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%. 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. Timothy _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
