* cherry pick test=develop

* cleanup test=develop test=release/1.6

* cleanup test=develop test=release/1.6

* add api check in fc test=develop

* enforce shape error info of sum op test=develop

* fix spelling test=develop

* print x_dims info test=develop

* enhance shape error info test=develop

enhance shape error messages for reshape op.
test=release/1.6

test=release/1.6

* Add support for None for fluid.data (#20228)

* Refine Error Message for New Data API (#20204)

* Modify English doc of fluid.data (#20248)

* Add detailed error messages for nce layer

* Fix some problems

* Fix unit test coverage

test=release/1.6

test=release/1.6

* fix the error message for reduce_mean and reduce_sum op (#20063)

* fix the error message for reduce_mean and reduce_sum op test=develop

* fix typo test=develop

* fix according review advice test=develop

* fix the test test=develop

* fix test=develop

* Fill constant error message fix (#20075)

* fix the constant error message test=develop

* fix typo test=develop

* fix typo test=develop

* fix code style test=develop

* fix comment and bugs test=develop

* fix the bug test=develop

* fix and add unittest test=develop

* fix the typo test=develop

* add support for the fill_constant op test=develop

* add test for ci coverage test=develop

* add error log

add executor.FetchHandler for train/infer from the dataset

* test=develop, fix docker with paddle nccl problem

* test=develop, Add Variable api and refine dygraph related API

* test=develop, Add Variable api and refine dygraph related API

* test=develop, refine test for new api and error info

* test=develop, refine error info and test_layers

* test=develop, add API.spec

* test=devleop, fix to_string python2 and python3 compat error and refien doc

* test=devleop, add API spec

* test=devleop, update API spec

* test=devleop, update API spec

* test=develop, invoke ci

* test=develop, fix example code

* test=develop, update API spec

* test=develop, fix auto_prune_error_on_leaf

* test=develop, fix auto prune error on loss stop_gradient

* test=develop, remove useless error check

* test=develop, add more ut for sorted gradient

* Update crf_decoding api & example

* Update api spec

* Fix linear chain crf api

* Avoid sharing data pointer with input

* Simplify the logic in linear_chain_crf_decoding

* Add unittest for crf_decoding when label & path both are set

* Update API spec

* Add unittest for layers && correct infer_shape in chunk_eval

test=release/1.6

test=release/1.6

* Add multihead op for ernie opt

* Refine softmax

* Refine kernel.

* Refine cuda kernel

* Refine cuda version

* Refine cmake

1.support asymmetric padding;
2.support padding algorithm:"SAME" and "VALID";
3.support channel_last: data_format NHWC and NDHWC;
4.change doc of python API and c++;

test=release/1.6

* refector geo sgd & communicator

* add a default value for _prune interface

* modify document

* test=develop, argument shape support tensor and tensor in list

* test=develop,Increasing the coverage of CI tests

* test=develop, modify the document and update API.spec

* test=develop, modify the doc and update API.spec

* test=develop, modify the doc and update API.spec

* test=develop, modify the interface of UniformInitializer

* test=develop, modify the interface of XavierInitializer and MSRAInitializer

* test=develop, modify based on review's comments

* test=develop, modify based on review's comments

*  test=develop, modify based on review's comments

* fix pool2d pool3d:
1. support asymmetric padding;
2. support padding algorithm:"SAME" and "VALID";
3. support channel_last: data_format NHWC and NDHWC;
4. support inferring shape when input with negative dims in compile time;
5. change doc of python API and c++;
6. fix bug in cuda kernel when Attr(adaptive) is true.

test=develop,test=document_preview

* fix 'tensors' to 'Tensors'. test=develop,test=document_preview

* add test for converage ValueError.test=develop,test=document_preview

* resolve conflict in test_pool2d. test=develop

* opt FC

* opt rest of dygraph.nn

* new param shape check and unittest

* add kwargs for Layer

* add new set_value api

* use property decorator

* update API.spec, test=develop

* use UserList, separate gettersetters, test=develop

* update test_custom_layer_with_kwargs, test=develop

* fix UserList compatibility, test=develop

* fix UserList compatibility, test=develop

* keep FC._w, test=develop

* add unittests, Conv3D bug fix, test=develop

* clean code, test=develop

* fix dygraph guard in unittest, test=develop

* add property setters, remove unused param in tracer, test=develop

* tracer none check, test=develop

* merge, test=develop

* refine, test=develop

* bug fix in  prelu and conv3d_transpose, test=develop

* rm __set__, test=develop

* set tensor value instead of assign op

* fix property setter call, test=develop

* fix api.spec, test=develop

* fix doc sample, test=develop

* add parameter shape check when load parameter from file; test=develop

* fix test error; test=develop

* add wrong shape check; test=develop

* remove useless code; test=develop

* add testcase setup

* add teardown, remove temp model_path; test=develop

* add clean process; test=develop

* test=develop, fix docker with paddle nccl problem

* test=develop, Add Variable api and refine dygraph related API

* test=develop, Add Variable api and refine dygraph related API

* test=develop, refine test for new api and error info

* test=develop, refine error info and test_layers

* test=develop, add API.spec

* test=devleop, fix to_string python2 and python3 compat error and refien doc

* test=devleop, add API spec

* test=devleop, update API spec

* test=devleop, update API spec

* test=develop, invoke ci

* test=develop, fix example code

* test=develop, update API spec

* test=develop, add compat test and fix inplace campat dict error

* fix pool infershape. test=develop

* fix unittest converage. test=develop

* fix format. test=develop

* make pad and split support fp16
test=develop

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

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

* impove error message when passing ndarray with object dtype

* imporve message format

* change assert to raise TypeError

* remind user how to locate the irregular data instead of printing

* add unittest for input array type check

* Fix conv2d+dequantize squash for residual fusion

test=develop

* Correct int8 input

test=develop

* Add if exclude or include padding in pool2d mkldnn

test=develop

* x.dims == y.dims test=develop

* refine comment

* Expose `mutable_data` as python binding

test=develop

* Add test for device pointer binding

test=develop

* Make test compatible with python 2

* fix input shape check test=develop

* move PADDLE_ENFORCE test=develop

Add dtype for coalesce_tensor_op

The new "fluid.data" changes old "fluid.layers.data":

1. Add shape and dtype check.
2. Remove "append_batch_size" parameter. We won't offer this in the new data layer because other deep learning platforms don't have this kind of data layer pre-processing. It may confuse users.
3. Remove "stop gradient" parameter because the data layer doesn't do back-propagation

TODO：
Now data layer feeded by executor is checked, will we want to check the feed data of readers in the future?

* add kernel for fill_op, test=develop

* modify PADDLE_ENFORCE to PADDLE_ENFORCE_EQ, test=develop

* add op test for fill_op, test=develop

* REGISTER COP CUDA KERNEL, test=develop

* update test_fill_op.py, test=develop

* change FillConstantOpVarTypeInference to FillOpVarTypeInference, test=develop

* fix op test, test=develop

* add head file, test=develop