transformers.py

# SPDX-License-Identifier: Apache-2.0
# SPDX-FileCopyrightText: Copyright contributors to the vLLM project

# Copyright 2024 The vLLM team.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""Wrapper around `transformers` models"""
from collections.abc import Iterable, Mapping
from contextlib import contextmanager
from typing import Literal, Optional, Union

import regex as re
import torch
from torch import nn
from transformers import (AutoModel, BatchFeature, PretrainedConfig,
                          PreTrainedModel)
from transformers.modeling_utils import ALL_ATTENTION_FUNCTIONS

from vllm.attention import Attention
from vllm.compilation.decorators import support_torch_compile
from vllm.config import (CacheConfig, DeviceConfig, ModelConfig,
                         ParallelConfig, VllmConfig)
from vllm.distributed import get_pp_group, get_tensor_model_parallel_world_size
from vllm.distributed.utils import get_pp_indices
from vllm.logger import init_logger
from vllm.model_executor.layers.linear import (ColumnParallelLinear,
                                               ReplicatedLinear,
                                               RowParallelLinear)
from vllm.model_executor.layers.logits_processor import LogitsProcessor
from vllm.model_executor.layers.quantization import QuantizationConfig
from vllm.model_executor.layers.vocab_parallel_embedding import (
    ParallelLMHead, VocabParallelEmbedding)
from vllm.model_executor.sampling_metadata import SamplingMetadata
from vllm.multimodal import MULTIMODAL_REGISTRY, MultiModalKwargs
from vllm.multimodal.inputs import (MultiModalDataDict, MultiModalFieldConfig,
                                    MultiModalInputs, PlaceholderRange)
from vllm.multimodal.parse import ImageProcessorItems, MultiModalDataItems
from vllm.multimodal.processing import (BaseMultiModalProcessor,
                                        BaseProcessingInfo)
from vllm.multimodal.profiling import BaseDummyInputsBuilder
from vllm.sequence import IntermediateTensors
from vllm.utils import is_list_of

from .interfaces import (SupportsLoRA, SupportsMultiModal, SupportsPP,
                         SupportsQuant)
from .utils import (AutoWeightsLoader, PPMissingLayer, WeightsMapper,
                    flatten_bn, make_empty_intermediate_tensors_factory,
                    maybe_prefix)

logger = init_logger(__name__)


def vllm_flash_attention_forward(
        # Transformers args
        module: torch.nn.Module,
        query: torch.Tensor,
        key: torch.Tensor,
        value: torch.Tensor,
        attention_mask: torch.Tensor,
        # Transformers kwargs
        scaling: Optional[float] = None,
        # vLLM kwargs
        attention_instances: Optional[dict[Attention]] = None,
        **kwargs):
    self_attn = attention_instances[module.layer_idx]
    if scaling is not None:
        self_attn.impl.scale = float(scaling)
    hidden = query.shape[-2]
    query, key, value = (x.transpose(1, 2) for x in (query, key, value))
    query, key, value = (x.reshape(hidden, -1) for x in (query, key, value))
    return self_attn.forward(query, key, value), None


ALL_ATTENTION_FUNCTIONS["vllm"] = vllm_flash_attention_forward


def log_replacement(name: str, old_module: nn.Module, new_module: nn.Module):
    logger.debug("%s: %s -> %s", name, old_module, new_module)


def replace_linear_class(
    linear: nn.Linear, style: Literal["colwise", "rowwise"],
    quant_config: QuantizationConfig
) -> Union[ColumnParallelLinear, RowParallelLinear, ReplicatedLinear]:
    """
    Replace nn.Linear with one of vLLM's tensor parallel linear classes.

    Args:
        linear (nn.Linear): `nn.Linear` to be replaced.
        style (str): Tensor parallel style of the new linear, e.g. "colwise".
        quant_config (QuantConfig): Quantization config for the new linear.
    Returns:
        Union[ColumnParallelLinear, RowParallelLinear]: The new linear.
    """

    if not isinstance(style, str):
        raise ValueError(
            f"Unsupported parallel style type {type(style)}, expected str")

    vllm_linear_cls, vllm_linear_kwargs = {
        "colwise": (ColumnParallelLinear, {}),
        "colwise_rep": (ColumnParallelLinear, {
            "gather_output": True
        }),
        "rowwise": (RowParallelLinear, {}),
        "rowwise_rep": (RowParallelLinear, {
            "input_is_parallel": False
        }),
        "replicate": (ReplicatedLinear, {}),
    }.get(style, (ReplicatedLinear, {}))

    return vllm_linear_cls(
        input_size=linear.in_features,
        output_size=linear.out_features,
        bias=linear.bias is not None,
        quant_config=quant_config,
        return_bias=False,
        **vllm_linear_kwargs,
    )


