Re: State of AutoFDO in GCC

[Jan Hubicka <hubicka@ucw.cz>]

> 
> It uses create_llvm_prof tool which is in the same git repo. The data
> parsing part is shared with create_gcov, but the writer is obviously
> different for the two tools.

OK and what are the main differences between llvmand gcc format?

Honza
> 
> David
> 
> 
> > Honza
> > >
> > > 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 <hubicka@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
> > > > >>>>>
> > > > >>>>
> > > > >>>
> > > >
> > > >
> >