mirror of
https://github.com/RGBCube/serenity
synced 2025-10-31 16:32:45 +00:00
LibJS: Stop making shapes unique
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
parent
ef86cf4646
commit
3d92c26445
8 changed files with 63 additions and 214 deletions
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@ -83,10 +83,8 @@ ThrowCompletionOr<Value> get_by_id(VM& vm, DeprecatedFlyString const& property,
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auto base_obj = TRY(base_object_for_get(vm, base_value));
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// OPTIMIZATION: If the shape of the object hasn't changed, we can use the cached property offset.
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// NOTE: Unique shapes don't change identity, so we compare their serial numbers instead.
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auto& shape = base_obj->shape();
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if (&shape == cache.shape
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&& (!shape.is_unique() || shape.unique_shape_serial_number() == cache.unique_shape_serial_number)) {
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if (&shape == cache.shape) {
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return base_obj->get_direct(cache.property_offset.value());
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}
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@ -96,7 +94,6 @@ ThrowCompletionOr<Value> get_by_id(VM& vm, DeprecatedFlyString const& property,
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if (cacheable_metadata.type == CacheablePropertyMetadata::Type::OwnProperty) {
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cache.shape = shape;
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cache.property_offset = cacheable_metadata.property_offset.value();
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cache.unique_shape_serial_number = shape.unique_shape_serial_number();
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}
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return value;
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@ -176,11 +173,9 @@ ThrowCompletionOr<Value> get_global(Bytecode::Interpreter& interpreter, Deprecat
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auto& declarative_record = realm.global_environment().declarative_record();
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// OPTIMIZATION: If the shape of the object hasn't changed, we can use the cached property offset.
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// NOTE: Unique shapes don't change identity, so we compare their serial numbers instead.
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auto& shape = binding_object.shape();
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if (cache.environment_serial_number == declarative_record.environment_serial_number()
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&& &shape == cache.shape
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&& (!shape.is_unique() || shape.unique_shape_serial_number() == cache.unique_shape_serial_number)) {
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&& &shape == cache.shape) {
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return binding_object.get_direct(cache.property_offset.value());
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}
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@ -207,7 +202,6 @@ ThrowCompletionOr<Value> get_global(Bytecode::Interpreter& interpreter, Deprecat
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if (cacheable_metadata.type == CacheablePropertyMetadata::Type::OwnProperty) {
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cache.shape = shape;
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cache.property_offset = cacheable_metadata.property_offset.value();
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cache.unique_shape_serial_number = shape.unique_shape_serial_number();
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}
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return value;
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}
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@ -243,9 +237,7 @@ ThrowCompletionOr<void> put_by_property_key(VM& vm, Value base, Value this_value
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break;
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}
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case Op::PropertyKind::KeyValue: {
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if (cache
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&& cache->shape == &object->shape()
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&& (!object->shape().is_unique() || object->shape().unique_shape_serial_number() == cache->unique_shape_serial_number)) {
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if (cache && cache->shape == &object->shape()) {
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object->put_direct(*cache->property_offset, value);
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return {};
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}
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@ -256,7 +248,6 @@ ThrowCompletionOr<void> put_by_property_key(VM& vm, Value base, Value this_value
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if (succeeded && cache && cacheable_metadata.type == CacheablePropertyMetadata::Type::OwnProperty) {
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cache->shape = object->shape();
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cache->property_offset = cacheable_metadata.property_offset.value();
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cache->unique_shape_serial_number = object->shape().unique_shape_serial_number();
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}
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if (!succeeded && vm.in_strict_mode()) {
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@ -28,11 +28,9 @@ namespace JS::Bytecode {
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struct PropertyLookupCache {
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static FlatPtr shape_offset() { return OFFSET_OF(PropertyLookupCache, shape); }
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static FlatPtr property_offset_offset() { return OFFSET_OF(PropertyLookupCache, property_offset); }
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static FlatPtr unique_shape_serial_number_offset() { return OFFSET_OF(PropertyLookupCache, unique_shape_serial_number); }
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WeakPtr<Shape> shape;
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Optional<u32> property_offset;
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u64 unique_shape_serial_number { 0 };
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};
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struct GlobalVariableCache : public PropertyLookupCache {
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@ -1665,39 +1665,6 @@ void Compiler::compile_get_by_id(Bytecode::Op::GetById const& op)
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Assembler::Operand::Register(GPR1),
