Reland of Rehash and clear deleted entries in weak collections during GC

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index efa49e2fcbfcbdecb67e689e08ab5a30b60346a4..65869fe60639c1079c8e456f153ab1fc03bc351f 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -16867,6 +16867,16 @@ void HashTable<Derived, Shape, Key>::Rehash(Key key) {
       }
     }
   }
+  // Wipe deleted entries.
+  Heap* heap = GetHeap();
+  Object* the_hole = heap->the_hole_value();
+  Object* undefined = heap->undefined_value();
+  for (uint32_t current = 0; current < capacity; current++) {
+    if (get(EntryToIndex(current)) == the_hole) {
+      set(EntryToIndex(current), undefined);
+    }
+  }
+  SetNumberOfDeletedElements(0);
 }
 
 
@@ -18217,6 +18227,12 @@ Handle<ObjectHashTable> ObjectHashTable::Put(Handle<ObjectHashTable> table,
     return table;
   }
 
+  // Rehash if more than 25% of the entries are deleted entries.
+  // TODO(jochen): Consider to shrink the fixed array in place.
+  if ((table->NumberOfDeletedElements() << 1) > table->NumberOfElements()) {
+    table->Rehash(isolate->factory()->undefined_value());
+  }
+
   // Check whether the hash table should be extended.
   table = EnsureCapacity(table, 1, key);
   table->AddEntry(table->FindInsertionEntry(hash), *key, *value);