GRExprEngine.cpp

    Dst.Add(Pred);
    return;
  }
  
  Ex = Ex->IgnoreParens();
  
  if (isa<DeclRefExpr>(Ex)) {
    Dst.Add(Pred);
    return;
  }
  
  if (UnaryOperator* U = dyn_cast<UnaryOperator>(Ex))
    if (U->getOpcode() == UnaryOperator::Deref) {
      VisitDeref(U, Pred, Dst, true);
      return;
    }
  
  Visit(Ex, Pred, Dst);
}

void GRExprEngine::VisitAsmStmt(AsmStmt* A, NodeTy* Pred, NodeSet& Dst) {
  VisitAsmStmtHelperOutputs(A, A->begin_outputs(), A->end_outputs(), Pred, Dst);
}  

void GRExprEngine::VisitAsmStmtHelperOutputs(AsmStmt* A,
                                             AsmStmt::outputs_iterator I,
                                             AsmStmt::outputs_iterator E,
                                             NodeTy* Pred, NodeSet& Dst) {
  if (I == E) {
    VisitAsmStmtHelperInputs(A, A->begin_inputs(), A->end_inputs(), Pred, Dst);
    return;
  }
  
  NodeSet Tmp;
  VisitLVal(*I, Pred, Tmp);
  
  ++I;
  
  for (NodeSet::iterator NI = Tmp.begin(), NE = Tmp.end(); NI != NE; ++NI)
    VisitAsmStmtHelperOutputs(A, I, E, *NI, Dst);
}

void GRExprEngine::VisitAsmStmtHelperInputs(AsmStmt* A,
                                            AsmStmt::inputs_iterator I,
                                            AsmStmt::inputs_iterator E,
                                            NodeTy* Pred, NodeSet& Dst) {
  if (I == E) {
    
    // We have processed both the inputs and the outputs.  All of the outputs
    // should evaluate to LVals.  Nuke all of their values.
    
    // FIXME: Some day in the future it would be nice to allow a "plug-in"
    // which interprets the inline asm and stores proper results in the
    // outputs.
    
    ValueState* St = GetState(Pred);
    
    for (AsmStmt::outputs_iterator OI = A->begin_outputs(),
                                   OE = A->end_outputs(); OI != OE; ++OI) {
      
      RVal X = GetLVal(St, *OI);
      
      assert (!isa<NonLVal>(X));
      
      if (isa<LVal>(X))
        St = SetRVal(St, cast<LVal>(X), UnknownVal());
    }
    
    Nodify(Dst, A, Pred, St);
    return;
  }
  
  NodeSet Tmp;
  Visit(*I, Pred, Tmp);
  
  ++I;
  
  for (NodeSet::iterator NI = Tmp.begin(), NE = Tmp.end(); NI != NE; ++NI)
    VisitAsmStmtHelperInputs(A, I, E, *NI, Dst);
}


void GRExprEngine::VisitBinaryOperator(BinaryOperator* B,
                                       GRExprEngine::NodeTy* Pred,
                                       GRExprEngine::NodeSet& Dst) {
  NodeSet S1;
  
  if (B->isAssignmentOp())
    VisitLVal(B->getLHS(), Pred, S1);
  else
    Visit(B->getLHS(), Pred, S1);

  for (NodeSet::iterator I1=S1.begin(), E1=S1.end(); I1 != E1; ++I1) {

    NodeTy* N1 = *I1;
    
    // When getting the value for the LHS, check if we are in an assignment.
    // In such cases, we want to (initially) treat the LHS as an LVal,
    // so we use GetLVal instead of GetRVal so that DeclRefExpr's are
    // evaluated to LValDecl's instead of to an NonLVal.

    RVal LeftV = B->isAssignmentOp() ? GetLVal(GetState(N1), B->getLHS())
                                     : GetRVal(GetState(N1), B->getLHS());
    
    // Visit the RHS...
    