# Copied from `accelerate`
@contextmanager
def init_on_device_without_buffers(device: torch.device):
    """
    A context manager under which models are initialized with all
    parameters on the specified device. However buffers are not
    initialized on specified device.

    Args:
        device (`torch.device`):
            Device to initialize all parameters on.
    """

    old_register_parameter = nn.Module.register_parameter

    def register_empty_parameter(module, name, param):
        old_register_parameter(module, name, param)
        if param is not None:
            param_cls = type(module._parameters[name])
            kwargs = module._parameters[name].__dict__
            kwargs["requires_grad"] = param.requires_grad
            module._parameters[name] = param_cls(
                module._parameters[name].to(device), **kwargs)

    tensor_constructors_to_patch = {}

    def patch_tensor_constructor(fn):

        def wrapper(*args, **kwargs):
            kwargs["device"] = device
            return fn(*args, **kwargs)

        return wrapper

    try:
        nn.Module.register_parameter = register_empty_parameter
        for torch_function_name in tensor_constructors_to_patch:
            setattr(
                torch, torch_function_name,
                patch_tensor_constructor(getattr(torch, torch_function_name)))
        yield
    finally:
        nn.Module.register_parameter = old_register_parameter
        for torch_function_name, old_torch_function in (
                tensor_constructors_to_patch.items()):
            setattr(torch, torch_function_name, old_torch_function)


class MultiModalProcessingInfo(BaseProcessingInfo):

    def get_hf_config(self):
        return self.ctx.model_config.hf_config

    def get_supported_mm_limits(self):
        return {"image": None}

    def get_mm_max_tokens_per_item(self, seq_len, mm_counts):
        return {"image": self.get_max_image_tokens()}

    def get_max_image_tokens(self) -> int:
        width, height = self.get_max_image_size()
        processor = self.get_hf_processor()
        mm_processor_kwargs = self.ctx.model_config.mm_processor_kwargs or {}
        mm_tokens = processor._get_num_multimodal_tokens(
            image_sizes=([height, width], ), **mm_processor_kwargs)
        image_tokens = mm_tokens["num_image_tokens"][0]
        return image_tokens

    def get_max_image_size(self):
        return 10_000, 10_000  # hardcode for arbitrary very large size


class MultiModalDummyInputsBuilder(
        BaseDummyInputsBuilder[MultiModalProcessingInfo]):

    def get_dummy_text(self, mm_counts: Mapping[str, int]) -> str:
        num_images = mm_counts.get("image", 0)

        processor = self.info.get_hf_processor()
        if "gemma3" in processor.__class__.__name__.lower():
            image_token = processor.boi_token
        else:
            image_token = getattr(processor, "image_token", "")
        return image_token * num_images

    def get_dummy_mm_data(
        self,
        seq_len: int,
        mm_counts: Mapping[str, int],
    ) -> MultiModalDataDict:
        num_images = mm_counts.get("image", 0)

        target_width, target_height = self.info.get_max_image_size()

        return {
            "image":
            self._get_dummy_images(width=target_width,
                                   height=target_height,
                                   num_images=num_images),
        }


class MultiModalProcessor(BaseMultiModalProcessor[MultiModalProcessingInfo]):

    def _get_prompt_updates(
        self,
        mm_items: MultiModalDataItems,
        hf_processor_mm_kwargs: Mapping[str, object],
        out_mm_kwargs: MultiModalKwargs,
    ):
        """
        Given the original multi-modal items for this modality
        and HF-processed data, output the updates to perform.

        The information returned by this method is used to update token inputs
        which bypass the HF processor. It is also used to update the output of
        HF processor if the HF process does not apply prompt updates to text
        inputs.

