Update on "[aoti-backend-consolidation 2/3] backend.py"

Differential Revision: [D85704977](https://our.internmc.facebook.com/intern/diff/D85704977/)

[ghstack-poisoned]

Author: Gasoonjia

exir/backend/backend_api.py

@@ -10,7 +10,7 @@
 from contextlib import contextmanager, nullcontext
 from dataclasses import dataclass
 from functools import singledispatch
-from typing import Dict, Generator, List, Mapping
+from typing import Dict, Generator, List, Mapping, Set
 
 import torch
 
@@ -581,9 +581,21 @@ def lower_all_submodules_to_backend(
         for method_name, call_submodule_nodes in method_to_submodules_nodes.items()
     }
 
+    def _get_all_final_backend_details_subclasses(cls) -> Set[type]:
+        subclasses = set()
+        for subclass in cls.__subclasses__():
+            # Check if subclass is a final class (marked as @final)
+            if getattr(subclass, "__final__", False):
+                subclasses.add(subclass)
+            # Recursively check subclasses
+            subclasses.update(_get_all_final_backend_details_subclasses(subclass))
+        return subclasses
+
     backend_name_to_subclass = {
-        subclass.__name__: subclass for subclass in BackendDetails.__subclasses__()
+        subclass.__name__: subclass
+        for subclass in _get_all_final_backend_details_subclasses(BackendDetails)
     }
+
     if backend_id not in backend_name_to_subclass:
         raise NotImplementedError(f"Backend {backend_id} was not found.")