src/efficientvit/models/nn/ops.py

# EfficientViT: Multi-Scale Linear Attention for High-Resolution Dense Prediction
# Han Cai, Junyan Li, Muyan Hu, Chuang Gan, Song Han
# International Conference on Computer Vision (ICCV), 2023

import torch
import torch.nn as nn
import torch.nn.functional as F
from torch.cuda.amp import autocast

from src.efficientvit.models.nn.act import build_act
from src.efficientvit.models.nn.norm import build_norm
from src.efficientvit.models.utils import (get_same_padding, list_sum, resize,
                                       val2list, val2tuple)

__all__ = [
    "ConvLayer",
    "UpSampleLayer",
    "LinearLayer",
    "IdentityLayer",
    "DSConv",
    "MBConv",
    "FusedMBConv",
    "ResBlock",
    "LiteMLA",
    "EfficientViTBlock",
    "ResidualBlock",
    "DAGBlock",
    "OpSequential",
]


#################################################################################
#                             Basic Layers                                      #
#################################################################################


class ConvLayer(nn.Module):
    def __init__(
        self,
        in_channels: int,
        out_channels: int,
        kernel_size=3,
        stride=1,
        dilation=1,
        groups=1,
        use_bias=False,
        dropout=0,
        norm="bn2d",
        act_func="relu",
    ):
        super(ConvLayer, self).__init__()

        padding = get_same_padding(kernel_size)
        padding *= dilation

        self.dropout = nn.Dropout2d(dropout, inplace=False) if dropout > 0 else None
        self.conv = nn.Conv2d(
            in_channels,
            out_channels,
            kernel_size=(kernel_size, kernel_size),
            stride=(stride, stride),
            padding=padding,
            dilation=(dilation, dilation),
            groups=groups,
            bias=use_bias,
        )
        self.norm = build_norm(norm, num_features=out_channels)
        self.act = build_act(act_func)

    def forward(self, x: torch.Tensor) -> torch.Tensor:
        if self.dropout is not None:
            x = self.dropout(x)
        x = self.conv(x)
        if self.norm:
            x = self.norm(x)
        if self.act:
            x = self.act(x)
        return x


class UpSampleLayer(nn.Module):
    def __init__(
        self,
        mode="bicubic",
        size: int or tuple[int, int] or list[int] or None = None,
        factor=2,
        align_corners=False,
    ):
        super(UpSampleLayer, self).__init__()
        self.mode = mode
        self.size = val2list(size, 2) if size is not None else None
        self.factor = None if self.size is not None else factor
        self.align_corners = align_corners

    def forward(self, x: torch.Tensor) -> torch.Tensor:
        if (
            self.size is not None and tuple(x.shape[-2:]) == self.size
        ) or self.factor == 1:
            return x
        return resize(x, self.size, self.factor, self.mode, self.align_corners)


class LinearLayer(nn.Module):
    def __init__(
        self,
        in_features: int,
        out_features: int,
        use_bias=True,
        dropout=0,
        norm=None,
        act_func=None,
    ):
        super(LinearLayer, self).__init__()

        self.dropout = nn.Dropout(dropout, inplace=False) if dropout > 0 else None
        self.linear = nn.Linear(in_features, out_features, use_bias)
        self.norm = build_norm(norm, num_features=out_features)
        self.act = build_act(act_func)

    def _try_squeeze(self, x: torch.Tensor) -> torch.Tensor:
        if x.dim() > 2:
            x = torch.flatten(x, start_dim=1)
        return x

    def forward(self, x: torch.Tensor) -> torch.Tensor:
        x = self._try_squeeze(x)
        if self.dropout:
            x = self.dropout(x)
        x = self.linear(x)
        if self.norm:
            x = self.norm(x)
        if self.act:
            x = self.act(x)
        return x


class IdentityLayer(nn.Module):
    def forward(self, x: torch.Tensor) -> torch.Tensor:
        return x


