[Bug tree-optimization/37916] [4.3/4.4/4.5/4.6 Regression] SSA names causing register pressure; unnecessarily many simultaneously "live" names.

[Bug tree-optimization/37916] [4.3/4.4/4.5/4.6 Regression] SSA names causing register pressure; unnecessarily many simultaneously "live" names.

[steven at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37916

Steven Bosscher <steven at gcc dot gnu.org> changed:

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

--- Comment #19 from Steven Bosscher <steven at gcc dot gnu.org> 2011-03-05 00:18:29 UTC ---
(In reply to comment #11)
> (In reply to comment #10)
> > Is scheduling before reload enabled for your target?  If not can you try
> > -fschedule-insns1?
> 
> No such option, I presume you mean -fschedule-insns.  But, as there's no
> scheduler description defined for the architecture, all I get is of course:
> warning: instruction scheduling not supported on this target machine
> with no difference in the output with -O2 -march=v10 -mno-mul-bug-workaround
> -fno-ivopts -fno-reorder-blocks -fno-gcse.
> 
> Besides, scheduling would move uses away from definitions, not closer to them.
> :)  Also, if this is meant as a permanent solution, that pass seems a bit late.

Random thought on this PR: With a scheduler description, -fschedule-insns
-fsched-pressure may help.

Is there a reason why there is no scheduler description?

[Bug tree-optimization/37916] [4.3/4.4/4.5/4.6 Regression] SSA names causing register pressure; unnecessarily many simultaneously "live" names.

[hp at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37916

--- Comment #20 from Hans-Peter Nilsson <hp at gcc dot gnu.org> 2011-03-11 01:31:14 UTC ---
(In reply to comment #19)
> Random thought on this PR: With a scheduler description, -fschedule-insns
> -fsched-pressure may help.

That theory should be testable by compiling for e.g. a x86_64 target; see
comment #12, but to answer your question...

> Is there a reason why there is no scheduler description?

Yes.  For a while, there was nothing to schedule.

...except for CPUs in systems a cache, where it helps to schedule to avoid RaW
hazards.
...and then pipelined variants came, with other hazards to schedule (to avoid
bubbles, no mips1-type madness).
...but then, I noticed that scheduling with the "new" scheduler wasn't
supported for CC0 targets.
...which later was either fixed, or just a plain misunderstanding (cf.
m68k/cf.md).
...and when checking the cycle-correct simulator, I found that there weren't
many cycles to schedule away, hence a fair amount of work for no apparent gain,
at least for the intended purpose of insn scheduling.

There you go, the reasons in a nutshell.  And while there's still a possibility
that it's a pragmatic solution (modulo #c12), it doesn't strike me as requiring
a scheduler to be the Right Thing to do for a fix to this problem.
(Though from a general GCC maintenance perspective, automatically defaulting to
a trivial scheduler might be a good idea.)

[Bug tree-optimization/37916] [4.3/4.4/4.5/4.6/4.7 Regression] SSA names causing register pressure; unnecessarily many simultaneously "live" names.

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37916

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.3.6                       |4.4.7

--- Comment #21 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-06-27 12:14:46 UTC ---
4.3 branch is being closed, moving to 4.4.7 target.

[Bug tree-optimization/37916] [4.5/4.6/4.7/4.8 Regression] SSA names causing register pressure; unnecessarily many simultaneously "live" names.

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37916

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.4.7                       |4.5.4

--- Comment #22 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-03-13 12:48:22 UTC ---
4.4 branch is being closed, moving to 4.5.4 target.

[Bug tree-optimization/37916] [4.6/4.7/4.8 Regression] SSA names causing register pressure; unnecessarily many simultaneously "live" names.

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37916

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.5.4                       |4.6.4

[Bug tree-optimization/37916] [4.7/4.8/4.9 Regression] SSA names causing register pressure; unnecessarily many simultaneously "live" names.

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37916

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.6.4                       |4.7.4

--- Comment #23 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-04-12 15:17:09 UTC ---
GCC 4.6.4 has been released and the branch has been closed.

