But this may only happen when no virtual / overridden methods are involved, no VMT to look up in, no polymorphism at play. This is tanamount to composition, which should be preferred over inheritance anyway.
In this regard, Go and Rust do classes / objects right, Java provides the classical pitfalls, and C++ is the territory where unspeakable horrors can be freely implemented, as usual.
Overriding is fine. The issue comes with polymorphism and would even without inheritance per se, as can be seen in Go where interfaces provide polymorphism without inheritance.
You're right, the issue comes from polymorphism, and from use of polymorphic values when the specific class cannot be determined statically. But this is sort of the point of polymorphism, can't do much about it, except maybe caching the looked-up value(s) when looping over a polymorphic collection.
Parent is correct - if the compiler has the information to devirtualize it becomes direct dispatch regardless of the mechanisms involved at the source level. This is also typically true for JITs.
This is true as long as the compiler actually can de-virtualize the method, that is, that it can prove that the objects it's handling at a particular call site do not override it. Quite often this is not the case, because of the pattern when the programmer is expected to override / implement an abstract method to plug in the desired functionality. The lookup can be fast if there are few classes involved, and their vtables get cached.
JITs can do many fascinating optimizations based on profiling the actual code. They must always be on guard though for a case when their profiling-based conclusions fail to hold with some new data, and they have to de-optimize. This being on guard also has its cost.
Even if you call a pure virtual function of an abstract base class, the compiler can devirtualize if it can determine the type anyway due to data flow analysis. There are limitations but with LTO you’d be surprised at how effective the compiler is here. Also in Rust you’re never going through the vtable unless it’s a &dyn Trait and the compiler fails to devirtualize.
In this regard, Go and Rust do classes / objects right, Java provides the classical pitfalls, and C++ is the territory where unspeakable horrors can be freely implemented, as usual.