modeling_mpt.py

"""A simple, flexible implementation of a GPT model.

Inspired by https://github.com/karpathy/minGPT/blob/master/mingpt/model.py
"""
import math
import warnings
from typing import List, Optional, Tuple, Union
import torch
import torch.nn as nn
import torch.nn.functional as F
from transformers import PreTrainedModel, PreTrainedTokenizer, PreTrainedTokenizerFast
from transformers.modeling_outputs import (
    BaseModelOutputWithPast,
    CausalLMOutputWithPast,
)
from .attention import attn_bias_shape, build_attn_bias
from .blocks import MPTBlock
from .norm import NORM_CLASS_REGISTRY
from .configuration_mpt import MPTConfig
from .adapt_tokenizer import AutoTokenizerForMOD, adapt_tokenizer_for_denoising
from .hf_prefixlm_converter import (
    add_bidirectional_mask_if_missing,
    convert_hf_causal_lm_to_prefix_lm,
)
from .meta_init_context import init_empty_weights
from .param_init_fns import MODEL_INIT_REGISTRY, generic_param_init_fn_

Tokenizer = Union[PreTrainedTokenizer, PreTrainedTokenizerFast]


class MPTPreTrainedModel(PreTrainedModel):
    config_class = MPTConfig
    base_model_prefix = "model"
    supports_gradient_checkpointing = True
    _no_split_modules = ["MPTBlock"]


class MPTModel(MPTPreTrainedModel):
    def __init__(self, config: MPTConfig):
        config._validate_config()
        super().__init__(config)
        self.attn_impl = config.attn_config["attn_impl"]
        self.prefix_lm = config.attn_config["prefix_lm"]
        self.attn_uses_sequence_id = config.attn_config["attn_uses_sequence_id"]
        self.alibi = config.attn_config["alibi"]
        self.alibi_bias_max = config.attn_config["alibi_bias_max"]
        if config.norm_type.lower() not in NORM_CLASS_REGISTRY.keys():
            norm_options = " | ".join(NORM_CLASS_REGISTRY.keys())
            raise NotImplementedError(
                f"Requested norm type ({config.norm_type}) is not implemented within this repo (Options: {norm_options})."
            )
        norm_class = NORM_CLASS_REGISTRY[config.norm_type.lower()]
        self.embedding_fraction = config.embedding_fraction
        self.wte = nn.Embedding(
            config.vocab_size, config.d_model, device=config.init_device
        )
        if not self.alibi:
            self.wpe = nn.Embedding(
                config.max_seq_len, config.d_model, device=config.init_device
            )
        self.emb_drop = nn.Dropout(config.emb_pdrop)
        self.blocks = nn.ModuleList(
            [
                MPTBlock(device=config.init_device, **config.to_dict())
                for _ in range(config.n_layers)
            ]
        )
        self.norm_f = norm_class(config.d_model, device=config.init_device)
        if config.init_device != "meta":
            self.apply(self.param_init_fn)
        self.is_causal = not self.prefix_lm
        self._attn_bias_initialized = False
        self.attn_bias = None
        self.attn_bias_shape = attn_bias_shape(
            self.attn_impl,
            config.n_heads,
            config.max_seq_len,
            self.alibi,
            prefix_lm=self.prefix_lm,
            causal=self.is_causal,
            use_sequence_id=self.attn_uses_sequence_id,
        )
        if config.no_bias:
            for module in self.modules():
                if hasattr(module, "bias") and isinstance(module.bias, nn.Parameter):
                    if config.verbose:
                        warnings.warn(f"Removing bias ({module.bias}) from {module}.")
                    module.register_parameter("bias", None)
        if config.verbose and config.verbose > 2:
            print(self)
        if "verbose" not in self.config.init_config:
            self.config.init_config["verbose"] = self.config.verbose
        if self.config.init_config["verbose"] > 1:
            init_fn_name = self.config.init_config["name"]
            warnings.warn(f"Using {init_fn_name} initialization.")

