clang/Analysis/CFG.h

//===--- CFG.h - Classes for representing and building CFGs------*- 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 CFG and CFGBuilder classes for representing and
//  building Control-Flow Graphs (CFGs) from ASTs.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_CLANG_CFG_H
#define LLVM_CLANG_CFG_H

#include "clang/AST/Stmt.h"
#include "clang/Analysis/Support/BumpVector.h"
#include "clang/Basic/SourceLocation.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/GraphTraits.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/PointerIntPair.h"
#include "llvm/Support/Allocator.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/raw_ostream.h"
#include <bitset>
#include <cassert>
#include <iterator>
#include <memory>

namespace clang {
  class CXXDestructorDecl;
  class Decl;
  class Stmt;
  class Expr;
  class FieldDecl;
  class VarDecl;
  class CXXCtorInitializer;
  class CXXBaseSpecifier;
  class CXXBindTemporaryExpr;
  class CFG;
  class PrinterHelper;
  class LangOptions;
  class ASTContext;
  class CXXRecordDecl;
  class CXXDeleteExpr;
  class CXXNewExpr;
  class BinaryOperator;

/// CFGElement - Represents a top-level expression in a basic block.
class CFGElement {
public:
  enum Kind {
    // main kind
    Statement,
    Initializer,
    NewAllocator,
    // dtor kind
    AutomaticObjectDtor,
    DeleteDtor,
    BaseDtor,
    MemberDtor,
    TemporaryDtor,
    DTOR_BEGIN = AutomaticObjectDtor,
    DTOR_END = TemporaryDtor
  };

protected:
  // The int bits are used to mark the kind.
  llvm::PointerIntPair<void *, 2> Data1;
  llvm::PointerIntPair<void *, 2> Data2;

  CFGElement(Kind kind, const void *Ptr1, const void *Ptr2 = nullptr)
    : Data1(const_cast<void*>(Ptr1), ((unsigned) kind) & 0x3),
      Data2(const_cast<void*>(Ptr2), (((unsigned) kind) >> 2) & 0x3) {
    assert(getKind() == kind);
  }

  CFGElement() {}
public:

  /// \brief Convert to the specified CFGElement type, asserting that this
  /// CFGElement is of the desired type.
  template<typename T>
  T castAs() const {
    assert(T::isKind(*this));
    T t;
    CFGElement& e = t;
    e = *this;
    return t;
  }

  /// \brief Convert to the specified CFGElement type, returning None if this
  /// CFGElement is not of the desired type.
  template<typename T>
  Optional<T> getAs() const {
    if (!T::isKind(*this))
      return None;
    T t;
    CFGElement& e = t;
    e = *this;
    return t;
  }

  Kind getKind() const {
    unsigned x = Data2.getInt();
    x <<= 2;
    x |= Data1.getInt();
    return (Kind) x;
  }
};

class CFGStmt : public CFGElement {
public:
  CFGStmt(Stmt *S) : CFGElement(Statement, S) {}

  const Stmt *getStmt() const {
    return static_cast<const Stmt *>(Data1.getPointer());
  }

private:
  friend class CFGElement;
  CFGStmt() {}
  static bool isKind(const CFGElement &E) {
    return E.getKind() == Statement;
  }
};

/// CFGInitializer - Represents C++ base or member initializer from
/// constructor's initialization list.
class CFGInitializer : public CFGElement {
public:
  CFGInitializer(CXXCtorInitializer *initializer)
      : CFGElement(Initializer, initializer) {}

  CXXCtorInitializer* getInitializer() const {
    return static_cast<CXXCtorInitializer*>(Data1.getPointer());
  }

private:
  friend class CFGElement;
  CFGInitializer() {}
  static bool isKind(const CFGElement &E) {
    return E.getKind() == Initializer;
  }
};

/// CFGNewAllocator - Represents C++ allocator call.
class CFGNewAllocator : public CFGElement {
public:
  explicit CFGNewAllocator(const CXXNewExpr *S)
    : CFGElement(NewAllocator, S) {}

  // Get the new expression.
  const CXXNewExpr *getAllocatorExpr() const {
    return static_cast<CXXNewExpr *>(Data1.getPointer());
  }

private:
  friend class CFGElement;
  CFGNewAllocator() {}
  static bool isKind(const CFGElement &elem) {
    return elem.getKind() == NewAllocator;
  }
};

/// CFGImplicitDtor - Represents C++ object destructor implicitly generated
/// by compiler on various occasions.
class CFGImplicitDtor : public CFGElement {
protected:
  CFGImplicitDtor() {}
  CFGImplicitDtor(Kind kind, const void *data1, const void *data2 = nullptr)
    : CFGElement(kind, data1, data2) {
    assert(kind >= DTOR_BEGIN && kind <= DTOR_END);
  }

public:
  const CXXDestructorDecl *getDestructorDecl(ASTContext &astContext) const;
  bool isNoReturn(ASTContext &astContext) const;

private:
  friend class CFGElement;
  static bool isKind(const CFGElement &E) {
    Kind kind = E.getKind();
    return kind >= DTOR_BEGIN && kind <= DTOR_END;
  }
};

