[vm] Support arbitrary superclasses for enums

With enhanced enums language feature enum classes can have a mixin, so
its superclass is an arbitrary class and not necessarily _Enum.
This change removes lookups of 'index' and '_name' fields in the
superclass of an enum class. They are now looked up once in _Enum
class and saved in the object store.

TEST=co19/LanguageFeatures/Enhanced-Enum/semantics_A01_t01

Issue: #47861
Change-Id: I2b93d389ab92e0274641e0f1bd65471e6407f3f9
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/228220
Reviewed-by: Ben Konyi <[email protected]>
Commit-Queue: Alexander Markov <[email protected]>

Author: alexmarkov

pkg/front_end/testcases/strong.status

@@ -15,7 +15,6 @@ static_field_lowering/opt_in: SemiFuzzFailure
 
 constructor_tearoffs/call_instantiation: TypeCheckError
 constructor_tearoffs/lowering/invalid_redirect: VerificationError
-enhanced_enums/enum_as_supertype: RuntimeError
 enhanced_enums/simple_mixins: RuntimeError
 extension_types/access_setter_as_getter: ExpectationFileMismatchSerialized # Expected.
 extension_types/call_not_get: ExpectationFileMismatchSerialized # Expected.

pkg/front_end/testcases/text_serialization.status

@@ -8,7 +8,6 @@
 
 constructor_tearoffs/call_instantiation: TypeCheckError
 constructor_tearoffs/lowering/invalid_redirect: VerificationError
-enhanced_enums/enum_as_supertype: RuntimeError
 enhanced_enums/simple_mixins: RuntimeError
 extension_types/access_setter_as_getter: ExpectationFileMismatchSerialized # Expected.
 extension_types/call_not_get: ExpectationFileMismatchSerialized # Expected.

pkg/front_end/testcases/weak.status

@@ -22,7 +22,6 @@ static_field_lowering/opt_in: SemiFuzzFailure
 
 constructor_tearoffs/call_instantiation: TypeCheckError
 constructor_tearoffs/lowering/invalid_redirect: VerificationError
-enhanced_enums/enum_as_supertype: RuntimeError
 enhanced_enums/simple_mixins: RuntimeError
 extension_types/access_setter_as_getter: ExpectationFileMismatchSerialized # Expected.
 extension_types/call_not_get: ExpectationFileMismatchSerialized # Expected.

runtime/vm/class_finalizer.cc

@@ -1223,6 +1223,7 @@ ErrorPtr ClassFinalizer::LoadClassMembers(const Class& cls) {
 void ClassFinalizer::AllocateEnumValues(const Class& enum_cls) {
   Thread* thread = Thread::Current();
   Zone* zone = thread->zone();
+  ObjectStore* object_store = thread->isolate_group()->object_store();
 
   const auto& values_field =
       Field::Handle(zone, enum_cls.LookupStaticField(Symbols::Values()));
@@ -1237,16 +1238,11 @@ void ClassFinalizer::AllocateEnumValues(const Class& enum_cls) {
     ASSERT(values.IsArray());
   }
 
-  // The enum_cls is the actual declared class.
-  // The shared super-class holds the fields for index and name.
-  const auto& super_cls = Class::Handle(zone, enum_cls.SuperClass());
-
   const auto& index_field =
-      Field::Handle(zone, super_cls.LookupInstanceField(Symbols::Index()));
+      Field::Handle(zone, object_store->enum_index_field());
   ASSERT(!index_field.IsNull());
 
-  const auto& name_field = Field::Handle(
-      zone, super_cls.LookupInstanceFieldAllowPrivate(Symbols::_name()));
+  const auto& name_field = Field::Handle(zone, object_store->enum_name_field());
   ASSERT(!name_field.IsNull());
 
   const auto& enum_name = String::Handle(zone, enum_cls.ScrubbedName());

runtime/vm/compiler/runtime_offsets_extracted.h

@@ -302,10 +302,11 @@ void Class::ReplaceEnum(ProgramReloadContext* reload_context,
   ASSERT(is_finalized());
   ASSERT(old_enum.is_finalized());
 
-  Zone* zone = Thread::Current()->zone();
+  Thread* thread = Thread::Current();
+  Zone* zone = thread->zone();
+  ObjectStore* object_store = thread->isolate_group()->object_store();
 
