Bookkeeping for allocation site pretenuring

src/objects.h

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@@ skipping 8086 matching lines @@
 enum AllocationSiteMode {
   DONT_TRACK_ALLOCATION_SITE,
   TRACK_ALLOCATION_SITE,
   LAST_ALLOCATION_SITE_MODE = TRACK_ALLOCATION_SITE
 };
 
 
 class AllocationSite: public Struct {
  public:
   static const uint32_t kMaximumArrayBytesToPretransition = 8 * 1024;
+  static const int kUndecided = 0;
+  static const int kDontTenure = 1;
+  static const int kTenure = 2;
+  static const int kZombie = 3;

[Hannes Payer (out of office), 2013/11/21 20:52:24]

Right now the state diagram (should) looks like that:
0 -> 1
0 -> 2
1 -> 3
2 -> 3
The 0 ->  3 transition is missing see my comments.
A follow up CL should add the 1 -> 2 and 2 -> 1 transitions.

[mvstanton, 2013/11/22 11:18:51]

Thx. I made these 4 state values into an enum to indicate grouping and because
of a compiler issue.

The new TODO in heap.cc talks about revisiting the decision for the 1->2 and
2->1 cases.

Finally, I think the zombie state is okay. But it's a strange concept so I added
a long comment right before IsZombie(), lets chat about that.

 
   DECL_ACCESSORS(transition_info, Object)
   // nested_site threads a list of sites that represent nested literals
   // walked in a particular order. So [[1, 2], 1, 2] will have one
   // nested_site, but [[1, 2], 3, [4]] will have a list of two.
   DECL_ACCESSORS(nested_site, Object)
   DECL_ACCESSORS(memento_found_count, Smi)
   DECL_ACCESSORS(memento_create_count, Smi)
   DECL_ACCESSORS(pretenure_decision, Smi)
   DECL_ACCESSORS(dependent_code, DependentCode)
   DECL_ACCESSORS(weak_next, Object)
 
   inline void Initialize();
 
-  bool HasNestedSites() {
-    return nested_site()->IsAllocationSite();
-  }
-
   // This method is expensive, it should only be called for reporting.
   bool IsNestedSite();
 
   class ElementsKindBits:       public BitField<ElementsKind, 0,  15> {};
   class UnusedBits:             public BitField<int,          15, 14> {};
   class DoNotInlineBit:         public BitField<bool,         29,  1> {};
 

[Hannes Payer (out of office), 2013/11/21 20:52:24]

Can we have newlines between the methods?

[mvstanton, 2013/11/22 11:18:51]

Done.

+  inline void IncrementMementoFoundCount();
+  inline void IncrementMementoCreateCount();
+  PretenureFlag GetPretenureMode() {
+    int mode = pretenure_decision()->value();
+    // Zombie objects "decide" to be untenured.
+    return (mode == kTenure) ? TENURED : NOT_TENURED;
+  }
+  bool IsZombie() {
+    return pretenure_decision()->value() == kZombie;
+  }
+  inline void MarkZombie();
+  bool DecisionMade() {
+    return pretenure_decision()->value() != kUndecided;
+  }
+  void Decide() {
+    ASSERT(!DecisionMade());
+    if (ShouldPretenure()) {
+      set_pretenure_decision(Smi::FromInt(kTenure));
+    } else {
+      set_pretenure_decision(Smi::FromInt(kDontTenure));
+    }
+  }
+  void Clear() {
+    set_memento_found_count(Smi::FromInt(0));
+    set_memento_create_count(Smi::FromInt(0));
+  }
+
   ElementsKind GetElementsKind() {
     ASSERT(!SitePointsToLiteral());
     int value = Smi::cast(transition_info())->value();
     return ElementsKindBits::decode(value);
   }
 
   void SetElementsKind(ElementsKind kind) {
     int value = Smi::cast(transition_info())->value();
     set_transition_info(Smi::FromInt(ElementsKindBits::update(value, kind)),
                         SKIP_WRITE_BARRIER);
@@ skipping 53 matching lines @@
   static const int kPointerFieldsBeginOffset = kTransitionInfoOffset;
   static const int kPointerFieldsEndOffset = kDependentCodeOffset;
 
   // For other visitors, use the fixed body descriptor below.
   typedef FixedBodyDescriptor<HeapObject::kHeaderSize,
                               kDependentCodeOffset + kPointerSize,
                               kSize> BodyDescriptor;
 
  private:
   inline DependentCode::DependencyGroup ToDependencyGroup(Reason reason);
+  inline bool ShouldPretenure();
+
   DISALLOW_IMPLICIT_CONSTRUCTORS(AllocationSite);
 };
 
 
 class AllocationMemento: public Struct {
  public:
   static const int kAllocationSiteOffset = HeapObject::kHeaderSize;
   static const int kSize = kAllocationSiteOffset + kPointerSize;
 
   DECL_ACCESSORS(allocation_site, Object)
 
-  bool IsValid() { return allocation_site()->IsAllocationSite(); }
+  bool IsValid() {
+    return allocation_site()->IsAllocationSite() &&
+        !AllocationSite::cast(allocation_site())->IsZombie();
+  }
   AllocationSite* GetAllocationSite() {
     ASSERT(IsValid());
     return AllocationSite::cast(allocation_site());
   }
 
   DECLARE_PRINTER(AllocationMemento)
   DECLARE_VERIFIER(AllocationMemento)
 
   // Returns NULL if no AllocationMemento is available for object.
   static AllocationMemento* FindForJSObject(JSObject* object,
@@ skipping 2348 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_