def generate(self,
models,
sample,
prefix_tokens=None,
bos_token=None,
**kwargs):
"""Generate a batch of translations.
Args:
models (List[~fairseq.models.FairseqModel]): ensemble of models
sample (dict): batch
prefix_tokens (torch.LongTensor, optional): force decoder to begin
with these tokens
"""
model = EnsembleModel(models)
if not self.retain_dropout:
model.eval()
# model.forward normally channels prev_output_tokens into the decoder
# separately, but SequenceGenerator directly calls model.encoder
encoder_input = {
k: v
for k, v in sample['net_input'].items()
if k != 'prev_output_tokens'
}
src_tokens = encoder_input['src_tokens']
src_lengths = (src_tokens.ne(self.eos)
& src_tokens.ne(self.pad)).long().sum(dim=1)
input_size = src_tokens.size()
# batch dimension goes first followed by source lengths
bsz = input_size[0]
src_len = input_size[1]
beam_size = self.beam_size
if self.match_source_len:
max_len = src_lengths.max().item()
else:
max_len = min(
int(self.max_len_a * src_len + self.max_len_b),
# exclude the EOS marker
model.max_decoder_positions() - 1,
)
# compute the encoder output for each beam
encoder_outs = model.forward_encoder(encoder_input)
new_order = torch.arange(bsz).view(-1, 1).repeat(1, beam_size).view(-1)
new_order = new_order.to(src_tokens.device).long()
encoder_outs = model.reorder_encoder_out(encoder_outs, new_order)
# initialize buffers
scores = src_tokens.new(bsz * beam_size, max_len + 1).float().fill_(0)
scores_buf = scores.clone()
tokens = src_tokens.data.new(bsz * beam_size,
max_len + 2).long().fill_(self.pad)
tokens_buf = tokens.clone()
tokens[:, 0] = bos_token or self.eos
attn, attn_buf = None, None
nonpad_idxs = None
# list of completed sentences
finalized = [[] for i in range(bsz)]
finished = [False for i in range(bsz)]
worst_finalized = [{
'idx': None,
'score': -math.inf
} for i in range(bsz)]
num_remaining_sent = bsz
# number of candidate hypos per step
cand_size = 2 * beam_size # 2 x beam size in case half are EOS
# offset arrays for converting between different indexing schemes
bbsz_offsets = (torch.arange(0, bsz) *
beam_size).unsqueeze(1).type_as(tokens)
cand_offsets = torch.arange(0, cand_size).type_as(tokens)
# helper function for allocating buffers on the fly
buffers = {}
def buffer(name, type_of=tokens): # noqa
if name not in buffers:
buffers[name] = type_of.new()
return buffers[name]
def is_finished(sent, step, unfinalized_scores=None):
"""
Check whether we've finished generation for a given sentence, by
comparing the worst score among finalized hypotheses to the best
possible score among unfinalized hypotheses.
"""
assert len(finalized[sent]) <= beam_size
if len(finalized[sent]) == beam_size:
if self.stop_early or step == max_len or unfinalized_scores is None:
return True
# stop if the best unfinalized score is worse than the worst
# finalized one
best_unfinalized_score = unfinalized_scores[sent].max()
if self.normalize_scores:
best_unfinalized_score /= max_len**self.len_penalty
if worst_finalized[sent]['score'] >= best_unfinalized_score:
return True
return False
def finalize_hypos(step,
bbsz_idx,
eos_scores,
unfinalized_scores=None):
"""
Finalize the given hypotheses at this step, while keeping the total
number of finalized hypotheses per sentence <= beam_size.
Note: the input must be in the desired finalization order, so that
hypotheses that appear earlier in the input are preferred to those
that appear later.
Args:
step: current time step
bbsz_idx: A vector of indices in the range [0, bsz*beam_size),
indicating which hypotheses to finalize
eos_scores: A vector of the same size as bbsz_idx containing
scores for each hypothesis
unfinalized_scores: A vector containing scores for all
unfinalized hypotheses
"""
assert bbsz_idx.numel() == eos_scores.numel()
# clone relevant token and attention tensors
tokens_clone = tokens.index_select(0, bbsz_idx)
tokens_clone = tokens_clone[:, 1:step +
2] # skip the first index, which is EOS
tokens_clone[:, step] = self.eos
attn_clone = attn.index_select(
0, bbsz_idx)[:, :, 1:step + 2] if attn is not None else None
# compute scores per token position
pos_scores = scores.index_select(0, bbsz_idx)[:, :step + 1]
pos_scores[:, step] = eos_scores
# convert from cumulative to per-position scores
pos_scores[:, 1:] = pos_scores[:, 1:] - pos_scores[:, :-1]
# normalize sentence-level scores
if self.normalize_scores:
eos_scores /= (step + 1)**self.len_penalty
cum_unfin = []
prev = 0
for f in finished:
if f:
prev += 1
else:
cum_unfin.append(prev)
sents_seen = set()
for i, (idx, score) in enumerate(
