Fix symbolic_trace with kv cache (#28724)

* fix symbolic_trace with kv cache

* comment & better test

src/transformers/utils/fx.py

@@ -765,7 +765,7 @@ class HFTracer(Tracer):
             )
 
     def _generate_dummy_input(
-        self, model: PreTrainedModel, input_name: str, shape: List[int]
+        self, model: PreTrainedModel, input_name: str, shape: List[int], input_names: List[str]
     ) -> Dict[str, torch.Tensor]:
         """Generates dummy input for model inference recording."""
         # Retrieving the model class, either from the "class_for_deserialization" attribute if the model was restored
@@ -774,6 +774,11 @@ class HFTracer(Tracer):
         device = model.device
         inputs_dict = {}
 
+        # when tracing a model with KV cache, we simply need to unsure that the KV cache length is larger than one to
+        # rightfully pass certain controlflows (Example: https://github.com/huggingface/transformers/blob/5c8d941d66734811d2ef6f57f15b44f7fb7a98c4/src/transformers/modeling_attn_mask_utils.py#L162).
+        # After tracing, the model can then still be used with arbitrary lengths different than the one used during tracing.
+        kv_cache_length = 5
+
         if input_name in ["labels", "start_positions", "end_positions"]:
             batch_size = shape[0]
             if model_class_name in [
@@ -883,7 +888,14 @@ class HFTracer(Tracer):
             # Generating big sequence length for audio inputs.
             seq_length = _generate_random_int(low=10000, high=20000)
             inputs_dict[input_name] = torch.zeros(batch_size, seq_length, dtype=torch.float, device=device)
-        elif "mask" in input_name or "ids" in input_name:
+        elif "mask" in input_name:
+            if "past_key_values" in input_names:
+                mask_shape = [shape[0], shape[1] + kv_cache_length]
+            else:
+                mask_shape = shape
+
+            inputs_dict[input_name] = torch.zeros(mask_shape, dtype=torch.long, device=device)
+        elif "ids" in input_name:
             inputs_dict[input_name] = torch.zeros(shape, dtype=torch.long, device=device)
         elif "past_key_values" in input_name:
             if model.config.model_type not in _FX_SUPPORTED_MODELS_WITH_KV_CACHE:
@@ -893,7 +905,7 @@ class HFTracer(Tracer):
             num_heads = model.config.num_attention_heads
             head_dim = model.config.hidden_size // model.config.num_attention_heads
 
-            cache_shape = (shape[0], num_heads, 0, head_dim)
+            cache_shape = (shape[0], num_heads, kv_cache_length, head_dim)
             pkv = tuple(
                 (
                     torch.rand(cache_shape, dtype=torch.float, device=device),
@@ -1095,7 +1107,7 @@ class HFTracer(Tracer):
             if isinstance(root, self.supported_archs) or type(root).__qualname__.startswith(
                 ("_deserialize_graph_module", "_CodeOnlyModule")
             ):
-                inputs.update(self._generate_dummy_input(root, input_name, shape))
+                inputs.update(self._generate_dummy_input(root, input_name, shape, input_names=input_names))
             else:
                 raise RuntimeError(
                     f"Could not generate input named {input_name} for because root is not a"

tests/test_modeling_common.py

@@ -1053,7 +1053,9 @@ class ModelTesterMixin:
             model.eval()
             inputs = self._prepare_for_class(inputs_dict, model_class, return_labels=output_loss)
 
-            try:
+            # We may want to test several inputs (various shapes, etc.).
+            inputs_to_test = [inputs]
+
             if model.config.is_encoder_decoder:
                 model.config.use_cache = False  # FSTM still requires this hack -> FSTM should probably be refactored similar to BART afterward
                 labels = inputs.get("labels", None)
@@ -1067,14 +1069,6 @@ class ModelTesterMixin:
                 ]
                 if labels is not None:
                     input_names.append("labels")
-
-                    filtered_inputs = {k: v for (k, v) in inputs.items() if k in input_names}
-                    input_names = list(filtered_inputs.keys())
-
-                    model_output = model(**filtered_inputs)
-
-                    traced_model = symbolic_trace(model, input_names)
-                    traced_output = traced_model(**filtered_inputs)
             else:
                 input_names = [
                     "attention_mask",
@@ -1108,7 +1102,7 @@ class ModelTesterMixin:
                         head_dim = model.config.hidden_size // model.config.num_attention_heads
 
                         cache_shape = (batch_size, num_heads, 0, head_dim)
-                            pkv = tuple(
+                        empty_pkv = tuple(
                             (
                                 torch.rand(cache_shape, dtype=torch.float, device=torch_device),
                                 torch.rand(cache_shape, dtype=torch.float, device=torch_device),
@@ -1116,9 +1110,30 @@ class ModelTesterMixin:
                             for i in range(model.config.num_hidden_layers)
                         )
 
-                            inputs["past_key_values"] = pkv
+                        cache_length = 9
+                        cache_shape = (batch_size, num_heads, cache_length, head_dim)
+                        non_empty_pkv = tuple(
+                            (
+                                torch.rand(cache_shape, dtype=torch.float, device=torch_device),
+                                torch.rand(cache_shape, dtype=torch.float, device=torch_device),
+                            )
+                            for i in range(model.config.num_hidden_layers)
+                        )
 
-                    filtered_inputs = {k: v for (k, v) in inputs.items() if k in input_names}
+                        inps = copy.deepcopy(inputs_to_test[0])
+
+                        inputs_to_test[0]["past_key_values"] = empty_pkv
+
+                        inps["past_key_values"] = non_empty_pkv
+                        inputs_to_test.append(inps)
+
+                        past_mask = torch.ones(batch_size, cache_length, device=torch_device, dtype=torch.float)
+                        inputs_to_test[1]["attention_mask"] = torch.cat(
+                            (past_mask, inputs_to_test[1]["attention_mask"]), dim=1
+                        )
+
+            for inps in inputs_to_test:
+                filtered_inputs = {k: v for (k, v) in inps.items() if k in input_names}
                 input_names = list(filtered_inputs.keys())
 
                 if model.__class__.__name__ in set(MODEL_FOR_SEQUENCE_CLASSIFICATION_MAPPING_NAMES.values()) and (
@@ -1132,9 +1147,6 @@ class ModelTesterMixin:
                     traced_output = traced_model(**filtered_inputs)
                     model_output = model(**filtered_inputs)
 
-            except Exception as e:
-                self.fail(f"Couldn't trace module: {e}")
-
                 def flatten_output(output):
                     flatten = []
                     for x in output: