[aoti-backend-consolidation 2/3] backend.py (#15528)

Summary:

# Summary

This diff consolidates the backend functionality into a single target
`//executorch/backends/aoti:aoti_backend` and simplifies the cuda
backend target by making it dependent on the consolidated backend
target.

The following changes are made in this diff:

* Creation of a new target `//executorch/backends/aoti:aoti_backend` in
`fbcode/executorch/backends/aoti/targets.bzl` which includes the
necessary dependencies for the AOTI backend.
* Update of the `//executorch/backends/cuda:cuda_backend` target in
`fbcode/executorch/backends/cuda/TARGETS` to depend on the new
`//executorch/backends/aoti:aoti_backend` target instead of individual
AOTI backend dependencies.
* Creation of a new file
`fbcode/executorch/backends/aoti/aoti_backend.py` which imports the
necessary dependencies and passes for the AOTI backend.
* Simplification of the `xplat/executorch/backends/cuda/cuda_backend.py`
file by removing unnecessary imports and using the new `AotiBackend`
class from the `aoti_backend.py` file.
ghstack-source-id: 319556735

Reviewed By: larryliu0820

Differential Revision: D85704977

---------

Co-authored-by: Copilot <[email protected]>

Author: Gasoonjia

backends/aoti/aoti_backend.py

@@ -0,0 +1,278 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the BSD-style license found in the
+# LICENSE file in the root directory of this source tree.
+
+import contextlib
+import os
+import typing
+from abc import ABC, abstractmethod
+from enum import Enum
+from typing import Any, Dict, List, Optional, Set
+
+import torch
+from executorch.backends.aoti.passes.replace_view_copy_with_view import (
+    ReplaceViewCopyWithViewPass,
+)
+from executorch.exir._serialize._named_data_store import NamedDataStore
+from executorch.exir._warnings import experimental
+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
+
+
+class COMPILE_SPEC_KEYS(Enum):
+    METHOD_NAME = "method_name"
+
+
+@experimental(
+    "This API and all of aoti-driven backend related functionality are experimental."
+)
+class AotiBackend(ABC):
+    """
+    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 backends.
+    Concrete backends (e.g., CudaBackend, MetalBackend) should inherit from both
+    BackendDetails and AotiBackend to get the full functionality.
+    """
+
+    @classmethod
+    @abstractmethod
+    def get_device_name(cls) -> str:
+        """Return the device name for this backend (e.g., 'cuda', 'metal')."""
+        pass
+
+    @classmethod
+    @abstractmethod
+    def get_supported_fallback_kernels(cls) -> Dict[str, Any]:
+        """Return the set of supported fallback kernels for this backend."""
+        pass
+
+    @classmethod
+    @abstractmethod
+    def get_decomposition_table(cls) -> Dict[Any, Any]:
+        """Return the decomposition table for this backend."""
+        pass
+
+    @classmethod
+    @abstractmethod
+    def get_aoti_compile_options(
+        cls, compile_specs: List[CompileSpec]
+    ) -> Dict[str, typing.Any]:
+        """Return the AOTInductor compilation options for this backend."""
+        pass
+
+    @classmethod
+    @abstractmethod
+    def get_custom_passes(cls) -> List[typing.Any]:
+        """Return the list of custom passes to apply after ReplaceViewCopyWithViewPass and before decomposition."""
+        pass
+
+    @classmethod
+    @contextlib.contextmanager
+    def collect_unsupported_fallback_kernels(cls, missing_fallback_kernels: Set[str]):
+        """
+        Context manager to collect unsupported fallback kernels during compilation.
+        Monitors both extern kernel calls and runtime lookup.
+        """
+        supported_kernels = cls.get_supported_fallback_kernels()
+
+        original_generate_c_shim_extern_kernel_call = (
+            CppWrapperCpu.generate_c_shim_extern_kernel_call
+        )
+        original_generate_fallback_kernel_with_runtime_lookup_aot = (
+            CppWrapperCpu.generate_fallback_kernel_with_runtime_lookup_aot
+        )
+
+        def generate_c_shim_extern_kernel_call_and_collect_unsupported_kernels(
+            self,
+            kernel: str,
+            args: list[str],
+            device: str,
+            *,
+            debug_args: Optional[list[str]] = None,
+            debug_handle: Optional[int] = None,
+        ):
+            if kernel not in supported_kernels:
+                missing_fallback_kernels.add(kernel)
+
+            original_generate_c_shim_extern_kernel_call(
+                self,
+                kernel,
+                args,
+                device,
+                debug_args=debug_args,
+                debug_handle=debug_handle,
+            )
+
+        def generate_fallback_kernel_with_runtime_lookup_aot_and_collect_unsupported_kernels(
+            self,
+            op_overload,
+            raw_args,
+            output_args,
+            raw_outputs,
+        ):
+            kernel_name = getattr(op_overload, "_name", str(op_overload))
+            if kernel_name not in supported_kernels:
+                missing_fallback_kernels.add(kernel_name)
+
+            original_generate_fallback_kernel_with_runtime_lookup_aot(
+                self, op_overload, raw_args, output_args, raw_outputs
+            )
+
+        CppWrapperCpu.generate_c_shim_extern_kernel_call = (
+            generate_c_shim_extern_kernel_call_and_collect_unsupported_kernels
+        )
+        CppWrapperCpu.generate_fallback_kernel_with_runtime_lookup_aot = generate_fallback_kernel_with_runtime_lookup_aot_and_collect_unsupported_kernels
+
+        try:
+            yield
+        finally:
+            CppWrapperCpu.generate_c_shim_extern_kernel_call = (
+                original_generate_c_shim_extern_kernel_call
+            )
