Would it be possible to fix the missed optimization to give the better asm without having to do -ffast-math as mentioned here:
https://gcc.gnu.org/ml/gcc-help/2014-11/msg00034.html If so, then the proposed implementation would be optimized for the simple case. On Fri, Jul 22, 2016 at 3:55 AM, Jonathan Wakely <jwak...@redhat.com> wrote: > On 22/07/16 08:51 +0100, Jonathan Wakely wrote: >> >> On 21/07/16 19:38 -0400, NightStrike wrote: >>> >>> On Thu, Jul 14, 2016 at 7:50 PM, Ed Smith-Rowland <3dw...@verizon.net> >>> wrote: >>>> >>>> Here is an implementation of P0025 >>>> An algorithm to "clamp" a value between a pair of boundary values. >>>> >>>> Testing is almost finished - looks good so far. >>>> >>>> OK if testing passes? >>>> >>>> I didn't see a feature test in any of the SD-6 papers or P0025. >>>> >>> >>> This is not an efficient implementation. See here: >>> >>> https://gcc.gnu.org/ml/gcc-help/2014-10/msg00112.html >>> >>> Which I derived from this SO answer (which is sadly not the accepted >>> answer at this time): >>> >>> http://stackoverflow.com/a/16659263 >>> >>> I suggest using the very efficient method that requires a temporary. >> >> >> That isn't a valid implementation of std::clamp, since it performs a >> copy. The template argument might not even be copyable. > > > > We could possibly dispatch to such an implementation for arithmetic > types, but we wouldn't want to do it for all copyable types. There's > no way you can know whether making that local copy is expensive for an > arbitrary type, and making a copy isn't allowed anyway. >
