microsoft/spirv_to_dxil: Allow forcing per-sample shading

Needed to support VkPipelineMultisampleStateCreateInfo::sampleShadingEnable.

Reviewed-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15916>

src/microsoft/spirv_to_dxil/spirv_to_dxil.c

@@ -565,6 +565,13 @@ spirv_to_dxil(const uint32_t *words, size_t word_count,
 
    NIR_PASS_V(nir, nir_lower_system_values);
 
+   // Force sample-rate shading if we're asked to.
+   if (conf->force_sample_rate_shading) {
+      assert(stage == MESA_SHADER_FRAGMENT);
+      nir_foreach_shader_in_variable(var, nir)
+         var->data.sample = true;
+   }
+
    if (conf->zero_based_vertex_instance_id) {
       // vertex_id and instance_id should have already been transformed to
       // base zero before spirv_to_dxil was called. Therefore, we can zero out

src/microsoft/spirv_to_dxil/spirv_to_dxil.h

@@ -165,6 +165,9 @@ struct dxil_spirv_runtime_conf {
    // The caller supports read-only images to be turned into SRV accesses,
    // which allows us to run the nir_opt_access() pass
    bool read_only_images_as_srvs;
+
+   // Force sample rate shading on a fragment shader
+   bool force_sample_rate_shading;
 };
 
 struct dxil_spirv_debug_options {