torch/ao/quantization/quantize.py

# mypy: allow-untyped-defs
import copy
import inspect
import itertools
import typing_extensions
import warnings

import torch
import torch.ao.nn.quantized as nnq
import torch.nn as nn
from torch.ao.nn.intrinsic import _FusedModule
from torch.ao.quantization.observer import _is_activation_post_process
from torch.ao.quantization.qconfig import (
    _activation_is_memoryless,
    _add_module_to_qconfig_obs_ctr,
    default_dynamic_qconfig,
    float16_dynamic_qconfig,
    float_qparams_weight_only_qconfig,
    float_qparams_weight_only_qconfig_4bit,
)
from torch.ao.quantization.quantization_mappings import (
    _get_special_act_post_process,
    _has_special_act_post_process,
    get_default_dynamic_quant_module_mappings,
    get_default_qat_module_mappings,
    get_default_qconfig_propagation_list,
    get_default_static_quant_module_mappings,
    get_default_static_quant_reference_module_mappings,
    no_observer_set,
)
from torch.ao.quantization.stubs import DeQuantStub, QuantWrapper
from torch.nn.utils.parametrize import type_before_parametrizations

from .utils import (
    DEPRECATION_WARNING,
    get_qparam_dict,
    has_no_children_ignoring_parametrizations,
)


__all__ = [
    "get_default_custom_config_dict",
    "propagate_qconfig_",
    "add_quant_dequant",
    "prepare",
    "quantize",
    "quantize_dynamic",
    "prepare_qat",
    "quantize_qat",
    "convert",
    "swap_module",
]


# TODO remove this once BC is no longer required to avoid a SEV
is_activation_post_process = _is_activation_post_process


_DEFAULT_CUSTOM_CONFIG_DICT = {
    "float_to_observed_custom_module_class": {
        nn.LSTM: nn.quantizable.LSTM,
        nn.MultiheadAttention: nn.quantizable.MultiheadAttention,
    },
    "observed_to_quantized_custom_module_class": {
        nn.quantizable.LSTM: nn.quantized.LSTM,
        nn.quantizable.MultiheadAttention: nn.quantized.MultiheadAttention,
    },
}


def get_default_custom_config_dict():
    r"""Defines the default custom config dict."""
    return _DEFAULT_CUSTOM_CONFIG_DICT


def _propagate_qconfig_helper(
    module,
    qconfig_dict,
    qconfig_parent=None,
    prefix="",
    prepare_custom_config_dict=None,
):
    r"""This is a helper function for `propagate_qconfig_`

    Args:
        module: input module
        qconfig_dict: dictionary that maps from name of submodule to quantization
                     configuration
        qconfig_parent: quantization config of parent module, we will fallback to
                       this config when there is no specified config for current
                       module
        prefix: corresponding prefix of the current module, used as key in
                qconfig_dict
        prepare_custom_config_dict: dictionary for custom handling of modules
                                    see docs for :func:`~torch.ao.quantization.prepare_fx`

    Return:
        None, module is modified inplace with qconfig attached
    """

    module_qconfig = qconfig_dict.get(
        type_before_parametrizations(module), qconfig_parent
    )
    module_qconfig = qconfig_dict.get(prefix, module_qconfig)
    module_qconfig = getattr(module, "qconfig", module_qconfig)

    torch.ao.quantization.qconfig._assert_valid_qconfig(module_qconfig, module)

    qconfig_with_device_check = _add_module_to_qconfig_obs_ctr(module_qconfig, module)
    module.qconfig = qconfig_with_device_check

    for name, child in module.named_children():
        module_prefix = prefix + "." + name if prefix else name
        #  do no not propagate qconfig to child if child is non traceable
        if prepare_custom_config_dict is None or not (
            name in prepare_custom_config_dict.get("non_traceable_module_name", [])
            or type(child)
            in prepare_custom_config_dict.get("non_traceable_module_class", [])
        ):
            _propagate_qconfig_helper(
                child, qconfig_dict, qconfig_with_device_check, module_prefix
            )


def propagate_qconfig_(module, qconfig_dict=None, prepare_custom_config_dict=None):
    r"""Propagate qconfig through the module hierarchy and assign `qconfig`
    attribute on each leaf module

