// The new finalization semantics says that registration of
// finalizable objects must be performed on successful return from the
// Object.<init> constructor.  We could implement this trivially if
// <init> were never rewritten but since JVMTI allows this to occur, a
// more complicated solution is required.  A special return bytecode
// is used only by Object.<init> to signal the finalization
// registration point.  Additionally local 0 must be preserved so it's
// available to pass to the registration function.  For simplicty we
// require that local 0 is never overwritten so it's available as an
// argument for registration.

void Rewriter::rewrite_Object_init(methodHandle method, TRAPS) {

  {- -------------------------------------------
  (1) メソッド内の全部のバイトコードを辿り, 
      return 命令であれば Bytecodes::_return_register_finalizer 命令に書き換える.

      (なお, 局所変数領域の 0 番(this)を変更するバイトコード命令がある場合は IncompatibleClassChangeError
       (理由は上記コメント部参照))
      ---------------------------------------- -}

      RawBytecodeStream bcs(method);
      while (!bcs.is_last_bytecode()) {
        Bytecodes::Code opcode = bcs.raw_next();
        switch (opcode) {
          case Bytecodes::_return: *bcs.bcp() = Bytecodes::_return_register_finalizer; break;

          case Bytecodes::_istore:
          case Bytecodes::_lstore:
          case Bytecodes::_fstore:
          case Bytecodes::_dstore:
          case Bytecodes::_astore:
            if (bcs.get_index() != 0) continue;

            // fall through
          case Bytecodes::_istore_0:
          case Bytecodes::_lstore_0:
          case Bytecodes::_fstore_0:
          case Bytecodes::_dstore_0:
          case Bytecodes::_astore_0:
            THROW_MSG(vmSymbols::java_lang_IncompatibleClassChangeError(),
                      "can't overwrite local 0 in Object.<init>");
            break;
        }
      }
    }