/// CFGAutomaticObjDtor - Represents C++ object destructor implicitly generated
/// for automatic object or temporary bound to const reference at the point
/// of leaving its local scope.
class CFGAutomaticObjDtor: public CFGImplicitDtor {
public:
  CFGAutomaticObjDtor(const VarDecl *var, const Stmt *stmt)
      : CFGImplicitDtor(AutomaticObjectDtor, var, stmt) {}

  const VarDecl *getVarDecl() const {
    return static_cast<VarDecl*>(Data1.getPointer());
  }

  // Get statement end of which triggered the destructor call.
  const Stmt *getTriggerStmt() const {
    return static_cast<Stmt*>(Data2.getPointer());
  }

private:
  friend class CFGElement;
  CFGAutomaticObjDtor() {}
  static bool isKind(const CFGElement &elem) {
    return elem.getKind() == AutomaticObjectDtor;
  }
};

/// CFGDeleteDtor - Represents C++ object destructor generated
/// from a call to delete.
class CFGDeleteDtor : public CFGImplicitDtor {
public:
  CFGDeleteDtor(const CXXRecordDecl *RD, const CXXDeleteExpr *DE)
      : CFGImplicitDtor(DeleteDtor, RD, DE) {}

  const CXXRecordDecl *getCXXRecordDecl() const {
    return static_cast<CXXRecordDecl*>(Data1.getPointer());
  }

  // Get Delete expression which triggered the destructor call.
  const CXXDeleteExpr *getDeleteExpr() const {
    return static_cast<CXXDeleteExpr *>(Data2.getPointer());
  }


private:
  friend class CFGElement;
  CFGDeleteDtor() {}
  static bool isKind(const CFGElement &elem) {
    return elem.getKind() == DeleteDtor;
  }
};

/// CFGBaseDtor - Represents C++ object destructor implicitly generated for
/// base object in destructor.
class CFGBaseDtor : public CFGImplicitDtor {
public:
  CFGBaseDtor(const CXXBaseSpecifier *base)
      : CFGImplicitDtor(BaseDtor, base) {}

  const CXXBaseSpecifier *getBaseSpecifier() const {
    return static_cast<const CXXBaseSpecifier*>(Data1.getPointer());
  }

private:
  friend class CFGElement;
  CFGBaseDtor() {}
  static bool isKind(const CFGElement &E) {
    return E.getKind() == BaseDtor;
  }
};

/// CFGMemberDtor - Represents C++ object destructor implicitly generated for
/// member object in destructor.
class CFGMemberDtor : public CFGImplicitDtor {
public:
  CFGMemberDtor(const FieldDecl *field)
      : CFGImplicitDtor(MemberDtor, field, nullptr) {}

  const FieldDecl *getFieldDecl() const {
    return static_cast<const FieldDecl*>(Data1.getPointer());
  }

private:
  friend class CFGElement;
  CFGMemberDtor() {}
  static bool isKind(const CFGElement &E) {
    return E.getKind() == MemberDtor;
  }
};

/// CFGTemporaryDtor - Represents C++ object destructor implicitly generated
/// at the end of full expression for temporary object.
class CFGTemporaryDtor : public CFGImplicitDtor {
public:
  CFGTemporaryDtor(CXXBindTemporaryExpr *expr)
      : CFGImplicitDtor(TemporaryDtor, expr, nullptr) {}

  const CXXBindTemporaryExpr *getBindTemporaryExpr() const {
    return static_cast<const CXXBindTemporaryExpr *>(Data1.getPointer());
  }

private:
  friend class CFGElement;
  CFGTemporaryDtor() {}
  static bool isKind(const CFGElement &E) {
    return E.getKind() == TemporaryDtor;
  }
};

/// CFGTerminator - Represents CFGBlock terminator statement.
///
/// TemporaryDtorsBranch bit is set to true if the terminator marks a branch
/// in control flow of destructors of temporaries. In this case terminator
/// statement is the same statement that branches control flow in evaluation
/// of matching full expression.
class CFGTerminator {
  llvm::PointerIntPair<Stmt *, 1> Data;
public:
  CFGTerminator() {}
  CFGTerminator(Stmt *S, bool TemporaryDtorsBranch = false)
      : Data(S, TemporaryDtorsBranch) {}

  Stmt *getStmt() { return Data.getPointer(); }
  const Stmt *getStmt() const { return Data.getPointer(); }

  bool isTemporaryDtorsBranch() const { return Data.getInt(); }

  operator Stmt *() { return getStmt(); }
  operator const Stmt *() const { return getStmt(); }

  Stmt *operator->() { return getStmt(); }
  const Stmt *operator->() const { return getStmt(); }

  Stmt &operator*() { return *getStmt(); }
  const Stmt &operator*() const { return *getStmt(); }

  LLVM_EXPLICIT operator bool() const { return getStmt(); }
};

