I have read various optimization guides that claim ADD 1 is faster than using INC in x86. Is this really true?
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I have read various optimization guides that claim ADD 1 is faster than using INC in x86. Is this really true?
On some micro-architectures, with some instruction streams,
INCwill incur a “partial flags update stall” (because it updates some of the flags while preserving the others).ADDsets the value of all of the flags, and so does not risk such a stall.ADDis not always faster thanINC, 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.For more details, consult Intel’s Optimization Reference Manual or Agner Fog’s micro-architecture notes.