On Thu, Nov 7, 2019 at 5:40 PM Richard Sandiford
<richard.sandif...@arm.com> wrote:
>
> Richard Biener <richard.guent...@gmail.com> writes:
> > 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?
>
> To summarise what we said on IRC: the problem with that is that we
> need to count VF scalar stmts, where VF might be a runtime value.
> The follow-on loop costing code copes with variable VF without
> relying on vect_vf_for_cost.
>
> Calling vectorizable_assignment from the scalar costing code
> seemed like too much of a hack. And it turns out that we can't
> delay the scalar costing until after vect_analyze_stmts because
> vect_enhance_data_refs_alignment needs it before then. Reworking
> this whole thing is too much work for GCC 10 at this stage.
>
> So this patch goes with your suggestion of using a test based on
> tree_nop_conversion. To make sure that the scalar and vector costs
> stay somewhat consistent, vectorizable_assignment continues to cost
> stmts for which the new predicate is false.
>
> Tested as before.
OK.
thanks,
Richard.
> Thanks,
> Richard
>
>
> 2019-11-07 Richard Sandiford <richard.sandif...@arm.com>
>
> gcc/
> * tree-vectorizer.h (vect_nop_conversion_p): Declare.
> * tree-vect-stmts.c (vect_nop_conversion_p): New function.
> (vectorizable_assignment): Don't add a cost for nop conversions.
> * tree-vect-loop.c (vect_compute_single_scalar_iteration_cost):
> Likewise.
> * tree-vect-slp.c (vect_bb_slp_scalar_cost): Likewise.
>
> Index: gcc/tree-vectorizer.h
> ===================================================================
> --- gcc/tree-vectorizer.h 2019-11-07 15:11:22.290972236 +0000
> +++ gcc/tree-vectorizer.h 2019-11-07 16:32:14.817523866 +0000
> @@ -1654,6 +1654,7 @@ extern tree vect_get_vec_def_for_stmt_co
> extern bool vect_transform_stmt (stmt_vec_info, gimple_stmt_iterator *,
> slp_tree, slp_instance);
> extern void vect_remove_stores (stmt_vec_info);
> +extern bool vect_nop_conversion_p (stmt_vec_info);
> extern opt_result vect_analyze_stmt (stmt_vec_info, bool *, slp_tree,
> slp_instance, stmt_vector_for_cost *);
> extern void vect_get_load_cost (stmt_vec_info, int, bool,
> Index: gcc/tree-vect-stmts.c
> ===================================================================
> --- gcc/tree-vect-stmts.c 2019-11-07 15:11:50.134775028 +0000
> +++ gcc/tree-vect-stmts.c 2019-11-07 16:32:14.817523866 +0000
> @@ -5284,6 +5284,29 @@ vectorizable_conversion (stmt_vec_info s
> return true;
> }
>
> +/* Return true if we can assume from the scalar form of STMT_INFO that
> + neither the scalar nor the vector forms will generate code. STMT_INFO
> + is known not to involve a data reference. */
> +
> +bool
> +vect_nop_conversion_p (stmt_vec_info stmt_info)
> +{
> + gassign *stmt = dyn_cast <gassign *> (stmt_info->stmt);
> + if (!stmt)
> + return false;
> +
> + tree lhs = gimple_assign_lhs (stmt);
> + tree_code code = gimple_assign_rhs_code (stmt);
> + tree rhs = gimple_assign_rhs1 (stmt);
> +
> + if (code == SSA_NAME || code == VIEW_CONVERT_EXPR)
> + return true;
> +
> + if (CONVERT_EXPR_CODE_P (code))
> + return tree_nop_conversion_p (TREE_TYPE (lhs), TREE_TYPE (rhs));
> +
> + return false;
> +}
>
> /* Function vectorizable_assignment.
>
> @@ -5399,7 +5422,9 @@ 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);
> + if (!vect_nop_conversion_p (stmt_info))
> + vect_model_simple_cost (stmt_info, ncopies, dt, ndts, slp_node,
> + cost_vec);
> return true;
> }
>
> Index: gcc/tree-vect-loop.c
> ===================================================================
> --- gcc/tree-vect-loop.c 2019-11-07 15:11:22.290972236 +0000
> +++ gcc/tree-vect-loop.c 2019-11-07 16:32:14.813523891 +0000
> @@ -1126,7 +1126,9 @@ vect_compute_single_scalar_iteration_cos
> else
> kind = scalar_store;
> }
> - else
> + else if (vect_nop_conversion_p (stmt_info))
> + continue;
> + else
> kind = scalar_stmt;
>
> record_stmt_cost (&LOOP_VINFO_SCALAR_ITERATION_COST (loop_vinfo),
> Index: gcc/tree-vect-slp.c
> ===================================================================
> --- gcc/tree-vect-slp.c 2019-11-07 15:11:22.290972236 +0000
> +++ gcc/tree-vect-slp.c 2019-11-07 16:32:14.817523866 +0000
> @@ -3037,6 +3037,8 @@ vect_bb_slp_scalar_cost (basic_block bb,
> else
> kind = scalar_store;
> }
> + else if (vect_nop_conversion_p (stmt_info))
> + continue;
> else
> kind = scalar_stmt;
> record_stmt_cost (cost_vec, 1, kind, stmt_info, 0, vect_body);