zip(bbsz_idx.tolist(), eos_scores.tolist())):
unfin_idx = idx // beam_size
sent = unfin_idx + cum_unfin[unfin_idx]
sents_seen.add((sent, unfin_idx))
if self.match_source_len and step > src_lengths[unfin_idx]:
score = -math.inf
def get_hypo():
if attn_clone is not None:
# remove padding tokens from attn scores
hypo_attn = attn_clone[i][nonpad_idxs[sent]]
_, alignment = hypo_attn.max(dim=0)
else:
hypo_attn = None
alignment = None
return {
'tokens': tokens_clone[i],
'score': score,
'attention': hypo_attn, # src_len x tgt_len
'alignment': alignment,
'positional_scores': pos_scores[i],
}
if len(finalized[sent]) < beam_size:
finalized[sent].append(get_hypo())
elif not self.stop_early and score > worst_finalized[sent][
'score']:
# replace worst hypo for this sentence with new/better one
worst_idx = worst_finalized[sent]['idx']
if worst_idx is not None:
finalized[sent][worst_idx] = get_hypo()
# find new worst finalized hypo for this sentence
idx, s = min(enumerate(finalized[sent]),
key=lambda r: r[1]['score'])
worst_finalized[sent] = {
'score': s['score'],
'idx': idx,
}
newly_finished = []
for sent, unfin_idx in sents_seen:
# check termination conditions for this sentence
if not finished[sent] and is_finished(sent, step,
unfinalized_scores):
finished[sent] = True
newly_finished.append(unfin_idx)
return newly_finished
reorder_state = None
batch_idxs = None
for step in range(max_len + 1): # one extra step for EOS marker
# reorder decoder internal states based on the prev choice of beams
if reorder_state is not None:
if batch_idxs is not None:
# update beam indices to take into account removed sentences
corr = batch_idxs - torch.arange(
batch_idxs.numel()).type_as(batch_idxs)
reorder_state.view(-1, beam_size).add_(
corr.unsqueeze(-1) * beam_size)
model.reorder_incremental_state(reorder_state)
model.reorder_encoder_out(encoder_outs, reorder_state)
lprobs, avg_attn_scores = model.forward_decoder(
tokens[:, :step + 1], encoder_outs)
lprobs[:, self.pad] = -math.inf # never select pad
lprobs[:, self.unk] -= self.unk_penalty # apply unk penalty
if self.no_repeat_ngram_size > 0:
# for each beam and batch sentence, generate a list of previous ngrams
gen_ngrams = [{} for bbsz_idx in range(bsz * beam_size)]
for bbsz_idx in range(bsz * beam_size):
gen_tokens = tokens[bbsz_idx].tolist()
for ngram in zip(*[
gen_tokens[i:]
for i in range(self.no_repeat_ngram_size)
]):
gen_ngrams[bbsz_idx][tuple(ngram[:-1])] = \
gen_ngrams[bbsz_idx].get(tuple(ngram[:-1]), []) + [ngram[-1]]
# Record attention scores
if avg_attn_scores is not None:
if attn is None:
attn = scores.new(bsz * beam_size, src_tokens.size(1),
max_len + 2)
attn_buf = attn.clone()
nonpad_idxs = src_tokens.ne(self.pad)
attn[:, :, step + 1].copy_(avg_attn_scores)
scores = scores.type_as(lprobs)
scores_buf = scores_buf.type_as(lprobs)
eos_bbsz_idx = buffer('eos_bbsz_idx')
eos_scores = buffer('eos_scores', type_of=scores)
if step < max_len:
self.search.set_src_lengths(src_lengths)
if self.no_repeat_ngram_size > 0:
def calculate_banned_tokens(bbsz_idx):
# before decoding the next token, prevent decoding of ngrams that have already appeared
ngram_index = tuple(
tokens[bbsz_idx,
step + 2 - self.no_repeat_ngram_size:step +
1].tolist())
return gen_ngrams[bbsz_idx].get(ngram_index, [])
if step + 2 - self.no_repeat_ngram_size >= 0:
# no banned tokens if we haven't generated no_repeat_ngram_size tokens yet
banned_tokens = [
calculate_banned_tokens(bbsz_idx)
for bbsz_idx in range(bsz * beam_size)
]
else:
banned_tokens = [[]
for bbsz_idx in range(bsz * beam_size)
]
for bbsz_idx in range(bsz * beam_size):
lprobs[bbsz_idx, banned_tokens[bbsz_idx]] = -math.inf
if prefix_tokens is not None and step < prefix_tokens.size(1):
probs_slice = lprobs.view(bsz, -1, lprobs.size(-1))[:,
0, :]
cand_scores = torch.gather(
probs_slice,
dim=1,
index=prefix_tokens[:, step].view(-1, 1)).view(
-1, 1).repeat(1, cand_size)
if step > 0:
# save cumulative scores for each hypothesis
cand_scores.add_(scores[:, step - 1].view(
bsz, beam_size).repeat(1, 2))
cand_indices = prefix_tokens[:, step].view(-1, 1).repeat(
1, cand_size)
cand_beams = torch.zeros_like(cand_indices)
# handle prefixes of different lengths
partial_prefix_mask = prefix_tokens[:, step].eq(self.pad)
if partial_prefix_mask.any():
partial_scores, partial_indices, partial_beams = self.search.step(
step,
lprobs.view(bsz, -1, self.vocab_size),
scores.view(bsz, beam_size, -1)[:, :, :step],
)
cand_scores[partial_prefix_mask] = partial_scores[
partial_prefix_mask]
cand_indices[partial_prefix_mask] = partial_indices[
