2016-03-18 11:27, Olivier Matz: > On 03/18/2016 11:18 AM, Bruce Richardson wrote: > >>> + /* Avoid the unnecessary cmpset operation below, which is also > >>> + * potentially harmful when n equals 0. */ > >>> + if (n == 0) > >>> > >> > >> What about using unlikely here? > >> > > > > Unless there is a measurable performance increase by adding in > > likely/unlikely > > I'd suggest avoiding it's use. In general, likely/unlikely should only be > > used > > for things like catestrophic errors because the penalty for taking the > > unlikely > > leg of the code can be quite severe. For normal stuff, where the code nearly > > always goes one way in the branch but occasionally goes the other, the > > hardware > > branch predictors generally do a good enough job. > > Do you mean using likely/unlikely could be worst than not using it > in this case? > > To me, using unlikely here is not a bad idea: it shows to the compiler > and to the reader of the code that is case is not the usual case.
It would be nice to have a guideline section about likely/unlikely in doc/guides/contributing/design.rst Bruce gave a talk at Dublin about this kind of things. I'm sure he could contribute more design guidelines ;)
