torch/fx/experimental/optimization.py

# mypy: allow-untyped-defs
import copy
import logging
import operator
import time
from collections import defaultdict
from collections.abc import Iterable
from enum import Enum
from typing import Any, cast, Optional

import torch
import torch.fx as fx
import torch.nn as nn
import torch.nn.functional as F
import torch.utils.mkldnn as th_mkldnn
from torch.fx.node import Argument, Target
from torch.fx.passes.shape_prop import ShapeProp
from torch.nn.utils.fusion import fuse_conv_bn_eval, fuse_linear_bn_eval


__all__ = [
    "matches_module_pattern",
    "replace_node_module",
    "fuse",
    "remove_dropout",
    "extract_subgraph",
    "modules_to_mkldnn",
    "reset_modules",
    "MklSubgraph",
    "gen_mkl_autotuner",
    "use_mkl_length",
    "UnionFind",
    "optimize_for_inference",
]


def _parent_name(target: str) -> tuple[str, str]:
    """
    Splits a qualname into parent path and last atom.
    For example, `foo.bar.baz` -> (`foo.bar`, `baz`)
    """
    *parent, name = target.rsplit(".", 1)
    return parent[0] if parent else "", name


# Works for length 2 patterns with 2 modules
def matches_module_pattern(
    pattern: Iterable[type], node: fx.Node, modules: dict[str, Any]
):
    if len(node.args) == 0:
        return False
    nodes: tuple[Any, fx.Node] = (node.args[0], node)
    for expected_type, current_node in zip(pattern, nodes):
        if not isinstance(current_node, fx.Node):
            return False
        if current_node.op != "call_module":
            return False
        if not isinstance(current_node.target, str):
            return False
        if current_node.target not in modules:
            return False
        if type(modules[current_node.target]) is not expected_type:
            return False
    return True


def replace_node_module(
    node: fx.Node, modules: dict[str, Any], new_module: torch.nn.Module
):
    assert isinstance(node.target, str)
    parent_name, name = _parent_name(node.target)
    modules[node.target] = new_module
    setattr(modules[parent_name], name, new_module)


def fuse(model: torch.nn.Module, inplace=False, no_trace=False) -> torch.nn.Module:
    """
    Fuses convolution/BN and linear/BN layers for inference purposes.
    Will deepcopy your model by default, but can modify the model inplace as well.
    """
    patterns = [
        (nn.Conv1d, nn.BatchNorm1d),
        (nn.Conv2d, nn.BatchNorm2d),
        (nn.Conv3d, nn.BatchNorm3d),
        (nn.Linear, nn.BatchNorm1d),
    ]
    if not inplace:
        model = copy.deepcopy(model)
    if not no_trace or not isinstance(model, torch.fx.GraphModule):
        fx_model = fx.symbolic_trace(model)
    else:
        fx_model = model
    modules = dict(fx_model.named_modules())
    new_graph = copy.deepcopy(fx_model.graph)

    for pattern in patterns:
        for node in new_graph.nodes:
            if matches_module_pattern(pattern, node, modules):
                if len(node.args[0].users) > 1:
                    # Output of conv/linear is used by other nodes
                    continue
                first_layer = modules[node.args[0].target]
                bn = modules[node.target]
                if not bn.track_running_stats:
                    continue
                if pattern[0] in [nn.Conv1d, nn.Conv2d, nn.Conv3d]:
                    fused_layer = fuse_conv_bn_eval(first_layer, bn)
                else:  # nn.Linear
                    fused_layer = fuse_linear_bn_eval(first_layer, bn)
                replace_node_module(node.args[0], modules, fused_layer)
                node.replace_all_uses_with(node.args[0])
                new_graph.erase_node(node)
    return fx.GraphModule(fx_model, new_graph)


def remove_dropout(model: nn.Module) -> nn.Module:
    """
    Removes all dropout layers from the module.
    """
    fx_model = fx.symbolic_trace(model)

    class DropoutRemover(torch.fx.Transformer):
        def call_module(
            self, target: Target, args: tuple[Argument, ...], kwargs: dict[str, Any]
        ) -> Any:
            if isinstance(self.submodules[target], nn.Dropout):
                assert len(args) == 1
                return args[0]
            else:
                return super().call_module(target, args, kwargs)

    return DropoutRemover(fx_model).transform()


