[Bug tree-optimization/107946] New: [13 Regression] 507.cactuBSSN_r regresses by ~9% on znver3 with PGO since r13-3875-g9e11ceef165bc0

[Bug tree-optimization/107946] New: [13 Regression] 507.cactuBSSN_r regresses by ~9% on znver3 with PGO since r13-3875-g9e11ceef165bc0

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107946

            Bug ID: 107946
           Summary: [13 Regression] 507.cactuBSSN_r regresses by ~9% on
                    znver3 with PGO since r13-3875-g9e11ceef165bc0
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: marxin at gcc dot gnu.org
                CC: jamborm at gcc dot gnu.org, rguenth at gcc dot gnu.org
            Blocks: 26163
  Target Milestone: ---

The revision r13-3875-g9e11ceef165bc0 was supposed to speed up the benchmark,
but it makes it slower w/ -O2 -flto and PGO:
https://lnt.opensuse.org/db_default/v4/SPEC/graph?plot.0=694.437.0

Similar regression can be seen w/o LTO as well:
https://lnt.opensuse.org/db_default/v4/SPEC/graph?plot.0=463.437.0


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 tree-optimization/107946] [13 Regression] 507.cactuBSSN_r regresses by ~9% on znver3 with PGO since r13-3875-g9e11ceef165bc0

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107946

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |13.0

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Nope, it wasn't supposed to speedup the benchmark but it indeed (with -Ofast)
causes the hot loop kernels to be unswitched.

Btw, do we know if train and ref data align up in these loops?

Btw, with -Ofast on znver2 I didn't observe any change when benchmarking this.

I'm trying to reproduce.

OK, so with -O2 -flto -march=znver2 and FDO I get a runtime of 173s while
adding -fno-unswitch-loops gets me 188s.  There's currently no knob to
specifically disable outer loop unswitching so I have to instead patch
that up.  With -O2 -flto -funswitch-loops (w/o FDO) I get 178s.  I'm going
to add a --param to allow easier reproduction.

[Bug tree-optimization/107946] [13 Regression] 507.cactuBSSN_r regresses by ~9% on znver3 with PGO since r13-3875-g9e11ceef165bc0

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107946

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
So with --param max-unswitch-depth=1 and -O2 -flto -march=znver2 + FDO I get
176s which is slower than with unswitching outer loops.

Means I cannot reproduce (at least with this specific feature, aka this
revision).

[Bug tree-optimization/107946] [13 Regression] 507.cactuBSSN_r regresses by ~9% on znver3 with PGO since r13-3875-g9e11ceef165bc0

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107946

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Richard Biener <rguenth@gcc.gnu.org>:

https://gcc.gnu.org/g:5b50850c3c6f2eceb8012dcc8d3cd5ddd94fac6c

commit r13-4458-g5b50850c3c6f2eceb8012dcc8d3cd5ddd94fac6c
Author: Richard Biener <rguenther@suse.de>
Date:   Thu Dec 1 16:14:14 2022 +0100

    Add --param max-unswitch-depth

    The following adds a --param to limit the depth of unswitched loop
    nests.  One can use --param max-unswitch-depth=1 to disable unswitching
    of outer loops (the innermost loop will then be unswitched).

            PR tree-optimization/107946
            * params.opt (-param=max-unswitch-depth=): New.
            * doc/invoke.texi (--param=max-unswitch-depth): Document.
            * tree-ssa-loop-unswitch.cc (init_loop_unswitch_info): Honor
            --param=max-unswitch-depth

[Bug tree-optimization/107946] [13 Regression] 507.cactuBSSN_r regresses by ~9% on znver3 with PGO since r13-3875-g9e11ceef165bc0

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107946

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
The data found for other machines/flags is also rather inconclusive with ups
and downs.

[Bug tree-optimization/107946] [13/14 Regression] 507.cactuBSSN_r regresses by ~9% on znver3 with PGO since r13-3875-g9e11ceef165bc0

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107946

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|13.0                        |13.2

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 13.1 is being released, retargeting bugs to GCC 13.2.

[Bug tree-optimization/107946] [13/14 Regression] 507.cactuBSSN_r regresses by ~9% on znver3 with PGO since r13-3875-g9e11ceef165bc0

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107946

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|13.2                        |13.3

--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 13.2 is being released, retargeting bugs to GCC 13.3.

[Bug tree-optimization/107946] [13/14 Regression] 507.cactuBSSN_r regresses by ~9% on znver3 with PGO since r13-3875-g9e11ceef165bc0

[jamborm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107946

Martin Jambor <jamborm at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2024-01-26
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW

--- Comment #7 from Martin Jambor <jamborm at gcc dot gnu.org> ---
This regression is still there (as the graphs linked in the summary show).

[Bug tree-optimization/107946] [13/14 Regression] 507.cactuBSSN_r regresses by ~9% on znver3 with PGO since r13-3875-g9e11ceef165bc0

[law at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107946

Jeffrey A. Law <law at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |law at gcc dot gnu.org
           Priority|P3                          |P2