Fast body iteration for objects without unboxed fields.

Currently BodyDescriptorBase::IterateBodyImpl does a run-time check
for obj->map()->HasFastPointerLayout(), which is redundant for all
non-JSObject heap objects.

BUG=chromium:694255

Review-Url: https://codereview.chromium.org/2774553003
Cr-Commit-Position: refs/heads/master@{#44111}

src/objects-body-descriptors-inl.h

@@ -17,7 +17,6 @@ int FlexibleBodyDescriptor<start_offset>::SizeOf(Map* map, HeapObject* object) {
   return object->SizeFromMap(map);
 }
 
-
 bool BodyDescriptorBase::IsValidSlotImpl(HeapObject* obj, int offset) {
   if (!FLAG_unbox_double_fields || obj->map()->HasFastPointerLayout()) {
     return true;
@@ -53,7 +52,6 @@ void BodyDescriptorBase::IterateBodyImpl(HeapObject* obj, int start_offset,
   }
 }
 
-
 template <typename StaticVisitor>
 void BodyDescriptorBase::IterateBodyImpl(Heap* heap, HeapObject* obj,
                                          int start_offset, int end_offset) {
@@ -76,39 +74,62 @@ void BodyDescriptorBase::IterateBodyImpl(Heap* heap, HeapObject* obj,
   }
 }
 
-
 template <typename ObjectVisitor>
-DISABLE_CFI_PERF
-void BodyDescriptorBase::IteratePointers(HeapObject* obj, int start_offset,
-                                         int end_offset, ObjectVisitor* v) {
+DISABLE_CFI_PERF void BodyDescriptorBase::IteratePointers(HeapObject* obj,
+                                                          int start_offset,
+                                                          int end_offset,
+                                                          ObjectVisitor* v) {
   v->VisitPointers(HeapObject::RawField(obj, start_offset),
                    HeapObject::RawField(obj, end_offset));
 }
 
-
 template <typename StaticVisitor>
-DISABLE_CFI_PERF
-void BodyDescriptorBase::IteratePointers(Heap* heap, HeapObject* obj,
-                                         int start_offset, int end_offset) {
+DISABLE_CFI_PERF void BodyDescriptorBase::IteratePointers(Heap* heap,
+                                                          HeapObject* obj,
+                                                          int start_offset,
+                                                          int end_offset) {
   StaticVisitor::VisitPointers(heap, obj,
                                HeapObject::RawField(obj, start_offset),
                                HeapObject::RawField(obj, end_offset));
 }
 
-
 template <typename ObjectVisitor>
 void BodyDescriptorBase::IteratePointer(HeapObject* obj, int offset,
                                         ObjectVisitor* v) {
   v->VisitPointer(HeapObject::RawField(obj, offset));
 }
 
-
 template <typename StaticVisitor>
 void BodyDescriptorBase::IteratePointer(Heap* heap, HeapObject* obj,
                                         int offset) {
   StaticVisitor::VisitPointer(heap, obj, HeapObject::RawField(obj, offset));
 }
 
+class JSObject::BodyDescriptor final : public BodyDescriptorBase {
+ public:
+  static const int kStartOffset = JSReceiver::kPropertiesOffset;
+
+  static bool IsValidSlot(HeapObject* obj, int offset) {
+    if (offset < kStartOffset) return false;
+    return IsValidSlotImpl(obj, offset);
+  }
+
+  template <typename ObjectVisitor>
+  static inline void IterateBody(HeapObject* obj, int object_size,
+                                 ObjectVisitor* v) {
+    IterateBodyImpl(obj, kStartOffset, object_size, v);
+  }
+
+  template <typename StaticVisitor>
+  static inline void IterateBody(HeapObject* obj, int object_size) {
+    Heap* heap = obj->GetHeap();
+    IterateBodyImpl<StaticVisitor>(heap, obj, kStartOffset, object_size);
+  }
+
+  static inline int SizeOf(Map* map, HeapObject* object) {
+    return map->instance_size();
+  }
+};
 
 // Iterates the function object according to the visiting policy.
 template <JSFunction::BodyVisitingPolicy body_visiting_policy>
@@ -160,7 +181,6 @@ class JSFunction::BodyDescriptorImpl final : public BodyDescriptorBase {
   }
 };
 
-
 class JSArrayBuffer::BodyDescriptor final : public BodyDescriptorBase {
  public:
   STATIC_ASSERT(kByteLengthOffset + kPointerSize == kBackingStoreOffset);
@@ -193,7 +213,6 @@ class JSArrayBuffer::BodyDescriptor final : public BodyDescriptorBase {
   }
 };
 
