[wasm] reuse the first compiled module

src/snapshot/code-serializer.h

 // 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.
 
 #ifndef V8_SNAPSHOT_CODE_SERIALIZER_H_
 #define V8_SNAPSHOT_CODE_SERIALIZER_H_
 
 #include "src/parsing/preparse-data.h"
 #include "src/snapshot/serializer.h"
 
@@ skipping 18 matching lines @@
  protected:
   explicit CodeSerializer(Isolate* isolate, uint32_t source_hash)
       : Serializer(isolate), source_hash_(source_hash) {}
   ~CodeSerializer() override { OutputStatistics("CodeSerializer"); }
 
   virtual void SerializeCodeObject(Code* code_object, HowToCode how_to_code,
                                    WhereToPoint where_to_point) {
     UNREACHABLE();
   }
 
+  virtual bool ElideObject(Object* obj) { return false; }
   void SerializeGeneric(HeapObject* heap_object, HowToCode how_to_code,
                         WhereToPoint where_to_point);
 
  private:
   void SerializeObject(HeapObject* o, HowToCode how_to_code,
                        WhereToPoint where_to_point, int skip) override;
 
   void SerializeBuiltin(int builtin_index, HowToCode how_to_code,
                         WhereToPoint where_to_point);
   void SerializeCodeStub(Code* code_stub, HowToCode how_to_code,
@@ skipping 17 matching lines @@
                            WhereToPoint where_to_point) override {
     Code::Kind kind = code_object->kind();
     if (kind == Code::WASM_FUNCTION || kind == Code::WASM_TO_JS_FUNCTION ||
         kind == Code::JS_TO_WASM_FUNCTION) {
       SerializeGeneric(code_object, how_to_code, where_to_point);
     } else {
       UNREACHABLE();
     }
   }
 
+  bool ElideObject(Object* obj) override { return obj->IsWeakCell(); };
+
  private:
   WasmCompiledModuleSerializer(Isolate* isolate, uint32_t source_hash)
       : CodeSerializer(isolate, source_hash) {}
   DISALLOW_COPY_AND_ASSIGN(WasmCompiledModuleSerializer);
 };
 
 // Wrapper around ScriptData to provide code-serializer-specific functionality.
 class SerializedCodeData : public SerializedData {
  public:
   enum SanityCheckResult {
@@ skipping 58 matching lines @@
   static const int kPayloadLengthOffset = kNumCodeStubKeysOffset + kInt32Size;
   static const int kChecksum1Offset = kPayloadLengthOffset + kInt32Size;
   static const int kChecksum2Offset = kChecksum1Offset + kInt32Size;
   static const int kHeaderSize = kChecksum2Offset + kInt32Size;
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_SNAPSHOT_CODE_SERIALIZER_H_