Show references from weak containers as weak in heap snapshots.

src/heap-snapshot-generator.cc

Index: src/heap-snapshot-generator.cc
diff --git a/src/heap-snapshot-generator.cc b/src/heap-snapshot-generator.cc
index 332d0dbf6ff3705318f28a666d7134667e12295c..b23b60f3f537a699735720cfb56b96762b51a58b 100644
--- a/src/heap-snapshot-generator.cc
+++ b/src/heap-snapshot-generator.cc
@@ -1101,10 +1101,8 @@ class IndexedReferencesExtractor : public ObjectVisitor {
 };
 
 
-void V8HeapExplorer::ExtractReferences(HeapObject* obj) {
-  HeapEntry* heap_entry = GetEntry(obj);
-  if (heap_entry == NULL) return;  // No interest in this object.
-  int entry = heap_entry->index();
+bool V8HeapExplorer::ExtractReferencesPass1(int entry, HeapObject* obj) {
+  if (obj->IsFixedArray()) return false;  // FixedArrays are processed on pass 2
 
   if (obj->IsJSGlobalProxy()) {
     ExtractJSGlobalProxyReferences(entry, JSGlobalProxy::cast(obj));
@@ -1114,8 +1112,6 @@ void V8HeapExplorer::ExtractReferences(HeapObject* obj) {
     ExtractJSObjectReferences(entry, JSObject::cast(obj));
   } else if (obj->IsString()) {
     ExtractStringReferences(entry, String::cast(obj));
-  } else if (obj->IsContext()) {
-    ExtractContextReferences(entry, Context::cast(obj));
   } else if (obj->IsMap()) {
     ExtractMapReferences(entry, Map::cast(obj));
   } else if (obj->IsSharedFunctionInfo()) {
@@ -1137,12 +1133,19 @@ void V8HeapExplorer::ExtractReferences(HeapObject* obj) {
   } else if (obj->IsAllocationSite()) {
     ExtractAllocationSiteReferences(entry, AllocationSite::cast(obj));
   }
-  SetInternalReference(obj, entry, "map", obj->map(), HeapObject::kMapOffset);
+  return true;
+}
+
 
-  // Extract unvisited fields as hidden references and restore tags
-  // of visited fields.
-  IndexedReferencesExtractor refs_extractor(this, obj, entry);
-  obj->Iterate(&refs_extractor);
+bool V8HeapExplorer::ExtractReferencesPass2(int entry, HeapObject* obj) {
+  if (!obj->IsFixedArray()) return false;
+
+  if (obj->IsContext()) {
+    ExtractContextReferences(entry, Context::cast(obj));
+  } else {
+    ExtractFixedArrayReferences(entry, FixedArray::cast(obj));
+  }
+  return true;
 }
 
 
@@ -1320,6 +1323,7 @@ void V8HeapExplorer::ExtractMapReferences(int entry, Map* map) {
     SetInternalReference(transitions, transitions_entry,
                          "back_pointer", back_pointer);
     TagObject(transitions, "(transition array)");
+    MarkAsWeakContainer(transitions);
     SetInternalReference(map, entry,
                          "transitions", transitions,
                          Map::kTransitionsOrBackPointerOffset);
@@ -1336,6 +1340,7 @@ void V8HeapExplorer::ExtractMapReferences(int entry, Map* map) {
                        "descriptors", descriptors,
                        Map::kDescriptorsOffset);
 
+  MarkAsWeakContainer(map->code_cache());
   SetInternalReference(map, entry,
                        "code_cache", map->code_cache(),
                        Map::kCodeCacheOffset);
@@ -1345,6 +1350,7 @@ void V8HeapExplorer::ExtractMapReferences(int entry, Map* map) {
                        "constructor", map->constructor(),
                        Map::kConstructorOffset);
   TagObject(map->dependent_code(), "(dependent code)");
+  MarkAsWeakContainer(map->dependent_code());
   SetInternalReference(map, entry,
                        "dependent_code", map->dependent_code(),
                        Map::kDependentCodeOffset);
@@ -1506,6 +1512,7 @@ void V8HeapExplorer::ExtractPropertyCellReferences(int entry,
   ExtractCellReferences(entry, cell);
   SetInternalReference(cell, entry, "type", cell->type(),
                        PropertyCell::kTypeOffset);
+  MarkAsWeakContainer(cell->dependent_code());
   SetInternalReference(cell, entry, "dependent_code", cell->dependent_code(),
                        PropertyCell::kDependentCodeOffset);
 }
@@ -1517,6 +1524,7 @@ void V8HeapExplorer::ExtractAllocationSiteReferences(int entry,
                        AllocationSite::kTransitionInfoOffset);
   SetInternalReference(site, entry, "nested_site", site->nested_site(),
                        AllocationSite::kNestedSiteOffset);
+  MarkAsWeakContainer(site->dependent_code());
   SetInternalReference(site, entry, "dependent_code", site->dependent_code(),
                        AllocationSite::kDependentCodeOffset);
   // Do not visit weak_next as it is not visited by the StaticVisitor,
@@ -1562,6 +1570,20 @@ void V8HeapExplorer::ExtractJSArrayBufferReferences(
 }
 
