1. All data allocated on the JavaScript heap is placed into a type-specific vector. Numbers go into the numbers vector, strings into the strings vector, and so on.
2. All heap references are type-discriminated indexes: A heap number is identified by its discriminant value and the index to which it points to in the numbers vector.
3. Objects are also split up into object kind -specific vectors. Ordinary objects go into one vector, Arrays go into another, DataViews into yet another, and so on.
4. Unordinary objects' heap data does not contain ordinary object data but instead they contain an optional index to the ordinary objects vector.
5. Objects are aggressively split into parts to avoid common use-cases having to reading parts that are known to be unused.
If this sounds interesting, I've written a few blog posts on the internals of Nova over in our blog, you can jump into that here: https://trynova.dev/blog/what-is-the-nova-javascript-engine
It reads like an experimental approach because someone decided to will it into existence. That and to see if they can achieve better performance because of the architectural choices.
> Luckily, we do have an idea, a new spin on the ECMAScript specification. The starting point is data-oriented design (...)
> So, when you read a cache line you should aim for the entire cache line to be used. The best data structure in the world, bar none, is the humble vector (...)
> So what we want to explore is then: What sort of an engine do you get when almost everything is a vector or an index into a vector, and data structures are optimised for cache line usage? Join us in finding out (...)
(1) Why doesn't V8, whose whole point is performance, lay out memory in an optimal way?
(2) Will Nova need to also implement all of V8's other optimizations, to see if Nova's layout makes any significant difference?
The heap vector "trick" is basically impossible, I believe. It wouldn't be a refactoring so much as it would be a complete rewrite of the engine. The entirety of V8 assumes it deals in pointers, and all of that would need to change to using indexes instead. I will eat my hat if they do it. Without heap vectors they can still split object data apart using pointer-keyed hash maps, so maybe they could take advantage of some of the ideas still.
V8 does offer ways to run code without optimisations, which we can use for a more apples-to-apples comparison. The most important optimisation that Nova really needs before any big performance comparisons become meaningful is property access inline caching, which requires implementing object shapes.
I'd say that once object shapes are done, then limited performance comparisons can probably be made, especially if V8's JIT is disabled.