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/GRTransferFuncs.h"

#include "llvm/Support/Streams.h"

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

GRExprEngine::StateTy
GRExprEngine::SetValue(StateTy St, Expr* S, const RValue& V) {

  if (!StateCleaned) {
    St = RemoveDeadBindings(CurrentStmt, St);
    StateCleaned = true;
  }

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

  return StateMgr.SetValue(St, S, isBlkExpr, V);
}

const GRExprEngine::StateTy::BufferTy&
GRExprEngine::SetValue(StateTy St, Expr* S, const RValue::BufferTy& RB,
                      StateTy::BufferTy& RetBuf) {
  
  assert (RetBuf.empty());
  
  for (RValue::BufferTy::const_iterator I=RB.begin(), E=RB.end(); I!=E; ++I)
    RetBuf.push_back(SetValue(St, S, *I));
                     
  return RetBuf;
}

GRExprEngine::StateTy
GRExprEngine::SetValue(StateTy St, const LValue& LV, const RValue& V) {
  
  if (LV.isUnknown())
    return St;
  
  if (!StateCleaned) {
    St = RemoveDeadBindings(CurrentStmt, St);
    StateCleaned = true;
  }
  
  return StateMgr.SetValue(St, LV, V);
}

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

  // Remove old bindings for subexpressions.
  StateTy PrevState = StateMgr.RemoveSubExprBindings(builder.getState());
  
  // Check for NULL conditions; e.g. "for(;;)"
  if (!Condition) { 
    builder.markInfeasible(false);
    
    // Get the current block counter.
    GRBlockCounter BC = builder.getBlockCounter();
    unsigned BlockID = builder.getTargetBlock(true)->getBlockID();
    unsigned NumVisited = BC.getNumVisited(BlockID);
        
    if (NumVisited < 1) builder.generateNode(PrevState, true);
    else builder.markInfeasible(true);

    return;
  }
  
  RValue V = GetValue(PrevState, Condition);
  
  switch (V.getBaseKind()) {
    default:
      break;

    case RValue::UnknownKind:
      builder.generateNode(PrevState, true);
      builder.generateNode(PrevState, false);
      return;
      
    case RValue::UninitializedKind: {      
      NodeTy* N = builder.generateNode(PrevState, true);

      if (N) {
        N->markAsSink();
        UninitBranches.insert(N);
      }
      
      builder.markInfeasible(false);
      return;
    }      
  }
  
  // Get the current block counter.
  GRBlockCounter BC = builder.getBlockCounter();
  unsigned BlockID = builder.getTargetBlock(true)->getBlockID();
  unsigned NumVisited = BC.getNumVisited(BlockID);
  
  if (isa<nonlval::ConcreteInt>(V) || 
      BC.getNumVisited(builder.getTargetBlock(true)->getBlockID()) < 1) {
    
    // Process the true branch.

    bool isFeasible = true;
    
    StateTy St = Assume(PrevState, V, true, isFeasible);

    if (isFeasible)
      builder.generateNode(St, true);
    else
      builder.markInfeasible(true);
  }
  else
    builder.markInfeasible(true);
  
  BlockID = builder.getTargetBlock(false)->getBlockID();
  NumVisited = BC.getNumVisited(BlockID);
  
  if (isa<nonlval::ConcreteInt>(V) || 
      BC.getNumVisited(builder.getTargetBlock(false)->getBlockID()) < 1) {
    
    // Process the false branch.  
    
    bool isFeasible = false;
    
    StateTy St = Assume(PrevState, V, false, isFeasible);
    
    if (isFeasible)
      builder.generateNode(St, false);
    else
      builder.markInfeasible(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) {

  StateTy St = builder.getState();  
  LValue V = cast<LValue>(GetValue(St, builder.getTarget()));
  
  // Three possibilities:
  //
  //   (1) We know the computed label.
  //   (2) The label is NULL (or some other constant), or Uninitialized.
  //   (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<UninitializedVal>(V)) {
    // Dispatch to the first target and mark it as a sink.
    NodeTy* N = builder.generateNode(builder.begin(), St, true);
    UninitBranches.insert(N);
    return;
  }
  
  // This is really a catch-all.  We don't support symbolics yet.
  
  assert (isa<UnknownVal>(V));
  
  for (iterator I=builder.begin(), E=builder.end(); I != E; ++I)
    builder.generateNode(I, St);
}

