private void adopt(Label target) {
    if (target.code == this) {
      return; // already adopted
    }
    if (target.code != null) {
      throw new IllegalArgumentException("Cannot adopt label; it belongs to another Code");
    }
    target.code = this;
    labels.add(target);
  }
Assigns {@code target} to this code.
android/android_framework/dex-maker/src/main/java/com/android/dx/Code.java