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238 lines
9.2 KiB
238 lines
9.2 KiB
5 months ago
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import functools
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import warnings
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from typing import Any, Callable, List, Optional, Tuple, Union
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import torch
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from torch import Tensor
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from torch.utils._pytree import _broadcast_to_and_flatten, tree_flatten, tree_unflatten
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in_dims_t = Union[int, Tuple]
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out_dims_t = Union[int, Tuple[int, ...]]
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# Checks that all args-to-be-batched have the same batch dim size
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def _validate_and_get_batch_size(
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flat_in_dims: List[Optional[int]], flat_args: List
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) -> int:
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batch_sizes = [
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arg.size(in_dim)
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for in_dim, arg in zip(flat_in_dims, flat_args)
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if in_dim is not None
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]
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if batch_sizes and any(size != batch_sizes[0] for size in batch_sizes):
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raise ValueError(
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f"vmap: Expected all tensors to have the same size in the mapped "
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f"dimension, got sizes {batch_sizes} for the mapped dimension"
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)
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return batch_sizes[0]
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def _num_outputs(batched_outputs: Union[Tensor, Tuple[Tensor, ...]]) -> int:
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if isinstance(batched_outputs, tuple):
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return len(batched_outputs)
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return 1
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# If value is a tuple, check it has length `num_elements`.
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# If value is not a tuple, make a tuple with `value` repeated `num_elements` times
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def _as_tuple(
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value: Any, num_elements: int, error_message_lambda: Callable[[], str]
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) -> Tuple:
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if not isinstance(value, tuple):
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return (value,) * num_elements
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if len(value) != num_elements:
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raise ValueError(error_message_lambda())
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return value
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# Creates BatchedTensors for every Tensor in arg that should be batched.
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# Returns the (potentially) batched arguments and the batch_size.
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def _create_batched_inputs(
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in_dims: in_dims_t, args: Tuple, vmap_level: int, func: Callable
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) -> Tuple[Tuple, int]:
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if not isinstance(in_dims, int) and not isinstance(in_dims, tuple):
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raise ValueError(
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f"vmap({_get_name(func)}, in_dims={in_dims}, ...)(<inputs>): "
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f"expected `in_dims` to be int or a (potentially nested) tuple "
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f"matching the structure of inputs, got: {type(in_dims)}."
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)
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if len(args) == 0:
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raise ValueError(
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f"vmap({_get_name(func)})(<inputs>): got no inputs. Maybe you forgot to add "
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f"inputs, or you are trying to vmap over a function with no inputs. "
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f"The latter is unsupported."
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)
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flat_args, args_spec = tree_flatten(args)
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flat_in_dims = _broadcast_to_and_flatten(in_dims, args_spec)
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if flat_in_dims is None:
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raise ValueError(
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f"vmap({_get_name(func)}, in_dims={in_dims}, ...)(<inputs>): "
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f"in_dims is not compatible with the structure of `inputs`. "
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f"in_dims has structure {tree_flatten(in_dims)[1]} but inputs "
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f"has structure {args_spec}."
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)
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for arg, in_dim in zip(flat_args, flat_in_dims):
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if not isinstance(in_dim, int) and in_dim is not None:
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raise ValueError(
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f"vmap({_get_name(func)}, in_dims={in_dims}, ...)(<inputs>): "
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f"Got in_dim={in_dim} for an input but in_dim must be either "
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f"an integer dimension or None."
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)
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if isinstance(in_dim, int) and not isinstance(arg, Tensor):
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raise ValueError(
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f"vmap({_get_name(func)}, in_dims={in_dims}, ...)(<inputs>): "
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f"Got in_dim={in_dim} for an input but the input is of type "
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f"{type(arg)}. We cannot vmap over non-Tensor arguments, "
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f"please use None as the respective in_dim"
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)
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if in_dim is not None and (in_dim < 0 or in_dim >= arg.dim()):
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raise ValueError(
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f"vmap({_get_name(func)}, in_dims={in_dims}, ...)(<inputs>): "
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f"Got in_dim={in_dim} for some input, but that input is a Tensor "
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f"of dimensionality {arg.dim()} so expected in_dim to satisfy "
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f"0 <= in_dim < {arg.dim()}."
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)
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batch_size = _validate_and_get_batch_size(flat_in_dims, flat_args)
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# See NOTE [Ignored _remove_batch_dim, _add_batch_dim]
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batched_inputs = [
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arg if in_dim is None else torch._add_batch_dim(arg, in_dim, vmap_level)
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for in_dim, arg in zip(flat_in_dims, flat_args)
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]
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return tree_unflatten(batched_inputs, args_spec), batch_size
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# Undos the batching (and any batch dimensions) associated with the `vmap_level`.