/// 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;
  
  StateTy St = builder.getState();  
  Expr* CondE = builder.getCondition();
  NonLValue CondV = cast<NonLValue>(GetValue(St, CondE));

  if (isa<UninitializedVal>(CondV)) {
    NodeTy* N = builder.generateDefaultCaseNode(St, true);
    UninitBranches.insert(N);
    return;
  }
  
  StateTy  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(),
                                           CondE->getExprLoc());

  APSInt V1(bits, false);
  APSInt V2 = V1;
  
  for (iterator I=builder.begin(), E=builder.end(); I!=E; ++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 NonLValues.
        
    do {      
      nonlval::ConcreteInt CaseVal(ValMgr.getValue(V1));
      
      NonLValue Res = EvalBinaryOp(BinaryOperator::EQ, CondV, CaseVal);
      
      // Now "assume" that the case matches.
      bool isFeasible = false;
      
      StateTy 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).
      
      StNew = Assume(DefaultSt, Res, false, isFeasible);
      
      if (isFeasible)
        DefaultSt = StNew;

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


void GRExprEngine::VisitLogicalExpr(BinaryOperator* B, NodeTy* Pred,
                                   NodeSet& Dst) {

  bool hasR2;
  StateTy PrevState = Pred->getState();

  RValue R1 = GetValue(PrevState, B->getLHS());
  RValue R2 = GetValue(PrevState, B->getRHS(), hasR2);
  
  if (hasR2) {
    if (isa<UninitializedVal>(R2) || isa<UnknownVal>(R2)) {
      Nodify(Dst, B, Pred, SetValue(PrevState, B, R2));
      return;
    }
  }
  else if (isa<UninitializedVal>(R1) || isa<UnknownVal>(R1)) {
    Nodify(Dst, B, Pred, SetValue(PrevState, B, R1));
    return;
  }

  // R1 is an expression that can evaluate to either 'true' or 'false'.
  if (B->getOpcode() == BinaryOperator::LAnd) {
    // hasR2 == 'false' means that LHS evaluated to 'false' and that
    // we short-circuited, leading to a value of '0' for the '&&' expression.
    if (hasR2 == false) { 
      Nodify(Dst, B, Pred, SetValue(PrevState, B, GetRValueConstant(0U, B)));
      return;
    }
  }
  else {
    assert (B->getOpcode() == BinaryOperator::LOr);
    // hasR2 == 'false' means that the LHS evaluate to 'true' and that
    //  we short-circuited, leading to a value of '1' for the '||' expression.
    if (hasR2 == false) {
      Nodify(Dst, B, Pred, SetValue(PrevState, B, GetRValueConstant(1U, B)));
      return;      
    }
  }
    
  // If we reach here we did not short-circuit.  Assume R2 == true and
  // R2 == false.
    
  bool isFeasible;
  StateTy St = Assume(PrevState, R2, true, isFeasible);
  
  if (isFeasible)
    Nodify(Dst, B, Pred, SetValue(PrevState, B, GetRValueConstant(1U, B)));

  St = Assume(PrevState, R2, false, isFeasible);
  
  if (isFeasible)
    Nodify(Dst, B, Pred, SetValue(PrevState, B, GetRValueConstant(0U, B)));  
}



void GRExprEngine::ProcessStmt(Stmt* S, StmtNodeBuilder& builder) {
  Builder = &builder;

  StmtEntryNode = builder.getLastNode();
  CurrentStmt = S;
  NodeSet Dst;
  StateCleaned = false;

  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) {
    StateTy St = RemoveDeadBindings(S, StmtEntryNode->getState());
    builder.generateNode(S, St, StmtEntryNode);
  }
  
  CurrentStmt = NULL;
  StmtEntryNode = NULL;
  Builder = NULL;
}

GRExprEngine::NodeTy*
GRExprEngine::Nodify(NodeSet& Dst, Stmt* S, NodeTy* Pred, StateTy St) {
 
  // If the state hasn't changed, don't generate a new node.
  if (St == Pred->getState())
    return NULL;
  
  NodeTy* N = Builder->generateNode(S, St, Pred);
  Dst.Add(N);
  return N;
}

void GRExprEngine::Nodify(NodeSet& Dst, Stmt* S, NodeTy* Pred,
                         const StateTy::BufferTy& SB) {
  
  for (StateTy::BufferTy::const_iterator I=SB.begin(), E=SB.end(); I!=E; ++I)
    Nodify(Dst, S, Pred, *I);
}

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.
  
