Add T5 Model to TorchText (#1845)

* compute relative position buckets for relative attention bias

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* compute relative position bias for t5 attention

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* compute attention scores for t5 model using relative attention bias

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* perform multihead attention using relative attention bias for t5 model

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* create T5MultiheadAttention module

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* add layer norm module for t5 model

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* add t5 layer module that can be used for both encoder or decoder stack

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* add t5 stack that can function as either the encoder or decoder of a t5 model

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* Update base for Update on "add t5 model that can function as both encodery-only or encoder-decoder model"




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* Update base for Update on "add t5 model that can function as both encodery-only or encoder-decoder model"




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* Update base for Update on "add t5 model that can function as both encodery-only or encoder-decoder model"




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* Update base for Update on "add t5 model that can function as both encodery-only or encoder-decoder model"




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* Update base for Update on "add t5 model that can function as both encodery-only or encoder-decoder model"




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* Update base for Update on "add t5 model that can function as both encodery-only or encoder-decoder model"




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* Update base for Update on "add t5 model that can function as both encodery-only or encoder-decoder model"




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* add t5 model that can function as both encodery-only or encoder-decoder model (#1829)

Author: pmabbo13

torchtext/prototype/t5/model.py

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+from typing import Dict, Optional, Tuple, Union, Callable
+
+import torch
+import torch.nn as nn
+from torch import Tensor
+
+from .modules import T5Stack, T5LayerNorm
+
+
+# NOTE: Comparable HuggingFace implentation can be found at https://github.com/huggingface/transformers/blob/8581a798c0a48fca07b29ce2ca2ef55adcae8c7e/src/transformers/models/t5/modeling_t5.py#L1269
+class T5Model(nn.Module):
+    r"""A T5 model. User is able to modify the attributes as needed. The architecture
+    is based on the paper "Exploring the Limits of Transfer Learning with a Unified Text-to-Text Transformer".
+    Colin Raffel, Noam Shazeer, Adam Roberts, Katherine Lee, Sharan Narang, Michael Matena,
+    Yanqi Zhou, Wei Li, and Peter J. Liu. 2020. Journal of Machine Learning Research.
+    Volume 21 Issue 140 pages 1-67. http://jmlr.org/papers/v21/20-074.html
+    Args:
+        encoder_only: Whether or not model should consist of only the encoder as opposed to encoder-decoder (required)
+        d_model: Number of expected features in the encoder/decoder inputs (default=768).
+        nhead: Number of heads in the multiheadattention models (default=12).
+        num_encoder_layers: Number of encoder layers in the encoder (default=12).
+        num_decoder_layers: Number of decoder layers in the decoder (default=12).
+        dim_feedforward: Dimension of the feedforward network model (default=3072).
+        dropout: Dropout value (default=0.1).
+        activation: Activation function of encoder/decoder intermediate layer, can be a string
+            ("relu" or "gelu") or a unary callable. Default: relu
+        layer_norm_eps: The eps value in layer normalization components (default=1e-6).
+        relative_attention_num_buckets: Number of relative position buckets (default: 32)
+        relative_attention_max_distance: Maximum threshold on the relative distance used to
+            allocate buckets. Anything larger gets placed in the same bucket (default: 128)
+        padding_idx: Index assigned to padding token in vocabulary (default: 0)
+        max_seq_len: Maximum sequence length (default: 512)
+        vocab_size: Size of vocabulary (default: 32128)
+    Examples::
+        >>> t5_model = T5Model(encoder_only=False)
+        >>> src = torch.rand((32, 10, 512))
+        >>> tgt = torch.rand((32, 20, 512))
+        >>> out = t5_model(src, tgt)
+    """
+
+    def __init__(
+        self,
+        encoder_only: bool,
+        d_model: int = 768,
+        nhead: int = 12,
+        num_encoder_layers: int = 12,
+        num_decoder_layers: int = 12,
+        dim_feedforward: int = 3072,
+        dropout: float = 0.1,
+        activation: Union[str, Callable[[Tensor], Tensor]] = "relu",
+        layer_norm_eps: float = 1e-6,
+        relative_attention_num_buckets: int = 32,
+        relative_attention_max_distance: int = 128,
+        padding_idx: int = 0,
+        max_seq_len: int = 512,
+        vocab_size: int = 32128,
+        device=None,
+        dtype=None,
+    ) -> None:
+        super().__init__()
+
+        self.encoder_only = encoder_only
+        self.d_model = d_model
+        self.dim_feedforward = dim_feedforward
+        self.dropout = dropout
+        self.activation = activation
+        self.layer_norm_eps = layer_norm_eps
+        self.nhead = nhead
+        self.num_encoder_layers = num_encoder_layers
+        self.num_decoder_layers = num_decoder_layers
+        self.relative_attention_num_buckets = relative_attention_num_buckets
+        self.realtive_attention_max_distance = relative_attention_max_distance
+        self.padding_idx = padding_idx
+        self.max_seq_len = max_seq_len
+        self.vocab_size = vocab_size
+        self.device = device
+        self.dtype = dtype
+
