* add half_async in the communicator
* fix DistributedStrategy

* remove unused inputs, test=develop

* remove unused inputs, test=develop

* update dtype, test=develop

* remove unused inputs, test=develop

* update op_use_default_grad_op_maker, tese=develop

* resolve conflicts, test=develop

* follow comments, test=develop

* update center_loss_grad, test=develop

* add multiprocess for dygraph data loader, test=develop

* polish code & add safe gurad, test=develop

* refactor dygraph dataloader & add signal handler, test=develop

* fix member initializer compile error on ci, test=develop

* fix member initializer compile error one more, test=develop

* remove useless config, test=develop

* skip windows incompatible problem, test=develop

* add unittest for coverage, test=coverage

* add more exception unittest case, test=develop

* deal with signal handler coverage, test=develop

* polish code & add signal handler tests, test=develop

* deal with coverage ci problem, test=develop

* split data loader test & coverage ci fix, test=develop

* remove test_imperative_data_loader_with_exception, test=develop

* remove singal process except test case, test=develop

* add exception tests again & remove sample list test, test=develop

* split normal and exception unittests to diff class, test=develop

* polish doc for use_multiprocess effect in static mode, test=develop

* polish grad op check, test=develop, test=document_fix

* keep op_use_default_grad_maker.spec to avoid conflict, test=develop, test=document_fix

* fix fsp_op, test=develop

* fix fsp grad op maker, test=develop

* update op_use_default_grad_op_maker.spec, test=develop

* remove the useless third_party library from C++ inference library

* revert removing the install directory

faster build by reduce by-product, reduce linking library and fix compile warning of std=c++11 (#22164)

* add collective communication library in fleet to replace mpi
* test=develop

- fluid和lite精度比较替换为相对误差

* test=develop, bug fix for sparse recorder

* polish error message of parallel executor, test=develop

* change PADDLE_ENFORCE, test=develop

- 添加了fluid-lite子图方式运行resnet的单测
- 修改了依赖Lite的git commit id

* fix the bug of profile update test=develop

* add backward gradient computation for op argsort test=developo

* use pre-commit test=develop

* add bn and relu fuse pass

* add op attr assert and dtype assert

* fix some inputs&&outputs bugs for the fused op and pattern.

* add the unittest for fuse_bn_act_pass. test=develop

* use normative enforce statements. test=develop

* add the cpu test. test=develop

* add the support of batch_size=1 for the bn with relu op. test=develop

* add the error type for paddle throws. test=develop

* add fused_batch_norm_act and fused_batch_norm_act_grad to op_has_unsed_vars_white_list. test=develop

* test Optimizer in dygraph, test=develop

* add optest for Optimizer in dygraph, test=develop

* fix adagrad optimizer, test=develop

* fix dpsgd optimizer, test=develop

* fix test_optimizer.py, test=develop

* fix dpsgd optimizer, this op only support cpu, test=develop

* add optest for optimizer, test=develop

* add description for dpsgd, test=develop

* add rmsprop to white_list in unused_var_check.cc, test=develop

* polish code style, test=develop

* polish code style, test=develop

* delete seed attribute for DpsgdOptimizer, test=develop

* change testing to debugging, test=develop

* Polish the PADDLE_ENFORCE in fusion_group pass related codes.
test=develop

* Correct the unittest because of the change relu_grad's formula.
test=develop

* add support for nested profiling event and printing in different level

stack's wait cost a lot of cpu time, use cuda kernel to do memory copy
will reduce cpu time.
Signed-off-by: Nzhaoyuchen <zhaoyuchen01@baidu.com>

* modify fc to linear in sample code, test=develop

* remove FC, test=develop

* remove warnings, test=develop

* drop fluid/imperative/README.md , test=develop

* change fc to linear, test=develop

* polish code style, test=develop