> Except in case of profile-guided optimization (which few people use), the compiler has one massive weakness: it doesn't know the "shape" and distribution of your data. If it did, it would be able to do quite a bit more, but it mostly does not.
Well, that's only true because programmers define functions in terms of types that are not sufficiently specific wrt their runtime invariants; in a dependently-typed language you could have an optimizing compiler that makes use of type-level information to do better optimizations. For instance, in a dependently-typed language, you could have a type of integers divisible by 11, and it will have no runtime overhead with respect to a machine integer. Of course, this comes with a cost: if you want to use such specific types, you have to prove to the compiler that the data it is getting really does satisfy the property (and yes, you can do such proofs even with data that is only available at runtime, by simply implementing a runtime check).
Well, that's only true because programmers define functions in terms of types that are not sufficiently specific wrt their runtime invariants; in a dependently-typed language you could have an optimizing compiler that makes use of type-level information to do better optimizations. For instance, in a dependently-typed language, you could have a type of integers divisible by 11, and it will have no runtime overhead with respect to a machine integer. Of course, this comes with a cost: if you want to use such specific types, you have to prove to the compiler that the data it is getting really does satisfy the property (and yes, you can do such proofs even with data that is only available at runtime, by simply implementing a runtime check).