File size: 25,927 Bytes
17ff0d8
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
from dataclasses import dataclass
from typing import Optional, Tuple, Union

import numpy as np
import torch
import torch.nn.functional as F
from diffusers.pipelines.pipeline_utils import DiffusionPipeline
from diffusers.utils import BaseOutput

from sdlm.inference.inference_utils import logits_projection
from sdlm.models.utils import check_tokenizer_equal, is_cdcd_check, load_classifier
from sdlm.utils import scale, self_condition_preds, convert_to_simplex


@dataclass
class SimplexDiffusionPipelineOutput(BaseOutput):
    """
    Output class for simplex diffusion pipelines.
    Args:
        simplex (`np.ndarray`)
            numpy array showing the denoised simplex representation.
        logits (`np.ndarray`) final generated logits before applying the projection.
    """

    simplex: np.ndarray
    logits: np.ndarray
    loss: np.ndarray


def yield_func(x):
    yield x


class SimplexDDPMPipeline(DiffusionPipeline):
    r"""
    This model inherits from [`DiffusionPipeline`]. Check the superclass documentation for the generic methods the
    library implements for all the pipelines (such as downloading or saving, running on a particular device, etc.)
    Parameters:
        model: Model architecture to denoise the latents (encoded token ids).
        scheduler ([`SchedulerMixin`]): A scheduler to denoise the encoded latent.
    """

    def __init__(
        self,
        model,
        scheduler,
        simplex_value,
        top_p,
        sampling_type,
        is_conditional_generation,
        tokenizer,
        classifier_free_uncond_input,
        temperature,
        guidance_softmax_combination,
    ):
        super().__init__()
        self.register_modules(model=model, scheduler=scheduler)
        self.simplex_value = simplex_value
        self.top_p = top_p
        self.sampling_type = sampling_type
        self.is_conditional_generation = is_conditional_generation
        self.tokenizer = tokenizer
        self.classifier_free_uncond_input = classifier_free_uncond_input
        self.temperature = temperature
        self.guidance_softmax_combination = guidance_softmax_combination

    @torch.inference_mode()
    def __call__(
        self,
        seq_length: int = 512,
        generator: Optional[torch.Generator] = None,
        batch: Optional[torch.FloatTensor] = None,
        guidance_scale: float = 1.0,
        is_generator: bool = False,
    ) -> Union[SimplexDiffusionPipelineOutput, Tuple]:
        r"""
        Args:
            batch_size (`int`, *optional*, defaults to 1):
                The number of images to generate.
            seq_length: (`int`), sequence length for the generated samples.
            generator (`torch.Generator`, *optional*):
                A [torch generator](https://pytorch.org/docs/stable/generated/torch.Generator.html) to make generation
                deterministic.
            batch (`torch.FloatTensor`): batch of input data, mostly used in the conditional generation setting.
        Returns:
            [`~pipeline_utils.SimplexDiffusionPipelineOutput`]: returns the generated simplex.
        """
        # Classifier_free guidance works only in the conditional generation case.
        classifier_free_guidance = (
            guidance_scale > 1.0 and self.is_conditional_generation
        )
        """
        if classifier_free_guidance:
            # Makes unconditional input for max sequence length, later we truncate it.
            uncond_input = self.tokenizer(
                [""] * batch_size, padding="max_length", max_length=seq_length, return_tensors="pt"
            ).to(self.device)
            # Converts this to a simplex (batch_size, max_seq, vocab_size)
            uncond_simplex = convert_to_simplex(uncond_input["input_ids"], self.simplex_value, self.model.config.vocab_size)
        """
        # Sample gaussian noise to begin loop
        vocab_size = self.model.config.vocab_size
        if batch is not None:
            # TODO(rabeeh): is giving the length cheating for this setting?
            # Adapts the sequence length to the given `span_mask`'s length.
            seq_length = batch["input_ids"].shape[1]
        # idk why i have the bsz argument.
        batch_size = batch["input_ids"].shape[0]
        simplex_shape = (batch_size, seq_length, vocab_size)
        simplex = self.simplex_value * torch.randn(
            simplex_shape, generator=generator, device=self.device
        )
        if self.model.config.self_condition is not None:
            previous_pred = torch.zeros(
                (batch_size, seq_length, vocab_size), device=self.device
            )
        logits_projection_fct = lambda x: logits_projection(  # noqa: E731
            x, self.sampling_type, self.top_p, self.simplex_value, self.temperature
        )
        losses = []
        previous_hidden = None

