import com.google.javascript.jscomp.LiveVariablesAnalysis.LiveVariableLattice; //导入依赖的package包/类
/**
 * 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) {
  List<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);
  }
}
 

import com.google.javascript.jscomp.LiveVariablesAnalysis.LiveVariableLattice; //导入依赖的package包/类
/**
 * 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);
  }
}
 

import com.google.javascript.jscomp.LiveVariablesAnalysis.LiveVariableLattice; //导入依赖的package包/类
private UndiGraph<Var, Void> computeVariableNamesInterferenceGraph(
    NodeTraversal t, ControlFlowGraph<Node> cfg, Set<Var> escaped) {
  UndiGraph<Var, Void> interferenceGraph =
      new LinkedUndirectedGraph<Var, Void>();
  Scope scope = t.getScope();

  // First create a node for each non-escaped variable.
  for (Iterator<Var> i = scope.getVars(); i.hasNext();) {
    Var v = i.next();
    if (!escaped.contains(v)) {
      
      // TODO(user): In theory, we CAN coalesce function names just like
      // any variables. Our Liveness analysis captures this just like it as
      // described in the specification. However, we saw some zipped and
      // and unzipped size increase after this. We are not totally sure why
      // that is but, for now, we will respect the dead functions and not play
      // around with it.
      if (!NodeUtil.isFunction(v.getParentNode())) {
        interferenceGraph.createNode(v);
      }
    }
  }

  // Go through every single point of the program and look at each variable
  // pairs. If they are both live at the same time, at an edge between them.
  for (DiGraphNode<Node, Branch> cfgNode : cfg.getDirectedGraphNodes()) {
    FlowState<LiveVariableLattice> state = cfgNode.getAnnotation();
    if (cfg.isImplicitReturn(cfgNode)) {
      continue;
    }

    int varsInScope = scope.getVarCount();
    ArrayList<CombinedLiveRangeChecker> rangesToCheck =
        new ArrayList<CombinedLiveRangeChecker>(
            varsInScope * varsInScope);

    for (Iterator<Var> i1 = scope.getVars(); i1.hasNext();) {
      Var v1 = i1.next();
      for (Iterator<Var> i2 = scope.getVars(); i2.hasNext();) {
        Var v2 = i2.next();

        if (v1 == v2 || !interferenceGraph.hasNode(v1) ||
            !interferenceGraph.hasNode(v2)) {
          // Skip nodes that were not added. They are globals and escaped
          // locals. Also avoid merging a variable with itself.
          continue;
        }

        boolean v1OutLive = state.getOut().isLive(v1);
        boolean v2OutLive = state.getOut().isLive(v2);
        // Finally, check the live states and add edge when possible.
        if (v1.getParentNode().getType() == Token.LP &&
            v2.getParentNode().getType() == Token.LP) {
          interferenceGraph.connectIfNotFound(v1, null, v2);
        } else if ((state.getIn().isLive(v1) && state.getIn().isLive(v2)) ||
            (v1OutLive && v2OutLive)) {
          interferenceGraph.connectIfNotFound(v1, null, v2);
        } else {
          LiveRangeChecker checker1 =
              new LiveRangeChecker(v1, v2OutLive ? null : v2);
          LiveRangeChecker checker2 =
              new LiveRangeChecker(v2, v1OutLive ? null : v1);
          rangesToCheck.add(new CombinedLiveRangeChecker(checker1, checker2));
        }
      }
    }

    // Do the collected live range checks.
    checkRanges(rangesToCheck, cfgNode.getValue());
    for (CombinedLiveRangeChecker range : rangesToCheck) {
      range.connectIfCrossed(interferenceGraph);
    }
  }
  return interferenceGraph;
}
 

import com.google.javascript.jscomp.LiveVariablesAnalysis.LiveVariableLattice; //导入依赖的package包/类
private void tryRemoveAssignment(NodeTraversal t, Node n,
    FlowState<LiveVariableLattice> state) {
  tryRemoveAssignment(t, n, n, state);
}
 

import com.google.javascript.jscomp.LiveVariablesAnalysis.LiveVariableLattice; //导入依赖的package包/类
private UndiGraph<Var, Void> computeVariableNamesInterferenceGraph(
    NodeTraversal t, ControlFlowGraph<Node> cfg, Set<Var> escaped) {
  UndiGraph<Var, Void> interferenceGraph =
      new LinkedUndirectedGraph<Var, Void>();
  Scope scope = t.getScope();

