[Mesa-dev] [PATCH 4/4] radv/gfx10: do not always execute a barrier before the second shader

[Samuel Pitoiset]

On 7/18/19 2:29 AM, Bas Nieuwenhuizen wrote:
> On Wed, Jul 17, 2019 at 3:44 PM Samuel Pitoiset
> <samuel.pitoiset at gmail.com> wrote:
>> With NGG, empty waves may still be required to export data.
>>
>> This fixes dEQP-VK.ycbcr.format.*_unorm.geometry_*.
>>
>> Signed-off-by: Samuel Pitoiset <samuel.pitoiset at gmail.com>
>> ---
>>   src/amd/vulkan/radv_nir_to_llvm.c | 31 ++++++++++++++++++++++++++++++-
>>   1 file changed, 30 insertions(+), 1 deletion(-)
>>
>> diff --git a/src/amd/vulkan/radv_nir_to_llvm.c b/src/amd/vulkan/radv_nir_to_llvm.c
>> index 3e18303879e..7e623414adc 100644
>> --- a/src/amd/vulkan/radv_nir_to_llvm.c
>> +++ b/src/amd/vulkan/radv_nir_to_llvm.c
>> @@ -4448,8 +4448,37 @@ LLVMModuleRef ac_translate_nir_to_llvm(struct ac_llvm_compiler *ac_llvm,
>>                          declare_esgs_ring(&ctx);
>>                  }
>>
>> -               if (i)
>> +               bool nested_barrier = false;
>> +
>> +               if (i) {
>> +                       if (shaders[i]->info.stage == MESA_SHADER_GEOMETRY &&
>> +                           ctx.options->key.vs_common_out.as_ngg) {
>> +                               nested_barrier = false;
>> +                       } else {
>> +                               nested_barrier = true;
>> +                       }
>> +               }
> We can simplify this to
>
> nested_barrier = i && (shaders[i]->info.stage != MESA_SHADER_GEOMETRY
> || !ctx.options->key.vs_common_out.as_ngg);
>
> Otherwise r-b, I'm just surprised an s_barrier is okay.
I'm going to move the NGG GS prologue into that inner if, so I would 
prefer to keep this way.
>> +
>> +               if (nested_barrier) {
>> +                       /* Execute a barrier before the second shader in
>> +                        * a merged shader.
>> +                        *
>> +                        * Execute the barrier inside the conditional block,
>> +                        * so that empty waves can jump directly to s_endpgm,
>> +                        * which will also signal the barrier.
>> +                        *
>> +                        * This is possible in gfx9, because an empty wave
>> +                        * for the second shader does not participate in
>> +                        * the epilogue. With NGG, empty waves may still
>> +                        * be required to export data (e.g. GS output vertices),
>> +                        * so we cannot let them exit early.
>> +                        *
>> +                        * If the shader is TCS and the TCS epilog is present
>> +                        * and contains a barrier, it will wait there and then
>> +                        * reach s_endpgm.
>> +                       */
>>                          ac_emit_barrier(&ctx.ac, ctx.stage);
>> +               }
>>
>>                  nir_foreach_variable(variable, &shaders[i]->outputs)
>>                          scan_shader_output_decl(&ctx, variable, shaders[i], shaders[i]->info.stage);
>> --
>> 2.22.0
>>
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