/// CFGBlock - Represents a single basic block in a source-level CFG.
///  It consists of:
///
///  (1) A set of statements/expressions (which may contain subexpressions).
///  (2) A "terminator" statement (not in the set of statements).
///  (3) A list of successors and predecessors.
///
/// Terminator: The terminator represents the type of control-flow that occurs
/// at the end of the basic block.  The terminator is a Stmt* referring to an
/// AST node that has control-flow: if-statements, breaks, loops, etc.
/// If the control-flow is conditional, the condition expression will appear
/// within the set of statements in the block (usually the last statement).
///
/// Predecessors: the order in the set of predecessors is arbitrary.
///
/// Successors: the order in the set of successors is NOT arbitrary.  We
///  currently have the following orderings based on the terminator:
///
///     Terminator       Successor Ordering
///  -----------------------------------------------------
///       if            Then Block;  Else Block
///     ? operator      LHS expression;  RHS expression
///     &&, ||          expression that uses result of && or ||, RHS
///
/// But note that any of that may be NULL in case of optimized-out edges.
///
class CFGBlock {
  class ElementList {
    typedef BumpVector<CFGElement> ImplTy;
    ImplTy Impl;
  public:
    ElementList(BumpVectorContext &C) : Impl(C, 4) {}

    typedef std::reverse_iterator<ImplTy::iterator>       iterator;
    typedef std::reverse_iterator<ImplTy::const_iterator> const_iterator;
    typedef ImplTy::iterator                              reverse_iterator;
    typedef ImplTy::const_iterator                       const_reverse_iterator;
    typedef ImplTy::const_reference                       const_reference;

    void push_back(CFGElement e, BumpVectorContext &C) { Impl.push_back(e, C); }
    reverse_iterator insert(reverse_iterator I, size_t Cnt, CFGElement E,
        BumpVectorContext &C) {
      return Impl.insert(I, Cnt, E, C);
    }

    const_reference front() const { return Impl.back(); }
    const_reference back() const { return Impl.front(); }

    iterator begin() { return Impl.rbegin(); }
    iterator end() { return Impl.rend(); }
    const_iterator begin() const { return Impl.rbegin(); }
    const_iterator end() const { return Impl.rend(); }
    reverse_iterator rbegin() { return Impl.begin(); }
    reverse_iterator rend() { return Impl.end(); }
    const_reverse_iterator rbegin() const { return Impl.begin(); }
    const_reverse_iterator rend() const { return Impl.end(); }

   CFGElement operator[](size_t i) const  {
     assert(i < Impl.size());
     return Impl[Impl.size() - 1 - i];
   }

    size_t size() const { return Impl.size(); }
    bool empty() const { return Impl.empty(); }
  };

  /// Stmts - The set of statements in the basic block.
  ElementList Elements;

  /// Label - An (optional) label that prefixes the executable
  ///  statements in the block.  When this variable is non-NULL, it is
  ///  either an instance of LabelStmt, SwitchCase or CXXCatchStmt.
  Stmt *Label;

  /// Terminator - The terminator for a basic block that
  ///  indicates the type of control-flow that occurs between a block
  ///  and its successors.
  CFGTerminator Terminator;

  /// LoopTarget - Some blocks are used to represent the "loop edge" to
  ///  the start of a loop from within the loop body.  This Stmt* will be
  ///  refer to the loop statement for such blocks (and be null otherwise).
  const Stmt *LoopTarget;

  /// BlockID - A numerical ID assigned to a CFGBlock during construction
  ///   of the CFG.
  unsigned BlockID;

public:
  /// This class represents a potential adjacent block in the CFG.  It encodes
  /// whether or not the block is actually reachable, or can be proved to be
  /// trivially unreachable.  For some cases it allows one to encode scenarios
  /// where a block was substituted because the original (now alternate) block
  /// is unreachable.
  class AdjacentBlock {
    enum Kind {
      AB_Normal,
      AB_Unreachable,
      AB_Alternate
    };

    CFGBlock *ReachableBlock;
    llvm::PointerIntPair<CFGBlock*, 2> UnreachableBlock;

  public:
    /// Construct an AdjacentBlock with a possibly unreachable block.
    AdjacentBlock(CFGBlock *B, bool IsReachable);

    /// Construct an AdjacentBlock with a reachable block and an alternate
    /// unreachable block.
    AdjacentBlock(CFGBlock *B, CFGBlock *AlternateBlock);

    /// Get the reachable block, if one exists.
    CFGBlock *getReachableBlock() const {
      return ReachableBlock;
    }

    /// Get the potentially unreachable block.
    CFGBlock *getPossiblyUnreachableBlock() const {
      return UnreachableBlock.getPointer();
    }

    /// Provide an implicit conversion to CFGBlock* so that
    /// AdjacentBlock can be substituted for CFGBlock*.
    operator CFGBlock*() const {
      return getReachableBlock();
    }

    CFGBlock& operator *() const {
      return *getReachableBlock();
    }

    CFGBlock* operator ->() const {
      return getReachableBlock();
    }

    bool isReachable() const {
      Kind K = (Kind) UnreachableBlock.getInt();
      return K == AB_Normal || K == AB_Alternate;
    }
  };

private:
  /// Predecessors/Successors - Keep track of the predecessor / successor
  /// CFG blocks.
  typedef BumpVector<AdjacentBlock> AdjacentBlocks;
  AdjacentBlocks Preds;
  AdjacentBlocks Succs;

