pytorch/torch/_dynamo/backends/common.py

# mypy: ignore-errors

"""
This module provides common utilities and base classes for TorchDynamo backends.

Key components:
- AotAutograd: Base class for implementing AOT (Ahead-of-Time) autograd backends
- Backend utilities for handling:
  - Fake tensor conversion
  - Device/dtype detection from inputs
  - Memory efficient fusion
  - Graph flattening
  - Common compiler configurations

The utilities here are used by various backend implementations to handle
common operations and provide consistent behavior across different backends.
AOT autograd functionality is particularly important as it enables ahead-of-time
optimization of both forward and backward passes.
"""

import contextlib
import functools
import logging
from unittest.mock import patch

import torch
from torch._dynamo import disable
from torch._dynamo.exc import TensorifyScalarRestartAnalysis
from torch._dynamo.utils import counters, defake, flatten_graph_inputs
from torch._functorch.aot_autograd import (
    aot_module_simplified,
    SerializableAOTDispatchCompiler,
)
from torch.utils._python_dispatch import _disable_current_modes


log = logging.getLogger(__name__)


class AotAutograd:
    def __init__(self, **kwargs) -> None:
        self.__name__ = "compiler_fn"
        self.kwargs = kwargs

    def __call__(self, gm: torch.fx.GraphModule, example_inputs, **kwargs):
        if kwargs:
            log.warning("aot_autograd-based backend ignoring extra kwargs %s", kwargs)

        if any(isinstance(x, (list, tuple, dict)) for x in example_inputs):
            return flatten_graph_inputs(
                gm,
                example_inputs,
                self,
            )

        # Hack to get around circular import problems with aot_eager_decomp_partition
        if callable(self.kwargs.get("decompositions")):
            self.kwargs["decompositions"] = self.kwargs["decompositions"]()

        # NB: dont delete counter increment
        counters["aot_autograd"]["total"] += 1
        use_fallback = False

        if use_fallback:
            log.debug("Unable to use AOT Autograd because graph has mutation")
            counters["aot_autograd"]["not_ok"] += 1
            return gm

        def wrap_bw_compiler(bw_compiler_fn):
            def _wrapped_bw_compiler(*args, **kwargs):
                # Note [Wrapping bw_compiler in disable]
                # The two disables here:
                # - stop TorchDynamo from trying to compile the bw_compiler function itself
                # - stop TorchDynamo from trying to compile our the generated backwards pass bw_compiler produces
                return disable(
                    disable(
                        bw_compiler_fn, reason="do not trace backward compiler function"
                    )(*args, **kwargs),
                    reason="do not trace generated backwards pass",
                )

            return _wrapped_bw_compiler

        bw_compiler = self.kwargs.get("bw_compiler") or self.kwargs["fw_compiler"]

        if isinstance(bw_compiler, SerializableAOTDispatchCompiler):
            bw_compiler.compiler_fn = wrap_bw_compiler(bw_compiler.compiler_fn)
        else:
            bw_compiler = wrap_bw_compiler(bw_compiler)

        self.kwargs["bw_compiler"] = bw_compiler
        self.kwargs["inference_compiler"] = (
            self.kwargs.get("inference_compiler") or self.kwargs["fw_compiler"]
        )

        from functorch.compile import nop
        from torch._inductor.debug import enable_aot_logging

        # debug asserts slow down compile time noticeably,
        # So only default them on when the aot_eager backend is used.
        if self.kwargs.get("fw_compiler", None) == nop:
            patch_config = patch("functorch.compile.config.debug_assert", True)
        else:
            patch_config = contextlib.nullcontext()

        try:
            # NB: NOT cloned!
            with enable_aot_logging(), patch_config:
                cg = aot_module_simplified(gm, example_inputs, **self.kwargs)
                counters["aot_autograd"]["ok"] += 1
                return disable(cg, reason="do not trace AOT-compiled graph")
        except TensorifyScalarRestartAnalysis:
            raise
        except Exception:
            counters["aot_autograd"]["not_ok"] += 1
            raise


def aot_autograd(**kwargs) -> AotAutograd:
    return AotAutograd(**kwargs)


def mem_efficient_fusion_kwargs(use_decomps):
    from functorch.compile import (
        default_decompositions,
        min_cut_rematerialization_partition,
        ts_compile,
    )

    kwargs = {
        # these are taken from memory_efficient_fusion()
        "fw_compiler": ts_compile,
        "bw_compiler": ts_compile,
        "partition_fn": min_cut_rematerialization_partition,
    }

    if use_decomps:
        kwargs["decompositions"] = default_decompositions

    return kwargs


def fake_tensor_unsupported(fn):
    """
    Decorator for backends that need real inputs.  We swap out fake
    tensors for zero tensors.
    """

    @functools.wraps(fn)
    def wrapper(model, inputs, **kwargs):
        with _disable_current_modes():
            inputs = list(map(defake, inputs))
            return fn(model, inputs, **kwargs)

    return wrapper


def device_from_inputs(example_inputs) -> torch.device:
    for x in example_inputs:
        if hasattr(x, "device"):
            return x.device


def dtype_from_inputs(example_inputs) -> torch.dtype:
    for x in example_inputs:
        if hasattr(x, "dtype"):
            return x.dtype