st/mesa: Optionally call nir_vectorize_tess_levels()

This lets us vectorize gl_TessLevel{Inner,Outer} writes, using a pass
developed for RADV.  Not all backends are prepared to handle this, so
we make it optional.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Caio Oliveira <caio.oliveira@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17944>

src/compiler/nir/nir.h

@@ -3495,6 +3495,7 @@ typedef struct nir_shader_compiler_options {
     * for IO purposes and would prefer loads/stores be vectorized.
     */
    bool vectorize_io;
+   bool vectorize_tess_levels;
    bool lower_to_scalar;
    nir_instr_filter_cb lower_to_scalar_filter;
 

src/mesa/state_tracker/st_glsl_to_nir.cpp

@@ -598,6 +598,11 @@ st_nir_vectorize_io(nir_shader *producer, nir_shader *consumer)
       return;
 
    NIR_PASS_V(producer, nir_lower_io_to_vector, nir_var_shader_out);
+
+   if (producer->info.stage == MESA_SHADER_TESS_CTRL &&
+       producer->options->vectorize_tess_levels)
+      NIR_PASS_V(producer, nir_vectorize_tess_levels);
+
    NIR_PASS_V(producer, nir_opt_combine_stores, nir_var_shader_out);
 
    if ((producer)->info.stage != MESA_SHADER_TESS_CTRL) {