Revert "Revert "Revert "[global-handles] Remove dead code"""

This reverts commit c836a95e.

Reason for revert: I don't think this was related.

Original change's description:
> Revert "Revert "[global-handles] Remove dead code""
> 
> This reverts commit 58020872.
> 
> Reason for revert: Turned out to be a bot issue, reverting the revert. 
> 
> Original change's description:
> > Revert "[global-handles] Remove dead code"
> > 
> > This reverts commit e2890c19.
> > 
> > Reason for revert: Looks like this CL causes slowdown on multiple builders, Check tests timeout and raise exceptions on the bot. Possible it is a bot issue as well, see tracking bug - https://bugs.chromium.org/p/chromium/issues/detail?id=720606
> > 
> > Original change's description:
> > > [global-handles] Remove dead code
> > > 
> > > Bug: chromium:720477
> > > Change-Id: I090168c575c41b7038af5dfba6cd8973d1154c51
> > > Reviewed-on: https://chromium-review.googlesource.com/501790
> > > Reviewed-by: Hannes Payer <hpayer@chromium.org>
> > > Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
> > > Cr-Commit-Position: refs/heads/master@{#45241}
> > 
> > TBR=hpayer@chromium.org,mlippautz@chromium.org,jochen@chromium.org
> > NOPRESUBMIT=true
> > NOTREECHECKS=true
> > NOTRY=true
> > Bug: chromium:720477
> > 
> > Change-Id: I92f40d8c4dbfdb5208b3068648612e8c5b97fb20
> > Reviewed-on: https://chromium-review.googlesource.com/502029
> > Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
> > Commit-Queue: Deepti Gandluri <gdeepti@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#45243}
> 
> TBR=hpayer@chromium.org,gdeepti@chromium.org,mlippautz@chromium.org,jochen@chromium.org,v8-reviews@googlegroups.com
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> Bug: chromium:720477
> 
> Change-Id: I70e190e0c27074228a8128aa849e5a419af915e8
> Reviewed-on: https://chromium-review.googlesource.com/502030
> Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
> Commit-Queue: Deepti Gandluri <gdeepti@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#45244}

TBR=hpayer@chromium.org,gdeepti@chromium.org,mlippautz@chromium.org,jochen@chromium.org,v8-reviews@googlegroups.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
Bug: chromium:720477

Change-Id: If3e4abea51d87546e25076b906a4c91e5ccf947b
Reviewed-on: https://chromium-review.googlesource.com/503007Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45246}

src/global-handles.cc

@@ -647,6 +647,19 @@ void GlobalHandles::IterateNewSpaceStrongAndDependentRoots(RootVisitor* v) {
   }
 }
 
+
+void GlobalHandles::IdentifyNewSpaceWeakIndependentHandles(
+    WeakSlotCallbackWithHeap f) {
+  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->IsWeak() &&
+        f(isolate_->heap(), node->location())) {
+      node->MarkPending();
+    }
+  }
+}
+
 void GlobalHandles::IterateNewSpaceWeakIndependentRoots(RootVisitor* v) {
   for (int i = 0; i < new_space_nodes_.length(); ++i) {
     Node* node = new_space_nodes_[i];
@@ -690,6 +703,7 @@ void GlobalHandles::MarkNewSpaceWeakUnmodifiedObjectsPending(
   }
 }
 
+template <GlobalHandles::IterationMode mode>
 void GlobalHandles::IterateNewSpaceWeakUnmodifiedRoots(RootVisitor* v) {
   for (int i = 0; i < new_space_nodes_.length(); ++i) {
     Node* node = new_space_nodes_[i];
@@ -698,18 +712,36 @@ void GlobalHandles::IterateNewSpaceWeakUnmodifiedRoots(RootVisitor* v) {
         node->IsWeakRetainer()) {
       // Pending weak phantom handles die immediately. Everything else survives.
       if (node->IsPendingPhantomResetHandle()) {
-        node->ResetPhantomHandle();
-        ++number_of_phantom_handle_resets_;
+        if (mode == IterationMode::HANDLE_PHANTOM_NODES ||
+            mode == IterationMode::HANDLE_PHANTOM_NODES_VISIT_OTHERS) {
+          node->ResetPhantomHandle();
+          ++number_of_phantom_handle_resets_;
+        }
       } else if (node->IsPendingPhantomCallback()) {
-        node->CollectPhantomCallbackData(isolate(),
-                                         &pending_phantom_callbacks_);
+        if (mode == IterationMode::HANDLE_PHANTOM_NODES ||
+            mode == IterationMode::HANDLE_PHANTOM_NODES_VISIT_OTHERS) {
+          node->CollectPhantomCallbackData(isolate(),
+                                           &pending_phantom_callbacks_);
+        }
       } else {
-        v->VisitRootPointer(Root::kGlobalHandles, node->location());
+        if (mode == IterationMode::VISIT_OTHERS ||
+            mode == IterationMode::HANDLE_PHANTOM_NODES_VISIT_OTHERS) {
+          v->VisitRootPointer(Root::kGlobalHandles, node->location());
+        }
       }
     }
   }
 }
 