partial_prefix_mask]
cand_beams[partial_prefix_mask] = partial_beams[
partial_prefix_mask]
else:
cand_scores, cand_indices, cand_beams = self.search.step(
step,
lprobs.view(bsz, -1, self.vocab_size),
scores.view(bsz, beam_size, -1)[:, :, :step],
)
else:
# make probs contain cumulative scores for each hypothesis
lprobs.add_(scores[:, step - 1].unsqueeze(-1))
# finalize all active hypotheses once we hit max_len
# pick the hypothesis with the highest prob of EOS right now
torch.sort(
lprobs[:, self.eos],
descending=True,
out=(eos_scores, eos_bbsz_idx),
)
num_remaining_sent -= len(
finalize_hypos(step, eos_bbsz_idx, eos_scores))
assert num_remaining_sent == 0
break
# cand_bbsz_idx contains beam indices for the top candidate
# hypotheses, with a range of values: [0, bsz*beam_size),
# and dimensions: [bsz, cand_size]
cand_bbsz_idx = cand_beams.add(bbsz_offsets)
# finalize hypotheses that end in eos
eos_mask = cand_indices.eq(self.eos)
finalized_sents = set()
if step >= self.min_len:
# only consider eos when it's among the top beam_size indices
torch.masked_select(
cand_bbsz_idx[:, :beam_size],
mask=eos_mask[:, :beam_size],
out=eos_bbsz_idx,
)
if eos_bbsz_idx.numel() > 0:
torch.masked_select(
cand_scores[:, :beam_size],
mask=eos_mask[:, :beam_size],
out=eos_scores,
)
finalized_sents = finalize_hypos(step, eos_bbsz_idx,
eos_scores, cand_scores)
num_remaining_sent -= len(finalized_sents)
assert num_remaining_sent >= 0
if num_remaining_sent == 0:
break
assert step < max_len
if len(finalized_sents) > 0:
new_bsz = bsz - len(finalized_sents)
# construct batch_idxs which holds indices of batches to keep for the next pass
batch_mask = cand_indices.new_ones(bsz)
batch_mask[cand_indices.new(finalized_sents)] = 0
batch_idxs = batch_mask.nonzero().squeeze(-1)
eos_mask = eos_mask[batch_idxs]
cand_beams = cand_beams[batch_idxs]
bbsz_offsets.resize_(new_bsz, 1)
cand_bbsz_idx = cand_beams.add(bbsz_offsets)
cand_scores = cand_scores[batch_idxs]
cand_indices = cand_indices[batch_idxs]
if prefix_tokens is not None:
prefix_tokens = prefix_tokens[batch_idxs]
src_lengths = src_lengths[batch_idxs]
scores = scores.view(bsz, -1)[batch_idxs].view(
new_bsz * beam_size, -1)
scores_buf.resize_as_(scores)
tokens = tokens.view(bsz, -1)[batch_idxs].view(
new_bsz * beam_size, -1)
tokens_buf.resize_as_(tokens)
if attn is not None:
attn = attn.view(bsz, -1)[batch_idxs].view(
new_bsz * beam_size, attn.size(1), -1)
attn_buf.resize_as_(attn)
bsz = new_bsz
else:
batch_idxs = None
# set active_mask so that values > cand_size indicate eos hypos
# and values < cand_size indicate candidate active hypos.
# After, the min values per row are the top candidate active hypos
active_mask = buffer('active_mask')
torch.add(
eos_mask.type_as(cand_offsets) * cand_size,
cand_offsets[:eos_mask.size(1)],
out=active_mask,
)
# get the top beam_size active hypotheses, which are just the hypos
# with the smallest values in active_mask
active_hypos, _ignore = buffer('active_hypos'), buffer('_ignore')
torch.topk(active_mask,
k=beam_size,
dim=1,
largest=False,
out=(_ignore, active_hypos))
active_bbsz_idx = buffer('active_bbsz_idx')
torch.gather(
cand_bbsz_idx,
dim=1,
index=active_hypos,
out=active_bbsz_idx,
)
active_scores = torch.gather(
cand_scores,
dim=1,
index=active_hypos,
out=scores[:, step].view(bsz, beam_size),
)
active_bbsz_idx = active_bbsz_idx.view(-1)
active_scores = active_scores.view(-1)
# copy tokens and scores for active hypotheses
torch.index_select(
tokens[:, :step + 1],
dim=0,
index=active_bbsz_idx,
out=tokens_buf[:, :step + 1],
)
torch.gather(
cand_indices,
dim=1,
index=active_hypos,
out=tokens_buf.view(bsz, beam_size, -1)[:, :, step + 1],
)
if step > 0:
torch.index_select(
scores[:, :step],
dim=0,
index=active_bbsz_idx,
out=scores_buf[:, :step],
)
torch.gather(
cand_scores,
dim=1,
index=active_hypos,
out=scores_buf.view(bsz, beam_size, -1)[:, :, step],
)
# copy attention for active hypotheses
if attn is not None:
torch.index_select(
attn[:, :, :step + 2],
dim=0,
index=active_bbsz_idx,
out=attn_buf[:, :, :step + 2],
)
# swap buffers
tokens, tokens_buf = tokens_buf, tokens
scores, scores_buf = scores_buf, scores
if attn is not None:
attn, attn_buf = attn_buf, attn
# reorder incremental state in decoder
reorder_state = active_bbsz_idx
# sort by score descending
for sent in range(len(finalized)):
finalized[sent] = sorted(finalized[sent],
key=lambda r: r['score'],
reverse=True)
return finalized
def generate(self,
models,
sample,
prefix_tokens=None,
bos_token=None,
**kwargs):
"""Generate a batch of translations.
