This PR implements `Hidden Classes`, I named them as `Shapes` (like Spidermonkey does), calling them maps like v8 seems confusing because there already is a JS builtin, likewise with `Hidden classes` since there are already classes in JS.
There are two types of shapes: `shared` shapes that create the transition tree, and are shared between objects, this is mainly intended for user defined objects this makes more sense because shapes can create transitions trees, doing that for the builtins seems wasteful (unless users wanted to creating an object with the same property names and the same property attributes in the same order... which seems unlikely). That's why I added `unique` shapes, only one object has it. This is similar to previous solution, but this architecture enables us to use inline caching.
There will probably be a performance hit until we implement inline caching.
There still a lot of work that needs to be done, on this:
- [x] Move Property Attributes to shape
- [x] Move Prototype to shape
- [x] ~~Move extensible flag to shape~~, On further evaluation this doesn't give any benefit (at least right now), since it isn't used by inline caching also adding one more transition.
- [x] Implement delete for unique shapes.
- [x] If the chain is too long we should probably convert it into a `unique` shape
- [x] Figure out threshold ~~(maybe more that 256 properties ?)~~ curently set to an arbitrary number (`1024`)
- [x] Implement shared property table between shared shapes
- [x] Add code Document
- [x] Varying size storage for properties (get+set = 2, data = 1)
- [x] Add shapes to more object:
- [x] ordinary object
- [x] Arrays
- [x] Functions
- [x] Other builtins
- [x] Add `shapes.md` doc explaining shapes in depth with mermaid diagrams :)
- [x] Add `$boa.shape` module
- [x] `$boa.shape.id(o)`
- [x] `$boa.shape.type(o)`
- [x] `$boa.shape.same(o1, o2)`
- [x] add doc to `boa_object.md`
For each js script in the bench_scripts folder, we create three benchmarks:
Parser => lexing and parsing of the source code
Compiler => compilation of the parsed statement list into bytecode
Execution => execution of the bytecode in the vm
The idea is to check the performance of Boa in different scenarios.
Different parts of Boa are benchmarked separately to make the impact of local changes visible.
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