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

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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
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37
Userland/Libraries/LibJS/Runtime/Iterator.h
View file

@ -17,26 +17,47 @@
namespace JS {
// 7.4.1 Iterator Records, https://tc39.es/ecma262/#sec-iterator-records
struct IteratorRecord {
class IteratorRecord final : public Object {
JS_OBJECT(IteratorRecord, Object);
JS_DECLARE_ALLOCATOR(IteratorRecord);
public:
IteratorRecord(Realm& realm, GCPtr<Object> iterator, Value next_method, bool done)
: Object(ConstructWithoutPrototypeTag::Tag, realm)
, iterator(iterator)
, next_method(next_method)
, done(done)
{
}
GCPtr<Object> iterator; // [[Iterator]]
Value next_method; // [[NextMethod]]
bool done { false }; // [[Done]]
private:
virtual void visit_edges(Cell::Visitor&) override;
virtual bool is_iterator_record() const override { return true; }
};
template<>
inline bool Object::fast_is<IteratorRecord>() const { return is_iterator_record(); }
class Iterator : public Object {
JS_OBJECT(Iterator, Object);
JS_DECLARE_ALLOCATOR(Iterator);
public:
static NonnullGCPtr<Iterator> create(Realm&, Object& prototype, IteratorRecord iterated);
static NonnullGCPtr<Iterator> create(Realm&, Object& prototype, NonnullGCPtr<IteratorRecord> iterated);
IteratorRecord const& iterated() const { return m_iterated; }
private:
Iterator(Object& prototype, IteratorRecord iterated);
Iterator(Object& prototype, NonnullGCPtr<IteratorRecord> iterated);
explicit Iterator(Object& prototype);
IteratorRecord m_iterated; // [[Iterated]]
virtual void visit_edges(Cell::Visitor&) override;
NonnullGCPtr<IteratorRecord> m_iterated; // [[Iterated]]
};
enum class IteratorHint {
@ -49,10 +70,10 @@ enum class StringHandling {
RejectStrings,
};
ThrowCompletionOr<IteratorRecord> get_iterator_from_method(VM&, Value, NonnullGCPtr<FunctionObject>);
ThrowCompletionOr<IteratorRecord> get_iterator(VM&, Value, IteratorHint);
ThrowCompletionOr<IteratorRecord> get_iterator_direct(VM&, Object&);
ThrowCompletionOr<IteratorRecord> get_iterator_flattenable(VM&, Value, StringHandling);
ThrowCompletionOr<NonnullGCPtr<IteratorRecord>> get_iterator_from_method(VM&, Value, NonnullGCPtr<FunctionObject>);
ThrowCompletionOr<NonnullGCPtr<IteratorRecord>> get_iterator(VM&, Value, IteratorHint);
ThrowCompletionOr<NonnullGCPtr<IteratorRecord>> get_iterator_direct(VM&, Object&);
ThrowCompletionOr<NonnullGCPtr<IteratorRecord>> get_iterator_flattenable(VM&, Value, StringHandling);
ThrowCompletionOr<NonnullGCPtr<Object>> iterator_next(VM&, IteratorRecord const&, Optional<Value> = {});
ThrowCompletionOr<GCPtr<Object>> iterator_step(VM&, IteratorRecord const&);
ThrowCompletionOr<bool> iterator_complete(VM&, Object& iterator_result);