[cleanup] Make PropertyDescriptorObject inherit from Struct

There is no particular reason that PropertyDescriptorObject should be a
subclass of FixedArray. By using a separate struct type, we get better
generated accessor functions, automatic verification, and runtime type
info, plus we save four bytes per instance.

Change-Id: If076782832aa9398806794e4ee6d019aea2f92b7
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1999463Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Seth Brenith <seth.brenith@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#65756}

BUILD.gn

@@ -1085,6 +1085,7 @@ torque_files = [
   "src/objects/promise.tq",
   "src/objects/property-array.tq",
   "src/objects/property-cell.tq",
+  "src/objects/property-descriptor-object.tq",
   "src/objects/prototype-info.tq",
   "src/objects/regexp-match-info.tq",
   "src/objects/scope-info.tq",

src/builtins/builtins-object-gen.cc

@@ -34,7 +34,7 @@ class ObjectBuiltinsAssembler : public CodeStubAssembler {
                          Handle<Name> name, TNode<Object> value,
                          Label* bailout);
   TNode<JSObject> FromPropertyDescriptor(TNode<Context> context,
-                                         TNode<FixedArray> desc);
+                                         TNode<PropertyDescriptorObject> desc);
   TNode<JSObject> FromPropertyDetails(TNode<Context> context,
                                       TNode<Object> raw_value,
                                       TNode<Word32T> details,
@@ -1369,10 +1369,10 @@ TF_BUILTIN(ObjectGetOwnPropertyDescriptor, ObjectBuiltinsAssembler) {
 
     GotoIf(IsUndefined(desc), &return_undefined);
 
-    TNode<FixedArray> desc_array = CAST(desc);
+    TNode<PropertyDescriptorObject> desc_object = CAST(desc);
 
     // 4. Return FromPropertyDescriptor(desc).
-    TNode<JSObject> js_desc = FromPropertyDescriptor(context, desc_array);
+    TNode<JSObject> js_desc = FromPropertyDescriptor(context, desc_object);
     args.PopAndReturn(js_desc);
   }
   BIND(&return_undefined);
@@ -1392,7 +1392,7 @@ void ObjectBuiltinsAssembler::AddToDictionaryIf(
 }
 
 TNode<JSObject> ObjectBuiltinsAssembler::FromPropertyDescriptor(
-    TNode<Context> context, TNode<FixedArray> desc) {
+    TNode<Context> context, TNode<PropertyDescriptorObject> desc) {
   TVARIABLE(JSObject, js_descriptor);
 
   TNode<Int32T> flags = LoadAndUntagToWord32ObjectField(

src/compiler/types.cc

@@ -274,6 +274,7 @@ Type::bitset BitsetType::Lub(const MapRefLike& map) {
     case ACCESSOR_PAIR_TYPE:
     case EMBEDDER_DATA_ARRAY_TYPE:
     case FIXED_ARRAY_TYPE:
+    case PROPERTY_DESCRIPTOR_OBJECT_TYPE:
     case HASH_TABLE_TYPE:
     case ORDERED_HASH_MAP_TYPE:
     case ORDERED_HASH_SET_TYPE:

src/diagnostics/objects-debug.cc

@@ -62,6 +62,7 @@
 #include "src/objects/module-inl.h"
 #include "src/objects/oddball-inl.h"
 #include "src/objects/promise-inl.h"
+#include "src/objects/property-descriptor-object-inl.h"
 #include "src/objects/stack-frame-info-inl.h"
 #include "src/objects/struct-inl.h"
 #include "src/objects/template-objects-inl.h"

src/diagnostics/objects-printer.cc

@@ -58,6 +58,7 @@
 #include "src/objects/module-inl.h"
 #include "src/objects/oddball-inl.h"
 #include "src/objects/promise-inl.h"
+#include "src/objects/property-descriptor-object-inl.h"
 #include "src/objects/stack-frame-info-inl.h"
 #include "src/objects/struct-inl.h"
 #include "src/objects/template-objects-inl.h"