+        self.token_embeddings = nn.Embedding(vocab_size, d_model, padding_idx)
+        self.encoder = T5Stack(
+            is_decoder=False,
+            d_model=d_model,
+            nhead=nhead,
+            num_layers=num_encoder_layers,
+            dim_feedforward=dim_feedforward,
+            dropout=dropout,
+            activation=activation,
+            layer_norm_eps=layer_norm_eps,
+            relative_attention_num_buckets=relative_attention_num_buckets,
+            relative_attention_max_distance=relative_attention_max_distance,
+            device=device,
+            dtype=dtype,
+        )
+        self.norm1 = T5LayerNorm(d_model)
+        self.dropout1 = nn.Dropout(dropout)
+        self.dropout2 = nn.Dropout(dropout)
+
+        if not encoder_only:
+            self.decoder = T5Stack(
+                is_decoder=True,
+                d_model=d_model,
+                nhead=nhead,
+                num_layers=num_decoder_layers,
+                dim_feedforward=dim_feedforward,
+                dropout=dropout,
+                activation=activation,
+                layer_norm_eps=layer_norm_eps,
+                relative_attention_num_buckets=relative_attention_num_buckets,
+                relative_attention_max_distance=relative_attention_max_distance,
+                device=device,
+                dtype=dtype,
+            )
+            self.norm2 = T5LayerNorm(d_model)
+            self.dropout3 = nn.Dropout(dropout)
+            self.dropout4 = nn.Dropout(dropout)
+
+    def forward(
+        self,
+        encoder_tokens: Tensor,
+        decoder_tokens: Tensor = None,
+        encoder_mask: Optional[Tensor] = None,
+        decoder_mask: Optional[Tensor] = None,
+    ) -> Dict[str, Union[Tensor, Tuple[Tensor]]]:
+        r"""Pass the inputs (and mask) through the decoder layer in turn.
+        Args:
+            encoder_tokens: Tokenized input sequence to the encoder.
+                Must be batch first with shape (B, Ne) where B is the batch size and Ne is the
+                encoder input sequence length. (required).
+            decoder_tokens: Tokenized input sequence to the decoder.
+                Must be batch first with shape (B, Nd) where B is the batch size and Nd is the
+                decoder input sequence length. (required).
+            encoder_mask: Self-attention mask for the encoder input sequence.
+                Must have shape (Ne, Ne) (optional).
+            decoder_mask: Self-attention mask for the decoder input sequence.
+                Must have shape (Nd, Nd) (optional).
+        Returns:
+            encoder_output: Output Tensor from the final layer of the encoder
+            encoder_hidden_states: Tuple of output Tensors from each layer of the encoder
+            encoder_position_bias: Tensor of relative attention bias computed for input sequence to encoder
+            encoder_sa_scores: Tuple of self-attention scores computed at each layer of the encoder
+            decoder_output: Output Tensor from the final layer of the decoder
+            decoder_hidden_states: Tuple of output Tensors from each layer of the decoder
+            decoder_position_bias: Tensor of relative attention bias computed for input sequence to decoder
+            encoder_sa_scores: Tuple of self-attention scores computed at each layer of the decoder
+            encoder_ca_scores: Tuple of cross-attention scores computed at each layer of the decoder
+        """
+        encoder_padding_mask = encoder_tokens.eq(self.padding_idx)
+        encoder_embeddings = self.dropout1(self.token_embeddings(encoder_tokens))
+        encoder_output, encoder_hidden_states, encoder_position_bias, encoder_sa, _ = self.encoder(
+            encoder_embeddings, tgt_mask=encoder_mask, tgt_key_padding_mask=encoder_padding_mask
+        )
+
+        encoder_output = self.norm1(encoder_output)
+        encoder_output = self.dropout2(encoder_output)
+        encoder_hidden_states = encoder_hidden_states + (encoder_output,)
+
+        if not self.encoder_only:
+            assert decoder_tokens is not None
+            if decoder_mask is None:
+                tgt_len = decoder_tokens.shape[1]
+                decoder_mask = torch.triu(torch.ones((tgt_len, tgt_len), dtype=torch.float64), diagonal=1).bool()
+
+            decoder_padding_mask = decoder_tokens.eq(self.padding_idx)
+            # T5 implemention uses padding idx to start sequence. Want to ignore this when masking
+            decoder_padding_mask[:, 0] = False
+
+            decoder_embeddings = self.dropout3(self.token_embeddings(decoder_tokens))
+            decoder_output, decoder_hidden_states, decoder_position_bias, decoder_sa, decoder_ca = self.decoder(
+                decoder_embeddings,
+                memory=encoder_output,
+                tgt_mask=decoder_mask,
+                memory_mask=encoder_mask,
+                tgt_key_padding_mask=decoder_padding_mask,
+                memory_key_padding_mask=encoder_padding_mask,
+            )
+
+            decoder_output = self.norm2(decoder_output)
+            decoder_output = self.dropout4(decoder_output)
+            decoder_hidden_states = decoder_hidden_states + (decoder_output,)
+
+            t5_output = {
+                "encoder_output": encoder_output,
+                "encoder_hidden_states": encoder_hidden_states,
+                "encoder_position_bias": encoder_position_bias,
+                "encoder_sa_scores": encoder_sa,
+                "decoder_output": decoder_output,
+                "decoder_hidden_states": decoder_hidden_states,
+                "decoder_position_bias": decoder_position_bias,
+                "decoder_sa_scores": decoder_sa,
+                "decoder_ca_scores": decoder_ca,
+            }
+        else:
+            t5_output = {
+                "encoder_output": encoder_output,
+                "encoder_hidden_states": encoder_hidden_states,
+                "encoder_position_bias": encoder_position_bias,
+                "encoder_sa_scores": encoder_sa,
+            }
+
+        return t5_output