  /// NoReturn - This bit is set when the basic block contains a function call
  /// or implicit destructor that is attributed as 'noreturn'. In that case,
  /// control cannot technically ever proceed past this block. All such blocks
  /// will have a single immediate successor: the exit block. This allows them
  /// to be easily reached from the exit block and using this bit quickly
  /// recognized without scanning the contents of the block.
  ///
  /// Optimization Note: This bit could be profitably folded with Terminator's
  /// storage if the memory usage of CFGBlock becomes an issue.
  unsigned HasNoReturnElement : 1;

  /// Parent - The parent CFG that owns this CFGBlock.
  CFG *Parent;

public:
  explicit CFGBlock(unsigned blockid, BumpVectorContext &C, CFG *parent)
    : Elements(C), Label(nullptr), Terminator(nullptr), LoopTarget(nullptr),
      BlockID(blockid), Preds(C, 1), Succs(C, 1), HasNoReturnElement(false),
      Parent(parent) {}
  ~CFGBlock() {}

  // Statement iterators
  typedef ElementList::iterator                      iterator;
  typedef ElementList::const_iterator                const_iterator;
  typedef ElementList::reverse_iterator              reverse_iterator;
  typedef ElementList::const_reverse_iterator        const_reverse_iterator;

  CFGElement                 front()       const { return Elements.front();   }
  CFGElement                 back()        const { return Elements.back();    }

  iterator                   begin()             { return Elements.begin();   }
  iterator                   end()               { return Elements.end();     }
  const_iterator             begin()       const { return Elements.begin();   }
  const_iterator             end()         const { return Elements.end();     }

  reverse_iterator           rbegin()            { return Elements.rbegin();  }
  reverse_iterator           rend()              { return Elements.rend();    }
  const_reverse_iterator     rbegin()      const { return Elements.rbegin();  }
  const_reverse_iterator     rend()        const { return Elements.rend();    }

  unsigned                   size()        const { return Elements.size();    }
  bool                       empty()       const { return Elements.empty();   }

  CFGElement operator[](size_t i) const  { return Elements[i]; }

  // CFG iterators
  typedef AdjacentBlocks::iterator                              pred_iterator;
  typedef AdjacentBlocks::const_iterator                  const_pred_iterator;
  typedef AdjacentBlocks::reverse_iterator              pred_reverse_iterator;
  typedef AdjacentBlocks::const_reverse_iterator  const_pred_reverse_iterator;

  typedef AdjacentBlocks::iterator                              succ_iterator;
  typedef AdjacentBlocks::const_iterator                  const_succ_iterator;
  typedef AdjacentBlocks::reverse_iterator              succ_reverse_iterator;
  typedef AdjacentBlocks::const_reverse_iterator  const_succ_reverse_iterator;

  pred_iterator                pred_begin()        { return Preds.begin();   }
  pred_iterator                pred_end()          { return Preds.end();     }
  const_pred_iterator          pred_begin()  const { return Preds.begin();   }
  const_pred_iterator          pred_end()    const { return Preds.end();     }

  pred_reverse_iterator        pred_rbegin()       { return Preds.rbegin();  }
  pred_reverse_iterator        pred_rend()         { return Preds.rend();    }
  const_pred_reverse_iterator  pred_rbegin() const { return Preds.rbegin();  }
  const_pred_reverse_iterator  pred_rend()   const { return Preds.rend();    }

  succ_iterator                succ_begin()        { return Succs.begin();   }
  succ_iterator                succ_end()          { return Succs.end();     }
  const_succ_iterator          succ_begin()  const { return Succs.begin();   }
  const_succ_iterator          succ_end()    const { return Succs.end();     }

  succ_reverse_iterator        succ_rbegin()       { return Succs.rbegin();  }
  succ_reverse_iterator        succ_rend()         { return Succs.rend();    }
  const_succ_reverse_iterator  succ_rbegin() const { return Succs.rbegin();  }
  const_succ_reverse_iterator  succ_rend()   const { return Succs.rend();    }

  unsigned                     succ_size()   const { return Succs.size();    }
  bool                         succ_empty()  const { return Succs.empty();   }

  unsigned                     pred_size()   const { return Preds.size();    }
  bool                         pred_empty()  const { return Preds.empty();   }


  class FilterOptions {
  public:
    FilterOptions() {
      IgnoreNullPredecessors = 1;
      IgnoreDefaultsWithCoveredEnums = 0;
    }

    unsigned IgnoreNullPredecessors : 1;
    unsigned IgnoreDefaultsWithCoveredEnums : 1;
  };

  static bool FilterEdge(const FilterOptions &F, const CFGBlock *Src,
       const CFGBlock *Dst);

  template <typename IMPL, bool IsPred>
  class FilteredCFGBlockIterator {
  private:
    IMPL I, E;
    const FilterOptions F;
    const CFGBlock *From;
  public:
    explicit FilteredCFGBlockIterator(const IMPL &i, const IMPL &e,
                                      const CFGBlock *from,
                                      const FilterOptions &f)
        : I(i), E(e), F(f), From(from) {
      while (hasMore() && Filter(*I))
        ++I;
    }

