com.google.javascript.jscomp.graph.DiGraph.DiGraphNode Java Examples

/**
 * Asserts the priority order of CFG nodes.
 *
 * Checks that the node type of the highest-priority node matches the
 * first element of the list, the type of the second node matches the
 * second element of the list, and so on.
 *
 * @param cfg The control flow graph.
 * @param nodeTypes The expected node types, in order.
 */
private void assertNodeOrder(ControlFlowGraph<Node> cfg,
    List<Integer> nodeTypes) {
  List<DiGraphNode<Node, Branch>> cfgNodes =
      Lists.newArrayList(cfg.getDirectedGraphNodes());
  Collections.sort(cfgNodes, cfg.getOptionalNodeComparator(true));

  // IMPLICIT RETURN must always be last.
  Node implicitReturn = cfgNodes.remove(cfgNodes.size() - 1).getValue();
  assertNull(implicitReturn == null ? "null" : implicitReturn.toStringTree(),
      implicitReturn);

  assertEquals("Wrong number of CFG nodes",
      nodeTypes.size(), cfgNodes.size());
  for (int i = 0; i < cfgNodes.size(); i++) {
    int expectedType = nodeTypes.get(i);
    int actualType = cfgNodes.get(i).getValue().getType();
    assertEquals(
        "node type mismatch at " + i + ".\n" +
        "found   : " + Token.name(actualType) + "\n" +
        "required: " + Token.name(expectedType) + "\n",
        expectedType, actualType);
  }
}
 

/**
 * Given an entry node, find all the nodes reachable from that node
 * and prioritize them.
 */
private void prioritizeFromEntryNode(DiGraphNode<Node, Branch> entry) {
  PriorityQueue<DiGraphNode<Node, Branch>> worklist =
      new PriorityQueue<DiGraphNode<Node, Branch>>(10, priorityComparator);
  worklist.add(entry);

  while (!worklist.isEmpty()) {
    DiGraphNode<Node, Branch> current = worklist.remove();
    if (nodePriorities.containsKey(current)) {
      continue;
    }

    nodePriorities.put(current, ++priorityCounter);

    List<DiGraphNode<Node, Branch>> successors =
        cfg.getDirectedSuccNodes(current);
    for (DiGraphNode<Node, Branch> candidate : successors) {
      worklist.add(candidate);
    }
  }
}
 

/**
 * Given an entry node, find all the nodes reachable from that node
 * and prioritize them.
 */
private void prioritizeFromEntryNode(DiGraphNode<Node, Branch> entry) {
  PriorityQueue<DiGraphNode<Node, Branch>> worklist =
      new PriorityQueue<DiGraphNode<Node, Branch>>(10, priorityComparator);
  worklist.add(entry);

  while (!worklist.isEmpty()) {
    DiGraphNode<Node, Branch> current = worklist.remove();
    if (nodePriorities.containsKey(current)) {
      continue;
    }

    nodePriorities.put(current, ++priorityCounter);

    List<DiGraphNode<Node, Branch>> successors =
        cfg.getDirectedSuccNodes(current);
    for (DiGraphNode<Node, Branch> candidate : successors) {
      worklist.add(candidate);
    }
  }
}
 

/**
 * Given an entry node, find all the nodes reachable from that node
 * and prioritize them.
 */
private void prioritizeFromEntryNode(DiGraphNode<Node, Branch> entry) {
  PriorityQueue<DiGraphNode<Node, Branch>> worklist =
      new PriorityQueue<DiGraphNode<Node, Branch>>(10, priorityComparator);
  worklist.add(entry);

  while (!worklist.isEmpty()) {
    DiGraphNode<Node, Branch> current = worklist.remove();
    if (nodePriorities.containsKey(current)) {
      continue;
    }

    nodePriorities.put(current, ++priorityCounter);

    List<DiGraphNode<Node, Branch>> successors =
        cfg.getDirectedSuccNodes(current);
    for (DiGraphNode<Node, Branch> candidate : successors) {
      worklist.add(candidate);
    }
  }
}
 

/**
 * Given an entry node, find all the nodes reachable from that node
 * and prioritize them.
 */
private void prioritizeFromEntryNode(DiGraphNode<Node, Branch> entry) {
  PriorityQueue<DiGraphNode<Node, Branch>> worklist =
      new PriorityQueue<DiGraphNode<Node, Branch>>(10, priorityComparator);
  worklist.add(entry);

  while (!worklist.isEmpty()) {
    DiGraphNode<Node, Branch> current = worklist.remove();
    if (nodePriorities.containsKey(current)) {
      continue;
    }

    nodePriorities.put(current, ++priorityCounter);

