I'm not a compiler expert, but just a note regarding your last point, devirtualization of a function call and dynamic_cast are different beasts; in fact I've ne

I'm not a compiler expert, but just a note regarding your last point, devirtualization of a function call and dynamic_cast are different beasts; in fact I've never heard of an optimization of the latter as being referred to as devirtualization. (Though perhaps this is just me?) From what I've seen, dynamic_cast is implemented as an opaque external function call (and quite a complicated one), so the compiler would need to explicitly make assumptions about its behavior before it can optimize it away. (Which it certainly could, but that's extra work for the compiler writer that would need to be worth the payoff, which in this case I imagine is probably debatable.) Virtual functions, on the other hand, don't involve an opaque call for mere target resolution, and their vtables have definitions available at compile time, so they're much more tame. So expecting devirtualization to come with dynamic_cast getting optimized away seems a bit of a non-sequitur IMO.