3 ms·

I concur here. 20 years ago I was a JIT cheerleader and in the intervening time I've realized that you're only going to get the super-optimized hot inner loop p

by titzer 2y ago

I concur here. 20 years ago I was a JIT cheerleader and in the intervening time I've realized that you're only going to get the super-optimized hot inner loop perfect after the JIT and runtime has chugged through a ton of other slop that tends to make programs bloated and slow. And the Java ecosystem in particular has a tendency to build a ton of ceremony and abstractions that the runtime system has to boil away, but can only really managed to do so with deep inlining and a lot of optimizations, many of which are speculative. > JITs make dynamic languages faster and they are better at doing that than AOTs Indeed.

theLiminator 2y ago
Yeah, i'm curious how well JIT works on languages with less dynamism. Perhaps a combination of AOT + JIT on a strong statically typed language might provide the best of both worlds. Though I suppose PGO kinda does that.
- titzer 2y ago
  I think about this a bit in the context of Virgil. Virgil's compiler is a whole-program optimizing compiler that does a lot of devirtualization and constant-folding. In the higher optimizations it does a bit of inlining, but I haven't found the huge 10X speedups that you get in, e.g. Java. More like 10-40% performance improvements from inlining. I think Virgil could benefit a little from runtime information. For example, it could make better inlining and register allocation decisions, as well as code layout. I have a feeling that Virgil code would benefit a little from guarded inlining, but I don't think full-on speculation would help. In general, a lot of polymorphism can melt away if you can look at the whole program. Couple that also with Virgil's compiler doing monomorphization, which means that using parametric polymorphism costs only code space, and I think the gap is pretty small. I'd expect you could maybe get another 10-20% from these things all together--that's a lot of work to get a small amount.

by titzer 2y ago

theLiminator 2y ago

Yeah, i'm curious how well JIT works on languages with less dynamism. Perhaps a combination of AOT + JIT on a strong statically typed language might provide the best of both worlds. Though I suppose PGO kinda does that.

titzer 2y ago
I think about this a bit in the context of Virgil. Virgil's compiler is a whole-program optimizing compiler that does a lot of devirtualization and constant-folding. In the higher optimizations it does a bit of inlining, but I haven't found the huge 10X speedups that you get in, e.g. Java. More like 10-40% performance improvements from inlining. I think Virgil could benefit a little from runtime information. For example, it could make better inlining and register allocation decisions, as well as code layout. I have a feeling that Virgil code would benefit a little from guarded inlining, but I don't think full-on speculation would help. In general, a lot of polymorphism can melt away if you can look at the whole program. Couple that also with Virgil's compiler doing monomorphization, which means that using parametric polymorphism costs only code space, and I think the gap is pretty small. I'd expect you could maybe get another 10-20% from these things all together--that's a lot of work to get a small amount.