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LibJS: Remove transition avoidance & start caching prototype transitions

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The way that transition avoidance (foo_without_transition) was
implemented led to shapes being unshareable and caused shape explosion
instead, precisely what we were trying to avoid.

This patch removes all the attempts to avoid transitioning shapes, and
instead *adds* transitions when changing an object's prototype.
This makes transitions flow naturally, and as a result we end up with
way fewer shape objects in real-world situations.

When we run out of big problems, we can get back to avoiding transitions
as an optimization, but for now, let's avoid ballooning our processes
with a unique shape for every object.
This commit is contained in:
Andreas Kling 2021-10-01 02:43:57 +02:00
parent 46686f7f94
commit 14c57b4b7f
7 changed files with 35 additions and 67 deletions
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16
Userland/Libraries/LibJS/Runtime/GlobalObject.cpp
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@ -139,10 +139,8 @@ void GlobalObject::initialize_global_object()
// Normally Heap::allocate() takes care of this, but these are allocated via allocate_without_global_object().
static_cast<FunctionPrototype*>(m_function_prototype)->initialize(*this);
m_function_prototype->set_initialized(Badge<GlobalObject> {});
static_cast<ObjectPrototype*>(m_object_prototype)->initialize(*this);
m_object_prototype->set_initialized(Badge<GlobalObject> {});
auto success = Object::internal_set_prototype_of(m_object_prototype).release_value();
VERIFY(success);
@ -159,7 +157,7 @@ void GlobalObject::initialize_global_object()
// %GeneratorFunction.prototype.prototype% must be initialized separately as it has no
// companion constructor
m_generator_object_prototype = heap().allocate<GeneratorObjectPrototype>(*this, *this);
m_generator_object_prototype->define_direct_property_without_transition(vm.names.constructor, m_generator_function_constructor, Attribute::Configurable);
m_generator_object_prototype->define_direct_property(vm.names.constructor, m_generator_function_constructor, Attribute::Configurable);
#define __JS_ENUMERATE(ClassName, snake_name, PrototypeName, ConstructorName, ArrayType) \
if (!m_##snake_name##_prototype) \
@ -204,13 +202,13 @@ void GlobalObject::initialize_global_object()
vm.throw_exception<TypeError>(global_object, ErrorType::RestrictedFunctionPropertiesAccess);
return Value();
});
m_throw_type_error_function->define_direct_property_without_transition(vm.names.length, Value(0), 0);
m_throw_type_error_function->define_direct_property_without_transition(vm.names.name, js_string(vm, ""), 0);
m_throw_type_error_function->define_direct_property(vm.names.length, Value(0), 0);
m_throw_type_error_function->define_direct_property(vm.names.name, js_string(vm, ""), 0);
(void)m_throw_type_error_function->internal_prevent_extensions();
// 10.2.4 AddRestrictedFunctionProperties ( F, realm ), https://tc39.es/ecma262/#sec-addrestrictedfunctionproperties
m_function_prototype->define_direct_accessor_without_transition(vm.names.caller, m_throw_type_error_function, m_throw_type_error_function, Attribute::Configurable);
m_function_prototype->define_direct_accessor_without_transition(vm.names.arguments, m_throw_type_error_function, m_throw_type_error_function, Attribute::Configurable);
m_function_prototype->define_direct_accessor(vm.names.caller, m_throw_type_error_function, m_throw_type_error_function, Attribute::Configurable);
m_function_prototype->define_direct_accessor(vm.names.arguments, m_throw_type_error_function, m_throw_type_error_function, Attribute::Configurable);
define_native_function(vm.names.encodeURI, encode_uri, 1, attr);
define_native_function(vm.names.decodeURI, decode_uri, 1, attr);
@ -269,13 +267,11 @@ void GlobalObject::initialize_global_object()
// The generator constructor cannot be initialized with add_constructor as it has no global binding
m_generator_function_constructor = heap().allocate<GeneratorFunctionConstructor>(*this, *this);
// 27.3.3.1 GeneratorFunction.prototype.constructor, https://tc39.es/ecma262/#sec-generatorfunction.prototype.constructor
m_generator_function_prototype->define_direct_property_without_transition(vm.names.constructor, m_generator_function_constructor, Attribute::Configurable);
m_generator_function_prototype->define_direct_property(vm.names.constructor, m_generator_function_constructor, Attribute::Configurable);
m_array_prototype_values_function = &m_array_prototype->get_without_side_effects(vm.names.values).as_function();
m_eval_function = &get_without_side_effects(vm.names.eval).as_function();
m_temporal_time_zone_prototype_get_offset_nanoseconds_for_function = &m_temporal_time_zone_prototype->get_without_side_effects(vm.names.getOffsetNanosecondsFor).as_function();
set_initialized(Badge<GlobalObject> {});
}
GlobalObject::~GlobalObject()