partial_program.py

# Copyright (c) 2020 PaddlePaddle Authors. All Rights Reserved.
#
# 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.

from __future__ import print_function
import numpy as np
import six

import paddle
from paddle.fluid import framework, backward, core, program_guard
from paddle.fluid.executor import _is_enable_standalone_executor, _is_dy2st_enable_standalone_executor
from paddle.fluid.dygraph import layers
from paddle.fluid.dygraph.base import switch_to_static_graph
from paddle.fluid.dygraph.dygraph_to_static import logging_utils
from paddle.fluid.dygraph.dygraph_to_static.return_transformer import RETURN_NO_VALUE_MAGIC_NUM
from paddle.fluid.layers.utils import flatten
from paddle.fluid.layers.utils import pack_sequence_as
from paddle.fluid.layers.utils import _hash_with_id
from paddle.fluid.compiler import BuildStrategy
from paddle.fluid.framework import _apply_pass
from paddle.fluid.contrib.mixed_precision.decorator import AutoMixedPrecisionLists
from paddle.fluid.contrib.mixed_precision.fp16_utils import rewrite_program, cast_model_to_fp16
from paddle.fluid.dygraph.amp.auto_cast import _in_amp_guard, _in_pure_fp16_guard
import paddle.compat as cpt
from paddle import _C_ops, _legacy_C_ops


class NestSequence(object):
    """
    A wrapper class that easily to flatten and restore the nest structure of
    given sequence.
    """

    def __init__(self, raw_input, need_check=False):
        self.__raw_input = raw_input
        self.__input_list = self.tolist()
        self.__var_ids = self._get_var_ids()
        self._check_non_variable(need_check)

    def tolist(self):
        """
        Flattens the nested sequences into single list.
        """
        return flatten(self.__raw_input)

    def restore(self, value_list):
        """
        Restores the nested sequence from value list.
        """
        assert len(self.__input_list) == len(value_list)
        return pack_sequence_as(self.__raw_input, value_list)

    def _get_var_ids(self):
        var_ids = []
        for idx, var in enumerate(self.__input_list):
            if isinstance(
                    var, (framework.Variable, core.VarBase, core.eager.Tensor)):
                var_ids.append(idx)

        return var_ids

    def _check_non_variable(self, need_check):
        """
        Raises warning if output of traced function contains non-tensor type values.
        """
        if need_check:
            warning_types = set()
            for var in self.__input_list:
                if not isinstance(
                        var,
                    (framework.Variable, core.VarBase, core.eager.Tensor)):
                    warning_types.add(type(var))
            if warning_types:
                logging_utils.warn(
                    "Output of traced function contains non-tensor type values: {}. "
                    "Currently, We don't support to update them while training and will return "
                    "what we first saw. Please try to return them as tensor.".
                    format(list(warning_types)))

    @property
    def var_ids(self):
        return self.__var_ids

    def __getitem__(self, item):
        return self.__input_list[item]


class LazyInitialized(object):
    """
    Descriptor to implement lazy initialization of property.
    """

    def __init__(self, function):
        self.function = function

    def __get__(self, instance, cls):
        val = self.function(instance)
        setattr(instance, self.function.__name__, val)
        return val


def _change_is_test_status(program, is_test):
    # change all `is_test` attributes
    for block in program.blocks:
        for op in block.ops:
            if op.has_attr('is_test'):
                op._set_attr('is_test', is_test)
    return program


class PartialProgramLayer:
    """
    PartialProgramLayer wraps all the ops from layers decorated by `@declarative`
    and execute them as a static subgraph.

    .. note::
        **1. This is a very low level API. Users should not use this API
             directly. Please use `partial_program_from(concrete_program)`
             to create it.
        **2. LoDTensorArray is not currently supported in the output.

