GCC 优化级别有多少? [英] How many GCC optimization levels are there?

问题描述

有多少个 GCC 优化级别?

How many GCC optimization levels are there?

我尝试了 gcc -O1、gcc -O2、gcc -O3 和 gcc -O4

I tried gcc -O1, gcc -O2, gcc -O3, and gcc -O4

如果我使用一个非常大的数字，它将不起作用.

If I use a really large number, it won't work.

不过，我试过了

gcc -O100

它编译了.

有多少优化级别?

推荐答案

为了迂腐，有 8 种不同的有效 -O 选项可以提供给 gcc，尽管有些意思相同.

To be pedantic, there are 8 different valid -O options you can give to gcc, though there are some that mean the same thing.

这个答案的原始版本说有 7 个选项.GCC 此后添加了 -Og 使总数达到 8

The original version of this answer stated there were 7 options. GCC has since added -Og to bring the total to 8

来自 手册页:

• -O(同-O1)
• -O0(不做优化，不指定优化级别则默认)
• -O1(最小优化)
• -O2(优化更多)
• -O3(进一步优化)
• -Ofast(非常积极地优化到违反标准的程度)
• -Og(优化调试体验.-Og启用不干扰调试的优化.应该是标准编辑-编译-调试周期的优化级别选择，提供合理的优化级别同时保持快速编译和良好的调试体验.)
• -Os(针对大小进行优化.-Os 启用通常不会增加代码大小的所有 -O2 优化.它还执行进一步的优化优化旨在减少代码大小.-Os 禁用以下优化标志: -falign-functions -falign-jumps -falign-loops -falign-labels -freorder-blocks -freorder-blocks-and-partition -fprefetch-loop-arrays -ftree-vect-loop-version)

• -O (Same as -O1)
• -O0 (do no optimization, the default if no optimization level is specified)
• -O1 (optimize minimally)
• -O2 (optimize more)
• -O3 (optimize even more)
• -Ofast (optimize very aggressively to the point of breaking standard compliance)
• -Og (Optimize debugging experience. -Og enables optimizations that do not interfere with debugging. It should be the optimization level of choice for the standard edit-compile-debug cycle, offering a reasonable level of optimization while maintaining fast compilation and a good debugging experience.)
• -Os (Optimize for size. -Os enables all -O2 optimizations that do not typically increase code size. It also performs further optimizations designed to reduce code size. -Os disables the following optimization flags: -falign-functions -falign-jumps -falign-loops -falign-labels -freorder-blocks -freorder-blocks-and-partition -fprefetch-loop-arrays -ftree-vect-loop-version)

也可能有特定于平台的优化，正如@pauldoo 所说，OS X 有 -Oz

There may also be platform specific optimizations, as @pauldoo notes, OS X has -Oz

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