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.