    List<DiGraphNode<Node, Branch>> successors =
        cfg.getDirectedSuccNodes(current);
    for (DiGraphNode<Node, Branch> candidate : successors) {
      worklist.add(candidate);
    }
  }
}
 

@Override
public void visit(NodeTraversal t, Node n, Node parent) {
  if (parent == null || n.isFunction() || n.isScript()) {
    return;
  }
  DiGraphNode<Node, Branch> gNode = cfg.getDirectedGraphNode(n);
  if (gNode == null) { // Not in CFG.
    return;
  }
  if (gNode.getAnnotation() != GraphReachability.REACHABLE ||
      (removeNoOpStatements && !NodeUtil.mayHaveSideEffects(n, compiler))) {
    removeDeadExprStatementSafely(n);
    return;
  }
  tryRemoveUnconditionalBranching(n);
}
 

@Override
public void visit(NodeTraversal t, Node n, Node parent) {
  if (parent == null || n.isFunction() || n.isScript()) {
    return;
  }
  DiGraphNode<Node, Branch> gNode = cfg.getDirectedGraphNode(n);
  if (gNode == null) { // Not in CFG.
    return;
  }
  if (gNode.getAnnotation() != GraphReachability.REACHABLE ||
      (removeNoOpStatements && !NodeUtil.mayHaveSideEffects(n, compiler))) {
    removeDeadExprStatementSafely(n);
    return;
  }
  tryRemoveUnconditionalBranching(n);
}
 

@Override
public void visit(NodeTraversal t, Node n, Node parent) {
  if (parent == null) {
    return;
  }
  if (n.getType() == Token.FUNCTION || n.getType() == Token.SCRIPT) {
    return;
  }

  DiGraphNode<Node, Branch> gNode = curCfg.getDirectedGraphNode(n);
  if (gNode == null) { // Not in CFG.
    return;
  }
  if (gNode.getAnnotation() != GraphReachability.REACHABLE ||
      (removeNoOpStatements && !NodeUtil.mayHaveSideEffects(n))) {
    removeDeadExprStatementSafely(n);
    return;
  }

  tryRemoveUnconditionalBranching(n);
}
 

@Override
public void visit(NodeTraversal t, Node n, Node parent) {
  if (parent == null) {
    return;
  }
  if (n.getType() == Token.FUNCTION || n.getType() == Token.SCRIPT) {
    return;
  }

  DiGraphNode<Node, Branch> gNode = curCfg.getDirectedGraphNode(n);
  if (gNode == null) { // Not in CFG.
    return;
  }
  if (gNode.getAnnotation() != GraphReachability.REACHABLE ||
      (removeNoOpStatements && !NodeUtil.mayHaveSideEffects(n))) {
    removeDeadExprStatementSafely(n);
    return;
  }

  tryRemoveUnconditionalBranching(n);
}
 

/**
 * Given an entry node, find all the nodes reachable from that node
 * and prioritize them.
 */
private void prioritizeFromEntryNode(DiGraphNode<Node, Branch> entry) {
  PriorityQueue<DiGraphNode<Node, Branch>> worklist =
      new PriorityQueue<DiGraphNode<Node, Branch>>(10, priorityComparator);
  worklist.add(entry);

  while (!worklist.isEmpty()) {
    DiGraphNode<Node, Branch> current = worklist.remove();
    if (nodePriorities.containsKey(current)) {
      continue;
    }

    nodePriorities.put(current, ++priorityCounter);

    List<DiGraphNode<Node, Branch>> successors =
        cfg.getDirectedSuccNodes(current);
    for (DiGraphNode<Node, Branch> candidate : successors) {
      worklist.add(candidate);
    }
  }
}
 

/**
 * Given an entry node, find all the nodes reachable from that node
 * and prioritize them.
 */
private void prioritizeFromEntryNode(DiGraphNode<Node, Branch> entry) {
  PriorityQueue<DiGraphNode<Node, Branch>> worklist =
      new PriorityQueue<DiGraphNode<Node, Branch>>(10, priorityComparator);
  worklist.add(entry);

  while (!worklist.isEmpty()) {
    DiGraphNode<Node, Branch> current = worklist.remove();
    if (nodePriorities.containsKey(current)) {
      continue;
    }

    nodePriorities.put(current, ++priorityCounter);

