Refactoring AssistedCandidateGenerator for Improved Modularity and Reusability

src/transformers/generation/candidate_generator.py

@@ -208,56 +208,15 @@ def get_candidates(self, input_ids: torch.LongTensor) -> Tuple[torch.LongTensor,
             vocabulary_size)` containing the logits associated to each candidate.
         """
         input_ids = input_ids.to(self.assistant_model.device)
-
-        # Don't generate more than `max_length - 1` candidates since the target model generates one extra token.
-        new_cur_len = input_ids.shape[-1]
-        max_new_tokens = min(int(self.num_assistant_tokens), self.generation_config.max_length - new_cur_len - 1)
-        min_new_tokens = max(min(max_new_tokens, self.main_model_min_length - new_cur_len), 0)
+        # Calculate new tokens to generate
+        min_new_tokens, max_new_tokens = self._calculate_new_tokens(input_ids)
         if max_new_tokens == 0:
             return input_ids, None
-
-        # 1. If it is not the first round of candidate generation, prepare the inputs based on the input_ids length
-        # (which implicitly contains the number of accepted candidates from the previous round)
-        has_past_key_values = self.assistant_kwargs.get("past_key_values", None) is not None
-        if has_past_key_values:
-            new_cache_size = new_cur_len - 1
-            self.assistant_kwargs["past_key_values"] = _crop_past_key_values(
-                self.assistant_model, self.assistant_kwargs["past_key_values"], new_cache_size - 1
-            )  # the assistant does not have the token after the last match, hence the -1
-
-            self.assistant_kwargs = _prepare_attention_mask(
-                self.assistant_kwargs, new_cur_len, self.assistant_model.config.is_encoder_decoder
-            )
-            self.assistant_kwargs = _prepare_token_type_ids(self.assistant_kwargs, new_cur_len)
-
-        # 2. Forecast next N tokens using the assistant model.
-        assistant_generation_kwargs = {
-            self.input_ids_key: input_ids,
-            "min_new_tokens": min_new_tokens,
-            "max_new_tokens": max_new_tokens,
-            "generation_config": self.generation_config,
-            "logits_processor": self.logits_processor,
-        }
-
-        assistant_output = self.assistant_model.generate(**assistant_generation_kwargs, **self.assistant_kwargs)
-
-        # 3. Update variables for the next round of candidate generation
-        self.assistant_kwargs["past_key_values"] = assistant_output.past_key_values
-
-        if (
-            is_sklearn_available()
-            and self.assistant_model.generation_config.assistant_confidence_threshold
-            and type(self) is AssistedCandidateGenerator
-        ):
-            scores_tensor = torch.cat(assistant_output.scores, dim=0)
-            scores_softmax = torch.softmax(scores_tensor, dim=-1)
-            ids = assistant_output.sequences[-1, -len(assistant_output.scores) :]
-            p = scores_softmax[range(len(ids)), ids]
-            self.probs.extend(p.tolist())
-
-        # 4. Prepare variables for output
-        candidate_logits = torch.stack(assistant_output.scores, dim=1)
-        candidate_ids = assistant_output.sequences
+        # Update past key values and masks
+        self._update_past_and_masks(input_ids)
+        # Generate candidates
+        generation_args = self._prepare_generation_args(input_ids, min_new_tokens, max_new_tokens)
+        candidate_ids, candidate_logits = self._generate_candidates(generation_args)
         return candidate_ids, candidate_logits
 
     def update_candidate_strategy(self, input_ids: torch.LongTensor, scores: torch.FloatTensor, num_matches: int):
@@ -318,6 +277,55 @@ def update_candidate_strategy(self, input_ids: torch.LongTensor, scores: torch.F
 
                 self.assistant_model.generation_config.assistant_confidence_threshold = best_threshold
 
