GRExprEngine.cpp

//=-- GRExprEngine.cpp - Path-Sensitive Expression-Level Dataflow ---*- 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 a meta-engine for path-sensitive dataflow analysis that
//  is built on GREngine, but provides the boilerplate to execute transfer
//  functions and build the ExplodedGraph at the expression level.
//
//===----------------------------------------------------------------------===//

#include "clang/Analysis/PathSensitive/GRExprEngine.h"
#include "clang/Analysis/PathSensitive/BugReporter.h"
#include "clang/Basic/SourceManager.h"
#include "llvm/Support/Streams.h"

#ifndef NDEBUG
#include "llvm/Support/GraphWriter.h"
#include <sstream>
#endif

using namespace clang;
using llvm::dyn_cast;
using llvm::cast;
using llvm::APSInt;

//===----------------------------------------------------------------------===//
// Engine construction and deletion.
//===----------------------------------------------------------------------===//


GRExprEngine::GRExprEngine(CFG& cfg, Decl& CD, ASTContext& Ctx)
  : CoreEngine(cfg, CD, Ctx, *this), 
    G(CoreEngine.getGraph()),
    Liveness(G.getCFG()),
    Builder(NULL),
    StateMgr(G.getContext(), G.getAllocator()),
    BasicVals(StateMgr.getBasicValueFactory()),
    TF(NULL), // FIXME
    SymMgr(StateMgr.getSymbolManager()),
    StmtEntryNode(NULL), CleanedState(NULL), CurrentStmt(NULL) {
  
  // Compute liveness information.
  Liveness.runOnCFG(G.getCFG());
  Liveness.runOnAllBlocks(G.getCFG(), NULL, true);
}

GRExprEngine::~GRExprEngine() {
  for (BugTypeSet::iterator I = BugTypes.begin(), E = BugTypes.end(); I!=E; ++I)
    delete *I;
    
  for (SimpleChecksTy::iterator I = CallChecks.begin(), E = CallChecks.end();
       I != E; ++I)
    delete *I;
  
  for (SimpleChecksTy::iterator I=MsgExprChecks.begin(), E=MsgExprChecks.end();
       I != E; ++I)
    delete *I;  
}

//===----------------------------------------------------------------------===//
// Utility methods.
//===----------------------------------------------------------------------===//

// SaveAndRestore - A utility class that uses RIIA to save and restore
//  the value of a variable.
template<typename T>
struct VISIBILITY_HIDDEN SaveAndRestore {
  SaveAndRestore(T& x) : X(x), old_value(x) {}
  ~SaveAndRestore() { X = old_value; }
  T get() { return old_value; }
  
  T& X;
  T old_value;
};

// SaveOr - Similar to SaveAndRestore.  Operates only on bools; the old
//  value of a variable is saved, and during the dstor the old value is
//  or'ed with the new value.
struct VISIBILITY_HIDDEN SaveOr {
  SaveOr(bool& x) : X(x), old_value(x) { x = false; }
  ~SaveOr() { X |= old_value; }
  
  bool& X;
  bool old_value;
};


void GRExprEngine::EmitWarnings(Diagnostic& Diag, PathDiagnosticClient* PD) {
  for (bug_type_iterator I = bug_types_begin(), E = bug_types_end(); I!=E; ++I){
    BugReporter BR(Diag, PD, getContext(), *this);
    (*I)->EmitWarnings(BR);
  }
  
  for (SimpleChecksTy::iterator I = CallChecks.begin(), E = CallChecks.end();
       I != E; ++I) {
    BugReporter BR(Diag, PD, getContext(), *this);
    (*I)->EmitWarnings(BR);
  }
  
  for (SimpleChecksTy::iterator I=MsgExprChecks.begin(), E=MsgExprChecks.end();
       I != E; ++I) {
    BugReporter BR(Diag, PD, getContext(), *this);
    (*I)->EmitWarnings(BR);
  }
}

void GRExprEngine::setTransferFunctions(GRTransferFuncs* tf) {
  TF = tf;
  TF->RegisterChecks(*this);
}

void GRExprEngine::AddCallCheck(GRSimpleAPICheck* A) {
  CallChecks.push_back(A);
}

void GRExprEngine::AddObjCMessageExprCheck(GRSimpleAPICheck* A) {
  MsgExprChecks.push_back(A);
}

