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

[David Edelsohn <dje.gcc@gmail.com>]

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.
>
> 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