Remove prototype checks for leaf maps in optimized code.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 1f6e7cc0878c87a8630b77f4e05bd40f7d89cc18..f86190a2cdfb861e07d26498965f5a042fdc5835 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -862,7 +862,7 @@ class MaybeObject BASE_EMBEDDED {
   V(TransitionArray)                           \
   V(DeoptimizationInputData)                   \
   V(DeoptimizationOutputData)                  \
-  V(DependentCodes)                            \
+  V(DependentCode)                            \
   V(TypeFeedbackCells)                         \
   V(FixedArray)                                \
   V(FixedDoubleArray)                          \
@@ -4695,32 +4695,43 @@ class Code: public HeapObject {
 // 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 {
+class DependentCode: public FixedArray {
  public:
   enum DependencyGroup {
     // Group of codes that weakly embed this map and depend on being

[Toon Verwaest, 2013/02/13 15:18:25]

Group of code

[ulan, 2013/02/14 09:30:46]

Done.

     // deoptimized when the map is garbage collected.
     kWeaklyEmbeddedGroup,
-    kGroupCount = kWeaklyEmbeddedGroup + 1
+    // 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.
+    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(DependentCode* codes);
+    void Recompute(DependentCode* 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);
+  static inline DependentCode* cast(Object* object);
   bool Contains(DependencyGroup group, Code* code);
-  static Handle<DependentCodes> Insert(Handle<DependentCodes> codes,
+  static Handle<DependentCode> Insert(Handle<DependentCode> codes,
                                        DependencyGroup group,
                                        Handle<Code> value);
 
@@ -4962,7 +4973,7 @@ class Map: public HeapObject {
   DECL_ACCESSORS(code_cache, Object)
 
   // [dependent codes]: list of optimized codes that have this map embedded.
-  DECL_ACCESSORS(dependent_codes, DependentCodes)
+  DECL_ACCESSORS(dependent_code, DependentCode)
 
   // [back pointer]: points back to the parent map from which a transition
   // leads to this map. The field overlaps with prototype transitions and the
@@ -5179,9 +5190,16 @@ class Map: public HeapObject {
     return instance_type() >= FIRST_JS_OBJECT_TYPE;
   }
 
-  inline void AddDependentCode(DependentCodes::DependencyGroup group,
+
+  inline void NotifyObjectLayoutChange();
+
+  inline bool CanOmitPrototypeChecks();
+
+  inline void AddDependentCode(DependentCode::DependencyGroup group,
                                Handle<Code> code);
 
+  void DeoptimizeDependentCode(DependentCode::DependencyGroup group);
+
   // Dispatched behavior.
   DECLARE_PRINTER(Map)
   DECLARE_VERIFIER(Map)
@@ -5230,8 +5248,8 @@ class Map: public HeapObject {
   static const int kDescriptorsOffset =
       kTransitionsOrBackPointerOffset + kPointerSize;
   static const int kCodeCacheOffset = kDescriptorsOffset + kPointerSize;
-  static const int kDependentCodesOffset = kCodeCacheOffset + kPointerSize;
-  static const int kBitField3Offset = kDependentCodesOffset + kPointerSize;
+  static const int kDependentCodeOffset = kCodeCacheOffset + kPointerSize;
+  static const int kBitField3Offset = kDependentCodeOffset + kPointerSize;
   static const int kSize = kBitField3Offset + kPointerSize;
 
   // Layout of pointer fields. Heap iteration code relies on them