  StateTy St = Pred->getState();
  
  Nodify(Dst, D, Pred, SetValue(St, D, GetValue(St, D)));
}

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

  // If we reach here we have processed all of the arguments.  Evaluate
  // the callee expression.
  NodeSet DstTmp;
  Visit(CE->getCallee(), Pred, DstTmp);
  
  // Finally, evaluate the function call.
  for (NodeSet::iterator DI=DstTmp.begin(), DE=DstTmp.end(); DI!=DE; ++DI) {
    StateTy St = (*DI)->getState();    
    LValue L = GetLValue(St, CE->getCallee());

    // Check for uninitialized control-flow.
    if (isa<UninitializedVal>(L)) {
      NodeTy* N = Builder->generateNode(CE, St, *DI);
      N->markAsSink();
      UninitBranches.insert(N);
      continue;
    }
    
    // Note: EvalCall must handle the case where the callee is "UnknownVal."
    Nodify(Dst, CE, *DI, EvalCall(CE, (*DI)->getState()));
  }
}

void GRExprEngine::VisitCast(Expr* CastE, Expr* E, NodeTy* Pred, NodeSet& Dst) {
  
  NodeSet S1;
  Visit(E, Pred, S1);

  QualType T = CastE->getType();
  
  // Check for redundant casts or casting to "void"
  if (T->isVoidType() ||
      E->getType() == T || 
      (T->isPointerType() && E->getType()->isFunctionType())) {
    
    for (NodeSet::iterator I1=S1.begin(), E1=S1.end(); I1 != E1; ++I1)
      Dst.Add(*I1);

    return;
  }
  
  for (NodeSet::iterator I1=S1.begin(), E1=S1.end(); I1 != E1; ++I1) {
    NodeTy* N = *I1;
    StateTy St = N->getState();
    const RValue& V = GetValue(St, E);
    Nodify(Dst, CastE, N, SetValue(St, CastE, EvalCast(ValMgr, V, CastE)));
  }
}

void GRExprEngine::VisitDeclStmt(DeclStmt* DS, GRExprEngine::NodeTy* Pred,
                                GRExprEngine::NodeSet& Dst) {
  
  StateTy St = Pred->getState();
  
  for (const ScopedDecl* D = DS->getDecl(); D; D = D->getNextDeclarator())
    if (const VarDecl* VD = dyn_cast<VarDecl>(D)) {
      
      // FIXME: Add support for local arrays.
      if (VD->getType()->isArrayType())
        continue;
      
      const Expr* E = VD->getInit();      
      St = SetValue(St, lval::DeclVal(VD),
                    E ? GetValue(St, E) : UninitializedVal());
    }

  Nodify(Dst, DS, Pred, St);
  
  if (Dst.empty())
    Dst.Add(Pred);  
}


void GRExprEngine::VisitGuardedExpr(Expr* S, Expr* LHS, Expr* RHS,
                                   NodeTy* Pred, NodeSet& Dst) {
  
  StateTy St = Pred->getState();
  
  RValue R = GetValue(St, LHS);
  if (isa<UnknownVal>(R)) R = GetValue(St, RHS);
  
  Nodify(Dst, S, Pred, SetValue(St, S, R));
}

/// VisitSizeOfAlignOfTypeExpr - Transfer function for sizeof(type).
void GRExprEngine::VisitSizeOfAlignOfTypeExpr(SizeOfAlignOfTypeExpr* S,
                                             NodeTy* Pred,
                                             NodeSet& Dst) {
  
  // 6.5.3.4 sizeof: "The result type is an integer."
  
  QualType T = S->getArgumentType();
  
  // FIXME: Add support for VLAs.
  if (!T.getTypePtr()->isConstantSizeType())
    return;
  
  SourceLocation L = S->getExprLoc();
  uint64_t size = getContext().getTypeSize(T, L) / 8;
  
  Nodify(Dst, S, Pred,
         SetValue(Pred->getState(), S,
                  NonLValue::GetValue(ValMgr, size, S->getType(), L)));
  
}

void GRExprEngine::VisitDeref(UnaryOperator* U, NodeTy* Pred, NodeSet& Dst) {

  Expr* E = U->getSubExpr()->IgnoreParens();
    
  NodeSet DstTmp;
  
  if (!isa<DeclRefExpr>(E))
    DstTmp.Add(Pred);
  else
    Visit(E, Pred, DstTmp);
  
  for (NodeSet::iterator I=DstTmp.begin(), DE=DstTmp.end(); I != DE; ++I) {

    NodeTy* N = *I;
    StateTy St = N->getState();
    
    // FIXME: Bifurcate when dereferencing a symbolic with no constraints?
    
