Update past_key_values in GPT-2

src/transformers/generation_utils.py

@@ -503,18 +503,10 @@ def _update_model_kwargs_for_generation(
 
         return model_kwargs
 
-    @staticmethod
-    def _reorder_cache(past: Tuple[torch.Tensor], beam_idx: torch.Tensor) -> Tuple[torch.Tensor]:
-        """
-        This function is used to re-order the :obj:`past_key_values` or :obj:`mems` cache if
-        :meth:`~transformers.PretrainedModel.beam_search` or :meth:`~transformers.PretrainedModel.beam_sample` is
-        called. This is required to match :obj:`past_key_values` or :obj:`mems` with the correct beam_idx at every
-        generation step.
-
-        For custom re-ordering of :obj:`past_key_values` or :obj:`mems`, the function should be implemented in
-        subclasses of :class:`~transformers.PreTrainedModel`.
-        """
-        return tuple(layer_past.index_select(1, beam_idx.to(layer_past.device)) for layer_past in past)
+    def _reorder_cache(self, past, beam_idx):
+        raise NotImplementedError(
+            f"Make sure that a `_reorder_cache` function is correctly implemented in {self.__class__.__module__} to enable beam search for {self.__class__}"
+        )
 
     def _get_logits_warper(
         self, top_k: int = None, top_p: float = None, temperature: float = None, num_beams: int = None

src/transformers/models/ctrl/modeling_ctrl.py

@@ -15,6 +15,8 @@
 # limitations under the License.
 """ PyTorch CTRL model."""
 
+from typing import Tuple
+
 import numpy as np
 import torch
 import torch.nn as nn
@@ -262,7 +264,7 @@ def _init_weights(self, module):
             details.
 
             `What are input IDs? <../glossary.html#input-ids>`__
-        past_key_values (:obj:`List[torch.FloatTensor]` of length :obj:`config.n_layers`):
+        past_key_values (:obj:`Tuple[Tuple[torch.FloatTensor]]` of length :obj:`config.n_layers`):
             Contains pre-computed hidden-states (key and values in the attention blocks) as computed by the model (see
             :obj:`past_key_values` output below). Can be used to speed up sequential decoding. The ``input_ids`` which
             have their past given to this model should not be passed as input ids as they have already been computed.
@@ -389,7 +391,7 @@ def forward(
 
         if past_key_values is None:
             past_length = 0
-            past_key_values = [None] * len(self.h)
+            past_key_values = tuple([None] * len(self.h))
         else:
             past_length = past_key_values[0][0].size(-2)
         if position_ids is None:
@@ -575,6 +577,18 @@ def forward(
             attentions=transformer_outputs.attentions,
         )
 
+    @staticmethod
+    def _reorder_cache(past: Tuple[Tuple[torch.Tensor]], beam_idx: torch.Tensor) -> Tuple[Tuple[torch.Tensor]]:
+        """
+        This function is used to re-order the :obj:`past_key_values` cache if
+        :meth:`~transformers.PretrainedModel.beam_search` or :meth:`~transformers.PretrainedModel.beam_sample` is
+        called. This is required to match :obj:`past_key_values` with the correct beam_idx at every generation step.
+        """
+        return tuple(
+            tuple(past_state.index_select(0, beam_idx.to(past_state.device)) for past_state in layer_past)
+            for layer_past in past
+        )
+
 
 @add_start_docstrings(
     """

src/transformers/models/gpt2/modeling_gpt2.py

@@ -17,7 +17,7 @@
 
 import os
 from dataclasses import dataclass
-from typing import List, Optional, Tuple
+from typing import Optional, Tuple
 
 import torch
 import torch.nn as nn
@@ -232,7 +232,7 @@ def forward(
             value = torch.cat((past_value, value), dim=-2)
 
         if use_cache is True:
-            present = torch.stack((key.transpose(-2, -1), value))  # transpose to have same shapes for stacking
+            present = (key.transpose(-2, -1), value)  # transpose to have same shapes
         else:
             present = None
 
