* The arg of append() can be not Tensor temporarily.

* Add Seq2Seq as ProgramTranslator Unit Test. 

* set dtype of vocab_size_tensor to int64 to pass Windows-CI. 

* fix bug of prelu when rank not equal 4, test=develop

* fix prelu inference, test=develop

* fix api, test=develop

* fix shape when mode is chennel, test=develop

* remove debug code, test=develop

* add unittest, test=develop

As the title

* Add a StatValue class in the backend to represent a stat.
* Add a singleton StatRegistry to maintain the collection of stats.
* For the sake of code neatness, we only support type of int and float, which can cover most of the scenarios.

Some big models can timeout on Windows CPU machine. I added some timeout properties.

Add TSM as ProgramTranslator Unit Test. The TSM code is referred from PaddlePaddle/models#4229

* add MobileNet unittest test=develop

* fix cudnn random test=develop

* fix sync barrier with barrier monitor, test=develop

* enable load_program_state run in imperative mode; test=develop

* remove useless code; test=develop

[Dy2Static]Convert var.shape stmt and Convert the return variables of Tensor-dependent 'if' staments to Tensor if it not  (#24911)

* Support int and long: int or long -> six.integer_types. 

* Modify test_tensor_shape: fix bug and modify comment. 

* Support convert_var_shape to convert var.shape stmt

* Modify code in ifelse_simple_func.py because don't support return non-Tensor in Tensor-dependent 'if' stament currently. 

* Convert the return variables of Tensor-dependent 'if' staments to Tensor if it not. test=develop

[Dy2stat] decrease the batch size to decrease GPU usage.

* Move function 'convert_len' to file convert_operators.py 

* Support that for statements are transformed to while statements.

* Fix bug: raise None -> return None. 

* Support variable loaded and created in loop.

* Use int64 in Py2 and Py3 in function to_static_variable.

Fix the bug for elementwise_div op, when the first var is scalar; Use the shape 1 replace the -1 in shape.

[Dy2stat] Add word2vec as unittest

Add the support the 5d,6d tensor support for the reduce ops;
Add the same time, the compile time, it was 22 minutes, it was 21 minutes after fixed.

test=develop

* Support LoDTensorArray in reverse_op test=develop

* polish en doc and unittest code test=develop

* refine sample code test=develop

* add example of LoDTensorArray test=develop

* fix typo test=develop

* refine err_msg of pybind.cc, test=develop

* refine err_msg in tensor_py.h, test=develop

* refine error msg, test=develop

* fix test_exception, test=develop

* follow comments, test=develop

* cast var in convert_logical_XX. 

* Add convert_ifelse function in convert_operators.py  

* Add logical_transformer. Remove LogicalTransformer from loop_transformer.py 

* Revert modified tests in PR24799(convert_while_stmt). 

* Comment and modify code that doesn't support `return` statement. 

* Remove unnecessary class: MergeAssignTransformer, NodeTestTransformer and IfConditionVisitor in ifelse_transformer. 

* support selectedrows allreduce in multi-cards dygraph, test=develop

* remove useless import modules in unittests, test=develop

* add nccl cmake to get nccl version, test=develop

* add if-condition to compiled correctly, test=develop

* add detail version parseing for old nccl, test=develop

* polish camke details, test=develop

* fix remove test cmake error, test=develop

* fix cmake condition, test=develop

* change unittest camke list, test=develop

* fix unittest cmake rule, test=develop, test=framep0

* rewrite the sigmoid_focal_loss code example. test=develop

* fix spelling mistake in comments of code example.test=develop

The random failure at Windows may due to some random gt_boxes can cause some numbers in YoloV3 to be negative thus access the invalid memory. This PR tries to solve it.

* add user defined func test=develop

* update test=develop

* update test=develop

* fix name conflicts test=develop

* add unittest test=develop

* change 2018 to 2020 test=develop

* add comment test=develop

* add comment for function test=develop

* fix details test=develop

* fix details test=develop

Add Yolov3 as ProgramTranslator Unit Test. The YoloV3 code is referred from PaddlePaddle/models/dygraph/yolov3

* add the support of device index for device_guard.

* add mock barrier all
test=develop

* fix
test=develop

* fix
test=develop

* fix
test=develop

* add queue_generator_op, dequeue_op, enqueue_op and ut, test=develop

* Fix the field length in LoD scenario
* Fix the missed lod info when copy tensor in dump field
* Add some log to make debug easy