def extract_subgraph(
    orig_module: nn.Module,
    nodes: list[fx.Node],
    inputs: list[fx.Node],
    outputs: list[fx.Node],
):
    """
    Given lists of nodes from an existing graph that represent a subgraph, returns a submodule that executes that subgraph.
    """
    new_graph = fx.Graph()
    env: dict[fx.Node, fx.Node] = {}
    for input in inputs:
        new_node = new_graph.placeholder(input.name)
        env[input] = new_node
    for node in nodes:
        new_node = new_graph.node_copy(node, lambda x: env[x])
        env[node] = new_node
    new_graph.output([env[output] for output in outputs])
    new_graph.lint()
    return fx.GraphModule(orig_module, new_graph)


mkldnn_supported = [
    nn.Conv2d,
    nn.Linear,
    nn.BatchNorm2d,
    nn.ReLU,
    nn.MaxPool2d,
    nn.AvgPool2d,
    nn.AdaptiveAvgPool2d,
    torch.relu,
    torch.transpose,
    torch.sigmoid,
    F.relu,
    F.avg_pool2d,
    F.adaptive_avg_pool2d,
]
# These are operators that may not be convertible into MKLDNN ops (e.g. the
# args are scalar values). Thus, we only include them in the subgraph if their
# arguments are already in MKLDNN.
# TODO: Determine whether this can be removed after type inference.
mkldnn_supported_unknown = [operator.add, operator.mul]
mkldnn_map = {
    nn.Conv2d: th_mkldnn.MkldnnConv2d,
    nn.Linear: th_mkldnn.MkldnnLinear,
    nn.BatchNorm2d: lambda a, _: th_mkldnn.MkldnnBatchNorm(a),
}


def modules_to_mkldnn(nodes: list[fx.Node], modules: dict[str, nn.Module]):
    """
    For each node, if it's a module that can be preconverted into MKLDNN,
    then we do so and create a mapping to allow us to convert from the MKLDNN
    version of the module to the original.
    """
    old_modules: dict[nn.Module, nn.Module] = {}
    for node in nodes:
        if node.op == "call_module":
            assert isinstance(node.target, str)
            cur_module = modules[node.target]
            if type(cur_module) in mkldnn_map:
                new_module = mkldnn_map[type(cur_module)](cur_module, torch.float)
                assert isinstance(new_module, nn.Module)
                old_modules[new_module] = copy.deepcopy(cur_module)
                replace_node_module(node, modules, new_module)
    return old_modules


def reset_modules(
    nodes: list[fx.Node],
    modules: dict[str, nn.Module],
    old_modules: dict[nn.Module, nn.Module],
):
    """
    Maps each module that's been changed with `modules_to_mkldnn` back to its
    original.
    """
    for node in nodes:
        if node.op == "call_module":
            assert isinstance(node.target, str)
            cur_module = modules[node.target]
            if cur_module in old_modules:
                replace_node_module(node, modules, old_modules[cur_module])


class MklSubgraph:
    def __init__(self, fx_graph: fx.Graph):
        self.fx_graph = fx_graph
        self.nodes: list[fx.Node] = []
        self.start_nodes: list[fx.Node] = []
        self.end_nodes: list[fx.Node] = []


def gen_mkl_autotuner(example_inputs, iters=10, warmup=1):
    """
    This generates a heuristic that can be passed into `optimize_for_inference` that
    determines whether a subgraph should be run in MKL by running it with the example_inputs.

    Example usage:
        heuristic = gen_mkl_autotuner(example_inputs, iters=10)
        fast_model = optimization.optimize_for_inference(model, heuristic)
    """
    fx_model = None
    old_modules = None

    def use_mkl_heuristic(graph: MklSubgraph) -> bool:
        nonlocal fx_model, old_modules
        input_nodes = graph.start_nodes
        if fx_model is None:
            fx_model = graph.fx_graph.owning_module
            old_modules = graph.fx_graph.old_modules  # type: ignore[attr-defined]
            ShapeProp(fx_model).propagate(example_inputs)
        sample_inputs = [torch.randn(node.shape) for node in input_nodes]  # type: ignore[attr-defined]
        output_args = cast(list[fx.Node], [node.args[0] for node in graph.end_nodes])
        submodule = extract_subgraph(fx_model, graph.nodes, input_nodes, output_args)

        def benchmark(f):
            for _ in range(warmup):
                f()
            begin = time.time()
            for _ in range(iters):
                f()
            return time.time() - begin

