[Mesa-dev] [PATCH v4] glsl: enforce invariant conditions for built-in variables

[Lars Hamre]

v3/v4:
 - compare varying slot locations rather than names (Ilia Mirkin)
v2:
 - ES version check (Tapani Pälli)

The conditions for which certain built-in special variables
can be declared invariant were not being checked.

GLSL ES 1.00 specification, Section "Invariance and linkage" says:

For the built-in special variables, gl_FragCoord can
only be declared invariant if and only if gl_Position is
declared invariant. Similarly gl_PointCoord can only be
declared invariant if and only if gl_PointSize is declared
invariant. It is an error to declare gl_FrontFacing as invariant.

This fixes the following piglit tests in spec/glsl-es-1.00/linker:
glsl-fcoord-invariant
glsl-fface-invariant
glsl-pcoord-invariant

Signed-off-by: Lars Hamre <chemecse at gmail.com>

---

CC: Ilia Mirkin <imirkin at alum.mit.edu>

NOTE: Someone with access will need to commit this after the
      review process

 src/compiler/glsl/link_varyings.cpp | 43 +++++++++++++++++++++++++++++++++++--
 1 file changed, 41 insertions(+), 2 deletions(-)

diff --git a/src/compiler/glsl/link_varyings.cpp b/src/compiler/glsl/link_varyings.cpp
index 34e82c7..c7c9f5f 100644
--- a/src/compiler/glsl/link_varyings.cpp
+++ b/src/compiler/glsl/link_varyings.cpp
@@ -352,13 +352,23 @@ cross_validate_outputs_to_inputs(struct gl_shader_program *prog,
    glsl_symbol_table parameters;
    ir_variable *explicit_locations[MAX_VARYING][4] = { {NULL, NULL} };

+   bool is_gl_position_invariant = false;
+   bool is_gl_point_size_invariant = false;
+
    /* Find all shader outputs in the "producer" stage.
     */
    foreach_in_list(ir_instruction, node, producer->ir) {
       ir_variable *const var = node->as_variable();

       if ((var == NULL) || (var->data.mode != ir_var_shader_out))
-	 continue;
+         continue;
+
+      if (prog->IsES && prog->Version < 300) {
+         if (var->data.location == VARYING_SLOT_POS)
+            is_gl_position_invariant = var->data.invariant;
+         if (var->data.location == VARYING_SLOT_PSIZ)
+            is_gl_point_size_invariant = var->data.invariant;
+      }

       if (!var->data.explicit_location
           || var->data.location < VARYING_SLOT_VAR0)
@@ -442,7 +452,36 @@ cross_validate_outputs_to_inputs(struct gl_shader_program *prog,
       ir_variable *const input = node->as_variable();

       if ((input == NULL) || (input->data.mode != ir_var_shader_in))
-	 continue;
+         continue;
+
+      /*
+       * GLSL ES 1.00 specification, Section "Invariance and linkage" says:
+       *
+       *  "For the built-in special variables, gl_FragCoord can
+       *  only be declared invariant if and only if gl_Position is
+       *  declared invariant. Similarly gl_PointCoord can only be
+       *  declared invariant if and only if gl_PointSize is declared
+       *  invariant. It is an error to declare gl_FrontFacing as invariant."
+       */
+      if (prog->IsES && prog->Version < 300 && input->data.invariant) {
+         if (input->data.location == VARYING_SLOT_FACE) {
+            linker_error(prog,
+                         "gl_FrontFacing cannot be declared invariant");
+            return;
+         } else if (!is_gl_position_invariant &&
+                    input->data.location == VARYING_SLOT_POS) {
+            linker_error(prog,
+                         "gl_FragCoord cannot be declared invariant "
+                         "unless gl_Position is also invariant");
+            return;
+         } else if (!is_gl_point_size_invariant &&
+                    input->data.location == VARYING_SLOT_PNTC) {
+            linker_error(prog,
+                         "gl_PointCoord cannot be declared invariant "
+                         "unless gl_PointSize is also invariant");
+            return;
+         }
+      }

       if (strcmp(input->name, "gl_Color") == 0 && input->data.used) {
          const ir_variable *const front_color =
--
2.5.5