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LibJS+LibWeb: Add fast path for builtin iterators in iterator_step()

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We already have fast path for built-in iterators that skips `next()`
lookup and iteration result object allocation applied for `for..of` and
`for..in` loops. This change extends it to `iterator_step()` to cover
`Array.from()`, `[...arr]` and many other cases.

Makes following function go 2.35x faster on my computer:
```js
(function f() {
  let arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
  for (let i = 0; i < 1000000; i++) {
    let [a, ...rest] = arr;
  }
})();
```
This commit is contained in:
Aliaksandr Kalenik
2025-05-12 00:31:51 +03:00
committed by Alexander Kalenik
parent 31301ef08b
commit bb53485dea
Notes: github-actions[bot] 2025-05-13 12:15:28 +00:00 
Author: https://github.com/kalenikaliaksandr
Commit: https://github.com/LadybirdBrowser/ladybird/commit/bb53485dea1
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/4704
6 changed files with 38 additions and 18 deletions
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4
Libraries/LibWeb/Animations/KeyframeEffect.cpp
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@@ -346,12 +346,12 @@ static WebIDL::ExceptionOr<Vector<BaseKeyframe>> process_a_keyframes_argument(JS
auto next = TRY(JS::iterator_step(vm, iter));
// 3. If next is false abort this loop.
if (!next)
if (!next.has<JS::IterationResult>())
break;
// 4. Let nextItem be IteratorValue(next).
// 5. Check the completion record of nextItem.
auto next_item = TRY(JS::iterator_value(vm, *next));
auto next_item = TRY(next.get<JS::IterationResult>().value);
// 6. If Type(nextItem) is not Undefined, Null or Object, then throw a TypeError and abort these steps.
if (!next_item.is_nullish() && !next_item.is_object())