    Args:
        module: input module
        qconfig_dict: dictionary that maps from name or type of submodule to
            quantization configuration, qconfig applies to all submodules of a
            given module unless qconfig for the submodules are specified (when
            the submodule already has qconfig attribute)
        prepare_custom_config_dict: dictionary for custom handling of modules
            see docs for :func:`~torch.ao.quantization.prepare_fx`

    Return:
        None, module is modified inplace with qconfig attached
    """
    if qconfig_dict is None:
        qconfig_dict = {}
    if prepare_custom_config_dict is None:
        prepare_custom_config_dict = {}
    _propagate_qconfig_helper(
        module, qconfig_dict, prepare_custom_config_dict=prepare_custom_config_dict
    )


def _observer_forward_hook(self, input, output):
    r"""Forward hook that calls observer on the output"""
    return self.activation_post_process(output)


def _observer_forward_pre_hook(self, input):
    r"""Forward pre hook that calls observer on the output"""
    return self.activation_post_process(input[0])


def _register_activation_post_process_hook(module, pre_hook=False):
    assert hasattr(module, "activation_post_process"), (
        "Expect activation_post_process attribute already attached to the module"
    )
    if pre_hook:
        module.register_forward_pre_hook(_observer_forward_pre_hook, prepend=True)
    else:
        module.register_forward_hook(_observer_forward_hook, prepend=True)


def _add_observer_(
    module,
    qconfig_propagation_list=None,
    non_leaf_module_list=None,
    device=None,
    custom_module_class_mapping=None,
):
    r"""Add observer for the leaf child of the module.

    This function insert observer module to all leaf child module that
    has a valid qconfig attribute.

    Args:
        module: input module with qconfig attributes for all the leaf modules that we want to quantize
        qconfig_propagation_list: a list of quantizable modules that will have observers added to them
            if they are leaf nodes
        device: parent device, if any
        non_leaf_module_list: list of non-leaf modules we want to add observer

    Return:
        None, module is modified inplace with added observer modules and forward_hooks
    """
    if qconfig_propagation_list is None:
        qconfig_propagation_list = get_default_qconfig_propagation_list()

    if custom_module_class_mapping is None:
        custom_module_class_mapping = {}

    # respect device affinity when adding observers
    if device is None:
        devices = _get_unique_devices_(module)
        assert len(devices) <= 1, (
            f"_add_observer_ only works with cpu or single-device CUDA modules, but got devices {devices}"
        )
        device = next(iter(devices)) if len(devices) > 0 else None

    def get_activation_post_process(qconfig, device, special_act_post_process=None):
        activation = (
            qconfig.activation()
            if special_act_post_process is None
            else special_act_post_process()
        )
        if device is not None:
            activation.to(device)
        return activation

    def needs_observation(m):
        return hasattr(m, "qconfig") and m.qconfig is not None

    def insert_activation_post_process(m, special_act_post_process=None):
        """Adds an activation post process module and register
        a pre or post hook that calls the module
        """
        # We don't insert observer/fake_quantize for DeQuantStub
        if needs_observation(m) and not isinstance(m, DeQuantStub):
            # observer and hook will be gone after we swap the module
            m.add_module(
                "activation_post_process",
                get_activation_post_process(
                    m.qconfig, device, special_act_post_process
                ),
            )
            # Register observer as the first entry in the hook list
            # All post forward hooks are preserved and will be executed after the observer before convert
            _register_activation_post_process_hook(
                m, pre_hook=_activation_is_memoryless(m.qconfig)
            )

