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# Copyright (c) Facebook, Inc. and its affiliates.
#
# This source code is licensed under the MIT license found in the
# LICENSE file in the root directory of this source tree.
from typing import Dict, Optional, Tuple
import torch
from fairseq import utils
from fairseq.modules.quant_noise import quant_noise
from torch import Tensor, nn
from torch.nn import Parameter
from fairseq.modules.multihead_attention import MultiheadAttention
from ..modules.multihead_functional import multi_head_attention_forward
class MultiheadAttentionSelection(MultiheadAttention):
def __init__(
self,
embed_dim,
total_num_heads,
num_heads,
kdim=None,
vdim=None,
dropout=0.0,
bias=True,
add_bias_kv=False,
add_zero_attn=False,
self_attention=False,
encoder_decoder_attention=False,
q_noise=0.0,
qn_block_size=8,
layer_idx=0,
attn_head_selector=None
):
super().__init__(
embed_dim,
num_heads,
kdim=kdim,
vdim=vdim,
dropout=dropout,
bias=bias,
add_bias_kv=add_bias_kv,
add_zero_attn=add_zero_attn,
self_attention=self_attention,
encoder_decoder_attention=encoder_decoder_attention,
q_noise=q_noise,
qn_block_size=qn_block_size,
)
self.layer_idx = layer_idx
self.attn_head_selector = attn_head_selector
self.total_num_heads = total_num_heads
self.total_embed_dim = self.head_dim * total_num_heads
self.k_proj = quant_noise(
nn.Linear(self.kdim, self.total_embed_dim, bias=bias), q_noise, qn_block_size
)
self.v_proj = quant_noise(
nn.Linear(self.vdim, self.total_embed_dim, bias=bias), q_noise, qn_block_size
)
self.q_proj = quant_noise(
nn.Linear(embed_dim, self.total_embed_dim, bias=bias), q_noise, qn_block_size
)
if add_bias_kv:
self.bias_k = Parameter(torch.Tensor(1, 1, self.total_embed_dim))
self.bias_v = Parameter(torch.Tensor(1, 1, self.total_embed_dim))
else:
self.bias_k = self.bias_v = None
self.reset_parameters()
def forward(
self,
query,
key: Optional[Tensor],
value: Optional[Tensor],
key_padding_mask: Optional[Tensor] = None,
incremental_state: Optional[Dict[str, Dict[str, Optional[Tensor]]]] = None,
need_weights: bool = True,
static_kv: bool = False,
attn_mask: Optional[Tensor] = None,
before_softmax: bool = False,
need_head_weights: bool = False,
# subset_heads: Optional[Tensor] = None,
# subset_weights: Optional[Tensor] = None
) -> Tuple[Tensor, Optional[Tensor]]:
if need_head_weights:
need_weights = True
is_tpu = query.device.type == "xla"
subset_heads, subset_weights = self.attn_head_selector(self.layer_idx)
tgt_len, bsz, embed_dim = query.size()
src_len = tgt_len
assert list(query.size()) == [tgt_len, bsz, self.embed_dim]
if key is not None:
src_len, key_bsz, _ = key.size()
if not torch.jit.is_scripting():
assert key_bsz == bsz
assert value is not None
assert src_len, bsz == value.shape[:2]