[Bug tree-optimization/37916] [4.7/4.8/4.9/4.10 Regression] SSA names causing register pressure; unnecessarily many simultaneously "live" names.

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=37916

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.7.4                       |4.8.4

--- Comment #24 from Richard Biener <rguenth at gcc dot gnu.org> ---
The 4.7 branch is being closed, moving target milestone to 4.8.4.

[Bug tree-optimization/37916] [4.8/4.9/5 Regression] SSA names causing register pressure; unnecessarily many simultaneously "live" names.

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=37916

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.8.4                       |4.8.5

--- Comment #25 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 4.8.4 has been released.

[Bug tree-optimization/37916] [4.8/4.9/5/6 Regression] SSA names causing register pressure; unnecessarily many simultaneously "live" names.

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=37916

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.8.5                       |4.9.3

--- Comment #26 from Richard Biener <rguenth at gcc dot gnu.org> ---
The gcc-4_8-branch is being closed, re-targeting regressions to 4.9.3.

[Bug tree-optimization/37916] [4.9/5/6 Regression] SSA names causing register pressure; unnecessarily many simultaneously "live" names.

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=37916

--- Comment #27 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 4.9.3 has been released.

[Bug tree-optimization/37916] [4.9/5/6 Regression] SSA names causing register pressure; unnecessarily many simultaneously "live" names.

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=37916

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.9.3                       |4.9.4

[Bug tree-optimization/37916] [8/9/10/11/12 Regression] SSA names causing register pressure; unnecessarily many simultaneously "live" names.

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=37916

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED

[Bug tree-optimization/37916] [9/10/11/12 Regression] SSA names causing register pressure; unnecessarily many simultaneously "live" names.

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=37916

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|8.5                         |9.4

--- Comment #33 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 8 branch is being closed.

[Bug tree-optimization/37916] [9/10/11/12 Regression] SSA names causing register pressure; unnecessarily many simultaneously "live" names.

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=37916

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|9.4                         |9.5

--- Comment #34 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 9.4 is being released, retargeting bugs to GCC 9.5.

[Bug tree-optimization/37916] [10/11/12/13 Regression] SSA names causing register pressure; unnecessarily many simultaneously "live" names.

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=37916

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|9.5                         |10.4

--- Comment #35 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 9 branch is being closed

[Bug tree-optimization/37916] [10/11/12/13 Regression] SSA names causing register pressure; unnecessarily many simultaneously "live" names.

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=37916

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|10.4                        |10.5

--- Comment #36 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 10.4 is being released, retargeting bugs to GCC 10.5.

[Bug tree-optimization/37916] [10/11/12/13/14 Regression] SSA names causing register pressure; unnecessarily many simultaneously "live" names.

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=37916

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |NEW
           Assignee|hp at gcc dot gnu.org              |unassigned at gcc dot gnu.org

--- Comment #37 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Hans-Peter Nilsson from comment #30)
> Unassigning myself to belatedly celebrate the 10th anniversary of this PR.
> I'm replacing with a reference to a patch (the start of a thread) that
> claims to fix the problem.  Thanks Michael, hope it gets an ok eventually!

Looks like you forgot to change Assignee and then Richi came along and change
the status back to assigned. I am going to fix both of that here.

[Bug tree-optimization/37916] [10/11/12/13/14 Regression] SSA names causing register pressure; unnecessarily many simultaneously "live" names.

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=37916

--- Comment #38 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
So for aarch64, I noticed that on the trunk, we no longer produce any stores to
the stack (GCC 13 had a save/restore of x29 and x30; x29 is the fp). The
difference is no longer using x30 as a register. I Have not looked why though.
GCC 7 had saving also x19.
I suspect that was some aarch64 specific change as x86_64 code generation
looked around the same between GCC 13 and the trunk.

[Bug tree-optimization/37916] [11/12/13/14 Regression] SSA names causing register pressure; unnecessarily many simultaneously "live" names.

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=37916

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|10.5                        |11.5

--- Comment #39 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 10 branch is being closed.