 
+void V8HeapExplorer::ExtractFixedArrayReferences(int entry, FixedArray* array) {
+  bool is_weak = weak_containers_.Contains(array);
+  for (int i = 0, l = array->length(); i < l; ++i) {
+    if (is_weak) {
+      SetWeakReference(array, entry,
+                       i, array->get(i), array->OffsetOfElementAt(i));
+    } else {
+      SetInternalReference(array, entry,
+                           i, array->get(i), array->OffsetOfElementAt(i));
+    }
+  }
+}
+
+
 void V8HeapExplorer::ExtractClosureReferences(JSObject* js_obj, int entry) {
   if (!js_obj->IsJSFunction()) return;
 
@@ -1833,6 +1855,25 @@ bool V8HeapExplorer::IterateAndExtractReferences(
   heap_->IterateRoots(&extractor, VISIT_ALL);
   extractor.FillReferences(this);
 
+  // We have to do two passes as sometimes FixedArrays are used
+  // to weakly hold their items, and it's impossible to distinguish
+  // between these cases without processing the array owner first.
+  bool interrupted =
+      IterateAndExtractSinglePass<&V8HeapExplorer::ExtractReferencesPass1>() ||
+      IterateAndExtractSinglePass<&V8HeapExplorer::ExtractReferencesPass2>();
+
+  if (interrupted) {
+    filler_ = NULL;
+    return false;
+  }
+
+  filler_ = NULL;
+  return progress_->ProgressReport(true);
+}
+
+
+template<V8HeapExplorer::ExtractReferencesMethod extractor>
+bool V8HeapExplorer::IterateAndExtractSinglePass() {
   // Now iterate the whole heap.
   bool interrupted = false;
   HeapIterator iterator(heap_, HeapIterator::kFilterUnreachable);
@@ -1840,18 +1881,22 @@ bool V8HeapExplorer::IterateAndExtractReferences(
   for (HeapObject* obj = iterator.next();
        obj != NULL;
        obj = iterator.next(), progress_->ProgressStep()) {
-    if (!interrupted) {
-      ExtractReferences(obj);
-      if (!progress_->ProgressReport(false)) interrupted = true;
+    if (interrupted) continue;
+
+    HeapEntry* heap_entry = GetEntry(obj);
+    int entry = heap_entry->index();
+    if ((this->*extractor)(entry, obj)) {
+      SetInternalReference(obj, entry,
+                           "map", obj->map(), HeapObject::kMapOffset);
+      // Extract unvisited fields as hidden references and restore tags
+      // of visited fields.
+      IndexedReferencesExtractor refs_extractor(this, obj, entry);
+      obj->Iterate(&refs_extractor);
     }
-  }
-  if (interrupted) {
-    filler_ = NULL;
-    return false;
-  }
 
-  filler_ = NULL;
-  return progress_->ProgressReport(true);
+    if (!progress_->ProgressReport(false)) interrupted = true;
+  }
+  return interrupted;
 }
 
 
@@ -1987,6 +2032,24 @@ void V8HeapExplorer::SetWeakReference(HeapObject* parent_obj,
 }
 
 
+void V8HeapExplorer::SetWeakReference(HeapObject* parent_obj,
+                                      int parent_entry,
+                                      int index,
+                                      Object* child_obj,
+                                      int field_offset) {
+  ASSERT(parent_entry == GetEntry(parent_obj)->index());
+  HeapEntry* child_entry = GetEntry(child_obj);
+  if (child_entry == NULL) return;
+  if (IsEssentialObject(child_obj)) {
+    filler_->SetNamedReference(HeapGraphEdge::kWeak,
+                               parent_entry,
+                               names_->GetFormatted("%d", index),
+                               child_entry);
+  }
+  IndexedReferencesExtractor::MarkVisitedField(parent_obj, field_offset);
+}
+
+
 void V8HeapExplorer::SetPropertyReference(HeapObject* parent_obj,
                                           int parent_entry,
                                           Name* reference_name,
@@ -2114,6 +2177,13 @@ void V8HeapExplorer::TagObject(Object* obj, const char* tag) {
 }
 
 
+void V8HeapExplorer::MarkAsWeakContainer(Object* object) {
+  if (IsEssentialObject(object) && object->IsFixedArray()) {
+    weak_containers_.Insert(object);
+  }
+}
+
+
 class GlobalObjectsEnumerator : public ObjectVisitor {
  public:
   virtual void VisitPointers(Object** start, Object** end) {
@@ -2504,7 +2574,7 @@ bool HeapSnapshotGenerator::GenerateSnapshot() {
   debug_heap->Verify();
 #endif
 
-  SetProgressTotal(1);  // 1 pass.
+  SetProgressTotal(2);  // 2 passes.
 
 #ifdef VERIFY_HEAP
   debug_heap->Verify();