src/heap/factory.cc

@@ -51,6 +51,7 @@
 #include "src/objects/microtask-inl.h"
 #include "src/objects/module-inl.h"
 #include "src/objects/promise-inl.h"
+#include "src/objects/property-descriptor-object-inl.h"
 #include "src/objects/scope-info.h"
 #include "src/objects/stack-frame-info-inl.h"
 #include "src/objects/struct-inl.h"
@@ -706,6 +707,17 @@ Handle<AccessorPair> Factory::NewAccessorPair() {
   return accessors;
 }
 
+Handle<PropertyDescriptorObject> Factory::NewPropertyDescriptorObject() {
+  Handle<PropertyDescriptorObject> object =
+      Handle<PropertyDescriptorObject>::cast(
+          NewStruct(PROPERTY_DESCRIPTOR_OBJECT_TYPE, AllocationType::kYoung));
+  object->set_flags(Smi::zero());
+  object->set_value(*the_hole_value(), SKIP_WRITE_BARRIER);
+  object->set_get(*the_hole_value(), SKIP_WRITE_BARRIER);
+  object->set_set(*the_hole_value(), SKIP_WRITE_BARRIER);
+  return object;
+}
+
 // Internalized strings are created in the old generation (data space).
 Handle<String> Factory::InternalizeUtf8String(
     const Vector<const char>& string) {

src/heap/factory.h

@@ -225,6 +225,9 @@ class V8_EXPORT_PRIVATE Factory {
   // Create a pre-tenured empty AccessorPair.
   Handle<AccessorPair> NewAccessorPair();
 
+  // Create a new PropertyDescriptorObject struct.
+  Handle<PropertyDescriptorObject> NewPropertyDescriptorObject();
+
   // Finds the internalized copy for string in the string table.
   // If not found, a new string is added to the table and returned.
   Handle<String> InternalizeUtf8String(const Vector<const char>& str);

src/heap/setup-heap-internal.cc

@@ -34,6 +34,7 @@
 #include "src/objects/oddball-inl.h"
 #include "src/objects/ordered-hash-table.h"
 #include "src/objects/promise.h"
+#include "src/objects/property-descriptor-object.h"
 #include "src/objects/script.h"
 #include "src/objects/shared-function-info.h"
 #include "src/objects/smi.h"

src/objects/instance-type.h

@@ -210,13 +210,12 @@ V8_EXPORT_PRIVATE std::ostream& operator<<(std::ostream& os,
                                            InstanceType instance_type);
 
 // List of object types that have a single unique instance type.
-#define INSTANCE_TYPE_CHECKERS_SINGLE(V)                   \
-  TORQUE_INSTANCE_CHECKERS_SINGLE_FULLY_DEFINED(V)         \
-  TORQUE_INSTANCE_CHECKERS_SINGLE_ONLY_DECLARED(V)         \
-  V(BigInt, BIGINT_TYPE)                                   \
-  V(CoverageInfo, FIXED_ARRAY_TYPE)                        \
-  V(FixedArrayExact, FIXED_ARRAY_TYPE)                     \
-  V(PropertyDescriptorObject, FIXED_ARRAY_TYPE)
+#define INSTANCE_TYPE_CHECKERS_SINGLE(V)           \
+  TORQUE_INSTANCE_CHECKERS_SINGLE_FULLY_DEFINED(V) \
+  TORQUE_INSTANCE_CHECKERS_SINGLE_ONLY_DECLARED(V) \
+  V(BigInt, BIGINT_TYPE)                           \
+  V(CoverageInfo, FIXED_ARRAY_TYPE)                \
+  V(FixedArrayExact, FIXED_ARRAY_TYPE)
 