    for name, child in module.named_children():
        # TODO remove Dropout special after codebase stable
        if type_before_parametrizations(child) in [nn.Dropout]:
            continue
        elif issubclass(
            type_before_parametrizations(child), (nnq.FloatFunctional, nnq.QFunctional)
        ):
            if needs_observation(child):
                assert hasattr(child, "activation_post_process"), (
                    f"functional class {type_before_parametrizations(child)} has no pre-defined `activation_post_process`"
                )
                child.activation_post_process = get_activation_post_process(
                    child.qconfig, device
                )
        elif isinstance(child, _FusedModule):
            # activation_post_process are now added directly to nn.Sequential/_FusedModule
            if needs_observation(child):
                insert_activation_post_process(child)
        elif (
            non_leaf_module_list is not None
            and type_before_parametrizations(child) in non_leaf_module_list
        ):
            if needs_observation(child):
                insert_activation_post_process(child)
        elif _has_special_act_post_process(child):
            special_act_post_process = _get_special_act_post_process(child)
            insert_activation_post_process(child, special_act_post_process)
        elif (
            needs_observation(child)
            and type_before_parametrizations(child) in custom_module_class_mapping
        ):
            observed_class = custom_module_class_mapping[
                type_before_parametrizations(child)
            ]
            observed_child = observed_class.from_float(child)
            setattr(module, name, observed_child)
            # TODO: These are the modules that cannot be observed
            #       Once there are more, we should move them to a separate list
            if not issubclass(observed_class, tuple(no_observer_set())):
                insert_activation_post_process(observed_child)
        else:
            _add_observer_(
                child,
                qconfig_propagation_list,
                non_leaf_module_list,
                device,
                custom_module_class_mapping,
            )

    # Insert observers only for leaf nodes, note that this observer is for
    # the output of the module, for input QuantStub will observe them
    if (
        has_no_children_ignoring_parametrizations(module)
        and not isinstance(module, torch.nn.Sequential)
        and type_before_parametrizations(module) in qconfig_propagation_list
    ):
        insert_activation_post_process(module)
    # This is a special case for AdaRound eager mode
    # AdaRound contains weight_fake_quant to be propagated from API to convert
    # leaf node check with a number of children looks naive assumption that blocks
    # Adding an exception case for AdaRound
    if (
        hasattr(module, "weight_fake_quant")
        and not isinstance(module, torch.nn.Sequential)
        and type_before_parametrizations(module) in qconfig_propagation_list
    ):
        insert_activation_post_process(module)


def _get_unique_devices_(module):
    return {p.device for p in module.parameters() if p.device.type != "meta"} | {
        p.device for p in module.buffers() if p.device.type != "meta"
    }


def add_quant_dequant(module):
    r"""Wrap the leaf child module in QuantWrapper if it has a valid qconfig
    Note that this function will modify the children of module inplace and it
    can return a new module which wraps the input module as well.

    Args:
        module: input module with qconfig attributes for all the leaf modules
        that we want to quantize

    Return:
        Either the inplace modified module with submodules wrapped in
        `QuantWrapper` based on qconfig or a new `QuantWrapper` module which
        wraps the input module, the latter case only happens when the input
        module is a leaf module and we want to quantize it.
    """
    if (
        has_no_children_ignoring_parametrizations(module)
        and hasattr(module, "qconfig")
        and module.qconfig
    ):
        return QuantWrapper(module)

    for name, child in module.named_children():
        module._modules[name] = add_quant_dequant(child)
    return module


@typing_extensions.deprecated(DEPRECATION_WARNING)
def prepare(
    model,
    inplace=False,
    allow_list=None,
    observer_non_leaf_module_list=None,
    prepare_custom_config_dict=None,
):
    r"""Prepares a copy of the model for quantization calibration or quantization-aware training.

    Quantization configuration should be assigned preemptively
    to individual submodules in `.qconfig` attribute.

    The model will be attached with observer or fake quant modules, and qconfig
    will be propagated.