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slow_case);
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// (!object->shape().is_unique() || object->shape().unique_shape_serial_number() == cache.unique_shape_serial_number)) {
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Assembler::Label fast_case;
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// GPR1 = object->shape().is_unique()
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m_assembler.mov8(
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Assembler::Operand::Register(GPR1),
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Assembler::Operand::Mem64BaseAndOffset(GPR2, Shape::is_unique_offset()));
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m_assembler.jump_if(
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Assembler::Operand::Register(GPR1),
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Assembler::Condition::EqualTo,
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Assembler::Operand::Imm(0),
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fast_case);
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// GPR1 = object->shape().unique_shape_serial_number()
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m_assembler.mov(
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Assembler::Operand::Register(GPR1),
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Assembler::Operand::Mem64BaseAndOffset(GPR2, Shape::unique_shape_serial_number_offset()));
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// GPR2 = cache.unique_shape_serial_number
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m_assembler.mov(
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Assembler::Operand::Register(GPR2),
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Assembler::Operand::Mem64BaseAndOffset(ARG5, Bytecode::PropertyLookupCache::unique_shape_serial_number_offset()));
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// if (GPR1 != GPR2) goto slow_case;
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m_assembler.jump_if(
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Assembler::Operand::Register(GPR1),
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Assembler::Condition::NotEqualTo,
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Assembler::Operand::Register(GPR2),
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slow_case);
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fast_case.link(m_assembler);
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// return object->get_direct(*cache.property_offset);
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// GPR0 = object
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// GPR1 = *cache.property_offset * sizeof(Value)
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@ -1953,38 +1920,6 @@ void Compiler::compile_get_global(Bytecode::Op::GetGlobal const& op)
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Assembler::Operand::Register(GPR0),
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slow_case);
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Assembler::Label fast_case {};
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// GPR2 = shape->unique()
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m_assembler.mov8(
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Assembler::Operand::Register(GPR2),
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Assembler::Operand::Mem64BaseAndOffset(GPR0, Shape::is_unique_offset()));
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// if (!GPR2) goto fast_case;
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m_assembler.jump_if(
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Assembler::Operand::Register(GPR2),
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Assembler::Condition::EqualTo,
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Assembler::Operand::Imm(0),
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fast_case);
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// GPR2 = shape->unique_shape_serial_number()
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m_assembler.mov(
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Assembler::Operand::Register(GPR2),
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Assembler::Operand::Mem64BaseAndOffset(GPR0, Shape::unique_shape_serial_number_offset()));
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// GPR0 = cache.unique_shape_serial_number
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m_assembler.mov(
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Assembler::Operand::Register(GPR0),
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Assembler::Operand::Mem64BaseAndOffset(ARG2, Bytecode::PropertyLookupCache::unique_shape_serial_number_offset()));
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// if (GPR2 != GPR0) goto slow_case;
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m_assembler.jump_if(
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Assembler::Operand::Register(GPR2),
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Assembler::Condition::NotEqualTo,
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Assembler::Operand::Register(GPR0),
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slow_case);
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fast_case.link(m_assembler);
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// accumulator = GPR1->get_direct(*cache.property_offset);
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// GPR0 = GPR1
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// GPR1 = *cache.property_offset * sizeof(Value)
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@ -2295,39 +2230,6 @@ void Compiler::compile_put_by_id(Bytecode::Op::PutById const& op)
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Assembler::Operand::Register(GPR1),
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slow_case);
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// (!object->shape().is_unique() || object->shape().unique_shape_serial_number() == cache.unique_shape_serial_number)) {
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Assembler::Label fast_case;
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// GPR1 = object->shape().is_unique()
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m_assembler.mov8(
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Assembler::Operand::Register(GPR1),
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Assembler::Operand::Mem64BaseAndOffset(GPR2, Shape::is_unique_offset()));
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m_assembler.jump_if(
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Assembler::Operand::Register(GPR1),
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Assembler::Condition::EqualTo,
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Assembler::Operand::Imm(0),
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fast_case);
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// GPR1 = object->shape().unique_shape_serial_number()
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m_assembler.mov(
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Assembler::Operand::Register(GPR1),
