CFRefCount.cpp

  // Create the "drain" selector.
  Summ = getPersistentSummary(E, isGCEnabled() ? DoNothing : DecRef);
  addNSObjectMethSummary(GetNullarySelector("drain", Ctx), Summ);

  // Create the "autorelease" selector.
  Summ = getPersistentSummary(E, isGCEnabled() ? DoNothing : Autorelease);
  addNSObjectMethSummary(GetNullarySelector("autorelease", Ctx), Summ);
  
  // For NSWindow, allocated objects are (initially) self-owned.  
  RetainSummary *NSWindowSumm =
    getPersistentSummary(RetEffect::MakeReceiverAlias(), SelfOwn);
  
  addInstMethSummary("NSWindow", NSWindowSumm, "initWithContentRect",
                     "styleMask", "backing", "defer", NULL);
  
  addInstMethSummary("NSWindow", NSWindowSumm, "initWithContentRect",
                     "styleMask", "backing", "defer", "screen", NULL);
    
  // For NSPanel (which subclasses NSWindow), allocated objects are not
  //  self-owned.
  addInstMethSummary("NSPanel", InitSumm, "initWithContentRect",
                     "styleMask", "backing", "defer", NULL);
  
  addInstMethSummary("NSPanel", InitSumm, "initWithContentRect",
                     "styleMask", "backing", "defer", "screen", NULL);

  // Create NSAssertionHandler summaries.
  addPanicSummary("NSAssertionHandler", "handleFailureInFunction", "file",
                  "lineNumber", "description", NULL); 
  
  addPanicSummary("NSAssertionHandler", "handleFailureInMethod", "object",
                  "file", "lineNumber", "description", NULL);
}

//===----------------------------------------------------------------------===//
// Reference-counting logic (typestate + counts).
//===----------------------------------------------------------------------===//

namespace {
  
class VISIBILITY_HIDDEN RefVal {
public:  
  
  enum Kind {
    Owned = 0, // Owning reference.    
    NotOwned,  // Reference is not owned by still valid (not freed).    
    Released,  // Object has been released.
    ReturnedOwned, // Returned object passes ownership to caller.
    ReturnedNotOwned, // Return object does not pass ownership to caller.
    ErrorUseAfterRelease, // Object used after released.    
    ErrorReleaseNotOwned, // Release of an object that was not owned.
    ErrorLeak  // A memory leak due to excessive reference counts.
  };
  
private:
  
  Kind kind;
  unsigned Cnt;
  QualType T;

  RefVal(Kind k, unsigned cnt, QualType t) : kind(k), Cnt(cnt), T(t) {}
  RefVal(Kind k, unsigned cnt = 0) : kind(k), Cnt(cnt) {}

public:  
  
  Kind getKind() const { return kind; }

  unsigned getCount() const { return Cnt; }  
  QualType getType() const { return T; }
  
  // Useful predicates.
  
  static bool isError(Kind k) { return k >= ErrorUseAfterRelease; }
  
  static bool isLeak(Kind k) { return k == ErrorLeak; }
  
  bool isOwned() const {
    return getKind() == Owned;
  }
  
  bool isNotOwned() const {
    return getKind() == NotOwned;
  }
  
  bool isReturnedOwned() const {
    return getKind() == ReturnedOwned;
  }
  
  bool isReturnedNotOwned() const {
    return getKind() == ReturnedNotOwned;
  }
  
  bool isNonLeakError() const {
    Kind k = getKind();
    return isError(k) && !isLeak(k);
  }
  
  // State creation: normal state.
  
  static RefVal makeOwned(QualType t, unsigned Count = 1) {
    return RefVal(Owned, Count, t);
  }
  
  static RefVal makeNotOwned(QualType t, unsigned Count = 0) {
    return RefVal(NotOwned, Count, t);
  }

  static RefVal makeReturnedOwned(unsigned Count) {
    return RefVal(ReturnedOwned, Count);
  }
  
  static RefVal makeReturnedNotOwned() {
    return RefVal(ReturnedNotOwned);
  }
  
  // Comparison, profiling, and pretty-printing.
  
  bool operator==(const RefVal& X) const {
    return kind == X.kind && Cnt == X.Cnt && T == X.T;
  }
  
  RefVal operator-(size_t i) const {
    return RefVal(getKind(), getCount() - i, getType());
  }
  
  RefVal operator+(size_t i) const {
    return RefVal(getKind(), getCount() + i, getType());
  }
  
