def gen_function(
    func_attrs, backend_spec, tanh_def, element_func=None, extra_header_template=None
):
    """Generates function body.

    Parameters
    ----------
    func_attrs : Dict[str, Any]
        Stores the operation attributes.
    backend_spec: dataclass
        Backend specification.
    element_func: str
        Attributes for ease of tanh concatenate fusion, default is None.
    extra_header_template: str
        Header for fast_tanh, default is None.


    Returns
    -------
    str
        Rendered function body.
    """
    # TODO: consider to profile elems_per_thread
    elems_per_thread = 8 if len(func_attrs["inputs"]) == 1 else 256
    element_func_def = None if element_func is None else tanh_def.render()
    # slice_reshape_scatter is a temporary solution for a special fusion pattern.
    # It will be replaced with a more general slice + concat pass once it's
    # ready. Second, the constrains of slice_reshape_scatter ensure that its
    # output_accessor's stride is actually linear offset in the output tensor.
    # So, let's not to pollute a common slice kernel with output TensorAccessors
    # at the moment since we do not support output TensorAccessors for slice
    # op yet, which may have perf implication to the kernel as well.
    output_accessor = func_attrs["output_accessors"][0]
    output_offset = output_accessor.offset
    return slice_common.gen_function(
        func_attrs,
        backend_spec=backend_spec,
        output_offset=output_offset,
        elems_per_thread=elems_per_thread,
        update_output_shape=False,
        element_func=element_func,
        element_func_def=element_func_def,
        extra_header_template=extra_header_template,
    )
Generates function body.

Parameters
----------
func_attrs : Dict[str, Any]
Stores the operation attributes.
backend_spec: dataclass
Backend specification.
element_func: str
Attributes for ease of tanh concatenate fusion, default is None.
extra_header_template: str
Header for fast_tanh, default is None.


Returns
-------
str
Rendered function body.
python/aitemplate/backend/common/tensor/slice_reshape_scatter_common.py