    bool hasMore() const { return I != E; }

    FilteredCFGBlockIterator &operator++() {
      do { ++I; } while (hasMore() && Filter(*I));
      return *this;
    }

    const CFGBlock *operator*() const { return *I; }
  private:
    bool Filter(const CFGBlock *To) {
      return IsPred ? FilterEdge(F, To, From) : FilterEdge(F, From, To);
    }
  };

  typedef FilteredCFGBlockIterator<const_pred_iterator, true>
          filtered_pred_iterator;

  typedef FilteredCFGBlockIterator<const_succ_iterator, false>
          filtered_succ_iterator;

  filtered_pred_iterator filtered_pred_start_end(const FilterOptions &f) const {
    return filtered_pred_iterator(pred_begin(), pred_end(), this, f);
  }

  filtered_succ_iterator filtered_succ_start_end(const FilterOptions &f) const {
    return filtered_succ_iterator(succ_begin(), succ_end(), this, f);
  }

  // Manipulation of block contents

  void setTerminator(CFGTerminator Term) { Terminator = Term; }
  void setLabel(Stmt *Statement) { Label = Statement; }
  void setLoopTarget(const Stmt *loopTarget) { LoopTarget = loopTarget; }
  void setHasNoReturnElement() { HasNoReturnElement = true; }

  CFGTerminator getTerminator() { return Terminator; }
  const CFGTerminator getTerminator() const { return Terminator; }

  Stmt *getTerminatorCondition(bool StripParens = true);

  const Stmt *getTerminatorCondition(bool StripParens = true) const {
    return const_cast<CFGBlock*>(this)->getTerminatorCondition(StripParens);
  }

  const Stmt *getLoopTarget() const { return LoopTarget; }

  Stmt *getLabel() { return Label; }
  const Stmt *getLabel() const { return Label; }

  bool hasNoReturnElement() const { return HasNoReturnElement; }

  unsigned getBlockID() const { return BlockID; }

  CFG *getParent() const { return Parent; }

  void dump() const;

  void dump(const CFG *cfg, const LangOptions &LO, bool ShowColors = false) const;
  void print(raw_ostream &OS, const CFG* cfg, const LangOptions &LO,
             bool ShowColors) const;
  void printTerminator(raw_ostream &OS, const LangOptions &LO) const;
  void printAsOperand(raw_ostream &OS, bool /*PrintType*/) {
    OS << "BB#" << getBlockID();
  }

  /// Adds a (potentially unreachable) successor block to the current block.
  void addSuccessor(AdjacentBlock Succ, BumpVectorContext &C);

  void appendStmt(Stmt *statement, BumpVectorContext &C) {
    Elements.push_back(CFGStmt(statement), C);
  }

  void appendInitializer(CXXCtorInitializer *initializer,
                        BumpVectorContext &C) {
    Elements.push_back(CFGInitializer(initializer), C);
  }

  void appendNewAllocator(CXXNewExpr *NE,
                          BumpVectorContext &C) {
    Elements.push_back(CFGNewAllocator(NE), C);
  }

  void appendBaseDtor(const CXXBaseSpecifier *BS, BumpVectorContext &C) {
    Elements.push_back(CFGBaseDtor(BS), C);
  }

  void appendMemberDtor(FieldDecl *FD, BumpVectorContext &C) {
    Elements.push_back(CFGMemberDtor(FD), C);
  }

  void appendTemporaryDtor(CXXBindTemporaryExpr *E, BumpVectorContext &C) {
    Elements.push_back(CFGTemporaryDtor(E), C);
  }

  void appendAutomaticObjDtor(VarDecl *VD, Stmt *S, BumpVectorContext &C) {
    Elements.push_back(CFGAutomaticObjDtor(VD, S), C);
  }

  void appendDeleteDtor(CXXRecordDecl *RD, CXXDeleteExpr *DE, BumpVectorContext &C) {
    Elements.push_back(CFGDeleteDtor(RD, DE), C);
  }

  // Destructors must be inserted in reversed order. So insertion is in two
  // steps. First we prepare space for some number of elements, then we insert
  // the elements beginning at the last position in prepared space.
  iterator beginAutomaticObjDtorsInsert(iterator I, size_t Cnt,
      BumpVectorContext &C) {
    return iterator(Elements.insert(I.base(), Cnt,
                                    CFGAutomaticObjDtor(nullptr, 0), C));
  }
  iterator insertAutomaticObjDtor(iterator I, VarDecl *VD, Stmt *S) {
    *I = CFGAutomaticObjDtor(VD, S);
    return ++I;
  }
};

/// \brief CFGCallback defines methods that should be called when a logical
/// operator error is found when building the CFG.
class CFGCallback {
public:
  CFGCallback() {}
  virtual void compareAlwaysTrue(const BinaryOperator *B, bool isAlwaysTrue) {}
  virtual void compareBitwiseEquality(const BinaryOperator *B,
                                      bool isAlwaysTrue) {}
  virtual ~CFGCallback() {}
};

