[GC] Small clean-ups

- const return type on Full{,Maybe,Heap}ObjectSlot::operator*
- Removed stale friend declarations
- Moved a method to the right section

Bug: v8:8557
Change-Id: I0bd3efdb96a7d997b4404d3a247bea55b083d611
Reviewed-on: https://chromium-review.googlesource.com/c/1467781Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59546}

src/heap/heap.h

@@ -2010,7 +2010,6 @@ class Heap {
   friend class AlwaysAllocateScope;
   friend class ArrayBufferCollector;
   friend class ConcurrentMarking;
-  friend class EphemeronHashTableMarkingTask;
   friend class GCCallbacksScope;
   friend class GCTracer;
   friend class MemoryController;

src/heap/mark-compact.h

@@ -906,7 +906,6 @@ class MarkCompactCollector final : public MarkCompactCollectorBase {
   // used, so it is okay if this counter overflows and wraps around.
   unsigned epoch_ = 0;
 
-  friend class EphemeronHashTableMarkingTask;
   friend class FullEvacuator;
   friend class Heap;
   friend class RecordMigratedSlotVisitor;

src/heap/objects-visiting-inl.h

@@ -161,6 +161,19 @@ ResultType HeapVisitor<ResultType, ConcreteVisitor>::VisitFreeSpace(
   return static_cast<ResultType>(object->size());
 }
 
+template <typename ResultType, typename ConcreteVisitor>
+ResultType HeapVisitor<ResultType, ConcreteVisitor>::VisitWeakArray(
+    Map map, HeapObject object) {
+  ConcreteVisitor* visitor = static_cast<ConcreteVisitor*>(this);
+  if (!visitor->ShouldVisit(object)) return ResultType();
+  int size = WeakArrayBodyDescriptor::SizeOf(map, object);
+  if (visitor->ShouldVisitMapPointer()) {
+    visitor->VisitMapPointer(object, object->map_slot());
+  }
+  WeakArrayBodyDescriptor::IterateBody(map, object, size, visitor);
+  return size;
+}
+
 template <typename ConcreteVisitor>
 int NewSpaceVisitor<ConcreteVisitor>::VisitNativeContext(Map map,
                                                          NativeContext object) {
@@ -191,19 +204,6 @@ int NewSpaceVisitor<ConcreteVisitor>::VisitWeakCell(Map map,
   return 0;
 }
 
-template <typename ResultType, typename ConcreteVisitor>
-ResultType HeapVisitor<ResultType, ConcreteVisitor>::VisitWeakArray(
-    Map map, HeapObject object) {
-  ConcreteVisitor* visitor = static_cast<ConcreteVisitor*>(this);
-  if (!visitor->ShouldVisit(object)) return ResultType();
-  int size = WeakArrayBodyDescriptor::SizeOf(map, object);
-  if (visitor->ShouldVisitMapPointer()) {
-    visitor->VisitMapPointer(object, object->map_slot());
-  }
-  WeakArrayBodyDescriptor::IterateBody(map, object, size, visitor);
-  return size;
-}
-
 }  // namespace internal
 }  // namespace v8
 

src/objects/slots-inl.h

@@ -31,7 +31,7 @@ bool FullObjectSlot::contains_value(Address raw_value) const {
   return base::AsAtomicPointer::Relaxed_Load(location()) == raw_value;
 }
 
-Object FullObjectSlot::operator*() const { return Object(*location()); }
+const Object FullObjectSlot::operator*() const { return Object(*location()); }
 
 void FullObjectSlot::store(Object value) const { *location() = value->ptr(); }
 
@@ -61,7 +61,7 @@ Object FullObjectSlot::Release_CompareAndSwap(Object old, Object target) const {
 // FullMaybeObjectSlot implementation.
 //
 
-MaybeObject FullMaybeObjectSlot::operator*() const {
+const MaybeObject FullMaybeObjectSlot::operator*() const {
   return MaybeObject(*location());
 }
 
@@ -86,7 +86,7 @@ void FullMaybeObjectSlot::Release_CompareAndSwap(MaybeObject old,
 // FullHeapObjectSlot implementation.
 //
 
-HeapObjectReference FullHeapObjectSlot::operator*() const {
+const HeapObjectReference FullHeapObjectSlot::operator*() const {
   return HeapObjectReference(*location());
 }
 

src/objects/slots.h

@@ -110,7 +110,7 @@ class FullObjectSlot
   // raw value.
   inline bool contains_value(Address raw_value) const;
 
-  inline Object operator*() const;
+  inline const Object operator*() const;
   inline void store(Object value) const;
 
   inline Object Acquire_Load() const;
@@ -143,7 +143,7 @@ class FullMaybeObjectSlot
   explicit FullMaybeObjectSlot(SlotBase<T, TData, kSlotDataSize> slot)
       : SlotBase(slot.address()) {}
 
-  inline MaybeObject operator*() const;
+  inline const MaybeObject operator*() const;
   inline void store(MaybeObject value) const;
 
   inline MaybeObject Relaxed_Load() const;
@@ -169,7 +169,7 @@ class FullHeapObjectSlot
   explicit FullHeapObjectSlot(SlotBase<T, TData, kSlotDataSize> slot)
       : SlotBase(slot.address()) {}
 
-  inline HeapObjectReference operator*() const;
+  inline const HeapObjectReference operator*() const;
   inline void store(HeapObjectReference value) const;
 
   inline HeapObject ToHeapObject() const;