+            CppWrapperCpu.generate_fallback_kernel_with_runtime_lookup_aot = (
+                original_generate_fallback_kernel_with_runtime_lookup_aot
+            )
+
+    @classmethod
+    def preprocess(
+        cls,
+        edge_program: ExportedProgram,
+        compile_specs: List[CompileSpec],
+    ) -> PreprocessResult:
+        """
+        Preprocess the edge program and compile it using AOTInductor.
+        Weights are always separated from the SO file.
+        """
+        device_name = cls.get_device_name()
+        decomposition_table = cls.get_decomposition_table()
+        options = cls.get_aoti_compile_options(compile_specs)
+
+        # Move the edge_program to the target device
+        device_edge_program = move_to_device_pass(
+            edge_program, device_name if device_name != "metal" else "mps"
+        )
+
+        # Replace view_copy with view
+        ReplaceViewCopyWithViewPass()(device_edge_program.graph_module)
+
+        # Apply custom backend-specific passes
+        custom_passes = cls.get_custom_passes()
+        for custom_pass in custom_passes:
+            custom_pass(device_edge_program.graph_module)
+
+        # Run decompositions if any
+        if decomposition_table:
+            device_edge_program = device_edge_program.run_decompositions(
+                decomposition_table
+            )
+
+        edge_program_module = device_edge_program.module()
+
+        # Grab all input placeholders from the graph
+        user_input_names = device_edge_program.graph_signature.user_inputs
+        user_input_placeholders = []
+        for node in device_edge_program.graph.nodes:
+            if node.op == "placeholder" and node.name in user_input_names:
+                user_input_placeholders.append(node.meta["val"])
+
+        # Track missing fallback kernels
+        missing_fallback_kernels: Set[str] = set()
+
+        # Compile with fallback kernel collection
+        with cls.collect_unsupported_fallback_kernels(
+            missing_fallback_kernels
+        ), torch.no_grad():
+            paths = torch._inductor.aot_compile(
+                edge_program_module, tuple(user_input_placeholders), options=options
+            )
+
+            if len(missing_fallback_kernels) > 0:
+                formatted_kernels = "\n  - ".join(sorted(missing_fallback_kernels))
+                method_name = cls.method_name_from_compile_specs(compile_specs)
+                raise RuntimeError(
+                    f"Method {method_name} missing fallback kernels ({len(missing_fallback_kernels)} total):\n  - {formatted_kernels}\n"
+                    "Please add them to the AOTI backend."
+                )
+
+        # Extract paths - weights are always separated
+        so_path = None
+        blob_path = None
+
+        if isinstance(paths, list):
+            for path in paths:
+                if path.endswith(".wrapper.so"):
+                    so_path = path
+                elif path.endswith(".wrapper_weights.blob"):
+                    blob_path = path
+        else:
+            so_path = paths
+
+        if so_path is None or blob_path is None:
+            raise RuntimeError(
+                f"Could not find required files in compiled paths, got {paths}"
+            )
+
+        # Read SO file
+        with open(so_path, "rb") as f:
+            so_data = f.read()
+
+        # Read weights blob
+        with open(blob_path, "rb") as f:
+            blob_data = f.read()
+
+        # Create named data store
+        named_data_store = NamedDataStore()
+        method_name = cls.method_name_from_compile_specs(compile_specs)
+
+        # Add SO and weights blob separately
+        named_data_store.add_named_data(method_name + "_so_blob", so_data, 1, None)
+        weights_blob_data_type = f"aoti_{device_name}_blob"
+        named_data_store.add_named_data(
+            method_name + "_weights_blob", blob_data, 1, weights_blob_data_type
+        )
+
+        # Clean up the generated files
+        os.remove(so_path)
+        os.remove(blob_path)
+
+        return PreprocessResult(
+            processed_bytes=b"",
+            debug_handle_map={},
+            data_store_output=named_data_store.get_named_data_store_output(),
+        )
+
+    @classmethod
+    def generate_method_name_compile_spec(
+        cls,
+        method_name: str,
+    ) -> CompileSpec:
+        """
+        Generate a CompileSpec for the given method name.
+        """
+        return CompileSpec(
+            COMPILE_SPEC_KEYS.METHOD_NAME.value,
+            method_name.encode("utf-8"),
+        )
+
+    @classmethod
+    def method_name_from_compile_specs(
+        cls,
+        compile_specs: List[CompileSpec],
+    ) -> str:
+        """
+        Extract the method name from the compile specs.
+        """
+        for spec in compile_specs:
+            if spec.key == COMPILE_SPEC_KEYS.METHOD_NAME.value:
+                return spec.value.decode("utf-8")
+        raise RuntimeError(
+            f"Could not find method name in compile specs: {compile_specs}"
+        )

backends/aoti/targets.bzl

@@ -16,6 +16,23 @@ def define_common_targets():
         ],
     )
 
+    runtime.python_library(
+        name = "aoti_backend",
+        srcs = [
+            "aoti_backend.py",
+        ],
+        visibility = [
+            "//executorch/...",
+        ],
+        deps = [
+            "//caffe2:torch",
+            "//executorch/backends/aoti/passes:passes",
+            "//executorch/exir/_serialize:lib",
+            "//executorch/exir/backend:backend_details",
+            "//executorch/exir/backend:compile_spec_schema",
+        ],
+    )
+
     # AOTI common shims functionality
     runtime.cxx_library(
         name = "common_shims",