    NodeSet S2;    
    Visit(B->getRHS(), N1, S2);
    
    // Process the binary operator.
  
    for (NodeSet::iterator I2 = S2.begin(), E2 = S2.end(); I2 != E2; ++I2) {

      NodeTy* N2 = *I2;
      ValueState* St = GetState(N2);
      Expr* RHS = B->getRHS();
      RVal RightV = GetRVal(St, RHS);

      BinaryOperator::Opcode Op = B->getOpcode();
      
      if ((Op == BinaryOperator::Div || Op == BinaryOperator::Rem)
          && RHS->getType()->isIntegerType()) {

        // Check if the denominator is undefined.
        
        if (!RightV.isUnknown()) {
        
          if (RightV.isUndef()) {
            NodeTy* DivUndef = Builder->generateNode(B, St, N2);
            
            if (DivUndef) {
              DivUndef->markAsSink();
              ExplicitBadDivides.insert(DivUndef);
            }
            
            continue;
          }
            
          // Check for divide/remainder-by-zero.
          //
          // First, "assume" that the denominator is 0 or undefined.
          
          bool isFeasibleZero = false;
          ValueState* ZeroSt =  Assume(St, RightV, false, isFeasibleZero);
          
          // Second, "assume" that the denominator cannot be 0.
          
          bool isFeasibleNotZero = false;
          St = Assume(St, RightV, true, isFeasibleNotZero);
          
          // Create the node for the divide-by-zero (if it occurred).
          
          if (isFeasibleZero)
            if (NodeTy* DivZeroNode = Builder->generateNode(B, ZeroSt, N2)) {
              DivZeroNode->markAsSink();
              
              if (isFeasibleNotZero)
                ImplicitBadDivides.insert(DivZeroNode);
              else
                ExplicitBadDivides.insert(DivZeroNode);

            }
          
          if (!isFeasibleNotZero)
            continue;
        }
        
        // Fall-through.  The logic below processes the divide.
      }
      
      
      if (Op <= BinaryOperator::Or) {
        
        // Process non-assignements except commas or short-circuited
        // logical expressions (LAnd and LOr).
        
        RVal Result = EvalBinOp(Op, LeftV, RightV);
        
        if (Result.isUnknown()) {
          Dst.Add(N2);
          continue;
        }
        
        if (Result.isUndef() && !LeftV.isUndef() && !RightV.isUndef()) {
          
          // The operands were not undefined, but the result is undefined.
          
          if (NodeTy* UndefNode = Builder->generateNode(B, St, N2)) {
            UndefNode->markAsSink();            
            UndefResults.insert(UndefNode);
          }
          
          continue;
        }
        
        Nodify(Dst, B, N2, SetRVal(St, B, Result));
        continue;
      }
        
      // Process assignments.
    
      switch (Op) {        
          
        case BinaryOperator::Assign: {
          
          // Simple assignments.

          if (LeftV.isUndef()) {
            HandleUndefinedStore(B, N2);
            continue;
          }
          
          // EXPERIMENTAL: "Conjured" symbols.
          
          if (RightV.isUnknown()) {            
            unsigned Count = Builder->getCurrentBlockCount();
            SymbolID Sym = SymMgr.getConjuredSymbol(B->getRHS(), Count);
            
            RightV = B->getRHS()->getType()->isPointerType() 
                     ? cast<RVal>(lval::SymbolVal(Sym)) 
                     : cast<RVal>(nonlval::SymbolVal(Sym));            
          }
          
          // Even if the LHS evaluates to an unknown L-Value, the entire
          // expression still evaluates to the RHS.
          
          if (LeftV.isUnknown()) {
            St = SetRVal(St, B, RightV);
            break;
          }
          
          // Simulate the effects of a "store":  bind the value of the RHS
          // to the L-Value represented by the LHS.

          St = SetRVal(SetRVal(St, B, RightV), cast<LVal>(LeftV), RightV);
          break;
        }

          // Compound assignment operators.
          
        default: { 
          
          assert (B->isCompoundAssignmentOp());
          
          if (Op >= BinaryOperator::AndAssign)
            ((int&) Op) -= (BinaryOperator::AndAssign - BinaryOperator::And);
          else
            ((int&) Op) -= BinaryOperator::MulAssign;  
          
          // Check if the LHS is undefined.
          
          if (LeftV.isUndef()) {
            HandleUndefinedStore(B, N2);
            continue;
          }
          
          if (LeftV.isUnknown()) {
            assert (isa<UnknownVal>(GetRVal(St, B)));
            Dst.Add(N2);
            continue;
          }
          
          // At this pointer we know that the LHS evaluates to an LVal
          // that is neither "Unknown" or "Undefined."
          
