[Mesa-dev] [PATCH 1/2] glsl: add a mechanism to allow layout qualifiers on function params

[Timothy Arceri]

The spec is quite clear this is not allowed:

    From Section 4.4. (Layout Qualifiers) of the GLSL 4.60 spec:

       "Layout qualifiers can appear in several forms of declaration.
       They can appear as part of an interface block definition or
       block member, as shown in the grammar in the previous section.
       They can also appear with just an interface-qualifier to establish
       layouts of other declarations made with that qualifier:

          layout-qualifier interface-qualifier ;

       Or, they can appear with an individual variable declared with
       an interface qualifier:

          layout-qualifier interface-qualifier declaration ;"

    From Section 4.10 (Memory Qualifiers) of the GLSL 4.60 spec:

       "Layout qualifiers cannot be used on formal function parameters,
       and layout qualification is not included in parameter matching."

However on the Nvidia binary driver they actually fail to compile
if image function params don't have a layout qualifier. This results
in applications such as No Mans Sky using layout qualifiers on params.

I've submitted a CTS test to expose this problem in the Nvidia driver
but until that is resolved this patch will help Mesa drivers work
around the issue.
---
 src/compiler/glsl/glsl_parser.yy         | 17 +++++++++++++++++
 src/compiler/glsl/glsl_parser_extras.cpp |  2 ++
 src/compiler/glsl/glsl_parser_extras.h   |  1 +
 src/mesa/main/mtypes.h                   |  5 +++++
 4 files changed, 25 insertions(+)

diff --git a/src/compiler/glsl/glsl_parser.yy b/src/compiler/glsl/glsl_parser.yy
index bc2571b6844..fd1592beca0 100644
--- a/src/compiler/glsl/glsl_parser.yy
+++ b/src/compiler/glsl/glsl_parser.yy
@@ -897,6 +897,23 @@ parameter_declarator:
       $$->identifier = $2;
       state->symbols->add_variable(new(state) ir_variable(NULL, $2, ir_var_auto));
    }
+   | layout_qualifier type_specifier any_identifier
+   {
+      if (state->allow_layout_qualifier_on_function_parameter) {
+         void *ctx = state->linalloc;
+         $$ = new(ctx) ast_parameter_declarator();
+         $$->set_location_range(@2, @3);
+         $$->type = new(ctx) ast_fully_specified_type();
+         $$->type->set_location(@2);
+         $$->type->specifier = $2;
+         $$->identifier = $3;
+         state->symbols->add_variable(new(state) ir_variable(NULL, $3, ir_var_auto));
+      } else {
+         _mesa_glsl_error(&@1, state,
+                          "is is not allowed on function parameter");
+         YYERROR;
+      }
+   }
    | type_specifier any_identifier array_specifier
    {
       void *ctx = state->linalloc;
diff --git a/src/compiler/glsl/glsl_parser_extras.cpp b/src/compiler/glsl/glsl_parser_extras.cpp
index 0a7d0d78b14..efd1a013dbd 100644
--- a/src/compiler/glsl/glsl_parser_extras.cpp
+++ b/src/compiler/glsl/glsl_parser_extras.cpp
@@ -311,6 +311,8 @@ _mesa_glsl_parse_state::_mesa_glsl_parse_state(struct gl_context *_ctx,
       ctx->Const.AllowGLSLExtensionDirectiveMidShader;
    this->allow_builtin_variable_redeclaration =
       ctx->Const.AllowGLSLBuiltinVariableRedeclaration;
+   this->allow_layout_qualifier_on_function_parameter =
+      ctx->Const.AllowLayoutQualifiersOnFunctionParameters;
 
    this->cs_input_local_size_variable_specified = false;
 
diff --git a/src/compiler/glsl/glsl_parser_extras.h b/src/compiler/glsl/glsl_parser_extras.h
index 2c8353214aa..69aa6cf9cf3 100644
--- a/src/compiler/glsl/glsl_parser_extras.h
+++ b/src/compiler/glsl/glsl_parser_extras.h
@@ -866,6 +866,7 @@ struct _mesa_glsl_parse_state {
 
    bool allow_extension_directive_midshader;
    bool allow_builtin_variable_redeclaration;
+   bool allow_layout_qualifier_on_function_parameter;
 
    /**
     * Known subroutine type declarations.
diff --git a/src/mesa/main/mtypes.h b/src/mesa/main/mtypes.h
index 9d058cef6d9..1f640b063c0 100644
--- a/src/mesa/main/mtypes.h
+++ b/src/mesa/main/mtypes.h
@@ -3764,6 +3764,11 @@ struct gl_constants
     */
    GLboolean AllowHigherCompatVersion;
 
+   /**
+    * Allow layout qualifiers on function parameters.
+    */
+   GLboolean AllowLayoutQualifiersOnFunctionParameters;
+
    /**
     * Force computing the absolute value for sqrt() and inversesqrt() to follow
     * D3D9 when apps rely on this behaviour.
-- 
2.17.1