On Thu, Oct 22, 2015 at 8:42 AM, Ganesh Ajjanagadde <gajja...@mit.edu> wrote: > On Thu, Oct 22, 2015 at 8:33 AM, Michael Niedermayer > <mich...@niedermayer.cc> wrote: >> On Thu, Oct 22, 2015 at 07:04:41AM -0400, Ganesh Ajjanagadde wrote: >>> On Thu, Oct 22, 2015 at 5:49 AM, Carl Eugen Hoyos <ceho...@ag.or.at> wrote: >>> > Ganesh Ajjanagadde <gajjanagadde <at> gmail.com> writes: >>> > >>> >> > This broke fate with -ftrapv >>> > >>> >> > The problem seems to be in av_gcd() and not the De-Bruijn version of >>> >> > ff_ctzll since the gcc builtin is being used. >>> >> >>> >> Don't have the time to investigate right now - revert for now unless >>> >> someone can fix it quickly. >>> > >>> > Ping? >>> > >>> > Please revert if nobody can fix this. >>> >>> "Fixing" this at the moment is highly dubious - read the thread. It >>> does not even occur in a reproducible way, does not trigger on ubsan, >>> I can't even see it on ftrapv. Show me why it is not a toolchain >>> issue. >> >> IMO never just assume that a problem that appears after a change you do >> is not caused by your code. >> Because if you do and you are wrong the bug might never be fixed >> while OTOH, if you assume its in your code you will sooner or later >> by debuging find the bug or more details, and that may be a >> code generation issue in the toolchain outside your code in case >> you where wrong. >> Its the safer default assumtation as the failure path if you are wrong >> is less bad. >> >> either way, bug fixed >> the reason for non reproduceablility likely was that the x86 asm >> overrode the C code in which the bug was > > Ok, go ahead and revert. I just did not see the hurry for reverting; > since it does not break normal builds.
Just saw your commit. I guess a lot of the confusion stemmed from the fact that James's report was slightly misleading - it seemed to target av_gcd as opposed to the De-Bruijn implementation, where it seems the bug really was. > >> >> >> [...] >> -- >> Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB >> >> I have often repented speaking, but never of holding my tongue. >> -- Xenocrates >> >> _______________________________________________ >> 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