* support dump param of model into afs (#20302)

* support dump param to afs
test=develop

* code style
test=develop

* code style
test=develop

* dump param
test=develop

* dump param
test=develop

* dump param
test=develop

* dump param
test=develop

* find lookup table in order (#20932)

test=develop

* cherry-pick
test=develop

* solve pslib core in stop worker
test=develop

* print table stat info for pslib
test=develop

* fix cache table bug, add save_paddle_inference_model, fix hdfs util bug (#21052)

* fix cache table bug
* add save_paddle_inference_model
* fix hdfs util bug
* test=develop

* fix several sparse table issuses (#20686)

* no longer need to define all embedding layers (no one less) of all slots in each program. make trainer_param repeated in ps.proto.
* add find_distributed_lookup_table_grads instead of hard code GRAD
* support embedding stop gradient. push sparse has error before fix this.* 
* fix fill sparse, skip slots which do not have embedding. each slot's embedding in a sparse table should be used in all training programs before fix this.
* fix pull sparse, skip slots which do not have embedding.
* fix collect feasign label info, skip slots which do not have embedding.
* support when there are multi sparse tables in one or multi training programs, each program can pull/push its own related sparse tables instead of all sparse tables.
* test=develop

* add copy table (#21086)

* copy some feasigns and corresponding embeddings from one sparse table to another
* copy all feasigns and corresponding embeddings from one sparse table to another
* copy all dense params from one table to another
* copy some local vars to other local vars

* fix fs_client_param bug (#21212)

* fix fs_client_param bug， user can set this config through fleet_desc_file or fleet config
* test=develop

* fix fleet util bug (#21254)

* fix fleet util bug in save paddle inference model
* test=develop

* add pre condition check for fuse optimizer op pass, test=develop

* add log & set init to zero, test=develop

* fix test_fuse_all_reduce_pass failed, test=develop

* polish details, test=develop

* refine PADDLE_ENFORCE & remove needless VLOG, test=develop

* refactor op check method, test=develop

* delete paddle infershape enforce marco (#20832)

* Polish and arrange code in enforce.h (#20901)

* Enrich the type of error and declare the error type interfaces (#21024)

* Enrich the type of error and declare the error type interfaces, test=develop

* adjust tests to adapt new form, test=develop

* add inference deps with error_codes.pb.h, test=develop

* restore stack iter start pos, test=develop

* polish code based review comments, test=develop

* Add dependency for error_codes.proto (#21084)

* fix activation_functions deps, test=develop, test=document_fix

* add error_codes_proto deps, test=develop, test=document_fix

* try delete enforce.h, test=develop, test=document_fix

* change cuda enforce & add example (#21142)
test=release/1.6

[cherry-pick] fix squared_mat_sub_fuse_pass bug when elementwise_op input is persistable param test=develop test=release/1.6 (#21044)

fix squared_mat_sub_fuse_pass bug when elementwise_op input is persistable param

* fix infer crashes caused by conv/pool upgrades, test=release/1.6

* fix bug, test=release/1.6

cherry-pick1.6 simplify master+patch，remove ins when size != merge_size or has conflict slot  (#20941)

* simplify master+patch，remove ins when size != merge_size or has conflict slot
* test=develop

* add check nan / inf in downpour worker during training
* test=develop

* update pserver decay blocks

* update distributed notify handler

* add support to gcc8, add docker env
* remove the warning issue

* Serialize to pickle format (#20820)

test=develop

* save load problem fix and new feature add (#20823)

* fix persistable;

* fix save load bugs; test=develop

* fix bug; test=develop

* add example for new io api; test=develop

* addd example; test=develop

* Add IndicateVarDataType interface to block tensor is not initialized problem in OP GetExceptedKernelType (#20044)

* add indicate_var_data_type inferface, test=develop

* add unittests & polish error message, test=develop

* remove needless include, test=develop

* extract public function & polish message, test=develop

* delete empty var check, test=develop

* change data_type to pointer parameter, test=develop

* polish details, test=develop

* Replace risky GetInputType method with secure IndicateVarDataType interface (#20668)

