On Wed, Nov 6, 2019 at 4:58 PM Richard Sandiford
<richard.sandif...@arm.com> wrote:
>
> Richard Biener <richard.guent...@gmail.com> writes:
> > On Tue, Nov 5, 2019 at 3:27 PM Richard Sandiford
> > <richard.sandif...@arm.com> wrote:
> >>
> >> vectorizable_assignment handles true SSA-to-SSA copies (which hopefully
> >> we don't see in practice) and no-op conversions that are required
> >> to maintain correct gimple, such as changes between signed and
> >> unsigned types. These cases shouldn't generate any code and so
> >> shouldn't count against either the scalar or vector costs.
> >>
> >> Later patches test this, but it seemed worth splitting out.
> >
> > Hmm, but you have to adjust vect_compute_single_scalar_iteration_cost and
> > possibly the SLP cost walk as well, otherwise we're artificially making
> > those copies cheaper when vectorized.
>
> Ah, yeah. It looks complicated to reproduce the conditions exactly
> there, so how about just costing 1 copy in vectorizable_assignment
> to counteract it, and ignore ncopies?
I guess costing a single scalar_stmt ought to make it exactly offset
the scalar cost?
> Seems like vectorizable_* ought to be costing the scalar code as
> well as the vector code, but that's too much for GCC 10 at this stage.
Yeah.
Richard.
> Thanks,
> Richard
>
>
> >
> >>
> >> 2019-11-04 Richard Sandiford <richard.sandif...@arm.com>
> >>
> >> gcc/
> >> * tree-vect-stmts.c (vectorizable_assignment): Don't add a cost.
> >>
> >> Index: gcc/tree-vect-stmts.c
> >> ===================================================================
> >> --- gcc/tree-vect-stmts.c 2019-11-05 14:17:43.330141911 +0000
> >> +++ gcc/tree-vect-stmts.c 2019-11-05 14:18:39.169752725 +0000
> >> @@ -5305,7 +5305,7 @@ vectorizable_conversion (stmt_vec_info s
> >> static bool
> >> vectorizable_assignment (stmt_vec_info stmt_info, gimple_stmt_iterator
> >> *gsi,
> >> stmt_vec_info *vec_stmt, slp_tree slp_node,
> >> - stmt_vector_for_cost *cost_vec)
> >> + stmt_vector_for_cost *)
> >> {
> >> tree vec_dest;
> >> tree scalar_dest;
> >> @@ -5313,7 +5313,6 @@ vectorizable_assignment (stmt_vec_info s
> >> loop_vec_info loop_vinfo = STMT_VINFO_LOOP_VINFO (stmt_info);
> >> tree new_temp;
> >> enum vect_def_type dt[1] = {vect_unknown_def_type};
> >> - int ndts = 1;
> >> int ncopies;
> >> int i, j;
> >> vec<tree> vec_oprnds = vNULL;
> >> @@ -5409,7 +5408,8 @@ vectorizable_assignment (stmt_vec_info s
> >> {
> >> STMT_VINFO_TYPE (stmt_info) = assignment_vec_info_type;
> >> DUMP_VECT_SCOPE ("vectorizable_assignment");
> >> - vect_model_simple_cost (stmt_info, ncopies, dt, ndts, slp_node,
> >> cost_vec);
> >> + /* Don't add a cost here. SSA copies and no-op conversions
> >> + shouldn't generate any code in either scalar or vector form. */
> >> return true;
> >> }
> >>
