Aoti support multi method (#14715)

This pull request introduces several improvements to the CUDA backend.
The main changes include adding a new graph pass to replace unnecessary
`slice_copy` operations, improving how method names are tracked in
compilation artifacts, and making the preprocessing pipeline more robust
and accurate.

**Key changes:**

### Graph optimization and preprocessing

* Introduced `ReplaceSliceCopyWithSlicePass`, a new export pass that
replaces non-mutated `slice_copy` operations with more efficient `slice`
view operations in the computational graph
(`replace_slice_copy_with_slice.py`, used in `cuda_backend.py`).
[[1]](diffhunk://#diff-c4a228b182f50f778545991d472609ad705d2325994342174093ff374738851dR1-R113)
[[2]](diffhunk://#diff-5b5ea2257772b3aba04b2534f5ea1429a0c631bfd25a7ef531f526e76c471d7aR115-R117)
* Added context management for attention kernel selection and no-grad
mode during AOT compilation to ensure correct backend selection for
decomposition. This is needed in the short term until we have a flash
attention cuda kernel.

### Method name and compile specification handling

* Added a `COMPILE_SPEC_KEYS` enum and utility methods
(`generate_method_name_compile_spec`, `method_name_from_compile_specs`)
to consistently embed and retrieve the method name in compile specs and
as a key in the data store, improving traceability of compiled
artifacts.
[[1]](diffhunk://#diff-5b5ea2257772b3aba04b2534f5ea1429a0c631bfd25a7ef531f526e76c471d7aL24-R35)
[[2]](diffhunk://#diff-5b5ea2257772b3aba04b2534f5ea1429a0c631bfd25a7ef531f526e76c471d7aL161-R158)
[[3]](diffhunk://#diff-5b5ea2257772b3aba04b2534f5ea1429a0c631bfd25a7ef531f526e76c471d7aR169-R195)

### Code cleanup and maintainability

* Minor refactor in `cuda_partitioner.py` to clarify delegation tag
assignment.
* Improved imports and code organization for clarity in
`cuda_backend.py`.

These changes collectively improve the reliability, performance, and
maintainability of the CUDA backend pipeline.

Author: larryliu0820

backends/cuda/cuda_backend.py

@@ -7,10 +7,14 @@
 import contextlib
 import os
 import typing
+from enum import Enum
 
 from typing import Any, Dict, final, List, Optional, Set
 
 import torch
+from executorch.backends.cuda.replace_slice_copy_with_slice import (
+    ReplaceSliceCopyWithSlicePass,
+)
 from executorch.exir._serialize._named_data_store import NamedDataStore
 from executorch.exir._warnings import experimental
 from executorch.exir.backend.backend_details import (
@@ -21,7 +25,7 @@
 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
-
+from torch.nn.attention import SDPBackend
 
 # exist fallback operators in et namespace;
 supported_fallback_kernels: Dict[str, Any] = {}
@@ -30,6 +34,10 @@
 missing_fallback_kernels: Set[str] = set()
 
 
+class COMPILE_SPEC_KEYS(Enum):
+    METHOD_NAME = "method_name"
+
+
 # context manager for non-fallback guarantee
 # it will raise exception when generating fallback kernels during aoti compile
 @contextlib.contextmanager
@@ -108,6 +116,9 @@ def preprocess(
         # Move the edge_program from CPU to CUDA for aoti compile
         cuda_edge_program = move_to_device_pass(edge_program, "cuda")
 
+        # replace slice_copy with slice
+        ReplaceSliceCopyWithSlicePass()(cuda_edge_program.graph_module)
+
         edge_program_module = cuda_edge_program.module()
 
         # Grab all input placeholders from the graph
@@ -132,7 +143,10 @@ def preprocess(
             "max_autotune_conv_backends": "TRITON",
         }
 
-        with collect_unsupported_fallback_kernels():
+        with collect_unsupported_fallback_kernels(), torch.nn.attention.sdpa_kernel(
+            [SDPBackend.MATH]
+        ), torch.no_grad():
+            # torch._logging.set_logs(post_grad_graphs=True)
             so_path = torch._inductor.aot_compile(edge_program_module, tuple(user_input_placeholders), options=options)  # type: ignore[arg-type]
             if len(missing_fallback_kernels) > 0:
                 formatted_kernels = "\n  - ".join(sorted(missing_fallback_kernels))
@@ -146,7 +160,10 @@ def preprocess(
             so_data = f.read()
 
         named_data_store = NamedDataStore()
-        named_data_store.add_named_data("so_blob", so_data, 1, "aoti_cuda_blob")
+        method_name = CudaBackend.method_name_from_compile_specs(compile_specs)
+        named_data_store.add_named_data(
+            method_name + "_so_blob", so_data, 1, "aoti_cuda_blob"
+        )
 
