turnip: force sample interpolations for sample shading

Sample shading has similiar definitions in Vulkan and OpenGL, and they
both require unique associated data.  While the definition for Vulkan
might change, we should stick to the current definition until the change
takes place and until apps (i.e., ANGLE) are updated.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16700>

src/freedreno/vulkan/tu_pipeline.c

@@ -2360,8 +2360,32 @@ tu_pipeline_shader_key_init(struct ir3_shader_key *key,
       key->msaa = true;
    }
 
-   /* note: not actually used by ir3, just checked in tu6_emit_fs_inputs */
-   if (msaa_info->sampleShadingEnable)
+   /* The 1.3.215 spec says:
+    *
+    *    Sample shading can be used to specify a minimum number of unique
+    *    samples to process for each fragment. If sample shading is enabled,
+    *    an implementation must provide a minimum of
+    *
+    *       max(ceil(minSampleShadingFactor * totalSamples), 1)
+    *
+    *    unique associated data for each fragment, where
+    *    minSampleShadingFactor is the minimum fraction of sample shading.
+    *
+    * The definition is pretty much the same as OpenGL's GL_SAMPLE_SHADING.
+    * They both require unique associated data.
+    *
+    * There are discussions to change the definition, such that
+    * sampleShadingEnable does not imply unique associated data.  Before the
+    * discussions are settled and before apps (i.e., ANGLE) are fixed to
+    * follow the new and incompatible definition, we should stick to the
+    * current definition.
+    *
+    * Note that ir3_shader_key::sample_shading is not actually used by ir3,
+    * just checked in tu6_emit_fs_inputs.  We will also copy the value to
+    * tu_shader_key::force_sample_interp in a bit.
+    */
+   if (msaa_info->sampleShadingEnable &&
+       (msaa_info->minSampleShading * msaa_info->rasterizationSamples) > 1.0f)
       key->sample_shading = true;
 
    /* We set this after we compile to NIR because we need the prim mode */
@@ -2739,6 +2763,7 @@ tu_pipeline_builder_compile_shaders(struct tu_pipeline_builder *builder,
 
    keys[MESA_SHADER_VERTEX].multiview_mask = builder->multiview_mask;
    keys[MESA_SHADER_FRAGMENT].multiview_mask = builder->multiview_mask;
+   keys[MESA_SHADER_FRAGMENT].force_sample_interp = ir3_key.sample_shading;
 
    unsigned char pipeline_sha1[20];
    tu_hash_shaders(pipeline_sha1, stage_infos, builder->layout, keys, &ir3_key, compiler);

src/freedreno/vulkan/tu_private.h

@@ -1360,6 +1360,7 @@ struct tu_shader
 
 struct tu_shader_key {
    unsigned multiview_mask;
+   bool force_sample_interp;
    enum ir3_wavesize_option api_wavesize, real_wavesize;
 };
 

src/freedreno/vulkan/tu_shader.c

@@ -747,6 +747,13 @@ tu_shader_create(struct tu_device *dev,
                              &shader->multi_pos_output, dev);
    }
 
+   if (nir->info.stage == MESA_SHADER_FRAGMENT && key->force_sample_interp) {
+      nir_foreach_shader_in_variable(var, nir) {
+         if (!var->data.centroid)
+            var->data.sample = true;
+      }
+   }
+
    NIR_PASS_V(nir, nir_lower_explicit_io, nir_var_mem_push_const,
               nir_address_format_32bit_offset);