Re: Document how to build PGO-optimized GCC version

[Andrew Pinski <pinskia@gmail.com>]

On Tue, Dec 27, 2022 at 9:38 PM Alexander Zaitsev <zamazan4ik@tut.by> wrote:
>
> Hello.
>
> We are using GCC for our C++ projects. Our projects are huge, commit
> rate is quite huge, so our CI workers are always busy (so as any other
> CI workers, honestly). Since we want to increase build speed, one of the
> option is to optimize the compiler itself. Sounds like a good case for PGO.
>
> Clang has the infrastructure for building the Clang itself with PGO:
> https://llvm.org/docs/HowToBuildWithPGO.html . I have tried to find
> something like that for GCC but with no success.
>
> My proposal is:
>
>   * add support for building PGO-optimized GCC into the GCC build
>     infrastructure
>   * add documentation to the GCC site, how to build GCC with PGO
>     optimizations

It is already there, see the last section of
https://gcc.gnu.org/install/build.html (Building with profile
feedback).  It has been included in GCC and documented since June
2003.
https://gcc.gnu.org/r0-50361-g8f231b5d874dcb .

>   * (if GCC community provides prebuilt gcc binaries) use PGO for the
>     prebuilt binaries. E.g. Clang and rustc already uses this approach.

GCC community does not provide prebuilt gcc binaries for a few
different reasons.
But distros do provide more recent prebuilt binaries, you could ask
them to build using PGO (some do already I think).

Thanks,
Andrew Pinski

>
> Any feedback is appreciated.
>
> Thanks in advance!
>
> --
> Best regards,
> Alexander Zaitsev