glsl: Compile error if fs uses gl_FragCoord before first redeclaration

Section 4.3.8.1, page 39 of GLSL 1.50 spec says:
  "Within any shader, the first redeclarations of gl_FragCoord
   must appear before any use of gl_FragCoord."

GLSL compiler should generate an error in following case:

vec4 p = gl_FragCoord;
layout(origin_upper_left) in vec4 gl_FragCoord;

void main()
{
}

Signed-off-by: Anuj Phogat <[email protected]>
Cc: <[email protected]>
Reviewed-by: Ian Romanick <[email protected]>

1 files changed, 17 insertions, 0 deletions

diff --git a/src/glsl/ast_to_hir.cpp b/src/glsl/ast_to_hir.cpp
index 35220dd8cf5..f257a248680 100644
--- a/src/glsl/ast_to_hir.cpp
+++ b/src/glsl/ast_to_hir.cpp
@@ -2535,6 +2535,23 @@ apply_type_qualifier_to_variable(const struct ast_type_qualifier *qual,
 
    if (var->name != NULL && strcmp(var->name, "gl_FragCoord") == 0) {
 
+      /* Section 4.3.8.1, page 39 of GLSL 1.50 spec says:
+       *
+       *    "Within any shader, the first redeclarations of gl_FragCoord
+       *     must appear before any use of gl_FragCoord."
+       *
+       * Generate a compiler error if above condition is not met by the
+       * fragment shader.
+       */
+      ir_variable *earlier = state->symbols->get_variable("gl_FragCoord");
+      if (earlier != NULL &&
+          earlier->data.used &&
+          !state->fs_redeclares_gl_fragcoord) {
+         _mesa_glsl_error(loc, state,
+                          "gl_FragCoord used before its first redeclaration "
+                          "in fragment shader");
+      }
+
       /* Make sure all gl_FragCoord redeclarations specify the same layout
        * qualifiers.
        */