisting value in the
    /// program is copied or cloned, introducing a new value.  Note that analysis
    /// implementations should tolerate clients that use this method to introduce
    /// the same value multiple times: if the analysis already knows about a
    /// value, it should ignore the request.
    ///
    virtual void copyValue(Value *From, Value *To);
  
    /// addEscapingUse - This method should be used whenever an escaping use is
    /// added to a pointer value.  Analysis implementations may either return
    /// conservative responses for that value in the future, or may recompute
    /// some or all internal state to continue providing precise responses.
    ///
    /// Escaping uses are considered by anything _except_ the following:
    ///  - GEPs or bitcasts of the pointer
    ///  - Loads through the pointer
    ///  - Stores through (but not of) the pointer
    virtual void addEscapingUse(Use &U);
  
    /// replaceWithNewValue - This method is the obvious combination of the two
    /// above, and it provided as a helper to simplify client code.
    ///
    void replaceWithNewValue(Value *Old, Value *New) {
      copyValue(Old, New);
      deleteValue(Old);
    }
  };
  
  // Specialize DenseMapInfo for Location.
  template<>
  struct DenseMapInfo<AliasAnalysis::Location> {
    static inline AliasAnalysis::Location getEmptyKey() {
      return
        AliasAnalysis::Location(DenseMapInfo<const Value *>::getEmptyKey(),
                                0, 0);
    }
    static inline AliasAnalysis::Location getTombstoneKey() {
      return
        AliasAnalysis::Location(DenseMapInfo<const Value *>::getTombstoneKey(),
                                0, 0);
    }
    static unsigned getHashValue(const AliasAnalysis::Location &Val) {
      return DenseMapInfo<const Value *>::getHashValue(Val.Ptr) ^
             DenseMapInfo<uint64_t>::getHashValue(Val.Size) ^
             DenseMapInfo<const MDNode *>::getHashValue(Val.TBAATag);
    }
    static bool isEqual(const AliasAnalysis::Location &LHS,
                        const AliasAnalysis::Location &RHS) {
      return LHS.Ptr == RHS.Ptr &&
             LHS.Size == RHS.Size &&
             LHS.TBAATag == RHS.TBAATag;
    }
  };
  
  /// isNoAliasCall - Return true if this pointer is returned by a noalias
  /// function.
  bool isNoAliasCall(const Value *V);
  
  /// isIdentifiedObject - Return true if this pointer refers to a distinct and
  /// identifiable object.  This returns true for:
  ///    Global Variables and Functions (but not Global Aliases)
  ///    Allocas and Mallocs
  ///    ByVal and NoAlias Arguments
  ///    NoAlias returns
  ///
  bool isIdentifiedObject(const Value *V);
  
  /// isKnownNonNull - Return true if this pointer couldn't possibly be null by
  /// its definition.  This returns true for allocas, non-extern-weak globals and
  /// byval arguments.
  bool isKnownNonNull(const Value *V);
  
  } // End llvm namespace
  
  #endif
  