  RefVal operator^(Kind k) const {
    return RefVal(k, getCount(), getType());
  }
    
  
  void Profile(llvm::FoldingSetNodeID& ID) const {
    ID.AddInteger((unsigned) kind);
    ID.AddInteger(Cnt);
    ID.Add(T);
  }

  void print(std::ostream& Out) const;
};
  
void RefVal::print(std::ostream& Out) const {
  if (!T.isNull())
    Out << "Tracked Type:" << T.getAsString() << '\n';
    
  switch (getKind()) {
    default: assert(false);
    case Owned: { 
      Out << "Owned";
      unsigned cnt = getCount();
      if (cnt) Out << " (+ " << cnt << ")";
      break;
    }
      
    case NotOwned: {
      Out << "NotOwned";
      unsigned cnt = getCount();
      if (cnt) Out << " (+ " << cnt << ")";
      break;
    }
      
    case ReturnedOwned: { 
      Out << "ReturnedOwned";
      unsigned cnt = getCount();
      if (cnt) Out << " (+ " << cnt << ")";
      break;
    }
      
    case ReturnedNotOwned: {
      Out << "ReturnedNotOwned";
      unsigned cnt = getCount();
      if (cnt) Out << " (+ " << cnt << ")";
      break;
    }
            
    case Released:
      Out << "Released";
      break;
      
    case ErrorLeak:
      Out << "Leaked";
      break;            
      
    case ErrorUseAfterRelease:
      Out << "Use-After-Release [ERROR]";
      break;
      
    case ErrorReleaseNotOwned:
      Out << "Release of Not-Owned [ERROR]";
      break;
  }
}
  
} // end anonymous namespace

//===----------------------------------------------------------------------===//
// RefBindings - State used to track object reference counts.
//===----------------------------------------------------------------------===//
  
typedef llvm::ImmutableMap<SymbolID, RefVal> RefBindings;
static int RefBIndex = 0;

namespace clang {
  template<>
  struct GRStateTrait<RefBindings> : public GRStatePartialTrait<RefBindings> {
    static inline void* GDMIndex() { return &RefBIndex; }  
  };
}
  
//===----------------------------------------------------------------------===//
// Transfer functions.
//===----------------------------------------------------------------------===//

namespace {
  
class VISIBILITY_HIDDEN CFRefCount : public GRSimpleVals {
public:
  // Type definitions.  
  typedef llvm::DenseMap<GRExprEngine::NodeTy*,std::pair<Expr*, SymbolID> >
          ReleasesNotOwnedTy;

  typedef ReleasesNotOwnedTy UseAfterReleasesTy;
    
  typedef llvm::DenseMap<GRExprEngine::NodeTy*, std::vector<SymbolID>*>
          LeaksTy;

  class BindingsPrinter : public GRState::Printer {
  public:
    virtual void Print(std::ostream& Out, const GRState* state,
                       const char* nl, const char* sep);
  };

private:
  RetainSummaryManager Summaries;  
  const LangOptions&   LOpts;

  UseAfterReleasesTy   UseAfterReleases;
  ReleasesNotOwnedTy   ReleasesNotOwned;
  LeaksTy              Leaks;
  
  RefBindings Update(RefBindings B, SymbolID sym, RefVal V, ArgEffect E,
                     RefVal::Kind& hasErr, RefBindings::Factory& RefBFactory);
  
  RefVal::Kind& Update(GRStateRef& state, SymbolID sym, RefVal V,
                       ArgEffect E, RefVal::Kind& hasErr) {
    
    state = state.set<RefBindings>(Update(state.get<RefBindings>(), sym, V, 
                                          E, hasErr,
                                          state.get_context<RefBindings>()));
    return hasErr;
  }
  
  void ProcessNonLeakError(ExplodedNodeSet<GRState>& Dst,
                           GRStmtNodeBuilder<GRState>& Builder,
                           Expr* NodeExpr, Expr* ErrorExpr,                        
                           ExplodedNode<GRState>* Pred,
                           const GRState* St,
                           RefVal::Kind hasErr, SymbolID Sym);
  
  const GRState* HandleSymbolDeath(GRStateManager& VMgr,
                                      const GRState* St,
                                      SymbolID sid, RefVal V, bool& hasLeak);
  
public:
  
