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LibJS: Stop making shapes unique

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We previously had a concept of unique shapes, which meant that they
couldn't be shared between multiple objects.

Object shapes became unique in three situations:

- They were the shape of the global object.
- They had more than 100 properties added to them.
- They had one or more properties deleted from them.

Unfortunately, unique shapes presented an annoying problem for inline
caches, and we added a "unique shape serial number" for being able to
tell that a unique shape had been mutated.

This patch gets rid of the concept of unique shapes, simplifying all
the caching code, since inline caches can now simply perform a shape
check and then we're good.

To make this possible, we now have the concept of delete transitions,
which occur when a property is deleted from a shape.

Note that this patch by itself introduces a performance regression in
some situtations, since we now create a lot more shapes, and marking
their property keys can be very heavy. This will be addressed in a
subsequent patch.
This commit is contained in:
Andreas Kling 2023-12-11 14:29:40 +01:00
parent ef86cf4646
commit 3d92c26445
Notes: sideshowbarker 2024-07-17 03:03:37 +09:00
8 changed files with 63 additions and 214 deletions
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15
Userland/Libraries/LibJS/Bytecode/CommonImplementations.cpp
View file

@ -83,10 +83,8 @@ ThrowCompletionOr<Value> get_by_id(VM& vm, DeprecatedFlyString const& property,
auto base_obj = TRY(base_object_for_get(vm, base_value));
// OPTIMIZATION: If the shape of the object hasn't changed, we can use the cached property offset.
// NOTE: Unique shapes don't change identity, so we compare their serial numbers instead.
auto& shape = base_obj->shape();
if (&shape == cache.shape
&& (!shape.is_unique() || shape.unique_shape_serial_number() == cache.unique_shape_serial_number)) {
if (&shape == cache.shape) {
return base_obj->get_direct(cache.property_offset.value());
}
@ -96,7 +94,6 @@ ThrowCompletionOr<Value> get_by_id(VM& vm, DeprecatedFlyString const& property,
if (cacheable_metadata.type == CacheablePropertyMetadata::Type::OwnProperty) {
cache.shape = shape;
cache.property_offset = cacheable_metadata.property_offset.value();
cache.unique_shape_serial_number = shape.unique_shape_serial_number();
}
return value;
@ -176,11 +173,9 @@ ThrowCompletionOr<Value> get_global(Bytecode::Interpreter& interpreter, Deprecat
auto& declarative_record = realm.global_environment().declarative_record();
// OPTIMIZATION: If the shape of the object hasn't changed, we can use the cached property offset.
// NOTE: Unique shapes don't change identity, so we compare their serial numbers instead.
auto& shape = binding_object.shape();
if (cache.environment_serial_number == declarative_record.environment_serial_number()
&& &shape == cache.shape
&& (!shape.is_unique() || shape.unique_shape_serial_number() == cache.unique_shape_serial_number)) {
&& &shape == cache.shape) {
return binding_object.get_direct(cache.property_offset.value());
}
@ -207,7 +202,6 @@ ThrowCompletionOr<Value> get_global(Bytecode::Interpreter& interpreter, Deprecat
if (cacheable_metadata.type == CacheablePropertyMetadata::Type::OwnProperty) {
cache.shape = shape;
cache.property_offset = cacheable_metadata.property_offset.value();
cache.unique_shape_serial_number = shape.unique_shape_serial_number();
}
return value;
}
@ -243,9 +237,7 @@ ThrowCompletionOr<void> put_by_property_key(VM& vm, Value base, Value this_value
break;
}
case Op::PropertyKind::KeyValue: {
if (cache
&& cache->shape == &object->shape()
&& (!object->shape().is_unique() || object->shape().unique_shape_serial_number() == cache->unique_shape_serial_number)) {
if (cache && cache->shape == &object->shape()) {
object->put_direct(*cache->property_offset, value);
return {};
}
@ -256,7 +248,6 @@ ThrowCompletionOr<void> put_by_property_key(VM& vm, Value base, Value this_value
if (succeeded && cache && cacheable_metadata.type == CacheablePropertyMetadata::Type::OwnProperty) {
cache->shape = object->shape();
cache->property_offset = cacheable_metadata.property_offset.value();
cache->unique_shape_serial_number = object->shape().unique_shape_serial_number();
}
if (!succeeded && vm.in_strict_mode()) {