    def get_input_embeddings(self):
        return self.wte

    def set_input_embeddings(self, value):
        self.wte = value

    @torch.no_grad()
    def _attn_bias(
        self,
        device,
        dtype,
        attention_mask: Optional[torch.ByteTensor] = None,
        prefix_mask: Optional[torch.ByteTensor] = None,
        sequence_id: Optional[torch.LongTensor] = None,
    ):
        if not self._attn_bias_initialized:
            if self.attn_bias_shape:
                self.attn_bias = torch.zeros(
                    self.attn_bias_shape, device=device, dtype=dtype
                )
                self.attn_bias = build_attn_bias(
                    self.attn_impl,
                    self.attn_bias,
                    self.config.n_heads,
                    self.config.max_seq_len,
                    causal=self.is_causal,
                    alibi=self.alibi,
                    alibi_bias_max=self.alibi_bias_max,
                )
            self._attn_bias_initialized = True
        if self.attn_impl == "flash":
            return (self.attn_bias, attention_mask)
        if self.attn_bias is not None:
            self.attn_bias = self.attn_bias.to(dtype=dtype, device=device)
        attn_bias = self.attn_bias
        if self.prefix_lm:
            assert isinstance(attn_bias, torch.Tensor)
            assert isinstance(prefix_mask, torch.Tensor)
            attn_bias = self._apply_prefix_mask(attn_bias, prefix_mask)
        if self.attn_uses_sequence_id and sequence_id is not None:
            assert isinstance(attn_bias, torch.Tensor)
            attn_bias = self._apply_sequence_id(attn_bias, sequence_id)
        if attention_mask is not None:
            s_k = attention_mask.shape[-1]
            if attn_bias is None:
                attn_bias = torch.zeros((1, 1, 1, s_k), device=device, dtype=dtype)
            else:
                attn_bias = attn_bias[:, :, :, -s_k:]
            if prefix_mask is not None and attention_mask.shape != prefix_mask.shape:
                raise ValueError(
                    f"attention_mask shape={attention_mask.shape} "
                    + f"and prefix_mask shape={prefix_mask.shape} are not equal."
                )
            min_val = torch.finfo(attn_bias.dtype).min
            attn_bias = attn_bias.masked_fill(
                ~attention_mask.view(-1, 1, 1, s_k), min_val
            )
        return (attn_bias, None)

    def _apply_prefix_mask(self, attn_bias: torch.Tensor, prefix_mask: torch.Tensor):
        (s_k, s_q) = attn_bias.shape[-2:]
        if s_k != self.config.max_seq_len or s_q != self.config.max_seq_len:
            raise ValueError(
                "attn_bias does not match the expected shape. "
                + f"The last two dimensions should both be {self.config.max_length} "
                + f"but are {s_k} and {s_q}."
            )
        seq_len = prefix_mask.shape[-1]
        if seq_len > self.config.max_seq_len:
            raise ValueError(
                f"prefix_mask sequence length cannot exceed max_seq_len={self.config.max_seq_len}"
            )
        attn_bias = attn_bias[..., :seq_len, :seq_len]
        causal = torch.tril(
            torch.ones((seq_len, seq_len), dtype=torch.bool, device=prefix_mask.device)
        ).view(1, 1, seq_len, seq_len)
        prefix = prefix_mask.view(-1, 1, 1, seq_len)
        cannot_attend = ~torch.logical_or(causal, prefix.bool())
        min_val = torch.finfo(attn_bias.dtype).min
        attn_bias = attn_bias.masked_fill(cannot_attend, min_val)
        return attn_bias

    def _apply_sequence_id(
        self, attn_bias: torch.Tensor, sequence_id: torch.LongTensor
    ):
        seq_len = sequence_id.shape[-1]
        if seq_len > self.config.max_seq_len:
            raise ValueError(
                f"sequence_id sequence length cannot exceed max_seq_len={self.config.max_seq_len}"
            )
        attn_bias = attn_bias[..., :seq_len, :seq_len]
        cannot_attend = torch.logical_not(
            torch.eq(sequence_id.view(-1, seq_len, 1), sequence_id.view(-1, 1, seq_len))
        ).unsqueeze(1)
        min_val = torch.finfo(attn_bias.dtype).min
        attn_bias = attn_bias.masked_fill(cannot_attend, min_val)
        return attn_bias