  CFRefCount(ASTContext& Ctx, bool gcenabled, const LangOptions& lopts)
    : Summaries(Ctx, gcenabled),
      LOpts(lopts) {}
  
  virtual ~CFRefCount() {
    for (LeaksTy::iterator I = Leaks.begin(), E = Leaks.end(); I!=E; ++I)
      delete I->second;
  }
  
  virtual void RegisterChecks(GRExprEngine& Eng);
 
  virtual void RegisterPrinters(std::vector<GRState::Printer*>& Printers) {
    Printers.push_back(new BindingsPrinter());
  }
  
  bool isGCEnabled() const { return Summaries.isGCEnabled(); }
  const LangOptions& getLangOptions() const { return LOpts; }
  
  // Calls.

  void EvalSummary(ExplodedNodeSet<GRState>& Dst,
                   GRExprEngine& Eng,
                   GRStmtNodeBuilder<GRState>& Builder,
                   Expr* Ex,
                   Expr* Receiver,
                   RetainSummary* Summ,
                   ExprIterator arg_beg, ExprIterator arg_end,                             
                   ExplodedNode<GRState>* Pred);
    
  virtual void EvalCall(ExplodedNodeSet<GRState>& Dst,
                        GRExprEngine& Eng,
                        GRStmtNodeBuilder<GRState>& Builder,
                        CallExpr* CE, RVal L,
                        ExplodedNode<GRState>* Pred);  
  
  
  virtual void EvalObjCMessageExpr(ExplodedNodeSet<GRState>& Dst,
                                   GRExprEngine& Engine,
                                   GRStmtNodeBuilder<GRState>& Builder,
                                   ObjCMessageExpr* ME,
                                   ExplodedNode<GRState>* Pred);
  
  bool EvalObjCMessageExprAux(ExplodedNodeSet<GRState>& Dst,
                              GRExprEngine& Engine,
                              GRStmtNodeBuilder<GRState>& Builder,
                              ObjCMessageExpr* ME,
                              ExplodedNode<GRState>* Pred);

  // Stores.
  
  virtual void EvalStore(ExplodedNodeSet<GRState>& Dst,
                         GRExprEngine& Engine,
                         GRStmtNodeBuilder<GRState>& Builder,
                         Expr* E, ExplodedNode<GRState>* Pred,
                         const GRState* St, RVal TargetLV, RVal Val);
  // End-of-path.
  
  virtual void EvalEndPath(GRExprEngine& Engine,
                           GREndPathNodeBuilder<GRState>& Builder);
  
  virtual void EvalDeadSymbols(ExplodedNodeSet<GRState>& Dst,
                               GRExprEngine& Engine,
                               GRStmtNodeBuilder<GRState>& Builder,
                               ExplodedNode<GRState>* Pred,
                               Stmt* S,
                               const GRState* St,
                               const GRStateManager::DeadSymbolsTy& Dead);
  // Return statements.
  
  virtual void EvalReturn(ExplodedNodeSet<GRState>& Dst,
                          GRExprEngine& Engine,
                          GRStmtNodeBuilder<GRState>& Builder,
                          ReturnStmt* S,
                          ExplodedNode<GRState>* Pred);

  // Assumptions.

  virtual const GRState* EvalAssume(GRStateManager& VMgr,
                                       const GRState* St, RVal Cond,
                                       bool Assumption, bool& isFeasible);

  // Error iterators.

  typedef UseAfterReleasesTy::iterator use_after_iterator;  
  typedef ReleasesNotOwnedTy::iterator bad_release_iterator;
  typedef LeaksTy::iterator            leaks_iterator;
  
  use_after_iterator use_after_begin() { return UseAfterReleases.begin(); }
  use_after_iterator use_after_end() { return UseAfterReleases.end(); }
  
  bad_release_iterator bad_release_begin() { return ReleasesNotOwned.begin(); }
  bad_release_iterator bad_release_end() { return ReleasesNotOwned.end(); }
  
  leaks_iterator leaks_begin() { return Leaks.begin(); }
  leaks_iterator leaks_end() { return Leaks.end(); }
};

} // end anonymous namespace




void CFRefCount::BindingsPrinter::Print(std::ostream& Out, const GRState* state,
                                        const char* nl, const char* sep) {
    
