I never quite understood what the advantage of a JIT runtime is. A RegEx expression that gets complied to machine code but is specified at runtime makes sense, but as a general language paradigm, why is this useful compared to ahead of time compilation code that is known ahead of time? Is there some efficiency to be had from doing JIT vs not doing it and some heuristic you can deduce to find hot loops and optimize them as the program runs?
Jits are generally used for dynamic languages, where every type needs to be checked and untagged. But a jit compiler can observe the actual types used during runtime and specialize the code for that. Allows them to perform closer to static languages.
