glsl/linker: Add support for XFB varying lowering in geometry shader

Reviewed-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6723>

src/compiler/glsl/link_varyings.cpp

@@ -2810,6 +2810,7 @@ assign_varying_locations(struct gl_context *ctx,
           !tfeedback_decls[i].is_aligned(dmul, matched_candidate->offset)) ||
          (matched_candidate->toplevel_var->data.explicit_location &&
           matched_candidate->toplevel_var->data.location < VARYING_SLOT_VAR0 &&
+          (!consumer || consumer->Stage == MESA_SHADER_FRAGMENT) &&
           (ctx->Const.ShaderCompilerOptions[producer->Stage].LowerBuiltinVariablesXfb &
               BITFIELD_BIT(matched_candidate->toplevel_var->data.location)));
 

src/compiler/glsl/lower_xfb_varying.cpp

@@ -40,10 +40,13 @@ class lower_xfb_var_splicer : public ir_hierarchical_visitor
 {
 public:
    explicit lower_xfb_var_splicer(void *mem_ctx,
+                                  gl_shader_stage stage,
                                   const exec_list *instructions);
 
+   ir_visitor_status append_instructions(exec_node *node);
    virtual ir_visitor_status visit_leave(ir_return *ret);
    virtual ir_visitor_status visit_leave(ir_function_signature *sig);
+   virtual ir_visitor_status visit_leave(ir_emit_vertex *emit);
 
 private:
    /**
@@ -51,8 +54,10 @@ private:
     */
    void * const mem_ctx;
 
+   gl_shader_stage stage;
+
    /**
-    * Instructions that should be spliced into place before each return.
+    * Instructions that should be spliced into place before each return and EmitVertex().
     */
    const exec_list *instructions;
 };
@@ -60,18 +65,33 @@ private:
 } /* anonymous namespace */
 
 
-lower_xfb_var_splicer::lower_xfb_var_splicer(void *mem_ctx, const exec_list *instructions)
+lower_xfb_var_splicer::lower_xfb_var_splicer(void *mem_ctx, gl_shader_stage stage,
-   : mem_ctx(mem_ctx), instructions(instructions)
+                                             const exec_list *instructions)
+   : mem_ctx(mem_ctx), stage(stage), instructions(instructions)
 {
 }
 
+ir_visitor_status
+lower_xfb_var_splicer::append_instructions(exec_node *node)
+{
+   foreach_in_list(ir_instruction, ir, this->instructions) {
+      node->insert_before(ir->clone(this->mem_ctx, NULL));
+   }
+   return visit_continue;
+}
+
 ir_visitor_status
 lower_xfb_var_splicer::visit_leave(ir_return *ret)
 {
-   foreach_in_list(ir_instruction, ir, this->instructions) {
+   if (stage != MESA_SHADER_VERTEX)
-      ret->insert_before(ir->clone(this->mem_ctx, NULL));
-   }
       return visit_continue;
+   return append_instructions(ret);
+}
+
+ir_visitor_status
+lower_xfb_var_splicer::visit_leave(ir_emit_vertex *emit)
+{
+   return append_instructions(emit);
 }
 
 /** Insert a copy-back assignment at the end of the main() function */
@@ -81,12 +101,14 @@ lower_xfb_var_splicer::visit_leave(ir_function_signature *sig)
    if (strcmp(sig->function_name(), "main") != 0)
       return visit_continue;
 
+   if (this->stage == MESA_SHADER_VERTEX) {
       if (((ir_instruction*)sig->body.get_tail())->ir_type == ir_type_return)
          return visit_continue;
 
       foreach_in_list(ir_instruction, ir, this->instructions) {
          sig->body.push_tail(ir->clone(this->mem_ctx, NULL));
       }
+   }
 
    return visit_continue;
 }
@@ -215,7 +237,7 @@ lower_xfb_varying(void *mem_ctx,
    ir_assignment *new_assignment = new(mem_ctx) ir_assignment(lhs, deref);
    new_instructions.push_tail(new_assignment);
 
-   lower_xfb_var_splicer splicer(mem_ctx, &new_instructions);
+   lower_xfb_var_splicer splicer(mem_ctx, shader->Stage, &new_instructions);
    visit_list_elements(&splicer, shader->ir);
 
    return new_variable;

src/mesa/state_tracker/st_extensions.c

@@ -335,7 +335,7 @@ void st_init_limits(struct pipe_screen *screen,
        */
       options->LowerBufferInterfaceBlocks = !prefer_nir;
 
-      if (sh == MESA_SHADER_VERTEX) {
+      if (sh == PIPE_SHADER_VERTEX || sh == PIPE_SHADER_GEOMETRY) {
          if (screen->get_param(screen, PIPE_CAP_VIEWPORT_TRANSFORM_LOWERED))
             options->LowerBuiltinVariablesXfb |= VARYING_BIT_POS;
          if (screen->get_param(screen, PIPE_CAP_PSIZ_CLAMPED))