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LibJS: Make GetById cache polymorphic

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Instead of monomorphic (1 shape), GetById inline caches are now
polymorphic (4 shapes).

This improves inline cache hit rates greatly on most web JavaScript.
For example, Speedometer 2.1 sees 88% -> 97% cache hit rate improvement.

1.71x speedup on MicroBench/pic-get-own.js
1.82x speedup on MicroBench/pic-get-pchain.js
This commit is contained in:
Andreas Kling 2025-05-06 13:16:44 +02:00 • committed by Andreas Kling
parent 678c15a06a
commit a677d96b8f
Notes: github-actions[bot] 2025-05-06 22:28:14 +00:00
2 changed files with 59 additions and 43 deletions
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13
Libraries/LibJS/Bytecode/Executable.h
View file

@ -23,11 +23,16 @@
namespace JS::Bytecode { namespace JS::Bytecode {
// Represents one polymorphic inline cache used for property lookups.
struct PropertyLookupCache { struct PropertyLookupCache {
WeakPtr<Shape> shape; static constexpr size_t max_number_of_shapes_to_remember = 4;
Optional<u32> property_offset; struct Entry {
WeakPtr<Object> prototype; WeakPtr<Shape> shape;
WeakPtr<PrototypeChainValidity> prototype_chain_validity; Optional<u32> property_offset;
WeakPtr<Object> prototype;
WeakPtr<PrototypeChainValidity> prototype_chain_validity;
};
AK::Array<Entry, max_number_of_shapes_to_remember> entries;
}; };
struct GlobalVariableCache : public PropertyLookupCache { struct GlobalVariableCache : public PropertyLookupCache {

