Remove prototype checks for leaf maps in optimized code.

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 4677 matching lines @@
 // following layout for n dependency groups:
 //
 // +----+----+-----+----+---------+----------+-----+---------+-----------+
 // | C1 | C2 | ... | Cn | group 1 |  group 2 | ... | group n | undefined |
 // +----+----+-----+----+---------+----------+-----+---------+-----------+
 //
 // The first n elements are Smis, each of them specifies the number of codes
 // in the corresponding group. The subsequent elements contain grouped code
 // objects. The suffix of the array can be filled with the undefined value if
 // the number of codes is less than the length of the array.
-// 
+//
 // All code indexes used in the class are counted starting from the first
 // code object of the first group. In other words, code index 0 corresponds
 // to array index n = kCodesStartIndex.
 
 class DependentCodes: public FixedArray {
  public:
   enum DependencyGroup {
     // Group of codes that weakly embed this map and depend on being
     // deoptimized when the map is garbage collected.
     kWeaklyEmbeddedGroup,
-    kGroupCount = kWeaklyEmbeddedGroup + 1
+    // Group of codes that omitted prototype check for a prototype with this map
+    // and depend on being deoptimized when map layout changes.

[Toon Verwaest, 2013/02/13 10:40:07]

Group of code that omit run-time prototype checks for prototypes described by
this map. The group is deoptimized whenever an object described by this map
changes shape (and transitions to a new map), possibly invalidating the
assumptions embedded in the code.

[ulan, 2013/02/13 12:27:38]

Done.

+    kPrototypeCheckGroup,
+    kGroupCount = kPrototypeCheckGroup + 1
   };
   // Array for holding the index of the first code object of each group.
   // The last element stores the total number of code objects.
-  typedef int GroupStartIndexes[kGroupCount + 1];
+  class GroupStartIndexes {
+   public:
+    explicit GroupStartIndexes(DependentCodes* codes);
+    void Recompute(DependentCodes* codes);
+    int at(int i) { return start_indexes_[i]; }
+   private:
+    int start_indexes_[kGroupCount + 1];
+  };
   inline int number_of_codes(DependencyGroup group);
   inline void set_number_of_codes(DependencyGroup group, int value);
   inline Code* code_at(int i);
   inline void set_code_at(int i, Code* value);
   inline Object** code_slot_at(int i);
   inline void clear_code_at(int i);
   static inline DependentCodes* cast(Object* object);
-  inline void ComputeGroupStartIndexes(GroupStartIndexes starts);
   bool Contains(DependencyGroup group, Code* code);
   static Handle<DependentCodes> Insert(Handle<DependentCodes> codes,
                                        DependencyGroup group,
                                        Handle<Code> value);
 
  private:
   // Make a room at the end of the given group by moving out the first
   // code objects of the subsequent groups.
   inline void ExtendGroup(DependencyGroup group);
   static const int kCodesStartIndex = kGroupCount;
@@ skipping 440 matching lines @@
   // heap verification is turned on.
   void ZapPrototypeTransitions();
   void ZapTransitions();
 
   bool CanTransition() {
     // Only JSObject and subtypes have map transitions and back pointers.
     STATIC_ASSERT(LAST_TYPE == LAST_JS_OBJECT_TYPE);
     return instance_type() >= FIRST_JS_OBJECT_TYPE;
   }
 
+
+  inline void NotifyObjectLayoutChange();
+
+  inline bool CanOmitPrototypeChecks();
+
   inline void AddDependentCode(DependentCodes::DependencyGroup group,
                                Handle<Code> code);
 
+  void DeoptimizeDependentCodes(DependentCodes::DependencyGroup group);
+
   // Dispatched behavior.
   DECLARE_PRINTER(Map)
   DECLARE_VERIFIER(Map)
 
 #ifdef VERIFY_HEAP
   void SharedMapVerify();
 #endif
 
   inline int visitor_id();
   inline void set_visitor_id(int visitor_id);
@@ skipping 3719 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_