   Field& field = Field::Handle(zone);
-  Class& cls = Class::Handle(zone);
   String& enum_ident = String::Handle();
   Instance& old_enum_value = Instance::Handle(zone);
   Instance& enum_value = Instance::Handle(zone);
@@ -338,8 +339,7 @@ void Class::ReplaceEnum(ProgramReloadContext* reload_context,
     old_deleted_enum_sentinel ^= field.StaticConstFieldValue();
     ASSERT(!old_deleted_enum_sentinel.IsNull());
 
-    cls = old_enum.SuperClass();
-    field = cls.LookupInstanceFieldAllowPrivate(Symbols::_name());
+    field = object_store->enum_name_field();
     ASSERT(!field.IsNull());
 
     UnorderedHashMap<EnumMapTraits> enum_map(enum_map_storage.ptr());
@@ -374,8 +374,7 @@ void Class::ReplaceEnum(ProgramReloadContext* reload_context,
     deleted_enum_sentinel ^= field.StaticConstFieldValue();
     ASSERT(!deleted_enum_sentinel.IsNull());
 
-    cls = SuperClass();
-    field = cls.LookupInstanceFieldAllowPrivate(Symbols::_name());
+    field = object_store->enum_name_field();
     ASSERT(!field.IsNull());
 
     UnorderedHashMap<EnumMapTraits> enum_map(enum_map_storage.ptr());

runtime/vm/object_reload.cc

@@ -361,6 +361,8 @@ void ObjectStore::LazyInitCoreMembers() {
   if (list_class_.load() == Type::null()) {
     ASSERT(non_nullable_list_rare_type_.load() == Type::null());
     ASSERT(non_nullable_map_rare_type_.load() == Type::null());
+    ASSERT(enum_index_field_.load() == Field::null());
+    ASSERT(enum_name_field_.load() == Field::null());
     ASSERT(_object_equals_function_.load() == Function::null());
     ASSERT(_object_hash_code_function_.load() == Function::null());
     ASSERT(_object_to_string_function_.load() == Function::null());
@@ -382,6 +384,21 @@ void ObjectStore::LazyInitCoreMembers() {
     type ^= cls.RareType();
     non_nullable_map_rare_type_.store(type.ptr());
 
+    auto& field = Field::Handle(zone);
+
+    cls = core_lib.LookupClassAllowPrivate(Symbols::_Enum());
+    ASSERT(!cls.IsNull());
+    const auto& error = cls.EnsureIsFinalized(thread);
+    ASSERT(error == Error::null());
+
+    field = cls.LookupInstanceField(Symbols::Index());
+    ASSERT(!field.IsNull());
+    enum_index_field_.store(field.ptr());
+
+    field = cls.LookupInstanceFieldAllowPrivate(Symbols::_name());
+    ASSERT(!field.IsNull());
+    enum_name_field_.store(field.ptr());
+
     auto& function = Function::Handle(zone);
 
     function = core_lib.LookupFunctionAllowPrivate(Symbols::_objectHashCode());

runtime/vm/object_store.cc

@@ -47,6 +47,8 @@ class ObjectPointerVisitor;
   LAZY_CORE(Class, list_class)                                                 \
   LAZY_CORE(Type, non_nullable_list_rare_type)                                 \
   LAZY_CORE(Type, non_nullable_map_rare_type)                                  \
+  LAZY_CORE(Field, enum_index_field)                                           \
+  LAZY_CORE(Field, enum_name_field)                                            \
   LAZY_CORE(Function, _object_equals_function)                                 \
   LAZY_CORE(Function, _object_hash_code_function)                              \
   LAZY_CORE(Function, _object_to_string_function)                              \

runtime/vm/object_store.h

@@ -293,6 +293,7 @@ class ObjectPointerVisitor;
   V(_DeletedEnumPrefix, "Deleted enum value from ")                            \
   V(_DeletedEnumSentinel, "_deleted_enum_sentinel")                            \
   V(_Double, "_Double")                                                        \
+  V(_Enum, "_Enum")                                                            \
   V(_ExternalFloat32Array, "_ExternalFloat32Array")                            \
   V(_ExternalFloat32x4Array, "_ExternalFloat32x4Array")                        \
   V(_ExternalFloat64Array, "_ExternalFloat64Array")                            \