Move Maps' back pointers from "transitions" to "constructor" field

src/heap/heap.cc

 // Copyright 2012 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/v8.h"
 
 #include "src/accessors.h"
 #include "src/api.h"
 #include "src/base/bits.h"
 #include "src/base/once.h"
@@ skipping 2446 matching lines @@
                                    int instance_size,
                                    ElementsKind elements_kind) {
   HeapObject* result;
   AllocationResult allocation = AllocateRaw(Map::kSize, MAP_SPACE, MAP_SPACE);
   if (!allocation.To(&result)) return allocation;
 
   result->set_map_no_write_barrier(meta_map());
   Map* map = Map::cast(result);
   map->set_instance_type(instance_type);
   map->set_prototype(null_value(), SKIP_WRITE_BARRIER);
-  map->set_constructor(null_value(), SKIP_WRITE_BARRIER);
+  map->set_constructor_or_backpointer(null_value(), SKIP_WRITE_BARRIER);
   map->set_instance_size(instance_size);
   map->set_inobject_properties(0);
   map->set_pre_allocated_property_fields(0);
   map->set_code_cache(empty_fixed_array(), SKIP_WRITE_BARRIER);
   map->set_dependent_code(DependentCode::cast(empty_fixed_array()),
                           SKIP_WRITE_BARRIER);
-  map->init_back_pointer(undefined_value());
+  map->init_transitions(undefined_value());
   map->set_unused_property_fields(0);
   map->set_instance_descriptors(empty_descriptor_array());
   if (FLAG_unbox_double_fields) {
     map->set_layout_descriptor(LayoutDescriptor::FastPointerLayout());
   }
   // Must be called only after |instance_type|, |instance_size| and
   // |layout_descriptor| are set.
   map->set_visitor_id(StaticVisitorBase::GetVisitorId(map));
   map->set_bit_field(0);
   map->set_bit_field2(1 << Map::kIsExtensible);
@@ skipping 113 matching lines @@
   // Allocate the constant pool array.
   {
     AllocationResult allocation = AllocateEmptyConstantPoolArray();
     if (!allocation.To(&obj)) return false;
   }
   set_empty_constant_pool_array(ConstantPoolArray::cast(obj));
 
   // Fix the instance_descriptors for the existing maps.
   meta_map()->set_code_cache(empty_fixed_array());
   meta_map()->set_dependent_code(DependentCode::cast(empty_fixed_array()));
-  meta_map()->init_back_pointer(undefined_value());
+  meta_map()->init_transitions(undefined_value());
   meta_map()->set_instance_descriptors(empty_descriptor_array());
   if (FLAG_unbox_double_fields) {
     meta_map()->set_layout_descriptor(LayoutDescriptor::FastPointerLayout());
   }
 
   fixed_array_map()->set_code_cache(empty_fixed_array());
   fixed_array_map()->set_dependent_code(
       DependentCode::cast(empty_fixed_array()));
-  fixed_array_map()->init_back_pointer(undefined_value());
+  fixed_array_map()->init_transitions(undefined_value());
   fixed_array_map()->set_instance_descriptors(empty_descriptor_array());
   if (FLAG_unbox_double_fields) {
     fixed_array_map()->set_layout_descriptor(
         LayoutDescriptor::FastPointerLayout());
   }
 
   undefined_map()->set_code_cache(empty_fixed_array());
   undefined_map()->set_dependent_code(DependentCode::cast(empty_fixed_array()));
-  undefined_map()->init_back_pointer(undefined_value());
+  undefined_map()->init_transitions(undefined_value());
   undefined_map()->set_instance_descriptors(empty_descriptor_array());
   if (FLAG_unbox_double_fields) {
     undefined_map()->set_layout_descriptor(
         LayoutDescriptor::FastPointerLayout());
   }
 
