[Mesa-dev] [PATCH v2] glsl: Make #pragma STDGL invariant(all) only modify outputs.

[Kenneth Graunke]

According to the GLSL ES 3.20, GLSL 4.50, and GLSL 1.20 specs:

   "To force all output variables to be invariant, use the pragma

       #pragma STDGL invariant(all)

    before all declarations in a shader."

Notably, this is only supposed to affect output variables.  Furthermore,

   "Only variables output from a shader can be candidates for invariance."

It looks like this has been wrong since we first supported the pragma in
2011 (commit 86b4398cd158024f6be9fa830554a11c2a7ebe0c).

Fixes dEQP-GLES2.functional.shaders.preprocessor.pragmas.pragma_fragment.

v2: Now that all cases are identical (other than compute shaders, which
    have no output variables anyway), we can drop the switch statement
    entirely.  We also don't need the current_function == NULL check;
    this was a hold over from when we had a single var_mode_out for both
    function parameters and shader varyings, in the bad old days.

Reviewed-by: Iago Toral Quiroga <itoral at igalia.com> [v1]
Reviewed-by: Ilia Mirkin <imirkin at alum.mit.edu> [v1]
---
 src/compiler/glsl/ast_to_hir.cpp | 26 ++------------------------
 1 file changed, 2 insertions(+), 24 deletions(-)

Good call, Ilia :)  I'd originally had a /* Invariance isn't meaningful
for fragment shader outputs */ comment, but then I looked elsewhere in
the file and realized that it actually was allowed.  So, I changed the
case, but didn't think to combine it.

It turns out we can combine all of them...here's a better version.

diff --git a/src/compiler/glsl/ast_to_hir.cpp b/src/compiler/glsl/ast_to_hir.cpp
index 441404f86d3..1794a1af5cb 100644
--- a/src/compiler/glsl/ast_to_hir.cpp
+++ b/src/compiler/glsl/ast_to_hir.cpp
@@ -4077,30 +4077,8 @@ apply_type_qualifier_to_variable(const struct ast_type_qualifier *qual,
       }
    }
 
-   if (state->all_invariant && (state->current_function == NULL)) {
-      switch (state->stage) {
-      case MESA_SHADER_VERTEX:
-         if (var->data.mode == ir_var_shader_out)
-            var->data.invariant = true;
-         break;
-      case MESA_SHADER_TESS_CTRL:
-      case MESA_SHADER_TESS_EVAL:
-      case MESA_SHADER_GEOMETRY:
-         if ((var->data.mode == ir_var_shader_in)
-             || (var->data.mode == ir_var_shader_out))
-            var->data.invariant = true;
-         break;
-      case MESA_SHADER_FRAGMENT:
-         if (var->data.mode == ir_var_shader_in)
-            var->data.invariant = true;
-         break;
-      case MESA_SHADER_COMPUTE:
-         /* Invariance isn't meaningful in compute shaders. */
-         break;
-      default:
-         break;
-      }
-   }
+   if (state->all_invariant && var->data.mode == ir_var_shader_out)
+      var->data.invariant = true;
 
    var->data.interpolation =
       interpret_interpolation_qualifier(qual, var->type,
-- 
2.15.0