    Args:
        main_program(Program): The main program that contains ops need to be executed.
        inputs(list[Variable]): The input list of the decorated function by `@declarative`.
        outputs(list[Variable]): The output list of the decorated function by `@declarative`.
        parameters(list[VarBase]|None): All trainable parameters included in the program. Default None.

    Returns:
        Layer: A Layer object that run all ops internally in static mode.
    """

    def __init__(self,
                 main_program,
                 inputs,
                 outputs,
                 parameters=None,
                 **kwargs):
        super(PartialProgramLayer, self).__init__()
        self._inputs = NestSequence(inputs)
        self._outputs = NestSequence(outputs, need_check=True)
        self._params = parameters if parameters is not None else []

        self._build_strategy = kwargs.get('build_strategy', BuildStrategy())
        assert isinstance(self._build_strategy, BuildStrategy)

        self._origin_main_program = self._verify_program(main_program)
        self._cuda_graph_vec = self._create_cuda_graph_vec()
        self._cuda_graph_capture_mode = ""
        self._cuda_graph_pool_id = 0
        # Set default mode to train
        self.training = True

        custom_white_list, custom_black_list = None, None
        tracer = framework._dygraph_tracer()
        if tracer:
            custom_white_list, custom_black_list = tracer._get_amp_op_list()
        # For AMP training
        self._amp_list = AutoMixedPrecisionLists(
            custom_white_list=custom_white_list,
            custom_black_list=custom_black_list)

    @LazyInitialized
    def __fake_vars(self):
        return _create_fake_var()

    @LazyInitialized
    def _double_grads(self):
        return self._get_double_grads(self._origin_main_program)

    # whole
    @switch_to_static_graph
    def _create_program(self, is_infer_mode=False):
        if is_infer_mode:
            return self._origin_main_program.clone(for_test=is_infer_mode)
        else:
            train_program = self._append_backward_desc(
                self._origin_main_program)
            # Note: Only set grad type once after initializing train program. So we put it here.
            self._set_grad_type(self._params, train_program)
            return train_program

    @switch_to_static_graph
    def _create_amp_program(self, is_infer_mode=False):
        amp_program = self._origin_main_program.clone(for_test=is_infer_mode)
        with program_guard(amp_program):
            rewrite_program(amp_program, self._amp_list)
        if is_infer_mode:
            return amp_program
        else:
            train_amp_program = self._append_backward_desc(amp_program)
            self._set_grad_type(self._params, train_amp_program)
            return train_amp_program

    @switch_to_static_graph
    def _create_pure_fp16_program(self, is_infer_mode=False):
        pure_fp16_program = self._origin_main_program.clone(
            for_test=is_infer_mode)
        with program_guard(pure_fp16_program):
            cast_model_to_fp16(pure_fp16_program,
                               self._amp_list,
                               use_fp16_guard=False)
        if is_infer_mode:
            return pure_fp16_program
        else:
            train_pure_fp16_program = self._append_backward_desc(
                pure_fp16_program)
            self._set_grad_type(self._params, train_pure_fp16_program)
            return train_pure_fp16_program

    @switch_to_static_graph
    def _create_forward_backward_train_program(self):
        whole_program = self._create_program()
        forward_end_op_index = self._infer_program.desc.block(0).op_size()
        return self._get_forward_backward_program_form(whole_program,
                                                       forward_end_op_index)

    @switch_to_static_graph
    def _create_forward_backward_train_amp_program(self):
        whole_program = self._create_amp_program()
        forward_end_op_index = self._infer_amp_program.desc.block(0).op_size()
        return self._get_forward_backward_program_form(whole_program,
                                                       forward_end_op_index)

    @switch_to_static_graph
    def _create_forward_backward_train_pure_fp16_program(self):
        whole_program = self._create_pure_fp16_program()
        forward_end_op_index = self._infer_pure_fp16_program.desc.block(
            0).op_size()
        return self._get_forward_backward_program_form(whole_program,
                                                       forward_end_op_index)

