[heap] Further improve instance-based visitor

Bug: chromium:736641
Change-Id: I93e8c0bbdcc471750073d39b10b18c18ceee7d8a
Reviewed-on: https://chromium-review.googlesource.com/549416Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46234}

src/heap/objects-visiting-inl.h

@@ -637,11 +637,6 @@ ResultType HeapVisitor<ResultType, ConcreteVisitor>::Visit(Map* map,
   return ResultType();
 }
 
-template <typename ResultType, typename ConcreteVisitor>
-bool HeapVisitor<ResultType, ConcreteVisitor>::ShouldVisitMapPointer() {
-  return true;
-}
-
 template <typename ResultType, typename ConcreteVisitor>
 void HeapVisitor<ResultType, ConcreteVisitor>::VisitMapPointer(
     HeapObject* host, HeapObject** map) {
@@ -649,11 +644,6 @@ void HeapVisitor<ResultType, ConcreteVisitor>::VisitMapPointer(
       host, reinterpret_cast<Object**>(map));
 }
 
-template <typename ResultType, typename ConcreteVisitor>
-bool HeapVisitor<ResultType, ConcreteVisitor>::ShouldVisit(HeapObject* object) {
-  return true;
-}
-
 #define VISIT(type)                                                 \
   template <typename ResultType, typename ConcreteVisitor>          \
   ResultType HeapVisitor<ResultType, ConcreteVisitor>::Visit##type( \
@@ -757,14 +747,12 @@ ResultType HeapVisitor<ResultType, ConcreteVisitor>::VisitFreeSpace(
 
 int NewSpaceVisitor::VisitJSFunction(Map* map, JSFunction* object) {
   int size = JSFunction::BodyDescriptorWeak::SizeOf(map, object);
-  VisitMapPointer(object, object->map_slot());
   JSFunction::BodyDescriptorWeak::IterateBody(object, size, this);
   return size;
 }
 
 int NewSpaceVisitor::VisitNativeContext(Map* map, Context* object) {
   int size = Context::BodyDescriptor::SizeOf(map, object);
-  VisitMapPointer(object, object->map_slot());
   Context::BodyDescriptor::IterateBody(object, size, this);
   return size;
 }

src/heap/objects-visiting.h

@@ -291,9 +291,9 @@ class HeapVisitor : public ObjectVisitor {
   // A guard predicate for visiting the object.
   // If it returns false then the default implementations of the Visit*
   // functions bailout from iterating the object pointers.
-  V8_INLINE bool ShouldVisit(HeapObject* object);
+  V8_INLINE bool ShouldVisit(HeapObject* object) { return true; }
   // Guard predicate for visiting the objects map pointer separately.
-  V8_INLINE bool ShouldVisitMapPointer();
+  V8_INLINE bool ShouldVisitMapPointer() { return true; }
   // A callback for visiting the map pointer in the object header.
   V8_INLINE void VisitMapPointer(HeapObject* host, HeapObject** map);