That's not true. A lot of very simple and useful optimizations are very hard to prove correct (e.g. devirtualization) and so can't be done with AOT compilers. I

That's not true. A lot of very simple and useful optimizations are very hard to prove correct (e.g. devirtualization) and so can't be done with AOT compilers. It doesn't matter to people using languages that require the programmer to carefully control the compiler -- like C/C++ or Rust -- but it matters a great deal to languages that offer a smaller number of more general abstractions. It is virtually impossible to compile, say, JavaScript efficiently with an AOT compiler, but when compiled with a JIT it can have excellent performance.