        warped_steps = []
        prev_t = 0
        for t in self.progress_bar(self.scheduler.timesteps):
            original_t = torch.tensor([t], device=self.device).expand(
                batch_size, seq_length
            )
            if is_cdcd_check(self.model):
                # warp timesteps based on cdf
                # we are in inference mode, anything in span_mask is to gen.
                token_inputs = torch.where(
                    batch["span_mask"], self.tokenizer.pad_token_id, batch["input_ids"]
                )
                t = self.model.warp_timesteps(
                    original_t,
                    t_min=0,
                    t_max=len(self.scheduler) - 1,
                    token_input=token_inputs,
                    span_mask=batch["span_mask"],
                )
            else:
                t = original_t
            t_scaled = scale(t, len(self.scheduler))
            warped_steps.append(t)
            """
            if classifier_free_guidance:
                if self.classifier_free_uncond_input == "empty_token":
                    uncond_input = uncond_simplex[:, : batch["input_ids"].shape[1], :]
                elif self.classifier_free_uncond_input == "noisy_simplex":
                    uncond_input = self.simplex_value * torch.randn(simplex.shape, generator=generator, device=self.device)
                else:
                    raise NotImplementedError
            """
            # 1. predict noise model_output. Note we need not to pass the input_ids in case of
            # unconditional generation since the loss would be computed and it should not.
            model_output = self.model(
                input_ids=batch["input_ids"]
                if self.is_conditional_generation
                else None,
                span_mask=batch["span_mask"]
                if self.is_conditional_generation
                else None,
                simplex=simplex,
                timesteps=t_scaled,
                previous_pred=previous_pred
                if self.model.config.self_condition
                else None,
                classifier_free_guidance=classifier_free_guidance,
                reduce_loss="none",
                max_timestep=len(self.scheduler),
                previous_hidden=previous_hidden,
            )
            model_output_logits = model_output.logits
            previous_hidden = model_output.hidden_states

            # Performs classifier-free guidance.
            if classifier_free_guidance:
                logits_uncond, logits_pred = model_output_logits.chunk(2)
                if self.guidance_softmax_combination:
                    model_output_logits = F.softmax(
                        logits_uncond, dim=-1
                    ) + guidance_scale * (
                        F.softmax(logits_pred, dim=-1)
                        - F.softmax(logits_uncond, dim=-1)
                    )
                else:
                    model_output_logits = logits_uncond + guidance_scale * (
                        logits_pred - logits_uncond
                    )

            if self.model.config.self_condition is not None:
                if classifier_free_guidance:
                    prev_output_logits = model_output.logits.chunk(2)[1]
                else:
                    prev_output_logits = model_output_logits

                previous_pred = self_condition_preds(
                    self.model.config.self_condition,
                    prev_output_logits,
                    logits_projection_fct,
                )

            # Projection.
            projected_logits = logits_projection_fct(model_output_logits)

            old_simplex = simplex

            # 2. compute previous logits: x_t -> x_t-1
            noise = self.simplex_value * torch.randn(
                simplex_shape, generator=generator, device=self.device
            )
            if is_cdcd_check(self.model):
                # warp timesteps based on cdf
                token_inputs = torch.where(
                    batch["span_mask"], self.tokenizer.pad_token_id, batch["input_ids"]
                )
                prev_t = self.model.warp_timesteps(
                    original_t - 1,
                    t_min=0,
                    t_max=len(self.scheduler) - 1,
                    token_input=token_inputs,
                    span_mask=batch["span_mask"],
                ).long()
                # since the tokenwise can do some wild stuff.
                prev_t = torch.clamp(prev_t, min=0, max=len(self.scheduler) - 1)
            else:
                prev_t = original_t - 1
            simplex = self.scheduler.step(
                projected_logits,
                t,
                prev_t,
                noise,
                generator=generator,
            ).prev_sample

            # keep loss for logging
            losses.append(model_output.loss.detach().cpu())

            # yield over it. (prolly not optimal, but whatever)
            yield SimplexDiffusionPipelineOutput(
                simplex=old_simplex, logits=model_output_logits, loss=losses[-1]
            )
        # we take the mean loss over all timesteps
        loss = torch.stack(losses, dim=0)
        # from matplotlib import pyplot as plt
        # warped_steps = torch.stack(warped_steps, dim=0)
        # for i in range(warped_steps.shape[1]):
        #     plt.plot(warped_steps[:, i, 256:].cpu())
        #     plt.savefig(f"warps_prefix_tokenwise/warped_{i}.png")
        #     plt.clf()
        return SimplexDiffusionPipelineOutput(
            simplex=simplex, logits=model_output_logits, loss=loss
        )