89
Libraries/LibJS/Bytecode/Interpreter.cpp
View file

@ -998,44 +998,53 @@ inline ThrowCompletionOr<Value> get_by_id(VM& vm, Optional<IdentifierTableIndex>
auto& shape = base_obj->shape(); auto& shape = base_obj->shape();
if (cache.prototype) { for (auto& cache_entry : cache.entries) {
// OPTIMIZATION: If the prototype chain hasn't been mutated in a way that would invalidate the cache, we can use it. if (cache_entry.prototype) {
bool can_use_cache = [&]() -> bool { // OPTIMIZATION: If the prototype chain hasn't been mutated in a way that would invalidate the cache, we can use it.
if (&shape != cache.shape) bool can_use_cache = [&]() -> bool {
return false; if (&shape != cache_entry.shape)
if (!cache.prototype_chain_validity) return false;
return false; if (!cache_entry.prototype_chain_validity)
if (!cache.prototype_chain_validity->is_valid()) return false;
return false; if (!cache_entry.prototype_chain_validity->is_valid())
return true; return false;
}(); return true;
if (can_use_cache) { }();
auto value = cache.prototype->get_direct(cache.property_offset.value()); if (can_use_cache) {
auto value = cache_entry.prototype->get_direct(cache_entry.property_offset.value());
if (value.is_accessor())
return TRY(call(vm, value.as_accessor().getter(), this_value));
return value;
}
} else if (&shape == cache_entry.shape) {
// OPTIMIZATION: If the shape of the object hasn't changed, we can use the cached property offset.
auto value = base_obj->get_direct(cache_entry.property_offset.value());
if (value.is_accessor()) if (value.is_accessor())
return TRY(call(vm, value.as_accessor().getter(), this_value)); return TRY(call(vm, value.as_accessor().getter(), this_value));
return value; return value;
} }
} else if (&shape == cache.shape) {
// OPTIMIZATION: If the shape of the object hasn't changed, we can use the cached property offset.
auto value = base_obj->get_direct(cache.property_offset.value());
if (value.is_accessor())
return TRY(call(vm, value.as_accessor().getter(), this_value));
return value;
} }
CacheablePropertyMetadata cacheable_metadata; CacheablePropertyMetadata cacheable_metadata;
auto value = TRY(base_obj->internal_get(executable.get_identifier(property), this_value, &cacheable_metadata)); auto value = TRY(base_obj->internal_get(executable.get_identifier(property), this_value, &cacheable_metadata));
auto get_cache_slot = [&] -> PropertyLookupCache::Entry& {
for (size_t i = cache.entries.size() - 1; i >= 1; --i) {
cache.entries[i] = cache.entries[i - 1];
}
cache.entries[0] = {};
return cache.entries[0];
};
if (cacheable_metadata.type == CacheablePropertyMetadata::Type::OwnProperty) { if (cacheable_metadata.type == CacheablePropertyMetadata::Type::OwnProperty) {
cache = {}; auto& entry = get_cache_slot();
cache.shape = shape; entry.shape = shape;
cache.property_offset = cacheable_metadata.property_offset.value(); entry.property_offset = cacheable_metadata.property_offset.value();
} else if (cacheable_metadata.type == CacheablePropertyMetadata::Type::InPrototypeChain) { } else if (cacheable_metadata.type == CacheablePropertyMetadata::Type::InPrototypeChain) {
cache = {}; auto& entry = get_cache_slot();
cache.shape = &base_obj->shape(); entry.shape = &base_obj->shape();
cache.property_offset = cacheable_metadata.property_offset.value(); entry.property_offset = cacheable_metadata.property_offset.value();
cache.prototype = *cacheable_metadata.prototype; entry.prototype = *cacheable_metadata.prototype;
cache.prototype_chain_validity = *cacheable_metadata.prototype->shape().prototype_chain_validity(); entry.prototype_chain_validity = *cacheable_metadata.prototype->shape().prototype_chain_validity();
} }
return value; return value;
@ -1133,8 +1142,8 @@ inline ThrowCompletionOr<Value> get_global(Interpreter& interpreter, IdentifierT
// OPTIMIZATION: For global var bindings, if the shape of the global object hasn't changed, // OPTIMIZATION: For global var bindings, if the shape of the global object hasn't changed,
// we can use the cached property offset. // we can use the cached property offset.
if (&shape == cache.shape) { if (&shape == cache.entries[0].shape) {
auto value = binding_object.get_direct(cache.property_offset.value()); auto value = binding_object.get_direct(cache.entries[0].property_offset.value());
if (value.is_accessor()) if (value.is_accessor())
return TRY(call(vm, value.as_accessor().getter(), js_undefined())); return TRY(call(vm, value.as_accessor().getter(), js_undefined()));
return value; return value;
@ -1183,8 +1192,8 @@ inline ThrowCompletionOr<Value> get_global(Interpreter& interpreter, IdentifierT
CacheablePropertyMetadata cacheable_metadata; CacheablePropertyMetadata cacheable_metadata;
