make aoti_backend not a real backend

Author: Gasoonjia

backends/aoti/aoti_backend.py

@@ -17,11 +17,7 @@
 )
 from executorch.exir._serialize._named_data_store import NamedDataStore
 from executorch.exir._warnings import experimental
-from executorch.exir.backend.backend_details import (
-    BackendDetails,
-    ExportedProgram,
-    PreprocessResult,
-)
+from executorch.exir.backend.backend_details import ExportedProgram, PreprocessResult
 from executorch.exir.backend.compile_spec_schema import CompileSpec
 from torch._inductor.codegen.cpp_wrapper_cpu import CppWrapperCpu
 from torch.export.passes import move_to_device_pass
@@ -34,12 +30,16 @@ class COMPILE_SPEC_KEYS(Enum):
 @experimental(
     "This API and all of aoti-driven backend related functionality are experimental."
 )
-class AotiBackend(BackendDetails, ABC):
+class AotiBackend(ABC):
     """
-    Base backend class for AOTInductor-based backends.
+    Base mixin class for AOTInductor-based backends.
 
     This class provides common functionality for compiling models using AOTInductor
     with different device targets (CUDA, Metal, etc.).
+
+    This is a mixin class, not an actual backend object, for aoti-driven backens.
+    Concrete backends (e.g., CudaBackend, MetalBackend) should inherit from both
+    BackendDetails and AotiBackend to get the full functionality.
     """
 
     @staticmethod

backends/apple/metal/metal_backend.py

@@ -8,14 +8,15 @@
 from typing import Any, Dict, final
 
 from executorch.backends.aoti.aoti_backend import AotiBackend
+from executorch.exir.backend.backend_details import BackendDetails
 from executorch.exir._warnings import experimental
 
 
 @final
 @experimental(
     "This API and all of Metal backend related functionality are experimental."
 )
-class MetalBackend(AotiBackend):
+class MetalBackend(BackendDetails, AotiBackend):
     """
     MetalBackend is a backend that compiles a model to run on Metal/MPS devices. It uses the AOTInductor compiler to generate
     optimized Metal kernels for the model's operators with libtorch-free. The compiled model can be executed on Metal devices

backends/cuda/cuda_backend.py

@@ -9,6 +9,7 @@
 
 import torch
 from executorch.backends.aoti.aoti_backend import AotiBackend
+from executorch.exir.backend.backend_details import BackendDetails
 from executorch.exir._warnings import experimental
 from torch._inductor.decomposition import conv1d_to_conv2d
 
@@ -17,7 +18,7 @@
 @experimental(
     "This API and all of cuda backend related functionality are experimental."
 )
-class CudaBackend(AotiBackend):
+class CudaBackend(BackendDetails, AotiBackend):
     """
     CudaBackend is a backend that compiles a model to run on CUDA devices. It uses the AOTInductor compiler to generate
     optimized CUDA kernels for the model's operators with libtorch-free. The compiled model can be executed on CUDA devices

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, Set
+from typing import Dict, Generator, List, Mapping
 
 import torch
 
@@ -581,21 +581,9 @@ 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()
-        if len(cls.__subclasses__()) == 0:
-            return {cls}
-        else:
-            for subclass in cls.__subclasses__():
-                # Recursively check subclasses
-                subclasses.update(_get_all_final_backend_details_subclasses(subclass))
-        return subclasses
-
     backend_name_to_subclass = {
-        subclass.__name__: subclass
-        for subclass in _get_all_final_backend_details_subclasses(BackendDetails)
+        subclass.__name__: subclass for subclass in BackendDetails.__subclasses__()
     }
-
     if backend_id not in backend_name_to_subclass:
         raise NotImplementedError(f"Backend {backend_id} was not found.")