        Moreover, this information is critical to determine the token positions
        in order to construct  :class:`~vllm-multimodal.input.PlaceholderRange`
        for each multi-modal item.
        """
        return None

    def _get_mm_fields_config(
        self,
        hf_inputs,
        hf_processor_mm_kwargs,
        num_image_patches: torch.Tensor = None,
    ):
        # HF Processors always return a mask but vLLM doesn't need it
        hf_inputs.pop("attention_mask", None)
        mm_fields = {
            key: MultiModalFieldConfig.flat_from_sizes("image",
                                                       num_image_patches)
            for key in hf_inputs
        }
        mm_fields["image_embeds"] = MultiModalFieldConfig.flat_from_sizes(
            "image", num_image_patches)
        mm_fields["num_image_patches"] = MultiModalFieldConfig.batched("image")
        return mm_fields

    def _apply_hf_processor_text_mm(
        self,
        prompt_text: str,
        mm_items: MultiModalDataItems,
        hf_processor_mm_kwargs: Mapping[str, object],
        tokenization_kwargs: Mapping[str, object],
    ) -> tuple[list[int], BatchFeature, bool]:
        """
        Apply the HF processor on the prompt text and multi-modal data
        together.

        In addition, return whether prompt replacements have been applied.
        """
        processor_data, passthrough_data = self._get_hf_mm_data(mm_items)
        processor_data["return_mm_token_type_ids"] = True

        processed_data = self._call_hf_processor(
            prompt=prompt_text,
            mm_data=processor_data,
            mm_kwargs=hf_processor_mm_kwargs,
            tok_kwargs=tokenization_kwargs,
        )
        processed_data.update(passthrough_data)

        prompt_ids, = processed_data.pop("input_ids").tolist()
        mm_token_type_ids = processed_data.pop(
            "mm_token_type_ids"
        ) if "mm_token_type_ids" in processed_data else processed_data.pop(
            "token_type_ids")  # for gemma3 only

        return prompt_ids, processed_data, mm_token_type_ids

    def apply(
        self,
        prompt: Union[str, list[int]],
        mm_data: MultiModalDataDict,
        hf_processor_mm_kwargs: Mapping[str, object],
        tokenization_kwargs: Optional[Mapping[str, object]] = None,
        return_mm_hashes: bool = False,
    ) -> MultiModalInputs:
        """
        Process multi-modal inputs to be used in vLLM.

        Apply HF Processor on prompt text and multi-modal data together,
        outputting token IDs and processed tensors.
        """
        if tokenization_kwargs is None:
            tokenization_kwargs = {}

        mm_items = self._to_mm_items(mm_data)
        hf_processor = self.info.get_hf_processor(**hf_processor_mm_kwargs)
        if not isinstance(prompt, str):
            # the prompt is the tokenized ids which is not supported
            # by the hf_processor, which is why we would need to decode the ids
            # into string
            prompt = hf_processor.decode(prompt)

        (prompt_ids, processed_data,
         mm_token_type_ids) = self._apply_hf_processor_text_mm(
             prompt_text=prompt,
             mm_items=mm_items,
             hf_processor_mm_kwargs=hf_processor_mm_kwargs,
             tokenization_kwargs=tokenization_kwargs,
         )

        # HF processor will return `mm_token_type_ids` from which
        # we can infer mm_placeholders. Until then hardcode to make code run
        # Below tested on Llava. Prompts and `mm_token_type_ids` are always bs=1
        mm_positions = torch.where(mm_token_type_ids == 1)[1]
        images = mm_items.get_items("image", ImageProcessorItems)
        mm_processor_kwargs = (self.info.ctx.model_config.mm_processor_kwargs
                               or {})
        image_sizes = []
        for item_idx in range(len(images)):
            image_size = images.get_image_size(item_idx)
            image_sizes.append((image_size.height, image_size.width))

        mm_tokens_per_modality = hf_processor._get_num_multimodal_tokens(
            image_sizes=image_sizes, **mm_processor_kwargs)

        mm_placeholders = {}
        split_sizes = mm_tokens_per_modality["num_image_tokens"]
        if split_sizes:
            chunked_mm_positions = torch.split(mm_positions, split_sizes)
            mm_tokens = torch.tensor(prompt_ids)[mm_token_type_ids[0].bool()]
            chunked_mm_tokens = torch.split(mm_tokens, split_sizes)
            ranges = [
                PlaceholderRange(
                    offset=positions[0].item(),
                    length=positions.shape[0],
                    is_embed=(mm_tokens == hf_processor.image_token_id).bool())
                for positions, mm_tokens in zip(chunked_mm_positions,
                                                chunked_mm_tokens)
            ]
            mm_placeholders = {"image": ranges}