    List<DiGraphNode<Node, Branch>> successors =
        cfg.getDirectedSuccNodes(current);
    for (DiGraphNode<Node, Branch> candidate : successors) {
      worklist.add(candidate);
    }
  }
}
 

@Override
public void visit(NodeTraversal t, Node n, Node parent) {
  if (parent == null) {
    return;
  }
  if (n.isFunction() || n.isScript()) {
    return;
  }

  DiGraphNode<Node, Branch> gNode = cfg.getDirectedGraphNode(n);
  if (gNode == null) { // Not in CFG.
    return;
  }
  if (gNode.getAnnotation() != GraphReachability.REACHABLE ||
      (removeNoOpStatements && !NodeUtil.mayHaveSideEffects(n, compiler))) {
    removeDeadExprStatementSafely(n);
    return;
  }

  tryRemoveUnconditionalBranching(n);
}
 

@Override
public int compare(DiGraphNode<Name, Reference> node1,
    DiGraphNode<Name, Reference> node2) {
  Preconditions.checkNotNull(node1.getValue());
  Preconditions.checkNotNull(node2.getValue());

  if ((node1.getValue().getQualifiedName() == null) &&
      (node2.getValue().getQualifiedName() == null)) {
    return 0;
  }

  // Node 1, if null, comes before node 2.
  if (node1.getValue().getQualifiedName() == null) {
    return -1;
  }

  // Node 2, if null, comes before node 1.
  if (node2.getValue().getQualifiedName() == null) {
    return 1;
  }

  return node1.getValue().getQualifiedName().compareTo(
      node2.getValue().getQualifiedName());
}
 

@Override
protected void initialize() {
  orderedWorkSet.clear();
  for (DiGraphNode<N, Branch> node : getCfg().getDirectedGraphNodes()) {
    int outEdgeCount = getCfg().getOutEdges(node.getValue()).size();
    List<L> outLattices = Lists.newArrayList();
    for (int i = 0; i < outEdgeCount; i++) {
      outLattices.add(createInitialEstimateLattice());
    }
    node.setAnnotation(new BranchedFlowState<L>(
        createInitialEstimateLattice(), outLattices));
    if (node != getCfg().getImplicitReturn()) {
      orderedWorkSet.add(node);
    }
  }
}
 

@Override
protected void joinInputs(DiGraphNode<N, Branch> node) {
  BranchedFlowState<L> state = node.getAnnotation();
  List<DiGraphNode<N, Branch>> predNodes =
      getCfg().getDirectedPredNodes(node);
  List<L> values = new ArrayList<L>(predNodes.size());

  for (DiGraphNode<N, Branch> predNode : predNodes) {
    BranchedFlowState<L> predNodeState = predNode.getAnnotation();

    L in = predNodeState.out.get(
        getCfg().getDirectedSuccNodes(predNode).indexOf(node));

    values.add(in);
  }
  if (getCfg().getEntry() == node) {
    state.setIn(createEntryLattice());
  } else if (!values.isEmpty()) {
    state.setIn(joinOp.apply(values));
  }
}
 

/**
 * @returns true if all paths from block must exit with an explicit return.
 */
private boolean allPathsReturn(Node block) {
  // Computes the control flow graph.
  ControlFlowAnalysis cfa = new ControlFlowAnalysis(
      compiler, false, false);
  cfa.process(null, block);
  ControlFlowGraph<Node> cfg = cfa.getCfg();

  Node returnPathsParent = cfg.getImplicitReturn().getValue();
  for (DiGraphNode<Node, Branch> pred :
    cfg.getDirectedPredNodes(returnPathsParent)) {
    Node n = pred.getValue();
    if (!n.isReturn()) {
      return false;
    }
  }
  return true;
}
 

/**
 * Given an entry node, find all the nodes reachable from that node
 * and prioritize them.
 */
private void prioritizeFromEntryNode(DiGraphNode<Node, Branch> entry) {
  PriorityQueue<DiGraphNode<Node, Branch>> worklist =
      new PriorityQueue<DiGraphNode<Node, Branch>>(10, priorityComparator);
  worklist.add(entry);

  while (!worklist.isEmpty()) {
    DiGraphNode<Node, Branch> current = worklist.remove();
    if (nodePriorities.containsKey(current)) {
      continue;
    }

    nodePriorities.put(current, ++priorityCounter);