auto value = TRY(binding_object.internal_get(identifier, js_undefined(), &cacheable_metadata)); auto value = TRY(binding_object.internal_get(identifier, js_undefined(), &cacheable_metadata));
if (cacheable_metadata.type == CacheablePropertyMetadata::Type::OwnProperty) { if (cacheable_metadata.type == CacheablePropertyMetadata::Type::OwnProperty) {
cache.shape = shape; cache.entries[0].shape = shape;
cache.property_offset = cacheable_metadata.property_offset.value(); cache.entries[0].property_offset = cacheable_metadata.property_offset.value();
} }
return value; return value;
} }
@ -1192,7 +1201,7 @@ inline ThrowCompletionOr<Value> get_global(Interpreter& interpreter, IdentifierT
return vm.throw_completion<ReferenceError>(ErrorType::UnknownIdentifier, identifier); return vm.throw_completion<ReferenceError>(ErrorType::UnknownIdentifier, identifier);
} }
inline ThrowCompletionOr<void> put_by_property_key(VM& vm, Value base, Value this_value, Value value, Optional<FlyString const&> const& base_identifier, PropertyKey name, Op::PropertyKind kind, PropertyLookupCache* cache = nullptr) inline ThrowCompletionOr<void> put_by_property_key(VM& vm, Value base, Value this_value, Value value, Optional<FlyString const&> const& base_identifier, PropertyKey name, Op::PropertyKind kind, PropertyLookupCache* caches = nullptr)
{ {
// Better error message than to_object would give // Better error message than to_object would give
if (vm.in_strict_mode() && base.is_nullish()) if (vm.in_strict_mode() && base.is_nullish())
@ -1224,7 +1233,8 @@ inline ThrowCompletionOr<void> put_by_property_key(VM& vm, Value base, Value thi
break; break;
} }
case Op::PropertyKind::KeyValue: { case Op::PropertyKind::KeyValue: {
if (cache) { if (caches) {
auto* cache = &caches->entries[0];
if (cache->prototype) { if (cache->prototype) {
// OPTIMIZATION: If the prototype chain hasn't been mutated in a way that would invalidate the cache, we can use it. // OPTIMIZATION: If the prototype chain hasn't been mutated in a way that would invalidate the cache, we can use it.
bool can_use_cache = [&]() -> bool { bool can_use_cache = [&]() -> bool {
@ -1257,7 +1267,8 @@ inline ThrowCompletionOr<void> put_by_property_key(VM& vm, Value base, Value thi
CacheablePropertyMetadata cacheable_metadata; CacheablePropertyMetadata cacheable_metadata;
bool succeeded = TRY(object->internal_set(name, value, this_value, &cacheable_metadata)); bool succeeded = TRY(object->internal_set(name, value, this_value, &cacheable_metadata));
if (succeeded && cache) { if (succeeded && caches) {
auto* cache = &caches->entries[0];
if (cacheable_metadata.type == CacheablePropertyMetadata::Type::OwnProperty) { if (cacheable_metadata.type == CacheablePropertyMetadata::Type::OwnProperty) {
*cache = {}; *cache = {};
cache->shape = object->shape(); cache->shape = object->shape();
@ -2349,12 +2360,12 @@ ThrowCompletionOr<void> SetGlobal::execute_impl(Bytecode::Interpreter& interpret
if (cache.environment_serial_number == declarative_record.environment_serial_number()) { if (cache.environment_serial_number == declarative_record.environment_serial_number()) {
// OPTIMIZATION: For global var bindings, if the shape of the global object hasn't changed, // OPTIMIZATION: For global var bindings, if the shape of the global object hasn't changed,
// we can use the cached property offset. // we can use the cached property offset.
if (&shape == cache.shape) { if (&shape == cache.entries[0].shape) {
auto value = binding_object.get_direct(cache.property_offset.value()); auto value = binding_object.get_direct(cache.entries[0].property_offset.value());
if (value.is_accessor()) if (value.is_accessor())
TRY(call(vm, value.as_accessor().setter(), &binding_object, src)); TRY(call(vm, value.as_accessor().setter(), &binding_object, src));
else else
binding_object.put_direct(cache.property_offset.value(), src); binding_object.put_direct(cache.entries[0].property_offset.value(), src);
return {}; return {};
} }
@ -2416,8 +2427,8 @@ ThrowCompletionOr<void> SetGlobal::execute_impl(Bytecode::Interpreter& interpret
return vm.throw_completion<TypeError>(ErrorType::ObjectSetReturnedFalse); return vm.throw_completion<TypeError>(ErrorType::ObjectSetReturnedFalse);
} }
if (cacheable_metadata.type == CacheablePropertyMetadata::Type::OwnProperty) { if (cacheable_metadata.type == CacheablePropertyMetadata::Type::OwnProperty) {
cache.shape = shape; cache.entries[0].shape = shape;
cache.property_offset = cacheable_metadata.property_offset.value(); cache.entries[0].property_offset = cacheable_metadata.property_offset.value();
} }
return {}; return {};
} }