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LibJS: Stop converting between Object <-> IteratorRecord all the time

This patch makes IteratorRecord an Object. Although it's not exposed to
author code, this does allow us to store it in a VM register.

Now that we can store it in a VM register, we don't need to convert it
back and forth between IteratorRecord and Object when accessing it from
bytecode.

The big win here is avoiding 3 [[Get]] accesses on every iteration step
of for..of loops. There are also a bunch of smaller efficiencies gained.

20% speed-up on this microbenchmark:

    function go(a) {
        for (const p of a) {
        }
    }
    const a = [];
    a.length = 1_000_000;
    go(a);
This commit is contained in:
Andreas Kling 2023-12-07 10:44:41 +01:00
parent 4966c083df
commit 4699c81fc1
23 changed files with 226 additions and 144 deletions

View file

@ -70,12 +70,12 @@ JS_DEFINE_NATIVE_FUNCTION(IteratorConstructor::from)
auto iterator_record = TRY(get_iterator_flattenable(vm, object, StringHandling::IterateStrings));
// 2. Let hasInstance be ? OrdinaryHasInstance(%Iterator%, iteratorRecord.[[Iterator]]).
auto has_instance = TRY(ordinary_has_instance(vm, iterator_record.iterator, realm.intrinsics().iterator_constructor()));
auto has_instance = TRY(ordinary_has_instance(vm, iterator_record->iterator, realm.intrinsics().iterator_constructor()));
// 3. If hasInstance is true, then
if (has_instance.is_boolean() && has_instance.as_bool()) {
// a. Return iteratorRecord.[[Iterator]].
return iterator_record.iterator;
return iterator_record->iterator;
}
// 4. Let wrapper be OrdinaryObjectCreate(%WrapForValidIteratorPrototype%, « [[Iterated]] »).