  RefBindings B = state->get<RefBindings>();
  
  if (!B.isEmpty())
    Out << sep << nl;
  
  for (RefBindings::iterator I=B.begin(), E=B.end(); I!=E; ++I) {
    Out << (*I).first << " : ";
    (*I).second.print(Out);
    Out << nl;
  }
}

static inline ArgEffect GetArgE(RetainSummary* Summ, unsigned idx) {
  return Summ ? Summ->getArg(idx) : MayEscape;
}

static inline RetEffect GetRetEffect(RetainSummary* Summ) {
  return Summ ? Summ->getRetEffect() : RetEffect::MakeNoRet();
}

static inline ArgEffect GetReceiverE(RetainSummary* Summ) {
  return Summ ? Summ->getReceiverEffect() : DoNothing;
}

static inline bool IsEndPath(RetainSummary* Summ) {
  return Summ ? Summ->isEndPath() : false;
}

void CFRefCount::ProcessNonLeakError(ExplodedNodeSet<GRState>& Dst,
                                     GRStmtNodeBuilder<GRState>& Builder,
                                     Expr* NodeExpr, Expr* ErrorExpr,                        
                                     ExplodedNode<GRState>* Pred,
                                     const GRState* St,
                                     RefVal::Kind hasErr, SymbolID Sym) {
  Builder.BuildSinks = true;
  GRExprEngine::NodeTy* N  = Builder.MakeNode(Dst, NodeExpr, Pred, St);

  if (!N) return;
    
  switch (hasErr) {
    default: assert(false);
    case RefVal::ErrorUseAfterRelease:
      UseAfterReleases[N] = std::make_pair(ErrorExpr, Sym);
      break;
      
    case RefVal::ErrorReleaseNotOwned:
      ReleasesNotOwned[N] = std::make_pair(ErrorExpr, Sym);
      break;
  }
}

/// GetReturnType - Used to get the return type of a message expression or
///  function call with the intention of affixing that type to a tracked symbol.
///  While the the return type can be queried directly from RetEx, when
///  invoking class methods we augment to the return type to be that of
///  a pointer to the class (as opposed it just being id).
static QualType GetReturnType(Expr* RetE, ASTContext& Ctx) {

  QualType RetTy = RetE->getType();

  // FIXME: We aren't handling id<...>.
  const PointerType* PT = RetTy->getAsPointerType();
  if (!PT)
    return RetTy;
    
  // If RetEx is not a message expression just return its type.
  // If RetEx is a message expression, return its types if it is something
  /// more specific than id.
  
  ObjCMessageExpr* ME = dyn_cast<ObjCMessageExpr>(RetE);
  
  if (!ME || !Ctx.isObjCIdType(PT->getPointeeType()))
    return RetTy;
  
  ObjCInterfaceDecl* D = ME->getClassInfo().first;  

  // At this point we know the return type of the message expression is id.
  // If we have an ObjCInterceDecl, we know this is a call to a class method
  // whose type we can resolve.  In such cases, promote the return type to
  // Class*.  
  return !D ? RetTy : Ctx.getPointerType(Ctx.getObjCInterfaceType(D));
}


void CFRefCount::EvalSummary(ExplodedNodeSet<GRState>& Dst,
                             GRExprEngine& Eng,
                             GRStmtNodeBuilder<GRState>& Builder,
                             Expr* Ex,
                             Expr* Receiver,
                             RetainSummary* Summ,
                             ExprIterator arg_beg, ExprIterator arg_end,                             
                             ExplodedNode<GRState>* Pred) {
  
  // Get the state.
  GRStateRef state(Builder.GetState(Pred), Eng.getStateManager());

  // Evaluate the effect of the arguments.
  RefVal::Kind hasErr = (RefVal::Kind) 0;
  unsigned idx = 0;
  Expr* ErrorExpr = NULL;
  SymbolID ErrorSym = 0;                                        
  
  for (ExprIterator I = arg_beg; I != arg_end; ++I, ++idx) {    
    RVal V = state.GetRVal(*I);
    
    if (isa<lval::SymbolVal>(V)) {
      SymbolID Sym = cast<lval::SymbolVal>(V).getSymbol();
      if (RefBindings::data_type* T = state.get<RefBindings>(Sym))
        if (Update(state, Sym, *T, GetArgE(Summ, idx), hasErr)) {
          ErrorExpr = *I;
          ErrorSym = Sym;
          break;
        }
    }  
    else if (isa<LVal>(V)) {
#if 0
      // Nuke all arguments passed by reference.
      StateMgr.Unbind(StVals, cast<LVal>(V));
#else
      if (lval::MemRegionVal* MR = dyn_cast<lval::MemRegionVal>(&V)) {

        if (GetArgE(Summ, idx) == DoNothingByRef)
          continue;
        
        // Invalidate the value of the variable passed by reference.
        