Args:
models (List[~fairseq.models.FairseqModel]): ensemble of models
sample (dict): batch
prefix_tokens (torch.LongTensor, optional): force decoder to begin
with these tokens
"""
model = EnsembleModel(models)
incremental_states = torch.jit.annotate(
List[Dict[str, Dict[str, Optional[Tensor]]]],
[
torch.jit.annotate(Dict[str, Dict[str, Optional[Tensor]]], {})
for i in range(model.models_size)
],
)
if not self.retain_dropout:
model.eval()
# model.forward normally channels prev_output_tokens into the decoder
# separately, but SequenceGenerator directly calls model.encoder
encoder_input = {
k: v
for k, v in sample['net_input'].items()
if k != 'prev_output_tokens'
}
src_tokens = encoder_input['src_tokens']
src_lengths_no_eos = (src_tokens.ne(self.eos)
& src_tokens.ne(self.pad)).long().sum(dim=1)
input_size = src_tokens.size()
# batch dimension goes first followed by source lengths
bsz = input_size[0]
src_len = input_size[1]
beam_size = self.beam_size
if self.match_source_len:
max_len = src_lengths_no_eos.max().item()
else:
max_len = min(
int(self.max_len_a * src_len + self.max_len_b),
# exclude the EOS marker
model.max_decoder_positions() - 1,
)
# compute the encoder output for each beam
encoder_outs = model.forward_encoder(encoder_input)
new_order = torch.arange(bsz).view(-1, 1).repeat(1, beam_size).view(-1)
new_order = new_order.to(src_tokens.device).long()
encoder_outs = model.reorder_encoder_out(encoder_outs, new_order)
src_lengths = encoder_input['src_lengths']
# initialize buffers
scores = src_tokens.new(bsz * beam_size, max_len + 1).float().fill_(0)
lm_prefix_scores = src_tokens.new(bsz * beam_size).float().fill_(0)
scores_buf = scores.clone()
tokens = src_tokens.new(bsz * beam_size,
max_len + 2).long().fill_(self.pad)
tokens_buf = tokens.clone()
tokens[:, 0] = self.eos if bos_token is None else bos_token
# reorder source tokens so they may be used as a reference in generating P(S|T)
src_tokens = reorder_all_tokens(src_tokens, src_lengths,
self.src_dict.eos_index)
src_tokens = src_tokens.repeat(1, beam_size).view(-1, src_len)
src_lengths = src_lengths.view(bsz, -1).repeat(1, beam_size).view(
bsz * beam_size, -1)
attn, attn_buf = None, None
nonpad_idxs = None
# The cands_to_ignore indicates candidates that should be ignored.
# For example, suppose we're sampling and have already finalized 2/5
# samples. Then the cands_to_ignore would mark 2 positions as being ignored,
# so that we only finalize the remaining 3 samples.
cands_to_ignore = src_tokens.new_zeros(bsz, beam_size).eq(
-1) # forward and backward-compatible False mask
# list of completed sentences
finalized = [[] for i in range(bsz)]
finished = [False for i in range(bsz)]
num_remaining_sent = bsz
# number of candidate hypos per step
cand_size = 2 * beam_size # 2 x beam size in case half are EOS
# offset arrays for converting between different indexing schemes
bbsz_offsets = (torch.arange(0, bsz) *
beam_size).unsqueeze(1).type_as(tokens)
cand_offsets = torch.arange(0, cand_size).type_as(tokens)
# helper function for allocating buffers on the fly
buffers = {}
def buffer(name, type_of=tokens): # noqa
if name not in buffers:
buffers[name] = type_of.new()
return buffers[name]
def is_finished(sent, step, unfin_idx):
"""
Check whether we've finished generation for a given sentence, by
comparing the worst score among finalized hypotheses to the best
possible score among unfinalized hypotheses.
"""
assert len(finalized[sent]) <= beam_size
if len(finalized[sent]) == beam_size:
return True
return False
def finalize_hypos(step, bbsz_idx, eos_scores,
combined_noisy_channel_eos_scores):
"""
Finalize the given hypotheses at this step, while keeping the total
number of finalized hypotheses per sentence <= beam_size.
Note: the input must be in the desired finalization order, so that
hypotheses that appear earlier in the input are preferred to those
that appear later.
Args:
step: current time step
bbsz_idx: A vector of indices in the range [0, bsz*beam_size),
indicating which hypotheses to finalize
eos_scores: A vector of the same size as bbsz_idx containing
fw scores for each hypothesis
combined_noisy_channel_eos_scores: A vector of the same size as bbsz_idx containing
combined noisy channel scores for each hypothesis
"""
assert bbsz_idx.numel() == eos_scores.numel()
# clone relevant token and attention tensors
tokens_clone = tokens.index_select(0, bbsz_idx)
tokens_clone = tokens_clone[:, 1:step +
2] # skip the first index, which is EOS
assert not tokens_clone.eq(self.eos).any()
tokens_clone[:, step] = self.eos
attn_clone = attn.index_select(
0, bbsz_idx)[:, :, 1:step + 2] if attn is not None else None
# compute scores per token position
pos_scores = scores.index_select(0, bbsz_idx)[:, :step + 1]