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Assembler::Operand::Mem64BaseAndOffset(GPR2, Shape::unique_shape_serial_number_offset()));
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// GPR2 = cache.unique_shape_serial_number
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m_assembler.mov(
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Assembler::Operand::Register(GPR2),
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Assembler::Operand::Mem64BaseAndOffset(ARG5, Bytecode::PropertyLookupCache::unique_shape_serial_number_offset()));
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// if (GPR1 != GPR2) goto slow_case;
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m_assembler.jump_if(
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Assembler::Operand::Register(GPR1),
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Assembler::Condition::NotEqualTo,
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Assembler::Operand::Register(GPR2),
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slow_case);
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fast_case.link(m_assembler);
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// object->put_direct(*cache.property_offset, value);
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// GPR0 = object
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// GPR1 = *cache.property_offset * sizeof(Value)
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@ -92,7 +92,6 @@ JS_DEFINE_ALLOCATOR(GlobalObject);
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GlobalObject::GlobalObject(Realm& realm)
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: Object(GlobalObjectTag::Tag, realm)
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{
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ensure_shape_is_unique();
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Object::set_prototype(realm.intrinsics().object_prototype());
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}
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@ -1158,26 +1158,13 @@ void Object::storage_set(PropertyKey const& property_key, ValueAndAttributes con
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auto metadata = shape().lookup(property_key_string_or_symbol);
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if (!metadata.has_value()) {
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if (!m_shape->is_unique() && shape().property_count() > 100) {
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// If you add more than 100 properties to an object, let's stop doing
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// transitions to avoid filling up the heap with shapes.
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ensure_shape_is_unique();
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}
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if (m_shape->is_unique())
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m_shape->add_property_to_unique_shape(property_key_string_or_symbol, attributes);
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else
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set_shape(*m_shape->create_put_transition(property_key_string_or_symbol, attributes));
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set_shape(*m_shape->create_put_transition(property_key_string_or_symbol, attributes));
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m_storage.append(value);
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return;
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}
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if (attributes != metadata->attributes) {
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if (m_shape->is_unique())
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m_shape->reconfigure_property_in_unique_shape(property_key_string_or_symbol, attributes);
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else
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set_shape(*m_shape->create_configure_transition(property_key_string_or_symbol, attributes));
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set_shape(*m_shape->create_configure_transition(property_key_string_or_symbol, attributes));
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}
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m_storage[metadata->offset] = value;
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@ -1199,9 +1186,7 @@ void Object::storage_delete(PropertyKey const& property_key)
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auto metadata = shape().lookup(property_key.to_string_or_symbol());
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VERIFY(metadata.has_value());
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ensure_shape_is_unique();
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shape().remove_property_from_unique_shape(property_key.to_string_or_symbol(), metadata->offset);
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m_shape = m_shape->create_delete_transition(property_key.to_string_or_symbol());
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m_storage.remove(metadata->offset);
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}
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@ -1209,11 +1194,7 @@ void Object::set_prototype(Object* new_prototype)
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{
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if (prototype() == new_prototype)
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return;
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auto& shape = this->shape();
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if (shape.is_unique())
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shape.set_prototype_without_transition(new_prototype);
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else
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m_shape = shape.create_prototype_transition(new_prototype);
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m_shape = shape().create_prototype_transition(new_prototype);
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}
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void Object::define_native_accessor(Realm& realm, PropertyKey const& property_key, Function<ThrowCompletionOr<Value>(VM&)> getter, Function<ThrowCompletionOr<Value>(VM&)> setter, PropertyAttributes attribute)
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@ -1255,14 +1236,6 @@ void Object::define_intrinsic_accessor(PropertyKey const& property_key, Property
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intrinsics.set(property_key.as_string(), move(accessor));
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}
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void Object::ensure_shape_is_unique()
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{
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if (shape().is_unique())
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return;
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m_shape = m_shape->create_unique_clone();
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}
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// Simple side-effect free property lookup, following the prototype chain. Non-standard.