          LVal LeftLV = cast<LVal>(LeftV);
          
          // Fetch the value of the LHS (the value of the variable, etc.).
          
          RVal V = GetRVal(GetState(N1), LeftLV, B->getLHS()->getType());
          
          // Propagate undefined value (left-side).  We
          // propogate undefined values for the RHS below when
          // we also check for divide-by-zero.
          
          if (V.isUndef()) {
            St = SetRVal(St, B, V);
            break;
          }
          
          // Propagate unknown values.
          
          if (V.isUnknown()) {
            // The value bound to LeftV is unknown.  Thus we just
            // propagate the current node (as "B" is already bound to nothing).
            assert (isa<UnknownVal>(GetRVal(St, B)));
            Dst.Add(N2);
            continue;
          }
          
          if (RightV.isUnknown()) {
            assert (isa<UnknownVal>(GetRVal(St, B)));
            St = SetRVal(St, LeftLV, UnknownVal());
            break;
          }
            
          // At this point:
          //
          //  The LHS is not Undef/Unknown.
          //  The RHS is not Unknown.
          
          // Get the computation type.
          QualType CTy = cast<CompoundAssignOperator>(B)->getComputationType();
          
          // Perform promotions.
          V = EvalCast(V, CTy);
          RightV = EvalCast(RightV, CTy);
          
          // Evaluate operands and promote to result type.

          if ((Op == BinaryOperator::Div || Op == BinaryOperator::Rem)
              && RHS->getType()->isIntegerType()) {
            
            // Check if the denominator is undefined.
                
            if (RightV.isUndef()) {
              NodeTy* DivUndef = Builder->generateNode(B, St, N2);
              
              if (DivUndef) {
                DivUndef->markAsSink();
                ExplicitBadDivides.insert(DivUndef);
              }
              
              continue;
            }

            // First, "assume" that the denominator is 0.
            
            bool isFeasibleZero = false;
            ValueState* ZeroSt = Assume(St, RightV, false, isFeasibleZero);
            
            // Second, "assume" that the denominator cannot be 0.
            
            bool isFeasibleNotZero = false;
            St = Assume(St, RightV, true, isFeasibleNotZero);
            
            // Create the node for the divide-by-zero error (if it occurred).
            
            if (isFeasibleZero) {
              NodeTy* DivZeroNode = Builder->generateNode(B, ZeroSt, N2);
              
              if (DivZeroNode) {
                DivZeroNode->markAsSink();
                
                if (isFeasibleNotZero)
                  ImplicitBadDivides.insert(DivZeroNode);
                else
                  ExplicitBadDivides.insert(DivZeroNode);
              }
            }
            
            if (!isFeasibleNotZero)
              continue;
            
            // Fall-through.  The logic below processes the divide.
          }
          else {
            
            // Propagate undefined values (right-side).
            
            if (RightV.isUndef()) {
              St = SetRVal(SetRVal(St, B, RightV), LeftLV, RightV);
              break;
            }
            
          }

          RVal Result = EvalCast(EvalBinOp(Op, V, RightV), B->getType());
          
          if (Result.isUndef()) {
            
            // The operands were not undefined, but the result is undefined.
            
            if (NodeTy* UndefNode = Builder->generateNode(B, St, N2)) {
              UndefNode->markAsSink();            
              UndefResults.insert(UndefNode);
            }
            
            continue;
          }
          
          St = SetRVal(SetRVal(St, B, Result), LeftLV, Result);
        }
      }
    
      Nodify(Dst, B, N2, St);
    }
  }
}

void GRExprEngine::HandleUndefinedStore(Stmt* S, NodeTy* Pred) {  
  NodeTy* N = Builder->generateNode(S, GetState(Pred), Pred);
  N->markAsSink();
  UndefStores.insert(N);
}

void GRExprEngine::Visit(Stmt* S, NodeTy* Pred, NodeSet& Dst) {

  // FIXME: add metadata to the CFG so that we can disable
  //  this check when we KNOW that there is no block-level subexpression.
  //  The motivation is that this check requires a hashtable lookup.