pos_scores[:, step] = eos_scores
# convert from cumulative to per-position scores
pos_scores[:, 1:] = pos_scores[:, 1:] - pos_scores[:, :-1]
# normalize sentence-level scores
if self.normalize_scores:
combined_noisy_channel_eos_scores /= (step +
1)**self.len_penalty
cum_unfin = []
prev = 0
for f in finished:
if f:
prev += 1
else:
cum_unfin.append(prev)
sents_seen = set()
for i, (idx, score) in enumerate(
zip(bbsz_idx.tolist(),
combined_noisy_channel_eos_scores.tolist())):
unfin_idx = idx // beam_size
sent = unfin_idx + cum_unfin[unfin_idx]
sents_seen.add((sent, unfin_idx))
if self.match_source_len and step > src_lengths_no_eos[
unfin_idx]:
score = -math.inf
def get_hypo():
if attn_clone is not None:
# remove padding tokens from attn scores
hypo_attn = attn_clone[i][nonpad_idxs[sent]]
_, alignment = hypo_attn.max(dim=0)
else:
hypo_attn = None
alignment = None
return {
'tokens': tokens_clone[i],
'score': score,
'attention': hypo_attn, # src_len x tgt_len
'alignment': alignment,
'positional_scores': pos_scores[i],
}
if len(finalized[sent]) < beam_size:
finalized[sent].append(get_hypo())
newly_finished = []
for sent, unfin_idx in sents_seen:
# check termination conditions for this sentence
if not finished[sent] and is_finished(sent, step, unfin_idx):
finished[sent] = True
newly_finished.append(unfin_idx)
return newly_finished
def noisy_channel_rescoring(lprobs, beam_size, bsz, src_tokens, tokens,
k):
"""Rescore the top k hypothesis from each beam using noisy channel modeling
Returns:
new_fw_lprobs: the direct model probabilities after pruning the top k
new_ch_lm_lprobs: the combined channel and language model probabilities
new_lm_lprobs: the language model probabilities after pruning the top k
"""
with torch.no_grad():
lprobs_size = lprobs.size()
if prefix_tokens is not None and step < prefix_tokens.size(1):
probs_slice = lprobs.view(bsz, -1, lprobs.size(-1))[:,
0, :]
cand_scores = torch.gather(
probs_slice,
dim=1,
index=prefix_tokens[:, step].view(-1, 1).data).expand(
-1,
beam_size).contiguous().view(bsz * beam_size, 1)
cand_indices = prefix_tokens[:, step].view(-1, 1).expand(
bsz,
beam_size).data.contiguous().view(bsz * beam_size, 1)
# need to calculate and save fw and lm probs for prefix tokens
fw_top_k = cand_scores
fw_top_k_idx = cand_indices
k = 1
else:
# take the top k best words for every sentence in batch*beam
fw_top_k, fw_top_k_idx = torch.topk(lprobs.view(
beam_size * bsz, -1),
k=k)
eos_idx = torch.nonzero(
fw_top_k_idx.view(bsz * beam_size * k, -1) == self.eos)[:,
0]
ch_scores = fw_top_k.new_full((beam_size * bsz * k, ), 0)
src_size = torch.sum(
src_tokens[:, :] != self.src_dict.pad_index,
dim=1,
keepdim=True,
dtype=fw_top_k.dtype)
if self.combine_method != "lm_only":
temp_src_tokens_full = src_tokens[:, :].repeat(1, k).view(
bsz * beam_size * k, -1)
not_padding = temp_src_tokens_full[:,
1:] != self.src_dict.pad_index
cur_tgt_size = step + 2
# add eos to all candidate sentences except those that already end in eos
eos_tokens = tokens[:, 0].repeat(1, k).view(-1, 1)
eos_tokens[eos_idx] = self.tgt_dict.pad_index
if step == 0:
channel_input = torch.cat(
(fw_top_k_idx.view(-1, 1), eos_tokens), 1)
else:
# move eos from beginning to end of target sentence
channel_input = torch.cat(
(tokens[:, 1:step + 1].repeat(1, k).view(-1, step),
fw_top_k_idx.view(-1, 1), eos_tokens), 1)
ch_input_lengths = torch.tensor(
np.full(channel_input.size(0), cur_tgt_size))
ch_input_lengths[eos_idx] = cur_tgt_size - 1
if self.channel_scoring_type == "unnormalized":
ch_encoder_output = channel_model.encoder(
channel_input, src_lengths=ch_input_lengths)
ch_decoder_output, _ = channel_model.decoder(
temp_src_tokens_full,
encoder_out=ch_encoder_output,
features_only=True)
del ch_encoder_output
ch_intermed_scores = channel_model.decoder.unnormalized_scores_given_target(
ch_decoder_output,
target_ids=temp_src_tokens_full[:, 1:])
ch_intermed_scores = ch_intermed_scores.float()
ch_intermed_scores *= not_padding.float()
ch_scores = torch.sum(ch_intermed_scores, dim=1)
elif self.channel_scoring_type == "k2_separate":
for k_idx in range(k):
k_eos_tokens = eos_tokens[k_idx::k, :]
if step == 0:
k_ch_input = torch.cat(
(fw_top_k_idx[:, k_idx:k_idx + 1],
k_eos_tokens), 1)
else:
# move eos from beginning to end of target sentence
k_ch_input = torch.cat(
(tokens[:, 1:step + 1],
fw_top_k_idx[:, k_idx:k_idx + 1],
k_eos_tokens), 1)
k_ch_input_lengths = ch_input_lengths[k_idx::k]
k_ch_output = channel_model(
k_ch_input, k_ch_input_lengths, src_tokens)
k_ch_lprobs = channel_model.get_normalized_probs(
k_ch_output, log_probs=True)
k_ch_intermed_scores = torch.gather(
k_ch_lprobs[:, :-1, :], 2,
src_tokens[:, 1:].unsqueeze(2)).squeeze(2)
k_ch_intermed_scores *= not_padding.float()