/// CFG - Represents a source-level, intra-procedural CFG that represents the
///  control-flow of a Stmt.  The Stmt can represent an entire function body,
///  or a single expression.  A CFG will always contain one empty block that
///  represents the Exit point of the CFG.  A CFG will also contain a designated
///  Entry block.  The CFG solely represents control-flow; it consists of
///  CFGBlocks which are simply containers of Stmt*'s in the AST the CFG
///  was constructed from.
class CFG {
public:
  //===--------------------------------------------------------------------===//
  // CFG Construction & Manipulation.
  //===--------------------------------------------------------------------===//

  class BuildOptions {
    std::bitset<Stmt::lastStmtConstant> alwaysAddMask;
  public:
    typedef llvm::DenseMap<const Stmt *, const CFGBlock*> ForcedBlkExprs;
    ForcedBlkExprs **forcedBlkExprs;
    CFGCallback *Observer;
    bool PruneTriviallyFalseEdges;
    bool AddEHEdges;
    bool AddInitializers;
    bool AddImplicitDtors;
    bool AddTemporaryDtors;
    bool AddStaticInitBranches;
    bool AddCXXNewAllocator;

    bool alwaysAdd(const Stmt *stmt) const {
      return alwaysAddMask[stmt->getStmtClass()];
    }

    BuildOptions &setAlwaysAdd(Stmt::StmtClass stmtClass, bool val = true) {
      alwaysAddMask[stmtClass] = val;
      return *this;
    }

    BuildOptions &setAllAlwaysAdd() {
      alwaysAddMask.set();
      return *this;
    }

    BuildOptions()
      : forcedBlkExprs(nullptr), Observer(nullptr),
        PruneTriviallyFalseEdges(true), AddEHEdges(false),
        AddInitializers(false), AddImplicitDtors(false),
        AddTemporaryDtors(false), AddStaticInitBranches(false),
        AddCXXNewAllocator(false) {}
  };

  /// \brief Provides a custom implementation of the iterator class to have the
  /// same interface as Function::iterator - iterator returns CFGBlock
  /// (not a pointer to CFGBlock).
  class graph_iterator {
  public:
    typedef const CFGBlock                  value_type;
    typedef value_type&                     reference;
    typedef value_type*                     pointer;
    typedef BumpVector<CFGBlock*>::iterator ImplTy;

    graph_iterator(const ImplTy &i) : I(i) {}

    bool operator==(const graph_iterator &X) const { return I == X.I; }
    bool operator!=(const graph_iterator &X) const { return I != X.I; }

    reference operator*()    const { return **I; }
    pointer operator->()     const { return  *I; }
    operator CFGBlock* ()          { return  *I; }

    graph_iterator &operator++() { ++I; return *this; }
    graph_iterator &operator--() { --I; return *this; }

  private:
    ImplTy I;
  };

  class const_graph_iterator {
  public:
    typedef const CFGBlock                  value_type;
    typedef value_type&                     reference;
    typedef value_type*                     pointer;
    typedef BumpVector<CFGBlock*>::const_iterator ImplTy;

    const_graph_iterator(const ImplTy &i) : I(i) {}

    bool operator==(const const_graph_iterator &X) const { return I == X.I; }
    bool operator!=(const const_graph_iterator &X) const { return I != X.I; }

    reference operator*() const { return **I; }
    pointer operator->()  const { return  *I; }
    operator CFGBlock* () const { return  *I; }

    const_graph_iterator &operator++() { ++I; return *this; }
    const_graph_iterator &operator--() { --I; return *this; }

  private:
    ImplTy I;
  };

  /// buildCFG - Builds a CFG from an AST.  The responsibility to free the
  ///   constructed CFG belongs to the caller.
  static CFG* buildCFG(const Decl *D, Stmt *AST, ASTContext *C,
                       const BuildOptions &BO);

  /// createBlock - Create a new block in the CFG.  The CFG owns the block;
  ///  the caller should not directly free it.
  CFGBlock *createBlock();

  /// setEntry - Set the entry block of the CFG.  This is typically used
  ///  only during CFG construction.  Most CFG clients expect that the
  ///  entry block has no predecessors and contains no statements.
  void setEntry(CFGBlock *B) { Entry = B; }

  /// setIndirectGotoBlock - Set the block used for indirect goto jumps.
  ///  This is typically used only during CFG construction.
  void setIndirectGotoBlock(CFGBlock *B) { IndirectGotoBlock = B; }

  //===--------------------------------------------------------------------===//
  // Block Iterators
  //===--------------------------------------------------------------------===//

  typedef BumpVector<CFGBlock*>                    CFGBlockListTy;
  typedef CFGBlockListTy::iterator                 iterator;
  typedef CFGBlockListTy::const_iterator           const_iterator;
  typedef std::reverse_iterator<iterator>          reverse_iterator;
  typedef std::reverse_iterator<const_iterator>    const_reverse_iterator;

