一个好的 C++ 编译器会优化引用吗? [英] Will a good C++ compiler optimize a reference away?

问题描述

我想写一个模板函数，用 std::stack 和一个 T 的实例做一些事情，例如:

I want to write a template function that does something with a std::stack<T> and an instance of T, e.g.:

template<class StackType> inline
bool some_func( StackType const &s, typename StackType::value_type const &v ) {
  // ...
}

我通过引用传递 v 的原因当然是为了针对 StackType::value_type 是 struct 或 的情况进行优化>class 而不是按值复制整个对象.

The reason I pass v by reference is of course to optimize for the case where StackType::value_type is a struct or class and not copy an entire object by value.

然而，如果 StackType::value_type 是像 int 这样的简单"类型，那么当然最好直接按值传递.

However, if StackType::value_type is a "simple" type like int, then it's of course better simply to pass it by value.

问题是:对于像 int 这样的类型，它会变成 int const& 作为上述函数中的形式参数，编译器是否会优化掉引用和只是按值传递?

The question is: for a type such as int that would become int const& as a formal argument in the above function, will the compiler optimize away the reference and simply pass it by value?

推荐答案

我在这里查看 gcc 优化选项 http://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html

I look in gcc optimization options here http://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html

实际上您的情况有一个选项:

And actually there is an option for your case:

-fipa-sra

执行聚合的过程间标量替换，删除未使用的参数，并通过值传递的参数替换通过引用传递的参数.

Perform interprocedural scalar replacement of aggregates, removal of unused parameters and replacement of parameters passed by reference by parameters passed by value.

在 -O2、-O3 和 -Os 级别启用

Enabled at levels -O2, -O3 and -Os

据我所知，-O2 是 Linux 上发布版本的常用选项.

As far as I know, -O2 is usual option for release build on linux.

所以，简短的回答是:优秀的编译器之一

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