> The runtime doesn't know all that much […] If we are talking about JIT, yes, it does, for it instruments the runtime, gathers the information about hot code

> The runtime doesn't know all that much […] If we are talking about JIT, yes, it does, for it instruments the runtime, gathers the information about hot code paths and performs the in-place optimisation. Think of the profile guide compile time optimisation having been carried over into the runtime.