venv/lib/python3.10/site-packages/torch/export/_unlift.py

# mypy: allow-untyped-defs
import copy
import inspect
import math
import warnings
from collections.abc import Sequence
from itertools import chain
from typing import Any, Optional

import sympy

import torch
import torch.utils._pytree as pytree
from torch._export.non_strict_utils import (
    _enter_enable_graph_inputs_of_type_nn_module,
    _exit_enable_graph_inputs_of_type_nn_module,
    _get_graph_inputs_of_type_nn_module,
)
from torch._export.passes.add_runtime_assertions_for_constraints_pass import (
    _convert_range_to_int,
)
from torch._export.utils import _check_input_constraints_for_graph
from torch.export.unflatten import _assign_attr, _AttrKind
from torch.fx.experimental.proxy_tensor import _pytree_subclasses_that_lose_info
from torch.fx.graph import _PyTreeCodeGen, _PyTreeInfo
from torch.fx.traceback import NodeSource, NodeSourceAction
from torch.utils._sympy.solve import try_solve
from torch.utils._sympy.value_ranges import ValueRanges

from ._remove_effect_tokens_pass import _remove_effect_tokens
from ._tree_utils import reorder_kwargs
from .exported_program import (
    ExportedProgram,
    ExportGraphSignature,
    InputKind,
    OutputKind,
)


def eq_spec(self: pytree.TreeSpec, other: pytree.TreeSpec) -> bool:
    """
    Refinement of TreeSpec.__eq__ where, e.g., torch.Size(...) matches tuple(...).
    See _pytree_subclasses_that_lose_info in proxy_tensor.py for more details.
    """

    def _normalize_type(t):
        return str(_pytree_subclasses_that_lose_info.get(t, t))

    def _match_normalized_structure(a, b):
        if a is b:
            return True
        if _normalize_type(a.type) != _normalize_type(b.type):
            return False
        if a.context != b.context:
            return False
        if len(a.children_specs) != len(b.children_specs):
            return False
        return all(
            _match_normalized_structure(a, b)
            for a, b in zip(a.children_specs, b.children_specs)
        )

    return _match_normalized_structure(self, other)


def _check_inputs_match(args, kwargs, in_spec: pytree.TreeSpec) -> list:
    reordered_kwargs = reorder_kwargs(kwargs, in_spec)
    flat_args_with_path, received_spec = pytree.tree_flatten_with_path(
        (args, reordered_kwargs)
    )

    if not eq_spec(received_spec, in_spec):
        raise ValueError(  # noqa: B904
            "Trying to flatten user inputs with exported input tree spec: \n"
            f"{in_spec}\n"
            "but actually got inputs with tree spec of: \n"
            f"{received_spec}.\n"
            "Please check that the inputs have the same number and type of "
            "args and kwargs as the ones you used when tracing."
        )

    return flat_args_with_path


def _convert_guards_code_to_fn(
    guards_code: list[str],
    paths_of_placeholders: list[pytree.KeyPath],
):
    """
    Generates Python code given guards code and paths of placeholders.
    We assume that, based on source information,
    - the tracer generates the guards code
    - the input spec generates the paths of placeholders.

    Example:

    Suppose we are given the guards code "L['z']['k'].size()[1] == 3"
    and we are given that ['z']['k'] is the path of placeholder #2.
    Then we will generate:
    ```
    torch._assert(
        args[2].size()[0] == 3,
        "Guard failed: z['k'].size()[0] == 3",
    )
    ```

    FAQ: Why do we generate code based on (flattened) args instead of
    the original (unflattened) inputs? Because this would require
    inserting an additional pytree.unflatten call in our graph.

