ir: add method to return inheritance root of a class
diff --git a/loxi_ir/ir.py b/loxi_ir/ir.py
index 0e95473..7b9a0b6 100644
--- a/loxi_ir/ir.py
+++ b/loxi_ir/ir.py
@@ -145,6 +145,15 @@
     def is_subclassof(self, super_class_name):
         return self.name != super_class_name and self.is_instanceof(super_class_name)
 
+    def inheritance_root(self):
+        if not self.superclass:
+            if self.virtual:
+                return self
+            else:
+                return None
+        else:
+            return self.superclass.inheritance_root()
+
     @property
     def is_message(self):
         return self.is_instanceof("of_header")