[Bug c/108073] New: [rs6000] sub-optimal float member accessing on struct parameter

[Bug c/108073] New: [rs6000] sub-optimal float member accessing on struct parameter

[guojiufu at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108073

            Bug ID: 108073
           Summary: [rs6000] sub-optimal float member accessing on struct
                    parameter
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: guojiufu at gcc dot gnu.org
  Target Milestone: ---

For the below code:

typedef struct DF {double a[4]; long l; } DF;
double __attribute__ ((noipa)) foo_df (DF arg){return arg.a[3];}


At -O2, with gcc trunk(13.0), we get below sequence:

std 6,-24(1)
ori 2,2,0
lfd 1,-24(1)
blr

Actually, just one "mtvsrd 1, 6" is enough.

In this case, the argument is passed through integer registers. 

For below code, it is similar:

typedef struct SF {float a[4];short l; } SF;
float foo (SF arg){return arg.a[3];}  

        std 4,-24(1)
        ori 2,2,0
        lfs 1,-20(1)
vs. below seq seems faster.
        rldicr 4,4,0,31
        mtvsrd 1,4
        xscvspdpn 1,1

[Bug middle-end/108073] [rs6000] sub-optimal float member accessing on struct parameter

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108073

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization
           Severity|normal                      |enhancement

[Bug middle-end/108073] [rs6000] sub-optimal float member accessing on struct parameter

[jskumari at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108073

Surya Kumari Jangala <jskumari at gcc dot gnu.org> changed:

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

--- Comment #1 from Surya Kumari Jangala <jskumari at gcc dot gnu.org> ---
Hi Jiu Fu Guo, are you working on this bug? If not, I would like to take this
up.

[Bug middle-end/108073] [rs6000] sub-optimal float member accessing on struct parameter

[guojiufu at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108073

--- Comment #2 from Jiu Fu Guo <guojiufu at gcc dot gnu.org> ---
(In reply to Surya Kumari Jangala from comment #1)
> Hi Jiu Fu Guo, are you working on this bug? If not, I would like to take
> this up.

Thanks for your asking!
I drafted an experimental patch. Welcome for any comments or refactoring :)