    @LazyInitialized
    def _train_program(self):
        return self._create_program()

    @LazyInitialized
    def _infer_program(self):
        return self._create_program(is_infer_mode=True)

    @LazyInitialized
    def _train_amp_program(self):
        return self._create_amp_program()

    @LazyInitialized
    def _infer_amp_program(self):
        return self._create_amp_program(is_infer_mode=True)

    @LazyInitialized
    def _train_pure_fp16_program(self):
        return self._create_pure_fp16_program()

    @LazyInitialized
    def _infer_pure_fp16_program(self):
        return self._create_pure_fp16_program(is_infer_mode=True)

    @LazyInitialized
    def _train_forward_backward_program(self):
        program = self._create_forward_backward_train_program()
        return program

    @LazyInitialized
    def _train_amp_forward_backward_program(self):
        program = self._create_forward_backward_train_amp_program()
        return program

    @LazyInitialized
    def _train_pure_fp16_forward_backward_program(self):
        program = self._create_forward_backward_train_pure_fp16_program()
        return program

    @property
    def whole_program(self):
        if self.training:
            if _in_amp_guard():
                return self._train_amp_program
            elif _in_pure_fp16_guard():
                return self._train_pure_fp16_program
            else:
                return self._train_program
        else:
            if _in_amp_guard():
                return self._infer_amp_program
            elif _in_pure_fp16_guard():
                return self._infer_pure_fp16_program
            else:
                return self._infer_program

    @property
    def forward_program(self):
        if self.training:
            if _in_amp_guard():
                program = self._train_amp_forward_backward_program
                return program[0]
            elif _in_pure_fp16_guard():
                program = self._train_pure_fp16_forward_backward_program
                return program[0]
            else:
                program = self._train_forward_backward_program
                return program[0]
        else:
            if _in_amp_guard():
                return self._infer_amp_program
            elif _in_pure_fp16_guard():
                return self._infer_pure_fp16_program
            else:
                return self._infer_program

    @property
    def backward_program(self):
        if self.training:
            if _in_amp_guard():
                program = self._train_amp_forward_backward_program
                return program[1]
            elif _in_pure_fp16_guard():
                program = self._train_pure_fp16_forward_backward_program
                return program[1]
            else:
                program = self._train_forward_backward_program
                return program[1]
        else:
            return paddle.static.Program()

    @LazyInitialized
    def _train_program_id(self):
        program_id = _hash_with_id(self._train_program, self)
        core._set_cached_executor_build_strategy(program_id,
                                                 self._build_strategy)
        return program_id

    @LazyInitialized
    def _infer_program_id(self):
        return _hash_with_id(self._infer_program, self)

    @LazyInitialized
    def _train_amp_program_id(self):
        program_id = _hash_with_id(self._train_amp_program, self)
        core._set_cached_executor_build_strategy(program_id,
                                                 self._build_strategy)
        return program_id

    @LazyInitialized
    def _infer_amp_program_id(self):
        return _hash_with_id(self._infer_amp_program, self)

    @LazyInitialized
    def _train_pure_fp16_program_id(self):
        program_id = _hash_with_id(self._train_pure_fp16_program, self)
        core._set_cached_executor_build_strategy(program_id,
                                                 self._build_strategy)
        return program_id

    @LazyInitialized
    def _infer_pure_fp16_program_id(self):
        return _hash_with_id(self._infer_pure_fp16_program, self)

