derefLocationSet  = new BitSet();
derefLocationSet  = new HashSet<Location>();
	public void addDeref(ValueNumber vn, int offset) {		valueNumberSet.set(vn.getNumber());				BitSet derefLocationSet = derefLocationSetMap.get(vn);		if (derefLocationSet == null) {			derefLocationSet  = new BitSet();			derefLocationSetMap.put(vn, derefLocationSet);		}		derefLocationSet.set(offset);	}