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//===- BasicAliasAnalysis.h - Stateless, local Alias Analysis ---*- C++ -*-===//
//                     The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
/// \file
/// This is the interface for LLVM's primary stateless and local alias analysis.


#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/GetElementPtrTypeIterator.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/PassManager.h"
#include "llvm/Support/ErrorHandling.h"

namespace llvm {
class AssumptionCache;
class DominatorTree;
class LoopInfo;

/// This is the AA result object for the basic, local, and stateless alias
/// analysis. It implements the AA query interface in an entirely stateless
/// manner. As one consequence, it is never invalidated. While it does retain
/// some storage, that is used as an optimization and not to preserve
/// information from query to query.
class BasicAAResult : public AAResultBase<BasicAAResult> {
  friend AAResultBase<BasicAAResult>;

  const DataLayout &DL;
  const TargetLibraryInfo &TLI;
  AssumptionCache &AC;
  DominatorTree *DT;
  LoopInfo *LI;

  BasicAAResult(const DataLayout &DL, const TargetLibraryInfo &TLI,
                AssumptionCache &AC, DominatorTree *DT = nullptr,
                LoopInfo *LI = nullptr)
      : AAResultBase(), DL(DL), TLI(TLI), AC(AC), DT(DT), LI(LI) {}

  BasicAAResult(const BasicAAResult &Arg)
      : AAResultBase(Arg), DL(Arg.DL), TLI(Arg.TLI), AC(Arg.AC), DT(Arg.DT),
        LI(Arg.LI) {}
  BasicAAResult(BasicAAResult &&Arg)
      : AAResultBase(std::move(Arg)), DL(Arg.DL), TLI(Arg.TLI), AC(Arg.AC),
        DT(Arg.DT), LI(Arg.LI) {}

  /// Handle invalidation events from the new pass manager.
  /// By definition, this result is stateless and so remains valid.
  bool invalidate(Function &, const PreservedAnalyses &) { return false; }

  AliasResult alias(const MemoryLocation &LocA, const MemoryLocation &LocB);

  ModRefInfo getModRefInfo(ImmutableCallSite CS, const MemoryLocation &Loc);

  ModRefInfo getModRefInfo(ImmutableCallSite CS1, ImmutableCallSite CS2);

  /// Chases pointers until we find a (constant global) or not.
  bool pointsToConstantMemory(const MemoryLocation &Loc, bool OrLocal);

  /// Get the location associated with a pointer argument of a callsite.
  ModRefInfo getArgModRefInfo(ImmutableCallSite CS, unsigned ArgIdx);

  /// Returns the behavior when calling the given call site.
  FunctionModRefBehavior getModRefBehavior(ImmutableCallSite CS);

  /// Returns the behavior when calling the given function. For use when the
  /// call site is not known.
  FunctionModRefBehavior getModRefBehavior(const Function *F);

  // A linear transformation of a Value; this class represents ZExt(SExt(V,
  // SExtBits), ZExtBits) * Scale + Offset.
  struct VariableGEPIndex {

    // An opaque Value - we can't decompose this further.
    const Value *V;

    // We need to track what extensions we've done as we consider the same Value
    // with different extensions as different variables in a GEP's linear
    // expression;
    // e.g.: if V == -1, then sext(x) != zext(x).
    unsigned ZExtBits;
    unsigned SExtBits;

    int64_t Scale;

    bool operator==(const VariableGEPIndex &Other) const {
      return V == Other.V && ZExtBits == Other.ZExtBits &&
             SExtBits == Other.SExtBits && Scale == Other.Scale;

    bool operator!=(const VariableGEPIndex &Other) const {
      return !operator==(Other);

  // Represents the internal structure of a GEP, decomposed into a base pointer,
  // constant offsets, and variable scaled indices.
  struct DecomposedGEP {
    // Base pointer of the GEP
    const Value *Base;
    // Total constant offset w.r.t the base from indexing into structs
    int64_t StructOffset;
    // Total constant offset w.r.t the base from indexing through
    // pointers/arrays/vectors
    int64_t OtherOffset;
    // Scaled variable (non-constant) indices.
    SmallVector<VariableGEPIndex, 4> VarIndices;

  /// Track alias queries to guard against recursion.
  typedef std::pair<MemoryLocation, MemoryLocation> LocPair;
  typedef SmallDenseMap<LocPair, AliasResult, 8> AliasCacheTy;
  AliasCacheTy AliasCache;