        // FIXME: Either this logic should also be replicated in GRSimpleVals
        //  or should be pulled into a separate "constraint engine."
        
        // FIXME: We can have collisions on the conjured symbol if the
        //  expression *I also creates conjured symbols.  We probably want
        //  to identify conjured symbols by an expression pair: the enclosing
        //  expression (the context) and the expression itself.  This should
        //  disambiguate conjured symbols. 

        // Is the invalidated variable something that we were tracking?
        RVal X = state.GetRVal(*MR);
        
        if (isa<lval::SymbolVal>(X)) {
          SymbolID Sym = cast<lval::SymbolVal>(X).getSymbol();
          state = state.remove<RefBindings>(Sym);
        }
        
        TypedRegion* R = dyn_cast<TypedRegion>(MR->getRegion());
        if (R) {
          // Set the value of the variable to be a conjured symbol.
          unsigned Count = Builder.getCurrentBlockCount();
          QualType T = R->getType();
          SymbolID NewSym =
            Eng.getSymbolManager().getConjuredSymbol(*I, T, Count);
          
          state = state.SetRVal(*MR,
                                LVal::IsLValType(T)
                                ? cast<RVal>(lval::SymbolVal(NewSym))
                                : cast<RVal>(nonlval::SymbolVal(NewSym)));
        }
        else
          state = state.SetRVal(*MR, UnknownVal());
      }
      else {
        // Nuke all other arguments passed by reference.
        state = state.Unbind(cast<LVal>(V));
      }
#endif
    }
    else if (isa<nonlval::LValAsInteger>(V))
      state = state.Unbind(cast<nonlval::LValAsInteger>(V).getLVal());
  } 
  
  // Evaluate the effect on the message receiver.  
  if (!ErrorExpr && Receiver) {
    RVal V = state.GetRVal(Receiver);
    if (isa<lval::SymbolVal>(V)) {
      SymbolID Sym = cast<lval::SymbolVal>(V).getSymbol();
      if (const RefVal* T = state.get<RefBindings>(Sym))
        if (Update(state, Sym, *T, GetReceiverE(Summ), hasErr)) {
          ErrorExpr = Receiver;
          ErrorSym = Sym;
        }
    }
  }
  
  // Process any errors.  
  if (hasErr) {
    ProcessNonLeakError(Dst, Builder, Ex, ErrorExpr, Pred, state,
                        hasErr, ErrorSym);
    return;
  }
  
  // Consult the summary for the return value.  
  RetEffect RE = GetRetEffect(Summ);
  
  switch (RE.getKind()) {
    default:
      assert (false && "Unhandled RetEffect."); break;
      
    case RetEffect::NoRet:
      
      // Make up a symbol for the return value (not reference counted).
      // FIXME: This is basically copy-and-paste from GRSimpleVals.  We 
      //  should compose behavior, not copy it.
      
      if (Ex->getType() != Eng.getContext().VoidTy) {    
        unsigned Count = Builder.getCurrentBlockCount();
        SymbolID Sym = Eng.getSymbolManager().getConjuredSymbol(Ex, Count);
        
        RVal X = LVal::IsLValType(Ex->getType())
               ? cast<RVal>(lval::SymbolVal(Sym)) 
               : cast<RVal>(nonlval::SymbolVal(Sym));
        
        state = state.SetRVal(Ex, X, false);
      }      
      
      break;
      
    case RetEffect::Alias: {
      unsigned idx = RE.getIndex();
      assert (arg_end >= arg_beg);
      assert (idx < (unsigned) (arg_end - arg_beg));
      RVal V = state.GetRVal(*(arg_beg+idx));
      state = state.SetRVal(Ex, V, false);
      break;
    }
      
    case RetEffect::ReceiverAlias: {
      assert (Receiver);
      RVal V = state.GetRVal(Receiver);
      state = state.SetRVal(Ex, V, false);
      break;
    }
      
    case RetEffect::OwnedAllocatedSymbol:
    case RetEffect::OwnedSymbol: {
      unsigned Count = Builder.getCurrentBlockCount();
      SymbolID Sym = Eng.getSymbolManager().getConjuredSymbol(Ex, Count);
      QualType RetT = GetReturnType(Ex, Eng.getContext());
      
      state = state.set<RefBindings>(Sym, RefVal::makeOwned(RetT));
      state = state.SetRVal(Ex, lval::SymbolVal(Sym), false);

