Reduce space usage of simple transitions and descriptors holders.

src/objects.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 158 matching lines @@
   ALLOW_CREATION,
   OMIT_CREATION
 };
 
 
 // Indicates whether transitions can be added to a source map or not.
 enum TransitionFlag {
   INSERT_TRANSITION,
   OMIT_TRANSITION
 };
 

[Michael Starzinger, 2012/09/19 09:34:55]

Insert second empty newline here.

[Toon Verwaest, 2012/09/19 09:53:23]

Done.

+// Indicates whether the transition is simple: it either adds a property to a

[Michael Starzinger, 2012/09/19 09:34:55]

The comment is slightly confusing to me. Can we rephrase the second part? What
is "it" in this sentence?

[Toon Verwaest, 2012/09/19 09:53:23]

Done.

+// descriptor array; or it modifies the last added property.
+enum SimpleTransitionFlag {
+  SIMPLE_TRANSITION,
+  FULL_TRANSITION
+};
+

[Michael Starzinger, 2012/09/19 09:34:55]

Insert second empty newline here.

[Toon Verwaest, 2012/09/19 09:53:23]

Done.

 // Indicates whether we are only interested in the descriptors of a particular
 // map, or in all descriptors in the descriptor array.
 enum DescriptorFlag {
   ALL_DESCRIPTORS,
   OWN_DESCRIPTORS
 };
 
 
 // Instance size sentinel for objects of variable size.
 const int kVariableSizeSentinel = 0;
@@ skipping 4639 matching lines @@
                                         ElementsKind to_kind);
 
   bool StoresOwnDescriptors() { return HasTransitionArray(); }
   inline bool HasTransitionArray();
   inline bool HasElementsTransition();
   inline Map* elements_transition_map();
   MUST_USE_RESULT inline MaybeObject* set_elements_transition_map(
       Map* transitioned_map);
   inline void SetTransition(int transition_index, Map* target);
   inline Map* GetTransition(int transition_index);
-  MUST_USE_RESULT inline MaybeObject* AddTransition(String* key, Map* target);
+  MUST_USE_RESULT inline MaybeObject* AddTransition(
+      String* key,
+      Map* target,
+      SimpleTransitionFlag flag = SIMPLE_TRANSITION);

[Michael Starzinger, 2012/09/19 09:34:55]

The Google C++ Style Guide doesn't like default arguments. We sometimes break
that rule. But since this method only has two call-sites, I think it's not worth
here.

http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml#Default_Arguments

[Toon Verwaest, 2012/09/19 09:53:23]

Done.

   DECL_ACCESSORS(transitions, TransitionArray)
   inline void ClearTransitions(Heap* heap,
                                WriteBarrierMode mode = UPDATE_WRITE_BARRIER);
 
   // Tells whether the map is attached to SharedFunctionInfo
   // (for inobject slack tracking).
   inline void set_attached_to_shared_function_info(bool value);
 
   inline bool attached_to_shared_function_info();
 
@@ skipping 130 matching lines @@
 
   inline bool owns_descriptors();
   inline void set_owns_descriptors(bool is_shared);
 
   MUST_USE_RESULT MaybeObject* RawCopy(int instance_size);
   MUST_USE_RESULT MaybeObject* CopyWithPreallocatedFieldDescriptors();
   MUST_USE_RESULT MaybeObject* CopyDropDescriptors();
   MUST_USE_RESULT MaybeObject* CopyReplaceDescriptors(
       DescriptorArray* descriptors,
       String* name,
-      TransitionFlag flag);
+      TransitionFlag flag,
+      int descriptor_index = 0);

[Michael Starzinger, 2012/09/19 09:34:55]

Likewise. Although there are more call-sites here. But they are all in
objects.cc, so I also think it's not worth here.

[Toon Verwaest, 2012/09/19 09:53:23]

Done.

   MUST_USE_RESULT MaybeObject* ShareDescriptor(Descriptor* descriptor);
   MUST_USE_RESULT MaybeObject* CopyAddDescriptor(Descriptor* descriptor,
                                                  TransitionFlag flag);
   MUST_USE_RESULT MaybeObject* CopyInsertDescriptor(Descriptor* descriptor,
                                                     TransitionFlag flag);
   MUST_USE_RESULT MaybeObject* CopyReplaceDescriptor(Descriptor* descriptor,
                                                      int index,
                                                      TransitionFlag flag);
   MUST_USE_RESULT MaybeObject* CopyAsElementsKind(ElementsKind kind,
                                                   TransitionFlag flag);
@@ skipping 4005 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_