    Args:
        `model`: input model to be modified in-place
        `inplace`: carry out model transformations in-place, the original module is mutated
        `allow_list`: list of quantizable modules
        `observer_non_leaf_module_list`: list of non-leaf modules we want to add observer
        `prepare_custom_config_dict`: customization configuration dictionary for prepare function

    .. code-block:: python

       # Example of prepare_custom_config_dict:
       prepare_custom_config_dict = {
           # user will manually define the corresponding observed
           # module class which has a from_float class method that converts
           # float custom module to observed custom module
           "float_to_observed_custom_module_class": {CustomModule: ObservedCustomModule}
       }

    """
    torch._C._log_api_usage_once("quantization_api.quantize.prepare")
    if prepare_custom_config_dict is None:
        prepare_custom_config_dict = get_default_custom_config_dict()
    custom_module_class_mapping = prepare_custom_config_dict.get(
        "float_to_observed_custom_module_class", {}
    )

    if not inplace:
        model = copy.deepcopy(model)

    # TODO: remove allow_list
    qconfig_propagation_list = allow_list
    if allow_list is None:
        qconfig_propagation_list = get_default_qconfig_propagation_list()
    propagate_qconfig_(model, qconfig_dict=None)

    # sanity check common API misusage
    if not any(hasattr(m, "qconfig") and m.qconfig for m in model.modules()):
        warnings.warn(
            "None of the submodule got qconfig applied. Make sure you "
            "passed correct configuration through `qconfig_dict` or "
            "by assigning the `.qconfig` attribute directly on submodules"
        )

    _add_observer_(
        model,
        qconfig_propagation_list,
        observer_non_leaf_module_list,
        custom_module_class_mapping=custom_module_class_mapping,
    )
    return model


def _remove_activation_post_process(module):
    # TODO: maybe we should change activation_post_process to _activation_post_process
    # to prevent it from being used by user
    if hasattr(module, "activation_post_process") and _is_activation_post_process(
        module.activation_post_process
    ):
        delattr(module, "activation_post_process")

    # remove activation_post_process pre and post hooks
    def remove_hooks(pre_hook=False):
        hook_map = module._forward_pre_hooks if pre_hook else module._forward_hooks
        observer_hook = (
            _observer_forward_pre_hook if pre_hook else _observer_forward_hook
        )
        handle_ids_to_remove = set()
        for handle_id, hook_fn in hook_map.items():
            if hook_fn is observer_hook:
                handle_ids_to_remove.add(handle_id)
        for handle_id in handle_ids_to_remove:
            hook_map.pop(handle_id)

    remove_hooks(pre_hook=True)
    remove_hooks(pre_hook=False)


# TODO: rename to something more general
def _remove_qconfig(module):
    r"""Clean up the qconfig left in the module so that new qconfig can be
    propagated.

    Args:
        module: module to be cleaned up
    """
    for child in module.children():
        _remove_qconfig(child)

    if hasattr(module, "qconfig"):
        del module.qconfig

    _remove_activation_post_process(module)


@typing_extensions.deprecated(DEPRECATION_WARNING)
def quantize(model, run_fn, run_args, mapping=None, inplace=False):
    r"""Quantize the input float model with post training static quantization.

    First it will prepare the model for calibration, then it calls
    `run_fn` which will run the calibration step, after that we will
    convert the model to a quantized model.

    Args:
        model: input float model
        run_fn: a calibration function for calibrating the prepared model
        run_args: positional arguments for `run_fn`
        inplace: carry out model transformations in-place, the original module is mutated
        mapping: correspondence between original module types and quantized counterparts

    Return:
        Quantized model.
    """
    torch._C._log_api_usage_once("quantization_api.quantize.quantize")
    if mapping is None:
        mapping = get_default_static_quant_module_mappings()
    if not inplace:
        model = copy.deepcopy(model)
    model.eval()
    prepare(model, inplace=True)
    run_fn(model, *run_args)
    convert(model, mapping, inplace=True)
    return model


@typing_extensions.deprecated(DEPRECATION_WARNING)
def quantize_dynamic(
    model, qconfig_spec=None, dtype=torch.qint8, mapping=None, inplace=False
):
    r"""Converts a float model to dynamic (i.e. weights-only) quantized model.