+template void GlobalHandles::IterateNewSpaceWeakUnmodifiedRoots<
+    GlobalHandles::HANDLE_PHANTOM_NODES>(RootVisitor* v);
+
+template void GlobalHandles::IterateNewSpaceWeakUnmodifiedRoots<
+    GlobalHandles::VISIT_OTHERS>(RootVisitor* v);
+
+template void GlobalHandles::IterateNewSpaceWeakUnmodifiedRoots<
+    GlobalHandles::HANDLE_PHANTOM_NODES_VISIT_OTHERS>(RootVisitor* v);
+
 void GlobalHandles::InvokeSecondPassPhantomCallbacks(
     List<PendingPhantomCallback>* callbacks, Isolate* isolate) {
   while (callbacks->length() != 0) {
@@ -957,6 +989,30 @@ void GlobalHandles::IterateWeakRootsInNewSpaceWithClassIds(
   }
 }
 
+
+int GlobalHandles::NumberOfWeakHandles() {
+  int count = 0;
+  for (NodeIterator it(this); !it.done(); it.Advance()) {
+    if (it.node()->IsWeakRetainer()) {
+      count++;
+    }
+  }
+  return count;
+}
+
+
+int GlobalHandles::NumberOfGlobalObjectWeakHandles() {
+  int count = 0;
+  for (NodeIterator it(this); !it.done(); it.Advance()) {
+    if (it.node()->IsWeakRetainer() &&
+        it.node()->object()->IsJSGlobalObject()) {
+      count++;
+    }
+  }
+  return count;
+}
+
+
 void GlobalHandles::RecordStats(HeapStats* stats) {
   *stats->global_handle_count = 0;
   *stats->weak_global_handle_count = 0;
@@ -1016,7 +1072,9 @@ void GlobalHandles::Print() {
 
 #endif
 
-void GlobalHandles::TearDown() {}
+void GlobalHandles::TearDown() {
+  // TODO(1428): invoke weak callbacks.
+}
 
 EternalHandles::EternalHandles() : size_(0) {
   for (unsigned i = 0; i < arraysize(singleton_handles_); i++) {

src/global-handles.h

@@ -43,6 +43,12 @@ enum WeaknessType {
 
 class GlobalHandles {
  public:
+  enum IterationMode {
+    HANDLE_PHANTOM_NODES_VISIT_OTHERS,
+    VISIT_OTHERS,
+    HANDLE_PHANTOM_NODES
+  };
+
   ~GlobalHandles();
 
   // Creates a new global handle that is alive until Destroy is called.
@@ -79,6 +85,13 @@ class GlobalHandles {
 
   void RecordStats(HeapStats* stats);
 
+  // Returns the current number of weak handles.
+  int NumberOfWeakHandles();
+
+  // Returns the current number of weak handles to global objects.
+  // These handles are also included in NumberOfWeakHandles().
+  int NumberOfGlobalObjectWeakHandles();
+
   // Returns the current number of handles to global objects.
   int global_handles_count() const {
     return number_of_global_handles_;
@@ -143,6 +156,10 @@ class GlobalHandles {
   // Iterates over strong and dependent handles. See the node above.
   void IterateNewSpaceStrongAndDependentRoots(RootVisitor* v);
 
+  // Finds weak independent or partially independent handles satisfying
+  // the callback predicate and marks them as pending. See the note above.
+  void IdentifyNewSpaceWeakIndependentHandles(WeakSlotCallbackWithHeap f);
+
   // Iterates over weak independent or partially independent handles.
   // See the note above.
   void IterateNewSpaceWeakIndependentRoots(RootVisitor* v);
@@ -154,6 +171,7 @@ class GlobalHandles {
 
   // Iterates over weak independent or unmodified handles.
   // See the note above.
+  template <IterationMode mode>
   void IterateNewSpaceWeakUnmodifiedRoots(RootVisitor* v);
 
   // Identify unmodified objects that are in weak state and marks them

src/heap/heap.cc

@@ -1781,8 +1781,11 @@ void Heap::Scavenge() {
   isolate()->global_handles()->MarkNewSpaceWeakUnmodifiedObjectsPending(
       &IsUnscavengedHeapObject);
 
-  isolate()->global_handles()->IterateNewSpaceWeakUnmodifiedRoots(
-      &root_scavenge_visitor);
+  isolate()
+      ->global_handles()
+      ->IterateNewSpaceWeakUnmodifiedRoots<
+          GlobalHandles::HANDLE_PHANTOM_NODES_VISIT_OTHERS>(
+          &root_scavenge_visitor);
   new_space_front = DoScavenge(new_space_front);
 
   UpdateNewSpaceReferencesInExternalStringTable(

src/heap/mark-compact.cc

@@ -2547,8 +2547,10 @@ void MinorMarkCompactCollector::MarkLiveObjects() {
     TRACE_GC(heap()->tracer(), GCTracer::Scope::MINOR_MC_MARK_GLOBAL_HANDLES);
     isolate()->global_handles()->MarkNewSpaceWeakUnmodifiedObjectsPending(
         &IsUnmarkedObjectForYoungGeneration);
-    isolate()->global_handles()->IterateNewSpaceWeakUnmodifiedRoots(
-        &root_visitor);
+    isolate()
+        ->global_handles()
+        ->IterateNewSpaceWeakUnmodifiedRoots<
+            GlobalHandles::HANDLE_PHANTOM_NODES_VISIT_OTHERS>(&root_visitor);
     ProcessMarkingDeque();
   }