* add support for __get_item__ of Variable test=develop

fix ExecutionContext::HasInput and ExecutionContext::HasOutput depend on the scope structure, test=develop (#20721)

* add cuda place and remove fluid.layers.data for test of python API, test=develop

* add cuda place and remove fluid.layers.data for test of python API, test=develop

* modified batch size for Python API test, test=develop

* add dlpack include in third_party. test=develop

* test=develop, communicator_is_sgd_optimizer flags

* support MLU nums, test=develop

* change anakin apis, test=develop

* add support to gcc8, add docker env test=develop

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

* Revert "Refactor conv computeINT8 (#19574)"

This reverts commit 2c32c2d6.

test=develop

* replace PADDLE_ENFORCE
test=develop

modify the way to pass parameter out_size in function. 

* - 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

test=develop test=document_fix

* improve save and load behaviour, test=develop

* code cleaning, test=develop

* disable check_guards and update_guards in release version, test=develop

* fix compilation issue, test=develop

* add buddy_allocator speed test data, test=develop

* fix compilation issue, test=develop

* fix comment, test=develop

* update function names according to the google C++ style guide, test=develop

* tweak the test data format, test=develop

* move buddy_allocator_test_data to paddle/fluid/testdata, test=develop

* add accessor and mutator for Desc, test=develop

* refine reduce code to save compiling time and binary sizes, test=develop

* add reduce rank check to avoid bug, test=develop

* fix fetch handler error with pslib
* fix distributed lookup table op with 1 pserver

test=develop

* move pool2d to add_quant_dequant_pass, test=develop

* fix elementwise_floordiv_op and elementwise_mod_op, test=develop

* fix API.spec, test=develop

* fix API.spec, test=develop

* add condition judgement for performance improvement test=develop

* add condition judgement for performance improvement test=develop

* refine code style test=develop