    Replaces specified modules with dynamic weight-only quantized versions and output the quantized model.

    For simplest usage provide `dtype` argument that can be float16 or qint8. Weight-only quantization
    by default is performed for layers with large weights size - i.e. Linear and RNN variants.

    Fine grained control is possible with `qconfig` and `mapping` that act similarly to `quantize()`.
    If `qconfig` is provided, the `dtype` argument is ignored.

    Args:
        model: input model
        qconfig_spec: Either:

            - A dictionary that maps from name or type of submodule to quantization
              configuration, qconfig applies to all submodules of a given
              module unless qconfig for the submodules are specified (when the
              submodule already has qconfig attribute). Entries in the dictionary
              need to be QConfig instances.

            - A set of types and/or submodule names to apply dynamic quantization to,
              in which case the `dtype` argument is used to specify the bit-width

        inplace: carry out model transformations in-place, the original module is mutated
        mapping: maps type of a submodule to a type of corresponding dynamically quantized version
            with which the submodule needs to be replaced

    """
    torch._C._log_api_usage_once("quantization_api.quantize.quantize_dynamic")
    if qconfig_spec is None:
        if dtype == torch.qint8:
            qconfig_spec = {
                nn.Linear: default_dynamic_qconfig,
                nn.LSTM: default_dynamic_qconfig,
                nn.GRU: default_dynamic_qconfig,
                nn.LSTMCell: default_dynamic_qconfig,
                nn.RNNCell: default_dynamic_qconfig,
                nn.GRUCell: default_dynamic_qconfig,
            }
        elif dtype == torch.float16:
            qconfig_spec = {
                nn.Linear: float16_dynamic_qconfig,
                nn.LSTM: float16_dynamic_qconfig,
                nn.GRU: float16_dynamic_qconfig,
                nn.LSTMCell: float16_dynamic_qconfig,
                nn.RNNCell: float16_dynamic_qconfig,
                nn.GRUCell: float16_dynamic_qconfig,
            }
        elif dtype == torch.quint8:
            qconfig_spec = {
                nn.EmbeddingBag: float_qparams_weight_only_qconfig,
                nn.Embedding: float_qparams_weight_only_qconfig,
            }
        elif dtype == torch.quint4x2:
            qconfig_spec = {
                nn.EmbeddingBag: float_qparams_weight_only_qconfig_4bit,
            }
        else:
            raise ValueError(
                f"Don't know how to quantize with default settings for {dtype}. Provide full qconfig please"
            )
    elif isinstance(qconfig_spec, set):
        if dtype is torch.qint8:
            default_qconfig = default_dynamic_qconfig
        elif dtype is torch.float16:
            default_qconfig = float16_dynamic_qconfig
        elif dtype is torch.quint8:
            default_qconfig = float_qparams_weight_only_qconfig
        elif dtype is torch.quint4x2:
            default_qconfig = float_qparams_weight_only_qconfig_4bit
        else:
            raise RuntimeError(
                "Unknown dtype specified for quantize_dynamic: ", str(dtype)
            )
        qconfig_spec = dict(zip(qconfig_spec, itertools.repeat(default_qconfig)))

    if mapping is None:
        mapping = get_default_dynamic_quant_module_mappings()

    if not inplace:
        model = copy.deepcopy(model)
    model.eval()
    propagate_qconfig_(model, qconfig_spec)
    convert(model, mapping, inplace=True)
    return model


@typing_extensions.deprecated(DEPRECATION_WARNING)
def prepare_qat(model, mapping=None, inplace=False):
    r"""
    Prepares a copy of the model for quantization calibration or
    quantization-aware training and converts it to quantized version.