+    def _calculate_new_tokens(self, input_ids: torch.LongTensor) -> Tuple[int, int]:
+        """Calculate the minimum and maximum number of new tokens to generate."""
+        new_cur_len = input_ids.shape[-1]
+        max_new_tokens = min(int(self.num_assistant_tokens), self.generation_config.max_length - new_cur_len - 1)
+        min_new_tokens = max(min(max_new_tokens, self.main_model_min_length - new_cur_len), 0)
+        return min_new_tokens, max_new_tokens
+
+    def _update_past_and_masks(self, input_ids: torch.LongTensor, remove_from_pkv: int = 0) -> bool:
+        """Update past key values and attention masks for subsequent generation rounds."""
+        has_past_key_values = self.assistant_kwargs.get("past_key_values", None) is not None
+        if has_past_key_values:
+            new_cache_size = input_ids.shape[-1] - 1 - remove_from_pkv
+            self.assistant_kwargs["past_key_values"] = _crop_past_key_values(
+                self.assistant_model, self.assistant_kwargs["past_key_values"], new_cache_size - 1
+            )
+            self.assistant_kwargs = _prepare_attention_mask(
+                self.assistant_kwargs, input_ids.shape[-1], self.assistant_model.config.is_encoder_decoder
+            )
+            self.assistant_kwargs = _prepare_token_type_ids(self.assistant_kwargs, input_ids.shape[-1])
+        return has_past_key_values
+
+    def _prepare_generation_args(self, input_ids: torch.LongTensor, min_new_tokens: int, max_new_tokens: int) -> Dict:
+        """Prepare arguments for the generation call."""
+        return {
+            self.input_ids_key: input_ids,
+            "min_new_tokens": min_new_tokens,
+            "max_new_tokens": max_new_tokens,
+            "generation_config": self.generation_config,
+            "logits_processor": self.logits_processor,
+        }
+
+    def _generate_candidates(self, generation_args: Dict) -> Tuple[torch.LongTensor, Optional[torch.FloatTensor]]:
+        """Generate candidate sequences using the assistant model."""
+        assistant_output = self.assistant_model.generate(**generation_args, **self.assistant_kwargs)
+        self.assistant_kwargs["past_key_values"] = assistant_output.past_key_values
+        if (
+            is_sklearn_available()
+            and self.assistant_model.generation_config.assistant_confidence_threshold
+            and type(self) is AssistedCandidateGenerator
+        ):
+            scores_tensor = torch.cat(assistant_output.scores, dim=0)
+            scores_softmax = torch.softmax(scores_tensor, dim=-1)
+            ids = assistant_output.sequences[-1, -len(assistant_output.scores) :]
+            p = scores_softmax[range(len(ids)), ids]
+            self.probs.extend(p.tolist())
+        candidate_logits = torch.stack(assistant_output.scores, dim=1)
+        candidate_ids = assistant_output.sequences
+        return candidate_ids, candidate_logits
+
 
 class AssistedCandidateGeneratorDifferentTokenizers(AssistedCandidateGenerator):
     """
@@ -367,6 +375,7 @@ def __init__(
 
         self.target_tokenizer = target_tokenizer
         self.assistant_tokenizer = assistant_tokenizer
+        self.prev_target_ids_len: Optional[int] = None
         self.prev_assistant_ids = None
         self.target_lookbehind = assistant_model.generation_config.target_lookbehind
         self.assistant_lookbehind = assistant_model.generation_config.assistant_lookbehind
@@ -497,27 +506,50 @@ def get_candidates(self, input_ids: torch.LongTensor) -> Tuple[torch.LongTensor,
             return input_ids, None
 
         input_ids = input_ids.to(self.assistant_model.device)
+        remove_from_pkv = 0
+
+        assistant_input_ids, remove_from_pkv = self._prepare_assistant_input_ids(input_ids)
+        self.prev_assistant_ids = assistant_input_ids
+
+        min_new_tokens = max(min(max_new_tokens, self.main_model_min_length - assistant_input_ids.shape[-1]), 0)
+
+        self._update_past_and_masks(assistant_input_ids, remove_from_pkv)
+        generation_args = self._prepare_generation_args(assistant_input_ids, min_new_tokens, max_new_tokens)
+        self.assistant_kwargs.pop("attention_mask", None)
+
+        assistant_output = self.assistant_model.generate(**generation_args, **self.assistant_kwargs)
+        new_target_ids = self._process_assistant_outputs(input_ids, assistant_output.sequences, assistant_input_ids)
+
+        # Update state
+        self.prev_target_ids_len = input_ids.shape[1]
+        self.assistant_kwargs["past_key_values"] = assistant_output.past_key_values
+        self.prev_assistant_ids = assistant_output.sequences
+
+        if self.prev_target_ids_len >= new_target_ids.shape[1]:
+            return input_ids, None
+
+        return new_target_ids, None
+
+    def _prepare_assistant_input_ids(self, input_ids: torch.LongTensor) -> Tuple[torch.LongTensor, int]:
+        """Converts target input IDs to assistant input IDs, handling discrepancies."""
         convert_kwargs = {
             "source_tokenizer": self.target_tokenizer,
             "destination_tokenizer": self.assistant_tokenizer,
         }
         remove_from_pkv = 0
 