#################################################################################
#                             Basic Blocks                                      #
#################################################################################


class DSConv(nn.Module):
    def __init__(
        self,
        in_channels: int,
        out_channels: int,
        kernel_size=3,
        stride=1,
        use_bias=False,
        norm=("bn2d", "bn2d"),
        act_func=("relu6", None),
    ):
        super(DSConv, self).__init__()

        use_bias = val2tuple(use_bias, 2)
        norm = val2tuple(norm, 2)
        act_func = val2tuple(act_func, 2)

        self.depth_conv = ConvLayer(
            in_channels,
            in_channels,
            kernel_size,
            stride,
            groups=in_channels,
            norm=norm[0],
            act_func=act_func[0],
            use_bias=use_bias[0],
        )
        self.point_conv = ConvLayer(
            in_channels,
            out_channels,
            1,
            norm=norm[1],
            act_func=act_func[1],
            use_bias=use_bias[1],
        )

    def forward(self, x: torch.Tensor) -> torch.Tensor:
        x = self.depth_conv(x)
        x = self.point_conv(x)
        return x


class MBConv(nn.Module):
    def __init__(
        self,
        in_channels: int,
        out_channels: int,
        kernel_size=3,
        stride=1,
        mid_channels=None,
        expand_ratio=6,
        use_bias=False,
        norm=("bn2d", "bn2d", "bn2d"),
        act_func=("relu6", "relu6", None),
    ):
        super(MBConv, self).__init__()

        use_bias = val2tuple(use_bias, 3)
        norm = val2tuple(norm, 3)
        act_func = val2tuple(act_func, 3)
        mid_channels = mid_channels or round(in_channels * expand_ratio)

        self.inverted_conv = ConvLayer(
            in_channels,
            mid_channels,
            1,
            stride=1,
            norm=norm[0],
            act_func=act_func[0],
            use_bias=use_bias[0],
        )
        self.depth_conv = ConvLayer(
            mid_channels,
            mid_channels,
            kernel_size,
            stride=stride,
            groups=mid_channels,
            norm=norm[1],
            act_func=act_func[1],
            use_bias=use_bias[1],
        )
        self.point_conv = ConvLayer(
            mid_channels,
            out_channels,
            1,
            norm=norm[2],
            act_func=act_func[2],
            use_bias=use_bias[2],
        )

    def forward(self, x: torch.Tensor) -> torch.Tensor:
        x = self.inverted_conv(x)
        x = self.depth_conv(x)
        x = self.point_conv(x)
        return x


class FusedMBConv(nn.Module):
    def __init__(
        self,
        in_channels: int,
        out_channels: int,
        kernel_size=3,
        stride=1,
        mid_channels=None,
        expand_ratio=6,
        groups=1,
        use_bias=False,
        norm=("bn2d", "bn2d"),
        act_func=("relu6", None),
    ):
        super().__init__()
        use_bias = val2tuple(use_bias, 2)
        norm = val2tuple(norm, 2)
        act_func = val2tuple(act_func, 2)

        mid_channels = mid_channels or round(in_channels * expand_ratio)

        self.spatial_conv = ConvLayer(
            in_channels,
            mid_channels,
            kernel_size,
            stride,
            groups=groups,
            use_bias=use_bias[0],
            norm=norm[0],
            act_func=act_func[0],
        )
        self.point_conv = ConvLayer(
            mid_channels,
            out_channels,
            1,
            use_bias=use_bias[1],
            norm=norm[1],
            act_func=act_func[1],
        )

    def forward(self, x: torch.Tensor) -> torch.Tensor:
        x = self.spatial_conv(x)
        x = self.point_conv(x)
        return x


class ResBlock(nn.Module):
    def __init__(
        self,
        in_channels: int,
        out_channels: int,
        kernel_size=3,
        stride=1,
        mid_channels=None,
        expand_ratio=1,
        use_bias=False,
        norm=("bn2d", "bn2d"),
        act_func=("relu6", None),
    ):
        super().__init__()
        use_bias = val2tuple(use_bias, 2)
        norm = val2tuple(norm, 2)
        act_func = val2tuple(act_func, 2)