#if 0
      RefBindings B = GetRefBindings(StImpl);
      SetRefBindings(StImpl, RefBFactory.Add(B, Sym, RefVal::makeOwned(RetT)));
#endif 

      // FIXME: Add a flag to the checker where allocations are allowed to fail.      
      if (RE.getKind() == RetEffect::OwnedAllocatedSymbol)
        state = state.AddNE(Sym, Eng.getBasicVals().getZeroWithPtrWidth());
      
      break;
    }
      
    case RetEffect::NotOwnedSymbol: {
      unsigned Count = Builder.getCurrentBlockCount();
      SymbolID Sym = Eng.getSymbolManager().getConjuredSymbol(Ex, Count);
      QualType RetT = GetReturnType(Ex, Eng.getContext());
      
      state = state.set<RefBindings>(Sym, RefVal::makeNotOwned(RetT));
      state = state.SetRVal(Ex, lval::SymbolVal(Sym), false);
      break;
    }
  }
  
  // Is this a sink?
  if (IsEndPath(Summ))
    Builder.MakeSinkNode(Dst, Ex, Pred, state);
  else
    Builder.MakeNode(Dst, Ex, Pred, state);
}


void CFRefCount::EvalCall(ExplodedNodeSet<GRState>& Dst,
                          GRExprEngine& Eng,
                          GRStmtNodeBuilder<GRState>& Builder,
                          CallExpr* CE, RVal L,
                          ExplodedNode<GRState>* Pred) {

  RetainSummary* Summ = !isa<lval::FuncVal>(L) ? 0
                      : Summaries.getSummary(cast<lval::FuncVal>(L).getDecl());
  
  EvalSummary(Dst, Eng, Builder, CE, 0, Summ,
              CE->arg_begin(), CE->arg_end(), Pred);
}

void CFRefCount::EvalObjCMessageExpr(ExplodedNodeSet<GRState>& Dst,
                                     GRExprEngine& Eng,
                                     GRStmtNodeBuilder<GRState>& Builder,
                                     ObjCMessageExpr* ME,
                                     ExplodedNode<GRState>* Pred) {  
  RetainSummary* Summ;
  
  if (Expr* Receiver = ME->getReceiver()) {
    // We need the type-information of the tracked receiver object
    // Retrieve it from the state.
    ObjCInterfaceDecl* ID = 0;

    // FIXME: Wouldn't it be great if this code could be reduced?  It's just
    // a chain of lookups.
    const GRState* St = Builder.GetState(Pred);
    RVal V = Eng.getStateManager().GetRVal(St, Receiver );

    if (isa<lval::SymbolVal>(V)) {
      SymbolID Sym = cast<lval::SymbolVal>(V).getSymbol();
      
      if (const RefVal* T  = St->get<RefBindings>(Sym)) {
        QualType Ty = T->getType();
        
        if (const PointerType* PT = Ty->getAsPointerType()) {
          QualType PointeeTy = PT->getPointeeType();
          
          if (ObjCInterfaceType* IT = dyn_cast<ObjCInterfaceType>(PointeeTy))
            ID = IT->getDecl();
        }
      }
    }
    
    Summ = Summaries.getMethodSummary(ME, ID);
  }
  else
    Summ = Summaries.getClassMethodSummary(ME->getClassName(),
                                           ME->getSelector());

  EvalSummary(Dst, Eng, Builder, ME, ME->getReceiver(), Summ,
              ME->arg_begin(), ME->arg_end(), Pred);
}
  
// Stores.

void CFRefCount::EvalStore(ExplodedNodeSet<GRState>& Dst,
                           GRExprEngine& Eng,
                           GRStmtNodeBuilder<GRState>& Builder,
                           Expr* E, ExplodedNode<GRState>* Pred,
                           const GRState* St, RVal TargetLV, RVal Val) {
  
  // Check if we have a binding for "Val" and if we are storing it to something
  // we don't understand or otherwise the value "escapes" the function.
  
  if (!isa<lval::SymbolVal>(Val))
    return;
  
  // Are we storing to something that causes the value to "escape"?
  
