[psuter]

One thing JIT compilers are good at is specializing methods for common (runtime) types; e.g. you have a method operating on Iterable but it turns out most of the time you get a List as input; you can generate code that bypasses the method lookups for .size etc. The question of whether this pays off is usually only answerable at runtime.

[bad_user]

Actually that's not a thing most JIT compilers are good at, as such runtimes are hard to build. For the mainstream ones, you only have Java and the major Javascript runtimes.