commit a332c17c50341f63a034308b3fe1e6c42cd434c0
author Ömer Sinan Ağacan <omersa@google.com> Fri Nov 10 16:40:11 2023 +0000
committer Commit Queue <dart-scoped@luci-project-accounts.iam.gserviceaccount.com> Fri Nov 10 16:40:11 2023 +0000
tree 8a6c40fb139ebfc6aa28cf5e8c30cddb3c531c2b
parent 1807debf84f9cc5f6381cc0a5a1d82b4e5ce281f

[dart2wasm] Refactor JSCM typed list class hierarchy

- Add mixins to the implementation classes rather than the base classes.
  This makes `this.member` calls in the mixed-in members direct calls
  and allows inlining.

- Make immutable classes subclasses of mutable classes. This makes sure
  we have one `[]` implementation per typed list type and allows
  inlining `[]`.

- Implement specialized iterators for each typed list. This allows
  unboxed and unchecked iteration of array elements.

# Final class hierarchy:

- `final class JSARrayBufferImpl implements ByteBuffer`:
  The JS `ArrayBuffer` class.

- `final class JSDataViewImpl implements ByteData`:
  The JS `DataView` class.

- `abstract class JSArrayBase implements TypedData`:
  Base class for all typed array classes. Implements common operations
  on the the `DataView` `externref`.

## Array classes

- `_IntListMixin`:
  Implements `List<int>` operations. Declares unchecked getters and
  setters and uses them when possible for performance.

- `_UnmodifiableIntListMixin`:
  Overrides only `get buffer`, `[]=`, and `setRange` to convert a
  `List<int>` implemented with `_IntListMixin` to unmodifiable.

- `JSUint8ArrayImpl extends JSArrayBase with _IntListMixin implements Uint8List`:
  The `Uint8Array` class.

- One class as above for `Int8Array`, `Uint16Array` etc.

- `UnmodifiableJSUint8Array extends JSUint8ArrayImpl with _UnmodifiableIntListMixin implements UnmodifiableUint8ListView`:
  Same as `JSUint8ArrayImpl`, but made immutable with
  `_UnmodifiableIntListMixin`.

- One class as above for the rest of the int arrays.

- `double` classes have the same structure as the `int` classes.

## Iterator classes

To allow fast iteration with `get iterator`, each array class has its
own iterator class. Compared to a generic iterator shared by all
classes, these classes (1) do direct (instead of virtual) and unchecked
(instead of bound checked) calls to read the elements (2) avoid boxing
the `current` elements by having a field with the right non-nullable
type, `int` or `double`.

# Benchmarks

In a benchmark that decodes a 1.3M large protobuf:

- Before: 35.9 seconds.
- After: 3.2 seconds.

(Remaining performance issues in this benchmark are in the
`dart:convert` implementation for JSCM, which I will be optimizing
separately)

Change-Id: I5f29882600c1ca95972e2a62af22b181787cb73a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/334465
Commit-Queue: Ömer Ağacan <omersa@google.com>
Reviewed-by: Aske Simon Christensen <askesc@google.com>