[Bug other/96825] New: Commit r11-2645 degrades CPU2017 548.exchange2_r by 35%

[Bug other/96825] New: Commit r11-2645 degrades CPU2017 548.exchange2_r by 35%

[pthaugen at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96825

            Bug ID: 96825
           Summary: Commit r11-2645 degrades CPU2017 548.exchange2_r by
                    35%
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: other
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pthaugen at gcc dot gnu.org
                CC: bergner at gcc dot gnu.org, hubicka at gcc dot gnu.org,
                    segher at gcc dot gnu.org, seurer at gcc dot gnu.org,
                    wschmidt at gcc dot gnu.org
  Target Milestone: ---
              Host: powerpc64-unknown-linux-gnu
            Target: powerpc64-unknown-linux-gnu
             Build: powerpc64-unknown-linux-gnu

The given commit (1118a3ff9d3ad6a64bba25dc01e7703325e23d92) causes a 35%
degradation for exchange2_r on Power9 built with the options "-O2
-mcpu=power9". Switching to -O3 results in a 44% degradation. The degradation
occurs in __brute_force_MOD_digits_2().

[Bug ipa/96825] Commit r11-2645 degrades CPU2017 548.exchange2_r by 35%

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96825

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |marxin at gcc dot gnu.org
           Keywords|                            |missed-optimization
          Component|other                       |ipa

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Yep, known.  Still bugs need to be fixed.

[Bug ipa/96825] Commit r11-2645 degrades CPU2017 548.exchange2_r by 35%

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96825

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2020-08-28
             Blocks|                            |26163
             Status|UNCONFIRMED                 |NEW


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=26163
[Bug 26163] [meta-bug] missed optimization in SPEC (2k17, 2k and 2k6 and 95)

[Bug ipa/96825] [11 Regression] Commit r11-2645 degrades CPU2017 548.exchange2_r by 35%

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96825

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |11.0
                 CC|                            |jakub at gcc dot gnu.org
            Summary|Commit r11-2645 degrades    |[11 Regression] Commit
                   |CPU2017 548.exchange2_r by  |r11-2645 degrades CPU2017
                   |35%                         |548.exchange2_r by 35%

[Bug ipa/96825] [11 Regression] Commit r11-2645 degrades CPU2017 548.exchange2_r by 35%

[ktkachov at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96825

ktkachov at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ktkachov at gcc dot gnu.org

--- Comment #2 from ktkachov at gcc dot gnu.org ---
See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98782 for more analysis

[Bug ipa/96825] [11 Regression] Commit r11-2645 degrades CPU2017 548.exchange2_r by 35%

[wschmidt at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96825

--- Comment #3 from Bill Schmidt <wschmidt at gcc dot gnu.org> ---
Is this going to be addressed in GCC 11?  Should this be only a P3?

[Bug ipa/96825] [11 Regression] Commit r11-2645 degrades CPU2017 548.exchange2_r by 35%

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96825

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |WAITING

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
I believe there have been improvements recently - can you re-assess the
magnitude of the problem?  The corresponding ARM PR got re-targeted to GCC 12
(for a RA fix), I think Martin has improved the IPA CP parts, maybe not fully
though.

Martin?

[Bug ipa/96825] [11 Regression] Commit r11-2645 degrades CPU2017 548.exchange2_r by 35%

[jamborm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96825

--- Comment #5 from Martin Jambor <jamborm at gcc dot gnu.org> ---
I have not benchmark results from Power, but the reported regression has been
fixed/mitigated on Zens, see:

https://lnt.opensuse.org/db_default/v4/SPEC/graph?plot.0=275.407.0&plot.1=397.407.0&plot.2=294.407.0&

or

https://lnt.opensuse.org/db_default/v4/SPEC/graph?plot.0=260.407.0&plot.1=361.407.0&plot.2=33.407.0&

We can still do better even at -Ofast and have an -O2 regression with that
benchmark, I hope that both are covered by PR 98782 (which is IMHO quite
generic, not ARM specific).

So I think this is fixed and we should deal with the existing problems in the
other bug (but it would be nice if someone confirmed that Power also no longer
regresses this bad).

[Bug ipa/96825] [11 Regression] Commit r11-2645 degrades CPU2017 548.exchange2_r by 35%

[pthaugen at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96825

--- Comment #6 from pthaugen at gcc dot gnu.org ---
(In reply to Richard Biener from comment #4)
> I believe there have been improvements recently - can you re-assess the
> magnitude of the problem?  The corresponding ARM PR got re-targeted to GCC
> 12 (for a RA fix), I think Martin has improved the IPA CP parts, maybe not
> fully though.

There has been no improvement seen on Power since the degradation appeared.

[Bug ipa/96825] [11/12 Regression] Commit r11-2645 degrades CPU2017 548.exchange2_r by 35%

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96825

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|11.0                        |11.2

--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 11.1 has been released, retargeting bugs to GCC 11.2.

[Bug ipa/96825] [11/12 Regression] Commit r11-2645 degrades CPU2017 548.exchange2_r by 35%

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96825

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|11.2                        |11.3

--- Comment #8 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 11.2 is being released, retargeting bugs to GCC 11.3

[Bug ipa/96825] [11/12 Regression] Commit r11-2645 degrades CPU2017 548.exchange2_r by 35%

[hubicka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96825

Jan Hubicka <hubicka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |RESOLVED
         Resolution|---                         |DUPLICATE

--- Comment #9 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
We have two PRs about the same revision causing regression on exchange2.  It is
understood now that it is more of an IRA issue (which does not like more
realistic profile sadly)

*** This bug has been marked as a duplicate of bug 98782 ***