public final String identifierString() {
    if (address != -1) {
      return String.format("%04x", address);
    }

    return Hex.u4(System.identityHashCode(this));
  }
Gets the short identifier for this instruction. This is its address, if assigned, or its
identity hashcode if not.

@return {@code non-null;} the identifier
android/android_framework/dex-maker/src/main/java/com/android/dx/dex/code/DalvInsn.java