Re: Avoid unnecessary peeling for gaps with LD3

[Richard Biener <richard dot guenther at gmail dot com>]

On Fri, May 20, 2016 at 5:27 PM, Richard Sandiford
<richard.sandiford@arm.com> wrote:
> vectorizable_load forces peeling for gaps if the vectorisation factor
> is not a multiple of the group size, since in that case we'd normally load
> beyond the original scalar accesses but drop the excess elements as part
> of a following permute:
>
>       if (loop_vinfo
>           && ! STMT_VINFO_STRIDED_P (stmt_info)
>           && (GROUP_GAP (vinfo_for_stmt (first_stmt)) != 0
>               || (!slp && vf % GROUP_SIZE (vinfo_for_stmt (first_stmt)) != 0)))
>
> This isn't necessary for LOAD_LANES though, since it loads only the
> data needed and does the permute itself.
>
> Tested on aarch64-linux-gnu and x86_64-linux-gnu.  OK to install?

Ok.

Thanks,
Richard.

> Thanks,
> Richard
>
>
> gcc/
>         * tree-vect-stmts.c (vectorizable_load): Reorder checks so that
>         load_lanes/grouped_load classification comes first.  Don't check
>         whether the vectorization factor is a multiple of the group size
>         for load_lanes.
>
> gcc/testsuite/
>         * gcc.dg/vect/vect-load-lanes-peeling-1.c: New test.
>
> Index: gcc/tree-vect-stmts.c
> ===================================================================
> --- gcc/tree-vect-stmts.c
> +++ gcc/tree-vect-stmts.c
> @@ -6314,6 +6314,17 @@ vectorizable_load (gimple *stmt, gimple_stmt_iterator *gsi, gimple **vec_stmt,
>        gcc_assert (!nested_in_vect_loop && !STMT_VINFO_GATHER_SCATTER_P (stmt_info));
>
>        first_stmt = GROUP_FIRST_ELEMENT (stmt_info);
> +      group_size = GROUP_SIZE (vinfo_for_stmt (first_stmt));
> +
> +      if (!slp
> +         && !PURE_SLP_STMT (stmt_info)
> +         && !STMT_VINFO_STRIDED_P (stmt_info))
> +       {
> +         if (vect_load_lanes_supported (vectype, group_size))
> +           load_lanes_p = true;
> +         else if (!vect_grouped_load_supported (vectype, group_size))
> +           return false;
> +       }
>
>        /* If this is single-element interleaving with an element distance
>           that leaves unused vector loads around punt - we at least create
> @@ -6341,7 +6352,7 @@ vectorizable_load (gimple *stmt, gimple_stmt_iterator *gsi, gimple **vec_stmt,
>        if (loop_vinfo
>           && ! STMT_VINFO_STRIDED_P (stmt_info)
>           && (GROUP_GAP (vinfo_for_stmt (first_stmt)) != 0
> -             || (!slp && vf % GROUP_SIZE (vinfo_for_stmt (first_stmt)) != 0)))
> +             || (!slp && !load_lanes_p && vf % group_size != 0)))
>         {
>           if (dump_enabled_p ())
>             dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
> @@ -6361,8 +6372,6 @@ vectorizable_load (gimple *stmt, gimple_stmt_iterator *gsi, gimple **vec_stmt,
>        if (slp && SLP_TREE_LOAD_PERMUTATION (slp_node).exists ())
>         slp_perm = true;
>
> -      group_size = GROUP_SIZE (vinfo_for_stmt (first_stmt));
> -
>        /* ???  The following is overly pessimistic (as well as the loop
>           case above) in the case we can statically determine the excess
>          elements loaded are within the bounds of a decl that is accessed.
> @@ -6375,16 +6384,6 @@ vectorizable_load (gimple *stmt, gimple_stmt_iterator *gsi, gimple **vec_stmt,
>           return false;
>         }
>
> -      if (!slp
> -         && !PURE_SLP_STMT (stmt_info)
> -         && !STMT_VINFO_STRIDED_P (stmt_info))
> -       {
> -         if (vect_load_lanes_supported (vectype, group_size))
> -           load_lanes_p = true;
> -         else if (!vect_grouped_load_supported (vectype, group_size))
> -           return false;
> -       }
> -
>        /* Invalidate assumptions made by dependence analysis when vectorization
>          on the unrolled body effectively re-orders stmts.  */
>        if (!PURE_SLP_STMT (stmt_info)
> Index: gcc/testsuite/gcc.dg/vect/vect-load-lanes-peeling-1.c
> ===================================================================
> --- /dev/null
> +++ gcc/testsuite/gcc.dg/vect/vect-load-lanes-peeling-1.c
> @@ -0,0 +1,13 @@
> +/* { dg-do compile } */
> +/* { dg-require-effective-target vect_int } */
> +/* { dg-require-effective-target vect_load_lanes } */
> +
> +void
> +f (int *__restrict a, int *__restrict b)
> +{
> +  for (int i = 0; i < 96; ++i)
> +    a[i] = b[i * 3] + b[i * 3 + 1] + b[i * 3 + 2];
> +}
> +
> +/* { dg-final { scan-tree-dump-not "Data access with gaps" "vect" } } */
> +/* { dg-final { scan-tree-dump-not "epilog loop required" "vect" } } */