        mkl_time = benchmark(
            lambda: [
                i.to_dense() for i in submodule(*[i.to_mkldnn() for i in sample_inputs])
            ]
        )

        reset_modules(
            submodule.graph.nodes, dict(submodule.named_modules()), old_modules
        )
        no_mkl_time = benchmark(lambda: submodule(*sample_inputs))
        return mkl_time < no_mkl_time

    return use_mkl_heuristic


def use_mkl_length(graph: MklSubgraph) -> bool:
    """
    This is a heuristic that can be passed into `optimize_for_inference` that
    determines whether a subgraph should be run in MKL by checking if there
    are more than 2 nodes in it
    """
    return len(graph.nodes) > 2


class UnionFind:
    def __init__(self, n):
        self.parent: list[Optional[int]] = [None] * n
        self.size: list[int] = [0] * n

    def make_set(self, v: int):
        self.parent[v] = v
        self.size[v] = 1

    def find(self, v: int) -> int:
        par = self.parent[v]
        if v == par:
            return v
        assert par is not None
        self.parent[v] = self.find(par)
        return cast(int, self.parent[v])

    def join(self, a: int, b: int):
        a, b = self.find(a), self.find(b)
        if a == b:
            return a
        if self.size[a] < self.size[b]:
            a, b = b, a
        self.parent[b] = a
        self.size[a] += self.size[b]


def optimize_for_inference(
    model: torch.nn.Module,
    pass_config: Optional[dict[str, Any]] = None,
    tracer: type[fx.Tracer] = fx.Tracer,
) -> torch.nn.Module:
    """
    Performs a set of optimization passes to optimize a model for the
    purposes of inference. Specifically, the passes that are run are:
    1. Conv/BN fusion
    2. Dropout removal
    3. MKL layout optimizations

    The third optimization takes a function `use_mkl_heuristic` that's used
    to determine whether a subgraph should be explicitly run in MKL layout.

    Note: As FX does not currently handle aliasing, this pass currently
    assumes nothing aliases. If that isn't true, use at your own risk.
    """
    default_pass_config = {
        "conv_bn_fuse": True,
        "remove_dropout": True,
        "mkldnn_layout_optimize": {"heuristic": use_mkl_length},
    }
    if pass_config is None:
        pass_config = {}
    default_pass_config.update(pass_config)

    if default_pass_config["conv_bn_fuse"]:
        model = fuse(model)
    if default_pass_config["remove_dropout"]:
        model = remove_dropout(model)
    if default_pass_config["mkldnn_layout_optimize"] is False:
        return model
    if not isinstance(default_pass_config["mkldnn_layout_optimize"], dict):
        raise RuntimeError("mkldnn_layout_optimize config is not a dict")
    if "heuristic" not in default_pass_config["mkldnn_layout_optimize"]:
        raise RuntimeError("Heuristic not found in mkldnn_layout_optimize config")
    use_mkl_heuristic = default_pass_config["mkldnn_layout_optimize"]["heuristic"]

    cur_tracer = tracer()
    fx_graph = cur_tracer.trace(copy.deepcopy(model))
    fx.GraphModule(cur_tracer.root, fx_graph)
    modules: dict[str, nn.Module] = dict(model.named_modules())

    class MklSupport(Enum):
        NO = 1
        YES = 2
        UNKNOWN = 3

    # Inserts to_mkldnn and to_dense around every node we want to be a MKLDNN node.
    # If the op is in `mkldnn_supported` then we always treat it as a MKLDNN node.
    # However, if it's in `mkldnn_supported_unknown`, then we only treat it as
    # a MKLDNN node if its inputs are MKLDNN nodes.
    for node in list(fx_graph.nodes):
        supports_mkldnn = MklSupport.NO
        if node.op == "call_module":
            cur_module = modules[node.target]
            if type(cur_module) in mkldnn_supported:
                supports_mkldnn = MklSupport.YES
                sample_parameter = next(cur_module.parameters(), None)
                if sample_parameter is not None:
                    assert (
                        sample_parameter.dtype == torch.float
                    ), "this pass is only for torch.float modules"
                    assert sample_parameter.device == torch.device(
                        "cpu"
                    ), "this pass is only for CPU modules"
        elif node.op == "call_function":
            if node.target in mkldnn_supported:
                supports_mkldnn = MklSupport.YES
            elif node.target in mkldnn_supported_unknown:
                supports_mkldnn = MklSupport.UNKNOWN

        if supports_mkldnn != MklSupport.NO:
            if supports_mkldnn == MklSupport.UNKNOWN:
                if not any(arg.target == "to_dense" for arg in node.args):
                    continue
            with fx_graph.inserting_before(node):
                mkldnn_args = fx.map_arg(
                    node.args, lambda n: fx_graph.call_method("to_mkldnn", (n,))
                )

            node.args = cast(tuple[fx.node.Argument], mkldnn_args)

            with fx_graph.inserting_after(node):
                dense_x = fx_graph.create_node("call_method", "to_dense", (node,))
                node.replace_all_uses_with(dense_x)
                dense_x.args = (node,)

