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https://github.com/RGBCube/serenity
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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);
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parent
4966c083df
commit
4699c81fc1
23 changed files with 226 additions and 144 deletions
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@ -17,25 +17,26 @@
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namespace JS {
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JS_DEFINE_ALLOCATOR(Iterator);
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JS_DEFINE_ALLOCATOR(IteratorRecord);
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NonnullGCPtr<Iterator> Iterator::create(Realm& realm, Object& prototype, IteratorRecord iterated)
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NonnullGCPtr<Iterator> Iterator::create(Realm& realm, Object& prototype, NonnullGCPtr<IteratorRecord> iterated)
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{
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return realm.heap().allocate<Iterator>(realm, prototype, move(iterated));
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}
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Iterator::Iterator(Object& prototype, IteratorRecord iterated)
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Iterator::Iterator(Object& prototype, NonnullGCPtr<IteratorRecord> iterated)
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: Object(ConstructWithPrototypeTag::Tag, prototype)
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, m_iterated(move(iterated))
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{
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}
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Iterator::Iterator(Object& prototype)
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: Iterator(prototype, {})
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: Iterator(prototype, prototype.heap().allocate<IteratorRecord>(prototype.shape().realm(), prototype.shape().realm(), nullptr, js_undefined(), false))
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{
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}
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// 7.4.2 GetIteratorFromMethod ( obj, method ), https://tc39.es/ecma262/#sec-getiteratorfrommethod
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ThrowCompletionOr<IteratorRecord> get_iterator_from_method(VM& vm, Value object, NonnullGCPtr<FunctionObject> method)
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ThrowCompletionOr<NonnullGCPtr<IteratorRecord>> get_iterator_from_method(VM& vm, Value object, NonnullGCPtr<FunctionObject> method)
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{
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// 1. Let iterator be ? Call(method, obj).
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auto iterator = TRY(call(vm, *method, object));
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@ -48,14 +49,15 @@ ThrowCompletionOr<IteratorRecord> get_iterator_from_method(VM& vm, Value object,
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auto next_method = TRY(iterator.get(vm, vm.names.next));
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// 4. Let iteratorRecord be the Iterator Record { [[Iterator]]: iterator, [[NextMethod]]: nextMethod, [[Done]]: false }.
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auto iterator_record = IteratorRecord { .iterator = &iterator.as_object(), .next_method = next_method, .done = false };
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auto& realm = *vm.current_realm();
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auto iterator_record = vm.heap().allocate<IteratorRecord>(realm, realm, iterator.as_object(), next_method, false);
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// 5. Return iteratorRecord.
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return iterator_record;
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}
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// 7.4.3 GetIterator ( obj, kind ), https://tc39.es/ecma262/#sec-getiterator
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ThrowCompletionOr<IteratorRecord> get_iterator(VM& vm, Value object, IteratorHint kind)
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ThrowCompletionOr<NonnullGCPtr<IteratorRecord>> get_iterator(VM& vm, Value object, IteratorHint kind)
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{
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JS::GCPtr<FunctionObject> method;
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@ -95,20 +97,19 @@ ThrowCompletionOr<IteratorRecord> get_iterator(VM& vm, Value object, IteratorHin
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}
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// 2.1.1 GetIteratorDirect ( obj ), https://tc39.es/proposal-iterator-helpers/#sec-getiteratorflattenable
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ThrowCompletionOr<IteratorRecord> get_iterator_direct(VM& vm, Object& object)
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ThrowCompletionOr<NonnullGCPtr<IteratorRecord>> get_iterator_direct(VM& vm, Object& object)
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{
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// 1. Let nextMethod be ? Get(obj, "next").
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auto next_method = TRY(object.get(vm.names.next));
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// 2. Let iteratorRecord be Record { [[Iterator]]: obj, [[NextMethod]]: nextMethod, [[Done]]: false }.
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IteratorRecord iterator_record { .iterator = object, .next_method = next_method, .done = false };
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// 3. Return iteratorRecord.
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return iterator_record;
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auto& realm = *vm.current_realm();
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return vm.heap().allocate<IteratorRecord>(realm, realm, object, next_method, false);
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}
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// 2.1.2 GetIteratorFlattenable ( obj, stringHandling ), https://tc39.es/proposal-iterator-helpers/#sec-getiteratorflattenable
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ThrowCompletionOr<IteratorRecord> get_iterator_flattenable(VM& vm, Value object, StringHandling string_handling)
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ThrowCompletionOr<NonnullGCPtr<IteratorRecord>> get_iterator_flattenable(VM& vm, Value object, StringHandling string_handling)
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{
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// 1. If obj is not an Object, then
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if (!object.is_object()) {
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@ -320,4 +321,17 @@ Completion get_iterator_values(VM& vm, Value iterable, IteratorValueCallback cal
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}
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}
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void Iterator::visit_edges(Cell::Visitor& visitor)
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{
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Base::visit_edges(visitor);
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visitor.visit(m_iterated);
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}
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void IteratorRecord::visit_edges(Cell::Visitor& visitor)
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{
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Base::visit_edges(visitor);
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visitor.visit(iterator);
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visitor.visit(next_method);
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}
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}
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