    Quantization configuration should be assigned preemptively
    to individual submodules in `.qconfig` attribute.

    Args:
        model: input model to be modified in-place
        mapping: dictionary that maps float modules to quantized modules to be
                 replaced.
        inplace: carry out model transformations in-place, the original module
                 is mutated
    """
    torch._C._log_api_usage_once("quantization_api.quantize.prepare_qat")
    assert model.training, "prepare_qat only works on models in training mode"
    if mapping is None:
        mapping = get_default_qat_module_mappings()

    if not inplace:
        model = copy.deepcopy(model)

    propagate_qconfig_(model, qconfig_dict=None)
    convert(model, mapping=mapping, inplace=True, remove_qconfig=False)
    prepare(model, observer_non_leaf_module_list=set(mapping.values()), inplace=True)
    return model


@typing_extensions.deprecated(DEPRECATION_WARNING)
def quantize_qat(model, run_fn, run_args, inplace=False):
    r"""Do quantization aware training and output a quantized model

    Args:
        model: input model
        run_fn: a function for evaluating the prepared model, can be a
                function that simply runs the prepared model or a training
                loop
        run_args: positional arguments for `run_fn`

    Return:
        Quantized model.
    """
    torch._C._log_api_usage_once("quantization_api.quantize.quantize_qat")
    if not inplace:
        model = copy.deepcopy(model)
    model.train()
    prepare_qat(model, inplace=True)
    run_fn(model, *run_args)
    convert(model, inplace=True)
    return model


@typing_extensions.deprecated(DEPRECATION_WARNING)
def convert(
    module,
    mapping=None,
    inplace=False,
    remove_qconfig=True,
    is_reference=False,
    convert_custom_config_dict=None,
    use_precomputed_fake_quant=False,
):
    r"""Converts submodules in input module to a different module according to `mapping`
    by calling `from_float` method on the target module class. And remove qconfig at the
    end if remove_qconfig is set to True.

    Args:
        `module`: prepared and calibrated module
        `mapping`: a dictionary that maps from source module type to target
                   module type, can be overwritten to allow swapping user defined
                   Modules
        `inplace`: carry out model transformations in-place, the original module
                   is mutated
        `convert_custom_config_dict`: custom configuration dictionary for convert function
        `use_precomputed_fake_quant`: a flag to enable use of precomputed fake quant

    .. code-block:: python

       # Example of convert_custom_config_dict:
       convert_custom_config_dict = {
           # user will manually define the corresponding quantized
           # module class which has a from_observed class method that converts
           # observed custom module to quantized custom module
           "observed_to_quantized_custom_module_class": {
               ObservedCustomModule: QuantizedCustomModule
           }
       }

    """
    torch._C._log_api_usage_once("quantization_api.quantize.convert")
    if not inplace:
        module = copy.deepcopy(module)
    _convert(
        module,
        mapping,
        inplace=True,
        is_reference=is_reference,
        convert_custom_config_dict=convert_custom_config_dict,
        use_precomputed_fake_quant=use_precomputed_fake_quant,
    )
    if remove_qconfig:
        _remove_qconfig(module)
    return module


def _convert(
    module,
    mapping=None,
    inplace=False,
    is_reference=False,
    convert_custom_config_dict=None,
    use_precomputed_fake_quant=False,
):
    r"""Converts submodules in input module to a different module according to `mapping`
    by calling `from_float` method on the target module class

    Args:
        module: input module
        mapping: a dictionary that maps from source module type to target
                 module type, can be overwritten to allow swapping user defined
                 Modules
        inplace: carry out model transformations in-place, the original module
                 is mutated
        is_reference: a flag to enable quantized reference module
        use_precomputed_fake_quant: a flag to enable use of precomputed fake quant

