Bookkeeping for allocation site pretenuring

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index e6ec722cf92a86c535fd3eae9834d6a1fc4cccb4..2116d1533be591e63305fe43ea4afcdd084f3c66 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -8104,6 +8104,10 @@ enum AllocationSiteMode {
 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
@@ -8118,10 +8122,6 @@ class AllocationSite: public Struct {
 
   inline void Initialize();
 
-  bool HasNestedSites() {
-    return nested_site()->IsAllocationSite();
-  }
-
   // This method is expensive, it should only be called for reporting.
   bool IsNestedSite();
 
@@ -8129,6 +8129,33 @@ class AllocationSite: public Struct {
   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();
@@ -8202,6 +8229,8 @@ class AllocationSite: public Struct {
 
  private:
   inline DependentCode::DependencyGroup ToDependencyGroup(Reason reason);
+  inline bool ShouldPretenure();
+
   DISALLOW_IMPLICIT_CONSTRUCTORS(AllocationSite);
 };
 
@@ -8213,7 +8242,10 @@ class AllocationMemento: public Struct {
 
   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());