    FAQ: Why do we not emit RuntimeError on guard failure as we used to?
    Because it is inconvenient :/, get used to AssertionError instead.
    """

    import ast

    from torch.fx.experimental.symbolic_shapes import SYMPY_INTERP

    actual_guards_code = []
    shadow_guards_code = []
    for c in guards_code:
        a, s = c, c
        for idx, path in enumerate(paths_of_placeholders):
            # e.g., replace L['z']['k'] with args[2] for Python code (actual)
            a = a.replace("L" + pytree.keystr(path), f"args[{idx}]")
            # e.g., replace L['z']['k'] with z['k'] for error message (shadow)
            s = s.replace(
                "L" + pytree.keystr(path),
                path[0].key + pytree.keystr(path[1:]),  # type: ignore[attr-defined]
            )
        actual_guards_code.append(a)
        shadow_guards_code.append(s.replace("\n", ""))

    # generate function code as str
    code_str = "\ndef _(*args):\n"
    for actual, shadow in zip(actual_guards_code, shadow_guards_code):
        # printing guards code may potentially introduce redundant parens;
        # we can normalize them out for readability by parsing/unparsing
        # NOTE: this is not necessary for correctness, just deemed desirable
        _shadow = ast.unparse(ast.parse(shadow, mode="eval"))
        # actual code and shadow error message
        code_str += f'  torch._assert({actual}, "Guard failed: {_shadow}")\n'
    code_str += "  return\n"

    # populate namespace with sympy globals, materialize function (named `_`)
    namespace = {**SYMPY_INTERP}
    exec(code_str, namespace)

    # create and return a module whose forward is the materialized function
    # NOTE: we want Dynamo to trace through this module, to repopulate guards:
    # otherwise we would lose them when retracing
    # NOTE: calling this module will be a side effect (no users): so it must
    # be marked impure to avoid being not cleaned up by DCE
    guards_fn = GuardsFn()
    guards_fn.forward = torch._dynamo.dont_skip_tracing(namespace["_"])  # type: ignore[call-overload, method-assign]
    guards_fn._is_impure = True  # type: ignore[assignment]
    return guards_fn


@torch._dynamo.disable
def _check_input_constraints_for_module(self, args, kwargs):
    flat_args_with_path = _check_inputs_match(args, kwargs, self._in_spec)
    _check_input_constraints_for_graph(
        self.graph.find_nodes(op="placeholder"),
        flat_args_with_path,
        self.range_constraints,
    )


def _check_input_constraints_pre_hook(self, args, kwargs):
    # preserve current behavior for clients that do not want any validation
    if not self.validate_inputs:
        return

    # when a guards function exists, assume that the graph does calls it!
    # so we do not need to check input constraints...but we still want
    # to check inputs match, otherwise we'd get obscure pytree errors
    if hasattr(self, "_guards_fn"):
        _check_inputs_match(args, kwargs, self._in_spec)
        return

    # NOTE: this call is Dynamo disabled, as it used to be
    _check_input_constraints_for_module(self, args, kwargs)


def _unlift_inputs_as_getattr(
    gm: torch.fx.GraphModule,
    lifted_inputs: Sequence[Optional[str]],
) -> tuple[dict[str, torch.fx.Node], dict[str, torch.fx.Node]]:
    """
    Unlift inputs referring to params/buffers/constants as getattr nodes in the
    graph
    """
    unlifted_name_to_node = {}
    input_name_to_node = {}

    placeholder_nodes = [node for node in gm.graph.nodes if node.op == "placeholder"]
    assert len(lifted_inputs) == len(placeholder_nodes)
    for input_node, lifted_node in zip(placeholder_nodes, lifted_inputs):
        if lifted_node is None:
            input_name_to_node[input_node.name] = input_node

        else:
            with gm.graph.inserting_after(input_node):
                # It is fine to ignore this warning because
                # it is guaranteed that we will populate this
                # attr later.
                with warnings.catch_warnings():
                    warnings.simplefilter("ignore")
                    getattr_node = gm.graph.get_attr(lifted_node)
                input_node.replace_all_uses_with(getattr_node)
                metadata = input_node.meta
                gm.graph.erase_node(input_node)
                getattr_node.meta = metadata
                getattr_node.meta["from_node"] = [
                    NodeSource(
                        input_node,
                        "ExportedProgram.module().unlift()",
                        [NodeSourceAction.CREATE, NodeSourceAction.REPLACE],
                    )
                ]
                unlifted_name_to_node[lifted_node] = getattr_node