    def forward(
        self,
        input_ids: torch.LongTensor,
        past_key_values: Optional[List[Tuple[torch.FloatTensor]]] = None,
        attention_mask: Optional[torch.ByteTensor] = None,
        prefix_mask: Optional[torch.ByteTensor] = None,
        sequence_id: Optional[torch.LongTensor] = None,
        return_dict: Optional[bool] = None,
        output_attentions: Optional[bool] = None,
        output_hidden_states: Optional[bool] = None,
        use_cache: Optional[bool] = None,
    ):
        return_dict = (
            return_dict if return_dict is not None else self.config.return_dict
        )
        use_cache = use_cache if use_cache is not None else self.config.use_cache
        if attention_mask is not None:
            attention_mask = attention_mask.bool()
        if prefix_mask is not None:
            prefix_mask = prefix_mask.bool()
        if not return_dict:
            raise NotImplementedError(
                "return_dict False is not implemented yet for MPT"
            )
        if output_attentions:
            raise NotImplementedError(
                "output_attentions is not implemented yet for MPT"
            )
        if (
            attention_mask is not None
            and attention_mask[:, 0].sum() != attention_mask.shape[0]
            and self.training
        ):
            raise NotImplementedError(
                "MPT does not support training with left padding."
            )
        if self.prefix_lm and prefix_mask is None:
            raise ValueError(
                "prefix_mask is a required argument when MPT is configured with prefix_lm=True."
            )
        if self.training:
            if self.attn_uses_sequence_id and sequence_id is None:
                raise ValueError(
                    "sequence_id is a required argument when MPT is configured with attn_uses_sequence_id=True "
                    + "and the model is in train mode."
                )
            elif self.attn_uses_sequence_id is False and sequence_id is not None:
                warnings.warn(
                    "MPT received non-None input for `sequence_id` but is configured with attn_uses_sequence_id=False. "
                    + "This input will be ignored. If you want the model to use `sequence_id`, set attn_uses_sequence_id to True."
                )
        S = input_ids.size(1)
        assert (
            S <= self.config.max_seq_len
        ), f"Cannot forward input with seq_len={S}, this model only supports seq_len<={self.config.max_seq_len}"
        tok_emb = self.wte(input_ids)
        if self.alibi:
            x = tok_emb
        else:
            past_position = 0
            if past_key_values is not None:
                if len(past_key_values) != self.config.n_layers:
                    raise ValueError(
                        f"past_key_values must provide a past_key_value for each attention "
                        + f"layer in the network (len(past_key_values)={len(past_key_values)!r}; self.config.n_layers={self.config.n_layers!r})."
                    )
                past_position = past_key_values[0][0].size(1)
            if S + past_position > self.config.max_seq_len:
                raise ValueError(
                    f"Cannot forward input with past sequence length {past_position} and current sequence length {S + 1}, this model only supports total sequence length <= {self.config.max_seq_len}."
                )
            pos = torch.arange(
                past_position,
                S + past_position,
                dtype=torch.long,
                device=input_ids.device,
            ).unsqueeze(0)
            if attention_mask is not None:
                pos = torch.clamp(
                    pos
                    - torch.cumsum((~attention_mask).to(torch.int32), dim=1)[
                        :, past_position:
                    ],
                    min=0,
                )
            pos_emb = self.wpe(pos)
            x = tok_emb + pos_emb
        if self.embedding_fraction == 1:
            x = self.emb_drop(x)
        else:
            x_shrunk = x * self.embedding_fraction + x.detach() * (
                1 - self.embedding_fraction
            )
            assert isinstance(self.emb_drop, nn.Module)
            x = self.emb_drop(x_shrunk)
        (attn_bias, attention_mask) = self._attn_bias(
            device=x.device,
            dtype=x.dtype,
            attention_mask=attention_mask,
            prefix_mask=prefix_mask,
            sequence_id=sequence_id,
        )
        if use_cache and past_key_values is None:
            past_key_values = [() for _ in range(self.config.n_layers)]
        all_hidden_states = () if output_hidden_states else None
        for b_idx, block in enumerate(self.blocks):
            if output_hidden_states:
                assert all_hidden_states is not None
                all_hidden_states = all_hidden_states + (x,)
            past_key_value = (
                past_key_values[b_idx] if past_key_values is not None else None
            )
            (x, past_key_value) = block(
                x,
                past_key_value=past_key_value,
                attn_bias=attn_bias,
                attention_mask=attention_mask,
                is_causal=self.is_causal,
            )
            if past_key_values is not None:
                past_key_values[b_idx] = past_key_value
        x = self.norm_f(x)
        return BaseModelOutputWithPast(
            last_hidden_state=x,
            past_key_values=past_key_values,
            hidden_states=all_hidden_states,
        )

    def param_init_fn(self, module):
        init_fn_name = self.config.init_config["name"]
        MODEL_INIT_REGISTRY[init_fn_name](
            module=module,
            n_layers=self.config.n_layers,
            d_model=self.config.d_model,
            **self.config.init_config,
        )

    def fsdp_wrap_fn(self, module):
        return isinstance(module, MPTBlock)

    def activation_checkpointing_fn(self, module):
        return isinstance(module, MPTBlock)


class MPTForCausalLM(MPTPreTrainedModel):
    def __init__(self, config: MPTConfig):
        super().__init__(config)
        if not config.tie_word_embeddings:
            raise ValueError("MPTForCausalLM only supports tied word embeddings")
        self.transformer = MPTModel(config)
        self.logit_scale = None
        if config.logit_scale is not None:
            logit_scale = config.logit_scale
            if isinstance(logit_scale, str):
                if logit_scale == "inv_sqrt_d_model":
                    logit_scale = 1 / math.sqrt(config.d_model)
                else:
                    raise ValueError(
                        f"logit_scale={logit_scale!r} is not recognized as an option; use numeric value or 'inv_sqrt_d_model'."
                    )
            self.logit_scale = logit_scale

