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# Copyright 2022 The HuggingFace Team. All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import flax.linen as nn
import jax.numpy as jnp
class FlaxAttentionBlock(nn.Module):
r"""
A Flax multi-head attention module as described in: https://arxiv.org/abs/1706.03762
Parameters:
query_dim (:obj:`int`):
Input hidden states dimension
heads (:obj:`int`, *optional*, defaults to 8):
Number of heads
dim_head (:obj:`int`, *optional*, defaults to 64):
Hidden states dimension inside each head
dropout (:obj:`float`, *optional*, defaults to 0.0):
Dropout rate
dtype (:obj:`jnp.dtype`, *optional*, defaults to jnp.float32):
Parameters `dtype`
"""
query_dim: int
heads: int = 8
dim_head: int = 64
dropout: float = 0.0
dtype: jnp.dtype = jnp.float32
def setup(self):
inner_dim = self.dim_head * self.heads
self.scale = self.dim_head**-0.5
# Weights were exported with old names {to_q, to_k, to_v, to_out}
self.query = nn.Dense(inner_dim, use_bias=False, dtype=self.dtype, name="to_q")
self.key = nn.Dense(inner_dim, use_bias=False, dtype=self.dtype, name="to_k")
self.value = nn.Dense(inner_dim, use_bias=False, dtype=self.dtype, name="to_v")
self.proj_attn = nn.Dense(self.query_dim, dtype=self.dtype, name="to_out_0")
def reshape_heads_to_batch_dim(self, tensor):
batch_size, seq_len, dim = tensor.shape
head_size = self.heads
tensor = tensor.reshape(batch_size, seq_len, head_size, dim // head_size)
tensor = jnp.transpose(tensor, (0, 2, 1, 3))
tensor = tensor.reshape(batch_size * head_size, seq_len, dim // head_size)
return tensor
def reshape_batch_dim_to_heads(self, tensor):
batch_size, seq_len, dim = tensor.shape
head_size = self.heads
tensor = tensor.reshape(batch_size // head_size, head_size, seq_len, dim)
tensor = jnp.transpose(tensor, (0, 2, 1, 3))
tensor = tensor.reshape(batch_size // head_size, seq_len, dim * head_size)
return tensor
def __call__(self, hidden_states, context=None, deterministic=True):
context = hidden_states if context is None else context
query_proj = self.query(hidden_states)
key_proj = self.key(context)
value_proj = self.value(context)
query_states = self.reshape_heads_to_batch_dim(query_proj)
key_states = self.reshape_heads_to_batch_dim(key_proj)
value_states = self.reshape_heads_to_batch_dim(value_proj)
# compute attentions
attention_scores = jnp.einsum("b i d, b j d->b i j", query_states, key_states)
attention_scores = attention_scores * self.scale
attention_probs = nn.softmax(attention_scores, axis=2)
# attend to values
hidden_states = jnp.einsum("b i j, b j d -> b i d", attention_probs, value_states)
hidden_states = self.reshape_batch_dim_to_heads(hidden_states)
hidden_states = self.proj_attn(hidden_states)
return hidden_states
class FlaxBasicTransformerBlock(nn.Module):
r"""
A Flax transformer block layer with `GLU` (Gated Linear Unit) activation function as described in:
https://arxiv.org/abs/1706.03762
Parameters:
dim (:obj:`int`):
Inner hidden states dimension
n_heads (:obj:`int`):
Number of heads
d_head (:obj:`int`):
Hidden states dimension inside each head
dropout (:obj:`float`, *optional*, defaults to 0.0):
Dropout rate
only_cross_attention (`bool`, defaults to `False`):
Whether to only apply cross attention.