  // First create a node for each non-escaped variable.
  for (Iterator<Var> i = scope.getVars(); i.hasNext();) {
    Var v = i.next();
    if (!escaped.contains(v)) {

      // TODO(user): In theory, we CAN coalesce function names just like
      // any variables. Our Liveness analysis captures this just like it as
      // described in the specification. However, we saw some zipped and
      // and unzipped size increase after this. We are not totally sure why
      // that is but, for now, we will respect the dead functions and not play
      // around with it.
      if (!NodeUtil.isFunction(v.getParentNode())) {
        interferenceGraph.createNode(v);
      }
    }
  }

  // Go through every single point of the program and look at each variable
  // pairs. If they are both live at the same time, at an edge between them.
  for (DiGraphNode<Node, Branch> cfgNode : cfg.getDirectedGraphNodes()) {
    FlowState<LiveVariableLattice> state = cfgNode.getAnnotation();
    if (cfg.isImplicitReturn(cfgNode)) {
      continue;
    }

    int varsInScope = scope.getVarCount();
    ArrayList<CombinedLiveRangeChecker> rangesToCheck =
        new ArrayList<CombinedLiveRangeChecker>(
            varsInScope * varsInScope);

    for (Iterator<Var> i1 = scope.getVars(); i1.hasNext();) {
      Var v1 = i1.next();
      for (Iterator<Var> i2 = scope.getVars(); i2.hasNext();) {
        Var v2 = i2.next();

        if (v1 == v2 || !interferenceGraph.hasNode(v1) ||
            !interferenceGraph.hasNode(v2)) {
          // Skip nodes that were not added. They are globals and escaped
          // locals. Also avoid merging a variable with itself.
          continue;
        }

        boolean v1OutLive = state.getOut().isLive(v1);
        boolean v2OutLive = state.getOut().isLive(v2);
        // Finally, check the live states and add edge when possible.
        if (v1.getParentNode().getType() == Token.LP &&
            v2.getParentNode().getType() == Token.LP) {
          interferenceGraph.connectIfNotFound(v1, null, v2);
        } else if ((state.getIn().isLive(v1) && state.getIn().isLive(v2)) ||
            (v1OutLive && v2OutLive)) {
          interferenceGraph.connectIfNotFound(v1, null, v2);
        } else {
          LiveRangeChecker checker1 =
              new LiveRangeChecker(v1, v2OutLive ? null : v2);
          LiveRangeChecker checker2 =
              new LiveRangeChecker(v2, v1OutLive ? null : v1);
          rangesToCheck.add(new CombinedLiveRangeChecker(checker1, checker2));
        }
      }
    }

    // Do the collected live range checks.
    checkRanges(rangesToCheck, cfgNode.getValue());
    for (CombinedLiveRangeChecker range : rangesToCheck) {
      range.connectIfCrossed(interferenceGraph);
    }
  }
  return interferenceGraph;
}
 

import com.google.javascript.jscomp.LiveVariablesAnalysis.LiveVariableLattice; //导入依赖的package包/类
/**
 * 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,
    Map<String, Var> allVarsInFn) {
  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.getToken()) {
      case IF:
      case WHILE:
      case DO:
        tryRemoveAssignment(t, NodeUtil.getConditionExpression(n), state, allVarsInFn);
        continue;
      case FOR:
      case FOR_IN:
      case FOR_OF:
        if (n.isVanillaFor()) {
          tryRemoveAssignment(t, NodeUtil.getConditionExpression(n), state, allVarsInFn);
        }
        continue;
      case SWITCH:
      case CASE:
      case RETURN:
        if (n.hasChildren()) {
          tryRemoveAssignment(t, n.getFirstChild(), state, allVarsInFn);
        }
        continue;
        // TODO(user): case VAR: Remove var a=1;a=2;.....
      default:
        break;
    }

    tryRemoveAssignment(t, n, state, allVarsInFn);
  }
}
 

import com.google.javascript.jscomp.LiveVariablesAnalysis.LiveVariableLattice; //导入依赖的package包/类
private void tryRemoveAssignment(NodeTraversal t, Node n,
    FlowState<LiveVariableLattice> state, Map<String, Var> allVarsInFn) {
  tryRemoveAssignment(t, n, n, state, allVarsInFn);
}