On Mon, May 4, 2015 at 10:38 AM, David Blaikie <[email protected]> wrote:
> > > On Sat, May 2, 2015 at 11:47 AM, Nico Weber <[email protected]> wrote: > >> On Wed, Apr 29, 2015 at 2:41 AM, Benjamin Kramer <[email protected]> >> wrote: >> >>> On Wed, Apr 29, 2015 at 5:59 AM, Richard Trieu <[email protected]> >>> wrote: >>> > Since this warning did not exist when std::move was first introduced, >>> and >>> > many people are not familiar with copy elision rules, there have been >>> a lot >>> > of uses of the pessimizing move pattern. In relative numbers, the >>> > pessimizing move warning is over 5x more common than either the range >>> loop >>> > warning (-Wrange-loop-analysis) or the proposed comma warning >>> (-Wcomma). >>> > With such a high occurrence, it seemed better not to have it on by >>> default. >>> >>> And every single occurence is a potential performance issue and easy >>> to fix. While this may be too noisy for default, it's definitely a >>> candidate for -Wall imho. >>> >> >> +1. As-is, nobody will find this warning. And in general, the bar for >> warnings is "useful enough to be in -Wall, or it shouldn't be there", >> right? (Which this warning definitely is.) >> > > I think the bar at least used to be "useful enough to be on by default or > it shouldn't be there" (the big exception in any analysis based warning > because building the CFG costs some non-trivial % - so we keep /all/ of > those off by default). Doug particularly espoused this notion & I've mostly > been promoting it since then on the assumption that that was still the goal > - though I don't agree with it entirely myself. > > - David > > I created a patch (http://reviews.llvm.org/D9493) to place the std::move warnings into -Wmove and put that warning group into -Wmost, which gets pulled into -Wall.
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