class SimplexDDPMClassifierGuidancePipeline(SimplexDDPMPipeline):
    def __init__(
        self,
        model,
        scheduler,
        simplex_value,
        top_p,
        sampling_type,
        is_conditional_generation,
        tokenizer,
        classifier_free_uncond_input,
        temperature,
        guidance_softmax_combination,
        classifier_model_name_or_path,
    ) -> None:
        super().__init__(
            model,
            scheduler,
            simplex_value,
            top_p,
            sampling_type,
            is_conditional_generation,
            tokenizer,
            classifier_free_uncond_input,
            temperature,
            guidance_softmax_combination,
        )
        self.classifier = None
        if classifier_model_name_or_path is not None:
            classifier_tokenizer, classifier = load_classifier(
                classifier_model_name_or_path
            )
            check_tokenizer_equal(self.tokenizer, classifier_tokenizer)
            self.classifier = classifier.to(self.device)

    def get_reward(
        self,
        logits: torch.FloatTensor,
        use_gumbel_softmax: bool,
        do_hard_sample: bool,
        softmax_temperature: float,
        one_hot: Optional[torch.Tensor] = None,
        span_mask: Optional[torch.Tensor] = None,
    ) -> torch.FloatTensor:
        logits = logits.to(torch.bfloat16)
        logits.requires_grad = True
        if use_gumbel_softmax:
            simplex = F.gumbel_softmax(
                logits, tau=softmax_temperature, hard=do_hard_sample, dim=-1
            )
        else:
            simplex = torch.softmax(logits / softmax_temperature, dim=-1)
        # mask out context
        if span_mask is not None:
            simplex = torch.where(span_mask.unsqueeze(-1), simplex, one_hot)
        # forcibly add eos token to the simplex
        # eos_token = torch.nn.functional.one_hot(
        #     torch.tensor(self.tokenizer.eos_token_id),
        #     num_classes=self.classifier.config.vocab_size,
        # ).to(simplex.device)
        # eos_token = eos_token.unsqueeze(0).unsqueeze(0).expand_as(simplex)
        # simplex = torch.cat([simplex, eos_token], dim=1)
        inputs_embeds = F.linear(
            simplex, self.classifier.model.get_input_embeddings().weight.data.T
        )
        # forward pass through reward model
        reward = self.classifier(inputs_embeds=inputs_embeds).logits
        return reward
    

    @torch.no_grad()
    def __call__(
        self,
        seq_length: int = 512,
        generator: Optional[torch.Generator] = None,
        batch: Optional[torch.FloatTensor] = None,
        guidance_scale: float = 1.0,
        is_generator: bool = False,
        use_gumbel_softmax: bool = False,
        do_hard_sample: bool = False,
        softmax_temperature: float = 1.0,
        use_ddim_sampling: bool = False,
        num_guidance_steps: int = 5,
    ) -> Union[SimplexDiffusionPipelineOutput, Tuple]:
        # check for classifier guidance
        use_classifier_guidance = self.classifier is not None and guidance_scale > 0.0

        # NOTE: copied from SimplexDDPMPipeline
        # Sample gaussian noise to begin loop
        vocab_size = self.model.config.vocab_size
        if batch is not None:
            # TODO(rabeeh): is giving the length cheating for this setting?
            # Adapts the sequence length to the given `span_mask`'s length.
            seq_length = batch["input_ids"].shape[1]
        # idk why i have the bsz argument.
        batch_size = batch["input_ids"].shape[0]
        simplex_shape = (batch_size, seq_length, vocab_size)
        # simplex ~ N(0, kI)
        simplex = self.simplex_value * torch.randn(
            simplex_shape, generator=generator, device=self.device
        )
        if self.model.config.self_condition is not None:
            previous_pred = torch.zeros(
                (batch_size, seq_length, vocab_size), device=self.device
            )
        # logits -> hard sampled k / -k
        logits_projection_fct = lambda x: logits_projection(  # noqa: E731
            x, self.sampling_type, self.top_p, self.simplex_value, self.temperature
        )
        losses = []
        previous_hidden = None

        warped_steps = []
        prev_t = 0
        all_rewards = []
        for t in self.progress_bar(self.scheduler.timesteps):
            original_t = torch.tensor([t], device=self.device).expand(
                batch_size, seq_length
            )
            if is_cdcd_check(self.model):
                # warp timesteps based on cdf
                # we are in inference mode, anything in span_mask is to gen.
                token_inputs = torch.where(
                    batch["span_mask"], 50264, batch["input_ids"]
                )
                t = self.model.warp_timesteps(
                    original_t,
                    t_min=0,
                    t_max=len(self.scheduler) - 1,
                    token_input=token_inputs,
                    span_mask=batch["span_mask"],
                )
            else:
                t = original_t
            t_scaled = scale(t, len(self.scheduler))
            warped_steps.append(t)

