Is the compiler allowed to suppress b2 and/or b3 from the layout of the
object.
Yes, of course, in some cases. For example when whole program analysis tells it, it can.
The next question comes when b1,b2 and b3 are in various places in an inheritance path, would it be allowed to only keep the first reference in this path (provided of course that it can be proved that all references are bound to the same object).
Yes, of course, same reasoning.
The as-if rule is _very_ flexible.
