nir: Add a new "param" variable mode for parameters and return variables

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

src/compiler/nir/nir.h

@@ -88,7 +88,8 @@ typedef enum {
    nir_var_local,
    nir_var_uniform,
    nir_var_shader_storage,
-   nir_var_system_value
+   nir_var_system_value,
+   nir_var_param,
 } nir_variable_mode;
 
 /**
@@ -331,6 +332,12 @@ typedef struct nir_variable {
 #define nir_foreach_variable(var, var_list) \
    foreach_list_typed(nir_variable, var, node, var_list)
 
+static inline bool
+nir_variable_is_global(const nir_variable *var)
+{
+   return var->data.mode != nir_var_local && var->data.mode != nir_var_param;
+}
+
 typedef struct nir_register {
    struct exec_node node;