    @property
    def whole_program_id(self):
        if self.training:
            if _in_amp_guard():
                return self._train_amp_program_id
            elif _in_pure_fp16_guard():
                return self._train_pure_fp16_program_id
            else:
                return self._train_program_id
        else:
            if _in_amp_guard():
                return self._infer_amp_program_id
            elif _in_pure_fp16_guard():
                return self._infer_pure_fp16_program_id
            else:
                return self._infer_program_id

    def _verify_program(self, main_program):
        """
        Verify that the program parameter is initialized, prune some unused params,
        and remove redundant op callstack.
        """
        # 1. Check all params from main program can be found in self._params
        self._check_params_all_inited(main_program)
        # 2. Prune the parameters not used anywhere in the program.
        self._prune_unused_params(main_program)

        return main_program

    def prepare_gradient_aggregation(self, start_idx, main_program,
                                     target_program):
        """
        Why we need add gradient aggregation operation ?
        In some cases, if non leaf nodes are used as output, gradient overwriting will occur, such as
        def forward(self, in):
            x = 2 * in  # <---- x is a non-leaf node in program.
            y = x + 3
            return x, y
        
        loss = forward(in)[0].sum()
        loss.backward()  # <----- x@grad will be overwrited by elementwise_add_grad Op
        """

        def _need_aggregation(var):
            """
            if exist a op whose inputs is var, then return True
            """
            if not isinstance(var, framework.Variable) or var.type not in [
                    core.VarDesc.VarType.LOD_TENSOR,
                    core.VarDesc.VarType.SELECTED_ROWS
            ]:
                return False
            if var.dtype not in [paddle.float32, paddle.float64]:
                return False
            for op in main_program.block(0).ops:
                for in_arg in op.input_arg_names:
                    if in_arg == var.name:
                        return True
            return False

        def _insert_aggregation_ops_for_var(target_program, var):
            suffix = "@dy2static"
            var_grad_name = var.grad_name
            new_grad_name = var.name + suffix + "@GRAD"
            finded_ops = list(
                filter(
                    lambda x: x[0] >= start_idx and any([
                        out_arg == var_grad_name
                        for out_arg in x[1].output_arg_names
                    ]), enumerate(target_program.block(0).ops)))

            # len(finded_ops) may equals zero when stop_gradient works.
            # len(finded_ops) may > 1, because we may have fill_constant op.
            if len(finded_ops) == 0:
                return None
            # step1: create a new var named var.name@GRAD
            target_program.block(0).create_var(name=new_grad_name,
                                               type=var.type,
                                               dtype=var.dtype,
                                               shape=var.shape)
            # step2: rename the var.name@GRAD to var.name@GRAD@dy2static
            for idx, op in finded_ops:
                op._rename_input(var_grad_name, new_grad_name)
                op._rename_output(var_grad_name, new_grad_name)
            # step3: insert sum op to aggregate the gradient.
            #        var.name@GRAD = sum(var.name@dy2static@GRAD, var.name@GRAD)
            target_program.block(0)._insert_op(
                finded_ops[-1][0] + 1,
                type='sum',
                inputs={'X': [var_grad_name, new_grad_name]},
                outputs={"Out": var_grad_name})
            return None

        to_processed_vars = list(
            filter(_need_aggregation, self._outputs.tolist()))
        for _var in to_processed_vars:
            _insert_aggregation_ops_for_var(target_program, _var)

    @switch_to_static_graph
    def _append_backward_desc(self, main_program):
        # make sure all status of is_test are False in train mode.
        program = _change_is_test_status(main_program.clone(), is_test=False)
        targets = []
        for out in self._outputs.tolist():
            if isinstance(out, framework.Variable):
                targets.append(program.global_block().var(out.name))

        if targets and self._params:
            backward.gradients(targets=targets, inputs=[])

        start_idx = len(
            main_program.block(0).ops) + 2 * len(self._outputs.tolist())

        self.prepare_gradient_aggregation(start_idx, main_program, program)

        return program

    def _prune_unused_params(self, program):
        """
        Prune the parameters not used anywhere in the program.
        The `@declarative` may only decorated a sub function which
        contains some unused parameters created in `__init__`.
        So prune these parameters to avoid unnecessary operations in
        `run_program_op`.
        """
        required_params = []
        for param in self._params:
            found_param = False
            for block in program.blocks:
                for op in block.ops:
                    if param.name in op.input_arg_names or param.name in op.output_arg_names:
                        required_params.append(param)
                        found_param = True
                        break
                if found_param:
                    break

