tu: Lower ViewIndex to 0 when multiview is disabled

This is an optimization, but it also seems to be required because the HW
sometimes fails to set ViewIndex to 0. This fixes flakes with
dEQP-VK.renderpass2.fragment_density_map.*multiviewport where the VS for
the main renderpass is reused for the copy renderpass afterwards and it
copies ViewIndex to ViewportIndex expecting it to be 0 since multiview
is disabled for the copy renderpass.

Closes: #13534
Cc: mesa-stable
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/37206>

src/freedreno/ci/freedreno-a618-flakes.txt

@@ -270,7 +270,6 @@ dEQP-VK.tessellation.invariance.*
 # Updated by ci-collate
 spec@arb_gpu_shader_fp64@execution@arb_gpu_shader_fp64-wrong-type-setter
 spec@ext_external_objects@vk-image-display-overwrite
-bypass-dEQP-VK.renderpass2.fragment_density_map.2_views.render.non_divisible_density_size.2_samples.static_subsampled_2_2_multiviewport
 
 # SKQP test which seems to flake out
 SRGBReadWritePixels

src/freedreno/ci/freedreno-a660-flakes.txt

@@ -2,10 +2,6 @@ KHR-GL46.buffer_storage.map_persistent_dispatch
 KHR-GL46.buffer_storage.map_persistent_flush
 KHR-GL46.shader_subroutine.control_flow_and_returned_subroutine_values_used_as_subroutine_input
 
-# FDM flakes:
-# See https://gitlab.freedesktop.org/mesa/mesa/-/issues/13534 for possible reproducer.
-.*dEQP-VK.renderpass2.fragment_density_map.2_views.render.*divisible_density_size.2_samples.static_subsampled_[12]_[12]_multiviewport
-
 # a618 and a660 seem to have some general instability in tesselation and GS.
 # Some tess tests also use the GS (tesselation.invariance), but others
 # don't (spirv_assembly).  They don't appear to be correlated to any GPU

src/freedreno/ci/freedreno-a750-flakes.txt

@@ -204,10 +204,6 @@ dEQP-VK.query_pool.statistics_query.fragment_shader_invocations.primary.64bits_d
 
 dEQP-VK.renderpass.suballocation.multisample_resolve.layers_6.r16_sfloat.samples_4_resolve_level_2
 
-# FDM flakes:
-# See https://gitlab.freedesktop.org/mesa/mesa/-/issues/13534 for possible reproducer.
-.*dEQP-VK.renderpass2.fragment_density_map.2_views.render.*divisible_density_size.2_samples.static_subsampled_[12]_[12]_multiviewport
-
 dEQP-VK.renderpass2.suballocation.multisample_resolve.layers_6.r8g8b8a8_snorm.samples_4_resolve_level_2
 dEQP-VK.renderpass2.suballocation.multisample_resolve.r32g32b32a32_sfloat.max_attachments_8_samples_4
 

src/freedreno/vulkan/tu_shader.cc

@@ -1220,6 +1220,29 @@ tu_nir_lower_layered_fdm(nir_shader *shader,
                                      nir_metadata_control_flow, &state);
 }
 
+static bool
+lower_view_to_zero_filter(const nir_instr *instr, const void *cb)
+{
+   return instr->type == nir_instr_type_intrinsic;
+}
+
+static nir_def *
+lower_view_to_zero(nir_builder *b, nir_instr *instr, void *cb)
+{
+   nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
+   if (intrin->intrinsic != nir_intrinsic_load_view_index)
+      return NULL;
+
+   return nir_imm_int(b, 0);
+}
+
+static bool
+tu_nir_lower_view_to_zero(nir_shader *shader)
+{
+   return nir_shader_lower_instructions(shader, lower_view_to_zero_filter,
+                                        lower_view_to_zero, NULL);
+}
+
 static void
 shared_type_info(const struct glsl_type *type, unsigned *size, unsigned *align)
 {
@@ -2672,6 +2695,9 @@ tu_shader_create(struct tu_device *dev,
       tu_nir_lower_multiview(nir, key->multiview_mask, dev);
    }
 
+   if (!key->multiview_mask)
+      tu_nir_lower_view_to_zero(nir);
+
    if (nir->info.stage == MESA_SHADER_FRAGMENT && key->force_sample_interp) {
       nir->info.fs.uses_sample_shading = true;
       nir_foreach_shader_in_variable(var, nir) {