    def get_input_embeddings(self):
        return self.transformer.wte

    def set_input_embeddings(self, value):
        self.transformer.wte = value

    def get_output_embeddings(self):
        return self.transformer.wte

    def set_output_embeddings(self, new_embeddings):
        self.transformer.wte = new_embeddings

    def set_decoder(self, decoder):
        self.transformer = decoder

    def get_decoder(self):
        return self.transformer

    def forward(
        self,
        input_ids: torch.LongTensor,
        past_key_values: Optional[List[Tuple[torch.FloatTensor]]] = None,
        attention_mask: Optional[torch.ByteTensor] = None,
        prefix_mask: Optional[torch.ByteTensor] = None,
        sequence_id: Optional[torch.LongTensor] = None,
        labels: Optional[torch.LongTensor] = None,
        return_dict: Optional[bool] = None,
        output_attentions: Optional[bool] = None,
        output_hidden_states: Optional[bool] = None,
        use_cache: Optional[bool] = None,
    ):
        return_dict = (
            return_dict if return_dict is not None else self.config.return_dict
        )
        use_cache = use_cache if use_cache is not None else self.config.use_cache
        outputs = self.transformer(
            input_ids=input_ids,
            past_key_values=past_key_values,
            attention_mask=attention_mask,
            prefix_mask=prefix_mask,
            sequence_id=sequence_id,
            return_dict=return_dict,
            output_attentions=output_attentions,
            output_hidden_states=output_hidden_states,
            use_cache=use_cache,
        )
        logits = F.linear(outputs.last_hidden_state, self.transformer.wte.weight)
        if self.logit_scale is not None:
            if self.logit_scale == 0:
                warnings.warn(
                    f"Multiplying logits by self.logit_scale={self.logit_scale!r}. This will produce uniform (uninformative) outputs."
                )
            logits *= self.logit_scale
        loss = None
        if labels is not None:
            labels = torch.roll(labels, shifts=-1)
            labels[:, -1] = -100
            loss = F.cross_entropy(
                logits.view(-1, logits.size(-1)), labels.to(logits.device).view(-1)
            )
        return CausalLMOutputWithPast(
            loss=loss,
            logits=logits,
            past_key_values=outputs.past_key_values,
            hidden_states=outputs.hidden_states,
        )

    def param_init_fn(self, module):
        init_fn_name = self.config.init_config["name"]
        MODEL_INIT_REGISTRY[init_fn_name](
            module=module,
            n_layers=self.config.n_layers,
            d_model=self.config.d_model,
            **self.config.init_config,
        )

    def fsdp_wrap_fn(self, module):
        return isinstance(module, MPTBlock)

    def activation_checkpointing_fn(self, module):
        return isinstance(module, MPTBlock)

    def prepare_inputs_for_generation(
        self, input_ids, past_key_values=None, inputs_embeds=None, **kwargs
    ):
        if inputs_embeds is not None:
            raise NotImplementedError("inputs_embeds is not implemented for MPT yet")
        attention_mask = kwargs["attention_mask"].bool()
        if attention_mask[:, -1].sum() != attention_mask.shape[0]:
            raise NotImplementedError(
                "MPT does not support generation with right padding."
            )
        if self.transformer.attn_uses_sequence_id and self.training:
            sequence_id = torch.zeros_like(input_ids[:1])
        else:
            sequence_id = None
        if past_key_values is not None:
            input_ids = input_ids[:, -1].unsqueeze(-1)
        if self.transformer.prefix_lm:
            prefix_mask = torch.ones_like(attention_mask)
            if kwargs.get("use_cache") == False:
                raise NotImplementedError(
                    "MPT with prefix_lm=True does not support use_cache=False."
                )
        else:
            prefix_mask = None
        return {
            "input_ids": input_ids,
            "attention_mask": attention_mask,
            "prefix_mask": prefix_mask,
            "sequence_id": sequence_id,
            "past_key_values": past_key_values,
            "use_cache": kwargs.get("use_cache", True),
        }

    @staticmethod
    def _reorder_cache(past_key_values, beam_idx):
        """Used by HuggingFace generate when using beam search with kv-caching.

        See https://github.com/huggingface/transformers/blob/3ec7a47664ebe40c40f4b722f6bb1cd30c3821ec/src/transformers/models/gpt2/modeling_gpt2.py#L1122-L1133
        for an example in transformers.
        """
        reordered_past = []
        for layer_past in past_key_values:
            reordered_past += [
                tuple(
                    (past_state.index_select(0, beam_idx) for past_state in layer_past)
                )
            ]
        return reordered_past