        self._params = required_params

    def _get_double_grads(self, program):
        double_grads = []
        for block in program.blocks:
            for name in block.vars:
                if "@GRAD" in name:
                    var_desc = block.vars[name].desc
                    var_base = None
                    if not framework._in_eager_mode_:
                        var_base = core.VarBase(var_desc.dtype(),
                                                var_desc.shape(),
                                                var_desc.name(),
                                                var_desc.type(), False)
                    else:
                        var_base = core.eager.Tensor(var_desc.dtype(),
                                                     var_desc.shape(),
                                                     var_desc.name(),
                                                     var_desc.type(), False)
                    double_grads.append(var_base)
        return self._valid_vars(double_grads)

    def _get_end_op_index(self):
        if _in_amp_guard():
            infer_program = self._infer_amp_program
        elif _in_pure_fp16_guard():
            infer_program = self._infer_pure_fp16_program
        else:
            infer_program = self.infer_program
        return infer_program.desc.block(0).op_size()

    def __call__(self, inputs):
        in_vars, out_vars = self._prepare(inputs)

        self._cast_fp16_if_pure_fp16(in_vars)

        attrs = [
            'global_block',
            self.program.desc.block(0), 'start_op_index', 0, 'end_op_index',
            self._get_end_op_index(), 'is_test', not self.training,
            'program_id', self.program_id
        ]
        if self._cuda_graph_capture_mode:
            attrs.extend(
                ('cuda_graph_capture_mode', self._cuda_graph_capture_mode,
                 'cuda_graph_pool_id', self._cuda_graph_pool_id))

        use_interpretorcore = _is_enable_standalone_executor(
        ) and _is_dy2st_enable_standalone_executor()
        attrs.extend(('use_interpretorcore', use_interpretorcore))
        if use_interpretorcore:
            attrs.extend(
                ('forward_global_block', self.forward_program.desc.block(0),
                 'backward_global_block', self.backward_program.desc.block(0)))

        _legacy_C_ops.run_program(self._valid_vars(in_vars),
                                  self._valid_vars(self._params),
                                  self._valid_vars(out_vars),
                                  self._create_scope_vec(), self._double_grads,
                                  self._cuda_graph_vec, *attrs)
        restored_nest_out = self._restore_out(out_vars)
        return self._remove_no_value(restored_nest_out)

    def _cast_fp16_if_pure_fp16(self, in_vars):
        if _in_pure_fp16_guard():
            for i, var in enumerate(in_vars):
                name = var.name
                if (self.program.global_block().has_var(name)
                        and self.program.global_block().var(name).dtype
                        == paddle.float16):
                    in_vars[i] = var.astype('float16')
                    in_vars[i].name = name
                if (self.forward_program.global_block().has_var(name)
                        and self.forward_program.global_block().var(name).dtype
                        == paddle.float16):
                    in_vars[i] = var.astype('float16')
                    in_vars[i].name = name
                if (self.backward_program.global_block().has_var(name)
                        and self.backward_program.global_block().var(name).dtype
                        == paddle.float16):
                    in_vars[i] = var.astype('float16')
                    in_vars[i].name = name

    @property
    def program(self):
        return self.whole_program

    @property
    def program_id(self):
        return self.whole_program_id

    @property
    def train_program(self):
        if _in_amp_guard():
            return self._train_amp_program
        elif _in_pure_fp16_guard():
            return self._train_pure_fp16_program
        else:
            return self._train_program

    @property
    def infer_program(self):
        if _in_amp_guard():
            return self._infer_amp_program
        elif _in_pure_fp16_guard():
            return self._infer_pure_fp16_program
        else:
            return self._infer_program

