This paper discusses the target of loops optimization and various methods of program transformation which can significantly reduce the access time to subscripted variables , diminish some types of dependence , increase the " depth " of software pipelining , and merge some iterations of loops in order to make code compaction easier 程序变换可大大减少下标变数的访问时间;消除某些类型的相关,提高软件流水的“深度” ;合并多个循环,有利于进行代码压缩。