zoukankan      html  css  js  c++  java
  • KEIL5中C/C++优化等级问题

    知乎上有篇详解   https://zhuanlan.zhihu.com/p/24402180 强烈推荐

    C/C++的优化等级会对程序产生 不定性的影响,至于选择哪种优化等级必须从 现有的程序分析才行

    可参考知乎上的讲解

     

    原文

    0     Minimum optimization. Turns off most optimizations.It gives the best possible debug view and the lowest level of optimization.

                近乎不优化,用于调试代码。出现代码行不能设置断点可如此设置试试。

    1          Restrictedoptimization. Removes unused inline functions and unused static functions.Turns off optimizations that seriously degrade the debug view. Ifused with --debug, this option gives a satisfactorydebug view with good code density.

    部分优化。移除未调用的内联函数和静态函数,关闭debug窗口优化,此状态也能用于调试

    2          Highoptimization. If used with --debug, the debug viewmight be less satisfactory because the mapping of object code tosource code is not always clear.

    This is the default optimization level.

                默认优化等级。如果处于debug状态,部分代码行将不能被调试,具体做了什么优化好像没说

    3     Maximumoptimization. -O3 performs the same optimizationsas -O2 however the balance between space and timeoptimizations in the generated code is more heavily weighted towardsspace or time compared with -O2. That is:

    -O3 -Otime aims to produce fastercode than -O2 -Otime, at the risk of increasingyour image size

    -O3 -Ospace aims to produce smallercode than -O2 -Ospace, but performance might bedegraded.

    In addition, -O3 performs extra optimizationsthat are more aggressive, such as:

    High-levelscalar optimizations, including loop unrolling, for -O3 -Otime. Thiscan give significant performance benefits at a small code size cost,but at the risk of a longer build time.

    More aggressive inlining and automatic inliningfor -O3 -Otime.

    -O0
    最少的优化,可以最大程度上配合产生代码调试信息,可以在任何代码行打断点,特别是死代码处。

    -O1
    有限的优化,去除无用的inline和无用的static函数、死代码消除等,在影响到调试信息的地方均不进行优化。在适当的代码体积和充分的调试之间平衡,代码编写阶段最常用的优化等级。

    -O2
    高度优化,调试信息不友好,有可能会修改代码和函数调用执行流程,自动对函数进行内联等。

    -O3
    最大程度优化,产生极少量的调试信息。会进行更多代码优化,例如循环展开,更激进的函数内联等。

    另外,可以通过单独设置 --loop_optimization_level=option 来控制循环展开的优化等级。

    原文链接:https://blog.csdn.net/liuqi3256797/java/article/details/90137350

  • 相关阅读:
    BZOJ 1977: [BeiJing2010组队]次小生成树 Tree( MST + 树链剖分 + RMQ )
    BZOJ 2134: 单选错位( 期望 )
    BZOJ 1030: [JSOI2007]文本生成器( AC自动机 + dp )
    BZOJ 2599: [IOI2011]Race( 点分治 )
    BZOJ 3238: [Ahoi2013]差异( 后缀数组 + 单调栈 )
    ZOJ3732 Graph Reconstruction Havel-Hakimi定理
    HDU5653 Bomber Man wants to bomb an Array 简单DP
    HDU 5651 xiaoxin juju needs help 水题一发
    HDU 5652 India and China Origins 并查集
    HDU4725 The Shortest Path in Nya Graph dij
  • 原文地址:https://www.cnblogs.com/TonyJia/p/13380557.html
Copyright © 2011-2022 走看看