code: private static Comparable<?> getGroupElement(OpcodeStack.Item itm) {
          Comparable<?> groupElement = null;
  
          int reg = itm.getRegisterNumber();
          if (reg >= 0) {
              groupElement = Integer.valueOf(reg);
          } else {
              XField field = itm.getXField();
              if (field != null) {
                  int regLoad = itm.getFieldLoadedFromRegister();
                  if (regLoad >= 0) {
                      groupElement = field.getName() + ":{" + regLoad + '}';
                  }
              }
          }
  
          return groupElement;
      }
docs: given an register or field, look to see if this thing is associated with an already discovered loop
  
  @param itm
  the item containing the register or field
  @return the group element