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

[Bas Nieuwenhuizen]

r-b

On Thu, Jul 18, 2019 at 10:04 AM Samuel Pitoiset
<samuel.pitoiset at gmail.com> wrote:
>
>
> 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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