    """
    if mapping is None:
        mapping = (
            get_default_static_quant_reference_module_mappings()
            if is_reference
            else get_default_static_quant_module_mappings()
        )
    if convert_custom_config_dict is None:
        convert_custom_config_dict = get_default_custom_config_dict()
    custom_module_class_mapping = convert_custom_config_dict.get(
        "observed_to_quantized_custom_module_class", {}
    )

    if not inplace:
        module = copy.deepcopy(module)
    reassign = {}
    for name, mod in module.named_children():
        # both fused modules and observed custom modules are
        # swapped as one unit
        if (
            not isinstance(mod, _FusedModule)
            and type_before_parametrizations(mod) not in custom_module_class_mapping
        ):
            _convert(
                mod,
                mapping,
                True,  # inplace
                is_reference,
                convert_custom_config_dict,
                use_precomputed_fake_quant=use_precomputed_fake_quant,
            )
        reassign[name] = swap_module(
            mod, mapping, custom_module_class_mapping, use_precomputed_fake_quant
        )

    for key, value in reassign.items():
        module._modules[key] = value

    return module


def swap_module(
    mod, mapping, custom_module_class_mapping, use_precomputed_fake_quant=False
):
    r"""Swaps the module if it has a quantized counterpart and it has an
    `observer` attached.

    Args:
        mod: input module
        mapping: a dictionary that maps from nn module to nnq module

    Return:
        The corresponding quantized module of `mod`
    """
    new_mod = mod
    if hasattr(mod, "qconfig") and mod.qconfig is not None:
        swapped = False
        if type_before_parametrizations(mod) in custom_module_class_mapping:
            new_mod = custom_module_class_mapping[
                type_before_parametrizations(mod)
            ].from_observed(mod)
            swapped = True
        elif type_before_parametrizations(mod) in mapping:
            qmod = mapping[type_before_parametrizations(mod)]
            if hasattr(qmod, "_IS_REFERENCE") and qmod._IS_REFERENCE:
                assert mod.qconfig is not None
                weight_post_process = mod.qconfig.weight()
                weight_post_process(mod.weight)
                weight_qparams = get_qparam_dict(weight_post_process)
                new_mod = qmod.from_float(mod, weight_qparams)
            else:
                sig = inspect.signature(qmod.from_float)
                if "use_precomputed_fake_quant" in sig.parameters:
                    new_mod = qmod.from_float(
                        mod, use_precomputed_fake_quant=use_precomputed_fake_quant
                    )
                else:
                    new_mod = qmod.from_float(mod)
            swapped = True

        if swapped:
            # Preserve module's pre forward hooks. They'll be called on quantized input
            for pre_hook_fn in mod._forward_pre_hooks.values():
                new_mod.register_forward_pre_hook(pre_hook_fn)
            # Preserve module's post forward hooks except _observer_forward_hook
            # After convert they'll work with quantized output
            for hook_fn in mod._forward_hooks.values():
                if hook_fn is not _observer_forward_hook:
                    new_mod.register_forward_hook(hook_fn)

            # respect device affinity when swapping modules
            devices = _get_unique_devices_(mod)
            assert len(devices) <= 1 or (
                len(devices) == 2 and torch.device("meta") in devices
            ), (
                f"swap_module only works with cpu or single-device CUDA modules, but got devices {devices}"
            )
            device = next(iter(devices)) if len(devices) > 0 else None
            if device:
                new_mod.to(device)
    return new_mod


def _get_observer_dict(mod, target_dict, prefix=""):
    r"""Traverse the modules and save all observers into dict.
    This is mainly used for quantization accuracy debug
    Args:
        mod: the top module we want to save all observers
        prefix: the prefix for the current module
        target_dict: the dictionary used to save all the observers
    """

    def get_prefix(prefix):
        return prefix if prefix == "" else prefix + "."

    if hasattr(mod, "activation_post_process"):
        target_dict[get_prefix(prefix) + "activation_post_process"] = (
            mod.activation_post_process
        )
    for name, child in mod.named_children():
        module_prefix = get_prefix(prefix) + name if prefix else name
        _get_observer_dict(child, target_dict, module_prefix)