是Add 1比真快INC？ 86 [英] Is ADD 1 really faster than INC ? x86

问题描述

我已阅读，声称ADD 1比86使用INC更快的各种优化指南。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，具有一定的指令流， INC 将收取部分标志更新摊位（因为它更新一些标志，同时preserving其他）。 添加将所有标志的价值，因此不冒这样的摊位。

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.

添加并不总是比 INC 更快，但它几乎总是至少快（有某些旧的微架构少数极端情况，但他们是极其罕见），有时显著更快。

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.

有关详细信息，请参阅Intel's优化参考手册或瓦格纳雾的微架构说明。

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

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