  CFGBlock &                front()                { return *Blocks.front(); }
  CFGBlock &                back()                 { return *Blocks.back(); }

  iterator                  begin()                { return Blocks.begin(); }
  iterator                  end()                  { return Blocks.end(); }
  const_iterator            begin()       const    { return Blocks.begin(); }
  const_iterator            end()         const    { return Blocks.end(); }

  graph_iterator nodes_begin() { return graph_iterator(Blocks.begin()); }
  graph_iterator nodes_end() { return graph_iterator(Blocks.end()); }
  const_graph_iterator nodes_begin() const {
    return const_graph_iterator(Blocks.begin());
  }
  const_graph_iterator nodes_end() const {
    return const_graph_iterator(Blocks.end());
  }

  reverse_iterator          rbegin()               { return Blocks.rbegin(); }
  reverse_iterator          rend()                 { return Blocks.rend(); }
  const_reverse_iterator    rbegin()      const    { return Blocks.rbegin(); }
  const_reverse_iterator    rend()        const    { return Blocks.rend(); }

  CFGBlock &                getEntry()             { return *Entry; }
  const CFGBlock &          getEntry()    const    { return *Entry; }
  CFGBlock &                getExit()              { return *Exit; }
  const CFGBlock &          getExit()     const    { return *Exit; }

  CFGBlock *       getIndirectGotoBlock() { return IndirectGotoBlock; }
  const CFGBlock * getIndirectGotoBlock() const { return IndirectGotoBlock; }

  typedef std::vector<const CFGBlock*>::const_iterator try_block_iterator;
  try_block_iterator try_blocks_begin() const {
    return TryDispatchBlocks.begin();
  }
  try_block_iterator try_blocks_end() const {
    return TryDispatchBlocks.end();
  }

  void addTryDispatchBlock(const CFGBlock *block) {
    TryDispatchBlocks.push_back(block);
  }

  /// Records a synthetic DeclStmt and the DeclStmt it was constructed from.
  ///
  /// The CFG uses synthetic DeclStmts when a single AST DeclStmt contains
  /// multiple decls.
  void addSyntheticDeclStmt(const DeclStmt *Synthetic,
                            const DeclStmt *Source) {
    assert(Synthetic->isSingleDecl() && "Can handle single declarations only");
    assert(Synthetic != Source && "Don't include original DeclStmts in map");
    assert(!SyntheticDeclStmts.count(Synthetic) && "Already in map");
    SyntheticDeclStmts[Synthetic] = Source;
  }

  typedef llvm::DenseMap<const DeclStmt *, const DeclStmt *>::const_iterator
    synthetic_stmt_iterator;

  /// Iterates over synthetic DeclStmts in the CFG.
  ///
  /// Each element is a (synthetic statement, source statement) pair.
  ///
  /// \sa addSyntheticDeclStmt
  synthetic_stmt_iterator synthetic_stmt_begin() const {
    return SyntheticDeclStmts.begin();
  }

  /// \sa synthetic_stmt_begin
  synthetic_stmt_iterator synthetic_stmt_end() const {
    return SyntheticDeclStmts.end();
  }

  //===--------------------------------------------------------------------===//
  // Member templates useful for various batch operations over CFGs.
  //===--------------------------------------------------------------------===//

  template <typename CALLBACK>
  void VisitBlockStmts(CALLBACK& O) const {
    for (const_iterator I=begin(), E=end(); I != E; ++I)
      for (CFGBlock::const_iterator BI=(*I)->begin(), BE=(*I)->end();
           BI != BE; ++BI) {
        if (Optional<CFGStmt> stmt = BI->getAs<CFGStmt>())
          O(const_cast<Stmt*>(stmt->getStmt()));
      }
  }

  //===--------------------------------------------------------------------===//
  // CFG Introspection.
  //===--------------------------------------------------------------------===//

  /// getNumBlockIDs - Returns the total number of BlockIDs allocated (which
  /// start at 0).
  unsigned getNumBlockIDs() const { return NumBlockIDs; }

  /// size - Return the total number of CFGBlocks within the CFG
  /// This is simply a renaming of the getNumBlockIDs(). This is necessary
  /// because the dominator implementation needs such an interface.
  unsigned size() const { return NumBlockIDs; }

  //===--------------------------------------------------------------------===//
  // CFG Debugging: Pretty-Printing and Visualization.
  //===--------------------------------------------------------------------===//

  void viewCFG(const LangOptions &LO) const;
  void print(raw_ostream &OS, const LangOptions &LO, bool ShowColors) const;
  void dump(const LangOptions &LO, bool ShowColors) const;

  //===--------------------------------------------------------------------===//
  // Internal: constructors and data.
  //===--------------------------------------------------------------------===//

  CFG()
    : Entry(nullptr), Exit(nullptr), IndirectGotoBlock(nullptr), NumBlockIDs(0),
      Blocks(BlkBVC, 10) {}

  llvm::BumpPtrAllocator& getAllocator() {
    return BlkBVC.getAllocator();
  }

  BumpVectorContext &getBumpVectorContext() {
    return BlkBVC;
  }

private:
  CFGBlock *Entry;
  CFGBlock *Exit;
  CFGBlock* IndirectGotoBlock;  // Special block to contain collective dispatch
                                // for indirect gotos
  unsigned  NumBlockIDs;

  BumpVectorContext BlkBVC;

  CFGBlockListTy Blocks;

  /// C++ 'try' statements are modeled with an indirect dispatch block.
  /// This is the collection of such blocks present in the CFG.
  std::vector<const CFGBlock *> TryDispatchBlocks;