if (
not self.onnx_trace
and not is_tpu # don't use PyTorch version on TPUs
and incremental_state is None
and not static_kv
# A workaround for quantization to work. Otherwise JIT compilation
# treats bias in linear module as method.
and not torch.jit.is_scripting()
):
assert key is not None and value is not None
return multi_head_attention_forward(
query,
key,
value,
self.embed_dim,
self.total_num_heads,
self.num_heads,
torch.empty([0]),
torch.cat((self.q_proj.bias, self.k_proj.bias, self.v_proj.bias)),
self.bias_k,
self.bias_v,
self.add_zero_attn,
self.dropout_module.p,
self.out_proj.weight,
self.out_proj.bias,
self.training or self.dropout_module.apply_during_inference,
key_padding_mask,
need_weights,
attn_mask,
use_separate_proj_weight=True,
q_proj_weight=self.q_proj.weight,
k_proj_weight=self.k_proj.weight,
v_proj_weight=self.v_proj.weight,
subset_heads=subset_heads,
subset_weights=subset_weights
)
if incremental_state is not None:
saved_state = self._get_input_buffer(incremental_state)
if saved_state is not None and "prev_key" in saved_state:
# previous time steps are cached - no need to recompute
# key and value if they are static
if static_kv:
assert self.encoder_decoder_attention and not self.self_attention
key = value = None
else:
saved_state = None
if self.self_attention:
q = self.q_proj(query)
k = self.k_proj(query)
v = self.v_proj(query)
elif self.encoder_decoder_attention:
# encoder-decoder attention
q = self.q_proj(query)
if key is None:
assert value is None
k = v = None
else:
k = self.k_proj(key)
v = self.v_proj(key)
else:
assert key is not None and value is not None
q = self.q_proj(query)
k = self.k_proj(key)
v = self.v_proj(value)
q *= self.scaling
if self.bias_k is not None:
assert self.bias_v is not None
k = torch.cat([k, self.bias_k.repeat(1, bsz, 1)])
v = torch.cat([v, self.bias_v.repeat(1, bsz, 1)])
if attn_mask is not None:
attn_mask = torch.cat(
[attn_mask, attn_mask.new_zeros(attn_mask.size(0), 1)], dim=1
)
if key_padding_mask is not None:
key_padding_mask = torch.cat(
[
key_padding_mask,
key_padding_mask.new_zeros(key_padding_mask.size(0), 1),
],
dim=1,
)
q = (
q.contiguous()
.view(tgt_len, bsz * self.total_num_heads, self.head_dim)
.transpose(0, 1)
)
if k is not None:
k = (
k.contiguous()
.view(-1, bsz * self.total_num_heads, self.head_dim)
.transpose(0, 1)
)
if v is not None:
v = (
v.contiguous()
.view(-1, bsz * self.total_num_heads, self.head_dim)
.transpose(0, 1)
)
if saved_state is not None:
# saved states are stored with shape (bsz, num_heads, seq_len, head_dim)
if "prev_key" in saved_state:
_prev_key = saved_state["prev_key"]
assert _prev_key is not None
prev_key = _prev_key.view(bsz * self.total_num_heads, -1, self.head_dim)
if static_kv:
k = prev_key
else:
assert k is not None
k = torch.cat([prev_key, k], dim=1)
src_len = k.size(1)
if "prev_value" in saved_state:
_prev_value = saved_state["prev_value"]
assert _prev_value is not None
prev_value = _prev_value.view(bsz * self.total_num_heads, -1, self.head_dim)
if static_kv:
v = prev_value
else:
assert v is not None
v = torch.cat([prev_value, v], dim=1)
prev_key_padding_mask: Optional[Tensor] = None
if "prev_key_padding_mask" in saved_state:
prev_key_padding_mask = saved_state["prev_key_padding_mask"]
assert k is not None and v is not None
key_padding_mask = MultiheadAttention._append_prev_key_padding_mask(
key_padding_mask=key_padding_mask,
prev_key_padding_mask=prev_key_padding_mask,
batch_size=bsz,
src_len=k.size(1),
static_kv=static_kv,
)
saved_state["prev_key"] = k.view(bsz, self.total_num_heads, -1, self.head_dim)
saved_state["prev_value"] = v.view(bsz, self.total_num_heads, -1, self.head_dim)
saved_state["prev_key_padding_mask"] = key_padding_mask
# In this branch incremental_state is never None
assert incremental_state is not None
incremental_state = self._set_input_buffer(incremental_state, saved_state)
