modeling_step1.py

import math
from typing import Optional, Tuple, Union, List

import torch
import torch.utils.checkpoint
from torch import nn
from transformers.generation import GenerationMixin

from transformers.modeling_utils import PreTrainedModel
from transformers.utils import logging
from .configuration_step1 import Step1Config
from transformers.cache_utils import Cache, DynamicCache
from einops import rearrange
from transformers.modeling_outputs import (
    BaseModelOutputWithPast,
    CausalLMOutputWithPast,
)

logger = logging.get_logger(__name__)


def build_alibi_cache(block_size, n_heads, dtype, device):
    # get slopes
    n = 2 ** math.floor(math.log2(n_heads))  # nearest 2**n to n_heads
    m0 = 2.0 ** (-8.0 / n)
    # 2^(-8/n), 2^(-8*2/n), 2^(-8*3/n), ...
    slopes = torch.pow(m0, torch.arange(1, n + 1))
    if n < n_heads:
        m1 = 2.0 ** (-4.0 / n)
        # 2^(-8/(2n)), 2^(-8*3/(2n)), 2^(-8*5/(2n)), ...
        mm = torch.pow(m1, torch.arange(1, 1 + 2 * (n_heads - n), 2))
        slopes = torch.cat([slopes, mm])
    slopes = slopes.to(device)

    tril = torch.tril(torch.ones(1, 1, block_size, block_size, device=device))

    bias_rows = torch.arange(block_size, device=device).view(1, -1)
    bias_cols = torch.arange(block_size, device=device).view(-1, 1)
    bias = -torch.sqrt(bias_cols - bias_rows)
    bias = bias.view(1, block_size, block_size) * slopes.view(-1, 1, 1)
    bias = bias.masked_fill(tril == 0, float("-inf"))

    return bias.type(dtype)


class StepRMSNorm(torch.nn.Module):
    def __init__(self, hidden_size, eps=1e-5):
        super().__init__()
        self.weight = torch.nn.Parameter(torch.ones(hidden_size))
        self.eps = eps

    def forward(self, x: torch.Tensor):
        var = x.float().pow(2).mean(-1, keepdim=True)
        x = x * torch.rsqrt(var + self.eps).to(x.dtype)
        x = x * self.weight
        return x


class StepAttention(torch.nn.Module):
    def __init__(self, hidden_size, num_heads, num_groups, layer_idx: int):
        super().__init__()

        self.num_heads = num_heads
        self.num_groups = num_groups
        self.hidden_size = hidden_size
        self.head_dim = hidden_size // num_heads

        self.q_proj = torch.nn.Linear(hidden_size, hidden_size, bias=False)
        self.k_proj = torch.nn.Linear(
            hidden_size, num_groups * self.head_dim, bias=False
        )
        self.v_proj = torch.nn.Linear(
            hidden_size, num_groups * self.head_dim, bias=False
        )
        self.o_proj = torch.nn.Linear(hidden_size, hidden_size, bias=False)

        self.layer_idx = layer_idx

    def forward(
        self,
        x: torch.Tensor,
        past_key_value: Optional[Cache] = None,
        attention_mask: Optional[torch.Tensor] = None,
        cache_position: Optional[torch.LongTensor] = None,
    ):

        q: torch.Tensor = self.q_proj(x)
        k: torch.Tensor = self.k_proj(x)
        v: torch.Tensor = self.v_proj(x)
        if past_key_value is not None:
            cache_kwargs = {"cache_position": cache_position}
            k, v = past_key_value.update(k, v, self.layer_idx, cache_kwargs)

        q = rearrange(q, "b s (h d) -> b s h d", h=self.num_heads)
        k = rearrange(k, "b s (g d) -> b s g d", g=self.num_groups)
        v = rearrange(v, "b s (g d) -> b s g d", g=self.num_groups)

        k = k.repeat_interleave(self.num_heads // self.num_groups, dim=-2)
        v = v.repeat_interleave(self.num_heads // self.num_groups, dim=-2)

        attention_mask = build_alibi_cache(
            k.size(1), self.num_heads, dtype=q.dtype, device=q.device
        )[:, :, -q.size(1) :, :].contiguous()

        q = q.transpose(1, 2)
        k = k.transpose(1, 2)
        v = v.transpose(1, 2)

