* enable ngraph throught build_strategy test=develop

* add unittest test=develop

* put use_ngraph unconditional test=develop

* remove paddle_enforce test=develop

* remove paddle_enforce test=develop

* fix copyright test=develop

* limit for ngraph only test=develop

* increase num_iteration_per_drop_scope
test=develop

* Fix bug of while_op
test=develop

* fix bug of whileOp
test=develop

test=develop

Polish fleet API to support cuda collective mode and nccl2 mode

* Disable fuse optimization
test=develop

* remove legacy memory optimization codes, test=develop

* follow huihuang's comments,test=develop

* follow luotao's comments, test=develop

* open fuse optimization ops
test=develop

* first version memory optimize pass, test=develop

* remove move_tensor_sharing_pass, test=develop

* refine code comments, add unittests, test=develop

* turn off memory_optimize by default, test=develop

* follow huihuang's comments, test=develop

* follow chengduoZH's comments, test=develop

* fix grammar error, add const qualifier, fix pass_test exception message, test=develop

* follow chengduoZH's comments 2nd, test=develop

* support sparse gradients
test=develop

test=develop

* feature/buffer_shared_inplace, test=develop

* refine code, test=develop

* fix elementwise_add op cpu inplace and sum inplace bug, test=develop

* add unittest and debug log, test=develop

* fix parallel_executor scope bug, polish code, test=develop

* fix sum op, activation op, single_in_place_inference bug, test=develop

* remove kLocalExecScopeName, test=develop

* fix unittest,test=develop

* fix out_var first version bug, test=develop

* follow comments,test=develop

* clean code of dim and place, test=develop

* fix failed unittests, test=develop

* add is_runnning in communicator, test=develop

* clean build_strategy
test=develop

* DataBalanceOpHandle has been removed
test=develop

* debug

* update build_strategy.
test=develop

* fix code bug
test=develop

test=develop

* add event for fast executor and add threads for scopebuffer executor
test=develop

Async exe support communicator

test=develop

* add record_event
test=develop

* remove csp
test=develop

Refine the Executor when the num_thread=1

* make parallel_executor support FLAGS_use_mkldnn

test=develop

* add warning when set mkldnn_enabled_op_types_ in non-mkldnn env

test=develop

* reset drop local scope counter
test=develop

test=develop

* move pass to ir

* polish code
test=develop

* fix dependency
test=develop

* add use_cuda to inplace pass,test=develop

* add test softmax_with_xe_inplace test,test=develop

* fix potential inplace bug
test=develop

* add more skip vars in mem opt pass,test=develop

* follow comment,test=develop

* follow comments,move duplicate out arg check to program->graph,test=develop

* add use_cuda to inplace pass,test=develop

* add test softmax_with_xe_inplace test,test=develop

test=develop

* fix op graph view
test=develop

* rewrite inplace pass and fix reference count pass bug
test=develop

* fix unittest failed
test=develop

* follow comments, test=develop

test=develop

test=develop

test=develop

* Add fuse momenutum ops