@Nullable
  private String allocateLabel() {
    if (!myHasNestedLoops) return null;
    if (myLabel == null) {
      String base = StringUtil.toUpperCase(mySuffix);
      myLabel = IntStreamEx.ints().mapToObj(i -> i == 0 ? base : base + i)
        .remove(myUsedLabels::contains).findFirst().orElseThrow(IllegalArgumentException::new);
      myUsedLabels.add(myLabel);
    }
    return myLabel;
  }
@Nullable
  private String allocateLabel()