    LValue L = cast<LValue>(GetValue(St, E));
    
    if (isa<UninitializedVal>(L)) {
      NodeTy* Succ = Builder->generateNode(U, St, N);
      
      if (Succ) {
        Succ->markAsSink();
        UninitDeref.insert(Succ);
      }
      
      continue;
    }
    
    if (L.isUnknown()) {
      Dst.Add(N);
      continue;
    }
    
    // After a dereference, one of two possible situations arise:
    //  (1) A crash, because the pointer was NULL.
    //  (2) The pointer is not NULL, and the dereference works.
    // 
    // We add these assumptions.
    
    bool isFeasibleNotNull;
    
    // "Assume" that the pointer is Not-NULL.
    StateTy StNotNull = Assume(St, L, true, isFeasibleNotNull);
    
    if (isFeasibleNotNull) {
      QualType T = U->getType();
      
      // FIXME: Currently symbolic analysis "generates" new symbols
      //  for the contents of values.  We need a better approach.
      
      Nodify(Dst, U, N, SetValue(StNotNull, U, GetValue(StNotNull, L, &T)));
    }
    
    bool isFeasibleNull;
    
    // "Assume" that the pointer is NULL.
    StateTy StNull = Assume(St, L, false, isFeasibleNull);
    
    if (isFeasibleNull) {
      // We don't use "Nodify" here because the node will be a sink
      // and we have no intention of processing it later.
      NodeTy* NullNode = Builder->generateNode(U, StNull, N);
      
      if (NullNode) {
        NullNode->markAsSink();
        
        if (isFeasibleNotNull)
          ImplicitNullDeref.insert(NullNode);
        else
          ExplicitNullDeref.insert(NullNode);
      }
    }    
  }
}

void GRExprEngine::VisitUnaryOperator(UnaryOperator* U,
                                      NodeTy* Pred, NodeSet& Dst) {
  
  NodeSet S1;
  
  assert (U->getOpcode() != UnaryOperator::Deref);
  
  switch (U->getOpcode()) {
    case UnaryOperator::PostInc:
    case UnaryOperator::PostDec:
    case UnaryOperator::PreInc:
    case UnaryOperator::PreDec:
    case UnaryOperator::AddrOf:
      // Evalue subexpression as an LValue.
      VisitLValue(U->getSubExpr(), Pred, S1);
      break;
      
    case UnaryOperator::SizeOf:
    case UnaryOperator::AlignOf:
      // Do not evaluate subexpression.
      S1.Add(Pred);
      break;
      
    default:
      Visit(U->getSubExpr(), Pred, S1);
      break;
  }

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

    NodeTy* N1 = *I1;
    StateTy St = N1->getState();
    
    if (U->isIncrementDecrementOp()) {
      
      // Handle ++ and -- (both pre- and post-increment).
      
      const LValue& L1 = GetLValue(St, U->getSubExpr());
      QualType T = U->getType();
      RValue R1 = GetValue(St, L1, &T);
      
      BinaryOperator::Opcode Op = U->isIncrementOp() ? BinaryOperator::Add
                                                     : BinaryOperator::Sub;
      
      RValue Result = EvalBinaryOp(Op, R1, GetRValueConstant(1U, U));
      
      if (U->isPostfix())
        Nodify(Dst, U, N1, SetValue(SetValue(St, U, R1), L1, Result));
      else
        Nodify(Dst, U, N1, SetValue(SetValue(St, U, Result), L1, Result));
        
      continue;
    }    
    
    // Handle all other unary operators.
    