assert k is not None
assert k.size(1) == src_len
# This is part of a workaround to get around fork/join parallelism
# not supporting Optional types.
if key_padding_mask is not None and key_padding_mask.dim() == 0:
key_padding_mask = None
if key_padding_mask is not None:
assert key_padding_mask.size(0) == bsz
assert key_padding_mask.size(1) == src_len
if self.add_zero_attn:
assert v is not None
src_len += 1
k = torch.cat([k, k.new_zeros((k.size(0), 1) + k.size()[2:])], dim=1)
v = torch.cat([v, v.new_zeros((v.size(0), 1) + v.size()[2:])], dim=1)
if attn_mask is not None:
attn_mask = torch.cat(
[attn_mask, attn_mask.new_zeros(attn_mask.size(0), 1)], dim=1
)
if key_padding_mask is not None:
key_padding_mask = torch.cat(
[
key_padding_mask,
torch.zeros(key_padding_mask.size(0), 1).type_as(
key_padding_mask
),
],
dim=1,
)
attn_weights = torch.bmm(q, k.transpose(1, 2))
attn_weights = self.apply_sparse_mask(attn_weights, tgt_len, src_len, bsz)
assert list(attn_weights.size()) == [bsz * self.total_num_heads, tgt_len, src_len]
if attn_mask is not None:
attn_mask = attn_mask.unsqueeze(0)
if self.onnx_trace:
attn_mask = attn_mask.repeat(attn_weights.size(0), 1, 1)
attn_weights += attn_mask
if key_padding_mask is not None:
# don't attend to padding symbols
attn_weights = attn_weights.view(bsz, self.total_num_heads, tgt_len, src_len)
if not is_tpu:
attn_weights = attn_weights.masked_fill(
key_padding_mask.unsqueeze(1).unsqueeze(2).to(torch.bool),
float("-inf"),
)
else:
attn_weights = attn_weights.transpose(0, 2)
attn_weights = attn_weights.masked_fill(key_padding_mask, float("-inf"))
attn_weights = attn_weights.transpose(0, 2)
attn_weights = attn_weights.view(bsz * self.num_heads, tgt_len, src_len)
if before_softmax:
return attn_weights, v
attn_weights_float = utils.softmax(
attn_weights, dim=-1, onnx_trace=self.onnx_trace
)
attn_weights = attn_weights_float.type_as(attn_weights)
attn_probs = self.dropout_module(attn_weights)
assert v is not None
# evaluation
if subset_heads is not None and subset_heads.numel() == 1:
subset_heads = subset_heads.repeat(bsz)
subset_weights = subset_weights.repeat(bsz)
if subset_heads is None:
attn = torch.bmm(attn_probs, v)
else:
# training with head selection
mixed_attn = torch.bmm(attn_probs, v).contiguous().view(bsz, self.total_num_heads, tgt_len, self.head_dim)
attn = torch.stack(
[mixed_attn[torch.arange(bsz), subset_heads[:, col], :, :] for col in range(subset_heads.size(1))], dim=1
)
attn = attn * subset_weights.unsqueeze(2).unsqueeze(3)
attn = attn.contiguous().view(bsz * self.num_heads, tgt_len, self.head_dim)
assert list(attn.size()) == [bsz * self.num_heads, tgt_len, self.head_dim]
if self.onnx_trace and attn.size(1) == 1:
# when ONNX tracing a single decoder step (sequence length == 1)
# the transpose is a no-op copy before view, thus unnecessary
attn = attn.contiguous().view(tgt_len, bsz, embed_dim)
else:
attn = attn.transpose(0, 1).contiguous().view(tgt_len, bsz, embed_dim)
attn = self.out_proj(attn)
attn_weights: Optional[Tensor] = None
if need_weights:
if subset_heads is None:
attn_weights = attn_weights_float.view(
bsz, self.num_heads, tgt_len, src_len
).transpose(1, 0)
else:
mixed_attn_weights = attn_weights_float.view(
bsz, self.total_num_heads, tgt_len, src_len
)
attn_weights = torch.stack(
[mixed_attn_weights[torch.arange(bsz), subset_heads[:, col], :, :] for col in range(subset_heads.size(1))], dim=1
).transpose(1, 0)
if not need_head_weights:
# average attention weights over heads
attn_weights = attn_weights.mean(dim=0)
return attn, attn_weights
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