            # 1. predict noise model_output. Note we need not to pass the input_ids in case of
            # unconditional generation since the loss would be computed and it should not.
            model_output = self.model(
                input_ids=batch["input_ids"]
                if self.is_conditional_generation
                else None,
                span_mask=batch["span_mask"]
                if self.is_conditional_generation
                else None,
                simplex=simplex,
                timesteps=t_scaled,
                previous_pred=previous_pred
                if self.model.config.self_condition
                else None,
                classifier_free_guidance=False,
                reduce_loss="none",
                max_timestep=len(self.scheduler),
                previous_hidden=previous_hidden,
            )
            model_output_logits = model_output.logits
            previous_hidden = model_output.hidden_states

            # NOTE: classifier guidance!
            # compute one_hot
            span_mask = batch["span_mask"]
            one_hot = F.one_hot(batch["input_ids"], len(self.tokenizer)).to(
                torch.bfloat16
            )
            model_output_logits = model_output_logits.to(torch.bfloat16)

            if use_classifier_guidance:
                # use torch.optim api
                model_output_logits = torch.nn.Parameter(model_output_logits)
                optimizer = torch.optim.SGD([model_output_logits], lr=guidance_scale)
                 # guidance
                with torch.enable_grad():
                    for _ in range(num_guidance_steps):
                        reward = self.get_reward(
                            logits=model_output_logits,
                            use_gumbel_softmax=use_gumbel_softmax,
                            do_hard_sample=do_hard_sample,
                            softmax_temperature=softmax_temperature,
                            one_hot=one_hot,
                            span_mask=span_mask,
                        )
                        # all_rewards.append(reward.detach().cpu())
                        reward = reward.sum().neg()
                        reward.backward()
                        optimizer.step()
                        
                model_output_logits = model_output_logits.data

            if self.model.config.self_condition is not None:
                prev_output_logits = model_output_logits
                previous_pred = self_condition_preds(
                    self.model.config.self_condition,
                    prev_output_logits,
                    logits_projection_fct,
                )

            old_simplex = simplex

            # 2. compute previous logits: x_t -> x_t-1
            if is_cdcd_check(self.model):
                # warp timesteps based on cdf
                token_inputs = torch.where(
                    batch["span_mask"], 50264, batch["input_ids"]
                )
                prev_t = self.model.warp_timesteps(
                    original_t - 1,
                    t_min=0,
                    t_max=len(self.scheduler) - 1,
                    token_input=token_inputs,
                    span_mask=batch["span_mask"],
                ).long()
                # since the tokenwise can do some wild stuff.
                prev_t = torch.clamp(prev_t, min=0, max=len(self.scheduler) - 1)
            else:
                prev_t = original_t - 1

            if not use_ddim_sampling:
                # normal tess
                noise = self.simplex_value * torch.randn(
                    simplex_shape, generator=generator, device=self.device
                )
                # Projection.
                projected_logits = logits_projection_fct(model_output_logits)
                simplex = self.scheduler.step(
                    projected_logits,
                    t,
                    prev_t,
                    noise,
                    generator=generator,
                ).prev_sample
            else:
                # input: noisy k / -k
                # output: clean k / -k
                x_t = old_simplex
                x_0_hat = (
                    2 * self.simplex_value * torch.softmax(model_output_logits, dim=-1)
                    - self.simplex_value
                )
                alpha_prod_t = self.scheduler.alphas_cumprod[t[0, 0].item()]
                sqrt_alpha_prod_t = torch.sqrt(alpha_prod_t)
                sqrt_one_minus_alpha_prod_t = torch.sqrt(1 - alpha_prod_t)
                noise = (
                    x_t - sqrt_alpha_prod_t * x_0_hat
                ) / sqrt_one_minus_alpha_prod_t
                simplex = self.scheduler.step(
                    x_0_hat,
                    t,
                    prev_t,
                    noise,
                    generator=generator,
                ).prev_sample

