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| # Copyright (c) Facebook, Inc. and its affiliates. | |
| """ | |
| Wrappers around on some nn functions, mainly to support empty tensors. | |
| Ideally, add support directly in PyTorch to empty tensors in those functions. | |
| These can be removed once https://github.com/pytorch/pytorch/issues/12013 | |
| is implemented | |
| """ | |
| from typing import List | |
| import torch | |
| from torch.nn import functional as F | |
| from detectron2.utils.env import TORCH_VERSION | |
| def cat(tensors: List[torch.Tensor], dim: int = 0): | |
| """ | |
| Efficient version of torch.cat that avoids a copy if there is only a single element in a list | |
| """ | |
| assert isinstance(tensors, (list, tuple)) | |
| if len(tensors) == 1: | |
| return tensors[0] | |
| return torch.cat(tensors, dim) | |
| class _NewEmptyTensorOp(torch.autograd.Function): | |
| def forward(ctx, x, new_shape): | |
| ctx.shape = x.shape | |
| return x.new_empty(new_shape) | |
| def backward(ctx, grad): | |
| shape = ctx.shape | |
| return _NewEmptyTensorOp.apply(grad, shape), None | |
| class Conv2d(torch.nn.Conv2d): | |
| """ | |
| A wrapper around :class:`torch.nn.Conv2d` to support empty inputs and more features. | |
| """ | |
| def __init__(self, *args, **kwargs): | |
| """ | |
| Extra keyword arguments supported in addition to those in `torch.nn.Conv2d`: | |
| Args: | |
| norm (nn.Module, optional): a normalization layer | |
| activation (callable(Tensor) -> Tensor): a callable activation function | |
| It assumes that norm layer is used before activation. | |
| """ | |
| norm = kwargs.pop("norm", None) | |
| activation = kwargs.pop("activation", None) | |
| super().__init__(*args, **kwargs) | |
| self.norm = norm | |
| self.activation = activation | |
| def forward(self, x): | |
| # torchscript does not support SyncBatchNorm yet | |
| # https://github.com/pytorch/pytorch/issues/40507 | |
| # and we skip these codes in torchscript since: | |
| # 1. currently we only support torchscript in evaluation mode | |
| # 2. features needed by exporting module to torchscript are added in PyTorch 1.6 or | |
| # later version, `Conv2d` in these PyTorch versions has already supported empty inputs. | |
| if not torch.jit.is_scripting(): | |
| if x.numel() == 0 and self.training: | |
| # https://github.com/pytorch/pytorch/issues/12013 | |
| assert not isinstance( | |
| self.norm, torch.nn.SyncBatchNorm | |
| ), "SyncBatchNorm does not support empty inputs!" | |
| x = F.conv2d( | |
| x, self.weight, self.bias, self.stride, self.padding, self.dilation, self.groups | |
| ) | |
| if self.norm is not None: | |
| x = self.norm(x) | |
| if self.activation is not None: | |
| x = self.activation(x) | |
| return x | |
| ConvTranspose2d = torch.nn.ConvTranspose2d | |
| BatchNorm2d = torch.nn.BatchNorm2d | |
| interpolate = F.interpolate | |
| if TORCH_VERSION > (1, 5): | |
| Linear = torch.nn.Linear | |
| else: | |
| class Linear(torch.nn.Linear): | |
| """ | |
| A wrapper around :class:`torch.nn.Linear` to support empty inputs and more features. | |
| Because of https://github.com/pytorch/pytorch/issues/34202 | |
| """ | |
| def forward(self, x): | |
| if x.numel() == 0: | |
| output_shape = [x.shape[0], self.weight.shape[0]] | |
| empty = _NewEmptyTensorOp.apply(x, output_shape) | |
| if self.training: | |
| # This is to make DDP happy. | |
| # DDP expects all workers to have gradient w.r.t the same set of parameters. | |
| _dummy = sum(x.view(-1)[0] for x in self.parameters()) * 0.0 | |
| return empty + _dummy | |
| else: | |
| return empty | |
| x = super().forward(x) | |
| return x | |
| def nonzero_tuple(x): | |
| """ | |
| A 'as_tuple=True' version of torch.nonzero to support torchscript. | |
| because of https://github.com/pytorch/pytorch/issues/38718 | |
| """ | |
| if torch.jit.is_scripting(): | |
| if x.dim() == 0: | |
| return x.unsqueeze(0).nonzero().unbind(1) | |
| return x.nonzero().unbind(1) | |
| else: | |
| return x.nonzero(as_tuple=True) | |