        mid_channels = mid_channels or round(in_channels * expand_ratio)

        self.conv1 = ConvLayer(
            in_channels,
            mid_channels,
            kernel_size,
            stride,
            use_bias=use_bias[0],
            norm=norm[0],
            act_func=act_func[0],
        )
        self.conv2 = ConvLayer(
            mid_channels,
            out_channels,
            kernel_size,
            1,
            use_bias=use_bias[1],
            norm=norm[1],
            act_func=act_func[1],
        )

    def forward(self, x: torch.Tensor) -> torch.Tensor:
        x = self.conv1(x)
        x = self.conv2(x)
        return x


class LiteMLA(nn.Module):
    r"""Lightweight multi-scale linear attention"""

    def __init__(
        self,
        in_channels: int,
        out_channels: int,
        heads: int or None = None,
        heads_ratio: float = 1.0,
        dim=8,
        use_bias=False,
        norm=(None, "bn2d"),
        act_func=(None, None),
        kernel_func="relu",
        scales: tuple[int, ...] = (5,),
        eps=1.0e-15,
    ):
        super(LiteMLA, self).__init__()
        self.eps = eps
        heads = heads or int(in_channels // dim * heads_ratio)

        total_dim = heads * dim

        use_bias = val2tuple(use_bias, 2)
        norm = val2tuple(norm, 2)
        act_func = val2tuple(act_func, 2)

        self.dim = dim
        self.qkv = ConvLayer(
            in_channels,
            3 * total_dim,
            1,
            use_bias=use_bias[0],
            norm=norm[0],
            act_func=act_func[0],
        )
        self.aggreg = nn.ModuleList(
            [
                nn.Sequential(
                    nn.Conv2d(
                        3 * total_dim,
                        3 * total_dim,
                        scale,
                        padding=get_same_padding(scale),
                        groups=3 * total_dim,
                        bias=use_bias[0],
                    ),
                    nn.Conv2d(
                        3 * total_dim,
                        3 * total_dim,
                        1,
                        groups=3 * heads,
                        bias=use_bias[0],
                    ),
                )
                for scale in scales
            ]
        )
        self.kernel_func = build_act(kernel_func, inplace=False)

        self.proj = ConvLayer(
            total_dim * (1 + len(scales)),
            out_channels,
            1,
            use_bias=use_bias[1],
            norm=norm[1],
            act_func=act_func[1],
        )

    @autocast(enabled=False)
    def relu_linear_att(self, qkv: torch.Tensor) -> torch.Tensor:
        B, _, H, W = list(qkv.size())

        if qkv.dtype == torch.float16:
            qkv = qkv.float()

        qkv = torch.reshape(
            qkv,
            (
                B,
                -1,
                3 * self.dim,
                H * W,
            ),
        )
        qkv = torch.transpose(qkv, -1, -2)
        q, k, v = (
            qkv[..., 0 : self.dim],
            qkv[..., self.dim : 2 * self.dim],
            qkv[..., 2 * self.dim :],
        )

        # lightweight linear attention
        q = self.kernel_func(q)
        k = self.kernel_func(k)

        # linear matmul
        trans_k = k.transpose(-1, -2)

        v = F.pad(v, (0, 1), mode="constant", value=1)
        kv = torch.matmul(trans_k, v)
        out = torch.matmul(q, kv)
        out = out[..., :-1] / (out[..., -1:] + self.eps)

        out = torch.transpose(out, -1, -2)
        out = torch.reshape(out, (B, -1, H, W))
        return out

    def forward(self, x: torch.Tensor) -> torch.Tensor:
        # generate multi-scale q, k, v
        qkv = self.qkv(x)
        multi_scale_qkv = [qkv]
        for op in self.aggreg:
            multi_scale_qkv.append(op(qkv))
        multi_scale_qkv = torch.cat(multi_scale_qkv, dim=1)