    return unlifted_name_to_node, input_name_to_node


def _insert_copy_for_mutations(
    gm: torch.fx.GraphModule,
    mutated_outputs: Sequence[Optional[str]],
    unlifted_name_to_node: dict[str, torch.fx.Node],
    input_name_to_node: dict[str, torch.fx.Node],
) -> None:
    """
    Find the all the buffers and inputs that were mutated and insert copy_
    operators to reflect mutations.
    """
    output_node = gm.graph.output_node()
    outputs = pytree.tree_flatten(output_node.args)[0]
    assert len(outputs) == len(mutated_outputs)

    user_output_nodes = []
    return_nodes_to_copy = {}
    for return_node, mutated_node_name in zip(outputs, mutated_outputs):
        if mutated_node_name is None:
            user_output_nodes.append(return_node)
            continue

        if mutated_node_name in unlifted_name_to_node:
            mutated_node = unlifted_name_to_node[mutated_node_name]
        elif mutated_node_name in input_name_to_node:
            mutated_node = input_name_to_node[mutated_node_name]
        else:
            raise RuntimeError(
                f"Could not find {mutated_node_name} in either buffer or input nodes"
            )

        with gm.graph.inserting_before(output_node):
            copy_node = gm.graph.call_function(
                torch.ops.aten.copy_.default, (mutated_node, return_node)
            )
            return_nodes_to_copy[return_node] = copy_node

    output_args = tuple(
        return_nodes_to_copy[node] if node in return_nodes_to_copy else node
        for node in user_output_nodes
    )
    with gm.graph.inserting_before(output_node):
        # Only return user outputs
        new_output = gm.graph.output(output_args)
        output_node.replace_all_uses_with(new_output)
        gm.graph.erase_node(output_node)
        new_output.name = output_node.name
        new_output.meta.update(output_node.meta)
        new_output.meta["from_node"] = [
            NodeSource(
                output_node,
                "ExportedProgram.module().unlift()",
                [NodeSourceAction.CREATE, NodeSourceAction.REPLACE],
            )
        ]


def _get_codegen(
    in_spec: pytree.TreeSpec,
    out_spec: Optional[pytree.TreeSpec],
    forward_arg_names: Optional[list[str]] = None,
) -> _PyTreeCodeGen:
    """
    Create the codegen for the graph module based on the in/out specs
    """
    if forward_arg_names:
        names = forward_arg_names
    elif (
        in_spec.type == tuple
        and in_spec.num_children == 2
        and in_spec.children_specs[0].type == tuple
        and in_spec.children_specs[1].type == dict
    ):
        # if in_spec contains the args (tuple) and kwargs (dict)
        names = [f"arg_{i}" for i in range(in_spec.children_specs[0].num_children)]
        # add kwarg names
        names.extend(in_spec.children_specs[1].context)
    else:
        names = [f"arg_{i}" for i in range(in_spec.num_children)]

    return _PyTreeCodeGen(
        _PyTreeInfo(
            names,
            in_spec,
            out_spec,
        )
    )


def _unlift(
    gm: torch.fx.GraphModule,
    lifted_inputs: Sequence[Optional[str]],
    mutated_outputs: Sequence[Optional[str]],
    in_spec: pytree.TreeSpec,
    out_spec: Optional[pytree.TreeSpec],
    forward_arg_names: Optional[list[str]] = None,
):
    """
    Args:
        lifted_inputs: A list matching the graph module's input nodes. For
        an input node that is referring to a lifted parameter/buffer, this
        list will contain the fqn the corresponding attribute. Otherwise, this
        list will contain None. This is used to unlift the lifted parameters as
        get_attr nodes.

