spirv,nir: add support for SpvDecorationPerVertexKHR

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23254>

src/compiler/nir/nir.h

@@ -637,6 +637,12 @@ typedef struct nir_variable {
        */
       unsigned per_primitive:1;
 
+      /**
+       * Whether the variable is declared to indicate that a fragment shader
+       * input will not have interpolated values.
+       */
+      unsigned per_vertex:1;
+
       /**
        * \brief Layout qualifier for gl_FragDepth. See nir_depth_layout.
        *

src/compiler/nir/nir_linking_helpers.c

@@ -598,6 +598,12 @@ gather_varying_component_info(nir_shader *producer, nir_shader *consumer,
          if (in_var->data.location < VARYING_SLOT_VAR0)
             continue;
 
+         /* Do not remap per-vertex shader inputs because it's an array of
+          * 3-elements and this isn't supported.
+          */
+         if (in_var->data.per_vertex)
+            continue;
+
          unsigned location = in_var->data.location - VARYING_SLOT_VAR0;
          if (location >= MAX_VARYINGS_INCL_PATCH)
             continue;
@@ -1119,7 +1125,8 @@ replace_duplicate_input(nir_shader *shader, nir_variable *input_var,
 
          if (!does_varying_match(dup_out_var, in_var) ||
              in_var->data.interpolation != input_var->data.interpolation ||
-             get_interp_loc(in_var) != get_interp_loc(input_var))
+             get_interp_loc(in_var) != get_interp_loc(input_var) ||
+             in_var->data.per_vertex)
             continue;
 
          b.cursor = nir_before_instr(instr);

src/compiler/nir/nir_lower_io.c

@@ -136,10 +136,16 @@ nir_is_arrayed_io(const nir_variable *var, gl_shader_stage stage)
          return var->data.per_primitive;
    }
 
-   if (var->data.mode == nir_var_shader_in)
+   if (var->data.mode == nir_var_shader_in) {
+      if (var->data.per_vertex) {
+         assert(stage == MESA_SHADER_FRAGMENT);
+         return true;
+      }
+
       return stage == MESA_SHADER_GEOMETRY ||
              stage == MESA_SHADER_TESS_CTRL ||
              stage == MESA_SHADER_TESS_EVAL;
+   }
 
    if (var->data.mode == nir_var_shader_out)
       return stage == MESA_SHADER_TESS_CTRL ||
@@ -254,7 +260,8 @@ emit_load(struct lower_io_state *state,
           nir->options->use_interpolated_input_intrinsics &&
           var->data.interpolation != INTERP_MODE_FLAT &&
           !var->data.per_primitive) {
-         if (var->data.interpolation == INTERP_MODE_EXPLICIT) {
+         if (var->data.interpolation == INTERP_MODE_EXPLICIT ||
+             var->data.per_vertex) {
             assert(array_index != NULL);
             op = nir_intrinsic_load_input_vertex;
          } else {

src/compiler/nir/nir_validate.c

@@ -1548,6 +1548,9 @@ validate_var_decl(nir_variable *var, nir_variable_mode valid_modes,
       validate_assert(state, glsl_type_is_image(glsl_without_array(var->type)));
    }
 
+   if (var->data.per_vertex)
+      validate_assert(state, state->shader->info.stage == MESA_SHADER_FRAGMENT);
+
    /*
     * TODO validate some things ir_validate.cpp does (requires more GLSL type
     * support)

src/compiler/spirv/vtn_variables.c

@@ -1385,6 +1385,12 @@ apply_var_decoration(struct vtn_builder *b,
       var_data->per_view = true;
       break;
 
+   case SpvDecorationPerVertexKHR:
+      vtn_fail_if(b->shader->info.stage != MESA_SHADER_FRAGMENT,
+                  "PerVertexKHR decoration only allowed in Fragment shaders");
+      var_data->per_vertex = true;
+      break;
+
    default:
       vtn_fail_with_decoration("Unhandled decoration", dec->decoration);
    }