* Support assignment to a Variable in dynamic mode. Note: not deal with backward.

* Rewrite VarBase __setitem__ for high-performance.

* try to test 3 means to do __setitem__ and test the performance of 3 means.

* Retain the means of the highest performance: C++ code and don't trace op.

* include ncclRecv and ncclSend, test=develop

* add gloo initializer, test=develop

* Error message opt, test=develop

* solve comments, test=develop

* fix typo, test=develop

* add float64 input to ctc_loss

* modified error message of  warpctc

* update repo and tag of warpctc

* add test for warpctc with float64 input

* modified warpctc.cmake to make sure build always

* resolved sample code bug of warpctc

* add core.ops in warpctc dygraph

* fix a bug of test

* support elementwise add, activation, matmul on Baidu Kunlun
* test=kunlun

* minor
* test=kunlun

* reconstuct the xpu directory
* test=kunlun

* minor
* test=kunlun

* minor
* test=kunlun

* minor
* test=kunlun

* minor
* test=kunlun

* minor
* test=kunlun

register log double grad kernel for cpu and cuda

* fix sgd/momentum/dpsgd/rmsprop error message

* refine broadcast_op_handle

* refine some error messages

* refine some files

* fix bug

* fix bug

* fix bug

* follow comments

* follow comments

* fix test_dist_fleet_heter_ctr & peformance update

fix cpplint error for the autmic max/min

* refine err msg

* follow comments

This reverts commit 29f1560d.

* add xpu in heter mode
test=develop

* BOOST_CONST_GET; PADDLE_THROW
test=develop

* code style
test=develop

* code style
test=develop

* code style
test=develop

* refine
test=develop

* refine
test=develop

* refine
test=develop

* refine code
test=develop

* fix bn double grad, test=develop

* update, test=develop

* add fp16 for matmul

add abs support double grad for the api 2.0

* refine PADDLE_ENFORCE

* [buf fix]:fix unittest test_activation_op error

* split long-time unittests to smaller ones

* rename some unittests

fix cuda atomic for ARCH<350 for the automic_max

* Add pass compatibility check for four mkldnn pass, test=develop

* add unittest count of windows

* Reduce the number of retries

* fix error message in conv/conv_transpose. test=develop

* refine err msg in shuffle channel op

* fix tensorrt 6 build error. test=develop

* fix. test=develop

* bug fix

* test=develop

* use iwyu clean include, test=develop, test=win

* compilation error, test=develop

* fix compilation error2, test=develop

* fix compilation error3, test=develop

* fix compilation error4, test=develop

* fix compilation error5, test=develop

* fix compilation error6, test=develop

* fix compilation error7, test=develop

* fix compilation error8, test=develop

* fix compilation error8, test=develop

* fix compilation error10, test=develop

* fix compilation error11, test=develop

* refine the error message for bath size like