GCC:march 与 mtune 有何不同? [英] GCC: how is march different from mtune?

问题描述

我试图为此清理 GCC 手册页，但仍然不明白，真的.

I tried to scrub the GCC man page for this, but still don't get it, really.

-march 和 -mtune 有什么区别?

什么时候只使用-march，而不是同时使用?是否有可能只 -mtune?

When does one use just -march, vs. both? Is it ever possible to just -mtune?

推荐答案

如果你使用 -march 那么 GCC 将可以自由生成在指定 CPU 上工作的指令，但(通常)不在架构系列中较早的 CPU.

If you use -march then GCC will be free to generate instructions that work on the specified CPU, but (typically) not on earlier CPUs in the architecture family.

如果您只使用 -mtune，那么编译器将生成适用于其中任何一个的代码，但会偏向在您指定的特定 CPU 上运行速度最快的指令序列.例如为该 CPU 适当地设置循环展开启发式.

If you just use -mtune, then the compiler will generate code that works on any of them, but will favour instruction sequences that run fastest on the specific CPU you indicated. e.g. setting loop-unrolling heuristics appropriately for that CPU.

-march=foo 暗示 -mtune=foo，除非您还指定了不同的 -mtune.这就是为什么使用 -march 比只启用像 -mavx 这样的选项而不做任何调整更好的原因之一.

-march=foo implies -mtune=foo unless you also specify a different -mtune. This is one reason why using -march is better than just enabling options like -mavx without doing anything about tuning.

警告:在 GCC 未明确识别的 CPU 上的 -march=native 仍会启用 GCC 可以检测到的新指令集，但会保留 -mtune=generic.如果您希望它编写好的代码，请使用了解您的 CPU 的足够新的 GCC.

Caveat: -march=native on a CPU that GCC doesn't specifically recognize will still enable new instruction sets that GCC can detect, but will leave -mtune=generic. Use a new enough GCC that knows about your CPU if you want it to make good code.

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