        mutated_outputs: A list matching the graph module's output nodes. For
        an output node that is referring to a mutated buffer or user input, this
        list will contain the name of the corresponding buffer or user input
        that needs to be mutated. Otherwise, this list will contain None. This
        is used to re-insert an inplace copy_ operator to copy the mutated
        values back to the original node.
    """
    unlifted_name_to_node, input_name_to_node = _unlift_inputs_as_getattr(
        gm, lifted_inputs
    )
    _insert_copy_for_mutations(
        gm, mutated_outputs, unlifted_name_to_node, input_name_to_node
    )
    gm.graph._codegen = _get_codegen(in_spec, out_spec, forward_arg_names)
    gm.graph.lint()
    gm.recompile()
    return gm


def _register_attrs_to_new_gm(
    new_gm: torch.fx.GraphModule,
    graph_signature: ExportGraphSignature,
    state_dict: dict[str, Any],
    constants: dict[str, Any],
) -> None:
    non_persistent_buffers = set(graph_signature.non_persistent_buffers)
    for name in graph_signature.buffers:
        if name in non_persistent_buffers:
            persistent = False
            value = constants[name]
        else:
            persistent = True
            value = state_dict[name]
        _assign_attr(
            value, new_gm, name, attr_kind=_AttrKind.BUFFER, persistent=persistent
        )
    for name in graph_signature.parameters:
        value = state_dict[name]
        _assign_attr(
            value,
            new_gm,
            name,
            attr_kind=_AttrKind.PARAMETER,
        )

    # Technically this doesn't account for the aliased multiple constants but
    # it is ok because we have a separate pass later in the stack that populates
    # the final gm.
    for name in chain(
        graph_signature.lifted_custom_objs, graph_signature.lifted_tensor_constants
    ):
        value = constants[name]
        _assign_attr(
            value,
            new_gm,
            name,
            attr_kind=_AttrKind.CONSTANT,
        )


class _StatefulGraphModuleFactory(type):
    """
    Metaclass that ensures a private constructor for _StatefulGraphModule
    """

    def __call__(cls, *args, **kwargs):
        raise TypeError(
            f"{cls.__module__}.{cls.__qualname__} has no public constructor. "
        )

    def _create(cls, root, graph, range_constraints=None):
        return super().__call__(
            root,
            graph,
            range_constraints=range_constraints,
        )


class _StatefulGraphModule(torch.fx.GraphModule, metaclass=_StatefulGraphModuleFactory):
    def __init__(self, root, graph, range_constraints=None):
        super().__init__(root, graph)
        # Need to fix up non-persistent buffers.
        self.range_constraints = range_constraints or []
        self.validate_inputs = True


def _create_stateful_graph_module(
    plain_graph_module: torch.fx.GraphModule,
    range_constraints,
    ep: ExportedProgram,
) -> _StatefulGraphModule:
    stateful_gm = _StatefulGraphModule._create(
        plain_graph_module,
        plain_graph_module.graph,
        range_constraints=range_constraints,
    )

    module_types = _get_graph_inputs_of_type_nn_module(ep.example_inputs)
    stateful_gm.register_forward_pre_hook(
        lambda *args, **kwargs: _enter_enable_graph_inputs_of_type_nn_module(
            module_types
        )
    )
    stateful_gm.register_forward_pre_hook(
        _check_input_constraints_pre_hook, with_kwargs=True
    )

    stateful_gm.register_forward_hook(
        lambda *args, **kwargs: _exit_enable_graph_inputs_of_type_nn_module(
            module_types
        ),
        always_call=True,
    )

    # When we have a constant that has requires_grad=True, we need to detach it
    # when we unlift as the tensors that require gradients should be registered
    # via parameters. But this is problematic when we have aliasing two constants
    # because when we call detach, they will become different tensors. This dict
    # keeps track of this logic.
    original_tensor_to_detached_tensor = {}