ValueState* GRExprEngine::getInitialState() {

  // The LiveVariables information already has a compilation of all VarDecls
  // used in the function.  Iterate through this set, and "symbolicate"
  // any VarDecl whose value originally comes from outside the function.
  
  typedef LiveVariables::AnalysisDataTy LVDataTy;
  LVDataTy& D = Liveness.getAnalysisData();
  
  ValueState StateImpl = *StateMgr.getInitialState();
  
  for (LVDataTy::decl_iterator I=D.begin_decl(), E=D.end_decl(); I != E; ++I) {
    
    VarDecl* VD = cast<VarDecl>(const_cast<ScopedDecl*>(I->first));
    
    if (VD->hasGlobalStorage() || isa<ParmVarDecl>(VD)) {
      RVal X = RVal::GetSymbolValue(SymMgr, VD);
      StateMgr.BindVar(StateImpl, VD, X);
    }
  }
  
  return StateMgr.getPersistentState(StateImpl);
}      
      
ValueState* GRExprEngine::SetRVal(ValueState* St, Expr* Ex, RVal V) {

  bool isBlkExpr = false;
    
  if (Ex == CurrentStmt) {
    isBlkExpr = getCFG().isBlkExpr(Ex);
    
    if (!isBlkExpr)
      return St;
  }

  return StateMgr.SetRVal(St, Ex, V, isBlkExpr, false);
}

//===----------------------------------------------------------------------===//
// Top-level transfer function logic (Dispatcher).
//===----------------------------------------------------------------------===//

void GRExprEngine::ProcessStmt(Stmt* S, StmtNodeBuilder& builder) {
  
  Builder = &builder;
  StmtEntryNode = builder.getLastNode();
  CurrentStmt = S;
  NodeSet Dst;
  
  // Set up our simple checks.
  
  // FIXME: This can probably be installed directly in GRCoreEngine, obviating
  //  the need to do a copy every time we hit a block-level statement.
  
  if (!MsgExprChecks.empty())
    Builder->setObjCMsgExprAuditors((GRAuditor<ValueState>**) &MsgExprChecks[0],
         (GRAuditor<ValueState>**) (&MsgExprChecks[0] + MsgExprChecks.size()));
  
  
  if (!CallChecks.empty())
    Builder->setCallExprAuditors((GRAuditor<ValueState>**) &CallChecks[0],
         (GRAuditor<ValueState>**) (&CallChecks[0] + CallChecks.size()));
  
  // Create the cleaned state.
  
  CleanedState = StateMgr.RemoveDeadBindings(StmtEntryNode->getState(),
                                             CurrentStmt, Liveness);
  
  Builder->SetCleanedState(CleanedState);
  
  // Visit the statement.
  
  Visit(S, StmtEntryNode, Dst);
  
  // If no nodes were generated, generate a new node that has all the
  // dead mappings removed.
  
  if (Dst.size() == 1 && *Dst.begin() == StmtEntryNode && 
      !Builder->HasGeneratedNode)
    builder.generateNode(S, GetState(StmtEntryNode), StmtEntryNode);
  
  // NULL out these variables to cleanup.
  
  CurrentStmt = NULL;
  StmtEntryNode = NULL;
  Builder = NULL;
  CleanedState = NULL;
}

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::ArraySubscriptExprClass:
      VisitArraySubscriptExpr(cast<ArraySubscriptExpr>(S), Pred, Dst, false);
      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);
        MakeNode(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::MemberExprClass: {
      VisitMemberExpr(cast<MemberExpr>(S), Pred, Dst, false);
      break;
    }
      
    case Stmt::ObjCMessageExprClass: {
      VisitObjCMessageExpr(cast<ObjCMessageExpr>(S), Pred, Dst);
      break;
    }
      
    case Stmt::ParenExprClass:
      Visit(cast<ParenExpr>(S)->getSubExpr()->IgnoreParens(), 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()))
        MakeNode(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:
      VisitReturnStmt(cast<ReturnStmt>(S), Pred, Dst); 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;
    }
  }
}