    # Does pre-conversion of all modules into MKLDNN (when possible)
    old_modules = modules_to_mkldnn(list(fx_graph.nodes), modules)
    fx_graph.old_modules = old_modules  # type: ignore[attr-defined]

    # optimizes all a -> to_dense -> to_mkldnn -> b patterns into a -> b
    for node in fx_graph.nodes:
        if node.op == "call_method" and node.target == "to_dense":
            prv_node = node.args[0]
            users = list(node.users)
            for user in users:
                if user.op == "call_method" and user.target == "to_mkldnn":
                    user.replace_all_uses_with(prv_node)
                    fx_graph.erase_node(user)
            if len(node.users) == 0:
                fx_graph.erase_node(node)

    num_nodes = len(fx_graph.nodes)
    uf = UnionFind(num_nodes)

    def get_color(n):
        if hasattr(n, "color"):  # Current node is part of a MKL subgraph
            return uf.find(n.color)
        if hasattr(n, "start_color"):  # Current node is input to MKL subgraph
            return uf.find(n.start_color)
        return None

    # This code is to find each MKLDNN subgraph. Each MKLDNN subgraph consists
    # of input nodes (which are only `to_mkldnn` calls), output nodes
    # (`to_dense` calls), and intermediate nodes, which are run entirely on
    # MKLDNN layout tensors.
    #
    # Specifically, this code does a flood fill on a directed acyclic graph
    # (DAG), starting from each possible "start node" (i.e: `to_mkldnn` nodes).
    # If every node only had one input, this would be sufficient. However, in
    # the case that a node has multiple inputs coming from different start
    # nodes (i.e. colors), we need to join these 2 colors into 1. That's done
    # using a Disjoint Set Union.
    for cur_idx, node in enumerate(fx_graph.nodes):
        if node.op == "call_method" and node.target == "to_mkldnn":
            node.start_color = cur_idx
            uf.make_set(cur_idx)
        elif node.op == "call_method" and node.target == "to_dense":
            assert get_color(node.args[0]) is not None
            node.end_color = get_color(node.args[0])
        else:
            cur_colors = [
                get_color(i)
                for i in node.all_input_nodes
                if isinstance(i, fx.Node)
                if get_color(i) is not None
            ]

            if len(cur_colors) == 0:
                continue
            assert not any(i is None for i in cur_colors)
            cur_colors = sorted(cur_colors)
            node.color = cur_colors[0]
            for other_color in cur_colors[1:]:
                uf.join(cur_colors[0], other_color)

    mkldnn_graphs: dict[int, MklSubgraph] = defaultdict(lambda: MklSubgraph(fx_graph))
    for node in fx_graph.nodes:
        if hasattr(node, "color"):
            mkldnn_graphs[uf.find(node.color)].nodes.append(node)
        if hasattr(node, "start_color"):
            mkldnn_graphs[uf.find(node.start_color)].start_nodes.append(node)
        if hasattr(node, "end_color"):
            mkldnn_graphs[uf.find(node.end_color)].end_nodes.append(node)

    # Now that we have all the subgraphs, we need to decide which MKLDNN
    # subgraphs we actually want to keep in MKLDNN.
    for graph in mkldnn_graphs.values():
        if not use_mkl_heuristic(graph):
            for node in graph.start_nodes + graph.end_nodes:
                prv = node.args[0]
                node.replace_all_uses_with(prv)
                fx_graph.erase_node(node)
            reset_modules(graph.nodes, modules, old_modules)

    mkldnn_conversions = 0
    for node in fx_graph.nodes:
        if node.target == "to_mkldnn" or node.target == "to_dense":
            mkldnn_conversions += 1

    logging.getLogger(__name__).info("mkldnn conversions: %s", mkldnn_conversions)
    fx_graph.lint()
    result = fx.GraphModule(model, fx_graph)
    return result