 #define INSTANCE_TYPE_CHECKERS_RANGE(V)           \
   TORQUE_INSTANCE_CHECKERS_RANGE_FULLY_DEFINED(V) \

src/objects/object-list-macros.h

@@ -190,7 +190,6 @@ class ZoneForwardList;
   V(PromiseReactionJobTask)                    \
   V(PropertyArray)                             \
   V(PropertyCell)                              \
-  V(PropertyDescriptorObject)                  \
   V(RegExpMatchInfo)                           \
   V(ScopeInfo)                                 \
   V(ScriptContextTable)                        \

src/objects/objects-definitions.h

@@ -138,6 +138,8 @@ namespace internal {
   V(_, INTERPRETER_DATA_TYPE, InterpreterData, interpreter_data)              \
   V(_, PROMISE_CAPABILITY_TYPE, PromiseCapability, promise_capability)        \
   V(_, PROMISE_REACTION_TYPE, PromiseReaction, promise_reaction)              \
+  V(_, PROPERTY_DESCRIPTOR_OBJECT_TYPE, PropertyDescriptorObject,             \
+    property_descriptor_object)                                               \
   V(_, PROTOTYPE_INFO_TYPE, PrototypeInfo, prototype_info)                    \
   V(_, SCRIPT_TYPE, Script, script)                                           \
   V(_, SOURCE_TEXT_MODULE_INFO_ENTRY_TYPE, SourceTextModuleInfoEntry,         \

src/objects/objects.cc

@@ -98,6 +98,7 @@
 #include "src/objects/microtask-inl.h"
 #include "src/objects/module-inl.h"
 #include "src/objects/promise-inl.h"
+#include "src/objects/property-descriptor-object-inl.h"
 #include "src/objects/property-descriptor.h"
 #include "src/objects/prototype.h"
 #include "src/objects/slots-atomic-inl.h"

src/objects/objects.h

@@ -167,6 +167,7 @@
 //       - StackFrameInfo
 //       - StackTraceFrame
 //       - CodeCache
+//       - PropertyDescriptorObject
 //       - PrototypeInfo
 //       - Microtask
 //         - CallbackTask

src/objects/property-descriptor-object-inl.h

@@ -14,8 +14,7 @@
 namespace v8 {
 namespace internal {
 
-OBJECT_CONSTRUCTORS_IMPL(PropertyDescriptorObject, FixedArray)
-CAST_ACCESSOR(PropertyDescriptorObject)
+TQ_OBJECT_CONSTRUCTORS_IMPL(PropertyDescriptorObject)
 }
 }  // namespace v8
 

src/objects/property-descriptor-object.h

@@ -6,8 +6,7 @@
 #define V8_OBJECTS_PROPERTY_DESCRIPTOR_OBJECT_H_
 
 #include "src/base/bit-field.h"
-#include "src/objects/fixed-array.h"
-#include "src/objects/objects.h"
+#include "src/objects/struct.h"
 
 // Has to be the last include (doesn't have include guards):
 #include "src/objects/object-macros.h"
@@ -15,7 +14,9 @@
 namespace v8 {
 namespace internal {
 
-class PropertyDescriptorObject : public FixedArray {
+class PropertyDescriptorObject
+    : public TorqueGeneratedPropertyDescriptorObject<PropertyDescriptorObject,
+                                                     Struct> {
  public:
 #define FLAGS_BIT_FIELDS(V, _)      \
   V(IsEnumerableBit, bool, 1, _)    \
@@ -31,10 +32,6 @@ class PropertyDescriptorObject : public FixedArray {
   DEFINE_BIT_FIELDS(FLAGS_BIT_FIELDS)
 #undef FLAGS_BIT_FIELDS
 
-  enum { kFlagsIndex, kValueIndex, kGetIndex, kSetIndex, kLength };
-
-  DECL_CAST(PropertyDescriptorObject)
-
   static const int kRegularAccessorPropertyBits =
       HasEnumerableBit::kMask | HasConfigurableBit::kMask | HasGetBit::kMask |
       HasSetBit::kMask;
@@ -48,16 +45,7 @@ class PropertyDescriptorObject : public FixedArray {
                               HasWritableBit::kMask | HasValueBit::kMask |
                               HasGetBit::kMask | HasSetBit::kMask;
 