* replace part of the old implementation, test=develop

* restore concat op, test=develop

* update all ops implemention & delete GetDataTypeOfVar func, test=develop

test=release/1.6

* add more err msg, test=develop

* add more unittests, test=release/1.6

test=release/1.6

test=release/1.6

* - Flushing mkl-dnn cache

test=develop

- Disabled clearing cache for LoadModel

- Added clearing of mkl-dnn cache when Executor is created

test=develop

- Do not clear for GPU places

test=develop

- compilation fix

test=develop

* - Moved clearing of mkl-dnn cache in destructor of executor

test=develop

* - Compilation fix

test=develop

- Reverted conditional clearing of mkl-dnn cache in Executors's
  destructor

test=develop

- compilation fix

* fix op log bug, test=release/1.6

* add unittests, test=release/1.6

* Fix communicator slow bug & fix communicator stop bug (#20366)

* test=develop,Fix communicator slow bug

* test=develop, delete if() in stop_worker()

* test=develop

* fix UT, test=develop

* fix bug in fetch handler, test=develop

* fix bug in fetch handler, test=develop

* test=develop, fix fetch barrier bug

* test=develop, bug fix

* test=develop, bug fix

* test=develop, fix bug

* test=develop,test=release/1.6

* support dump multi file
test=develop

* dump fix num file
test=develop

Fix parse content in CreatePreLoadReaders. Before this fix, if you use dataset.set_parse_content and dataset.preload, parse content didn't work.

* Add Multihead matmul fuse pass (#20167)

* Add multihead fuse pass for ernie opt

* Refine softmax

test=develop

* Refine cuda kernel

* Refine cuda version

* Refine cmake

test=develop

* refine header file

* refine test case and pass
* refine comments

* Delete useless code.

test=develop
Signed-off-by: Nzhaoyuchen <zhaoyuchen01@baidu.com>

test=release/1.6

* add new save load interface; test=develop

* add new save interface; test=develop

* add save load interface ;

* fix save load error;

* fix dygraph set dict bug;

* add save load unit test; test=develop

* fix test_imperative_optimizer bug; test=develop

* fix unitest optimizer bug; test=develop

* fix code coverage; test=develop

* fix converage; test=develop

* add document for apis; test=develop

* fix unitest error; test=develop

* fix save load unit test error; test=develop

* fix error message; test=develop

* change set_parameter set_optimizer to save_dygraph; test=develop

* add load_graph check; test=develop

* fix api spec; test=develop

add executor.FetchHandler for train/infer from the dataset

* How to write custom op needs to follow framework OP spec.
* Package fluid_framework.so and headers into whl.
* Add paddle.sysconfig.get_include() and paddle.sysconfig.get_lib() to get include dir and lib dir.
* Export some C-APIs to merge OpInfo between core.so and custom_op.so.
* Add unit testing.
* Update API.spec.

* Follow Wangzhen's comment in PR 18970, test=develop

* Review comments, test=develop

* Leave fake quantization around mul

test=develop

* Replace Fake with Real Quantized Mul

test=develop

* Fix bug in quantize placement pass

Nodes in the graph now have checked type instead of node name when they are to be marked for quantization test=develop

* update operator compatible info, test=develop

* revert cmake/version.cmake, test=develop

* add unit_tests and fix bugs, test=develop

* update ../paddle/fluid/framework/framework.proto, test=develop

* fix bug of paddle/fluid/inference/api/analysis_predictor.cc, test=develop

* update paddle/fluid/framework/version_test.cc, test=develop

* add comments and rename interfaces, test=develop

* Fix conv2d+dequantize squash for residual fusion

test=develop

* Disable conv-requant squash

test=develop

* codegen code for reconstruction test=develop

* fix the cmake test=develop

* fix review advice test=develop

* add a base class for the Communicator
* add AsyncCommunicator Impl for async distributed training

* shape and optimize paddle error message stack, test=develop

* limit exception type & add unittest, test=develop

* fix multi-platform problem, test=develop

* fix related unnitest failed, test=develop

* add doc & fix unittest errors, test=develop

* fix function name error, test=develop

* update tensor test exception msg compare, test=develop

* remove unittest on win32, the dir format is different, test=develop

* remove useless package, test=develop

* add paddle enforce handler unittest, test=develop

* add exception checkout, test=develop

* fix coverage failed, test=develop

* fix op registry test failed, test=develop

* refactor whole pr, test=develop

* remove test in CMakelist, test=develop

* fix coverage, test=develop

test=develop