Speculative or unconditional devirtualization are reasonable things to do if you are the compiler.
Writing code by hand, it's quite unwieldy, since the compiler doesn't know that a `FinalFooFrobber` always contains has its vtable set to `FrobberVtable foo_vtable`, which often appears only after inlining.
Asking C programmers to do inlining by hand is not sane. This isn't like interpreted languages where inlining sucks - here, the compiler is quite capable of it, just the vtable stuff confuses it.
