Ejemplo n.º 1
0
  protected void addSuccessors(
      Stack<Integer> worklist,
      HashSet<Integer> visited,
      HashMap<String, Integer> labels,
      JilStmt stmt,
      int offset) {

    // First, add sequential exit if there is one.
    if (stmt instanceof JilStmt.Goto) {
      JilStmt.Goto gto = (JilStmt.Goto) stmt;
      int target = labels.get(gto.label());
      if (!visited.contains(target)) {
        worklist.add(target);
        visited.add(target);
      }
    } else if (stmt instanceof JilStmt.Switch) {
      JilStmt.Switch swt = (JilStmt.Switch) stmt;
      for (Pair<JilExpr.Number, String> c : swt.cases()) {
        int target = labels.get(c.second());
        if (!visited.contains(target)) {
          worklist.add(target);
          visited.add(target);
        }
      }
      // And, don't forget the default label!
      int deftarget = labels.get(swt.defaultLabel());
      if (!visited.contains(deftarget)) {
        worklist.add(deftarget);
        visited.add(deftarget);
      }
    } else if (!(stmt instanceof JilStmt.Return || stmt instanceof JilStmt.Throw)) {
      // this is a statement with a sequential exit
      if (!visited.contains(offset + 1)) {
        worklist.add(offset + 1);
        visited.add(offset + 1);
      }
    }

    // Second, check for conditional branch
    if (stmt instanceof JilStmt.IfGoto) {
      JilStmt.IfGoto gto = (JilStmt.IfGoto) stmt;
      int target = labels.get(gto.label());
      if (!visited.contains(target)) {
        worklist.add(target);
        visited.add(target);
      }
    }

    // Third, add any exceptional edges
    for (Pair<Type.Clazz, String> ex : stmt.exceptions()) {
      int target = labels.get(ex.second());
      if (!visited.contains(target)) {
        worklist.add(target);
        visited.add(target);
      }
    }
  }
Ejemplo n.º 2
0
  protected void eliminateDeadCode(JilMethod method) {
    HashMap<String, Integer> labels = new HashMap();
    List<JilStmt> body = method.body();
    Stack<Integer> worklist = new Stack();
    HashSet<Integer> visited = new HashSet();

    // first, initialiser label map
    int pos = 0;
    for (JilStmt s : body) {
      if (s instanceof JilStmt.Label) {
        JilStmt.Label lab = (JilStmt.Label) s;
        labels.put(lab.label(), pos);
      }
      pos++;
    }

    worklist.push(0);
    visited.add(0);

    while (!worklist.isEmpty()) {
      int idx = worklist.pop();

      if (idx != body.size()) {
        JilStmt stmt = body.get(idx);
        addSuccessors(worklist, visited, labels, stmt, idx);
      }
    }

    // Ok, now eliminate any dead statements (if there are any)
    if (visited.size() <= body.size()) {
      pos = 0;
      int size = body.size();
      for (int i = 0; i != size; ++i) {
        if (!visited.contains(i)) {
          body.remove(pos);
        } else {
          pos = pos + 1;
        }
      }
    }
  }