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LibJS: Skip iteration result allocation in AsyncFunctionDriverWrapper

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- Create less GC pressure by making each `await` in async function skip
  iteration result object allocation.
- Skip uncached `Object::get()` calls to extract `value` and `done` from
  the iteration result object.

With this change, following function goes 30% faster on my computer:
```js
(async () => {
    const resolved = Promise.resolve();
    for (let i = 0; i < 5_000_000; i++) {
        await resolved;
    }
})();
```
This commit is contained in:
Aliaksandr Kalenik 2025-05-09 04:23:30 +03:00 • committed by Andreas Kling
commit 4c789ac689
Notes: github-actions[bot] 2025-05-09 10:31:18 +00:00
7 changed files with 47 additions and 28 deletions
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18
Libraries/LibJS/Runtime/GeneratorObject.cpp
View file

@ -78,7 +78,7 @@ ThrowCompletionOr<GeneratorObject::GeneratorState> GeneratorObject::validate(VM&
return state;
}
ThrowCompletionOr<Value> GeneratorObject::execute(VM& vm, Completion const& completion)
ThrowCompletionOr<GeneratorObject::IterationResult> GeneratorObject::execute(VM& vm, Completion const& completion)
{
// Loosely based on step 4 of https://tc39.es/ecma262/#sec-generatorstart mixed with https://tc39.es/ecma262/#sec-generatoryield at the end.
@ -115,24 +115,26 @@ ThrowCompletionOr<Value> GeneratorObject::execute(VM& vm, Completion const& comp
if (result_value.is_throw_completion()) {
// Uncaught exceptions disable the generator.
m_generator_state = GeneratorState::Completed;
return result_value;
return result_value.throw_completion();
}
m_previous_value = result_value.release_value();
bool done = !generated_continuation(m_previous_value).has_value();
m_generator_state = done ? GeneratorState::Completed : GeneratorState::SuspendedYield;
return create_iterator_result_object(vm, generated_value(m_previous_value), done);
return IterationResult(generated_value(m_previous_value), done);
}
// 27.5.3.3 GeneratorResume ( generator, value, generatorBrand ), https://tc39.es/ecma262/#sec-generatorresume
ThrowCompletionOr<Value> GeneratorObject::resume(VM& vm, Value value, Optional<StringView> const& generator_brand)
ThrowCompletionOr<GeneratorObject::IterationResult> GeneratorObject::resume(VM& vm, Value value, Optional<StringView> const& generator_brand)
{
// 1. Let state be ? GeneratorValidate(generator, generatorBrand).
auto state = TRY(validate(vm, generator_brand));
// 2. If state is completed, return CreateIterResultObject(undefined, true).
if (state == GeneratorState::Completed)
return create_iterator_result_object(vm, js_undefined(), true);
if (state == GeneratorState::Completed) {
return IterationResult(js_undefined(), true);
}
// 3. Assert: state is either suspendedStart or suspendedYield.
VERIFY(state == GeneratorState::SuspendedStart || state == GeneratorState::SuspendedYield);
@ -163,7 +165,7 @@ ThrowCompletionOr<Value> GeneratorObject::resume(VM& vm, Value value, Optional<S
}
// 27.5.3.4 GeneratorResumeAbrupt ( generator, abruptCompletion, generatorBrand ), https://tc39.es/ecma262/#sec-generatorresumeabrupt
ThrowCompletionOr<Value> GeneratorObject::resume_abrupt(JS::VM& vm, JS::Completion abrupt_completion, Optional<StringView> const& generator_brand)
ThrowCompletionOr<GeneratorObject::IterationResult> GeneratorObject::resume_abrupt(JS::VM& vm, JS::Completion abrupt_completion, Optional<StringView> const& generator_brand)
{
// 1. Let state be ? GeneratorValidate(generator, generatorBrand).
auto state = TRY(validate(vm, generator_brand));
@ -185,7 +187,7 @@ ThrowCompletionOr<Value> GeneratorObject::resume_abrupt(JS::VM& vm, JS::Completi
// a. If abruptCompletion.[[Type]] is return, then
if (abrupt_completion.type() == Completion::Type::Return) {
// i. Return CreateIterResultObject(abruptCompletion.[[Value]], true).
return create_iterator_result_object(vm, abrupt_completion.value(), true);
return IterationResult(abrupt_completion.value(), true);
}
// b. Return ? abruptCompletion.