  if (S != CurrentStmt && getCFG().isBlkExpr(S)) {
    Dst.Add(Pred);
    return;
  }

  switch (S->getStmtClass()) {
      
    default:
      // Cases we intentionally have "default" handle:
      //   AddrLabelExpr, IntegerLiteral, CharacterLiteral
      
      Dst.Add(Pred); // No-op. Simply propagate the current state unchanged.
      break;
      
    case Stmt::AsmStmtClass:
      VisitAsmStmt(cast<AsmStmt>(S), Pred, Dst);
      break;
                                                       
    case Stmt::BinaryOperatorClass: {
      BinaryOperator* B = cast<BinaryOperator>(S);
 
      if (B->isLogicalOp()) {
        VisitLogicalExpr(B, Pred, Dst);
        break;
      }
      else if (B->getOpcode() == BinaryOperator::Comma) {
        ValueState* St = GetState(Pred);
        Nodify(Dst, B, Pred, SetRVal(St, B, GetRVal(St, B->getRHS())));
        break;
      }
      
      VisitBinaryOperator(cast<BinaryOperator>(S), Pred, Dst);
      break;
    }
      
    case Stmt::CallExprClass: {
      CallExpr* C = cast<CallExpr>(S);
      VisitCall(C, Pred, C->arg_begin(), C->arg_end(), Dst);
      break;      
    }

    case Stmt::CastExprClass: {
      CastExpr* C = cast<CastExpr>(S);
      VisitCast(C, C->getSubExpr(), Pred, Dst);
      break;
    }

      // FIXME: ChooseExpr is really a constant.  We need to fix
      //        the CFG do not model them as explicit control-flow.
      
    case Stmt::ChooseExprClass: { // __builtin_choose_expr
      ChooseExpr* C = cast<ChooseExpr>(S);
      VisitGuardedExpr(C, C->getLHS(), C->getRHS(), Pred, Dst);
      break;
    }
      
    case Stmt::CompoundAssignOperatorClass:
      VisitBinaryOperator(cast<BinaryOperator>(S), Pred, Dst);
      break;
      
    case Stmt::ConditionalOperatorClass: { // '?' operator
      ConditionalOperator* C = cast<ConditionalOperator>(S);
      VisitGuardedExpr(C, C->getLHS(), C->getRHS(), Pred, Dst);
      break;
    }
      
    case Stmt::DeclRefExprClass:
      VisitDeclRefExpr(cast<DeclRefExpr>(S), Pred, Dst);
      break;
      
    case Stmt::DeclStmtClass:
      VisitDeclStmt(cast<DeclStmt>(S), Pred, Dst);
      break;
      
    case Stmt::ImplicitCastExprClass: {
      ImplicitCastExpr* C = cast<ImplicitCastExpr>(S);
      VisitCast(C, C->getSubExpr(), Pred, Dst);
      break;
    }

    case Stmt::ParenExprClass:
      Visit(cast<ParenExpr>(S)->getSubExpr(), Pred, Dst);
      break;
      
    case Stmt::SizeOfAlignOfTypeExprClass:
      VisitSizeOfAlignOfTypeExpr(cast<SizeOfAlignOfTypeExpr>(S), Pred, Dst);
      break;
      
    case Stmt::StmtExprClass: {
      StmtExpr* SE = cast<StmtExpr>(S);
      
      ValueState* St = GetState(Pred);
      
      // FIXME: Not certain if we can have empty StmtExprs.  If so, we should
      // probably just remove these from the CFG.
      assert (!SE->getSubStmt()->body_empty());

      if (Expr* LastExpr = dyn_cast<Expr>(*SE->getSubStmt()->body_rbegin()))
        Nodify(Dst, SE, Pred, SetRVal(St, SE, GetRVal(St, LastExpr)));
      else
        Dst.Add(Pred);
      
      break;
    }
      
      // FIXME: We may wish to always bind state to ReturnStmts so
      //  that users can quickly query what was the state at the
      //  exit points of a function.
      
