Agreed, but we might be stepping outside the scope of the example. Likely, you can make most examples incorrect if you're allowed to add arbitrary code; I read

Agreed, but we might be stepping outside the scope of the example. Likely, you can make most examples incorrect if you're allowed to add arbitrary code; I read this section of the article with the implicit assumption that "the thread calling rlo() performs no other writes to x" and "there's no additional synchronization", since the author didn't put any such code in their example and only claimed that the optimization was possible for the example they gave. (This is Grice's maxim of quantity, I suppose?) Although they probably should have been more careful and clarified that the example they gave doesn't work regardless of context.