falcon.py

# Copyright (c) 2023, Tri Dao.

import math
import re

from collections import OrderedDict

import torch
import torch.nn.functional as F

from einops import rearrange

from transformers import GPT2Config, FalconConfig


def remap_state_dict_hf_falcon(state_dict, config):
    def key_mapping_layers(key):
        return re.sub(r'^transformer.h.', 'transformer.layers.', key)
    state_dict = OrderedDict((key_mapping_layers(k), v) for k, v in state_dict.items())
    # Word embedding
    def key_mapping_emb(key):
        return re.sub(r'^transformer.word_embeddings.', 'transformer.embeddings.word_embeddings.', key)
    state_dict = OrderedDict((key_mapping_emb(k), v) for k, v in state_dict.items())
    word_embeddings = state_dict.pop('transformer.embeddings.word_embeddings.weight')
    # It's possible that vocab_size is padded to be a multiple of 8, for example.
    pad_vocab_size_multiple = getattr(config, 'pad_vocab_size_multiple', 1)
    vocab_size = (math.ceil(config.vocab_size / pad_vocab_size_multiple) * pad_vocab_size_multiple)
    state_dict['transformer.embeddings.word_embeddings.weight'] = F.pad(
        word_embeddings, (0, 0, 0, vocab_size - word_embeddings.shape[0])
    )
    if getattr(config, 'tie_word_embeddings'):
        state_dict['lm_head.weight'] = state_dict['transformer.embeddings.word_embeddings.weight']
    else:
        output_embeddings = state_dict.pop('lm_head.weight')
        # It's possible that vocab_size is padded to be a multiple of 8, for example.
        state_dict['lm_head.weight'] = F.pad(
            output_embeddings, (0, 0, 0, vocab_size - output_embeddings.shape[0])
        )
        output_embeddings_bias = state_dict.pop('lm_head.bias')
        state_dict['lm_head.bias'] = F.pad(
            output_embeddings_bias, (0, vocab_size - output_embeddings_bias.shape[0])
        )

    # LayerNorm
    def key_mapping_ln(key):
        key = re.sub(r'^transformer.layers.(\d+).input_layernorm.',
                     r'transformer.layers.\1.norm1.', key)
        key = re.sub(r'^transformer.layers.(\d+).post_attention_layernorm.',
                     r'transformer.layers.\1.norm2.', key)
        key = re.sub(r'^transformer.layers.(\d+).ln_attn.', r'transformer.layers.\1.norm1.', key)
        key = re.sub(r'^transformer.layers.(\d+).ln_mlp.', r'transformer.layers.\1.norm2.', key)
        return key
    state_dict = OrderedDict((key_mapping_ln(k), v) for k, v in state_dict.items())

    # MLP
    def key_mapping_mlp(key):
        key = re.sub(r'^transformer.layers.(\d+).mlp.dense_h_to_4h.',
                     r'transformer.layers.\1.mlp.fc1.', key)
        key = re.sub(r'^transformer.layers.(\d+).mlp.dense_4h_to_h.',
                     r'transformer.layers.\1.mlp.fc2.', key)
        return key
    state_dict = OrderedDict((key_mapping_mlp(k), v) for k, v in state_dict.items())

    def key_mapping_attn(key):
        key = re.sub(r'^transformer.layers.(\d+).self_attention.query_key_value.',
                      r'transformer.layers.\1.mixer.Wqkv.', key)
        key = re.sub(r'^transformer.layers.(\d+).self_attention.dense.',
                      r'transformer.layers.\1.mixer.out_proj.', key)
        return key
    state_dict = OrderedDict((key_mapping_attn(k), v) for k, v in state_dict.items())
    n_head = config.n_head
    n_head_kv = getattr(config, "n_head_kv", 1)
    headdim = config.hidden_size // n_head
    for l in range(config.n_layer):
        # The weights are stored in a different layout compared to our implementation
        Wqkv = rearrange(state_dict.pop(f'transformer.layers.{l}.mixer.Wqkv.weight'),
                         "(group ratio headdim) ... -> group ratio headdim ...",
                         ratio=n_head // n_head_kv + 2, headdim=headdim)
        Wq = rearrange(Wqkv[:, :-2], "group ratio headdim ... -> (group ratio headdim) ...")
        Wk = rearrange(Wqkv[:, [-2]], "group ratio headdim ... -> (group ratio headdim) ...")
        Wv = rearrange(Wqkv[:, [-1]], "group ratio headdim ... -> (group ratio headdim) ...")
        state_dict[f'transformer.layers.{l}.mixer.Wqkv.weight'] = torch.cat([Wq, Wk, Wv], dim=0)

    return state_dict


def falcon_config_to_gpt2_config(falcon_config: FalconConfig) -> GPT2Config:
    # The 40b config uses "n_head_kv" instead of "num_kv_heads"
    n_head_kv = getattr(falcon_config, "n_head_kv",
                        1 if getattr(falcon_config, "multi_query", False)
                        else falcon_config.n_head)
    # HACK: the 40b config has 2 LN per layer instead of 1, but that's not reflected in the config.
    # So we have to infer it from the number of heads in the key/value block
    parallel_block_tied_norm = n_head_kv == 1
    return GPT2Config(
        vocab_size=falcon_config.vocab_size,
        n_positions=0,  # No absolute position embedding
        n_embd=falcon_config.hidden_size,
        n_layer=falcon_config.n_layer,
        n_head=falcon_config.n_head,
        n_inner=falcon_config.hidden_size * 4,
        activation_function="gelu",
        resid_pdrop=falcon_config.hidden_dropout,
        embd_pdrop=0.0,  # There doesn't seem to be any embedding dropout
        attn_pdrop=falcon_config.attention_dropout,
        layer_norm_epsilon=falcon_config.layer_norm_epsilon,
        initializer_range=falcon_config.initializer_range,
        bos_token_id=falcon_config.bos_token_id,
        eos_token_id=falcon_config.eos_token_id,
        # These are new arguments not in the original GPT2Config
        parallel_block=falcon_config.parallel_attn,
        n_head_kv=n_head_kv,
        parallel_block_tied_norm=parallel_block_tied_norm,
        rotary_emb_fraction=1.0,
        rotary_emb_interleaved=False,
        tie_word_embeddings=True,
        qkv_proj_bias=falcon_config.bias,
        out_proj_bias=falcon_config.bias,
        mlp_fc1_bias=falcon_config.bias,
        mlp_fc2_bias=falcon_config.bias,
        lm_head_bias=False,
    )