public void mark(Label label) {
    adopt(label);
    if (label.marked) {
      throw new IllegalStateException("already marked");
    }
    label.marked = true;
    if (currentLabel != null) {
      jump(label); // blocks must end with a branch, return or throw
    }
    currentLabel = label;
  }
Start defining instructions for the named label.
android/android_framework/dex-maker/src/main/java/com/android/dx/Code.java