  bool escapes = false;
  
  if (!isa<lval::MemRegionVal>(TargetLV))
    escapes = true;
  else {
    MemRegion* R = cast<lval::MemRegionVal>(TargetLV).getRegion();
    escapes = !Eng.getStateManager().hasStackStorage(R);
  }
  
  if (!escapes)
    return;
  
  SymbolID Sym = cast<lval::SymbolVal>(Val).getSymbol();
  
  GRStateRef state(St, Eng.getStateManager());
  
  if (!state.get<RefBindings>(Sym))
    return;
  
  // Nuke the binding.
  state = state.remove<RefBindings>(Sym);

  // Hand of the remaining logic to the parent implementation.
  GRSimpleVals::EvalStore(Dst, Eng, Builder, E, Pred, state, TargetLV, Val);
}

// End-of-path.

const GRState* CFRefCount::HandleSymbolDeath(GRStateManager& VMgr,
                                          const GRState* St, SymbolID sid,
                                          RefVal V, bool& hasLeak) {
    
  hasLeak = V.isOwned() || 
            ((V.isNotOwned() || V.isReturnedOwned()) && V.getCount() > 0);

  GRStateRef state(St, VMgr);

  if (!hasLeak)
    return state.remove<RefBindings>(sid);
  
  return state.set<RefBindings>(sid, V ^ RefVal::ErrorLeak);
}

void CFRefCount::EvalEndPath(GRExprEngine& Eng,
                             GREndPathNodeBuilder<GRState>& Builder) {
  
  const GRState* St = Builder.getState();
  RefBindings B = St->get<RefBindings>();
  
  llvm::SmallVector<SymbolID, 10> Leaked;
  
  for (RefBindings::iterator I = B.begin(), E = B.end(); I != E; ++I) {
    bool hasLeak = false;
    
    St = HandleSymbolDeath(Eng.getStateManager(), St,
                           (*I).first, (*I).second, hasLeak);
    
    if (hasLeak) Leaked.push_back((*I).first);
  }

  if (Leaked.empty())
    return;
  
  ExplodedNode<GRState>* N = Builder.MakeNode(St);  
  
  if (!N)
    return;
    
  std::vector<SymbolID>*& LeaksAtNode = Leaks[N];
  assert (!LeaksAtNode);
  LeaksAtNode = new std::vector<SymbolID>();
  
  for (llvm::SmallVector<SymbolID, 10>::iterator I=Leaked.begin(),
       E = Leaked.end(); I != E; ++I)
    (*LeaksAtNode).push_back(*I);
}

// Dead symbols.

void CFRefCount::EvalDeadSymbols(ExplodedNodeSet<GRState>& Dst,
                                 GRExprEngine& Eng,
                                 GRStmtNodeBuilder<GRState>& Builder,
                                 ExplodedNode<GRState>* Pred,
                                 Stmt* S,
                                 const GRState* St,
                                 const GRStateManager::DeadSymbolsTy& Dead) {
    
  // FIXME: a lot of copy-and-paste from EvalEndPath.  Refactor.
  
  RefBindings B = St->get<RefBindings>();
  llvm::SmallVector<SymbolID, 10> Leaked;
  
  for (GRStateManager::DeadSymbolsTy::const_iterator
       I=Dead.begin(), E=Dead.end(); I!=E; ++I) {
    
    const RefVal* T = B.lookup(*I);

    if (!T)
      continue;
    
    bool hasLeak = false;
    
    St = HandleSymbolDeath(Eng.getStateManager(), St, *I, *T, hasLeak);
    
    if (hasLeak)
      Leaked.push_back(*I);    
  }
  
  if (Leaked.empty())
    return;    
  
  ExplodedNode<GRState>* N = Builder.MakeNode(Dst, S, Pred, St);  
  
  if (!N)
    return;
  
  std::vector<SymbolID>*& LeaksAtNode = Leaks[N];
  assert (!LeaksAtNode);
  LeaksAtNode = new std::vector<SymbolID>();
  
  for (llvm::SmallVector<SymbolID, 10>::iterator I=Leaked.begin(),
       E = Leaked.end(); I != E; ++I)
    (*LeaksAtNode).push_back(*I);    
}

 // Return statements.

void CFRefCount::EvalReturn(ExplodedNodeSet<GRState>& Dst,
                            GRExprEngine& Eng,
                            GRStmtNodeBuilder<GRState>& Builder,
                            ReturnStmt* S,
                            ExplodedNode<GRState>* Pred) {
  