ch_scores[k_idx::k] = torch.sum(
k_ch_intermed_scores, dim=1)
elif self.channel_scoring_type == "src_vocab":
ch_encoder_output = channel_model.encoder(
channel_input, src_lengths=ch_input_lengths)
ch_decoder_output, _ = channel_model.decoder(
temp_src_tokens_full,
encoder_out=ch_encoder_output,
features_only=True)
del ch_encoder_output
ch_lprobs = normalized_scores_with_batch_vocab(
channel_model.decoder,
ch_decoder_output,
src_tokens,
k,
bsz,
beam_size,
self.src_dict.pad_index,
top_k=self.top_k_vocab)
ch_scores = torch.sum(ch_lprobs, dim=1)
elif self.channel_scoring_type == "src_vocab_batched":
ch_bsz_size = temp_src_tokens_full.shape[0]
ch_lprobs_list = [None] * len(
range(0, ch_bsz_size, self.ch_scoring_bsz))
for i, start_idx in enumerate(
range(0, ch_bsz_size, self.ch_scoring_bsz)):
end_idx = min(start_idx + self.ch_scoring_bsz,
ch_bsz_size)
temp_src_tokens_full_batch = temp_src_tokens_full[
start_idx:end_idx, :]
channel_input_batch = channel_input[
start_idx:end_idx, :]
ch_input_lengths_batch = ch_input_lengths[
start_idx:end_idx]
ch_encoder_output_batch = channel_model.encoder(
channel_input_batch,
src_lengths=ch_input_lengths_batch)
ch_decoder_output_batch, _ = channel_model.decoder(
temp_src_tokens_full_batch,
encoder_out=ch_encoder_output_batch,
features_only=True)
ch_lprobs_list[
i] = normalized_scores_with_batch_vocab(
channel_model.decoder,
ch_decoder_output_batch,
src_tokens,
k,
bsz,
beam_size,
self.src_dict.pad_index,
top_k=self.top_k_vocab,
start_idx=start_idx,
end_idx=end_idx)
ch_lprobs = torch.cat(ch_lprobs_list, dim=0)
ch_scores = torch.sum(ch_lprobs, dim=1)
else:
ch_output = channel_model(channel_input,
ch_input_lengths,
temp_src_tokens_full)
ch_lprobs = channel_model.get_normalized_probs(
ch_output, log_probs=True)
ch_intermed_scores = torch.gather(
ch_lprobs[:, :-1, :], 2,
temp_src_tokens_full[:, 1:].unsqueeze(
2)).squeeze().view(bsz * beam_size * k, -1)
ch_intermed_scores *= not_padding.float()
ch_scores = torch.sum(ch_intermed_scores, dim=1)
else:
cur_tgt_size = 0
ch_scores = ch_scores.view(bsz * beam_size, k)
expanded_lm_prefix_scores = lm_prefix_scores.unsqueeze(
1).expand(-1, k).flatten()
if self.share_tgt_dict:
lm_scores = get_lm_scores(
lm, tokens[:, :step + 1].view(-1, step + 1),
lm_incremental_states, fw_top_k_idx.view(-1, 1),
torch.tensor(np.full(tokens.size(0), step + 1)), k)
else:
new_lm_input = dict2dict(
tokens[:, :step + 1].view(-1, step + 1),
self.tgt_to_lm)
new_cands = dict2dict(fw_top_k_idx.view(-1, 1),
self.tgt_to_lm)
lm_scores = get_lm_scores(
lm, new_lm_input, lm_incremental_states, new_cands,
torch.tensor(np.full(tokens.size(0), step + 1)), k)
lm_scores.add_(expanded_lm_prefix_scores)
ch_lm_scores = combine_ch_lm(self.combine_method, ch_scores,
lm_scores, src_size, cur_tgt_size)
# initialize all as min value
new_fw_lprobs = ch_scores.new(lprobs_size).fill_(-1e17).view(
bsz * beam_size, -1)
new_ch_lm_lprobs = ch_scores.new(lprobs_size).fill_(
-1e17).view(bsz * beam_size, -1)
new_lm_lprobs = ch_scores.new(lprobs_size).fill_(-1e17).view(
bsz * beam_size, -1)
new_fw_lprobs[:, self.pad] = -math.inf
new_ch_lm_lprobs[:, self.pad] = -math.inf
new_lm_lprobs[:, self.pad] = -math.inf
new_fw_lprobs.scatter_(1, fw_top_k_idx, fw_top_k)
new_ch_lm_lprobs.scatter_(1, fw_top_k_idx, ch_lm_scores)
new_lm_lprobs.scatter_(1, fw_top_k_idx, lm_scores.view(-1, k))
return new_fw_lprobs, new_ch_lm_lprobs, new_lm_lprobs
def combine_ch_lm(combine_type, ch_scores, lm_scores1, src_size,
tgt_size):
if self.channel_scoring_type == "unnormalized":
ch_scores = self.log_softmax_fn(
ch_scores.view(-1, self.beam_size * self.k2)).view(
ch_scores.shape)
ch_scores = ch_scores * self.ch_weight
lm_scores1 = lm_scores1 * self.lm_weight
if combine_type == "lm_only":
# log P(T|S) + log P(T)
ch_scores = lm_scores1.view(ch_scores.size())
elif combine_type == "noisy_channel":
# 1/t log P(T|S) + 1/s log P(S|T) + 1/t log P(T)
if self.normalize_lm_scores_by_tgt_len:
ch_scores.div_(src_size)
lm_scores_norm = lm_scores1.view(
ch_scores.size()).div(tgt_size)
ch_scores.add_(lm_scores_norm)
# 1/t log P(T|S) + 1/s log P(S|T) + 1/s log P(T)
else:
ch_scores.add_(lm_scores1.view(ch_scores.size()))
ch_scores.div_(src_size)
return ch_scores
if self.channel_models is not None:
channel_model = self.channel_models[
0] # assume only one channel_model model
else:
channel_model = None
lm = EnsembleModel(self.lm_models)
lm_incremental_states = torch.jit.annotate(
List[Dict[str, Dict[str, Optional[Tensor]]]],
[
torch.jit.annotate(Dict[str, Dict[str, Optional[Tensor]]], {})
for i in range(lm.models_size)
],
)
reorder_state = None
batch_idxs = None
for step in range(max_len + 1): # one extra step for EOS marker
# reorder decoder internal states based on the prev choice of beams
if reorder_state is not None:
if batch_idxs is not None:
# update beam indices to take into account removed sentences
corr = batch_idxs - torch.arange(
batch_idxs.numel()).type_as(batch_idxs)
reorder_state.view(-1, beam_size).add_(
corr.unsqueeze(-1) * beam_size)
model.reorder_incremental_state(incremental_states,
reorder_state)
encoder_outs = model.reorder_encoder_out(
encoder_outs, reorder_state)
lm.reorder_incremental_state(lm_incremental_states,
reorder_state)
fw_lprobs, avg_attn_scores = model.forward_decoder(
tokens[:, :step + 1],
encoder_outs,
incremental_states,
temperature=self.temperature,
)
fw_lprobs[:, self.pad] = -math.inf # never select pad
fw_lprobs[:, self.unk] -= self.unk_penalty # apply unk penalty
fw_lprobs, ch_lm_lprobs, lm_lprobs = noisy_channel_rescoring(
fw_lprobs, beam_size, bsz, src_tokens, tokens, self.k2)
# handle min and max length constraints
if step >= max_len:
fw_lprobs[:, :self.eos] = -math.inf
fw_lprobs[:, self.eos + 1:] = -math.inf
elif step < self.min_len:
fw_lprobs[:, self.eos] = -math.inf
# handle prefix tokens (possibly with different lengths)
if prefix_tokens is not None and step < prefix_tokens.size(1):
prefix_toks = prefix_tokens[:, step].unsqueeze(-1).repeat(
1, beam_size).view(-1)
prefix_mask = prefix_toks.ne(self.pad)
prefix_fw_lprobs = fw_lprobs.gather(-1,
prefix_toks.unsqueeze(-1))
fw_lprobs[prefix_mask] = -math.inf
fw_lprobs[prefix_mask] = fw_lprobs[prefix_mask].scatter_(
-1, prefix_toks[prefix_mask].unsqueeze(-1),
prefix_fw_lprobs)
prefix_ch_lm_lprobs = ch_lm_lprobs.gather(
-1, prefix_toks.unsqueeze(-1))
ch_lm_lprobs[prefix_mask] = -math.inf
ch_lm_lprobs[prefix_mask] = ch_lm_lprobs[prefix_mask].scatter_(
-1, prefix_toks[prefix_mask].unsqueeze(-1),
prefix_ch_lm_lprobs)
prefix_lm_lprobs = lm_lprobs.gather(-1,
prefix_toks.unsqueeze(-1))
lm_lprobs[prefix_mask] = -math.inf
lm_lprobs[prefix_mask] = lm_lprobs[prefix_mask].scatter_(
-1, prefix_toks[prefix_mask].unsqueeze(-1),
prefix_lm_lprobs)
# if prefix includes eos, then we should make sure tokens and
# scores are the same across all beams
eos_mask = prefix_toks.eq(self.eos)
if eos_mask.any():
# validate that the first beam matches the prefix
first_beam = tokens[eos_mask].view(
-1, beam_size, tokens.size(-1))[:, 0, 1:step + 1]
eos_mask_batch_dim = eos_mask.view(-1, beam_size)[:, 0]
target_prefix = prefix_tokens[eos_mask_batch_dim][:, :step]
assert (first_beam == target_prefix).all()
def replicate_first_beam(tensor, mask):
tensor = tensor.view(-1, beam_size, tensor.size(-1))
tensor[mask] = tensor[mask][:, :1, :]
return tensor.view(-1, tensor.size(-1))
# copy tokens, scores and lprobs from the first beam to all beams
tokens = replicate_first_beam(tokens, eos_mask_batch_dim)
scores = replicate_first_beam(scores, eos_mask_batch_dim)
fw_lprobs = replicate_first_beam(fw_lprobs,
eos_mask_batch_dim)
ch_lm_lprobs = replicate_first_beam(
ch_lm_lprobs, eos_mask_batch_dim)
lm_lprobs = replicate_first_beam(lm_lprobs,
eos_mask_batch_dim)
if self.no_repeat_ngram_size > 0:
# for each beam and batch sentence, generate a list of previous ngrams
gen_ngrams = [{} for bbsz_idx in range(bsz * beam_size)]
for bbsz_idx in range(bsz * beam_size):
gen_tokens = tokens[bbsz_idx].tolist()
for ngram in zip(*[
gen_tokens[i:]
for i in range(self.no_repeat_ngram_size)
]):
gen_ngrams[bbsz_idx][tuple(ngram[:-1])] = \
gen_ngrams[bbsz_idx].get(tuple(ngram[:-1]), []) + [ngram[-1]]
# Record attention scores
if avg_attn_scores is not None:
if attn is None:
attn = scores.new(bsz * beam_size, src_tokens.size(1),
max_len + 2)
attn_buf = attn.clone()
nonpad_idxs = src_tokens.ne(self.pad)
attn[:, :, step + 1].copy_(avg_attn_scores)
scores = scores.type_as(fw_lprobs)
scores_buf = scores_buf.type_as(fw_lprobs)
self.search.set_src_lengths(src_lengths_no_eos)
if self.no_repeat_ngram_size > 0:
def calculate_banned_tokens(bbsz_idx):
# before decoding the next token, prevent decoding of ngrams that have already appeared
ngram_index = tuple(
tokens[bbsz_idx, step + 2 -
self.no_repeat_ngram_size:step + 1].tolist())
return gen_ngrams[bbsz_idx].get(ngram_index, [])
if step + 2 - self.no_repeat_ngram_size >= 0:
# no banned tokens if we haven't generated no_repeat_ngram_size tokens yet
banned_tokens = [
calculate_banned_tokens(bbsz_idx)
for bbsz_idx in range(bsz * beam_size)
]
else:
banned_tokens = [[] for bbsz_idx in range(bsz * beam_size)]
for bbsz_idx in range(bsz * beam_size):
fw_lprobs[bbsz_idx, banned_tokens[bbsz_idx]] = -math.inf
combined_noisy_channel_scores, fw_lprobs_top_k, lm_lprobs_top_k, cand_indices, cand_beams = self.search.step(
step, fw_lprobs.view(bsz, -1, self.vocab_size),
scores.view(bsz, beam_size, -1)[:, :, :step],
ch_lm_lprobs.view(bsz, -1, self.vocab_size),