-
 class BytecodeArray::BodyDescriptor final : public BodyDescriptorBase {
  public:
   static bool IsValidSlot(HeapObject* obj, int offset) {
@@ -222,7 +241,6 @@ class BytecodeArray::BodyDescriptor final : public BodyDescriptorBase {
   }
 };
 
-
 class FixedTypedArrayBase::BodyDescriptor final : public BodyDescriptorBase {
  public:
   static bool IsValidSlot(HeapObject* obj, int offset) {
@@ -246,7 +264,6 @@ class FixedTypedArrayBase::BodyDescriptor final : public BodyDescriptorBase {
   }
 };
 
-
 template <JSWeakCollection::BodyVisitingPolicy body_visiting_policy>
 class JSWeakCollection::BodyDescriptorImpl final : public BodyDescriptorBase {
  public:
@@ -285,7 +302,6 @@ class JSWeakCollection::BodyDescriptorImpl final : public BodyDescriptorBase {
   }
 };
 
-
 class Foreign::BodyDescriptor final : public BodyDescriptorBase {
  public:
   static bool IsValidSlot(HeapObject* obj, int offset) { return false; }
@@ -306,7 +322,6 @@ class Foreign::BodyDescriptor final : public BodyDescriptorBase {
   static inline int SizeOf(Map* map, HeapObject* object) { return kSize; }
 };
 
-
 class ExternalOneByteString::BodyDescriptor final : public BodyDescriptorBase {
  public:
   static bool IsValidSlot(HeapObject* obj, int offset) { return false; }
@@ -329,7 +344,6 @@ class ExternalOneByteString::BodyDescriptor final : public BodyDescriptorBase {
   static inline int SizeOf(Map* map, HeapObject* object) { return kSize; }
 };
 
-
 class ExternalTwoByteString::BodyDescriptor final : public BodyDescriptorBase {
  public:
   static bool IsValidSlot(HeapObject* obj, int offset) { return false; }
@@ -352,7 +366,6 @@ class ExternalTwoByteString::BodyDescriptor final : public BodyDescriptorBase {
   static inline int SizeOf(Map* map, HeapObject* object) { return kSize; }
 };
 
-
 class Code::BodyDescriptor final : public BodyDescriptorBase {
  public:
   STATIC_ASSERT(kRelocationInfoOffset + kPointerSize == kHandlerTableOffset);

src/objects-body-descriptors.h

@@ -82,7 +82,7 @@ class FixedBodyDescriptor final : public BodyDescriptorBase {
 
   template <typename ObjectVisitor>
   static inline void IterateBody(HeapObject* obj, ObjectVisitor* v) {
-    IterateBodyImpl(obj, start_offset, end_offset, v);
+    IteratePointers(obj, start_offset, end_offset, v);
   }
 
   template <typename ObjectVisitor>
@@ -94,7 +94,7 @@ class FixedBodyDescriptor final : public BodyDescriptorBase {
   template <typename StaticVisitor>
   static inline void IterateBody(HeapObject* obj) {
     Heap* heap = obj->GetHeap();
-    IterateBodyImpl<StaticVisitor>(heap, obj, start_offset, end_offset);
+    IteratePointers<StaticVisitor>(heap, obj, start_offset, end_offset);
   }
 
   template <typename StaticVisitor>
@@ -113,20 +113,19 @@ class FlexibleBodyDescriptor final : public BodyDescriptorBase {
   static const int kStartOffset = start_offset;
 
   static bool IsValidSlot(HeapObject* obj, int offset) {
-    if (offset < kStartOffset) return false;
-    return IsValidSlotImpl(obj, offset);
+    return (offset >= kStartOffset);
   }
 
   template <typename ObjectVisitor>
   static inline void IterateBody(HeapObject* obj, int object_size,
                                  ObjectVisitor* v) {
-    IterateBodyImpl(obj, start_offset, object_size, v);
+    IteratePointers(obj, start_offset, object_size, v);
   }
 
   template <typename StaticVisitor>
   static inline void IterateBody(HeapObject* obj, int object_size) {
     Heap* heap = obj->GetHeap();
-    IterateBodyImpl<StaticVisitor>(heap, obj, start_offset, object_size);
+    IteratePointers<StaticVisitor>(heap, obj, start_offset, object_size);
   }
 
   static inline int SizeOf(Map* map, HeapObject* object);

src/objects.h

@@ -2552,7 +2552,7 @@ class JSObject: public JSReceiver {
 
   STATIC_ASSERT(kHeaderSize == Internals::kJSObjectHeaderSize);
 
-  typedef FlexibleBodyDescriptor<JSReceiver::kPropertiesOffset> BodyDescriptor;
+  class BodyDescriptor;
 
   // Gets the number of currently used elements.
   int GetFastElementsUsage();