@@ -369,9 +369,9 @@ class GPT2DoubleHeadsModelOutput(ModelOutput):
             Prediction scores of the language modeling head (scores for each vocabulary token before SoftMax).
         mc_logits (:obj:`torch.FloatTensor` of shape :obj:`(batch_size, num_choices)`):
             Prediction scores of the multiple choice classification head (scores for each choice before SoftMax).
-        past_key_values (:obj:`List[torch.FloatTensor]`, `optional`, returned when ``use_cache=True`` is passed or when ``config.use_cache=True``):
-            List of :obj:`torch.FloatTensor` of length :obj:`config.n_layers`, with each tensor of shape :obj:`(2,
-            batch_size, num_heads, sequence_length, embed_size_per_head)`).
+        past_key_values (:obj:`Tuple[Tuple[torch.Tensor]]`, `optional`, returned when ``use_cache=True`` is passed or when ``config.use_cache=True``):
+            Tuple of length :obj:`config.n_layers`, containing tuples of tensors of shape :obj:`(batch_size, num_heads,
+            sequence_length, embed_size_per_head)`).
 
             Contains pre-computed hidden-states (key and values in the attention blocks) that can be used (see
             :obj:`past_key_values` input) to speed up sequential decoding.
@@ -392,7 +392,7 @@ class GPT2DoubleHeadsModelOutput(ModelOutput):
     mc_loss: Optional[torch.FloatTensor] = None
     logits: torch.FloatTensor = None
     mc_logits: torch.FloatTensor = None
-    past_key_values: Optional[List[torch.FloatTensor]] = None
+    past_key_values: Optional[Tuple[Tuple[torch.FloatTensor]]] = None
     hidden_states: Optional[Tuple[torch.FloatTensor]] = None
     attentions: Optional[Tuple[torch.FloatTensor]] = None
 
@@ -418,7 +418,7 @@ class GPT2DoubleHeadsModelOutput(ModelOutput):
     Args:
         input_ids (:obj:`torch.LongTensor` of shape :obj:`(batch_size, input_ids_length)`):
             :obj:`input_ids_length` = ``sequence_length`` if :obj:`past_key_values` is ``None`` else
-            ``past_key_values[0].shape[-2]`` (``sequence_length`` of input past key value states). Indices of input
+            ``past_key_values[0][0].shape[-2]`` (``sequence_length`` of input past key value states). Indices of input
             sequence tokens in the vocabulary.
 
             If :obj:`past_key_values` is used, only ``input_ids`` that do not have their past calculated should be
@@ -429,7 +429,7 @@ class GPT2DoubleHeadsModelOutput(ModelOutput):
             details.
 
             `What are input IDs? <../glossary.html#input-ids>`__
-        past_key_values (:obj:`List[torch.FloatTensor]` of length :obj:`config.n_layers`):
+        past_key_values (:obj:`Tuple[Tuple[torch.Tensor]]` of length :obj:`config.n_layers`):
             Contains precomputed hidden-states (key and values in the attention blocks) as computed by the model (see
             :obj:`past_key_values` output below). Can be used to speed up sequential decoding. The ``input_ids`` which
             have their past given to this model should not be passed as ``input_ids`` as they have already been
@@ -639,7 +639,7 @@ def forward(
 
         if past_key_values is None:
             past_length = 0
-            past_key_values = [None] * len(self.h)
+            past_key_values = tuple([None] * len(self.h))
         else:
             past_length = past_key_values[0][0].size(-2)
         if position_ids is None:
@@ -707,7 +707,7 @@ def forward(
                 torch.cuda.set_device(hidden_states.device)
                 # Ensure layer_past is on same device as hidden_states (might not be correct)
                 if layer_past is not None:
-                    layer_past = layer_past.to(hidden_states.device)
+                    layer_past = tuple(past_state.to(hidden_states.device) for past_state in layer_past)
                 # Ensure that attention_mask is always on the same device as hidden_states
                 if attention_mask is not None:
                     attention_mask = attention_mask.to(hidden_states.device)
@@ -717,18 +717,22 @@ def forward(
                 all_hidden_states = all_hidden_states + (hidden_states,)
 
             if getattr(self.config, "gradient_checkpointing", False):
+                if use_cache:
+                    raise ValueError(
+                        "When using `gradient_checkpointing, make sure that `use_cache=False` and `config.use_cache=False`."
+                    )
 
                 def create_custom_forward(module):
                     def custom_forward(*inputs):
-                        # checkpointing only works with tuple returns, not with lists
-                        return tuple(output for output in module(*inputs, use_cache, output_attentions))
+                        # None for past_key_value
+                        return module(*inputs, use_cache, output_attentions)
 
                     return custom_forward
 
                 outputs = torch.utils.checkpoint.checkpoint(
                     create_custom_forward(block),
                     hidden_states,
-                    layer_past,
+                    None,
                     attention_mask,
                     head_mask[i],
                     encoder_hidden_states,
@@ -931,6 +935,18 @@ def forward(
             cross_attentions=transformer_outputs.cross_attentions,
         )
 