        num_image_patches = torch.tensor(
            mm_tokens_per_modality["num_image_patches"]
        ) if "num_image_patches" in mm_tokens_per_modality else None
        processed_data['num_image_patches'] = num_image_patches
        mm_kwargs = MultiModalKwargs.from_hf_inputs(
            processed_data,
            self._get_mm_fields_config(processed_data, hf_processor_mm_kwargs,
                                       num_image_patches),
        )

        mm_hashes = self._hash_mm_items(mm_items, hf_processor_mm_kwargs,
                                        tokenization_kwargs)
        return MultiModalInputs(
            type="multimodal",
            prompt=prompt,
            prompt_token_ids=prompt_ids,
            mm_kwargs=mm_kwargs,
            mm_hashes=mm_hashes,
            mm_placeholders=mm_placeholders,
        )


class TransformersBase(nn.Module, SupportsQuant, SupportsLoRA, SupportsPP):
    embedding_padding_modules = ["lm_head"]
    embedding_modules = ["embed_tokens"
                         ]  # TODO transformers will have a util to get it

    def __init__(self, *, vllm_config: VllmConfig, prefix: str = ""):
        super().__init__()
        logger.info("Using Transformers backend.")

        self.config: PretrainedConfig = vllm_config.model_config.hf_config
        self.text_config: PretrainedConfig = self.config.get_text_config()
        self.cache_config: CacheConfig = vllm_config.cache_config
        self.device_config: DeviceConfig = vllm_config.device_config
        self.model_config: ModelConfig = vllm_config.model_config
        self.parallel_config: ParallelConfig = vllm_config.parallel_config
        self.quant_config: QuantizationConfig = vllm_config.quant_config

        self.pp_group = get_pp_group()
        self.pp_size = self.pp_group.world_size
        self.pp_rank = self.pp_group.rank_in_group
        self.tp_size = get_tensor_model_parallel_world_size()

        # To be updated in child classes for use in `load_weights`
        self.skip_prefixes: Optional[list[str]] = None

        # Set correct attn and init on "meta" to delay allocating GPU tensors
        # TODO: @raushan, use the public `model.set_attn_implementation()`
        # method once its checks are fixed in Transformers.
        self.text_config._attn_implementation = "vllm"
        with init_on_device_without_buffers("meta"):
            self.model: PreTrainedModel = AutoModel.from_config(
                self.config,
                torch_dtype=self.model_config.dtype,
                trust_remote_code=self.model_config.trust_remote_code,
            )

        self.pipeline_parallel()
        self.tensor_parallel()

        # Input embeddings
        if not isinstance(self.model.get_input_embeddings(), PPMissingLayer):
            self.model.set_input_embeddings(
                VocabParallelEmbedding(
                    self.text_config.vocab_size,
                    self.text_config.hidden_size,
                    org_num_embeddings=self.text_config.vocab_size,
                    quant_config=self.quant_config,
                ))

        # Attention layers
        self.attention_instances = self.create_attention_instances()

        # Initialize any parameters that have not had their modules replaced
        self.init_parameters(self.model)

        self.make_empty_intermediate_tensors = (
            make_empty_intermediate_tensors_factory(
                ["hidden_states"], self.text_config.hidden_size))

    def pipeline_parallel(self):
        """
        Apply the model's pipeline parallelization plan.
        """
        if self.pp_size <= 1:
            return

        if not self.model.supports_pp_plan:
            raise ValueError(
                f"{type(self.model)} does not support pipeline parallel yet!")

        module_lists = []
        module_list_idx = None
        pp_plan = list(self.model._pp_plan.keys())
        for i, name in enumerate(pp_plan):
            if isinstance(getattr(self.model, name), nn.ModuleList):
                module_lists.append(name)
                module_list_idx = i

        if len(module_lists) > 1:
            raise ValueError(
                "Pipeline parallel of models with multiple `ModuleList`s "
                "in the base model are not supported yet!")
        if module_list_idx is None:
            raise ValueError(
                f"Could not find `ModuleList` in {type(self.model)}")

        # Layers before module list
        for name in pp_plan[:module_list_idx]:
            if self.pp_group.is_first_rank or (
                    self.text_config.tie_word_embeddings
                    and self.pp_group.is_last_rank):
                continue
            setattr(self.model, name, PPMissingLayer())

