[Bug rtl-optimization/115523] New: [avr] Remove SFmode insns

[Bug rtl-optimization/115523] New: [avr] Remove SFmode insns

[gjl at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115523

            Bug ID: 115523
           Summary: [avr] Remove SFmode insns
           Product: gcc
           Version: 14.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gjl at gcc dot gnu.org
  Target Milestone: ---

Created attachment 58448
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=58448&action=edit
sfmode.c: C test case

There is currently the problem that subreg lowering is producing code that
later passes cannot really digest:

With avr-gcc v14.1:
$ avr-gcc sfmode.c -Os -c -mmcu=atmega8 -dp -save-temps -dumpbase ""   &&
avr-size sfmode.o
   text    data     bss     dec     hex filename
    160       0       0     160      a0 sfmode.o

whereas with v8:
   text    data     bss     dec     hex filename
     40       0       0      40      28 sfmode.o

[Bug rtl-optimization/115523] [avr] Remove SFmode insns

[gjl at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115523

--- Comment #1 from Georg-Johann Lay <gjl at gcc dot gnu.org> ---
That bloat can be worked around by taking away the SFmode insns in avr.md.

[Bug target/115523] [avr] Remove SFmode insns

[avr at gjlay dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115523

--- Comment #2 from Georg-Johann Lay <avr at gjlay dot de> ---
Am 17.06.24 um 17:06 schrieb pinskia at gcc dot gnu.org:
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115523
> 
> Andrew Pinski <pinskia at gcc dot gnu.org> changed:
> 
>             What    |Removed                     |Added
> ----------------------------------------------------------------------------
>                   CC|                            |pinskia at gcc dot gnu.org
>            Component|rtl-optimization            |target
> 

This is an issue in the RTL passes, subreg-lowering vs. reg alloc.

It's just the case that the backend can (partially) hack around it.

Johann

[Bug rtl-optimization/115523] [avr] Remove SFmode insns

[gjl at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115523

--- Comment #3 from Georg-Johann Lay <gjl at gcc dot gnu.org> ---
Andrew, in https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114243#c2 you wrote
that the issue is going to be fixed for RISC-V. You have a PR for that, and
what's the state of it?

[Bug rtl-optimization/115523] [avr] Remove SFmode insns

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115523

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Georg-Johann Lay from comment #3)
> Andrew, in https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114243#c2 you wrote
> that the issue is going to be fixed for RISC-V. You have a PR for that, and
> what's the state of it?

I am not 100% sure if this is the latest version of the patch set though, but
it was posted to the gcc-patches@ list in late May:
https://inbox.sourceware.org/gcc-patches/20240512225738.528917-2-juzhe.zhong@rivai.ai/

[Bug rtl-optimization/115523] [avr] Remove SFmode insns

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115523

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #4)
> I am not 100% sure if this is the latest version of the patch set though,
> but it was posted to the gcc-patches@ list in late May:
> https://inbox.sourceware.org/gcc-patches/20240512225738.528917-2-juzhe.
> zhong@rivai.ai/

Oh this is just the analysis part, the actually code changing part has not been
posted yet:
> And we will enable register coalsece with subreg liveness tracking in the followup patches.