    # Fix up lifted tensor constants.
    # fx.GraphModule() constructor silently turns a constant attribute of plain_graph_module
    # into a buffer in stateful_gm and creates an inconsistency with graph_signature.
    # We fix this by de-registering these buffers in lifted_tensor_constants
    # and call _assign_attr(attr_kind=CONSTANT) to register them as constants.
    for constant_fqn in ep.graph_signature.lifted_tensor_constants:
        # Sometimes, the constant can require gradient, this is probably a bug in user code,
        # e.g. `self.const = torch.randn(2, 2, requires_grad=True)`.
        # We call detach on the constant_val since they're tensor constants and we don't need to
        # compute their gradients anyway.
        # Users should properly register it as parameter if they want it to require gradient.
        buffer = stateful_gm.get_buffer(constant_fqn)
        if buffer.requires_grad:
            warnings.warn(
                f"A model attribute `{constant_fqn}` requires gradient. "
                f"but it's not properly registered as a parameter. "
                f"torch.export will detach it and treat it as a constant tensor "
                f"but please register it as parameter instead."
            )
            detached_buffer = buffer.detach()
            original_tensor_to_detached_tensor[buffer] = detached_buffer
            buffer = detached_buffer
        *prefix, field = constant_fqn.rsplit(".")
        submod = torch.fx.graph_module._get_attr_via_attr_list(stateful_gm, prefix)
        delattr(submod, field)
        _assign_attr(buffer, stateful_gm, constant_fqn, attr_kind=_AttrKind.CONSTANT)

    # Constants are not preserved well when we create a new GraphModule unlike param/buffers
    for const_name, value in ep.constants.items():
        if not torch.fx.graph_module._has_attr(stateful_gm, const_name):
            if isinstance(value, torch.Tensor):
                if value.requires_grad:
                    warnings.warn(
                        f"A model attribute `{const_name}` requires gradient "
                        f"but it's not properly registered as a parameter. "
                        f"torch.export will detach it and treat it as a constant tensor "
                        f"but please register it as parameter instead."
                    )
                    if value in original_tensor_to_detached_tensor:
                        value = original_tensor_to_detached_tensor[value]
                    else:
                        detached_value = value.detach()
                        original_tensor_to_detached_tensor[value] = detached_value
                        value = detached_value
            _assign_attr(
                value,
                stateful_gm,
                const_name,
                attr_kind=_AttrKind.CONSTANT,
            )

    # Fix up non-persistent buffers. torch.fx does not distinguish between
    # persistent and non-persistent buffers, so we must restore that distinction
    # here.
    for buffer in ep.graph_signature.non_persistent_buffers:
        _assign_attr(
            plain_graph_module.get_buffer(buffer),
            stateful_gm,
            buffer,
            attr_kind=_AttrKind.BUFFER,
            persistent=False,
        )

    return stateful_gm


def _get_input_paths(example_inputs, signature):
    """
    Generate paths of placeholders, needed for generating the guards function.

    NOTE: Here we make use of the example inputs used for export as well as
    the signature of the unlifted graph module (not preserved by export).
    """

    args, kwargs = example_inputs
    ctx = signature.bind(*args, **kwargs).arguments
    flat_example_inputs_with_paths = pytree.tree_leaves_with_path(ctx)
    return [path for path, _ in flat_example_inputs_with_paths]


def _get_input_guards_for_graph(
    placeholders: list[torch.fx.Node],
    range_constraints: dict[sympy.Symbol, ValueRanges],
    paths_for_placeholders: list[pytree.KeyPath],
):
    """
    Guards generated by the tracer include conditions observed in code, but
    but do not include some additional checks we typically do in export.
    For example, when dynamic shapes get specialized, are specified to be
    within a range, or are specified to be in some equational relation,
    corresponding input invalidation is done within a pre_hook, specifically,
    `_check_input_constraints_for_graph`.

