glsl: add language support for GL_ARM_shader_framebuffer_fetch_depth_stencil

This extension adds built-in variables gl_LastFragDepthARM and gl_LastFragStencilARM
which can be implemented almost the same as gl_LastFragData from color fetch extension.

Signed-off-by: Pavel Asyutchenko <sventeam@yandex.ru>
Reviewed-By: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/13979>

src/compiler/glsl/ast_to_hir.cpp

@@ -2066,18 +2066,31 @@ ast_expression::do_hir(exec_list *instructions,
                                this->primary_expression.identifier);
          }
 
+         if (var->is_fb_fetch_color_output()) {
             /* From the EXT_shader_framebuffer_fetch spec:
              *
              *   "Unless the GL_EXT_shader_framebuffer_fetch extension has been
              *    enabled in addition, it's an error to use gl_LastFragData if it
              *    hasn't been explicitly redeclared with layout(noncoherent)."
              */
-         if (var->data.fb_fetch_output && var->data.memory_coherent &&
-             !state->EXT_shader_framebuffer_fetch_enable) {
+            if (var->data.memory_coherent && !state->EXT_shader_framebuffer_fetch_enable) {
                _mesa_glsl_error(&loc, state,
                                 "invalid use of framebuffer fetch output not "
                                 "qualified with layout(noncoherent)");
             }
+         } else if (var->data.fb_fetch_output) {
+            /* From the ARM_shader_framebuffer_fetch_depth_stencil spec:
+             *
+             *   "It is not legal for a fragment shader to read from gl_LastFragDepthARM
+             *    and gl_LastFragStencilARM if the early_fragment_tests layout qualifier
+             *    is specified. This will result in a compile-time error."
+             */
+            if (state->fs_early_fragment_tests) {
+               _mesa_glsl_error(&loc, state,
+                                "invalid use of depth or stencil fetch "
+                                "with early fragment tests enabled");
+            }
+         }
 
       } else {
          _mesa_glsl_error(& loc, state, "`%s' undeclared",
@@ -4118,16 +4131,25 @@ apply_type_qualifier_to_variable(const struct ast_type_qualifier *qual,
    else if (qual->flags.q.shared_storage)
       var->data.mode = ir_var_shader_shared;
 
-   if (!is_parameter && state->has_framebuffer_fetch() &&
-       state->stage == MESA_SHADER_FRAGMENT) {
+   if (!is_parameter && state->stage == MESA_SHADER_FRAGMENT) {
+      if (state->has_framebuffer_fetch()) {
          if (state->is_version(130, 300))
             var->data.fb_fetch_output = qual->flags.q.in && qual->flags.q.out;
          else
             var->data.fb_fetch_output = (strcmp(var->name, "gl_LastFragData") == 0);
       }
 
-   if (var->data.fb_fetch_output) {
+      if (state->has_framebuffer_fetch_zs() &&
+          (strcmp(var->name, "gl_LastFragDepthARM") == 0 ||
+           strcmp(var->name, "gl_LastFragStencilARM") == 0)) {
+         var->data.fb_fetch_output = 1;
+      }
+   }
+
+   if (var->data.fb_fetch_output)
       var->data.assigned = true;
+
+   if (var->is_fb_fetch_color_output()) {
       var->data.memory_coherent = !qual->flags.q.non_coherent;
 
       /* From the EXT_shader_framebuffer_fetch spec:

src/compiler/glsl/builtin_variables.cpp

@@ -1368,6 +1368,22 @@ builtin_variable_generator::generate_fs_special_vars()
       var->data.memory_coherent = 1;
    }
 
+   if (state->has_framebuffer_fetch_zs()) {
+      ir_variable *const depth_var =
+         add_output(FRAG_RESULT_DEPTH, float_t,
+                    GLSL_PRECISION_HIGH, "gl_LastFragDepthARM");
+      depth_var->data.read_only = 1;
+      depth_var->data.fb_fetch_output = 1;
+      depth_var->data.memory_coherent = 1;
+
+      ir_variable *const stencil_var =
+         add_output(FRAG_RESULT_STENCIL, int_t,
+                    GLSL_PRECISION_LOW, "gl_LastFragStencilARM");
+      stencil_var->data.read_only = 1;
+      stencil_var->data.fb_fetch_output = 1;
+      stencil_var->data.memory_coherent = 1;
+   }
+
    if (state->es_shader && state->language_version == 100 && state->EXT_blend_func_extended_enable) {
       add_index_output(FRAG_RESULT_COLOR, 1, vec4_t,
                        GLSL_PRECISION_MEDIUM, "gl_SecondaryFragColorEXT");

src/compiler/glsl/glsl_parser_extras.cpp

@@ -744,6 +744,7 @@ static const _mesa_glsl_extension _mesa_glsl_supported_extensions[] = {
    EXT(AMD_vertex_shader_layer),
    EXT(AMD_vertex_shader_viewport_index),
    EXT(ANDROID_extension_pack_es31a),
+   EXT(ARM_shader_framebuffer_fetch_depth_stencil),
    EXT(EXT_blend_func_extended),
    EXT(EXT_demote_to_helper_invocation),
    EXT(EXT_frag_depth),

src/compiler/glsl/glsl_parser_extras.h

@@ -329,6 +329,11 @@ struct _mesa_glsl_parse_state {
              EXT_shader_framebuffer_fetch_non_coherent_enable;
    }
 
+   bool has_framebuffer_fetch_zs() const
+   {
+      return ARM_shader_framebuffer_fetch_depth_stencil_enable;
+   }
+
    bool has_texture_cube_map_array() const
    {
       return ARB_texture_cube_map_array_enable ||
@@ -827,6 +832,8 @@ struct _mesa_glsl_parse_state {
    bool AMD_vertex_shader_viewport_index_warn;
    bool ANDROID_extension_pack_es31a_enable;
    bool ANDROID_extension_pack_es31a_warn;
+   bool ARM_shader_framebuffer_fetch_depth_stencil_enable;
+   bool ARM_shader_framebuffer_fetch_depth_stencil_warn;
    bool EXT_blend_func_extended_enable;
    bool EXT_blend_func_extended_warn;
    bool EXT_clip_cull_distance_enable;

src/compiler/glsl/ir.h

@@ -612,6 +612,13 @@ public:
              this->name != this->name_storage;
    }
 
+   inline bool is_fb_fetch_color_output() const
+   {
+      return this->data.fb_fetch_output &&
+             this->data.location != FRAG_RESULT_DEPTH &&
+             this->data.location != FRAG_RESULT_STENCIL;
+   }
+
    /**
     * Enable emitting extension warnings for this variable
     */