glsl: make sure that interpolateAt arguments are variables

In the case of a constant, it might have been propagated through and
variable_referenced() returns NULL. Error out in that case.

Fixes 3 dEQP tests:

dEQP-GLES31.functional.shaders.multisample_interpolation.interpolate_at_sample.negative.interpolate_constant
dEQP-GLES31.functional.shaders.multisample_interpolation.interpolate_at_centroid.negative.interpolate_constant
dEQP-GLES31.functional.shaders.multisample_interpolation.interpolate_at_offset.negative.interpolate_constant

Signed-off-by: Ilia Mirkin <[email protected]>
Reviewed-by: Eduardo Lima Mitev <[email protected]>
Reviewed-by: Chris Forbes <[email protected]>

1 files changed, 1 insertions, 1 deletions

diff --git a/src/compiler/glsl/ast_function.cpp b/src/compiler/glsl/ast_function.cpp
index 37fb3e790c4..4db3dd0384b 100644
--- a/src/compiler/glsl/ast_function.cpp
+++ b/src/compiler/glsl/ast_function.cpp
@@ -209,7 +209,7 @@ verify_parameter_modes(_mesa_glsl_parse_state *state,
       /* Verify that shader_in parameters are shader inputs */
       if (formal->data.must_be_shader_input) {
          ir_variable *var = actual->variable_referenced();
-         if (var && var->data.mode != ir_var_shader_in) {
+         if (!var || var->data.mode != ir_var_shader_in) {
             _mesa_glsl_error(&loc, state,
                              "parameter `%s` must be a shader input",
                              formal->name);