path: root/include/llvm/Analysis/AliasAnalysis.h

//===- 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_ALIASANALYSIS_H
#define LLVM_ANALYSIS_ALIASANALYSIS_H

#include "llvm/ADT/DenseMap.h"
#include "llvm/Support/CallSite.h"

namespace llvm {

class LoadInst;
class StoreInst;
class VAArgInst;
class DataLayout;
class TargetLibraryInfo;
class Pass;
class AnalysisUsage;
class MemTransferInst;
class MemIntrinsic;
class DominatorTree;

class AliasAnalysis {
protected:
  const DataLayout *TD;
  const TargetLibraryInfo *TLI;

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), TLI(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);

  /// getDataLayout - Return a pointer to the current DataLayout object, or
  /// null if no DataLayout object is available.
  ///
  const DataLayout *getDataLayout() const { return TD; }

  /// getTargetLibraryInfo - Return a pointer to the current TargetLibraryInfo
  /// object, or null if no TargetLibraryInfo object is available.
  ///
  const TargetLibraryInfo *getTargetLibraryInfo() const { return TLI; }

  /// getTypeStoreSize - Return the DataLayout 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));
  }
  
  /// isNoAlias - A convenience wrapper.
  bool isNoAlias(const Value *V1, const Value *V2) {
    return isNoAlias(Location(V1), Location(V2));
  }
  
  /// 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