   null_map()->set_code_cache(empty_fixed_array());
   null_map()->set_dependent_code(DependentCode::cast(empty_fixed_array()));
-  null_map()->init_back_pointer(undefined_value());
+  null_map()->init_transitions(undefined_value());
   null_map()->set_instance_descriptors(empty_descriptor_array());
   if (FLAG_unbox_double_fields) {
     null_map()->set_layout_descriptor(LayoutDescriptor::FastPointerLayout());
   }
 
   constant_pool_array_map()->set_code_cache(empty_fixed_array());
   constant_pool_array_map()->set_dependent_code(
       DependentCode::cast(empty_fixed_array()));
-  constant_pool_array_map()->init_back_pointer(undefined_value());
+  constant_pool_array_map()->init_transitions(undefined_value());
   constant_pool_array_map()->set_instance_descriptors(empty_descriptor_array());
   if (FLAG_unbox_double_fields) {
     constant_pool_array_map()->set_layout_descriptor(
         LayoutDescriptor::FastPointerLayout());
   }
 
   // Fix prototype object for existing maps.
   meta_map()->set_prototype(null_value());
-  meta_map()->set_constructor(null_value());
+  meta_map()->set_constructor_or_backpointer(null_value());
 
   fixed_array_map()->set_prototype(null_value());
-  fixed_array_map()->set_constructor(null_value());
+  fixed_array_map()->set_constructor_or_backpointer(null_value());
 
   undefined_map()->set_prototype(null_value());
-  undefined_map()->set_constructor(null_value());
+  undefined_map()->set_constructor_or_backpointer(null_value());
 
   null_map()->set_prototype(null_value());
-  null_map()->set_constructor(null_value());
+  null_map()->set_constructor_or_backpointer(null_value());
 
   constant_pool_array_map()->set_prototype(null_value());
-  constant_pool_array_map()->set_constructor(null_value());
+  constant_pool_array_map()->set_constructor_or_backpointer(null_value());
 
   {  // Map allocation
 #define ALLOCATE_MAP(instance_type, size, field_name)               \
   {                                                                 \
     Map* map;                                                       \
     if (!AllocateMap((instance_type), size).To(&map)) return false; \
     set_##field_name##_map(map);                                    \
   }
 
 #define ALLOCATE_VARSIZE_MAP(instance_type, field_name) \
@@ skipping 1166 matching lines @@
   // fixed array (e.g. Heap::empty_fixed_array()).  Currently, the object
   // verification code has to cope with (temporarily) invalid objects.  See
   // for example, JSArray::JSArrayVerify).
   Object* filler;
   // We cannot always fill with one_pointer_filler_map because objects
   // created from API functions expect their internal fields to be initialized
   // with undefined_value.
   // Pre-allocated fields need to be initialized with undefined_value as well
   // so that object accesses before the constructor completes (e.g. in the
   // debugger) will not cause a crash.
-  if (map->constructor()->IsJSFunction() &&
-      JSFunction::cast(map->constructor())
-          ->IsInobjectSlackTrackingInProgress()) {
+  Object* constructor = map->GetConstructor();
+  if (constructor->IsJSFunction() &&
+      JSFunction::cast(constructor)->IsInobjectSlackTrackingInProgress()) {
     // We might want to shrink the object later.
     DCHECK(obj->GetInternalFieldCount() == 0);
     filler = Heap::one_pointer_filler_map();
   } else {
     filler = Heap::undefined_value();
   }
   obj->InitializeBody(map, Heap::undefined_value(), filler);
 }
 
 
@@ skipping 2657 matching lines @@
       static_cast<int>(object_sizes_last_time_[index]));
   CODE_AGE_LIST_COMPLETE(ADJUST_LAST_TIME_OBJECT_COUNT)
 #undef ADJUST_LAST_TIME_OBJECT_COUNT
 
   MemCopy(object_counts_last_time_, object_counts_, sizeof(object_counts_));
   MemCopy(object_sizes_last_time_, object_sizes_, sizeof(object_sizes_));
   ClearObjectStats();
 }
 }
 }  // namespace v8::internal