    switch (U->getOpcode()) {

      case UnaryOperator::Minus: {
        const NonLValue& R1 = cast<NonLValue>(GetValue(St, U->getSubExpr()));
        Nodify(Dst, U, N1, SetValue(St, U, EvalMinus(ValMgr, U, R1)));
        break;
      }
        
      case UnaryOperator::Plus: {
        const NonLValue& R1 = cast<NonLValue>(GetValue(St, U->getSubExpr()));
        Nodify(Dst, U, N1, SetValue(St, U, EvalPlus(ValMgr, U, R1)));
        break;
      }
        
      case UnaryOperator::Not: {
        const NonLValue& R1 = cast<NonLValue>(GetValue(St, U->getSubExpr()));
        Nodify(Dst, U, N1, SetValue(St, U, EvalComplement(ValMgr, R1)));
        break;
      }
        
      case UnaryOperator::LNot: {
        // C99 6.5.3.3: "The expression !E is equivalent to (0==E)."
        //
        //  Note: technically we do "E == 0", but this is the same in the
        //    transfer functions as "0 == E".
        
        RValue V1 = GetValue(St, U->getSubExpr());
        
        if (isa<LValue>(V1)) {
          const LValue& L1 = cast<LValue>(V1);
          lval::ConcreteInt V2(ValMgr.getZeroWithPtrWidth());
          Nodify(Dst, U, N1,
                 SetValue(St, U, EvalBinaryOp(BinaryOperator::EQ,
                                              L1, V2)));
        }
        else {
          const NonLValue& R1 = cast<NonLValue>(V1);
          nonlval::ConcreteInt V2(ValMgr.getZeroWithPtrWidth());
          Nodify(Dst, U, N1,
                 SetValue(St, U, EvalBinaryOp(BinaryOperator::EQ,
                                              R1, V2)));
        }
        
        break;
      }
      
      case UnaryOperator::SizeOf: {
        // 6.5.3.4 sizeof: "The result type is an integer."
        
        QualType T = U->getSubExpr()->getType();
        
        // FIXME: Add support for VLAs.
        if (!T.getTypePtr()->isConstantSizeType())
          return;
        
        SourceLocation L = U->getExprLoc();
        uint64_t size = getContext().getTypeSize(T, L) / 8;
                
        Nodify(Dst, U, N1,
               SetValue(St, U, NonLValue::GetValue(ValMgr, size,
                                                   U->getType(), L)));
        
        break;
      }
        
      case UnaryOperator::AddrOf: {
        const LValue& L1 = GetLValue(St, U->getSubExpr());
        Nodify(Dst, U, N1, SetValue(St, U, L1));
        break;
      }
                
      default: ;
        assert (false && "Not implemented.");
    }    
  }
}

void GRExprEngine::VisitLValue(Expr* E, NodeTy* Pred, NodeSet& Dst) {
  
  E = E->IgnoreParens();
  
  if (isa<DeclRefExpr>(E)) {
    Dst.Add(Pred);
    return;
  }
  
  if (UnaryOperator* U = dyn_cast<UnaryOperator>(E)) {
    if (U->getOpcode() == UnaryOperator::Deref) {
      E = U->getSubExpr()->IgnoreParens();
      
      if (isa<DeclRefExpr>(E))
        Dst.Add(Pred);
      else
        Visit(E, Pred, Dst);
      
      return;
    }
  }
  
  Visit(E, Pred, Dst);
}

void GRExprEngine::VisitBinaryOperator(BinaryOperator* B,
                                       GRExprEngine::NodeTy* Pred,
                                       GRExprEngine::NodeSet& Dst) {
  NodeSet S1;
  
  if (B->isAssignmentOp())
    VisitLValue(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 LValue,
    // so we use GetLValue instead of GetValue so that DeclRefExpr's are
    // evaluated to LValueDecl's instead of to an NonLValue.
    const RValue& V1 = 
      B->isAssignmentOp() ? GetLValue(N1->getState(), B->getLHS())
                          : GetValue(N1->getState(), B->getLHS());
    
    NodeSet S2;
    Visit(B->getRHS(), N1, S2);
  
    for (NodeSet::iterator I2=S2.begin(), E2=S2.end(); I2 != E2; ++I2) {

      NodeTy* N2 = *I2;
      StateTy St = N2->getState();
      const RValue& V2 = GetValue(St, B->getRHS());

      BinaryOperator::Opcode Op = B->getOpcode();
      
      if (Op <= BinaryOperator::Or) {
        
        if (isa<UnknownVal>(V1) || isa<UninitializedVal>(V1)) {
          Nodify(Dst, B, N2, SetValue(St, B, V1));
          continue;
        }
        
