如果您同时指定多个优化标志，gcc(和clang)会做什么? [英] What does gcc (and clang) do if you specify more than one optimization flag together?

问题描述

尽管可以配置一个附加标志，但无法弄清楚构建系统:在尝试进行一些快速和肮脏的测试时，我可以注入一个附加的-O3标志来查看程序的运行方式.性能是在-O3优化下进行的.

The build system is impossible to figure out, although it IS possible to configure an additional flag: In trying to do some quick-and-dirty tests, I'm able to inject an additional -O3 flag to see how the program's performance is under -O3 optimization.

但是，还指定了-O2，并且之后指定了-O2.

However, -O2 is also specified, and is specified afterwards.

问题是，对于编译器而言，只有最后一个优化标志会保留吗?还是(希望)采用最高指定的优化级别?还是未定义?毫无疑问，这绝对不是在抱怨或犯错.

The question is, is it well-defined that for the compiler only the last optimization flag will stick? Or will it (I hope) go with the highest-specified optimization level? Or is it undefined? It is definitely not complaining or erroring out, that's for sure.

推荐答案

全部在文档中.来自 gcc优化选项:

如果使用多个-O选项(带有或不带有级别编号)，则最后一个这样的选项才是有效的.

If you use multiple -O options, with or without level numbers, the last such option is the one that is effective.

---

如果同时指定多个优化标志，gcc(和clang)会做什么?

What does gcc (and clang) do if you specify more than one optimization flag together?

您使用的编译器使用在命令行上最后指定的优化 -O 选项.

The compilers you are using use the optimization -O option that was specified last on the command line.

对于编译器，只有最后一个优化标志会保留吗?

is it well-defined that for the compiler only the last optimization flag will stick?

它已记录在您的编译器文档中.

It's documented in your compilers documentation.

还是将其指定为最高的优化级别?

Or will it go with the highest-specified optimization level?

否.

还是未定义?

否.

这篇关于如果您同时指定多个优化标志，gcc(和clang)会做什么?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！