        o: torch.Tensor = torch.nn.functional.scaled_dot_product_attention(
            q, k, v, attn_mask=attention_mask
        )
        o = o.transpose(1, 2).flatten(-2, -1)

        o = self.o_proj(o)
        return o


class StepMLP(torch.nn.Module):
    def __init__(self, hidden_size, intermediate_size):
        super().__init__()
        self.gate_proj = torch.nn.Linear(hidden_size, intermediate_size, bias=False)
        self.up_proj = torch.nn.Linear(hidden_size, intermediate_size, bias=False)
        self.down_proj = torch.nn.Linear(intermediate_size, hidden_size, bias=False)

    def forward(self, x):
        gate = self.gate_proj(x)
        up = self.up_proj(x)
        x = torch.nn.functional.silu(gate) * up
        x = self.down_proj(x)
        return x


class StepLayer(torch.nn.Module):
    def __init__(self, config: Step1Config, layer_idx: int):
        super().__init__()
        self.layer_idx = layer_idx
        self.self_attn = StepAttention(
            hidden_size=config.hidden_size,
            num_heads=config.num_attention_heads,
            num_groups=config.num_attention_groups,
            layer_idx=layer_idx,
        )
        self.mlp = StepMLP(
            hidden_size=config.hidden_size,
            intermediate_size=config.intermediate_size,
        )
        self.input_layernorm = StepRMSNorm(
            hidden_size=config.hidden_size, eps=config.rms_norm_eps
        )
        self.post_attention_layernorm = StepRMSNorm(
            hidden_size=config.hidden_size, eps=config.rms_norm_eps
        )

    def forward(
        self,
        x,
        attention_mask: Optional[torch.Tensor] = None,
        past_key_value: Optional[Cache] = None,
        cache_position: Optional[torch.LongTensor] = None,
    ):
        def f(x):
            x = self.input_layernorm(x)
            x = self.self_attn(x, past_key_value, attention_mask, cache_position)
            return x

        x = x + f(x)

        def f(x):
            x = self.post_attention_layernorm(x)
            x = self.mlp(x)
            return x

        x = x + f(x)

        return x


class StepPreTrainedModel(PreTrainedModel):
    config_class = Step1Config
    base_model_prefix = "model"
    supports_gradient_checkpointing = True
    _no_split_modules = ["StepLayer"]
    _skip_keys_device_placement = ["past_key_values"]
    _supports_cache_class = True
    _supports_static_cache = True

    def _init_weights(self, module):
        std = self.config.initializer_range
        if isinstance(module, nn.Linear):
            module.weight.data.normal_(mean=0.0, std=std)
            if module.bias is not None:
                module.bias.data.zero_()
        elif isinstance(module, nn.Embedding):
            module.weight.data.normal_(mean=0.0, std=std)
            if module.padding_idx is not None:
                module.weight.data[module.padding_idx].zero_()


class Step1Model(StepPreTrainedModel):
    """
    Transformer decoder consisting of *config.num_hidden_layers* layers. Each layer is a [`LlamaDecoderLayer`]

    Args:
        config: Step1Config
    """

    def __init__(self, config: Step1Config):
        super().__init__(config)
        self.config = config
        self.embed_tokens = torch.nn.Embedding(config.vocab_size, config.hidden_size)

        self.layers = torch.nn.Sequential(
            *[
                StepLayer(config, layer_idx)
                for layer_idx in range(config.num_hidden_layers)
            ]
        )

        self.norm = StepRMSNorm(
            hidden_size=config.hidden_size, eps=config.rms_norm_eps
        )

        # Initialize weights and apply final processing
        self.post_init()

    def get_input_embeddings(self):
        return self.embed_tokens

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

    def forward(
        self,
        input_ids: torch.LongTensor = None,
        attention_mask: Optional[torch.Tensor] = None,
        past_key_values: Optional[Cache] = None,
        inputs_embeds: Optional[torch.FloatTensor] = None,
        use_cache: Optional[bool] = None,
        output_attentions: Optional[bool] = None,
        output_hidden_states: Optional[bool] = None,
        return_dict: Optional[bool] = None,
        cache_position: Optional[torch.LongTensor] = None,
    ) -> Union[Tuple, BaseModelOutputWithPast]:
        output_attentions = False
        output_hidden_states = False

        use_cache = use_cache if use_cache is not None else self.config.use_cache
        return_dict = (
            return_dict if return_dict is not None else self.config.use_return_dict
        )

