Use Torque-generated BodyDescriptor for ScopeInfo

With this change, the GC will compute the size for ScopeInfo instances
based on a combination of flags, context_local_count, and possibly
module_variable_count, rather than using the FixedArray-style length
field. After this change and a few more cleanups, we should be able to
remove that length field and save a few bytes.

Bug: v8:8952
Change-Id: Ica8e51ee106685b44fcc55556b4bb124afc91cfa
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2598461
Commit-Queue: Seth Brenith <seth.brenith@microsoft.com>
Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72231}

src/heap/objects-visiting.h

@@ -43,7 +43,6 @@ namespace internal {
   V(PropertyArray)               \
   V(PropertyCell)                \
   V(PrototypeInfo)               \
-  V(ScopeInfo)                   \
   V(SmallOrderedHashMap)         \
   V(SmallOrderedHashSet)         \
   V(SmallOrderedNameDictionary)  \

src/objects/map.cc

@@ -189,9 +189,6 @@ VisitorId Map::GetVisitorId(Map map) {
     case MAP_TYPE:
       return kVisitMap;
 
-    case SCOPE_INFO_TYPE:
-      return kVisitScopeInfo;
-
     case CODE_TYPE:
       return kVisitCode;
 

src/objects/map.h

@@ -58,7 +58,6 @@ enum InstanceType : uint16_t;
   V(PropertyArray)                 \
   V(PropertyCell)                  \
   V(PrototypeInfo)                 \
-  V(ScopeInfo)                     \
   V(ShortcutCandidate)             \
   V(SmallOrderedHashMap)           \
   V(SmallOrderedHashSet)           \

src/objects/objects-body-descriptors-inl.h

@@ -996,8 +996,6 @@ ReturnType BodyDescriptorApply(InstanceType type, T1 p1, T2 p2, T3 p3, T4 p4) {
     case WASM_MODULE_OBJECT_TYPE:
     case WASM_TABLE_OBJECT_TYPE:
       return Op::template apply<JSObject::BodyDescriptor>(p1, p2, p3, p4);
-    case SCOPE_INFO_TYPE:
-      return Op::template apply<ScopeInfo::BodyDescriptor>(p1, p2, p3, p4);
     case WASM_INSTANCE_OBJECT_TYPE:
       return Op::template apply<WasmInstanceObject::BodyDescriptor>(p1, p2, p3,
                                                                     p4);

src/objects/objects.cc

@@ -2298,9 +2298,6 @@ int HeapObject::SizeFromMap(Map map) const {
     return FeedbackVector::SizeFor(
         FeedbackVector::unchecked_cast(*this).length());
   }
-  if (instance_type == SCOPE_INFO_TYPE) {
-    return FixedArray::SizeFor(ScopeInfo::unchecked_cast(*this).length());
-  }
   if (instance_type == BIGINT_TYPE) {
     return BigInt::SizeFor(BigInt::unchecked_cast(*this).length());
   }

src/objects/scope-info.h

@@ -58,7 +58,7 @@ class ScopeInfo : public TorqueGeneratedScopeInfo<ScopeInfo, FixedArrayBase> {
                            int src_index, int len, WriteBarrierMode mode);
   inline ObjectSlot RawFieldOfElementAt(int index);
 
-  using BodyDescriptor = FlexibleBodyDescriptor<kHeaderSize>;
+  class BodyDescriptor;
 
   // Return the type of this scope.
   ScopeType scope_type() const;

src/objects/scope-info.tq

@@ -98,6 +98,7 @@ struct ModuleVariable {
 }
 
 @generateCppClass
+@generateBodyDescriptor
 extern class ScopeInfo extends FixedArrayBase {
   const flags: SmiTagged<ScopeFlags>;