torch-mlir/python/torch_mlir/dynamo.py

# Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
# See https://llvm.org/LICENSE.txt for license information.
# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
# Also available under a BSD-style license. See LICENSE.

from typing import List

import torch
from torch.fx.experimental.proxy_tensor import make_fx
from torch._functorch.compile_utils import strip_overloads
from torch._decomp import get_decompositions

import warnings
# https://github.com/pytorch/pytorch/issues/89064
warnings.filterwarnings("ignore", module="torch.jit._check")


def _get_decomposition_table():
    """Get a decomposition table suitable for Torch-MLIR.
    
    Sometimes TorchDynamo traces slightly different ops than what TorchScript
    captures. Historically we have been driven by the ops captured by
    TorchScript, so we try to decompose the ops captured by TorchDynamo into
    other ops that we already support.
    
    There isn't a highly principled solution here. Torch-MLIR currently supports
    a somewhat random set of ops, added in a demand-driven way over time,
    including direct backend support and decompositions internal to Torch-MLIR.
    As described in the
    [long-term roadmap](https://github.com/llvm/torch-mlir/blob/main/docs/long_term_roadmap.md),
    eventually this situation is expected to be made a lot more principled
    by aligning more with how Torch-MLIR would have looked if some of the new
    upstream PyTorch infra had been available at the beginning -- in particular
    the new decomposition infra and PrimTorch.
    """
    aten = torch.ops.aten
    return get_decompositions([
        aten._adaptive_avg_pool2d,
        aten.std.correction,
        aten.dot,
    ])


def _unwrap_single_tuple_return(fx_g: torch.fx.GraphModule) -> bool:
    """Canonicalize single-element tuple returns to just the element.

    Returns:
        True if unwrapping took place, and false otherwise.
    """
    did_unwrap = False
    for node in fx_g.graph.nodes:
        if node.op == "output":
            assert len(
                node.args) == 1, "Output node must have a single argument"
            node_arg = node.args[0]
            if isinstance(node_arg, tuple):
                if len(node_arg) == 1:
                    node.args = (node_arg[0],)
                    did_unwrap = True
                    break

    if did_unwrap:
        fx_g.graph.lint()
        fx_g.recompile()
    return did_unwrap


def make_simple_dynamo_backend(user_backend):
    """Wrapper for functions intended to be used as TorchDynamo backends.

    This function simplifies a few of the steps that are required to make
    TorchDynamo work with Torch-MLIR.

    Args:
        user_backend: A function with the signature used by ordinary
            TorchDynamo backends. But the torch.fx.GraphModule passed to it
            will be normalized for consumption by `torch_mlir.compile`.
    Returns:
        A function with the signature used by TorchDynamo backends.
    """
    def wrapper_backend(fx_graph: torch.fx.GraphModule,
                        example_inputs: List[torch.Tensor]):
        did_unwrap = _unwrap_single_tuple_return(fx_graph)
        dispatcher_ops = make_fx(
            fx_graph, decomposition_table=_get_decomposition_table())(*example_inputs)
        strip_overloads(dispatcher_ops)
        user_callable = user_backend(dispatcher_ops, example_inputs)

        def dynamo_callable(*inputs):
            result = user_callable(*inputs)
            return (result,) if did_unwrap else result
        return dynamo_callable
    return wrapper_backend