On 18 September 2017 at 15:40, Prathamesh Kulkarni <prathamesh.kulka...@linaro.org> wrote: > On 15 September 2017 at 22:09, Marc Glisse <marc.gli...@inria.fr> wrote: >> On Fri, 15 Sep 2017, Wilco Dijkstra wrote: >> >>> Marc Glisse wrote: >>> >>>> The question is whether, having computed c=a/b, it is cheaper to test a<b >>>> or c!=0. >>>> I think it is usually the second one, but not for all types on all >>>> targets. Although since >>>> you mention VRP, it is easier to do further optimizations using the >>>> information a<b. >>> >>> >>> No, a<b is always better. Division does have high latency and low >>> throughput on >>> all modern cores, so rather than having to wait until the division >>> finishes, you can >>> execute whatever depends on the comparison many cycles earlier. >>> >>> Generally you want to avoid division as much as possible and when that >>> fails >>> reduce any dependencies on the result of divisions. >> >> >> This would indicate that we do not need to check for single-use, makes the >> patch simpler, thanks. >> (let's ignore -Os) > Hi, > Thanks for the suggestions, I have updated the patch. > Is this OK ? > Bootstrap+test in progress on x86_64-unknown-linux-gnu. > I will try address the right shift by 4 case in follow up patch. > ping https://gcc.gnu.org/ml/gcc-patches/2017-09/msg01145.html
Thanks, Prathamesh > Thanks, > Prathamesh >> >> -- >> Marc Glisse
