[Mesa-dev] [PATCH 1/2] nir/subgroups: Add lowering for vote_ieq/vote_feq to a ballot

[Jason Ekstrand]

On Sat, Mar 10, 2018 at 10:18 AM, Jason Ekstrand <jason at jlekstrand.net>
wrote:

> This is based heavily on 97f10934edf8ac, "ac/nir: Add vote_ieq/vote_feq
> lowering pass." from Bas Nieuwenhuizen.  This version is a bit more
> general since it's in common code.  It also properly handles NaN due to
> not flipping the comparison for floats.
> ---
>  src/compiler/nir/nir.h                 |  1 +
>  src/compiler/nir/nir_lower_subgroups.c | 48
> ++++++++++++++++++++++++++++++++++
>  2 files changed, 49 insertions(+)
>
> diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
> index 5b28c72..40b1028 100644
> --- a/src/compiler/nir/nir.h
> +++ b/src/compiler/nir/nir.h
> @@ -2557,6 +2557,7 @@ typedef struct nir_lower_subgroups_options {
>     uint8_t ballot_bit_size;
>     bool lower_to_scalar:1;
>     bool lower_vote_trivial:1;
> +   bool lower_vote_eq_to_ballot:1;
>     bool lower_subgroup_masks:1;
>     bool lower_shuffle:1;
>     bool lower_quad:1;
> diff --git a/src/compiler/nir/nir_lower_subgroups.c
> b/src/compiler/nir/nir_lower_subgroups.c
> index f18ad00..e633ffe 100644
> --- a/src/compiler/nir/nir_lower_subgroups.c
> +++ b/src/compiler/nir/nir_lower_subgroups.c
> @@ -142,6 +142,51 @@ lower_vote_eq_to_scalar(nir_builder *b,
> nir_intrinsic_instr *intrin)
>  }
>
>  static nir_ssa_def *
> +lower_vote_eq_to_ballot(nir_builder *b, nir_intrinsic_instr *intrin,
> +                        const nir_lower_subgroups_options *options)
> +{
> +   assert(intrin->src[0].is_ssa);
> +   nir_ssa_def *value = intrin->src[0].ssa;
> +
> +   /* We have to implicitly lower to scalar */
> +   nir_ssa_def *all_eq = NULL;
> +   for (unsigned i = 0; i < intrin->num_components; i++) {
> +      nir_intrinsic_instr *rfi =
> +         nir_intrinsic_instr_create(b->shader,
> +                                    nir_intrinsic_read_first_invocation);
> +      nir_ssa_dest_init(&rfi->instr, &rfi->dest,
> +                        1, intrin->dest.ssa.bit_size, NULL);
> +      rfi->num_components = intrin->dest.ssa.num_components;
>

This should be 1 component. copy+paste and/or rebase fail.  Fixed locally.


> +      rfi->src[0] = nir_src_for_ssa(nir_channel(b, value, i));
> +      nir_builder_instr_insert(b, &rfi->instr);
> +
> +      nir_ssa_def *is_eq;
> +      if (intrin->intrinsic == nir_intrinsic_vote_feq) {
> +         is_eq = nir_feq(b, &rfi->dest.ssa, intrin->src[0].ssa);
> +      } else {
> +         is_eq = nir_ieq(b, &rfi->dest.ssa, intrin->src[0].ssa);
> +      }
> +
> +      if (all_eq == NULL) {
> +         all_eq = is_eq;
> +      } else {
> +         all_eq = nir_iand(b, all_eq, is_eq);
> +      }
> +   }
> +
> +   nir_intrinsic_instr *ballot =
> +      nir_intrinsic_instr_create(b->shader, nir_intrinsic_ballot);
> +   nir_ssa_dest_init(&ballot->instr, &ballot->dest,
> +                     1, options->ballot_bit_size, NULL);
> +   ballot->num_components = 1;
> +   ballot->src[0] = nir_src_for_ssa(nir_inot(b, all_eq));
> +   nir_builder_instr_insert(b, &ballot->instr);
> +
> +   return nir_ieq(b, &ballot->dest.ssa,
> +                  nir_imm_intN_t(b, 0, options->ballot_bit_size));
> +}
> +
> +static nir_ssa_def *
>  lower_shuffle(nir_builder *b, nir_intrinsic_instr *intrin,
>                bool lower_to_scalar)
>  {
> @@ -219,6 +264,9 @@ lower_subgroups_intrin(nir_builder *b,
> nir_intrinsic_instr *intrin,
>        if (options->lower_vote_trivial)
>           return nir_imm_int(b, NIR_TRUE);
>
> +      if (options->lower_vote_eq_to_ballot)
> +         return lower_vote_eq_to_ballot(b, intrin, options);
> +
>        if (options->lower_to_scalar && intrin->num_components > 1)
>           return lower_vote_eq_to_scalar(b, intrin);
>        break;
> --
> 2.5.0.400.gff86faf
>
>
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