        Nodify(Dst, B, N2, SetValue(St, B, EvalBinaryOp(Op, V1, V2)));
        continue;
      
      }
      
      switch (Op) {
        case BinaryOperator::Assign: {
          const LValue& L1 = cast<LValue>(V1);

          if (isa<UninitializedVal>(L1))
            HandleUninitializedStore(B, N2);
          else          
            Nodify(Dst, B, N2, SetValue(SetValue(St, B, V2), L1, V2));

          break;
        }

        default: { // Compound assignment operators.
          
          assert (B->isCompoundAssignmentOp());
                          
          const LValue& L1 = cast<LValue>(V1);
          
          if (isa<UninitializedVal>(L1)) {
            HandleUninitializedStore(B, N2);
            break;
          }
          
          if (isa<UninitializedVal>(V2)) {
            Nodify(Dst, B, N2, SetValue(SetValue(St, B, V2), L1, V2));
            break;
          }
          
          RValue Result = cast<NonLValue>(UnknownVal());
          
          if (Op >= BinaryOperator::AndAssign)
            ((int&) Op) -= (BinaryOperator::AndAssign - BinaryOperator::And);
          else
            ((int&) Op) -= BinaryOperator::MulAssign;          
          
          if (B->getType()->isPointerType()) { // Perform pointer arithmetic.
            const NonLValue& R2 = cast<NonLValue>(V2);
            Result = EvalBinaryOp(Op, L1, R2);
          }
          else if (isa<LValue>(V2)) {
            const LValue& L2 = cast<LValue>(V2);
            
            if (B->getRHS()->getType()->isPointerType()) {
              // LValue comparison.
              Result = EvalBinaryOp(Op, L1, L2);
            }
            else {
              QualType T1 = B->getLHS()->getType();
              QualType T2 = B->getRHS()->getType();
              
              // An operation between two variables of a non-lvalue type.
              Result =
                EvalBinaryOp(Op,
                            cast<NonLValue>(GetValue(N1->getState(), L1, &T1)),
                            cast<NonLValue>(GetValue(N2->getState(), L2, &T2)));
            }
          }
          else { // Any other operation between two Non-LValues.
            QualType T = B->getLHS()->getType();
            const NonLValue& R1 = cast<NonLValue>(GetValue(N1->getState(),
                                                           L1, &T));
            const NonLValue& R2 = cast<NonLValue>(V2);
            Result = EvalBinaryOp(Op, R1, R2);
          }
          
          Nodify(Dst, B, N2, SetValue(SetValue(St, B, Result), L1, Result));
          break;
        }
      }
    }
  }
}

void GRExprEngine::HandleUninitializedStore(Stmt* S, NodeTy* Pred) {
  
  NodeTy* N = Builder->generateNode(S, Pred->getState(), Pred);
  N->markAsSink();
  UninitStores.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
      
      Dst.Add(Pred); // No-op. Simply propagate the current state unchanged.
      break;
                                                       
    case Stmt::BinaryOperatorClass: {
      BinaryOperator* B = cast<BinaryOperator>(S);
 
      if (B->isLogicalOp()) {
        VisitLogicalExpr(B, Pred, Dst);
        break;
      }
      else if (B->getOpcode() == BinaryOperator::Comma) {
        StateTy St = Pred->getState();
        Nodify(Dst, B, Pred, SetValue(St, B, GetValue(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;
    }
      
      // While explicitly creating a node+state for visiting a CharacterLiteral
      // seems wasteful, it also solves a bunch of problems when handling
      // the ?, &&, and ||.
      
    case Stmt::CharacterLiteralClass: {
      CharacterLiteral* C = cast<CharacterLiteral>(S);
      StateTy St = Pred->getState();
      NonLValue X = NonLValue::GetValue(ValMgr, C->getValue(), C->getType(),
                                        C->getLoc());
      Nodify(Dst, C, Pred, SetValue(St, C, X));
      break;      
    }
      
    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;
      
      // While explicitly creating a node+state for visiting an IntegerLiteral
      // seems wasteful, it also solves a bunch of problems when handling
      // the ?, &&, and ||.
      
    case Stmt::IntegerLiteralClass: {      
      StateTy St = Pred->getState();
      IntegerLiteral* I = cast<IntegerLiteral>(S);
      NonLValue X = NonLValue::GetValue(ValMgr, I);
      Nodify(Dst, I, Pred, SetValue(St, I, X));
      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);