It may be that the aliasing rules are also required to fully justify my conclusion (ie. a Base can't have its stored value accessed via a pointer-to-derived due to the aliasing rules). But I have a very high degree of confidence in the conclusion itself. I think that you will find that your compiler implements the behavior I have described.

Replying to myself because depth limit.

Let me try to think of a good way to update the post to capture this better...