        if (input_ids is None) ^ (inputs_embeds is not None):
            raise ValueError(
                "You must specify exactly one of input_ids or inputs_embeds"
            )

        if inputs_embeds is None:
            inputs_embeds = self.embed_tokens(input_ids)

        if use_cache and past_key_values is None:
            past_key_values = DynamicCache()

        if cache_position is None:
            past_seen_tokens = (
                past_key_values.get_seq_length() if past_key_values is not None else 0
            )
            cache_position = torch.arange(
                past_seen_tokens,
                past_seen_tokens + inputs_embeds.shape[1],
                device=inputs_embeds.device,
            )

        causal_mask = attention_mask

        hidden_states = inputs_embeds

        for decoder_layer in self.layers[: self.config.num_hidden_layers]:
            layer_outputs = decoder_layer(
                hidden_states,
                attention_mask=causal_mask,
                past_key_value=past_key_values,
                cache_position=cache_position,
            )

            hidden_states = layer_outputs

        hidden_states = self.norm(hidden_states)

        output = BaseModelOutputWithPast(
            last_hidden_state=hidden_states,
            past_key_values=past_key_values if use_cache else None,
            hidden_states=hidden_states,
            attentions=None,
        )
        return output if return_dict else output.to_tuple()


class Step1ForCausalLM(StepPreTrainedModel, GenerationMixin):
    _tied_weights_keys = ["lm_head.weight"]

    def __init__(self, config):
        super().__init__(config)
        self.model = Step1Model(config)
        self.vocab_size = config.vocab_size
        self.lm_head = nn.Linear(config.hidden_size, config.vocab_size, bias=False)

        # Initialize weights and apply final processing
        self.post_init()

    def get_input_embeddings(self):
        return self.model.embed_tokens

    def set_input_embeddings(self, value):
        self.model.embed_tokens = value

    # def get_output_embeddings(self):
    #     return self.lm_head

    # def set_output_embeddings(self, new_embeddings):
    #     self.lm_head = new_embeddings

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

    def get_decoder(self):
        return self.model

    def forward(
        self,
        input_ids: torch.LongTensor = None,
        attention_mask: Optional[torch.Tensor] = None,
        position_ids: Optional[torch.LongTensor] = None,
        past_key_values: Optional[Union[Cache, List[torch.FloatTensor]]] = None,
        inputs_embeds: Optional[torch.FloatTensor] = None,
        labels: Optional[torch.LongTensor] = None,
        use_cache: Optional[bool] = None,
        output_attentions: Optional[bool] = None,
        output_hidden_states: Optional[bool] = None,
        return_dict: Optional[bool] = None,
        cache_position: Optional[torch.LongTensor] = None,
        num_logits_to_keep: int = 0,
    ) -> Union[Tuple, CausalLMOutputWithPast]:
        # output_attentions = output_attentions if output_attentions is not None else self.config.output_attentions
        output_attentions = False
        output_hidden_states = False
        # output_hidden_states = (
        #     output_hidden_states if output_hidden_states is not None else self.config.output_hidden_states
        # )
        return_dict = (
            return_dict if return_dict is not None else self.config.use_return_dict
        )

        # decoder outputs consists of (dec_features, layer_state, dec_hidden, dec_attn)
        outputs = self.model(
            input_ids=input_ids,
            attention_mask=attention_mask,
            past_key_values=past_key_values,
            inputs_embeds=inputs_embeds,
            use_cache=use_cache,
            output_attentions=output_attentions,
            output_hidden_states=output_hidden_states,
            return_dict=return_dict,
            cache_position=cache_position,
        )

        hidden_states = outputs[0]
        # Only compute necessary logits, and do not upcast them to float if we are not computing the loss

        logits = self.lm_head(hidden_states)

        # logits = torch.matmul(hidden_states, lm_stat)

        loss = None
        if labels is not None:
            loss = self.loss_function(
                logits=logits,
                labels=labels,
                vocab_size=self.config.vocab_size,
                **kwargs
            )

        if not return_dict:
            output = (logits,) + outputs[1:]
            return (loss,) + output if loss is not None else output

        return CausalLMOutputWithPast(
            loss=loss,
            logits=logits,
            past_key_values=outputs.past_key_values,
            hidden_states=outputs.hidden_states,
            attentions=outputs.attentions,
        )