         # Clean up the generated so file; it has been packaged into the NamdeDataStore
         # pyre-ignorep[6]: Incompatible parameter type
@@ -157,3 +174,30 @@ def preprocess(
             debug_handle_map={},
             data_store_output=named_data_store.get_named_data_store_output(),
         )
+
+    @staticmethod
+    def generate_method_name_compile_spec(
+        method_name: str,
+    ) -> CompileSpec:
+        """
+        Returns the compile spec representing the model compute precision, for additional details
+        please refer to the documentation for ``coremltools.precision``.
+        """
+        return CompileSpec(
+            COMPILE_SPEC_KEYS.METHOD_NAME.value,
+            method_name.encode("utf-8"),
+        )
+
+    @staticmethod
+    def method_name_from_compile_specs(
+        compile_specs: List[CompileSpec],
+    ) -> str:
+        """
+        Returns 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/cuda/cuda_partitioner.py

@@ -44,12 +44,14 @@ def partition(self, exported_program: ExportedProgram) -> PartitionResult:
         """
 
         partition_tags: Dict[str, DelegationSpec] = {}
+        tag = "tag0"
+
         for node in exported_program.graph.nodes:
             if node.op != "call_function":
                 continue
-            tag = "tag0"
             node.meta["delegation_tag"] = tag
-            partition_tags[tag] = self.delegation_spec
+
+        partition_tags[tag] = self.delegation_spec
 
         tag_constant_data(exported_program)
 

backends/cuda/replace_slice_copy_with_slice.py

@@ -0,0 +1,115 @@
+# 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.
+
+# pyre-strict
+
+from typing import Iterable
+
+import torch
+from executorch.exir.dialects._ops import ops
+from executorch.exir.pass_base import ExportPass, PassResult
+from torch import fx
+
+
+_SLICE_COPY_TARGETS = (
+    torch.ops.aten.slice_copy.Tensor,
+    ops.edge.aten.slice_copy.Tensor,
+)
+
+_SLICE_TARGETS = {
+    torch.ops.aten.slice_copy.Tensor: torch.ops.aten.slice.Tensor,
+    ops.edge.aten.slice_copy.Tensor: ops.edge.aten.slice.Tensor,
+}
+
+
+class ReplaceSliceCopyWithSlicePass(ExportPass):
+    """Replace non-mutated ``slice_copy`` results with ``slice`` views."""
+
+    def call(self, graph_module: fx.GraphModule) -> PassResult:
+        graph_changed = False
+
+        for node in graph_module.graph.nodes:
+            if node.op != "call_function" or node.target not in _SLICE_COPY_TARGETS:
+                continue
+
+            if self._has_blocking_user(node, node.users.keys()):
+                continue
+
+            node.target = _SLICE_TARGETS[node.target]
+            graph_changed = True
+
+        if graph_changed:
+            graph_module.graph.lint()
+            graph_module.recompile()
+
+        return PassResult(graph_module, graph_changed)
+
+    def _has_blocking_user(self, node: fx.Node, users: Iterable[fx.Node]) -> bool:
+        for user in users:
+            if self._is_mutating_user(node, user) or self._is_view_user(node, user):
+                return True
+        return False
+
+    def _is_mutating_user(self, node: fx.Node, user: fx.Node) -> bool:
+        if user.op == "call_method":
+            # Treat in-place tensor methods conservatively as mutations only when the
+            # method name ends with ``_`` which is the PyTorch convention for mutation.
+            return isinstance(user.target, str) and user.target.endswith("_")
+
+        if user.op != "call_function":
+            return False
+
+        target = user.target
+        if not hasattr(target, "_schema"):
+            return False
+
+        schema = target._schema  # pyre-ignore[16]
+        # Positional arguments
+        for index, arg in enumerate(user.args):
+            if arg is node and self._argument_mutates(schema, index):
+                return True
+
+        # Keyword arguments
+        for name, arg in user.kwargs.items():
+            if arg is node and self._argument_mutates(schema, name):
+                return True
+
+        return False
+
+    def _is_view_user(self, node: fx.Node, user: fx.Node) -> bool:
+        if user.op == "call_method":
+            # Treat tensor methods conservatively and assume they may be view-producing.
+            return True
+
+        if user.op != "call_function":
+            return False
+
+        target = user.target
+        if getattr(target, "is_view", False):
+            for arg in user.args:
+                if arg is node:
+                    return True
+            for arg in user.kwargs.values():
+                if arg is node:
+                    return True
+
+        return False
+
+    def _argument_mutates(
+        self, schema: torch._C.FunctionSchema, key
+    ) -> bool:  # pyre-ignore[11]
+        arguments = schema.arguments
+        if isinstance(key, int):
+            if key >= len(arguments):
+                return False
+            argument = arguments[key]
+        else:
+            argument = next((arg for arg in arguments if arg.name == key), None)
+            if argument is None:
+                return False
+
+        alias_info = argument.alias_info
+        return bool(alias_info and alias_info.is_write)