    case Stmt::ReturnStmtClass: {
      if (Expr* R = cast<ReturnStmt>(S)->getRetValue())
        Visit(R, Pred, Dst);
      else
        Dst.Add(Pred);
      
      break;
    }
      
    case Stmt::UnaryOperatorClass: {
      UnaryOperator* U = cast<UnaryOperator>(S);
      
      switch (U->getOpcode()) {
        case UnaryOperator::Deref: VisitDeref(U, Pred, Dst); break;
        case UnaryOperator::Plus:  Visit(U->getSubExpr(), Pred, Dst); break;
        case UnaryOperator::SizeOf: VisitSizeOfExpr(U, Pred, Dst); break;
        default: VisitUnaryOperator(U, Pred, Dst); break;
      }
      
      break;
    }
  }
}

//===----------------------------------------------------------------------===//
// "Assume" logic.
//===----------------------------------------------------------------------===//

ValueState* GRExprEngine::Assume(ValueState* St, LVal Cond,
                                           bool Assumption, 
                                           bool& isFeasible) {
  switch (Cond.getSubKind()) {
    default:
      assert (false && "'Assume' not implemented for this LVal.");
      return St;
      
    case lval::SymbolValKind:
      if (Assumption)
        return AssumeSymNE(St, cast<lval::SymbolVal>(Cond).getSymbol(),
                           BasicVals.getZeroWithPtrWidth(), isFeasible);
      else
        return AssumeSymEQ(St, cast<lval::SymbolVal>(Cond).getSymbol(),
                           BasicVals.getZeroWithPtrWidth(), isFeasible);
      
      
    case lval::DeclValKind:
    case lval::FuncValKind:
    case lval::GotoLabelKind:
      isFeasible = Assumption;
      return St;

    case lval::ConcreteIntKind: {
      bool b = cast<lval::ConcreteInt>(Cond).getValue() != 0;
      isFeasible = b ? Assumption : !Assumption;      
      return St;
    }
  }
}

ValueState* GRExprEngine::Assume(ValueState* St, NonLVal Cond,
                                         bool Assumption, 
                                         bool& isFeasible) {  
  switch (Cond.getSubKind()) {
    default:
      assert (false && "'Assume' not implemented for this NonLVal.");
      return St;
      
      
    case nonlval::SymbolValKind: {
      nonlval::SymbolVal& SV = cast<nonlval::SymbolVal>(Cond);
      SymbolID sym = SV.getSymbol();
      
      if (Assumption)
        return AssumeSymNE(St, sym, BasicVals.getValue(0, SymMgr.getType(sym)),
                           isFeasible);
      else
        return AssumeSymEQ(St, sym, BasicVals.getValue(0, SymMgr.getType(sym)),
                           isFeasible);
    }
      
    case nonlval::SymIntConstraintValKind:
      return
        AssumeSymInt(St, Assumption,
                     cast<nonlval::SymIntConstraintVal>(Cond).getConstraint(),
                     isFeasible);
      
    case nonlval::ConcreteIntKind: {
      bool b = cast<nonlval::ConcreteInt>(Cond).getValue() != 0;
      isFeasible = b ? Assumption : !Assumption;      
      return St;
    }
  }
}

ValueState*
GRExprEngine::AssumeSymNE(ValueState* St, SymbolID sym,
                         const llvm::APSInt& V, bool& isFeasible) {
  
  // First, determine if sym == X, where X != V.
  if (const llvm::APSInt* X = St->getSymVal(sym)) {
    isFeasible = *X != V;
    return St;
  }
  
  // Second, determine if sym != V.
  if (St->isNotEqual(sym, V)) {
    isFeasible = true;
    return St;
  }
      
  // If we reach here, sym is not a constant and we don't know if it is != V.
  // Make that assumption.
  
  isFeasible = true;
  return StateMgr.AddNE(St, sym, V);
}

ValueState*
GRExprEngine::AssumeSymEQ(ValueState* St, SymbolID sym,
                         const llvm::APSInt& V, bool& isFeasible) {
  
  // First, determine if sym == X, where X != V.
  if (const llvm::APSInt* X = St->getSymVal(sym)) {
    isFeasible = *X == V;
    return St;
  }
  
