I genuinely can't follow you completely, but half suspect you're violently agreeing with me. Are you saying the optimization in the linked article is, or is not, in violation of the standard?
Edit: this is the text I was remembering, from 6.5.16.1 ("Simple Assignment"): "If the value being stored in an object is read from another object that overlaps in any way the storage of the first object, then the overlap shall be exact and the two objects shall have qualified or unqualified versions of a compatible type; otherwise, the behavior is undefined.".
That pretty much matches exactly what I was saying: compilers are free to assume that basic types don't overlap, because if they do then any generated code will be undefined behavior anyway.
Edit: this is the text I was remembering, from 6.5.16.1 ("Simple Assignment"): "If the value being stored in an object is read from another object that overlaps in any way the storage of the first object, then the overlap shall be exact and the two objects shall have qualified or unqualified versions of a compatible type; otherwise, the behavior is undefined.".
That pretty much matches exactly what I was saying: compilers are free to assume that basic types don't overlap, because if they do then any generated code will be undefined behavior anyway.