    List<DiGraphNode<Node, Branch>> successors =
        cfg.getDirectedSuccNodes(current);
    for (DiGraphNode<Node, Branch> candidate : successors) {
      worklist.add(candidate);
    }
  }
}
 

/** Tests a graph with many valid paths. */
public void testManyValidPaths() {
  DiGraph<String, String> g = LinkedDirectedGraph.create();
  g.createDirectedGraphNode("a");
  g.createDirectedGraphNode("b");
  g.createDirectedGraphNode("c1");
  g.createDirectedGraphNode("c2");
  g.createDirectedGraphNode("c3");
  DiGraphNode<String, String> d = g.createDirectedGraphNode("d");

  g.connect("a",  "-", "b");
  g.connect("b",  "-", "c1");
  g.connect("b",  "-", "c2");
  g.connect("c2", "-", "d");
  g.connect("c1", "-", "d");
  g.connect("a",  "-", "c3");
  g.connect("c3", "-", "d");

  assertGood(createTest(g, "a", "d", new PrefixPredicate("c"), ALL_EDGE));
}
 

/**
 * Returns the lattice element at the exit point. Needs to be overridden
 * because we use a BranchedFlowState instead of a FlowState; ugh.
 */
@Override
L getExitLatticeElement() {
  DiGraphNode<N, Branch> node = getCfg().getImplicitReturn();
  BranchedFlowState<L> state = node.getAnnotation();
  return state.getIn();
}
 

/**
 * Finds a fixed-point solution. The function has the side effect of replacing
 * the existing node annotations with the computed solutions using {@link
 * com.google.javascript.jscomp.graph.GraphNode#setAnnotation(Annotation)}.
 *
 * <p>Initially, each node's input and output flow state contains the value
 * given by {@link #createInitialEstimateLattice()} (with the exception of the
 * entry node of the graph which takes on the {@link #createEntryLattice()}
 * value. Each node will use the output state of its predecessor and compute a
 * output state according to the instruction. At that time, any nodes that
 * depends on the node's newly modified output value will need to recompute
 * their output state again. Each step will perform a computation at one node
 * until no extra computation will modify any existing output state anymore.
 *
 * @param maxSteps Max number of iterations before the method stops and throw
 *        a {@link MaxIterationsExceededException}. This will prevent the
 *        analysis from going into a infinite loop.
 */
final void analyze(int maxSteps) {
  initialize();
  int step = 0;
  while (!orderedWorkSet.isEmpty()) {
    if (step > maxSteps) {
      throw new MaxIterationsExceededException(
        "Analysis did not terminate after " + maxSteps + " iterations");
    }
    DiGraphNode<N, Branch> curNode = orderedWorkSet.iterator().next();
    orderedWorkSet.remove(curNode);
    joinInputs(curNode);
    if (flow(curNode)) {
      // If there is a change in the current node, we want to grab the list
      // of nodes that this node affects.
      List<DiGraphNode<N, Branch>> nextNodes = isForward() ?
          cfg.getDirectedSuccNodes(curNode) :
          cfg.getDirectedPredNodes(curNode);
      for (DiGraphNode<N, Branch> nextNode : nextNodes) {
        if (nextNode != cfg.getImplicitReturn()) {
          orderedWorkSet.add(nextNode);
        }
      }
    }
    step++;
  }
  if (isForward()) {
    joinInputs(getCfg().getImplicitReturn());
  }
}
 

@Override
protected final boolean flow(DiGraphNode<N, Branch> node) {
  BranchedFlowState<L> state = node.getAnnotation();
  List<L> outBefore = state.out;
  state.out = branchedFlowThrough(node.getValue(), state.in);
  Preconditions.checkState(outBefore.size() == state.out.size());
  for (int i = 0; i < outBefore.size(); i++) {
    if (!outBefore.get(i).equals(state.out.get(i))) {
      return true;
    }
  }
  return false;
}
 