//===----------------------------------------------------------------------===//
// Block entrance.  (Update counters).
//===----------------------------------------------------------------------===//

bool GRExprEngine::ProcessBlockEntrance(CFGBlock* B, ValueState*,
                                        GRBlockCounter BC) {
  
  return BC.getNumVisited(B->getBlockID()) < 3;
}

//===----------------------------------------------------------------------===//
// Branch processing.
//===----------------------------------------------------------------------===//

ValueState* GRExprEngine::MarkBranch(ValueState* St, Stmt* Terminator,
                                     bool branchTaken) {
  
  switch (Terminator->getStmtClass()) {
    default:
      return St;
      
    case Stmt::BinaryOperatorClass: { // '&&' and '||'
      
      BinaryOperator* B = cast<BinaryOperator>(Terminator);
      BinaryOperator::Opcode Op = B->getOpcode();
      
      assert (Op == BinaryOperator::LAnd || Op == BinaryOperator::LOr);
      
      // For &&, if we take the true branch, then the value of the whole
      // expression is that of the RHS expression.
      //
      // For ||, if we take the false branch, then the value of the whole
      // expression is that of the RHS expression.
      
      Expr* Ex = (Op == BinaryOperator::LAnd && branchTaken) ||
                 (Op == BinaryOperator::LOr && !branchTaken)  
               ? B->getRHS() : B->getLHS();
        
      return SetBlkExprRVal(St, B, UndefinedVal(Ex));
    }
      
    case Stmt::ConditionalOperatorClass: { // ?:
      
      ConditionalOperator* C = cast<ConditionalOperator>(Terminator);
      
      // For ?, if branchTaken == true then the value is either the LHS or
      // the condition itself. (GNU extension).
      
      Expr* Ex;      
      
      if (branchTaken)
        Ex = C->getLHS() ? C->getLHS() : C->getCond();        
      else
        Ex = C->getRHS();
      
      return SetBlkExprRVal(St, C, UndefinedVal(Ex));
    }
      
    case Stmt::ChooseExprClass: { // ?:
      
      ChooseExpr* C = cast<ChooseExpr>(Terminator);
      
      Expr* Ex = branchTaken ? C->getLHS() : C->getRHS();      
      return SetBlkExprRVal(St, C, UndefinedVal(Ex));
    }
  }
}

void GRExprEngine::ProcessBranch(Expr* Condition, Stmt* Term,
                                 BranchNodeBuilder& builder) {

  // Remove old bindings for subexpressions.
  ValueState* PrevState = StateMgr.RemoveSubExprBindings(builder.getState());
  
  // Check for NULL conditions; e.g. "for(;;)"
  if (!Condition) { 
    builder.markInfeasible(false);
    return;
  }
  
  RVal V = GetRVal(PrevState, Condition);
  
  switch (V.getBaseKind()) {
    default:
      break;

    case RVal::UnknownKind:
      builder.generateNode(MarkBranch(PrevState, Term, true), true);
      builder.generateNode(MarkBranch(PrevState, Term, false), false);
      return;
      
    case RVal::UndefinedKind: {      
      NodeTy* N = builder.generateNode(PrevState, true);

      if (N) {
        N->markAsSink();
        UndefBranches.insert(N);
      }
      
      builder.markInfeasible(false);
      return;
    }      
  }
    
  // Process the true branch.

  bool isFeasible = false;  
  ValueState* St = Assume(PrevState, V, true, isFeasible);

  if (isFeasible)
    builder.generateNode(MarkBranch(St, Term, true), true);
  else
    builder.markInfeasible(true);
      
  // Process the false branch.  
  
  isFeasible = false;
  St = Assume(PrevState, V, false, isFeasible);
  
  if (isFeasible)
    builder.generateNode(MarkBranch(St, Term, false), false);
  else
    builder.markInfeasible(false);
}

/// ProcessIndirectGoto - Called by GRCoreEngine.  Used to generate successor
///  nodes by processing the 'effects' of a computed goto jump.
void GRExprEngine::ProcessIndirectGoto(IndirectGotoNodeBuilder& builder) {

  ValueState* St = builder.getState();  
  RVal V = GetRVal(St, builder.getTarget());
  
