[PATCH v2] vect/rs6000: Support vector with length cost modeling

[Richard Biener]

On Wed, Jul 22, 2020 at 3:26 AM Kewen.Lin <linkw@linux.ibm.com> wrote:
>
> Hi Richard,
>
> on 2020/7/21 下午3:57, Richard Biener wrote:
> > On Tue, Jul 21, 2020 at 7:52 AM Kewen.Lin <linkw@linux.ibm.com> wrote:
> >>
> >> Hi,
> >>
> >> This patch is to add the cost modeling for vector with length,
> >> it mainly follows what we generate for vector with length in
> >> functions vect_set_loop_controls_directly and vect_gen_len
> >> at the worst case.
> >>
> >> For Power, the length is expected to be in bits 0-7 (high bits),
> >> we have to model the cost of shifting bits.  To allow other targets
> >> not suffer this, I used one target hook to describe this extra cost,
> >> I'm not sure if it's a correct way.
> >>
> >> Bootstrapped/regtested on powerpc64le-linux-gnu (P9) with explicit
> >> param vect-partial-vector-usage=1.
> >>
> >> Any comments/suggestions are highly appreciated!
> >
> > I don't like the introduction of an extra target hook for this.  All
> > vectorizer cost modeling should ideally go through
> > init_cost/add_stmt_cost/finish_cost.  If the extra costing is
> > not per stmt then either init_cost or finish_cost is appropriate.
> > Currently init_cost only gets a struct loop while we should
> > probably give it a vec_info * parameter so targets can
> > check LOOP_VINFO_USING_PARTIAL_VECTORS_P and friends.
> >
>
> Thanks!  Nice, your suggested way looks better.  I've removed the hook
> and taken care of it in finish_cost.  The updated v2 is attached.
>
> Bootstrapped/regtested again on powerpc64le-linux-gnu (P9) with explicit
> param vect-partial-vector-usage=1.

LGTM (with assuming the first larger hunk is mostly re-indenting
under LOOP_VINFO_USING_PARTIAL_VECTORS_P).

Thanks,
Richard.

> BR,
> Kewen
> -----
> gcc/ChangeLog:
>
>         * config/rs6000/rs6000.c (adjust_vect_cost): New function.
>         (rs6000_finish_cost): Call function adjust_vect_cost.
>         * tree-vect-loop.c (vect_estimate_min_profitable_iters): Add cost
>         modeling for vector with length.