lm_lprobs.view(bsz, -1, self.vocab_size), self.combine_method)
# cand_bbsz_idx contains beam indices for the top candidate
# hypotheses, with a range of values: [0, bsz*beam_size),
# and dimensions: [bsz, cand_size]
cand_bbsz_idx = cand_beams.add(bbsz_offsets)
# finalize hypotheses that end in eos (except for candidates to be ignored)
eos_mask = cand_indices.eq(self.eos)
eos_mask[:, :beam_size] &= ~cands_to_ignore
# only consider eos when it's among the top beam_size indices
eos_bbsz_idx = torch.masked_select(cand_bbsz_idx[:, :beam_size],
mask=eos_mask[:, :beam_size])
finalized_sents = set()
if eos_bbsz_idx.numel() > 0:
eos_scores = torch.masked_select(
fw_lprobs_top_k[:, :beam_size],
mask=eos_mask[:, :beam_size])
combined_noisy_channel_eos_scores = torch.masked_select(
combined_noisy_channel_scores[:, :beam_size],
mask=eos_mask[:, :beam_size],
)
# finalize hypo using channel model score
finalized_sents = finalize_hypos(
step, eos_bbsz_idx, eos_scores,
combined_noisy_channel_eos_scores)
num_remaining_sent -= len(finalized_sents)
assert num_remaining_sent >= 0
if num_remaining_sent == 0:
break
if len(finalized_sents) > 0:
new_bsz = bsz - len(finalized_sents)
# construct batch_idxs which holds indices of batches to keep for the next pass
batch_mask = cand_indices.new_ones(bsz)
batch_mask[cand_indices.new(finalized_sents)] = 0
batch_idxs = torch.nonzero(batch_mask).squeeze(-1)
eos_mask = eos_mask[batch_idxs]
cand_beams = cand_beams[batch_idxs]
bbsz_offsets.resize_(new_bsz, 1)
cand_bbsz_idx = cand_beams.add(bbsz_offsets)
lm_lprobs_top_k = lm_lprobs_top_k[batch_idxs]
fw_lprobs_top_k = fw_lprobs_top_k[batch_idxs]
cand_indices = cand_indices[batch_idxs]
if prefix_tokens is not None:
prefix_tokens = prefix_tokens[batch_idxs]
src_lengths_no_eos = src_lengths_no_eos[batch_idxs]
cands_to_ignore = cands_to_ignore[batch_idxs]
scores = scores.view(bsz, -1)[batch_idxs].view(
new_bsz * beam_size, -1)
scores_buf.resize_as_(scores)
tokens = tokens.view(bsz, -1)[batch_idxs].view(
new_bsz * beam_size, -1)
tokens_buf.resize_as_(tokens)
src_tokens = src_tokens.view(bsz, -1)[batch_idxs].view(
new_bsz * beam_size, -1)
src_lengths = src_lengths.view(bsz, -1)[batch_idxs].view(
new_bsz * beam_size, -1)
lm_prefix_scores = lm_prefix_scores.view(
bsz, -1)[batch_idxs].view(new_bsz * beam_size,
-1).squeeze()
if attn is not None:
attn = attn.view(bsz, -1)[batch_idxs].view(
new_bsz * beam_size, attn.size(1), -1)
attn_buf.resize_as_(attn)
bsz = new_bsz
else:
batch_idxs = None
# Set active_mask so that values > cand_size indicate eos or
# ignored hypos and values < cand_size indicate candidate
# active hypos. After this, the min values per row are the top
# candidate active hypos.
eos_mask[:, :beam_size] |= cands_to_ignore
active_mask = torch.add(
eos_mask.type_as(cand_offsets) * cand_size,
cand_offsets[:eos_mask.size(1)],
)
# get the top beam_size active hypotheses, which are just the hypos
# with the smallest values in active_mask
active_hypos, new_cands_to_ignore = buffer('active_hypos'), buffer(
'new_cands_to_ignore')
torch.topk(active_mask,
k=beam_size,
dim=1,
largest=False,
out=(new_cands_to_ignore, active_hypos))
# update cands_to_ignore to ignore any finalized hypos
cands_to_ignore = new_cands_to_ignore.ge(cand_size)[:, :beam_size]
assert (~cands_to_ignore).any(dim=1).all()
active_bbsz_idx = buffer('active_bbsz_idx')
torch.gather(
cand_bbsz_idx,
dim=1,
index=active_hypos,
out=active_bbsz_idx,
)
active_scores = torch.gather(
fw_lprobs_top_k,
dim=1,
index=active_hypos,
out=scores[:, step].view(bsz, beam_size),
)
active_bbsz_idx = active_bbsz_idx.view(-1)
active_scores = active_scores.view(-1)
# copy tokens and scores for active hypotheses
torch.index_select(
tokens[:, :step + 1],
dim=0,
index=active_bbsz_idx,
out=tokens_buf[:, :step + 1],
)
torch.gather(
cand_indices,
dim=1,
index=active_hypos,
out=tokens_buf.view(bsz, beam_size, -1)[:, :, step + 1],
)
if step > 0:
torch.index_select(
scores[:, :step],
dim=0,
index=active_bbsz_idx,
out=scores_buf[:, :step],
)
torch.gather(
fw_lprobs_top_k,
dim=1,
index=active_hypos,
out=scores_buf.view(bsz, beam_size, -1)[:, :, step],
)
torch.gather(lm_lprobs_top_k,
dim=1,
index=active_hypos,
out=lm_prefix_scores.view(bsz, beam_size))
# copy attention for active hypotheses
if attn is not None:
torch.index_select(
attn[:, :, :step + 2],
dim=0,
index=active_bbsz_idx,
out=attn_buf[:, :, :step + 2],
)
# swap buffers
tokens, tokens_buf = tokens_buf, tokens
scores, scores_buf = scores_buf, scores
if attn is not None:
attn, attn_buf = attn_buf, attn
# reorder incremental state in decoder
reorder_state = active_bbsz_idx
# sort by score descending
for sent in range(len(finalized)):
finalized[sent] = sorted(finalized[sent],
key=lambda r: r['score'],
reverse=True)
return finalized