    Here we generate guards corresponding to the checks that happen in
    `_check_input_constraints_for_graph`, and add them to the guards already
    generated by the tracer. In the future, it may be worthwhile to separate
    them so that we can allow clients to turn off one but not the other.
    (Looking at you, AOTI.)

    NOTE: We should eventually reconcile this logic with `build_guards` that
    is used by AOT Precompile.
    """

    deferred_expressions = []
    new_guards_code = []
    sources: dict[sympy.Expr, str] = {}

    def handle_symint(expr, src):
        if len(expr.free_symbols) == 1:
            # complex equations (e.g., involving derived dims) need to
            # handled later, since we may not have enough information
            # just as we are passing through the placeholders in order
            deferred_expressions.append((src, expr))
        if expr in sources:
            # expressions that appear in multiple sources should force
            # inputs corresponding to those sources to be equal
            # e.g., x.shape[0] == y.shape[1]
            orig_src = sources[expr]
            new_guards_code.append(f"{src} == {orig_src}")
        else:
            sources[expr] = src
            # process value ranges as elsewhere in export
            min_val, max_val = _convert_range_to_int(range_constraints[expr])
            if min_val > 2:
                new_guards_code.append(f"{src} >= {min_val}")
            if max_val < math.inf:
                new_guards_code.append(f"{src} <= {max_val}")

    for placeholder, path in zip(placeholders, paths_for_placeholders):
        src = "L" + pytree.keystr(path)
        meta = placeholder.meta["val"]
        # specializations
        if isinstance(meta, int):
            new_guards_code.append(f"{src} == {meta}")
        if isinstance(meta, float):
            if meta == math.inf:
                new_guards_code.append(f"{src} == math.inf")
            elif meta == -math.inf:
                new_guards_code.append(f"{src} == -math.inf")
            else:
                new_guards_code.append(f"{src} == {meta}")
        elif isinstance(meta, str):
            new_guards_code.append(f"{src} == '{meta}'")
        # range constraints and equalities
        elif isinstance(meta, torch.SymInt) and meta.node.expr in range_constraints:
            handle_symint(meta.node.expr, src)
        elif isinstance(meta, torch.Tensor):
            for i, dim in enumerate(meta.shape):
                src = "L" + pytree.keystr(path) + f".size()[{i}]"
                if isinstance(dim, int):
                    # specializations
                    new_guards_code.append(f"{src} == {dim}")
                elif (
                    isinstance(dim, torch.SymInt) and dim.node.expr in range_constraints
                ):
                    # range constraints and equalities
                    handle_symint(dim.node.expr, src)

    unification_map: dict[sympy.Symbol, sympy.Expr] = {}
    py_printer = torch.utils._sympy.printers.PythonPrinter()

    # process complex equations (e.g., involving derived dims)
    for src, expr in deferred_expressions:
        # we know this is the only symbol in expr (see check above)
        symbol = next(iter(expr.free_symbols))
        if symbol in sources:
            # if s0 is already known to be directly sourced from inputs,
            # e.g., z.shape[2], we do not need to do anything further
            # (assume we have already processed constraints on s0 above)
            continue

        # otherwise s0 has some "hidden" source like 'dim'
        # example: src = y.shape[1], expr = s0 + 1
        if symbol in unification_map:
            # suppose that we already know that s0 = x.shape[0] * 2
            # so we can emit the guard: x.shape[0] * 2 + 1 = y.shape[1]
            substitution = expr.subs(unification_map)
            new_guards_code.append(
                py_printer.doprint(sympy.Eq(substitution, sympy.Symbol(src)))
            )
        else:
            # we do not yet know what s0 is, but given s0 + 1 = y.shape[1],
            # we can solve for s0...now knowing that s0 = y.shape[1] - 1
            solution = try_solve(sympy.Eq(expr, sympy.Symbol(src)), symbol)
            if solution is not None:
                definition = solution[1]
                unification_map[symbol] = definition

    return new_guards_code


def _unlift_exported_program_lifted_states(
    ep: ExportedProgram, check_guards=True
) -> torch.fx.GraphModule:
    # force check_guards=False for executorch because
    # its pass infra has too many calls to .module()
    # and but does not like call modules in the graph
    # TODO: update executorch to check_guards=False
    frame = inspect.currentframe()
    while frame is not None:
        if "executorch" in frame.f_code.co_filename:
            check_guards = False
            break
        frame = frame.f_back