  // Second, determine if sym != V.
  if (St->isNotEqual(sym, V)) {
    isFeasible = false;
    return St;
  }
  
  // If we reach here, sym is not a constant and we don't know if it is == V.
  // Make that assumption.
  
  isFeasible = true;
  return StateMgr.AddEQ(St, sym, V);
}

ValueState*
GRExprEngine::AssumeSymInt(ValueState* St, bool Assumption,
                          const SymIntConstraint& C, bool& isFeasible) {
  
  switch (C.getOpcode()) {
    default:
      // No logic yet for other operators.
      isFeasible = true;
      return St;
      
    case BinaryOperator::EQ:
      if (Assumption)
        return AssumeSymEQ(St, C.getSymbol(), C.getInt(), isFeasible);
      else
        return AssumeSymNE(St, C.getSymbol(), C.getInt(), isFeasible);
      
    case BinaryOperator::NE:
      if (Assumption)
        return AssumeSymNE(St, C.getSymbol(), C.getInt(), isFeasible);
      else
        return AssumeSymEQ(St, C.getSymbol(), C.getInt(), isFeasible);
  }
}

//===----------------------------------------------------------------------===//
// Visualization.
//===----------------------------------------------------------------------===//

#ifndef NDEBUG
static GRExprEngine* GraphPrintCheckerState;
static SourceManager* GraphPrintSourceManager;
static ValueState::CheckerStatePrinter* GraphCheckerStatePrinter;

namespace llvm {
template<>
struct VISIBILITY_HIDDEN DOTGraphTraits<GRExprEngine::NodeTy*> :
  public DefaultDOTGraphTraits {
    
  static void PrintVarBindings(std::ostream& Out, ValueState* St) {

    Out << "Variables:\\l";
    
    bool isFirst = true;
    
    for (ValueState::vb_iterator I=St->vb_begin(), E=St->vb_end(); I!=E;++I) {        

      if (isFirst)
        isFirst = false;
      else
        Out << "\\l";
      
      Out << ' ' << I.getKey()->getName() << " : ";
      I.getData().print(Out);
    }
    
  }
    
    
  static void PrintSubExprBindings(std::ostream& Out, ValueState* St){
    
    bool isFirst = true;
    
    for (ValueState::seb_iterator I=St->seb_begin(), E=St->seb_end();I!=E;++I) {        
      
      if (isFirst) {
        Out << "\\l\\lSub-Expressions:\\l";
        isFirst = false;
      }
      else
        Out << "\\l";
      
      Out << " (" << (void*) I.getKey() << ") ";
      I.getKey()->printPretty(Out);
      Out << " : ";
      I.getData().print(Out);
    }
  }
    
  static void PrintBlkExprBindings(std::ostream& Out, ValueState* St){
        
    bool isFirst = true;

    for (ValueState::beb_iterator I=St->beb_begin(), E=St->beb_end(); I!=E;++I){      
      if (isFirst) {
        Out << "\\l\\lBlock-level Expressions:\\l";
        isFirst = false;
      }
      else
        Out << "\\l";

      Out << " (" << (void*) I.getKey() << ") ";
      I.getKey()->printPretty(Out);
      Out << " : ";
      I.getData().print(Out);
    }
  }
    
  static void PrintEQ(std::ostream& Out, ValueState* St) {
    ValueState::ConstEqTy CE = St->ConstEq;
    
    if (CE.isEmpty())
      return;
    
    Out << "\\l\\|'==' constraints:";

    for (ValueState::ConstEqTy::iterator I=CE.begin(), E=CE.end(); I!=E;++I)
      Out << "\\l $" << I.getKey() << " : " << I.getData()->toString();
  }
    
  static void PrintNE(std::ostream& Out, ValueState* St) {
    ValueState::ConstNotEqTy NE = St->ConstNotEq;
    
    if (NE.isEmpty())
      return;
    
    Out << "\\l\\|'!=' constraints:";
    
    for (ValueState::ConstNotEqTy::iterator I=NE.begin(), EI=NE.end();
         I != EI; ++I){
      
      Out << "\\l $" << I.getKey() << " : ";
      bool isFirst = true;
      
