restore interpreter semantics

Author: Keryan-dev

src/mlang/backend_ir/bir_interpreter.ml

@@ -479,11 +479,10 @@ module Make (N : Bir_number.NumberInterface) = struct
                 | TableVar _ -> assert false
                 (* should not happen *)
               with Not_found ->
-                (* Cli.warning_print
-                 *   "Var %s used before definition, assumed undefined.\n%s"
-                 *   (Pos.unmark var.Variable.name)
-                 *   (Pos.retrieve_loc_text (Pos.get_position e)); *)
-                Undefined
+                Errors.raise_spanned_error
+                  ("Var not found (should not happen): "
+                  ^ Pos.unmark (Bir.var_to_mir var).Mir.Variable.name)
+                  (Pos.get_position e)
             in
             r
         | GenericTableIndex -> (