"Andre Vieira (lists) via Gcc-patches" <gcc-patches@gcc.gnu.org> writes:
> Hi,
>
> This patch changes the order in which we check outside and inside costs
> for epilogue loops, this is to ensure that a predicated epilogue is more
> likely to be picked over an unpredicated one, since it saves having to
> enter a scalar epilogue loop.
>
> gcc/ChangeLog:
>
> * tree-vect-loop.c (vect_better_loop_vinfo_p): Change how
> epilogue loop costs are compared.
OK, thanks. Sorry for the slow review.
Richard
> diff --git a/gcc/tree-vect-loop.c b/gcc/tree-vect-loop.c
> index
> 14f8150d7c262b9422784e0e997ca4387664a20a..038af13a91d43c9f09186d042cf415020ea73a38
> 100644
> --- a/gcc/tree-vect-loop.c
> +++ b/gcc/tree-vect-loop.c
> @@ -2881,17 +2881,75 @@ vect_better_loop_vinfo_p (loop_vec_info
> new_loop_vinfo,
> return new_simdlen_p;
> }
>
> + loop_vec_info main_loop = LOOP_VINFO_ORIG_LOOP_INFO (old_loop_vinfo);
> + if (main_loop)
> + {
> + poly_uint64 main_poly_vf = LOOP_VINFO_VECT_FACTOR (main_loop);
> + unsigned HOST_WIDE_INT main_vf;
> + unsigned HOST_WIDE_INT old_factor, new_factor, old_cost, new_cost;
> + /* If we can determine how many iterations are left for the epilogue
> + loop, that is if both the main loop's vectorization factor and number
> + of iterations are constant, then we use them to calculate the cost of
> + the epilogue loop together with a 'likely value' for the epilogues
> + vectorization factor. Otherwise we use the main loop's vectorization
> + factor and the maximum poly value for the epilogue's. If the target
> + has not provided with a sensible upper bound poly vectorization
> + factors are likely to be favored over constant ones. */
> + if (main_poly_vf.is_constant (&main_vf)
> + && LOOP_VINFO_NITERS_KNOWN_P (main_loop))
> + {
> + unsigned HOST_WIDE_INT niters
> + = LOOP_VINFO_INT_NITERS (main_loop) % main_vf;
> + HOST_WIDE_INT old_likely_vf
> + = estimated_poly_value (old_vf, POLY_VALUE_LIKELY);
> + HOST_WIDE_INT new_likely_vf
> + = estimated_poly_value (new_vf, POLY_VALUE_LIKELY);
> +
> + /* If the epilogue is using partial vectors we account for the
> + partial iteration here too. */
> + old_factor = niters / old_likely_vf;
> + if (LOOP_VINFO_USING_PARTIAL_VECTORS_P (old_loop_vinfo)
> + && niters % old_likely_vf != 0)
> + old_factor++;
> +
> + new_factor = niters / new_likely_vf;
> + if (LOOP_VINFO_USING_PARTIAL_VECTORS_P (new_loop_vinfo)
> + && niters % new_likely_vf != 0)
> + new_factor++;
> + }
> + else
> + {
> + unsigned HOST_WIDE_INT main_vf_max
> + = estimated_poly_value (main_poly_vf, POLY_VALUE_MAX);
> +
> + old_factor = main_vf_max / estimated_poly_value (old_vf,
> + POLY_VALUE_MAX);
> + new_factor = main_vf_max / estimated_poly_value (new_vf,
> + POLY_VALUE_MAX);
> +
> + /* If the loop is not using partial vectors then it will iterate one
> + time less than one that does. It is safe to subtract one here,
> + because the main loop's vf is always at least 2x bigger than that
> + of an epilogue. */
> + if (!LOOP_VINFO_USING_PARTIAL_VECTORS_P (old_loop_vinfo))
> + old_factor -= 1;
> + if (!LOOP_VINFO_USING_PARTIAL_VECTORS_P (new_loop_vinfo))
> + new_factor -= 1;
> + }
> +
> + /* Compute the costs by multiplying the inside costs with the factor
> and
> + add the outside costs for a more complete picture. The factor is the
> + amount of times we are expecting to iterate this epilogue. */
> + old_cost = old_loop_vinfo->vec_inside_cost * old_factor;
> + new_cost = new_loop_vinfo->vec_inside_cost * new_factor;
> + old_cost += old_loop_vinfo->vec_outside_cost;
> + new_cost += new_loop_vinfo->vec_outside_cost;
> + return new_cost < old_cost;
> + }
> +
> /* Limit the VFs to what is likely to be the maximum number of iterations,
> to handle cases in which at least one loop_vinfo is fully-masked. */
> - HOST_WIDE_INT estimated_max_niter;
> - loop_vec_info main_loop = LOOP_VINFO_ORIG_LOOP_INFO (old_loop_vinfo);
> - unsigned HOST_WIDE_INT main_vf;
> - if (main_loop
> - && LOOP_VINFO_NITERS_KNOWN_P (main_loop)
> - && LOOP_VINFO_VECT_FACTOR (main_loop).is_constant (&main_vf))
> - estimated_max_niter = LOOP_VINFO_INT_NITERS (main_loop) % main_vf;
> - else
> - estimated_max_niter = likely_max_stmt_executions_int (loop);
> + HOST_WIDE_INT estimated_max_niter = likely_max_stmt_executions_int (loop);
> if (estimated_max_niter != -1)
> {
> if (known_le (estimated_max_niter, new_vf))