    @switch_to_static_graph
    def _get_forward_backward_program_form(self, whole_program,
                                           forward_end_op_index):
        forward_builded_program = add_build_strategy_for(
            whole_program, 0, forward_end_op_index, self._build_strategy)
        backward_start_op_index = forward_end_op_index + 2 * len(
            self._outputs.var_ids)
        backward_end_op_index = whole_program.desc.block(0).op_size()
        backward_builded_program = add_build_strategy_for(
            whole_program, backward_start_op_index, backward_end_op_index,
            self._build_strategy)
        self._apply_inplace_pass(forward_builded_program,
                                 backward_builded_program)
        return [forward_builded_program, backward_builded_program]

    def _apply_inplace_pass(self, forward_program, backward_program):
        attr_types = {
            "use_cuda": "bool",
            "mem_opt_skip_vars": "list[str]",
            "for_partial_block": "bool"
        }
        empty_startup_program = paddle.static.Program()
        use_cuda = True if core.is_compiled_with_cuda() else False
        # skip data var
        forward_mem_opt_skip_vars = []
        backward_mem_opt_skip_vars = []
        for var_name, var in forward_program.global_block().vars.items():
            if var.is_data:
                forward_mem_opt_skip_vars.append(var_name)
        for var_name, var in backward_program.global_block().vars.items():
            if var.is_data:
                backward_mem_opt_skip_vars.append(var_name)
        for var in self._inputs:
            if isinstance(var, paddle.fluid.framework.Variable):
                forward_mem_opt_skip_vars.append(var.desc.name())
                backward_mem_opt_skip_vars.append(var.desc.name())
        for var in self._outputs:
            if isinstance(var, paddle.fluid.framework.Variable):
                forward_mem_opt_skip_vars.append(var.desc.name())
                backward_mem_opt_skip_vars.append(var.desc.name())
        for var_name in core.parse_safe_eager_deletion_skip_vars(
                backward_program.desc):
            forward_mem_opt_skip_vars.append(var_name)
        attrs = {
            "use_cuda": use_cuda,
            "mem_opt_skip_vars": forward_mem_opt_skip_vars,
            "for_partial_block": True
        }
        _apply_pass(forward_program, empty_startup_program,
                    "buffer_shared_inplace_pass", attrs, attr_types)
        attrs = {
            "use_cuda": use_cuda,
            "mem_opt_skip_vars": backward_mem_opt_skip_vars,
            "for_partial_block": True
        }
        _apply_pass(backward_program, empty_startup_program,
                    "buffer_shared_inplace_pass", attrs, attr_types)

    def _prepare(self, inputs):
        """
        Prepare inputs, outputs, attrs.
        """
        assert isinstance(inputs, (tuple, list))
        # Flatten inputs with nested structure into single list.
        flatten_inputs = flatten(inputs)
        # Convert variable into VarBase and feed in training data.
        input_vars = []
        expected_place = framework._current_expected_place()
        for i, value in enumerate(flatten_inputs):
            if isinstance(value, np.ndarray):
                var = None
                if not framework._in_eager_mode_:
                    var = core.VarBase(value=value,
                                       name=self._inputs[i].desc.name(),
                                       persistable=False,
                                       place=expected_place,
                                       zero_copy=True)
                else:
                    var = core.eager.Tensor(value=value,
                                            name=self._inputs[i].desc.name(),
                                            persistable=False,
                                            place=expected_place,
                                            zero_copy=True)
            elif isinstance(value, (core.VarBase, core.eager.Tensor)):
                # NOTE(Aurelius84): If var is on CPUPlace, it will be transformed multi times
                # into CUDAPlace when it's as input of multi Ops. so we move it in advance
                # to avoid this problem.
                if value.stop_gradient and not value.place._equals(
                        expected_place):
                    var = value._copy_to(expected_place, False)
                    var.stop_gradient = True
                else:
                    var = value
                var.name = self._inputs[i].desc.name()
            else:
                continue
            input_vars.append(var)

