Changed scavenge GC to collect unmodified references

src/global-handles.cc

Index: src/global-handles.cc
diff --git a/src/global-handles.cc b/src/global-handles.cc
index 650999f394c5cc7c2e5397afff53c74e3c186d20..fc1170e1588c5c9a3761f0b00772b393f05ddf1a 100644
--- a/src/global-handles.cc
+++ b/src/global-handles.cc
@@ -66,6 +66,7 @@ class GlobalHandles::Node {
     set_independent(false);
     set_partially_dependent(false);
     set_in_new_space_list(false);
+    set_unmodified(false);
     parameter_or_next_free_.next_free = NULL;
     weak_callback_ = NULL;
   }
@@ -77,6 +78,7 @@ class GlobalHandles::Node {
     set_state(FREE);
     set_weakness_type(NORMAL_WEAK);
     set_in_new_space_list(false);
+    set_unmodified(false);
     parameter_or_next_free_.next_free = *first_free;
     *first_free = this;
   }
@@ -87,6 +89,7 @@ class GlobalHandles::Node {
     class_id_ = v8::HeapProfiler::kPersistentHandleNoClassId;
     set_independent(false);
     set_partially_dependent(false);
+    set_unmodified(false);
     set_state(NORMAL);
     parameter_or_next_free_.parameter = NULL;
     weak_callback_ = NULL;
@@ -107,6 +110,7 @@ class GlobalHandles::Node {
     class_id_ = v8::HeapProfiler::kPersistentHandleNoClassId;
     set_independent(false);
     set_partially_dependent(false);
+    set_unmodified(false);
     weak_callback_ = NULL;
     DecreaseBlockUses();
   }
@@ -153,6 +157,10 @@ class GlobalHandles::Node {
     flags_ = IsInNewSpaceList::update(flags_, v);
   }
 
+  bool is_unmodified() { return flag_unmodified_; }
+
+  void set_unmodified(bool v) { flag_unmodified_ = v; }
+
   WeaknessType weakness_type() const {
     return NodeWeaknessType::decode(flags_);
   }
@@ -354,6 +362,8 @@ class GlobalHandles::Node {
   class NodeWeaknessType : public BitField<WeaknessType, 6, 2> {};
 
   uint8_t flags_;
+  // Merge this with flags_ later on. May be we need to extend flags_

[mythria, 2015/09/28 15:20:08]

I added a new field for the unmodified check.flags_ does not have any free bits
left. I am not sure if I should extend flags_ to 16 bits or just use a new
field.

[jochen (gone - plz use gerrit), 2015/09/28 15:56:19]

if the performance tests are looking good, we'll just rip the partially
dependent flag out...

+  bool flag_unmodified_;
 
   // Handle specific callback - might be a weak reference in disguise.
   WeakCallback weak_callback_;
@@ -648,7 +658,7 @@ void GlobalHandles::IterateNewSpaceStrongAndDependentRoots(ObjectVisitor* v) {
     Node* node = new_space_nodes_[i];
     if (node->IsStrongRetainer() ||
         (node->IsWeakRetainer() && !node->is_independent() &&
-         !node->is_partially_dependent())) {
+         !node->is_partially_dependent() && !node->is_unmodified())) {
         v->VisitPointer(node->location());
     }
   }
@@ -687,6 +697,48 @@ void GlobalHandles::IterateNewSpaceWeakIndependentRoots(ObjectVisitor* v) {
 }
 
 
+void GlobalHandles::IdentifyWeakUnmodifiedObjects(WeakSlotCallback f) {

[jochen (gone - plz use gerrit), 2015/09/28 15:56:19]

nit. f -> is_unmodified()

[mythria, 2015/10/02 15:29:16]

Done.

+  for (int i = 0; i < new_space_nodes_.length(); ++i) {
+    Node* node = new_space_nodes_[i];
+    if (node->IsWeak() && f(node->location())) {
+      node->set_partially_dependent(true);

[rmcilroy, 2015/09/28 17:32:46]

fix to set_unmodified(true);

[mythria, 2015/10/02 15:29:15]

Done.

+    }
+  }
+}
+
+
+void GlobalHandles::IdentifyNewSpaceWeakUnModifiedHandles(
+    WeakSlotCallbackWithHeap f) {

[jochen (gone - plz use gerrit), 2015/09/28 15:56:19]

f -> is_unscavenged

[mythria, 2015/10/02 15:29:15]

Done.

+  for (int i = 0; i < new_space_nodes_.length(); ++i) {
+    Node* node = new_space_nodes_[i];
+    DCHECK(node->is_in_new_space_list());
+    if ((node->is_independent() || node->is_unmodified()) && node->IsWeak() &&
+        f(isolate_->heap(), node->location())) {
+      node->MarkPending();
+    }
+  }
+}
+
+
+void GlobalHandles::IterateNewSpaceWeakUnModifiedRoots(ObjectVisitor* v) {
+  for (int i = 0; i < new_space_nodes_.length(); ++i) {
+    Node* node = new_space_nodes_[i];
+    DCHECK(node->is_in_new_space_list());
+    if ((node->is_independent() || node->is_unmodified()) &&
+        node->IsWeakRetainer()) {
+      // Pending weak phantom handles die immediately. Everything else survives.
+      if (node->state() == Node::PENDING &&
+          node->weakness_type() != NORMAL_WEAK) {
+        node->CollectPhantomCallbackData(isolate(),
+                                         &pending_phantom_callbacks_);
+      } else {
+        v->VisitPointer(node->location());
+      }
+    }
+  }
+}
+
+
 bool GlobalHandles::IterateObjectGroups(ObjectVisitor* v,
                                         WeakSlotCallbackWithHeap can_skip) {
   ComputeObjectGroupsAndImplicitReferences();
@@ -760,7 +812,8 @@ int GlobalHandles::PostScavengeProcessing(
     // Skip dependent handles. Their weak callbacks might expect to be
     // called between two global garbage collection callbacks which
     // are not called for minor collections.
-    if (!node->is_independent() && !node->is_partially_dependent()) {
+    if (!node->is_independent() && !node->is_partially_dependent() &&
+        !node->is_unmodified()) {
       continue;
     }
     node->clear_partially_dependent();