        # Module list
        start_layer, end_layer = get_pp_indices(
            self.text_config.num_hidden_layers, self.pp_rank, self.pp_size)
        layers_name = pp_plan[module_list_idx]
        layers = getattr(self.model, layers_name)
        for i in range(len(layers)):
            if start_layer <= i and i < end_layer:
                continue
            layers[i] = PPMissingLayer()

        # Layers after module list
        for name in pp_plan[module_list_idx + 1:]:
            # Modules that should be on last rank
            if not self.pp_group.is_last_rank:
                setattr(self.model, name, PPMissingLayer())

    def tensor_parallel(self):
        """
        Apply the model's tensor parallelization plan.
        Currently only supports linear layers.
        """
        # Look for tp plans in all of the PreTrainedModels found in self.model
        is_pretrained_model = lambda m: isinstance(m, PreTrainedModel)
        supports_tp_plan = lambda m: m.config.base_model_tp_plan is not None
        pretrained_models = filter(is_pretrained_model, self.model.modules())
        models_with_tp_plan = filter(supports_tp_plan, pretrained_models)

        if not any(models_with_tp_plan) and self.tp_size > 1:
            raise ValueError(
                f"{type(self.model)} does not support tensor parallel yet!")

        def _tensor_parallel(module: nn.Module,
                             prefix: str = "",
                             tp_plan=None):
            tp_plan = tp_plan or {}

            # If the current module is a PreTrainedModel, set the tp_plan for
            # all of its children
            if isinstance(module, PreTrainedModel):
                tp_plan = module.config.base_model_tp_plan or {}
                tp_plan = {
                    maybe_prefix(prefix, k): v
                    for k, v in tp_plan.items()
                }

            # Some weight loaders expect linear layers to inherit from vLLM's
            # LinearBase class, so we set a default style which causes any
            # unspecified linear layers to be replaced with ReplicatedLinear
            for child_name, child_module in module.named_children():
                qual_name = maybe_prefix(prefix, child_name)
                if isinstance(child_module, nn.Linear):
                    generator = (p for p in tp_plan if re.match(p, qual_name))
                    pattern = next(generator, None)
                    style = tp_plan.get(pattern, "replicate")
                    new_module = replace_linear_class(child_module, style,
                                                      self.quant_config)
                    setattr(module, child_name, new_module)
                    log_replacement(qual_name, child_module, new_module)
                else:
                    _tensor_parallel(child_module,
                                     prefix=qual_name,
                                     tp_plan=tp_plan)

        _tensor_parallel(self.model)

    def create_attention_instances(self) -> dict[int, Attention]:
        """
        Create `Attention` instances to inform KV cache allocation.
        """
        num_heads = self.model_config.get_num_attention_heads(
            self.parallel_config)
        head_size = self.model_config.get_head_size()
        num_kv_heads = self.model_config.get_num_kv_heads(self.parallel_config)
        start, end = get_pp_indices(self.text_config.num_hidden_layers,
                                    self.pp_rank, self.pp_size)

        attention_instances = {}
        for i in range(start, end):
            # Handle interleaved sliding window attention
            per_layer_sliding_window = None
            if (hasattr(self.config, "layer_types")
                    and self.config.layer_types[i] == "sliding_attention"):
                per_layer_sliding_window = self.config.sliding_window

            attention_instances[i] = Attention(
                num_heads=num_heads,
                head_size=head_size,
                # NOTE: We use Llama scale as default, if it's set by
                # Transformers, it's updated in vllm_flash_attention_forward
                scale=head_size**-0.5,
                num_kv_heads=num_kv_heads,
                cache_config=self.cache_config,
                quant_config=self.quant_config,
                per_layer_sliding_window=per_layer_sliding_window,
                prefix=f"{i}.attn")
        return attention_instances

    def init_parameters(self, module: nn.Module):
        """
        If a `parameter` is on the `meta` device, then its parent
        `module` is the original module created by:

        ```python
        with torch.device("meta"):
            self.model: PreTrainedModel = AutoModel.from_config(...)
        ```
        """
        for name, param in module.named_parameters(recurse=False):
            if param.device == torch.device("meta"):
                new_param = nn.Parameter(
                    torch.empty_like(param.data,
                                     dtype=self.model_config.dtype,
                                     device=self.device_config.device))
                setattr(module, name, new_param)
        for child in module.children():
            self.init_parameters(child)

    def forward(
        self,
        input_ids: Optional[torch.Tensor],
        positions: torch.Tensor,
        intermediate_tensors: Optional[IntermediateTensors] = None,
        inputs_embeds: Optional[torch.Tensor] = None,
    ) -> Union[torch.Tensor, IntermediateTensors]:
        if not get_pp_group().is_first_rank:
            assert intermediate_tensors is not None
            input_ids = None
            inputs_embeds = intermediate_tensors["hidden_states"]

        if input_ids is not None:
            input_ids = input_ids[None, ...]
        if inputs_embeds is not None:
            inputs_embeds = inputs_embeds[None, ...]

        if self.model_config.uses_mrope:
            position_ids = positions[:, None]
        else:
            position_ids = positions[None, ...]

        hidden_states = self.model(
            input_ids=input_ids,
            inputs_embeds=inputs_embeds,
            use_cache=False,
            position_ids=position_ids,
            attention_instances=self.attention_instances,
            return_dict=False)[0][0, ...]  # we remove batch dimension for now

        if not get_pp_group().is_last_rank:
            return IntermediateTensors({"hidden_states": hidden_states})

        return hidden_states

    def load_weights(self, weights: Iterable[tuple[str,
                                                   torch.Tensor]]) -> set[str]:
        loader = AutoWeightsLoader(self, skip_prefixes=self.skip_prefixes)
        return loader.load_weights(weights, mapper=self.hf_to_vllm_mapper)


@support_torch_compile
class TransformersModel(TransformersBase):
    hf_to_vllm_mapper = WeightsMapper(
        orig_to_new_prefix={
            # Add `model.` prefix for base model checkpoints
            "": "model.",
            # Remove `model.` from places it should not be
            "model.model.": "model.",
            "model.score": "score",
        })


@support_torch_compile
class TransformersForCausalLM(TransformersBase):

    def __init__(self, *, vllm_config: VllmConfig, prefix: str = ""):
        super().__init__(vllm_config=vllm_config, prefix=prefix)

        # Tell `TransformersBase.load_weights` to skip
        # `lm_head` if the model has tied word embeddings
        if self.text_config.tie_word_embeddings:
            self.skip_prefixes = ["lm_head."]

        if get_pp_group().is_last_rank:
            self.unpadded_vocab_size = self.text_config.vocab_size
            self.lm_head = ParallelLMHead(
                self.text_config.vocab_size,
                self.text_config.hidden_size,
                quant_config=self.quant_config,
                prefix=maybe_prefix(prefix, "lm_head"),
            )
            if self.text_config.tie_word_embeddings:
                self.lm_head = self.lm_head.tie_weights(
                    self.model.get_input_embeddings())

            logit_scale = getattr(self.text_config, "logit_scale", 1.0)
            self.logits_processor = LogitsProcessor(
                self.unpadded_vocab_size, self.text_config.vocab_size,
                logit_scale)
        else:
            self.lm_head = PPMissingLayer()

    def compute_logits(
        self,
        hidden_states: torch.Tensor,
        sampling_metadata: SamplingMetadata,
    ) -> Optional[torch.Tensor]:
        logits = self.logits_processor(self.lm_head, hidden_states,
                                       sampling_metadata)
        return logits


def flatten_and_concat(x: list[torch.Tensor]) -> torch.Tensor:
    """Flatten until a list of tensors can be concatenated then do concat"""

    def _can_concat(x: list[torch.Tensor]):
        return len(set(map(lambda _x: _x.shape[1:], x))) == 1

    if _can_concat(x):
        return torch.concat(x)
    return flatten_and_concat(flatten_bn(x))