        # mapping from name(string) -> VarBase
        out_varbase_map = {}

        def create_out(var_id):
            var = self._outputs[var_id]
            assert isinstance(var, framework.Variable)
            var_desc = var.desc
            varbase = None

            if var_desc.name() in out_varbase_map:
                return out_varbase_map[var_desc.name()]

            if not framework._in_eager_mode_:
                var_base = core.VarBase(var_desc.dtype(), var_desc.shape(),
                                        var_desc.name(), var_desc.type(), False)
            else:
                var_base = core.eager.Tensor(var_desc.dtype(), var_desc.shape(),
                                             var_desc.name(), var_desc.type(),
                                             False)
            var_base.stop_gradient = var.stop_gradient
            out_varbase_map[var_desc.name()] = var_base
            return var_base

        # Create VarBase to receive output data.
        out_vars = list(map(create_out, self._outputs.var_ids))

        return input_vars, out_vars

    def _create_scope_vec(self):
        # Hold forward variables
        tmp_scope_vec = None
        inner_scope = core.Scope()
        if not framework._in_eager_mode_:
            tmp_scope_vec = core.VarBase(core.VarDesc.VarType.FP32, [],
                                         "program_out_scope",
                                         core.VarDesc.VarType.STEP_SCOPES, True)
            tmp_scope_vec.value().set_scope(inner_scope)
        else:
            tmp_scope_vec = [inner_scope]
        return tmp_scope_vec

    def _create_cuda_graph_vec(self):
        var = core.VarBase(core.VarDesc.VarType.FP32, [], "cuda_graph",
                           core.VarDesc.VarType.RAW, True)
        var.stop_gradient = True
        return var

    def _restore_out(self, out_vars):
        """
        Restores same nested outputs by only replacing the Variable with VarBase.
        """

        flatten_outputs = self._outputs.tolist()
        for i, idx in enumerate(self._outputs.var_ids):
            flatten_outputs[idx] = out_vars[i]
        outs = self._outputs.restore(flatten_outputs)
        if outs is not None and len(outs) == 1:
            outs = outs[0]

        return outs

    @switch_to_static_graph
    def _clone_for_test(self, main_program):
        return main_program.clone(for_test=True)

    def _is_no_value(self, var):
        if isinstance(var,
                      (core.VarBase, core.eager.Tensor)) and var.shape == [1]:
            # NOTE: .numpy() will insert MemcpySync operation, it hits performance.
            if var.numpy()[0] == RETURN_NO_VALUE_MAGIC_NUM:
                return True
        return False

    def _remove_no_value(self, out_vars):
        """
        Removes invalid value for various-length return statement
        """
        if isinstance(out_vars, (core.VarBase, core.eager.Tensor)):
            if self._is_no_value(out_vars):
                return None
            return out_vars
        elif isinstance(out_vars, (tuple, list)):
            if isinstance(out_vars, tuple):
                res = tuple(var for var in out_vars
                            if not self._is_no_value(var))
            else:
                # isinstance(out_vars, list)
                res = [var for var in out_vars if not self._is_no_value(var)]

            has_removed = (len(out_vars) > len(res))
            # len(out_vars) > len(res) means we have removed var. This is
            # preventing out_vars is empty or just one element at the beginning
            if len(res) == 0 and has_removed:
                return None
            elif len(res) == 1 and has_removed:
                return res[0]
            return res

        return out_vars

    def _set_grad_type(self, params, train_program):
        # NOTE: if user set sparse gradient mode, the param's gradient
        # will be SelectedRows, not LoDTensor. But tracer will just
        # set param grad VarBase by forward VarBase(LoDTensor)
        # If we don't change grad_var type here, RunProgramOp need
        # transform SelectedRows to LoDTensor forcibly, it may not
        # be user wanted result.
        for param in params:
            grad_name = param.name + core.grad_var_suffix()
            grad_var = train_program.desc.block(0).find_var(
                cpt.to_bytes(grad_name))
            # NOTE: cannot find var desc maybe no problem, such as in batch_norm
            if grad_var is None:
                continue
            param._set_grad_type(grad_var.type())