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Value Object::get_without_side_effects(PropertyKey const& property_key) const
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{
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@ -49,7 +49,6 @@ struct CacheablePropertyMetadata {
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};
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Type type { Type::NotCacheable };
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Optional<u32> property_offset;
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u64 unique_shape_serial_number { 0 };
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};
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class Object : public Cell {
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@ -215,8 +214,6 @@ public:
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static FlatPtr shape_offset() { return OFFSET_OF(Object, m_shape); }
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void ensure_shape_is_unique();
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template<typename T>
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bool fast_is() const = delete;
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@ -12,18 +12,6 @@ namespace JS {
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JS_DEFINE_ALLOCATOR(Shape);
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Shape* Shape::create_unique_clone() const
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{
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auto new_shape = heap().allocate_without_realm<Shape>(m_realm);
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new_shape->m_unique = true;
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new_shape->m_prototype = m_prototype;
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ensure_property_table();
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new_shape->ensure_property_table();
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(*new_shape->m_property_table) = *m_property_table;
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new_shape->m_property_count = new_shape->m_property_table->size();
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return new_shape;
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}
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Shape* Shape::get_or_prune_cached_forward_transition(TransitionKey const& key)
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{
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if (!m_forward_transitions)
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@ -39,6 +27,21 @@ Shape* Shape::get_or_prune_cached_forward_transition(TransitionKey const& key)
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return it->value;
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}
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GCPtr<Shape> Shape::get_or_prune_cached_delete_transition(StringOrSymbol const& key)
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{
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if (!m_delete_transitions)
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return nullptr;
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auto it = m_delete_transitions->find(key);
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if (it == m_delete_transitions->end())
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return nullptr;
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if (!it->value) {
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// The cached delete transition has gone stale (from garbage collection). Prune it.
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m_delete_transitions->remove(it);
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return nullptr;
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}
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return it->value.ptr();
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}
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Shape* Shape::get_or_prune_cached_prototype_transition(Object* prototype)
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{
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if (!m_prototype_transitions)
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@ -105,6 +108,17 @@ Shape::Shape(Shape& previous_shape, StringOrSymbol const& property_key, Property
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{
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}
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Shape::Shape(Shape& previous_shape, StringOrSymbol const& property_key, TransitionType transition_type)
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: m_realm(previous_shape.m_realm)
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, m_previous(&previous_shape)
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, m_property_key(property_key)
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, m_prototype(previous_shape.m_prototype)
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, m_property_count(previous_shape.m_property_count - 1)
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, m_transition_type(transition_type)
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{
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VERIFY(transition_type == TransitionType::Delete);
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}
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Shape::Shape(Shape& previous_shape, Object* new_prototype)
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: m_realm(previous_shape.m_realm)
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, m_previous(&previous_shape)
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@ -132,6 +146,12 @@ void Shape::visit_edges(Cell::Visitor& visitor)
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for (auto& it : *m_forward_transitions)
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it.key.property_key.visit_edges(visitor);
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}
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// FIXME: The delete transition keys should be weak, but we have to mark them for now in case they go stale.