  // Three possibilities:
  //
  //   (1) We know the computed label.
  //   (2) The label is NULL (or some other constant), or Undefined.
  //   (3) We have no clue about the label.  Dispatch to all targets.
  //
  
  typedef IndirectGotoNodeBuilder::iterator iterator;

  if (isa<lval::GotoLabel>(V)) {
    LabelStmt* L = cast<lval::GotoLabel>(V).getLabel();
    
    for (iterator I=builder.begin(), E=builder.end(); I != E; ++I) {
      if (I.getLabel() == L) {
        builder.generateNode(I, St);
        return;
      }
    }
    
    assert (false && "No block with label.");
    return;
  }

  if (isa<lval::ConcreteInt>(V) || isa<UndefinedVal>(V)) {
    // Dispatch to the first target and mark it as a sink.
    NodeTy* N = builder.generateNode(builder.begin(), St, true);
    UndefBranches.insert(N);
    return;
  }
  
  // This is really a catch-all.  We don't support symbolics yet.
  
  assert (V.isUnknown());
  
  for (iterator I=builder.begin(), E=builder.end(); I != E; ++I)
    builder.generateNode(I, St);
}


void GRExprEngine::VisitGuardedExpr(Expr* Ex, Expr* L, Expr* R,
                                    NodeTy* Pred, NodeSet& Dst) {
  
  assert (Ex == CurrentStmt && getCFG().isBlkExpr(Ex));
  
  ValueState* St = GetState(Pred);
  RVal X = GetBlkExprRVal(St, Ex);
  
  assert (X.isUndef());
  
  Expr* SE = (Expr*) cast<UndefinedVal>(X).getData();
  
  assert (SE);
  
  X = GetBlkExprRVal(St, SE);
  
  // Make sure that we invalidate the previous binding.
  MakeNode(Dst, Ex, Pred, StateMgr.SetRVal(St, Ex, X, true, true));
}

/// ProcessSwitch - Called by GRCoreEngine.  Used to generate successor
///  nodes by processing the 'effects' of a switch statement.
void GRExprEngine::ProcessSwitch(SwitchNodeBuilder& builder) {
  
  typedef SwitchNodeBuilder::iterator iterator;
  
  ValueState* St = builder.getState();  
  Expr* CondE = builder.getCondition();
  RVal  CondV = GetRVal(St, CondE);

  if (CondV.isUndef()) {
    NodeTy* N = builder.generateDefaultCaseNode(St, true);
    UndefBranches.insert(N);
    return;
  }
  
  ValueState*  DefaultSt = St;
  
  // While most of this can be assumed (such as the signedness), having it
  // just computed makes sure everything makes the same assumptions end-to-end.
  
  unsigned bits = getContext().getTypeSize(CondE->getType());

  APSInt V1(bits, false);
  APSInt V2 = V1;
  bool DefaultFeasible = false;
  
  for (iterator I = builder.begin(), EI = builder.end(); I != EI; ++I) {

    CaseStmt* Case = cast<CaseStmt>(I.getCase());
    
    // Evaluate the case.
    if (!Case->getLHS()->isIntegerConstantExpr(V1, getContext(), 0, true)) {
      assert (false && "Case condition must evaluate to an integer constant.");
      return;
    }
    
    // Get the RHS of the case, if it exists.
    
    if (Expr* E = Case->getRHS()) {
      if (!E->isIntegerConstantExpr(V2, getContext(), 0, true)) {
        assert (false &&
                "Case condition (RHS) must evaluate to an integer constant.");
        return ;
      }
      
      assert (V1 <= V2);
    }
    else
      V2 = V1;
    
    // FIXME: Eventually we should replace the logic below with a range
    //  comparison, rather than concretize the values within the range.
    //  This should be easy once we have "ranges" for NonLVals.
        
    do {
      nonlval::ConcreteInt CaseVal(BasicVals.getValue(V1));
      
      RVal Res = EvalBinOp(BinaryOperator::EQ, CondV, CaseVal);
      
      // Now "assume" that the case matches.
      
      bool isFeasible = false;      
      ValueState* StNew = Assume(St, Res, true, isFeasible);
      
      if (isFeasible) {
        builder.generateCaseStmtNode(I, StNew);
       
        // If CondV evaluates to a constant, then we know that this
        // is the *only* case that we can take, so stop evaluating the
        // others.
        if (isa<nonlval::ConcreteInt>(CondV))
          return;
      }
      
      // Now "assume" that the case doesn't match.  Add this state
      // to the default state (if it is feasible).
      
