On Fri, Apr 23, 2021 at 12:18 AM Martin Liška <mli...@suse.cz> wrote:
> On 4/23/21 9:00 AM, Richard Biener via Gcc wrote: > > On Fri, Apr 23, 2021 at 7:28 AM Xinliang David Li via Gcc > > <gcc@gcc.gnu.org> wrote: > >> > >> Hi, the create_gcov tool was probably removed with the assumption that > it > >> was only used with Google GCC branch, but it is actually used with GCC > >> trunk as well. > >> > >> Given that, the tool will be restored in the github repo. It seems to > build > >> and work fine with the regression test. > >> > >> The tool may ust work as it is right now, but there is no guarantee it > >> won't break in the future unless someone in the GCC community tries to > >> maintain it. > > Hi. > > The current situation is that AutoFDO doesn't work with pretty simple > test-cases > we have in testsuite: > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71672 > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81379 > > These are ~5 years old and nothing has happened. > > I'm pretty sure the current autofdo can't emit a .gcda file format that > I've changed in the recent years. > I have not not looked into the details, but is it possible the problem is at GCC side (e.g, debug info quality etc)? > > > > > I think if we want to keep the feature it makes sense to provide > create_gcov > > functionality either directly from perf (input data producer) or from gcc > > (data consumer). Of course I have no idea about its complexity, license > > or implementation language ... > > For me, it's just an i386 feature (maybe aarch64 has perf counters too?), > supported > only by vendor (Intel) and I'm not planning working on that. > I don't like having a feature that is obviously broken and potential GCC > users get > bad experience every time they try to use it. > It must be working at sometime, so perhaps a bisect of GCC revisions can reveal when it regressed. > Can we at least deprecate the feature for GCC 11? If these is enough > interest, > we can fix it, if not, I would remove it in GCC 13 timeframe. > This is a major feature in Clang. Deprecating it in GCC will be unfortunate. David > > Thoughts? > Martin > > > > > Having the tool third-party makes keeping the whole chain working more > > difficult. > > > > Richard. > > > >> Thanks, > >> > >> David > >> > >> On Thu, Apr 22, 2021 at 3:29 PM Jan Hubicka <hubi...@ucw.cz> wrote: > >> > >>>> On 4/22/21 9:58 PM, Eugene Rozenfeld via Gcc wrote: > >>>>> GCC documentation for AutoFDO points to create_gcov tool that > converts > >>> perf.data file into gcov format that can be consumed by gcc with > >>> -fauto-profile ( > https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html, > >>> https://gcc.gnu.org/wiki/AutoFDO/Tutorial). > >>>>> > >>>>> I noticed that the source code for create_gcov has been deleted from > >>> https://github.com/google/autofdo on April 7. I asked about that > change > >>> in that repo and got the following reply: > >>>>> > >>>>> https://github.com/google/autofdo/pull/107#issuecomment-819108738 > >>>>> > >>>>> "Actually we didn't use create_gcov and havn't updated create_gcov > for > >>> years, and we also didn't have enough tests to guarantee it works (It > was > >>> gcc-4.8 when we used and verified create_gcov). If you need it, it is > >>> welcomed to update create_gcov and add it to the respository." > >>>>> > >>>>> Does this mean that AutoFDO is currently dead in gcc? > >>>> > >>>> Hello. > >>>> > >>>> Yes. I know that even basic test cases have been broken for years in > the > >>> GCC. > >>>> It's new to me that create_gcov was removed. > >>>> > >>>> I tend to send patch to GCC that will remove AutoFDO from GCC. > >>>> I known Bin spent some time working on AutoFDO, has he came up to > >>> something? > >>> > >>> The GCC side of auto-FDO is not that hard. We have most of > >>> infrastructure in place, but stopping point for me was always > difficulty > >>> to get gcov-tool working. If some maintainer steps up, I think I can > >>> fix GCC side. > >>> > >>> I am bit unsure how important feature it is - we have FDO that works > >>> quite well for most users but I know there are some users of the LLVM > >>> implementation and there is potential to tie this with other hardware > >>> events to asist i.e. if conversion (where one wants to know how well > CPU > >>> predicts the jump rather than just the jump probability) which I always > >>> found potentially interesting. > >>> > >>> Honza > >>>> > >>>> Martin > >>>> > >>>>> > >>>>> Thanks, > >>>>> > >>>>> Eugene > >>>>> > >>>> > >>> > >