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def _unwrap_batched(
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batched_outputs: Union[Tensor, Tuple[Tensor, ...]],
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out_dims: out_dims_t,
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vmap_level: int,
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batch_size: int,
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func: Callable,
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allow_none_pass_through: bool = False,
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) -> Tuple:
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num_outputs = _num_outputs(batched_outputs)
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out_dims_as_tuple = _as_tuple(
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out_dims,
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num_outputs,
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lambda: f"vmap({_get_name(func)}, ..., out_dims={out_dims}): `out_dims` must "
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f"have one dim per output (got {num_outputs} outputs) of {_get_name(func)}.",
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)
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# NOTE [Ignored _remove_batch_dim, _add_batch_dim]
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# There is something wrong with our type bindings for functions that begin
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# with '_', see #40397.
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if isinstance(batched_outputs, Tensor):
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out_dim = out_dims_as_tuple[0]
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return torch._remove_batch_dim(batched_outputs, vmap_level, batch_size, out_dim) # type: ignore[return-value]
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if allow_none_pass_through:
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return tuple(
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(
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torch._remove_batch_dim(out, vmap_level, batch_size, out_dim)
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if out is not None
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else None
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)
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for out, out_dim in zip(batched_outputs, out_dims_as_tuple)
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)
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else:
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return tuple(
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torch._remove_batch_dim(out, vmap_level, batch_size, out_dim)
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for out, out_dim in zip(batched_outputs, out_dims_as_tuple)
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)
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# Checks that `fn` returned one or more Tensors and nothing else.
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# NB: A python function that return multiple arguments returns a single tuple,
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# so we are effectively checking that `outputs` is a single Tensor or a tuple of
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# Tensors.
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def _validate_outputs(outputs: Any, func: Callable) -> None:
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if isinstance(outputs, Tensor):
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return
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if not isinstance(outputs, tuple):
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raise ValueError(
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f"vmap({_get_name(func)}, ...): `{_get_name(func)}` must only return "
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f"Tensors, got type {type(outputs)} as the return."
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)
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for idx, output in enumerate(outputs):
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if isinstance(output, Tensor):
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continue
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raise ValueError(
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f"vmap({_get_name(func)}, ...): `{_get_name(func)}` must only return "
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f"Tensors, got type {type(output)} for return {idx}."
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)
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def _check_out_dims_is_int_or_int_tuple(out_dims: out_dims_t, func: Callable) -> None:
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if isinstance(out_dims, int):
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return
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if not isinstance(out_dims, tuple) or not all(
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isinstance(out_dim, int) for out_dim in out_dims
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):
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raise ValueError(
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f"vmap({_get_name(func)}, ..., out_dims={out_dims}): `out_dims` must be "
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f"an int or a tuple of int representing where in the outputs the "
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f"vmapped dimension should appear."
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)
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def _get_name(func: Callable):
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if hasattr(func, "__name__"):
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return func.__name__
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# Not all callables have __name__, in fact, only static functions/methods do.
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# A callable created via functools.partial or an nn.Module, to name some
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# examples, don't have a __name__.
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return repr(func)
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# vmap(func)(inputs) wraps all Tensor inputs to be batched in BatchedTensors,
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# sends those into func, and then unwraps the output BatchedTensors. Operations
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# on BatchedTensors perform the batched operations that the user is asking for.
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def vmap(func: Callable, in_dims: in_dims_t = 0, out_dims: out_dims_t = 0) -> Callable:
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"""
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Please use torch.vmap instead of this API.
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"""
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warnings.warn(
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"Please use torch.vmap instead of torch._vmap_internals.vmap. ",
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stacklevel=2,
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)
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return _vmap(func, in_dims, out_dims)
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# A version of vmap but without the initial "experimental prototype" warning
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def _vmap(
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func: Callable,
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in_dims: in_dims_t = 0,
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out_dims: out_dims_t = 0,
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allow_none_pass_through: bool = False,
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) -> Callable:
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# The `allow_none_pass_through` argument is a temporary workaround may be removed.
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# Currently it enables us to wrap the call in `autograd.grad` to the autograd engine,
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# which may return None if any of the inputs are unused. See the issue discussing this:
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# https://github.com/facebookresearch/functorch/issues/159.
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@functools.wraps(func)
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def wrapped(*args):
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_check_out_dims_is_int_or_int_tuple(out_dims, func)
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vmap_level = torch._C._vmapmode_increment_nesting()
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try:
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batched_inputs, batch_size = _create_batched_inputs(
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in_dims, args, vmap_level, func
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)
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batched_outputs = func(*batched_inputs)
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if not allow_none_pass_through:
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_validate_outputs(batched_outputs, func)
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return _unwrap_batched(
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batched_outputs,
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out_dims,
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vmap_level,
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batch_size,
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func,
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allow_none_pass_through=allow_none_pass_through,
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)
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finally:
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torch._C._vmapmode_decrement_nesting()
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return wrapped
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