Practically - it never does. It is always cheaper to perform a direct, possibly inlined, call (devirtualization != inlining) than a virtual one.

Guarded devirtualization is also cheaper than virtual calls, even when it has to do

    if (instance is SpecificType st) { st.Call() }
    else { instance.Call() } 

or even chain multiple checks at once (with either regular ifs or emitting a jump table)

This technique is heavily used in various forms by .NET, JVM and JavaScript JIT implementations (other platforms also do that, but these are the major ones)

The first two devirtualize virtual and interface calls (important in Java because all calls default to virtual, important in C# because people like to abuse interfaces and occasionally inheritance, C# delegates are also devirtualized/inlined now). The JS JIT (like V8) performs "inline caching" which is similar where for known object shapes property access is shape type identifier comparison and direct property read instead of keyed lookup which is way more expensive.