      ValueState::IntSetTy::iterator J=I.getData().begin(),
                                    EJ=I.getData().end();      
      for ( ; J != EJ; ++J) {        
        if (isFirst) isFirst = false;
        else Out << ", ";
        
        Out << (*J)->toString();
      }    
    }
  }
    
  static std::string getNodeAttributes(const GRExprEngine::NodeTy* N, void*) {
    
    if (GraphPrintCheckerState->isImplicitNullDeref(N) ||
        GraphPrintCheckerState->isExplicitNullDeref(N) ||
        GraphPrintCheckerState->isUndefDeref(N) ||
        GraphPrintCheckerState->isUndefStore(N) ||
        GraphPrintCheckerState->isUndefControlFlow(N) ||
        GraphPrintCheckerState->isExplicitBadDivide(N) ||
        GraphPrintCheckerState->isImplicitBadDivide(N) ||
        GraphPrintCheckerState->isUndefResult(N) ||
        GraphPrintCheckerState->isBadCall(N) ||
        GraphPrintCheckerState->isUndefArg(N))
      return "color=\"red\",style=\"filled\"";
    
    if (GraphPrintCheckerState->isNoReturnCall(N))
      return "color=\"blue\",style=\"filled\"";
    
    return "";
  }
    
  static std::string getNodeLabel(const GRExprEngine::NodeTy* N, void*) {
    std::ostringstream Out;

    // Program Location.
    ProgramPoint Loc = N->getLocation();
    
    switch (Loc.getKind()) {
      case ProgramPoint::BlockEntranceKind:
        Out << "Block Entrance: B" 
            << cast<BlockEntrance>(Loc).getBlock()->getBlockID();
        break;
      
      case ProgramPoint::BlockExitKind:
        assert (false);
        break;
        
      case ProgramPoint::PostStmtKind: {
        const PostStmt& L = cast<PostStmt>(Loc);        
        Stmt* S = L.getStmt();
        SourceLocation SLoc = S->getLocStart();

        Out << S->getStmtClassName() << ' ' << (void*) S << ' ';        
        S->printPretty(Out);
        
        if (SLoc.isFileID()) {        
          Out << "\\lline="
            << GraphPrintSourceManager->getLineNumber(SLoc) << " col="
            << GraphPrintSourceManager->getColumnNumber(SLoc) << "\\l";          
        }
        
        if (GraphPrintCheckerState->isImplicitNullDeref(N))
          Out << "\\|Implicit-Null Dereference.\\l";
        else if (GraphPrintCheckerState->isExplicitNullDeref(N))
          Out << "\\|Explicit-Null Dereference.\\l";
        else if (GraphPrintCheckerState->isUndefDeref(N))
          Out << "\\|Dereference of undefialied value.\\l";
        else if (GraphPrintCheckerState->isUndefStore(N))
          Out << "\\|Store to Undefined LVal.";
        else if (GraphPrintCheckerState->isExplicitBadDivide(N))
          Out << "\\|Explicit divide-by zero or undefined value.";
        else if (GraphPrintCheckerState->isImplicitBadDivide(N))
          Out << "\\|Implicit divide-by zero or undefined value.";
        else if (GraphPrintCheckerState->isUndefResult(N))
          Out << "\\|Result of operation is undefined.";
        else if (GraphPrintCheckerState->isNoReturnCall(N))
          Out << "\\|Call to function marked \"noreturn\".";
        else if (GraphPrintCheckerState->isBadCall(N))
          Out << "\\|Call to NULL/Undefined.";
        else if (GraphPrintCheckerState->isUndefArg(N))
          Out << "\\|Argument in call is undefined";
        
        break;
      }
    
      default: {
        const BlockEdge& E = cast<BlockEdge>(Loc);
        Out << "Edge: (B" << E.getSrc()->getBlockID() << ", B"
            << E.getDst()->getBlockID()  << ')';
        
        if (Stmt* T = E.getSrc()->getTerminator()) {
          
          SourceLocation SLoc = T->getLocStart();
         
          Out << "\\|Terminator: ";
          
