[serializer] Move WeakFixedArray compaction to separate heap walk phase

src/api.cc

 // Copyright 2012 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/api.h"
 
 #include <string.h>  // For memcpy, strlen.
 #ifdef V8_USE_ADDRESS_SANITIZER
 #include <sanitizer/asan_interface.h>
 #endif  // V8_USE_ADDRESS_SANITIZER
@@ skipping 375 matching lines @@
       // Make sure all builtin scripts are cached.
       {
         HandleScope scope(isolate);
         for (int i = 0; i < i::Natives::GetBuiltinsCount(); i++) {
           internal_isolate->bootstrapper()->SourceLookup<i::Natives>(i);
         }
       }
       // If we don't do this then we end up with a stray root pointing at the
       // context even after we have disposed of the context.
       internal_isolate->heap()->CollectAllAvailableGarbage("mksnapshot");
+
+      // GC may have cleared weak cells, so compact any WeakFixedArrays
+      // found on the heap.
+      i::HeapIterator iterator(internal_isolate->heap(),
+                               i::HeapIterator::kFilterUnreachable);
+      for (i::HeapObject* o = iterator.next(); o != NULL; o = iterator.next()) {
+        if (o->IsPrototypeInfo()) {
+          i::Object* prototype_users =
+              i::PrototypeInfo::cast(o)->prototype_users();
+          if (prototype_users->IsWeakFixedArray()) {
+            i::WeakFixedArray* array = i::WeakFixedArray::cast(prototype_users);
+            array->Compact<i::JSObject::PrototypeRegistryCompactionCallback>();
+          }
+        } else if (o->IsScript()) {
+          i::Object* shared_list = i::Script::cast(o)->shared_function_infos();
+          if (shared_list->IsWeakFixedArray()) {
+            i::WeakFixedArray* array = i::WeakFixedArray::cast(shared_list);
+            array->Compact<i::WeakFixedArray::NullCallback>();
+          }
+        }
+      }
+
       i::Object* raw_context = *v8::Utils::OpenPersistent(context);
       context.Reset();
 
       i::SnapshotByteSink snapshot_sink;
       i::StartupSerializer ser(internal_isolate, &snapshot_sink);
       ser.SerializeStrongReferences();
 
       i::SnapshotByteSink context_sink;
       i::PartialSerializer context_ser(internal_isolate, &ser, &context_sink);
       context_ser.Serialize(&raw_context);
@@ skipping 8014 matching lines @@
   Address callback_address =
       reinterpret_cast<Address>(reinterpret_cast<intptr_t>(callback));
   VMState<EXTERNAL> state(isolate);
   ExternalCallbackScope call_scope(isolate, callback_address);
   callback(info);
 }
 
 
 }  // namespace internal
 }  // namespace v8