  Expr* RetE = S->getRetValue();
  if (!RetE) return;
  
  GRStateRef state(Builder.GetState(Pred), Eng.getStateManager());
  RVal V = state.GetRVal(RetE);
  
  if (!isa<lval::SymbolVal>(V))
    return;
  
  // Get the reference count binding (if any).
  SymbolID Sym = cast<lval::SymbolVal>(V).getSymbol();
  const RefVal* T = state.get<RefBindings>(Sym);
  
  if (!T)
    return;
  
  // Change the reference count.  
  RefVal X = *T;  
  
  switch (X.getKind()) {      
    case RefVal::Owned: { 
      unsigned cnt = X.getCount();
      assert (cnt > 0);
      X = RefVal::makeReturnedOwned(cnt - 1);
      break;
    }
      
    case RefVal::NotOwned: {
      unsigned cnt = X.getCount();
      X = cnt ? RefVal::makeReturnedOwned(cnt - 1)
              : RefVal::makeReturnedNotOwned();
      break;
    }
      
    default: 
      return;
  }
  
  // Update the binding.
  state = state.set<RefBindings>(Sym, X);
  Builder.MakeNode(Dst, S, Pred, state);
}

// Assumptions.

const GRState* CFRefCount::EvalAssume(GRStateManager& VMgr,
                                         const GRState* St,
                                         RVal Cond, bool Assumption,
                                         bool& isFeasible) {

  // FIXME: We may add to the interface of EvalAssume the list of symbols
  //  whose assumptions have changed.  For now we just iterate through the
  //  bindings and check if any of the tracked symbols are NULL.  This isn't
  //  too bad since the number of symbols we will track in practice are 
  //  probably small and EvalAssume is only called at branches and a few
  //  other places.
  RefBindings B = St->get<RefBindings>();
  
  if (B.isEmpty())
    return St;
  
  bool changed = false;
  
  GRStateRef state(St, VMgr);
  RefBindings::Factory& RefBFactory = state.get_context<RefBindings>();

  for (RefBindings::iterator I=B.begin(), E=B.end(); I!=E; ++I) {    
    // Check if the symbol is null (or equal to any constant).
    // If this is the case, stop tracking the symbol.
    if (VMgr.getSymVal(St, I.getKey())) {
      changed = true;
      B = RefBFactory.Remove(B, I.getKey());
    }
  }
  
  if (changed)
    state = state.set<RefBindings>(B);
  
  return state;
}

RefBindings CFRefCount::Update(RefBindings B, SymbolID sym,
                               RefVal V, ArgEffect E,
                               RefVal::Kind& hasErr,
                               RefBindings::Factory& RefBFactory) {
  
  // FIXME: This dispatch can potentially be sped up by unifiying it into
  //  a single switch statement.  Opt for simplicity for now.
  
  switch (E) {
    default:
      assert (false && "Unhandled CFRef transition.");

    case MayEscape:
      if (V.getKind() == RefVal::Owned) {
        V = V ^ RefVal::NotOwned;
        break;
      }
      // Fall-through.
    case DoNothingByRef:
    case DoNothing:
      if (!isGCEnabled() && V.getKind() == RefVal::Released) {
        V = V ^ RefVal::ErrorUseAfterRelease;
        hasErr = V.getKind();
        break;
      }      
      return B;

    case Autorelease:          
    case StopTracking:
      return RefBFactory.Remove(B, sym);

    case IncRef:      
      switch (V.getKind()) {
        default:
          assert(false);

        case RefVal::Owned:
        case RefVal::NotOwned:
          V = V + 1;
          break;          
        case RefVal::Released:
          if (isGCEnabled())
            V = V ^ RefVal::Owned;
          else {          
            V = V ^ RefVal::ErrorUseAfterRelease;
            hasErr = V.getKind();
          }
          break;
      }      
      break;
      
    case SelfOwn:
      V = V ^ RefVal::NotOwned;
      // Fall-through.      
    case DecRef:
      switch (V.getKind()) {
        default:
          assert (false);

        case RefVal::Owned:
          V = V.getCount() > 1 ? V - 1 : V ^ RefVal::Released;
          break;
          
        case RefVal::NotOwned:
          if (V.getCount() > 0)
            V = V - 1;
          else {
            V = V ^ RefVal::ErrorReleaseNotOwned;
            hasErr = V.getKind();
          }          
          break;