          E.getSrc()->printTerminator(Out);
          
          if (SLoc.isFileID()) {
            Out << "\\lline="
              << GraphPrintSourceManager->getLineNumber(SLoc) << " col="
              << GraphPrintSourceManager->getColumnNumber(SLoc);
          }
            
          if (isa<SwitchStmt>(T)) {
            Stmt* Label = E.getDst()->getLabel();
            
            if (Label) {                        
              if (CaseStmt* C = dyn_cast<CaseStmt>(Label)) {
                Out << "\\lcase ";
                C->getLHS()->printPretty(Out);
                
                if (Stmt* RHS = C->getRHS()) {
                  Out << " .. ";
                  RHS->printPretty(Out);
                }
                
                Out << ":";
              }
              else {
                assert (isa<DefaultStmt>(Label));
                Out << "\\ldefault:";
              }
            }
            else 
              Out << "\\l(implicit) default:";
          }
          else if (isa<IndirectGotoStmt>(T)) {
            // FIXME
          }
          else {
            Out << "\\lCondition: ";
            if (*E.getSrc()->succ_begin() == E.getDst())
              Out << "true";
            else
              Out << "false";                        
          }
          
          Out << "\\l";
        }
        
        if (GraphPrintCheckerState->isUndefControlFlow(N)) {
          Out << "\\|Control-flow based on\\lUndefined value.\\l";
        }
      }
    }
    
    Out << "\\|StateID: " << (void*) N->getState() << "\\|";

    N->getState()->printDOT(Out, GraphCheckerStatePrinter);
      
    Out << "\\l";
    return Out.str();
  }
};
} // end llvm namespace    
#endif

#ifndef NDEBUG

template <typename ITERATOR>
GRExprEngine::NodeTy* GetGraphNode(ITERATOR I) { return *I; }

template <>
GRExprEngine::NodeTy*
GetGraphNode<llvm::DenseMap<GRExprEngine::NodeTy*, Expr*>::iterator>
  (llvm::DenseMap<GRExprEngine::NodeTy*, Expr*>::iterator I) {
  return I->first;
}

template <typename ITERATOR>
static void AddSources(llvm::SmallVector<GRExprEngine::NodeTy*, 10>& Sources,
                       ITERATOR I, ITERATOR E) {
  
  llvm::SmallPtrSet<void*,10> CachedSources;
  
  for ( ; I != E; ++I ) {
    GRExprEngine::NodeTy* N = GetGraphNode(I);
    void* p = N->getLocation().getRawData();
    
    if (CachedSources.count(p))
      continue;
    
    CachedSources.insert(p);
    
    Sources.push_back(N);
  }
}
#endif

void GRExprEngine::ViewGraph(bool trim) {
#ifndef NDEBUG  
  if (trim) {
    llvm::SmallVector<NodeTy*, 10> Src;
    AddSources(Src, null_derefs_begin(), null_derefs_end());
    AddSources(Src, undef_derefs_begin(), undef_derefs_end());
    AddSources(Src, explicit_bad_divides_begin(), explicit_bad_divides_end());
    AddSources(Src, undef_results_begin(), undef_results_end());
    AddSources(Src, bad_calls_begin(), bad_calls_end());
    AddSources(Src, undef_arg_begin(), undef_arg_end());
    AddSources(Src, undef_branches_begin(), undef_branches_end());
    
    ViewGraph(&Src[0], &Src[0]+Src.size());
  }
  else {
    GraphPrintCheckerState = this;
    GraphPrintSourceManager = &getContext().getSourceManager();
    GraphCheckerStatePrinter = TF->getCheckerStatePrinter();

    llvm::ViewGraph(*G.roots_begin(), "GRExprEngine");
    
    GraphPrintCheckerState = NULL;
    GraphPrintSourceManager = NULL;
    GraphCheckerStatePrinter = NULL;
  }
#endif
}

void GRExprEngine::ViewGraph(NodeTy** Beg, NodeTy** End) {
#ifndef NDEBUG
  GraphPrintCheckerState = this;
  GraphPrintSourceManager = &getContext().getSourceManager();
  GraphCheckerStatePrinter = TF->getCheckerStatePrinter();
  
  GRExprEngine::GraphTy* TrimmedG = G.Trim(Beg, End);