    def _remove_op_call_stack(self, main_program):
        """
        Remove op's python call stack with redundant low-level error messages related to
        transforamtions to avoid confusing users.
        """
        assert isinstance(main_program, framework.Program)
        for block in main_program.blocks:
            for op in block.ops:
                if op.has_attr("op_callstack"):
                    op._remove_attr("op_callstack")

        return main_program

    def _check_params_all_inited(self, main_program):
        """
        Check all params from main program are already initialized, see details as follows:
            1. all parameters in self._params should be type `framework.ParamBase` which are created in dygraph.
            2. all parameters from transformed program can be found in self._params.
               Because they share same data with ParamBase of original dygraph.
        """
        if not isinstance(self._params, (list, tuple)):
            raise TypeError(
                "Type of self._params in PartialProgramLayer should be list or tuple, but received %s."
                % type(self._params))

        param_and_buffer_names_set = set()
        for i, var in enumerate(self._params):
            # self._params constains parameters and buffers with persistable=True.
            if not isinstance(var, (core.VarBase, core.eager.Tensor)):
                raise TypeError(
                    'Type of self._params[{}] in PartialProgramLayer should be Parameter or Variable, but received {}.'
                    .format(i, type(var)))
            param_and_buffer_names_set.add(var.name)

        for block in main_program.blocks:
            for name, var in six.iteritems(block.vars):
                if isinstance(var, framework.Parameter):
                    if name not in param_and_buffer_names_set:
                        raise ValueError(
                            "\n\tWe don't support to define layer with parameters in the function decorated by `@to_static`."
                            "\n\tBut we found parameter(%s) was created in the decorated function."
                            "\n"
                            "\n\tRevise suggestion: "
                            "\n\t\t1. Please ensure all your sublayers are inheritted from nn.Layer."
                            "\n\t\t2. Please use nn.ParameterList and nn.LayerList as container instead of using a native Python container such as List"
                            % name)

    def _valid_vars(self, vars):
        """
        Note: run_program_op.InferShape requires `X`/'Out' not be null.
        But it's common in dy2static, fake varBase is created to handle the
        problem.
        """
        return vars if vars else self.__fake_vars


def _create_fake_var():
    """
    Create a fake_var (force on CPU) to handle empty input or output
    """
    if not framework._in_eager_mode_:
        return [
            core.VarBase(core.VarDesc.VarType.FP32, [], "Fake_var",
                         core.VarDesc.VarType.RAW, False)
        ]
    else:
        return [
            core.eager.Tensor(core.VarDesc.VarType.FP32, [], "Fake_var",
                              core.VarDesc.VarType.RAW, False)
        ]


def partial_program_from(concrete_program):
    inputs = concrete_program.inputs
    if inputs and isinstance(inputs[0], layers.Layer):
        inputs = inputs[1:]

    return PartialProgramLayer(concrete_program.main_program, inputs,
                               concrete_program.outputs,
                               concrete_program.parameters,
                               **concrete_program.kwargs)


@switch_to_static_graph
def add_build_strategy_for(program,
                           start_op_index,
                           end_op_index,
                           build_strategy=None):
    if (start_op_index < end_op_index):
        compiled_program = paddle.static.CompiledProgram(
            core.Graph(program.desc, start_op_index, end_op_index),
            build_strategy=build_strategy)
        compiled_program._compile(core.Scope(),
                                  framework._current_expected_place())
        ir_graph = framework.IrGraph(compiled_program._graph)
        builded_program = ir_graph.to_program()
        if hasattr(compiled_program._program, 'lr_sheduler'):
            builded_program.lr_sheduler = compiled_program._program.lr_sheduler
    else:
        builded_program = program
    return builded_program