      isFeasible = false;
      StNew = Assume(DefaultSt, Res, false, isFeasible);
      
      if (isFeasible) {
        DefaultFeasible = true;
        DefaultSt = StNew;
      }

      // Concretize the next value in the range.
      if (V1 == V2)
        break;
      
      ++V1;
      assert (V1 <= V2);
      
    } while (true);
  }
  
  // If we reach here, than we know that the default branch is
  // possible.  
  if (DefaultFeasible) builder.generateDefaultCaseNode(DefaultSt);
}

//===----------------------------------------------------------------------===//
// Transfer functions: logical operations ('&&', '||').
//===----------------------------------------------------------------------===//

void GRExprEngine::VisitLogicalExpr(BinaryOperator* B, NodeTy* Pred,
                                    NodeSet& Dst) {
  
  assert (B->getOpcode() == BinaryOperator::LAnd ||
          B->getOpcode() == BinaryOperator::LOr);
  
  assert (B == CurrentStmt && getCFG().isBlkExpr(B));
  
  ValueState* St = GetState(Pred);
  RVal X = GetBlkExprRVal(St, B);
  
  assert (X.isUndef());
  
  Expr* Ex = (Expr*) cast<UndefinedVal>(X).getData();
  
  assert (Ex);
  
  if (Ex == B->getRHS()) {
    
    X = GetBlkExprRVal(St, Ex);
    
    // Handle undefined values.
    
    if (X.isUndef()) {
      MakeNode(Dst, B, Pred, SetBlkExprRVal(St, B, X));
      return;
    }
    
    // We took the RHS.  Because the value of the '&&' or '||' expression must
    // evaluate to 0 or 1, we must assume the value of the RHS evaluates to 0
    // or 1.  Alternatively, we could take a lazy approach, and calculate this
    // value later when necessary.  We don't have the machinery in place for
    // this right now, and since most logical expressions are used for branches,
    // the payoff is not likely to be large.  Instead, we do eager evaluation.
        
    bool isFeasible = false;
    ValueState* NewState = Assume(St, X, true, isFeasible);
    
    if (isFeasible)
      MakeNode(Dst, B, Pred,
               SetBlkExprRVal(NewState, B, MakeConstantVal(1U, B)));
      
    isFeasible = false;
    NewState = Assume(St, X, false, isFeasible);
    
    if (isFeasible)
      MakeNode(Dst, B, Pred,
               SetBlkExprRVal(NewState, B, MakeConstantVal(0U, B)));
  }
  else {
    // We took the LHS expression.  Depending on whether we are '&&' or
    // '||' we know what the value of the expression is via properties of
    // the short-circuiting.
    
    X = MakeConstantVal( B->getOpcode() == BinaryOperator::LAnd ? 0U : 1U, B);
    MakeNode(Dst, B, Pred, SetBlkExprRVal(St, B, X));
  }
}
 
//===----------------------------------------------------------------------===//
// Transfer functions: Loads and stores.
//===----------------------------------------------------------------------===//

void GRExprEngine::VisitDeclRefExpr(DeclRefExpr* D, NodeTy* Pred, NodeSet& Dst){

  if (D != CurrentStmt) {
    Dst.Add(Pred); // No-op. Simply propagate the current state unchanged.
    return;
  }
  
  // If we are here, we are loading the value of the decl and binding
  // it to the block-level expression.
  
  ValueState* St = GetState(Pred);  
  RVal X = RVal::MakeVal(BasicVals, D);
  RVal Y = isa<lval::DeclVal>(X) ? GetRVal(St, cast<lval::DeclVal>(X)) : X;
  MakeNode(Dst, D, Pred, SetBlkExprRVal(St, D, Y));
}

/// VisitArraySubscriptExpr - Transfer function for array accesses
void GRExprEngine::VisitArraySubscriptExpr(ArraySubscriptExpr* A, NodeTy* Pred,
                                           NodeSet& Dst, bool asLVal) {
  
  Expr* Base = A->getBase()->IgnoreParens();
  
  // Evaluate the base.  
  NodeSet Tmp1;
  Visit(Base, Pred, Tmp1);
  
  // Dereference the base.
  NodeSet Tmp2;

  for (NodeSet::iterator I=Tmp1.begin(), E=Tmp1.end(); I!=E; ++I) {
    ValueState* St = GetState(*I);
    VisitDeref(Base, GetRVal(St, Base), St, *I, Tmp2, true);
  }
  
