Review

3

com/google/javascript/jscomp/DataFlowAnalysis.java

analyze(int)

class DataFlowAnalysis {
  /**
   * 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());
    }
  }

}