[wasm] reuse the first compiled module

src/snapshot/code-serializer.cc

 // Copyright 2016 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/snapshot/code-serializer.h"
 
 #include <memory>
 
 #include "src/code-stubs.h"
 #include "src/log.h"
@@ skipping 80 matching lines @@
       case Code::FUNCTION:
         DCHECK(code_object->has_reloc_info_for_serialization());
         SerializeGeneric(code_object, how_to_code, where_to_point);
         return;
       default:
         return SerializeCodeObject(code_object, how_to_code, where_to_point);
     }
     UNREACHABLE();
   }
 
+  if (SkipOver(obj)) {
+    return SerializeGeneric(*isolate()->factory()->undefined_value(),

[bradnelson, 2016/09/02 16:56:59]

So the links contain undefined when serialized?

[Mircea Trofin, 2016/09/02 20:55:30]

Yes. The module obtained by deserializing this is its own separate
JSObject instance, with its own wasm module instances chain

+                            how_to_code, where_to_point);
+  }
   // Past this point we should not see any (context-specific) maps anymore.
   CHECK(!obj->IsMap());
   // There should be no references to the global object embedded.
   CHECK(!obj->IsJSGlobalProxy() && !obj->IsJSGlobalObject());
   // There should be no hash table embedded. They would require rehashing.
   CHECK(!obj->IsHashTable());
   // We expect no instantiated function objects or contexts.
   CHECK(!obj->IsJSFunction() && !obj->IsContext());
 
   SerializeGeneric(obj, how_to_code, where_to_point);
@@ skipping 294 matching lines @@
   *rejection_result = scd.SanityCheck(isolate, expected_source_hash);
   if (*rejection_result != CHECK_SUCCESS) {
     cached_data->Reject();
     return SerializedCodeData(nullptr, 0);
   }
   return scd;
 }
 
 }  // namespace internal
 }  // namespace v8