  // Get the index.
  Tmp1.clear();
  Expr* Index = A->getIdx()->IgnoreParens();
  
  for (NodeSet::iterator I=Tmp2.begin(), E=Tmp2.end(); I!=E; ++I)
    Visit(Index, *I, Dst);
}

/// VisitMemberExpr - Transfer function for member expressions.
void GRExprEngine::VisitMemberExpr(MemberExpr* M, NodeTy* Pred,
                                   NodeSet& Dst, bool asLVal) {
  
  Expr* Base = M->getBase()->IgnoreParens();

  NodeSet Tmp;
  VisitLVal(Base, Pred, Tmp);
  
  if (Base->getType()->isPointerType()) {
    NodeSet Tmp2;
    
    for (NodeSet::iterator I=Tmp.begin(), E=Tmp.end(); I!=E; ++I) {
      ValueState* St = GetState(*I);      
      VisitDeref(Base, GetRVal(St, Base), St, *I, Tmp2, true);
    }
    
    for (NodeSet::iterator I=Tmp2.begin(), E=Tmp2.end(); I!=E; ++I)
      VisitMemberExprField(M, Base, *I, Dst, asLVal);
  }
  else
    for (NodeSet::iterator I=Tmp.begin(), E=Tmp.end(); I!=E; ++I)
      VisitMemberExprField(M, Base, *I, Dst, asLVal);
}

void GRExprEngine::VisitMemberExprField(MemberExpr* M, Expr* Base, NodeTy* Pred,
                                        NodeSet& Dst, bool asLVal) {
  Dst.Add(Pred);  
}

void GRExprEngine::EvalStore(NodeSet& Dst, Expr* E, NodeTy* Pred,
                             ValueState* St, RVal TargetLV, RVal Val) {
  
  assert (Builder && "GRStmtNodeBuilder must be defined.");
  
  unsigned size = Dst.size();  

  SaveAndRestore<bool> OldSink(Builder->BuildSinks);
  SaveOr OldHasGen(Builder->HasGeneratedNode);

  assert (!TargetLV.isUndef());
  
  TF->EvalStore(Dst, *this, *Builder, E, Pred, St, TargetLV, Val);
  
  // Handle the case where no nodes where generated.  Auto-generate that
  // contains the updated state if we aren't generating sinks.
  
  if (!Builder->BuildSinks && Dst.size() == size && !Builder->HasGeneratedNode)
    TF->GRTransferFuncs::EvalStore(Dst, *this, *Builder, E, Pred, St,
                                   TargetLV, Val);
}

//===----------------------------------------------------------------------===//
// Transfer function: Function calls.
//===----------------------------------------------------------------------===//

void GRExprEngine::VisitCall(CallExpr* CE, NodeTy* Pred,
                             CallExpr::arg_iterator AI,
                             CallExpr::arg_iterator AE,
                             NodeSet& Dst) {
  
  // Process the arguments.
  
  if (AI != AE) {
    
    NodeSet DstTmp;      
    Visit(*AI, Pred, DstTmp);    
    ++AI;
    
    for (NodeSet::iterator DI=DstTmp.begin(), DE=DstTmp.end(); DI != DE; ++DI)
      VisitCall(CE, *DI, AI, AE, Dst);
    
    return;
  }

  // If we reach here we have processed all of the arguments.  Evaluate
  // the callee expression.
  
  NodeSet DstTmp;    
  Expr* Callee = CE->getCallee()->IgnoreParens();

  VisitLVal(Callee, Pred, DstTmp);
  
  // Finally, evaluate the function call.
  for (NodeSet::iterator DI = DstTmp.begin(), DE = DstTmp.end(); DI!=DE; ++DI) {

    ValueState* St = GetState(*DI);
    RVal L = GetLVal(St, Callee);

    // FIXME: Add support for symbolic function calls (calls involving
    //  function pointer values that are symbolic).
    
    // Check for undefined control-flow or calls to NULL.
    
    if (L.isUndef() || isa<lval::ConcreteInt>(L)) {      
      NodeTy* N = Builder->generateNode(CE, St, *DI);
      
      if (N) {
        N->markAsSink();
        BadCalls.insert(N);
      }
      
      continue;
    }
    
    // Check for the "noreturn" attribute.
    