        out = self.relu_linear_att(multi_scale_qkv)
        out = self.proj(out)

        return out


class EfficientViTBlock(nn.Module):
    def __init__(
        self,
        in_channels: int,
        heads_ratio: float = 1.0,
        dim=32,
        expand_ratio: float = 4,
        scales=(5,),
        norm="bn2d",
        act_func="hswish",
    ):
        super(EfficientViTBlock, self).__init__()
        self.context_module = ResidualBlock(
            LiteMLA(
                in_channels=in_channels,
                out_channels=in_channels,
                heads_ratio=heads_ratio,
                dim=dim,
                norm=(None, norm),
                scales=scales,
            ),
            IdentityLayer(),
        )
        local_module = MBConv(
            in_channels=in_channels,
            out_channels=in_channels,
            expand_ratio=expand_ratio,
            use_bias=(True, True, False),
            norm=(None, None, norm),
            act_func=(act_func, act_func, None),
        )
        self.local_module = ResidualBlock(local_module, IdentityLayer())

    def forward(self, x: torch.Tensor) -> torch.Tensor:
        x = self.context_module(x)
        x = self.local_module(x)
        return x


#################################################################################
#                             Functional Blocks                                 #
#################################################################################


class ResidualBlock(nn.Module):
    def __init__(
        self,
        main: nn.Module or None,
        shortcut: nn.Module or None,
        post_act=None,
        pre_norm: nn.Module or None = None,
    ):
        super(ResidualBlock, self).__init__()

        self.pre_norm = pre_norm
        self.main = main
        self.shortcut = shortcut
        self.post_act = build_act(post_act)

    def forward_main(self, x: torch.Tensor) -> torch.Tensor:
        if self.pre_norm is None:
            return self.main(x)
        else:
            return self.main(self.pre_norm(x))

    def forward(self, x: torch.Tensor) -> torch.Tensor:
        if self.main is None:
            res = x
        elif self.shortcut is None:
            res = self.forward_main(x)
        else:
            res = self.forward_main(x) + self.shortcut(x)
            if self.post_act:
                res = self.post_act(res)
        return res


class DAGBlock(nn.Module):
    def __init__(
        self,
        inputs: dict[str, nn.Module],
        merge: str,
        post_input: nn.Module or None,
        middle: nn.Module,
        outputs: dict[str, nn.Module],
    ):
        super(DAGBlock, self).__init__()

        self.input_keys = list(inputs.keys())
        self.input_ops = nn.ModuleList(list(inputs.values()))
        self.merge = merge
        self.post_input = post_input

        self.middle = middle

        self.output_keys = list(outputs.keys())
        self.output_ops = nn.ModuleList(list(outputs.values()))

    def forward(self, feature_dict: dict[str, torch.Tensor]) -> dict[str, torch.Tensor]:
        feat = [
            op(feature_dict[key]) for key, op in zip(self.input_keys, self.input_ops)
        ]
        if self.merge == "add":
            feat = list_sum(feat)
        elif self.merge == "cat":
            feat = torch.concat(feat, dim=1)
        else:
            raise NotImplementedError
        if self.post_input is not None:
            feat = self.post_input(feat)
        feat = self.middle(feat)
        for key, op in zip(self.output_keys, self.output_ops):
            feature_dict[key] = op(feat)
        return feature_dict


class OpSequential(nn.Module):
    def __init__(self, op_list: list[nn.Module or None]):
        super(OpSequential, self).__init__()
        valid_op_list = []
        for op in op_list:
            if op is not None:
                valid_op_list.append(op)
        self.op_list = nn.ModuleList(valid_op_list)

    def forward(self, x: torch.Tensor) -> torch.Tensor:
        for op in self.op_list:
            x = op(x)
        return x