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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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6
Userland/Libraries/LibJS/Runtime/IteratorHelper.h
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@ -22,7 +22,7 @@ public:
using Closure = JS::SafeFunction<ThrowCompletionOr<Value>(VM&, IteratorHelper&)>;
using AbruptClosure = JS::SafeFunction<ThrowCompletionOr<Value>(VM&, IteratorHelper&, Completion const&)>;
static ThrowCompletionOr<NonnullGCPtr<IteratorHelper>> create(Realm&, IteratorRecord, Closure, Optional<AbruptClosure> = {});
static ThrowCompletionOr<NonnullGCPtr<IteratorHelper>> create(Realm&, NonnullGCPtr<IteratorRecord>, Closure, Optional<AbruptClosure> = {});
IteratorRecord const& underlying_iterator() const { return m_underlying_iterator; }
@ -33,12 +33,12 @@ public:
ThrowCompletionOr<Value> close_result(VM&, Completion);
private:
IteratorHelper(Realm&, Object& prototype, IteratorRecord, Closure, Optional<AbruptClosure>);
IteratorHelper(Realm&, Object& prototype, NonnullGCPtr<IteratorRecord>, Closure, Optional<AbruptClosure>);
virtual void visit_edges(Visitor&) override;
virtual ThrowCompletionOr<Value> execute(VM&, JS::Completion const& completion) override;
IteratorRecord m_underlying_iterator; // [[UnderlyingIterator]]
NonnullGCPtr<IteratorRecord> m_underlying_iterator; // [[UnderlyingIterator]]
Closure m_closure;
Optional<AbruptClosure> m_abrupt_closure;