-  static const int kValueOffset =
-      FixedArray::OffsetOfElementAt(PropertyDescriptorObject::kValueIndex);
-  static const int kFlagsOffset =
-      FixedArray::OffsetOfElementAt(PropertyDescriptorObject::kFlagsIndex);
-  static const int kGetOffset =
-      FixedArray::OffsetOfElementAt(PropertyDescriptorObject::kGetIndex);
-  static const int kSetOffset =
-      FixedArray::OffsetOfElementAt(PropertyDescriptorObject::kSetIndex);
-
-  OBJECT_CONSTRUCTORS(PropertyDescriptorObject, FixedArray);
+  TQ_OBJECT_CONSTRUCTORS(PropertyDescriptorObject)
 };
 
 }  // namespace internal

src/objects/property-descriptor-object.tq

+// Copyright 2019 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include 'src/objects/property-descriptor-object.h'
+
+@generateCppClass
+@generatePrint
+extern class PropertyDescriptorObject extends Struct {
+  flags: Smi;
+  value: JSAny|TheHole;
+  get: JSAny|TheHole;
+  set: JSAny|TheHole;
+}

src/objects/property-descriptor.cc

@@ -341,8 +341,8 @@ void PropertyDescriptor::CompletePropertyDescriptor(Isolate* isolate,
 
 Handle<PropertyDescriptorObject> PropertyDescriptor::ToPropertyDescriptorObject(
     Isolate* isolate) {
-  Handle<PropertyDescriptorObject> obj = Handle<PropertyDescriptorObject>::cast(
-      isolate->factory()->NewFixedArray(PropertyDescriptorObject::kLength));
+  Handle<PropertyDescriptorObject> obj =
+      isolate->factory()->NewPropertyDescriptorObject();
 
   int flags =
       PropertyDescriptorObject::IsEnumerableBit::encode(enumerable_) |
@@ -355,14 +355,11 @@ Handle<PropertyDescriptorObject> PropertyDescriptor::ToPropertyDescriptorObject(
       PropertyDescriptorObject::HasGetBit::encode(has_get()) |
       PropertyDescriptorObject::HasSetBit::encode(has_set());
 
-  obj->set(PropertyDescriptorObject::kFlagsIndex, Smi::FromInt(flags));
+  obj->set_flags(Smi::FromInt(flags));
 
-  obj->set(PropertyDescriptorObject::kValueIndex,
-           has_value() ? *value_ : ReadOnlyRoots(isolate).the_hole_value());
-  obj->set(PropertyDescriptorObject::kGetIndex,
-           has_get() ? *get_ : ReadOnlyRoots(isolate).the_hole_value());
-  obj->set(PropertyDescriptorObject::kSetIndex,
-           has_set() ? *set_ : ReadOnlyRoots(isolate).the_hole_value());
+  if (has_value()) obj->set_value(*value_);
+  if (has_get()) obj->set_get(*get_);
+  if (has_set()) obj->set_set(*set_);
 
   return obj;
 }

src/torque/implementation-visitor.cc

@@ -3584,6 +3584,8 @@ void ImplementationVisitor::GenerateClassDefinitions(
     implementation << "#include \"src/objects/microtask-inl.h\"\n";
     implementation << "#include \"src/objects/module-inl.h\"\n";
     implementation << "#include \"src/objects/promise-inl.h\"\n";
+    implementation
+        << "#include \"src/objects/property-descriptor-object-inl.h\"\n";
     implementation << "#include \"src/objects/stack-frame-info-inl.h\"\n";
     implementation << "#include \"src/objects/struct-inl.h\"\n";
     implementation << "#include \"src/objects/template-objects-inl.h\"\n\n";