  /// Collects DeclStmts synthesized for this CFG and maps each one back to its
  /// source DeclStmt.
  llvm::DenseMap<const DeclStmt *, const DeclStmt *> SyntheticDeclStmts;
};
} // end namespace clang

//===----------------------------------------------------------------------===//
// GraphTraits specializations for CFG basic block graphs (source-level CFGs)
//===----------------------------------------------------------------------===//

namespace llvm {

/// Implement simplify_type for CFGTerminator, so that we can dyn_cast from
/// CFGTerminator to a specific Stmt class.
template <> struct simplify_type< ::clang::CFGTerminator> {
  typedef ::clang::Stmt *SimpleType;
  static SimpleType getSimplifiedValue(::clang::CFGTerminator Val) {
    return Val.getStmt();
  }
};

// Traits for: CFGBlock

template <> struct GraphTraits< ::clang::CFGBlock *> {
  typedef ::clang::CFGBlock NodeType;
  typedef ::clang::CFGBlock::succ_iterator ChildIteratorType;

  static NodeType* getEntryNode(::clang::CFGBlock *BB)
  { return BB; }

  static inline ChildIteratorType child_begin(NodeType* N)
  { return N->succ_begin(); }

  static inline ChildIteratorType child_end(NodeType* N)
  { return N->succ_end(); }
};

template <> struct GraphTraits< const ::clang::CFGBlock *> {
  typedef const ::clang::CFGBlock NodeType;
  typedef ::clang::CFGBlock::const_succ_iterator ChildIteratorType;

  static NodeType* getEntryNode(const clang::CFGBlock *BB)
  { return BB; }

  static inline ChildIteratorType child_begin(NodeType* N)
  { return N->succ_begin(); }

  static inline ChildIteratorType child_end(NodeType* N)
  { return N->succ_end(); }
};

template <> struct GraphTraits<Inverse< ::clang::CFGBlock*> > {
  typedef ::clang::CFGBlock NodeType;
  typedef ::clang::CFGBlock::const_pred_iterator ChildIteratorType;

  static NodeType *getEntryNode(Inverse< ::clang::CFGBlock*> G)
  { return G.Graph; }

  static inline ChildIteratorType child_begin(NodeType* N)
  { return N->pred_begin(); }

  static inline ChildIteratorType child_end(NodeType* N)
  { return N->pred_end(); }
};

template <> struct GraphTraits<Inverse<const ::clang::CFGBlock*> > {
  typedef const ::clang::CFGBlock NodeType;
  typedef ::clang::CFGBlock::const_pred_iterator ChildIteratorType;

  static NodeType *getEntryNode(Inverse<const ::clang::CFGBlock*> G)
  { return G.Graph; }

  static inline ChildIteratorType child_begin(NodeType* N)
  { return N->pred_begin(); }

  static inline ChildIteratorType child_end(NodeType* N)
  { return N->pred_end(); }
};

// Traits for: CFG

template <> struct GraphTraits< ::clang::CFG* >
    : public GraphTraits< ::clang::CFGBlock *>  {

  typedef ::clang::CFG::graph_iterator nodes_iterator;

  static NodeType     *getEntryNode(::clang::CFG* F) { return &F->getEntry(); }
  static nodes_iterator nodes_begin(::clang::CFG* F) { return F->nodes_begin();}
  static nodes_iterator   nodes_end(::clang::CFG* F) { return F->nodes_end(); }
  static unsigned              size(::clang::CFG* F) { return F->size(); }
};

template <> struct GraphTraits<const ::clang::CFG* >
    : public GraphTraits<const ::clang::CFGBlock *>  {

  typedef ::clang::CFG::const_graph_iterator nodes_iterator;

  static NodeType *getEntryNode( const ::clang::CFG* F) {
    return &F->getEntry();
  }
  static nodes_iterator nodes_begin( const ::clang::CFG* F) {
    return F->nodes_begin();
  }
  static nodes_iterator nodes_end( const ::clang::CFG* F) {
    return F->nodes_end();
  }
  static unsigned size(const ::clang::CFG* F) {
    return F->size();
  }
};

template <> struct GraphTraits<Inverse< ::clang::CFG*> >
  : public GraphTraits<Inverse< ::clang::CFGBlock*> > {

  typedef ::clang::CFG::graph_iterator nodes_iterator;

  static NodeType *getEntryNode( ::clang::CFG* F) { return &F->getExit(); }
  static nodes_iterator nodes_begin( ::clang::CFG* F) {return F->nodes_begin();}
  static nodes_iterator nodes_end( ::clang::CFG* F) { return F->nodes_end(); }
};

template <> struct GraphTraits<Inverse<const ::clang::CFG*> >
  : public GraphTraits<Inverse<const ::clang::CFGBlock*> > {

  typedef ::clang::CFG::const_graph_iterator nodes_iterator;

  static NodeType *getEntryNode(const ::clang::CFG* F) { return &F->getExit(); }
  static nodes_iterator nodes_begin(const ::clang::CFG* F) {
    return F->nodes_begin();
  }
  static nodes_iterator nodes_end(const ::clang::CFG* F) {
    return F->nodes_end();
  }
};
} // end llvm namespace
#endif