[Mesa-dev] [PATCH] ac: fix exclusive scans on GFX8-GFX9

[Bas Nieuwenhuizen]

On Wed, Aug 21, 2019 at 3:45 PM Samuel Pitoiset
<samuel.pitoiset at gmail.com> wrote:
>
> This fixes a regression introduced with scan&reduce operations
> on GFX10. Note that some subgroups CTS still fail on GFX10 but
> I assume it's a different issue.
>
> This fixes dEQP-VK.subgroups.arithmetic.*.subgroupexclusive*.
>
> Fixes: 227c29a80de "amd/common/gfx10: implement scan & reduce operations"
> Signed-off-by: Samuel Pitoiset <samuel.pitoiset at gmail.com>
> ---
>  src/amd/common/ac_llvm_build.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/src/amd/common/ac_llvm_build.c b/src/amd/common/ac_llvm_build.c
> index 05871f5ea98..d72eaa2db46 100644
> --- a/src/amd/common/ac_llvm_build.c
> +++ b/src/amd/common/ac_llvm_build.c
> @@ -4221,10 +4221,7 @@ ac_build_scan(struct ac_llvm_context *ctx, nir_op op, LLVMValueRef src, LLVMValu
>         if (ctx->chip_class >= GFX10) {
>                 result = inclusive ? src : identity;
>         } else {
> -               if (inclusive)
> -                       result = src;
> -               else
> -                       result = ac_build_dpp(ctx, identity, src, dpp_wf_sr1, 0xf, 0xf, false);
> +               result = src;
>         }
>         if (maxprefix <= 1)
>                 return result;
> @@ -4333,6 +4330,8 @@ ac_build_exclusive_scan(struct ac_llvm_context *ctx, LLVMValueRef src, nir_op op
>                 get_reduction_identity(ctx, op, ac_get_type_size(LLVMTypeOf(src)));
>         result = LLVMBuildBitCast(ctx->builder, ac_build_set_inactive(ctx, src, identity),
>                                   LLVMTypeOf(identity), "");
> +       if (ctx->chip_class <= GFX9)
> +               result = ac_build_dpp(ctx, identity, result, dpp_wf_sr1, 0xf, 0xf, false);

Kinda annoying that we still do the inclusive/exclusive logic for
gfx10 inside ac_build_scan. Can we keep this inside the function by
using a intermediate src?

>         result = ac_build_scan(ctx, op, result, identity, ctx->wave_size, false);
>
>         return ac_build_wwm(ctx, result);
> --
> 2.22.1
>
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