-        # Since re-encoding the tokens may result in tokenization discrepancies, we use 2 look behind values
-        # (one for each conversion) which mark where to start looking for the overlap between the
-        # source and target encodings, to ensure the new tokens include the correct prompt suffix.
-        if self.prev_assistant_ids is not None and input_ids.shape[1] > self.target_lookbehind:
+        if self.prev_assistant_ids is not None and self.prev_target_ids_len > self.target_lookbehind:
             # input_ids contains all target prompt input ids and some new target input ids
-            start_index_in_target_window = input_ids.shape[1] - self.target_lookbehind
+            start_index_in_target_window = self.prev_target_ids_len - self.target_lookbehind
 
             new_assistant_ids = self.convert_source_tokens_to_target_tokens(
                 input_ids[:, start_index_in_target_window:], **convert_kwargs
             )
             prompt_use_length = new_assistant_ids.shape[1]
             prompt_use = self.prev_assistant_ids[:, -prompt_use_length:]
 
-            discrepancy_length, new_tokens_only, discrepancy_only = (
-                AssistedCandidateGeneratorDifferentTokenizers._get_tokens_diag(prompt_use, new_assistant_ids)
+            discrepancy_length, new_tokens_only, discrepancy_only = self._get_tokens_diag(
+                prompt_use, new_assistant_ids
             )
             assistant_input_ids = self.prev_assistant_ids
 
@@ -538,58 +570,29 @@ def get_candidates(self, input_ids: torch.LongTensor) -> Tuple[torch.LongTensor,
             else:
                 # edge case: in case of no intersection between prompt and new_assistant_ids
                 assistant_input_ids = torch.cat([assistant_input_ids, new_assistant_ids], dim=-1)
-
         else:
             assistant_input_ids = self.convert_source_tokens_to_target_tokens(input_ids, **convert_kwargs)
+            self.prev_target_ids_len = input_ids.shape[1]
 
-        self.prev_assistant_ids = assistant_input_ids
-        new_cur_len = assistant_input_ids.shape[-1]
-        min_new_tokens = max(min(max_new_tokens, self.main_model_min_length - new_cur_len), 0)
-
-        # 1. If it is not the first round of candidate generation, prepare the inputs based on the input_ids length
-        # (which implicitly contains the number of accepted candidates from the previous round)
-        has_past_key_values = self.assistant_kwargs.get("past_key_values", None) is not None
-        if has_past_key_values:
-            new_cache_size = new_cur_len - 1 - remove_from_pkv
-            self.assistant_kwargs["past_key_values"] = _crop_past_key_values(
-                self.assistant_model, self.assistant_kwargs["past_key_values"], new_cache_size - 1
-            )  # the assistant does not have the token after the last match, hence the -1
-
-            self.assistant_kwargs = _prepare_attention_mask(
-                self.assistant_kwargs, new_cur_len, self.assistant_model.config.is_encoder_decoder
-            )
-            self.assistant_kwargs = _prepare_token_type_ids(self.assistant_kwargs, new_cur_len)
-
-        # 2. Forecast next N tokens using the assistant model.
-        assistant_generation_kwargs = {
-            self.input_ids_key: assistant_input_ids,
-            "min_new_tokens": min_new_tokens,
-            "max_new_tokens": max_new_tokens,
-            "generation_config": self.generation_config,
-            "logits_processor": self.logits_processor,
-        }
-
-        self.assistant_kwargs.pop("attention_mask", None)
-
-        assistant_output = self.assistant_model.generate(**assistant_generation_kwargs, **self.assistant_kwargs)
+        return assistant_input_ids, remove_from_pkv
 
