text: //===- llvm/Analysis/IVUsers.h - Induction Variable Users -------*- C++ -*-===//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  //
  // This file implements bookkeeping for "interesting" users of expressions
  // computed from induction variables.
  //
  //===----------------------------------------------------------------------===//
  
  #ifndef LLVM_ANALYSIS_IVUSERS_H
  #define LLVM_ANALYSIS_IVUSERS_H
  
  #include "llvm/Analysis/LoopPass.h"
  #include "llvm/Analysis/ScalarEvolutionNormalization.h"
  #include "llvm/IR/ValueHandle.h"
  
  namespace llvm {
  
  class DominatorTree;
  class Instruction;
  class Value;
  class ScalarEvolution;
  class SCEV;
  class IVUsers;
  class DataLayout;
  
  /// IVStrideUse - Keep track of one use of a strided induction variable.
  /// The Expr member keeps track of the expression, User is the actual user
  /// instruction of the operand, and 'OperandValToReplace' is the operand of
  /// the User that is the use.
  class IVStrideUse : public CallbackVH, public ilist_node<IVStrideUse> {
    friend class IVUsers;
  public:
    IVStrideUse(IVUsers *P, Instruction* U, Value *O)
      : CallbackVH(U), Parent(P), OperandValToReplace(O) {
    }
  
    /// getUser - Return the user instruction for this use.
    Instruction *getUser() const {
      return cast<Instruction>(getValPtr());
    }
  
    /// setUser - Assign a new user instruction for this use.
    void setUser(Instruction *NewUser) {
      setValPtr(NewUser);
    }
  
    /// getOperandValToReplace - Return the Value of the operand in the user
    /// instruction that this IVStrideUse is representing.
    Value *getOperandValToReplace() const {
      return OperandValToReplace;
    }
  
    /// setOperandValToReplace - Assign a new Value as the operand value
    /// to replace.
    void setOperandValToReplace(Value *Op) {
      OperandValToReplace = Op;
    }
  
    /// getPostIncLoops - Return the set of loops for which the expression has
    /// been adjusted to use post-inc mode.
    const PostIncLoopSet &getPostIncLoops() const {
      return PostIncLoops;
    }
  
    /// transformToPostInc - Transform the expression to post-inc form for the
    /// given loop.
    void transformToPostInc(const Loop *L);
  
  private:
    /// Parent - a pointer to the IVUsers that owns this IVStrideUse.
    IVUsers *Parent;
  
    /// OperandValToReplace - The Value of the operand in the user instruction
    /// that this IVStrideUse is representing.
    WeakVH OperandValToReplace;
  
    /// PostIncLoops - The set of loops for which Expr has been adjusted to
    /// use post-inc mode. This corresponds with SCEVExpander's post-inc concept.
    PostIncLoopSet PostIncLoops;
  
    /// Deleted - Implementation of CallbackVH virtual function to
    /// receive notification when the User is deleted.
    void deleted() override;
  };
  
  template<> struct ilist_traits<IVStrideUse>
    : public ilist_default_traits<IVStrideUse> {
    // createSentinel is used to get hold of a node that marks the end of
    // the list...
    // The sentinel is relative to this instance, so we use a non-static
    // method.
    IVStrideUse *createSentinel() const {
      // since i(p)lists always publicly derive from the corresponding
      // traits, placing a data member in this class will augment i(p)list.
      // But since the NodeTy is expected to publicly derive from
      // ilist_node<NodeTy>, there is a legal viable downcast from it
      // to NodeTy. We use this trick to superpose i(p)list with a "ghostly"
      // NodeTy, which becomes the sentinel. Dereferencing the sentinel is
      // forbidden (save the ilist_node<NodeTy>) so no one will ever notice
      // the superposition.
      return static_cast<IVStrideUse*>(&Sentinel);
    }
    static void destroySentinel(IVStrideUse*) {}
  
    IVStrideUse *provideInitialHead() const { return createSentinel(); }
    IVStrideUse *ensureHead(IVStrideUse*) const { return createSentinel(); }
    static void noteHead(IVStrideUse*, IVStrideUse*) {}
  
  private:
    mutable ilist_node<IVStrideUse> Sentinel;
  };
  
  class IVUsers : public LoopPass {
    friend class IVStrideUse;
    Loop *L;
    LoopInfo *LI;
    DominatorTree *DT;
    ScalarEvolution *SE;
    const DataLayout *DL;
    SmallPtrSet<Instruction*,16> Processed;
  
    /// IVUses - A list of all tracked IV uses of induction variable expressions
    /// we are interested in.
    ilist<IVStrideUse> IVUses;
  
    void getAnalysisUsage(AnalysisUsage &AU) const override;
  
    bool runOnLoop(Loop *L, LPPassManager &LPM) override;
  
    void releaseMemory() override;
  
  public:
    static char ID; // Pass ID, replacement for typeid
    IVUsers();
  
    Loop *getLoop() const { return L; }
  
    /// AddUsersIfInteresting - Inspect the specified Instruction.  If it is a
    /// reducible SCEV, recursively add its users to the IVUsesByStride set and
    /// return true.  Otherwise, return false.
    bool AddUsersIfInteresting(Instruction *I);
  
    IVStrideUse &AddUser(Instruction *User, Value *Operand);
  
    /// getReplacementExpr - Return a SCEV expression which computes the
    /// value of the OperandValToReplace of the given IVStrideUse.
    const SCEV *getReplacementExpr(const IVStrideUse &IU) const;
  
    /// getExpr - Return the expression for the use.
    const SCEV *getExpr(const IVStrideUse &IU) const;
  
    const SCEV *getStride(const IVStrideUse &IU, const Loop *L) const;
  
    typedef ilist<IVStrideUse>::iterator iterator;
    typedef ilist<IVStrideUse>::const_iterator const_iterator;
    iterator begin() { return IVUses.begin(); }
    iterator end()   { return IVUses.end(); }
    const_iterator begin() const { return IVUses.begin(); }
    const_iterator end() const   { return IVUses.end(); }
    bool empty() const { return IVUses.empty(); }
  
    bool isIVUserOrOperand(Instruction *Inst) const {
      return Processed.count(Inst);
    }
  
    void print(raw_ostream &OS, const Module* = nullptr) const override;
  
    /// dump - This method is used for debugging.
    void dump() const;
  protected:
    bool AddUsersImpl(Instruction *I, SmallPtrSetImpl<Loop*> &SimpleLoopNests);
  };
  
  Pass *createIVUsersPass();
  
  }
  
  #endif
  