@MULTIMODAL_REGISTRY.register_processor(
    MultiModalProcessor,
    info=MultiModalProcessingInfo,
    dummy_inputs=MultiModalDummyInputsBuilder)
class TransformersForMultimodalLM(TransformersForCausalLM, SupportsMultiModal):
    # Backwards compatibility for prev released models. State dicts back then
    # had different formats and cannot be loaded with `AutoModel` mapping as is
    hf_to_vllm_mapper = WeightsMapper(
        orig_to_new_prefix={
            "language_model.model": "model.language_model",
            "text_model.model": "model.text_model",
            "vision_tower": "model.vision_tower",
            "vqmodel": "model.vqmodel",
            "visual": "model.visual",
            "vision_model": "model.vision_model",
            "vision_embed_tokens": "model.vision_embed_tokens",
            "image_newline": "model.image_newline",
            "multi_modal_projector": "model.multi_modal_projector",
            "text_model.lm_head": "lm_head",
            "language_model.lm_head": "lm_head",
            # Qwen models used "model" as the name for the language model.
            # Therefore, we must map each of submodule explicitly to avoid
            # conflicts with newer models that use "model.language_model".
            "model.embed_tokens": "model.language_model.embed_tokens",
            "model.layers": "model.language_model.layers",
            "model.norm": "model.language_model.norm",
        })

    def __init__(self, *, vllm_config: VllmConfig, prefix: str = ""):
        super().__init__(vllm_config=vllm_config, prefix=prefix)

        self.dtype = vllm_config.model_config.dtype

    def forward(
        self,
        input_ids: Optional[torch.Tensor],
        positions: torch.Tensor,
        intermediate_tensors: Optional[IntermediateTensors] = None,
        inputs_embeds: Optional[torch.Tensor] = None,
        **kwargs: object,
    ) -> Union[torch.Tensor, IntermediateTensors]:
        # NOTE: In v1, inputs_embeds is always generated at model runner from
        # `get_multimodal_embeddings` and `get_input_embeddings`, this
        # condition is only for v0 compatibility.
        if inputs_embeds is None:
            multimodal_embeds = self.get_multimodal_embeddings(**kwargs)
            if multimodal_embeds is not None:
                inputs_embeds = self.get_input_embeddings(
                    input_ids, multimodal_embeds)
                input_ids = None

        model_output = super().forward(input_ids, positions,
                                       intermediate_tensors, inputs_embeds)
        return model_output

    def get_multimodal_embeddings(self, **kwargs):
        pixel_values = kwargs.pop("pixel_values", None)
        pixel_values = pixel_values if pixel_values is not None else kwargs.pop(
            "image_patches", None)
        image_embeds = kwargs.pop("image_embeds", None)

        if image_embeds is not None:
            return image_embeds

        if pixel_values is None and image_embeds is None:
            return None

        num_image_patches = kwargs.pop("num_image_patches")
        if pixel_values is not None:
            if isinstance(pixel_values, torch.Tensor):
                pixel_values = flatten_bn(pixel_values).to(self.dtype)
            elif is_list_of(pixel_values, torch.Tensor):
                pixel_values = flatten_and_concat(pixel_values).to(self.dtype)
            else:
                raise ValueError(
                    f"Unsupported pixel_values type {type(pixel_values)}. "
                    "Expected `torch.Tensor` or list of `torch.Tensor`.")

            if isinstance(num_image_patches, list):
                num_image_patches = torch.cat(num_image_patches)

            vision_embeddings = self.model.get_image_features(
                pixel_values,
                **{
                    k: v.flatten(0, 1)
                    for k, v in kwargs.items()
                },
            )

            if isinstance(vision_embeddings, torch.Tensor):
                if vision_embeddings.ndim == 2:
                    vision_embeddings = vision_embeddings.unsqueeze(0)

                # Embeddings have to be 2D tensors of length `num_images`
                # but transformers returns concat tensors if each patch
                # is of different size. We split it back to make vLLM happy
                vision_embeddings = torch.split(
                    vision_embeddings,
                    num_image_patches.flatten().tolist())
                vision_embeddings = [
                    embed.flatten(start_dim=0, end_dim=-2)
                    for embed in vision_embeddings
                ]

            return vision_embeddings

    def get_input_embeddings(
        self,
        input_ids: torch.Tensor,
        multimodal_embeddings=None,
    ) -> torch.Tensor:
        inputs_embeds = self.model.get_input_embeddings()(input_ids)
        if (multimodal_embeddings is not None
                and len(multimodal_embeddings) != 0):
            mask = (input_ids == self.config.image_token_id)
            mask = mask.unsqueeze(-1).expand_as(inputs_embeds)
            multimodal_embeddings = torch.cat(multimodal_embeddings)

            inputs_embeds = inputs_embeds.masked_scatter(
                mask, multimodal_embeddings)
        return inputs_embeds