/**
 * Try to remove useless assignments from a control flow graph that has been
 * annotated with liveness information.
 *
 * @param t The node traversal.
 * @param cfg The control flow graph of the program annotated with liveness
 *        information.
 */
private void tryRemoveDeadAssignments(NodeTraversal t,
    ControlFlowGraph<Node> cfg) {
  Iterable<DiGraphNode<Node, Branch>> nodes = cfg.getDirectedGraphNodes();

  for (DiGraphNode<Node, Branch> cfgNode : nodes) {
    FlowState<LiveVariableLattice> state =
        cfgNode.getAnnotation();
    Node n = cfgNode.getValue();
    if (n == null) {
      continue;
    }
    switch (n.getType()) {
      case Token.IF:
      case Token.WHILE:
      case Token.DO:
        tryRemoveAssignment(t, NodeUtil.getConditionExpression(n), state);
        continue;
      case Token.FOR:
        if (!NodeUtil.isForIn(n)) {
          tryRemoveAssignment(
              t, NodeUtil.getConditionExpression(n), state);
        }
        continue;
      case Token.SWITCH:
      case Token.CASE:
      case Token.RETURN:
        if (n.hasChildren()) {
          tryRemoveAssignment(t, n.getFirstChild(), state);
        }
        continue;
      // TODO(user): case Token.VAR: Remove var a=1;a=2;.....
    }

    tryRemoveAssignment(t, n, state);
  }
}
 

/**
 * Constructor.
 * @param entry The entry node.
 * @param priorities The map from nodes to position in the AST (to be
 *    filled by the {@link ControlFlowAnalysis#shouldTraverse}).
 */
private AstControlFlowGraph(Node entry,
    Map<DiGraphNode<Node, Branch>, Integer> priorities,
    boolean edgeAnnotations) {
  super(entry,
      true /* node annotations */, edgeAnnotations);
  this.priorities = priorities;
}
 

private void discoverBackEdges(DiGraphNode<N, E> u) {
  u.setAnnotation(GRAY);
  for (DiGraphEdge<N, E> e : u.getOutEdges()) {
    if (ignoreEdge(e)) {
      continue;
    }
    DiGraphNode<N, E> v = e.getDestination();
    if (v.getAnnotation() == WHITE) {
      discoverBackEdges(v);
    } else if (v.getAnnotation() == GRAY) {
      e.setAnnotation(BACK_EDGE);
    }
  }
  u.setAnnotation(BLACK);
}
 

/**
 * Verify that all non-looping paths from {@code a} to {@code b} pass
 * through at least one node where {@code nodePredicate} is true.
 */
private boolean checkAllPathsWithoutBackEdges(DiGraphNode<N, E> a,
    DiGraphNode<N, E> b) {
  if (nodePredicate.apply(a.getValue()) &&
      (inclusive || (a != start && a != end))) {
    return true;
  }
  if (a == b) {
    return false;
  }
  for (DiGraphEdge<N, E> e : a.getOutEdges()) {
    // Once we visited that edge once, we no longer need to
    // re-visit it again.
    if (e.getAnnotation() == VISITED_EDGE) {
      continue;
    }
    e.setAnnotation(VISITED_EDGE);

    if (ignoreEdge(e)) {
      continue;
    }
    if (e.getAnnotation() == BACK_EDGE) {
      continue;
    }

    DiGraphNode<N, E> next = e.getDestination();
    if (!checkAllPathsWithoutBackEdges(next, b)) {
      return false;
    }
  }
  return true;
}
 

/**
 * Generate the HTML for describing a specific declaration.
 * @param builder  contents of report to be generated
 * @param declarationNode declaration to describe
 */
private void generateDeclarationReport(StringBuilder builder,
    DiGraphNode<Name, Reference> declarationNode) {
  // Provide the name and location of declaration,
  // with an anchor to allow navigation to this declaration.
  String declName = declarationNode.getValue().getQualifiedName();
  JSType declType = declarationNode.getValue().getType();

  builder.append("<LI> ");
  builder.append("<A NAME=\"" + declName + "\">");
  builder.append(declName);
  builder.append("\n");

  // Provide the type of the declaration.
  // This is helpful for debugging.
  generateType(builder, declType);

  // List all the definitions of this name that were found in the code.
  // For each, list
  List<DefinitionsRemover.Definition> defs =
      declarationNode.getValue().getDeclarations();

  if (defs.size() == 0) {
     builder.append("<br>No definitions found<br>");
  } else {
    // Otherwise, provide a list of definitions in a dotted list.
    // For each definition, print the location where that definition is
    // found.
    builder.append("<ul>");
    for (DefinitionsRemover.Definition def : defs) {
      Node fnDef = def.getRValue();
      String sourceFileName = getSourceFile(fnDef);
      builder.append("<li> Defined: ");
      generateSourceReferenceLink(builder,
          sourceFileName, fnDef.getLineno(), fnDef.getCharno());
    }
    builder.append("</ul>");
  }
}
 