dtype (:obj:`jnp.dtype`, *optional*, defaults to jnp.float32):
Parameters `dtype`
"""
dim: int
n_heads: int
d_head: int
dropout: float = 0.0
only_cross_attention: bool = False
dtype: jnp.dtype = jnp.float32
def setup(self):
# self attention (or cross_attention if only_cross_attention is True)
self.attn1 = FlaxAttentionBlock(self.dim, self.n_heads, self.d_head, self.dropout, dtype=self.dtype)
# cross attention
self.attn2 = FlaxAttentionBlock(self.dim, self.n_heads, self.d_head, self.dropout, dtype=self.dtype)
self.ff = FlaxGluFeedForward(dim=self.dim, dropout=self.dropout, dtype=self.dtype)
self.norm1 = nn.LayerNorm(epsilon=1e-5, dtype=self.dtype)
self.norm2 = nn.LayerNorm(epsilon=1e-5, dtype=self.dtype)
self.norm3 = nn.LayerNorm(epsilon=1e-5, dtype=self.dtype)
def __call__(self, hidden_states, context, deterministic=True):
# self attention
residual = hidden_states
if self.only_cross_attention:
hidden_states = self.attn1(self.norm1(hidden_states), context, deterministic=deterministic)
else:
hidden_states = self.attn1(self.norm1(hidden_states), deterministic=deterministic)
hidden_states = hidden_states + residual
# cross attention
residual = hidden_states
hidden_states = self.attn2(self.norm2(hidden_states), context, deterministic=deterministic)
hidden_states = hidden_states + residual
# feed forward
residual = hidden_states
hidden_states = self.ff(self.norm3(hidden_states), deterministic=deterministic)
hidden_states = hidden_states + residual
return hidden_states
class FlaxTransformer2DModel(nn.Module):
r"""
A Spatial Transformer layer with Gated Linear Unit (GLU) activation function as described in:
https://arxiv.org/pdf/1506.02025.pdf
Parameters:
in_channels (:obj:`int`):
Input number of channels
n_heads (:obj:`int`):
Number of heads
d_head (:obj:`int`):
Hidden states dimension inside each head
depth (:obj:`int`, *optional*, defaults to 1):
Number of transformers block
dropout (:obj:`float`, *optional*, defaults to 0.0):
Dropout rate
use_linear_projection (`bool`, defaults to `False`): tbd
only_cross_attention (`bool`, defaults to `False`): tbd
dtype (:obj:`jnp.dtype`, *optional*, defaults to jnp.float32):
Parameters `dtype`
"""
in_channels: int
n_heads: int
d_head: int
depth: int = 1
dropout: float = 0.0
use_linear_projection: bool = False
only_cross_attention: bool = False
dtype: jnp.dtype = jnp.float32
def setup(self):
self.norm = nn.GroupNorm(num_groups=32, epsilon=1e-5)
inner_dim = self.n_heads * self.d_head
if self.use_linear_projection:
self.proj_in = nn.Dense(inner_dim, dtype=self.dtype)
else:
self.proj_in = nn.Conv(
inner_dim,
kernel_size=(1, 1),
strides=(1, 1),
padding="VALID",
dtype=self.dtype,
)
self.transformer_blocks = [
FlaxBasicTransformerBlock(
inner_dim,
self.n_heads,
self.d_head,
dropout=self.dropout,
only_cross_attention=self.only_cross_attention,
dtype=self.dtype,
)
for _ in range(self.depth)
]
if self.use_linear_projection:
self.proj_out = nn.Dense(inner_dim, dtype=self.dtype)
else:
self.proj_out = nn.Conv(
inner_dim,
kernel_size=(1, 1),
strides=(1, 1),
padding="VALID",
dtype=self.dtype,
)
def __call__(self, hidden_states, context, deterministic=True):
batch, height, width, channels = hidden_states.shape
residual = hidden_states
hidden_states = self.norm(hidden_states)
if self.use_linear_projection:
hidden_states = hidden_states.reshape(batch, height * width, channels)
hidden_states = self.proj_in(hidden_states)
else:
hidden_states = self.proj_in(hidden_states)
hidden_states = hidden_states.reshape(batch, height * width, channels)
for transformer_block in self.transformer_blocks:
hidden_states = transformer_block(hidden_states, context, deterministic=deterministic)
if self.use_linear_projection:
hidden_states = self.proj_out(hidden_states)
hidden_states = hidden_states.reshape(batch, height, width, channels)
else:
hidden_states = hidden_states.reshape(batch, height, width, channels)
hidden_states = self.proj_out(hidden_states)
hidden_states = hidden_states + residual
return hidden_states
class FlaxGluFeedForward(nn.Module):
r"""
Flax module that encapsulates two Linear layers separated by a gated linear unit activation from:
https://arxiv.org/abs/2002.05202
Parameters:
dim (:obj:`int`):
Inner hidden states dimension
dropout (:obj:`float`, *optional*, defaults to 0.0):
Dropout rate
dtype (:obj:`jnp.dtype`, *optional*, defaults to jnp.float32):
Parameters `dtype`
"""
dim: int
dropout: float = 0.0
dtype: jnp.dtype = jnp.float32
def setup(self):
# The second linear layer needs to be called
# net_2 for now to match the index of the Sequential layer
self.net_0 = FlaxGEGLU(self.dim, self.dropout, self.dtype)
self.net_2 = nn.Dense(self.dim, dtype=self.dtype)
def __call__(self, hidden_states, deterministic=True):
hidden_states = self.net_0(hidden_states)
hidden_states = self.net_2(hidden_states)
return hidden_states
class FlaxGEGLU(nn.Module):
r"""
Flax implementation of a Linear layer followed by the variant of the gated linear unit activation function from
https://arxiv.org/abs/2002.05202.
Parameters:
dim (:obj:`int`):
Input hidden states dimension
dropout (:obj:`float`, *optional*, defaults to 0.0):
Dropout rate
dtype (:obj:`jnp.dtype`, *optional*, defaults to jnp.float32):
Parameters `dtype`
"""
dim: int
dropout: float = 0.0
dtype: jnp.dtype = jnp.float32
def setup(self):
inner_dim = self.dim * 4
self.proj = nn.Dense(inner_dim * 2, dtype=self.dtype)
def __call__(self, hidden_states, deterministic=True):
hidden_states = self.proj(hidden_states)
hidden_linear, hidden_gelu = jnp.split(hidden_states, 2, axis=2)
return hidden_linear * nn.gelu(hidden_gelu)
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