glsl: init gl_FragColor if zero_init=true

This fixes shaders doing "gl_FragColor += ..." and doesn't hurt correct
shaders, because the zero init is discarded.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4607>

diff --git a/src/compiler/glsl/ast_to_hir.cpp b/src/compiler/glsl/ast_to_hir.cpp
index 630d807e1147459f109b520c64e03de9ea91fccc..9cd3af83a48d8c5b9ac652df8307af0b57ebde5c 100644 (file)
--- a/src/compiler/glsl/ast_to_hir.cpp
+++ b/src/compiler/glsl/ast_to_hir.cpp
@@ -8797,8 +8797,14 @@ detect_conflicting_assignments(struct _mesa_glsl_parse_state *state,
       if (!var || !var->data.assigned)
          continue;
 
-      if (strcmp(var->name, "gl_FragColor") == 0)
+      if (strcmp(var->name, "gl_FragColor") == 0) {
          gl_FragColor_assigned = true;
+         if (!var->constant_initializer && state->zero_init) {
+            const ir_constant_data data = { { 0 } };
+            var->data.has_initializer = true;
+            var->constant_initializer = new(var) ir_constant(var->type, &data);
+         }
+      }
       else if (strcmp(var->name, "gl_FragData") == 0)
          gl_FragData_assigned = true;
         else if (strcmp(var->name, "gl_SecondaryFragColorEXT") == 0)