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

src/objects.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/objects.h"
 
 #include <cmath>
 #include <iomanip>
 #include <sstream>
 
@@ skipping 16849 matching lines @@
           // The other element will be processed on the next iteration.
           current--;
         } else {
           // The place for the current element is occupied. Leave the element
           // for the next probe.
           done = false;
         }
       }
     }
   }
+  // 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);
 }
 
 
 template<typename Derived, typename Shape, typename Key>
 Handle<Derived> HashTable<Derived, Shape, Key>::EnsureCapacity(
     Handle<Derived> table,
     int n,
     Key key,
     PretenureFlag pretenure) {
   Isolate* isolate = table->GetIsolate();
@@ skipping 1330 matching lines @@
   Isolate* isolate = table->GetIsolate();
 
   int entry = table->FindEntry(isolate, key, hash);
 
   // Key is already in table, just overwrite value.
   if (entry != kNotFound) {
     table->set(EntryToIndex(entry) + 1, *value);
     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);
   return table;
 }
 
 
 Handle<ObjectHashTable> ObjectHashTable::Remove(Handle<ObjectHashTable> table,
                                                 Handle<Object> key,
                                                 bool* was_present) {
@@ skipping 1144 matching lines @@
   if (cell->value() != *new_value) {
     cell->set_value(*new_value);
     Isolate* isolate = cell->GetIsolate();
     cell->dependent_code()->DeoptimizeDependentCodeGroup(
         isolate, DependentCode::kPropertyCellChangedGroup);
   }
 }
 
 }  // namespace internal
 }  // namespace v8