* encapsulate the PaddleTensorToLoDTensor, test=develop

* serialize the pd_tensor, test=develop

* serialize tensors to file, test=develop

* add fluid.device_guard to specify the device type for Op

* functional dygraph enable/disable
test=develop

* use context manager instead
test=develop

* refine sample code
test=develop

* rename api & expose to fluid
test=develop

* fix sample code
test=develop

* test=develop, optimize distributedstrategy

test=develop

* change the function in op_teller, test=develop

* correct the commit-id, test=develop

Fix the big shape op test, elementwise_mul, elementwise_div, mul op
Fix the precision op test, mul op

* polish the profiler doc

* update ScopeBufferedSSAGraphExecutor&AsyncSSAGraphExecutor&ThreadedSSAGraphExecutor&FastThreadedSSAGraphExecutor&ParallelSSAGraphExecutor&ParallelExecutor for fetching unmerged results.

* add the unit test for fetch_unmerged.

* update ut for multi-card and multi-cpu.

* add the error message and the user suggestion in FetchOpHandle. test=develop

* fix basic gru lstm parameter attr bug; test=develop

* fix bias attr bug; test=develop

* add basic lstm gru name unitest; test=develop

fix bug that sourcecode of third_party can't be cached correctly,and add cache for xbyak and openblas (#22772)

* upgrade fp32 to fp64, remove no_grad_set, enlarge input shape for hsigmoid unittest test=develop

* revert "remove no_grad_set" test=develop

* add lodtensor share memory & serialization, test=develop

* fix windows compile error, test=develop

* deal vartype pickle & fix unittest matching error message, test=develop

* update timeout variable name, test=develop

* refactor memory map implement, test=develop

* clear mmap file discripter when exit unexpectedly, test=develop

* remove the child process fd in advance, test=develop

* remove mmap fds after Queue.put in child process, test=develop

* add hard unittests for register exit func, test=develop

* fix python2 compatibility problem in unittest, test=develop

* fix exception unittest error, test=develop

* polish code based review comment, test=develop

* fix inference c api lod, test=develop

* fix capi lod problem and enrich tests, test=develop

* delete useless header files and alter const_cast, test=develop

* add profiler_help.h to refine the code test=develop

* user can call dataset.set_download_cmd to set its customized download cmd
* add UT to cover this scenario

* test ResNet decorated by dygraph_to_static_output in static mode. test=develop

* Follow comments and change dygraph_to_static_output to dygraph_to_static_graph.test=develop

* Add the codegen and auto fusion for sum Op  in fusion group

* change dygraph_to_static_output to dygraph_to_static_graph. test=develop

* Remove duplicate code. test=develop

* Follow comments from Liujie. test=develop

* change dygraph_to_static_output to dygraph_to_static_graph. test=develop

* fix smooth l1 loss op shape > 100 test=develop

* remove from white list test=develop

* add mnist to test dygraph_to_static  test=develop

* Refine adam op, test=develop

* Fuse kernels together to reduce cpu time.

* Refine paddle enforce, test=develop

* Remove some comments, test=develop

* Refine code,test=develop

* Refine cuda kernel, test=develop

* Refine code according to comments, test=develop

* Support fetch and run program in the process of dygraph_to_static_output. test=develop

* fix to_source(gast) and remove dygraph API such as Conv2D, Linear. test=develop

* Correct CPU gradients of the argsort op, form a network to test its forward and backward process, test=develop

* fix dynamic threshold error in test_argsort_op, test=develop