+    def _process_assistant_outputs(
+        self, input_ids: torch.LongTensor, assistant_sequences: torch.LongTensor, assistant_input_ids: torch.LongTensor
+    ) -> torch.LongTensor:
+        """Processes assistant outputs to obtain target input IDs."""
         num_prev_assistant = self.prev_assistant_ids.shape[1]
         start_assistant_look_index = num_prev_assistant - self.assistant_lookbehind
-        if start_assistant_look_index < 0:
-            start_assistant_look_index = 0
 
         new_target_ids_from_window = self.convert_source_tokens_to_target_tokens(
-            assistant_output.sequences[:, start_assistant_look_index:],
+            assistant_sequences[:, start_assistant_look_index:],
             source_tokenizer=self.assistant_tokenizer,
             destination_tokenizer=self.target_tokenizer,
         )
         target_prompt_use_length = new_target_ids_from_window.shape[1]
 
         target_prompt_use = input_ids[:, -target_prompt_use_length:]
 
-        _, target_new_tokens_only, _ = AssistedCandidateGeneratorDifferentTokenizers._get_tokens_diag(
-            target_prompt_use, new_target_ids_from_window
-        )
+        _, target_new_tokens_only, _ = self._get_tokens_diag(target_prompt_use, new_target_ids_from_window)
 
         new_target_ids = input_ids
 
@@ -603,14 +606,7 @@ def get_candidates(self, input_ids: torch.LongTensor) -> Tuple[torch.LongTensor,
         if hasattr(self.generation_config, "max_length"):
             new_target_ids = new_target_ids[:, : self.generation_config.max_length]
 
-        # 3. Update variables for the next round of candidate generation
-        self.assistant_kwargs["past_key_values"] = assistant_output.past_key_values
-
-        # 4. Prepare variables for output
-        if input_ids.shape[1] >= new_target_ids.shape[1]:
-            return input_ids, None
-
-        return new_target_ids, None
+        return new_target_ids
 
 
 class PromptLookupCandidateGenerator(CandidateGenerator):

tests/generation/test_candidate_generator.py

@@ -0,0 +1,43 @@
+import unittest
+
+import numpy as np
+
+from transformers.generation.candidate_generator import AssistedCandidateGeneratorDifferentTokenizers
+
+
+class TestAssistedCandidateGeneratorDifferentTokenizers(unittest.TestCase):
+    def test_no_intersection(self):
+        prompt = np.array([[1, 2, 3]])
+        prompt_plus_new_tokens = np.array([[4, 5, 6]])
+        result = AssistedCandidateGeneratorDifferentTokenizers._get_tokens_diag(prompt, prompt_plus_new_tokens)
+        self.assertEqual(result, (None, None, None))
+
+    def test_complete_overlap(self):
+        prompt = np.array([[1, 2, 3]])
+        prompt_plus_new_tokens = np.array([[1, 2, 3, 4, 5]])
+        discrep_length, new_tokens_only, discrep_only = AssistedCandidateGeneratorDifferentTokenizers._get_tokens_diag(
+            prompt, prompt_plus_new_tokens
+        )
+        self.assertEqual(discrep_length, 0)
+        np.testing.assert_array_equal(new_tokens_only, np.array([[4, 5]]))
+        np.testing.assert_array_equal(discrep_only, np.array([[]]))
+
+    def test_partial_overlap(self):
+        prompt = np.array([[1, 2, 3]])
+        prompt_plus_new_tokens = np.array([[2, 3, 4, 5]])
+        discrep_length, new_tokens_only, discrep_only = AssistedCandidateGeneratorDifferentTokenizers._get_tokens_diag(
+            prompt, prompt_plus_new_tokens
+        )
+        self.assertEqual(discrep_length, 0)
+        np.testing.assert_array_equal(new_tokens_only, np.array([[4, 5]]))
+        np.testing.assert_array_equal(discrep_only, np.array([[]]))
+
+    def test_no_new_tokens(self):
+        prompt = np.array([[1, 2, 3]])
+        prompt_plus_new_tokens = np.array([[1, 2, 3]])
+        discrep_length, new_tokens_only, discrep_only = AssistedCandidateGeneratorDifferentTokenizers._get_tokens_diag(
+            prompt, prompt_plus_new_tokens
+        )
+        self.assertEqual(discrep_length, 0)
+        np.testing.assert_array_equal(new_tokens_only, np.array([[]]))
+        np.testing.assert_array_equal(discrep_only, np.array([[]]))