Honestly not sure what you mean by that - in C#, for example it doesn't matter to the compiler where the code comes from, it can be JITed/inlined just the same even if its coming from a different dll.

I haven't seen any perf impact of splitting stuff between files/js modules in typescript either.

What I'm guessing is that you mean that static compilers, like that of C++, need to be able to 'see' large amounts of code to make clever inlining optimizations.

Which shouldn't be the case if the code is well designed, and/or the compiler can prove invariants necessary for optimization without having to look at the body of the code.