            # keep loss for logging
            losses.append(model_output.loss.detach().cpu())

            # yield over it. (prolly not optimal, but whatever)
            yield SimplexDiffusionPipelineOutput(
                simplex=old_simplex, logits=model_output_logits, loss=losses[-1]
            )
        # we take the mean loss over all timesteps
        loss = torch.stack(losses, dim=0)
        # from matplotlib import pyplot as plt
        # all_rewardst = torch.cat(all_rewards, dim=-1)
        # plt.plot(all_rewardst.to(torch.float32).T)
        # plt.savefig("tmp.png")
        # import pdb; pdb.set_trace()
        return SimplexDiffusionPipelineOutput(
            simplex=simplex, logits=model_output_logits, loss=loss
        )


# A variant of the SimplexDDPMPipeline that is used for evaluation.
# Main difference is that we assume that you pass the ground truth, and
# want to compute the loss.
class SimplexDDPMPipelineForEvaluation(SimplexDDPMPipeline):
    @torch.inference_mode()
    def __call__(
        self,
        seq_length: int = 512,
        generator: Optional[torch.Generator] = None,
        batch: Optional[torch.FloatTensor] = None,
        guidance_scale: float = 1.0,
        is_generator: bool = False,
    ) -> Union[SimplexDiffusionPipelineOutput, Tuple]:
        # Classifier_free guidance works only in the conditional generation case.
        classifier_free_guidance = (
            guidance_scale > 1.0 and self.is_conditional_generation
        )
        # Sample gaussian noise to begin loop
        vocab_size = self.model.config.vocab_size
        if batch is not None:
            seq_length = batch["input_ids"].shape[1]
        # idk why i have the bsz argument.
        batch_size = batch["input_ids"].shape[0]
        simplex_shape = (batch_size, seq_length, vocab_size)
        # simplex here is the simplex of the actual input!
        simplex = convert_to_simplex(
            batch["input_ids"], self.simplex_value, self.model.config.vocab_size
        )
        noise = self.simplex_value * torch.randn(
            simplex_shape, generator=generator, device=self.device
        )
        if self.model.config.self_condition is not None:
            previous_pred = torch.zeros(
                (batch_size, seq_length, vocab_size), device=self.device
            )
        logits_projection_fct = lambda x: logits_projection(  # noqa: E731
            x, self.sampling_type, self.top_p, self.simplex_value, self.temperature
        )
        losses = []
        previous_hidden = None

        warped_steps = []
        prev_t = 0
        for t in self.progress_bar(self.scheduler.timesteps):
            original_t = torch.tensor([t], device=self.device).expand(
                batch_size, seq_length
            )
            if is_cdcd_check(self.model):
                # warp timesteps based on cdf
                # we are in inference mode, anything in span_mask is to gen.
                token_inputs = torch.where(
                    batch["span_mask"], self.tokenizer.pad_token_id, batch["input_ids"]
                )
                t = self.model.warp_timesteps(
                    original_t,
                    t_min=0,
                    t_max=len(self.scheduler) - 1,
                    token_input=token_inputs,
                    span_mask=batch["span_mask"],
                )
            else:
                t = original_t
            t_scaled = scale(t, len(self.scheduler))
            warped_steps.append(t)
            noisy_simplex = self.scheduler.add_noise(simplex, noise, t)

            attention_mask = batch["input_ids"] != self.tokenizer.pad_token_id

            # TODO: do we care about self-conditioning...?
            model_output = self.model(
                input_ids=batch["input_ids"],
                span_mask=batch["span_mask"],
                attention_mask=attention_mask,
                simplex=noisy_simplex,
                timesteps=t_scaled,
                classifier_free_guidance=classifier_free_guidance,
                reduce_loss="none",
                previous_pred=previous_pred,
                max_timestep=len(self.scheduler),
                previous_hidden=previous_hidden,
            )
            model_output_logits = model_output.logits
            previous_hidden = model_output.hidden_states
            losses.append(model_output.loss.detach().cpu())

            if self.model.config.self_condition is not None:
                prev_output_logits = model_output_logits
                previous_pred = self_condition_preds(
                    self.model.config.self_condition,
                    prev_output_logits,
                    logits_projection_fct,
                )

            old_simplex = simplex
            # no output stuff here, since all we care about is the loss.
            # yield over it. (prolly not optimal, but whatever)
            yield SimplexDiffusionPipelineOutput(
                simplex=noisy_simplex, logits=model_output_logits, loss=losses[-1]
            )
        # we take the mean loss over all timesteps
        loss = torch.stack(losses, dim=0)
        return SimplexDiffusionPipelineOutput(
            simplex=simplex, logits=model_output_logits, loss=loss
        )