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if (m_delete_transitions) {
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for (auto& it : *m_delete_transitions)
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it.key.visit_edges(visitor);
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}
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}
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Optional<PropertyMetadata> Shape::lookup(StringOrSymbol const& property_key) const
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@ -159,6 +179,7 @@ void Shape::ensure_property_table() const
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u32 next_offset = 0;
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Vector<Shape const&, 64> transition_chain;
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transition_chain.append(*this);
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for (auto shape = m_previous; shape; shape = shape->m_previous) {
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if (shape->m_property_table) {
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*m_property_table = *shape->m_property_table;
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@ -167,7 +188,6 @@ void Shape::ensure_property_table() const
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}
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transition_chain.append(*shape);
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}
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transition_chain.append(*this);
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for (auto const& shape : transition_chain.in_reverse()) {
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if (!shape.m_property_key.is_valid()) {
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@ -180,48 +200,29 @@ void Shape::ensure_property_table() const
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auto it = m_property_table->find(shape.m_property_key);
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VERIFY(it != m_property_table->end());
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it->value.attributes = shape.m_attributes;
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} else if (shape.m_transition_type == TransitionType::Delete) {
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auto remove_it = m_property_table->find(shape.m_property_key);
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VERIFY(remove_it != m_property_table->end());
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auto removed_offset = remove_it->value.offset;
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m_property_table->remove(remove_it);
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for (auto& it : *m_property_table) {
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if (it.value.offset > removed_offset)
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--it.value.offset;
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}
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--next_offset;
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}
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}
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}
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void Shape::add_property_to_unique_shape(StringOrSymbol const& property_key, PropertyAttributes attributes)
|
||||
NonnullGCPtr<Shape> Shape::create_delete_transition(StringOrSymbol const& property_key)
|
||||
{
|
||||
VERIFY(is_unique());
|
||||
VERIFY(m_property_table);
|
||||
VERIFY(!m_property_table->contains(property_key));
|
||||
m_property_table->set(property_key, { static_cast<u32>(m_property_table->size()), attributes });
|
||||
|
||||
VERIFY(m_property_count < NumericLimits<u32>::max());
|
||||
++m_property_count;
|
||||
|
||||
++m_unique_shape_serial_number;
|
||||
}
|
||||
|
||||
void Shape::reconfigure_property_in_unique_shape(StringOrSymbol const& property_key, PropertyAttributes attributes)
|
||||
{
|
||||
VERIFY(is_unique());
|
||||
VERIFY(m_property_table);
|
||||
auto it = m_property_table->find(property_key);
|
||||
VERIFY(it != m_property_table->end());
|
||||
it->value.attributes = attributes;
|
||||
m_property_table->set(property_key, it->value);
|
||||
|
||||
