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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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7
Libraries/LibJS/Runtime/AsyncFunctionDriverWrapper.cpp
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@ -131,11 +131,8 @@ void AsyncFunctionDriverWrapper::continue_async_execution(VM& vm, Value value, b
return generator_result.throw_completion();
auto result = generator_result.release_value();
VERIFY(result.is_object());
auto promise_value = TRY(result.get(vm, vm.names.value));
if (TRY(result.get(vm, vm.names.done)).to_boolean()) {
auto promise_value = result.value;
if (result.done) {
// When returning a promise, we need to unwrap it.
if (promise_value.is_object() && is<Promise>(promise_value.as_object())) {
auto& returned_promise = static_cast<Promise&>(promise_value.as_object());