> What do you mean? My understanding is that autoreleasepool is 100% at runtime. The compiler is not involved afaik except to know to register autorelease with the currently installed pool.

The compiler emits calls that always put something in the autorelease pool or always don't; there's no smart decisions at runtime that skips it or make the ordering of releases nondeterministic. A garbage collector runs whenever it feels like and so the ordering of finalizations changes.