v3dv: only flag 'shader writes point size' if the shader actually writes it

If the shader writes point size, then the compiler needs to ensure it
writes it in the appropriate vpm output slot and also clamp its value to
expected limits. This is why we have the per_vertex_point_size in the
shader key, so it doesn't really make sense to set this if the shader
doesn't write point size.

If the shader record flags that the shader writes point size then the
hardware will use the shader written value to override point size state
(set with the POINT_SIZE packet), so again, we really only want to set
this in the shader state record if the shader actually writes its value.

While we could also limit this to point primitives, since these are the
only primitives where point size has an effect, this is not really
required, and skipping this allows us to use the same shader with any
primitive type (otherwise we would have to compile 2 different shaders).

Finally, this change makes the vertex shader setup for point size match the
one we had been doing for geometry shaders, so it makes both stages behave
consistently regarding point size behavior.

Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/29413>

src/broadcom/vulkan/v3dv_pipeline.c

@@ -1299,16 +1299,8 @@ pipeline_populate_v3d_vs_key(struct v3d_vs_key *key,
 
    struct v3dv_pipeline *pipeline = p_stage->pipeline;
 
-   /* Vulkan specifies a point size per vertex, so true for if the prim are
-    * points, like on ES2)
-    */
-   const VkPipelineInputAssemblyStateCreateInfo *ia_info =
-      pCreateInfo->pInputAssemblyState;
-   uint8_t topology = vk_to_mesa_prim[ia_info->topology];
-
-   /* FIXME: PRIM_POINTS is not enough, in gallium the full check is
-    * MESA_PRIM_POINTS && v3d->rasterizer->base.point_size_per_vertex */
-   key->per_vertex_point_size = (topology == MESA_PRIM_POINTS);
+   key->per_vertex_point_size =
+      p_stage->nir->info.outputs_written & (1ull << VARYING_SLOT_PSIZ);
 
    key->is_coord = broadcom_shader_stage_is_binning(p_stage->stage);
 

src/broadcom/vulkan/v3dvx_pipeline.c

@@ -375,7 +375,9 @@ pack_shader_state_record(struct v3dv_pipeline *pipeline)
 
    bool point_size_in_shaded_vertex_data;
    if (!pipeline->has_gs) {
-      point_size_in_shaded_vertex_data = pipeline->topology == MESA_PRIM_POINTS;
+      struct v3d_vs_prog_data *prog_data_vs =
+         pipeline->shared_data->variants[BROADCOM_SHADER_VERTEX]->prog_data.vs;
+         point_size_in_shaded_vertex_data = prog_data_vs->writes_psiz;
    } else {
       struct v3d_gs_prog_data *prog_data_gs =
          pipeline->shared_data->variants[BROADCOM_SHADER_GEOMETRY]->prog_data.gs;