code: private static void checkNonDebugLabel(final Label label) {
          Field f = getLabelStatusField();
          int status = 0;
          try {
              status = f == null ? 0 : ((Integer) f.get(label)).intValue();
          } catch (IllegalAccessException e) {
              throw new Error("Internal error");
          }
          if ((status & 0x01) != 0) {
              throw new IllegalArgumentException(
                      "Labels used for debug info cannot be reused for control flow");
          }
      }
docs: Checks that the given label is not a label used only for debug purposes.
  
  @param label
  the label to be checked.