(译)编译器是如何处理没用到的代码的？
04 Dec 2020
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作者整理了一份测试的表格（这个大哥是真爱c++啊这种细节都要扣我感觉魔怔了有点）
| 编译器是否会对没被用到的___ 发出警告 | Clang | GCC | ICC | MSVC |
|---|---|---|---|---|
| static function | -Wall | -Wall | -W4 | |
| static variable | -Wall | -Wall | ||
| private data member | -Wall | |||
| private static data member | ||||
| private member function | ||||
| private static member function | ||||
| data member of private class | ||||
| static data member of private class | ||||
| member function of private class | ||||
| static member function of private class | ||||
| anonymous-namespaced function | -Wall | -Wall | ||
| anonymous-namespaced variable | -Wall | -Wall | ||
| data member of anonymous-namespaced class | ||||
| static data member of anonymous-namespaced class | -Wall | -Wall | ||
| member function of anonymous-namespaced class | -Wall | |||
| static member function of anonymous-namespaced class | -Wall | |||
| function taking anonymous-namespaced class | -Wall | -Wall |
| 编译器是否会优化掉未使用的____ | Clang | GCC | ICC | MSVC |
|---|---|---|---|---|
| static function | -O0 | -O1 | -O0 | -Od |
| static variable | -O0 | -O0 | -O1 | -Od |
| private data member | — | — | — | — |
| private static data member | — | — | — | — |
| private member function | — | — | — | — |
| private static member function | — | — | — | — |
| static data member of private class | — | — | — | — |
| member function of private class | — | — | — | — |
| static member function of private class | — | — | — | — |
| anonymous-namespaced function | -O0 | -O1 | -O0 | |
| anonymous-namespaced variable | -O0 | -O0 | -O1 | -Od |
| static data member of anonymous-namespaced class | -O0 | -O0 | -O1 | |
| member function of anonymous-namespaced class | -O0 | -O1 | -O1 | |
| static member function of anonymous-namespaced class | -O0 | -O1 | -O1 | |
| function taking anonymous-namespaced class | -O0 | -O1 | -O1 |
还有很多优化空间
注意 没用到的私有函数是不回被删掉的，所以有个hack: 模版参数是私有函数指针，通过显式实例化绕开private限制，实现静态注入/调用，详情看这篇文章
