* first commit

* Python API for while op

* Python Unittest for simple while_op forward

* fix out to be list

* Fix UT

* VarType

* Fix several bugs

* Fix bug

* Fix bug

* Fix Bug

* Fix bug

* Fix unittest

* Remove debug log

* Add comments

* add PADDLE_ENFORCE

* while_grad_op first commit

* Add `BlockDescBind::FindRecursiveOrCreateVar()` and fix bugs

* not sure how to setdim of while outputs

* push for test

* add executor vlog

* fix bug of while_op cond

* Several enhancement for code

1. Backward always infer shape & infer var type. Since there are RENAME
variables will be created when creating backward operator, but their
shape & var types are not inferenced.
2. Never use SomePtr-> directly, since every pointer could be nullptr if
it is a function return value. Add `detail::Ref` to cast pointer to
reference safely.
3. Enhance error message for backward.
4. Infer data type of variable in `sum` and `tensor_write`

* Fix bugs of while_op gradient

* Fix several bugs of while_op grad

* fix fill zeros like

* fix 3 >= 3

* fix place holder shouldn't be null

* fail on sum op

* Fix SumOp of TensorList

* clean up

* pass while test

* fix test_array_write_read

* pass sum op

* Support int/int64 for fill_constant_batch_size_like

* Fix compile

* adam sparse support

* fix gpu build error

* fix ci

* fix ci

* fix adagrad sparse update bug

* fix gpu build error

* "fix accuracy kernel bug"

* "relauch ci"

* Adding greater than and less than equal ops to compare op
* Changing the name of the less_than_equal and greater_than_equal op
* Also changing the name of the functors

* fix lod_tensor_array

* init test beam search decode op

* add test_beam_search_decode_op

* Conditional Block Forward

* Assign Operator.

Out=X, when type in [LoDTensor/SelectedRows/LoDTensorArray]

* Stash

* Add Scope::Rename

it is useful in gradient phase of an operator with block

* ConditionalBlock Grad Done

* Add comments

* yapf format code

* add split lod tensor operator

* add more test cast

* clean code

* add merge lod tensor operator

* fix bug

* clean code

* add grad operator

* make mask support GPU

* add comments

* Assign Operator.

Out=X, when type in [LoDTensor/SelectedRows/LoDTensorArray]

* Follow comments

The rank of the tensor from the chip() function is changed. In release mode, eigen_assert is not enabled and the dimenstion mismatch is not detected.

The dimension is not set correctly and is not being checked in release mode because eigen_assert is not enabled.

* init trieconcat_op

* add basic implementation

* add test

* add more test

* update unit test

* add PackAllSteps test

* fix PackAllSteps

* all test passed

* clean code

* remove state inside helper

* rename prob to score

* optimize RemoveFromEnd

* use deconstructor to delete BeamNode recursively

* optimize interface

* add comment to interface

* optimizer data structure

* use template to define the type of score

* use template parameter for BeamHelper

* change father to parent

* rename TrieConcat to BeamSearchOutConcat

* use LoDTensorArray

* rename BeamSearchOutConcat to BeamSearchDecode

* refine code

* remain all candidate sentence in beam_search_decode_op, do not consider endid

* use unique_ptr

* fix compare bug

* fix lod compile problem

* "fix ci failed"

* "comment out seq_concate op to unblock PRs"

TensorSetConstant struct is used both in math_function.cc and math_function.cu. Somehow the release version can correctly handle it. But in debug version, set_constant_with_place() in math_function.cu uses the TensorSetConstant in math_function.cc and causes crash.

it is useful in gradient phase of an operator with block

It caused by a bug of std::call_once described in https://stackoverflow.com/questions/41717579/stdcall-once-hangs-on-second-call-after-callable-threw-on-first-call. It is likely caused by a deeper bug of pthread_once, which is discussed in https://patchwork.ozlabs.org/patch/482350/