Re: [PATCH 10/11][RS6000] Migrate reduction optabs to reduc_..._scal

[Bill Schmidt <wschmidt at linux dot vnet dot ibm dot com>]

On Fri, 2014-10-24 at 19:49 -0400, David Edelsohn wrote:
> On Fri, Oct 24, 2014 at 8:06 AM, Alan Lawrence <alan.lawrence@arm.com> wrote:
> > This migrates the reduction patterns in altivec.md and vector.md to the new
> > names. I've not touched paired.md as I wasn't really sure how to fix that
> > (how do I vec_extractv2sf ?), moreover the testing I did didn't seem to
> > exercise any of those patterns (iow: I'm not sure what would be an
> > appropriate target machine?).
> >
> > I note the reduc_uplus_v16qi (which I've removed, as unsigned and signed
> > addition should be equivalent) differed from reduc_splus_v16qi in using
> > gen_altivec_vsum4ubs rather than gen_altivec_vsum4sbs.  Testcases
> > gcc.dg/vect/{slp-24-big-array.c,slp-24.c,vect-reduc-1char-big-array.c,vert-reduc-1char.c}
> > thus produce assembly which differs from previously (only) in that
> > "vsum4ubs" becomes "vsum4sbs". These tests are still passing so I assume
> > this is OK.

Given that the only 32-bit quantity being added here is zero, the
difference in saturation points for vsum4ubs and vsum4sbs won't come
into play, so I agree this should be fine.

I would like to ask Mike Meissner to look over the changes to the
reduction patterns in vector.md.  He wrote those and is more familiar
with that piece than I am.  On the surface I don't see any problems, but
I could miss something subtle.

Otherwise I'm ok with the patch.

Thanks,
Bill

(p.s. Sorry for the delay on reviewing this.  As David noted, I was
traveling, and I ended up having no access to my mail for most of the
week due to an IT snafu.)

> >
> > The combining of signed and unsigned addition also improves
> > gcc.dg/vect/{vect-outer-4i.c,vect-reduc-1short.c,vect-reduc-dot-u8b.c,vect-reduc-pattern-1c-big-array.c,vect-reduc-pattern-1c.c}
> > : these are now reduced using direct vector reduction, rather than with
> > shifts as previously (because there was only a reduc_splus rather than the
> > reduc_uplus these tests looked for).
> >
> > ((Side note: the RTL changes to vector.md are to match the combine patterns
> > in vsx.md; now that we now longer depend upon combine to generate those
> > patterns (as the optab outputs them directly), one might wish to remove the
> > smaller pattern from vsx.md, and/or simplify the RTL. I theorize that a
> > reduction of a two-element vector is just adding the first element to the
> > second, so maybe to something like
> >
> >   [(parallel [(set (match_operand:DF 0 "vfloat_operand" "")
> >                    (VEC_reduc:V2DF
> >                     (vec_select:DF
> >                      (match_operand:V2DF 1 "vfloat_operand" "")
> >                      (parallel [(const_int 1)]))
> >                     (vec_select:DF
> >                      (match_dup 1)
> >                      (parallel [(const_int 0)]))))
> >               (clobber (match_scratch:V2DF 2 ""))])]
> >
> > but I think it's best for me to leave that to the port maintainers.))
> >
> > Bootstrapped and check-gcc on powerpc64-none-linux-gnu
> > (gcc110.fsffrance.org, with thanks to the GCC Compile Farm).
> >
> > gcc/ChangeLog:
> >
> >         * config/rs6000/altivec.md (reduc_splus_<mode>): Rename to...
> >         (reduc_plus_scal_<mode>): ...this, and rs6000_expand_vector_extract.
> >         (reduc_uplus_v16qi): Remove.
> >
> >         * config/rs6000/vector.md (VEC_reduc_name): change "splus" to "plus"
> >         (reduc_<VEC_reduc_name>_v2df): Rename to...
> >         (reduc_<VEC_reduc_name>_scal_v2df): ...this, wrap VEC_reduc in a
> >         vec_select of element 1.
> >         (reduc_<VEC_reduc_name>_v4sf): Rename to...
> >         (reduc_<VEC_reduc_name>_scal_v4sf): ...this, wrap VEC_reduc in a
> >         vec_select of element 3, add scratch register.
> >
> 
> This needs some input from Bill, but he will be busy with a conference
> this week.
> 
> - David
>