It's kind of worse than this - a virtual function call is a load (from the object) to get the vtable pointer followed by a load from an offset of that followed

It's kind of worse than this - a virtual function call is a load (from the object) to get the vtable pointer followed by a load from an offset of that followed by a subroutine call from that pointer - it's kind of the worst thing you can do in a high performance microachitecture - because you're going to predict that branch (call) and often get it wrong, but you wont know you got it wrong until you've done the two loads (which can't be parallelised, because the address of one depends on the other). By the time you've resolved this you may be throwing away tens or a hundred instructions from your pipe if the prediction was wrong