On Tue, Nov 3, 2015 at 11:53 AM, Timothy Gu <timothyg...@gmail.com> wrote: > On Tue, Nov 3, 2015 at 4:47 AM Ganesh Ajjanagadde > - GCC vectorization > slows down compilation A LOT in all versions. The newer > >> > the worse. >> >> A ~ 20% slowdown on a build for a ~ 20% improvement in an overall FATE >> bench - sounds like a win to me especially with ccache. > > > Of course, but unfortunately the FATE improvement is on the order of 1-2%, > i.e. near negligible, rather than ~20%. > > >> >> > - If you are developing, use clang, and DON'T use GCC 5 with >> vectorization. >> >> This is an opinion, so I will state mine here: if you are developing >> use ccache + GCC > ccache + clang > clang = gcc. Reason for the first >> is due to the terrible interaction ccache has with clang. I still will >> use GCC 5.2 + ccache (with vectorization) for my builds, and will >> inform Arch packagers once we have finalized configure in this respect >> :). >> > > Personally ccache has proved itself to be more of a trouble than its worth > in my experiences, but if you have a fast enough machine or ccache working > that it doesn't matter. > > >> >> > - For release builds, an option to turn it on (or rather to not turn it >> > off) would be helpful; but if you really care about performance _that_ >> much >> > then you should probably use some other compilers instead. >> >> No, not true at all. Why do we bother with asm? Many times for such >> "last mile" optimizations. A 20% improvement in FATE across board is >> nothing to sneeze at given what I have seen in FFmpeg. > > > Again, the improvement is more like 2%.
Oops, can't do arithmetic, got an extra 0. My views still don't really change on this. > > Furthermore, barring ICC (for Intel), Clang and GCC are among the best >> quality compilers today. I don't know about what "other compilers" you >> are referring to. >> > > I meant ICC, which has a much more mature vectorizer. By the way, GCC is heavily working on its auto-vectorizer, so interesting things may happen soon. > > Timothy > _______________________________________________ > ffmpeg-devel mailing list > ffmpeg-devel@ffmpeg.org > http://ffmpeg.org/mailman/listinfo/ffmpeg-devel _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