    # TODO T206340015
    if ep.verifiers[0].dialect != "TRAINING":
        ep = _remove_effect_tokens(ep)

    new_gm = torch.fx.GraphModule(ep.graph_module, copy.deepcopy(ep.graph))
    _register_attrs_to_new_gm(new_gm, ep.graph_signature, ep.state_dict, ep.constants)
    forward_arg_names = (
        sig.forward_arg_names if (sig := ep.module_call_graph[0].signature) else None
    )
    lifted_inputs: list[Optional[str]] = [
        (
            in_spec.target
            if in_spec.kind
            in (
                InputKind.BUFFER,
                InputKind.CONSTANT_TENSOR,
                InputKind.PARAMETER,
                InputKind.CUSTOM_OBJ,
            )
            else None
        )
        for in_spec in ep.graph_signature.input_specs
    ]

    mutated_outputs: list[Optional[str]] = [
        (
            out_spec.target
            if out_spec.kind
            in (
                OutputKind.BUFFER_MUTATION,
                OutputKind.USER_INPUT_MUTATION,
                OutputKind.PARAMETER_MUTATION,
            )
            else None
        )
        for out_spec in ep.graph_signature.output_specs
    ]

    source_node_dict = {
        node.name: node for node in ep.graph.nodes if node.op != "placeholder"
    }
    # placeholder node name might change after deepcopy
    placeholder_source_node_dict = {
        node.target: node for node in ep.graph.nodes if node.op == "placeholder"
    }
    for node in new_gm.graph.nodes:
        source_node = None
        if node.op == "placeholder":
            source_node = placeholder_source_node_dict.get(node.target)
        else:
            source_node = source_node_dict.get(node.name)
        node.meta["from_node"] = [
            NodeSource(
                source_node,
                "ExportedProgram.module()",
                NodeSourceAction.CREATE,
            )
        ]

    assert ep.call_spec.in_spec is not None
    new_gm = _unlift(
        new_gm,
        lifted_inputs,
        mutated_outputs,
        ep.call_spec.in_spec,
        ep.call_spec.out_spec,
        forward_arg_names=forward_arg_names,
    )
    unlift_gm = _create_stateful_graph_module(new_gm, ep.range_constraints, ep)
    unlift_gm.meta.update(ep.graph_module.meta)

    # create a _guards_fn submodule and insert a call to it after placeholders
    graph = unlift_gm.graph
    placeholders = graph.find_nodes(op="placeholder")
    if check_guards and placeholders and ep.example_inputs:
        input_paths = _get_input_paths(
            ep.example_inputs,
            inspect.signature(unlift_gm.forward),
        )
        guards_code = _get_input_guards_for_graph(
            placeholders, ep.range_constraints, input_paths
        )
        guards_code.extend(ep._guards_code)
        unlift_gm._guards_fn = _convert_guards_code_to_fn(guards_code, input_paths)

        root_nn_module_stack = torch.fx._utils.first_call_function_nn_module_stack(
            graph
        )
        with graph.inserting_after(placeholders[-1]):
            node = graph.call_module("_guards_fn", tuple(placeholders))
            node.meta["nn_module_stack"] = root_nn_module_stack

        unlift_gm.recompile()

    return unlift_gm


class GuardsFn(torch.nn.Module):
    """
    Module class for guard functions.
    """

    def forward(self, *args):
        pass