+    @staticmethod
+    def _reorder_cache(past: Tuple[Tuple[torch.Tensor]], beam_idx: torch.Tensor) -> Tuple[Tuple[torch.Tensor]]:
+        """
+        This function is used to re-order the :obj:`past_key_values` cache if
+        :meth:`~transformers.PretrainedModel.beam_search` or :meth:`~transformers.PretrainedModel.beam_sample` is
+        called. This is required to match :obj:`past_key_values` with the correct beam_idx at every generation step.
+        """
+        return tuple(
+            tuple(past_state.index_select(0, beam_idx.to(past_state.device)) for past_state in layer_past)
+            for layer_past in past
+        )
+
 
 @add_start_docstrings(
     """
@@ -1094,6 +1110,18 @@ def forward(
             attentions=transformer_outputs.attentions,
         )
 
+    @staticmethod
+    def _reorder_cache(past: Tuple[Tuple[torch.Tensor]], beam_idx: torch.Tensor) -> Tuple[Tuple[torch.Tensor]]:
+        """
+        This function is used to re-order the :obj:`past_key_values` cache if
+        :meth:`~transformers.PretrainedModel.beam_search` or :meth:`~transformers.PretrainedModel.beam_sample` is
+        called. This is required to match :obj:`past_key_values` with the correct beam_idx at every generation step.
+        """
+        return tuple(
+            tuple(past_state.index_select(0, beam_idx.to(past_state.device)) for past_state in layer_past)
+            for layer_past in past
+        )
+
 
 @add_start_docstrings(
     """

src/transformers/models/transfo_xl/modeling_transfo_xl.py

@@ -1137,6 +1137,15 @@ def _resize_cutoffs(self, new_num_tokens, new_emb_size, new_embedding_shapes, la
         self.crit.cutoff_ends = [0] + new_cutoffs
         self.crit.n_token = new_num_tokens
 
+    @staticmethod
+    def _reorder_cache(mems: List[torch.Tensor], beam_idx: torch.Tensor) -> List[torch.Tensor]:
+        """
+        This function is used to re-order the :obj:`mems` cache if :meth:`~transformers.PretrainedModel.beam_search` or
+        :meth:`~transformers.PretrainedModel.beam_sample` is called. This is required to match :obj:`mems` with the
+        correct beam_idx at every generation step.
+        """
+        return [layer_past.index_select(1, beam_idx.to(layer_past.device)) for layer_past in mems]
+
 
 @add_start_docstrings(
     """

src/transformers/models/xlnet/modeling_xlnet.py

@@ -1462,6 +1462,15 @@ def forward(
             attentions=transformer_outputs.attentions,
         )
 
+    @staticmethod
+    def _reorder_cache(mems: List[torch.Tensor], beam_idx: torch.Tensor) -> List[torch.Tensor]:
+        """
+        This function is used to re-order the :obj:`mems` cache if :meth:`~transformers.PretrainedModel.beam_search` or
+        :meth:`~transformers.PretrainedModel.beam_sample` is called. This is required to match :obj:`mems` with the
+        correct beam_idx at every generation step.
+        """
+        return [layer_past.index_select(1, beam_idx.to(layer_past.device)) for layer_past in mems]
+
 
 @add_start_docstrings(
     """

tests/test_modeling_gpt2.py

@@ -131,6 +131,7 @@ def prepare_config_and_inputs(self, gradient_checkpointing=False):
             n_ctx=self.max_position_embeddings,
             # type_vocab_size=self.type_vocab_size,
             # initializer_range=self.initializer_range,
+            use_cache=not gradient_checkpointing,
             bos_token_id=self.bos_token_id,
             eos_token_id=self.eos_token_id,
             pad_token_id=self.pad_token_id,