ADD 1 真的比 INC 快吗?x86 [英] Is ADD 1 really faster than INC ? x86

问题描述

我阅读了各种优化指南，声称 ADD 1 比在 x86 中使用 INC 更快.这是真的吗?

I have read various optimization guides that claim ADD 1 is faster than using INC in x86. Is this really true?

推荐答案

在一些微架构上，对于一些指令流，INC 会导致部分标志更新停顿"(因为它更新了一些的标志，同时保留其他标志).ADD 设置所有标志的值，因此不会冒这种停顿的风险.

On some micro-architectures, with some instruction streams, INC will incur a "partial flags update stall" (because it updates some of the flags while preserving the others). ADD sets the value of all of the flags, and so does not risk such a stall.

ADD 并不总是比 INC 快，但它几乎总是至少一样快(在某些较旧的微架构上有一些极端情况，但它们非常罕见)，有时速度明显更快.

ADD is not always faster than INC, but it is almost always at least as fast (there are a few corner cases on certain older micro-architectures, but they are exceedingly rare), and sometimes significantly faster.

更多详情，请参阅Intel 的优化参考手册 或 Agner Fog 的微架构笔记.

For more details, consult Intel's Optimization Reference Manual or Agner Fog's micro-architecture notes.

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