    SaveAndRestore<bool> OldSink(Builder->BuildSinks);
    
    if (isa<lval::FuncVal>(L)) {      
      
      FunctionDecl* FD = cast<lval::FuncVal>(L).getDecl();
      
      if (FD->getAttr<NoReturnAttr>())
        Builder->BuildSinks = true;
      else {
        // HACK: Some functions are not marked noreturn, and don't return.
        //  Here are a few hardwired ones.  If this takes too long, we can
        //  potentially cache these results.
        const char* s = FD->getIdentifier()->getName();
        unsigned n = strlen(s);
        
        switch (n) {
          default:
            break;
            
          case 4:
            if (!memcmp(s, "exit", 4)) Builder->BuildSinks = true;
            break;

          case 5:
            if (!memcmp(s, "panic", 5)) Builder->BuildSinks = true;
            break;
          
          case 6:
            if (!memcmp(s, "Assert", 6)) Builder->BuildSinks = true;
            break;
          
          case 7:
            if (!memcmp(s, "assfail", 7)) Builder->BuildSinks = true;
            break;
            
          case 14:
            if (!memcmp(s, "dtrace_assfail", 14)) Builder->BuildSinks = true;
            break;
        }
        
      }
    }
    
    // Evaluate the call.

    if (isa<lval::FuncVal>(L)) {
      
      IdentifierInfo* Info = cast<lval::FuncVal>(L).getDecl()->getIdentifier();
      
      if (unsigned id = Info->getBuiltinID())
        switch (id) {
          case Builtin::BI__builtin_expect: {
            // For __builtin_expect, just return the value of the subexpression.
            assert (CE->arg_begin() != CE->arg_end());            
            RVal X = GetRVal(St, *(CE->arg_begin()));
            MakeNode(Dst, CE, *DI, SetRVal(St, CE, X));
            continue;            
          }
            
          default:
            break;
        }
    }

    // Check any arguments passed-by-value against being undefined.

    bool badArg = false;
    
    for (CallExpr::arg_iterator I = CE->arg_begin(), E = CE->arg_end();
         I != E; ++I) {

      if (GetRVal(GetState(*DI), *I).isUndef()) {        
        NodeTy* N = Builder->generateNode(CE, GetState(*DI), *DI);
      
        if (N) {
          N->markAsSink();
          UndefArgs[N] = *I;
        }
        
        badArg = true;
        break;
      }
    }
    
    if (badArg)
      continue;        

    // Dispatch to the plug-in transfer function.      
    
    unsigned size = Dst.size();
    SaveOr OldHasGen(Builder->HasGeneratedNode);
    EvalCall(Dst, CE, L, *DI);
    
    // Handle the case where no nodes where generated.  Auto-generate that
    // contains the updated state if we aren't generating sinks.
    
    if (!Builder->BuildSinks && Dst.size() == size &&
        !Builder->HasGeneratedNode)
      MakeNode(Dst, CE, *DI, St);
  }
}

//===----------------------------------------------------------------------===//
// Transfer function: Objective-C message expressions.
//===----------------------------------------------------------------------===//

void GRExprEngine::VisitObjCMessageExpr(ObjCMessageExpr* ME, NodeTy* Pred,
                                        NodeSet& Dst){
  
  VisitObjCMessageExprArgHelper(ME, ME->arg_begin(), ME->arg_end(),
                                Pred, Dst);
}  

void GRExprEngine::VisitObjCMessageExprArgHelper(ObjCMessageExpr* ME,
                                                 ObjCMessageExpr::arg_iterator AI,
                                                 ObjCMessageExpr::arg_iterator AE,
                                                 NodeTy* Pred, NodeSet& Dst) {
  if (AI == AE) {
    
    // Process the receiver.
    
    if (Expr* Receiver = ME->getReceiver()) {
      NodeSet Tmp;
      Visit(Receiver, Pred, Tmp);
      
      for (NodeSet::iterator NI = Tmp.begin(), NE = Tmp.end(); NI != NE; ++NI)
        VisitObjCMessageExprDispatchHelper(ME, *NI, Dst);
      
      return;
    }
    
    VisitObjCMessageExprDispatchHelper(ME, Pred, Dst);