/**
 * Verify that some non-looping paths from {@code a} to {@code b} pass
 * through at least one node where {@code nodePredicate} is true.
 */
private boolean checkSomePathsWithoutBackEdges(DiGraphNode<N, E> a,
    DiGraphNode<N, E> b) {
  if (nodePredicate.apply(a.getValue()) &&
      (inclusive || (a != start && a != end))) {
    return true;
  }
  if (a == b) {
    return false;
  }
  for (DiGraphEdge<N, E> e : a.getOutEdges()) {
    // Once we visited that edge once, we no longer need to
    // re-visit it again.
    if (e.getAnnotation() == VISITED_EDGE) {
      continue;
    }
    e.setAnnotation(VISITED_EDGE);

    if (ignoreEdge(e)) {
      continue;
    }
    if (e.getAnnotation() == BACK_EDGE) {
      continue;
    }

    DiGraphNode<N, E> next = e.getDestination();
    if (checkSomePathsWithoutBackEdges(next, b)) {
      return true;
    }
  }
  return false;
}
 

/**
 * Try to remove useless assignments from a control flow graph that has been
 * annotated with liveness information.
 *
 * @param t The node traversal.
 * @param cfg The control flow graph of the program annotated with liveness
 *        information.
 */
private void tryRemoveDeadAssignments(NodeTraversal t,
    ControlFlowGraph<Node> cfg) {
  Iterable<DiGraphNode<Node, Branch>> nodes = cfg.getDirectedGraphNodes();

  for (DiGraphNode<Node, Branch> cfgNode : nodes) {
    FlowState<LiveVariableLattice> state =
        cfgNode.getAnnotation();
    Node n = cfgNode.getValue();
    if (n == null) {
      continue;
    }
    switch (n.getType()) {
      case Token.IF:
      case Token.WHILE:
      case Token.DO:
        tryRemoveAssignment(t, NodeUtil.getConditionExpression(n), state);
        continue;
      case Token.FOR:
        if (!NodeUtil.isForIn(n)) {
          tryRemoveAssignment(
              t, NodeUtil.getConditionExpression(n), state);
        }
        continue;
      case Token.SWITCH:
      case Token.CASE:
      case Token.RETURN:
        if (n.hasChildren()) {
          tryRemoveAssignment(t, n.getFirstChild(), state);
        }
        continue;
      // TODO(user): case Token.VAR: Remove var a=1;a=2;.....
    }

    tryRemoveAssignment(t, n, state);
  }
}
 

/**
 * Try to remove useless assignments from a control flow graph that has been
 * annotated with liveness information.
 *
 * @param t The node traversal.
 * @param cfg The control flow graph of the program annotated with liveness
 *        information.
 */
private void tryRemoveDeadAssignments(NodeTraversal t,
    ControlFlowGraph<Node> cfg) {
  Iterable<DiGraphNode<Node, Branch>> nodes = cfg.getDirectedGraphNodes();

  for (DiGraphNode<Node, Branch> cfgNode : nodes) {
    FlowState<LiveVariableLattice> state =
        cfgNode.getAnnotation();
    Node n = cfgNode.getValue();
    if (n == null) {
      continue;
    }
    switch (n.getType()) {
      case Token.IF:
      case Token.WHILE:
      case Token.DO:
        tryRemoveAssignment(t, NodeUtil.getConditionExpression(n), state);
        continue;
      case Token.FOR:
        if (!NodeUtil.isForIn(n)) {
          tryRemoveAssignment(
              t, NodeUtil.getConditionExpression(n), state);
        }
        continue;
      case Token.SWITCH:
      case Token.CASE:
      case Token.RETURN:
        if (n.hasChildren()) {
          tryRemoveAssignment(t, n.getFirstChild(), state);
        }
        continue;
      // TODO(user): case Token.VAR: Remove var a=1;a=2;.....
    }

    tryRemoveAssignment(t, n, state);
  }
}
 

/**
 * Initializes the work list and the control flow graph.
 */
protected void initialize() {
  // TODO(user): Calling clear doesn't deallocate the memory in a
  // LinkedHashSet. Consider creating a new work set if we plan to repeatedly
  // call analyze.
  orderedWorkSet.clear();
  for (DiGraphNode<N, Branch> node : cfg.getDirectedGraphNodes()) {
    node.setAnnotation(new FlowState<L>(createInitialEstimateLattice(),
        createInitialEstimateLattice()));
    if (node != cfg.getImplicitReturn()) {
      orderedWorkSet.add(node);
    }
  }
}