  /// Tracks phi nodes we have visited.
  /// When interpret "Value" pointer equality as value equality we need to make
  /// sure that the "Value" is not part of a cycle. Otherwise, two uses could
  /// come from different "iterations" of a cycle and see different values for
  /// the same "Value" pointer.
  /// The following example shows the problem:
  ///   %p = phi(%alloca1, %addr2)
  ///   %l = load %ptr
  ///   %addr1 = gep, %alloca2, 0, %l
  ///   %addr2 = gep  %alloca2, 0, (%l + 1)
  ///      alias(%p, %addr1) -> MayAlias !
  ///   store %l, ...
  SmallPtrSet<const BasicBlock *, 8> VisitedPhiBBs;

  /// Tracks instructions visited by pointsToConstantMemory.
  SmallPtrSet<const Value *, 16> Visited;

  static const Value *
  GetLinearExpression(const Value *V, APInt &Scale, APInt &Offset,
                      unsigned &ZExtBits, unsigned &SExtBits,
                      const DataLayout &DL, unsigned Depth, AssumptionCache *AC,
                      DominatorTree *DT, bool &NSW, bool &NUW);

  static bool DecomposeGEPExpression(const Value *V, DecomposedGEP &Decomposed,
      const DataLayout &DL, AssumptionCache *AC, DominatorTree *DT);

  static bool isGEPBaseAtNegativeOffset(const GEPOperator *GEPOp,
      const DecomposedGEP &DecompGEP, const DecomposedGEP &DecompAlloca,
      uint64_t AllocaAccessSize);

  /// \brief A Heuristic for aliasGEP that searches for a constant offset
  /// between the variables.
  /// GetLinearExpression has some limitations, as generally zext(%x + 1)
  /// != zext(%x) + zext(1) if the arithmetic overflows. GetLinearExpression
  /// will therefore conservatively refuse to decompose these expressions.
  /// However, we know that, for all %x, zext(%x) != zext(%x + 1), even if
  /// the addition overflows.
  constantOffsetHeuristic(const SmallVectorImpl<VariableGEPIndex> &VarIndices,
                          uint64_t V1Size, uint64_t V2Size, int64_t BaseOffset,
                          AssumptionCache *AC, DominatorTree *DT);

  bool isValueEqualInPotentialCycles(const Value *V1, const Value *V2);

  void GetIndexDifference(SmallVectorImpl<VariableGEPIndex> &Dest,
                          const SmallVectorImpl<VariableGEPIndex> &Src);

  AliasResult aliasGEP(const GEPOperator *V1, uint64_t V1Size,
                       const AAMDNodes &V1AAInfo, const Value *V2,
                       uint64_t V2Size, const AAMDNodes &V2AAInfo,
                       const Value *UnderlyingV1, const Value *UnderlyingV2);

  AliasResult aliasPHI(const PHINode *PN, uint64_t PNSize,
                       const AAMDNodes &PNAAInfo, const Value *V2,
                       uint64_t V2Size, const AAMDNodes &V2AAInfo);

  AliasResult aliasSelect(const SelectInst *SI, uint64_t SISize,
                          const AAMDNodes &SIAAInfo, const Value *V2,
                          uint64_t V2Size, const AAMDNodes &V2AAInfo);

  AliasResult aliasCheck(const Value *V1, uint64_t V1Size, AAMDNodes V1AATag,
                         const Value *V2, uint64_t V2Size, AAMDNodes V2AATag);

/// Analysis pass providing a never-invalidated alias analysis result.
class BasicAA : public AnalysisInfoMixin<BasicAA> {
  friend AnalysisInfoMixin<BasicAA>;
  static char PassID;

  typedef BasicAAResult Result;

  BasicAAResult run(Function &F, AnalysisManager<Function> &AM);

/// Legacy wrapper pass to provide the BasicAAResult object.
class BasicAAWrapperPass : public FunctionPass {
  std::unique_ptr<BasicAAResult> Result;

  virtual void anchor();

  static char ID;


  BasicAAResult &getResult() { return *Result; }
  const BasicAAResult &getResult() const { return *Result; }

  bool runOnFunction(Function &F) override;
  void getAnalysisUsage(AnalysisUsage &AU) const override;

FunctionPass *createBasicAAWrapperPass();

/// A helper for the legacy pass manager to create a \c BasicAAResult object
/// populated to the best of our ability for a particular function when inside
/// of a \c ModulePass or a \c CallGraphSCCPass.
BasicAAResult createLegacyPMBasicAAResult(Pass &P, Function &F);