++m_unique_shape_serial_number;
|
||||
}
|
||||
|
||||
void Shape::remove_property_from_unique_shape(StringOrSymbol const& property_key, size_t offset)
|
||||
{
|
||||
VERIFY(is_unique());
|
||||
VERIFY(m_property_table);
|
||||
if (m_property_table->remove(property_key))
|
||||
--m_property_count;
|
||||
for (auto& it : *m_property_table) {
|
||||
VERIFY(it.value.offset != offset);
|
||||
if (it.value.offset > offset)
|
||||
--it.value.offset;
|
||||
}
|
||||
|
||||
++m_unique_shape_serial_number;
|
||||
if (auto existing_shape = get_or_prune_cached_delete_transition(property_key))
|
||||
return *existing_shape;
|
||||
auto new_shape = heap().allocate_without_realm<Shape>(*this, property_key, TransitionType::Delete);
|
||||
if (!m_delete_transitions)
|
||||
m_delete_transitions = make<HashMap<StringOrSymbol, WeakPtr<Shape>>>();
|
||||
m_delete_transitions->set(property_key, new_shape.ptr());
|
||||
return new_shape;
|
||||
}
|
||||
|
||||
void Shape::add_property_without_transition(StringOrSymbol const& property_key, PropertyAttributes attributes)
|
||||
|
|
|
|||
|
|
@ -48,20 +48,17 @@ public:
|
|||
Put,
|
||||
Configure,
|
||||
Prototype,
|
||||
Delete,
|
||||
};
|
||||
|
||||
Shape* create_put_transition(StringOrSymbol const&, PropertyAttributes attributes);
|
||||
Shape* create_configure_transition(StringOrSymbol const&, PropertyAttributes attributes);
|
||||
Shape* create_prototype_transition(Object* new_prototype);
|
||||
[[nodiscard]] NonnullGCPtr<Shape> create_delete_transition(StringOrSymbol const&);
|
||||
|
||||
void add_property_without_transition(StringOrSymbol const&, PropertyAttributes);
|
||||
void add_property_without_transition(PropertyKey const&, PropertyAttributes);
|
||||
|
||||
bool is_unique() const { return m_unique; }
|
||||
static FlatPtr is_unique_offset() { return OFFSET_OF(Shape, m_unique); }
|
||||
|
||||
Shape* create_unique_clone() const;
|
||||
|
||||
Realm& realm() const { return m_realm; }
|
||||
|
||||
Object* prototype() { return m_prototype; }
|
||||
|
|
@ -78,22 +75,17 @@ public:
|
|||
|
||||
void set_prototype_without_transition(Object* new_prototype) { m_prototype = new_prototype; }
|
||||
|
||||
void remove_property_from_unique_shape(StringOrSymbol const&, size_t offset);
|
||||
void add_property_to_unique_shape(StringOrSymbol const&, PropertyAttributes attributes);
|
||||
void reconfigure_property_in_unique_shape(StringOrSymbol const& property_key, PropertyAttributes attributes);
|
||||
|
||||
[[nodiscard]] u64 unique_shape_serial_number() const { return m_unique_shape_serial_number; }
|
||||
static FlatPtr unique_shape_serial_number_offset() { return OFFSET_OF(Shape, m_unique_shape_serial_number); }
|
||||
|
||||
private:
|
||||
explicit Shape(Realm&);
|
||||
Shape(Shape& previous_shape, StringOrSymbol const& property_key, PropertyAttributes attributes, TransitionType);
|
||||
Shape(Shape& previous_shape, StringOrSymbol const& property_key, TransitionType);
|
||||
Shape(Shape& previous_shape, Object* new_prototype);
|
||||
|
||||
virtual void visit_edges(Visitor&) override;
|
||||
|
||||
Shape* get_or_prune_cached_forward_transition(TransitionKey const&);
|
||||
Shape* get_or_prune_cached_prototype_transition(Object* prototype);
|
||||
[[nodiscard]] GCPtr<Shape> get_or_prune_cached_delete_transition(StringOrSymbol const&);
|
||||
|
||||
void ensure_property_table() const;
|
||||
|
||||
|
|
@ -103,6 +95,7 @@ private:
|
|||
|
||||
OwnPtr<HashMap<TransitionKey, WeakPtr<Shape>>> m_forward_transitions;
|
||||
OwnPtr<HashMap<GCPtr<Object>, WeakPtr<Shape>>> m_prototype_transitions;
|
||||
OwnPtr<HashMap<StringOrSymbol, WeakPtr<Shape>>> m_delete_transitions;
|
||||
GCPtr<Shape> m_previous;
|
||||
StringOrSymbol m_property_key;
|
||||
GCPtr<Object> m_prototype;
|
||||
|
|
@ -110,11 +103,6 @@ private:
|
|||
|
||||
PropertyAttributes m_attributes { 0 };
|
||||
TransitionType m_transition_type { TransitionType::Invalid };
|
||||
bool m_unique { false };
|
||||
|
||||
// Since unique shapes never change identity, inline caches use this incrementing serial number
|
||||
// to know whether its property table has been modified since last time we checked.
|
||||
u64 m_unique_shape_serial_number { 0 };
|
||||
};
|
||||
|
||||
}
|
||||
|
|
|
|||
Loading…
Add table
Add a link
Reference in a new issue