/**
  * Partition a congruence class.
  *
  * @param partition the class to partition
  */
 private void partitionClass(OPT_GVCongruenceClass partition) {
   // store a reference to the first node in c, which will serve
   // as a representative for this class
   Iterator i = partition.iterator();
   OPT_ValueGraphVertex first = (OPT_ValueGraphVertex) i.next();
   ArrayList newClasses = new ArrayList();
   // now check each other node in c, to see if it matches the
   // representative
   ArrayList toRemove = new ArrayList();
   for (; i.hasNext(); ) {
     OPT_ValueGraphVertex v = (OPT_ValueGraphVertex) i.next();
     if (!checkCongruence(first, v)) {
       // NOT CONGRUENT!!  split the partition.  first check if
       // v fits in any other newly created congruence classes
       int index = findCongruenceMatch(newClasses, v);
       if (index > -1) {
         // MATCH FOUND!! place v in newClasses[index]
         OPT_GVCongruenceClass match = (OPT_GVCongruenceClass) B.get(index);
         match.addVertex(v);
         v.setValueNumber(match.getValueNumber());
       } else {
         // NO MATCH FOUND!! create a new congruence class
         // find the appropriate label for the new congruence class
         // and create a new congruence class with this label
         OPT_GVCongruenceClass c = createCongruenceClass(v);
         newClasses.add(c);
         c.addVertex(v);
         v.setValueNumber(c.getValueNumber());
       }
       // mark v as to be removed from partition
       // (Can't remove it yet while iterating over the set);
       toRemove.add(v);
     }
   }
   // remove necessary vertices
   for (Iterator it = toRemove.iterator(); it.hasNext(); ) {
     OPT_ValueGraphVertex v = (OPT_ValueGraphVertex) it.next();
     partition.removeVertex(v);
   }
   // if needed place the original partition back on the work list
   if ((newClasses.size() > 0) && (partition.size() > 1)) {
     workList.push(partition);
   }
   // place any new congruence classes with size > 1 on the worklist
   // also place any classes which might indirectly be affected
   for (int j = 0; j < newClasses.size(); j++) {
     OPT_GVCongruenceClass c = (OPT_GVCongruenceClass) newClasses.get(j);
     if (c.size() > 1) workList.push(c);
     addDependentClassesToWorklist(c);
   }
 }
 /**
  * Assuming congruence class c has changed: find all other classes that might be affected, and add
  * them to the worklist
  *
  * @param c the congruence class that has changed
  */
 private void addDependentClassesToWorklist(OPT_GVCongruenceClass c) {
   // for each element of this congruence class:
   for (Iterator elements = c.iterator(); elements.hasNext(); ) {
     OPT_ValueGraphVertex v = (OPT_ValueGraphVertex) elements.next();
     // for each vertex which points to v in the value graph
     for (Enumeration e = v.inNodes(); e.hasMoreElements(); ) {
       OPT_ValueGraphVertex in = (OPT_ValueGraphVertex) e.nextElement();
       int vn = in.getValueNumber();
       OPT_GVCongruenceClass x = (OPT_GVCongruenceClass) B.get(vn);
       workList.push(x);
     }
   }
 }
 /**
  * Initialize the work list. A congruence class gets put on the work list if any two nodes in the
  * class point to corresponding targets in separate partitions.
  */
 private void initializeWorkList() {
   for (Iterator it = B.iterator(); it.hasNext(); ) {
     OPT_GVCongruenceClass c = (OPT_GVCongruenceClass) it.next();
     if (c.size() == 1) continue;
     // store a reference to the first node in c
     Iterator i = c.iterator();
     OPT_ValueGraphVertex first = (OPT_ValueGraphVertex) i.next();
     // now check that each other target matches the first element
     // if not, add this class to the work list
     congruenceClass:
     for (; i.hasNext(); ) {
       OPT_ValueGraphVertex v = (OPT_ValueGraphVertex) i.next();
       if (!checkCongruence(first, v)) {
         workList.push(c);
         break congruenceClass;
       }
     }
   }
 }