Re: State of AutoFDO in GCC

[Jan Hubicka <hubicka@ucw.cz>]

> 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
> > 
>