* cherry-pick:Add double grad in Squeeze and Unsqueeze to release/1.8, test=develop
Signed-off-by: NTeslaZhao <zhaolisoftware@163.com>

* cherry-pick:Add double grad in Squeeze and Unsqueeze to release/1.8, test=develop

* add matmul doublegrad op

* fix compile errors

* modify code according to review

* delete float16

* delete GetDimForInput to be consitent with release/1.8

[Cherry-Pick] Add Log double grad kernel (#27604)

 double grad support for abs 

* add batch norm double grad, test=release/1.8

* update, test=develop

* fix, test=develop

* optimize slice TRT plugin

This patch removes unnecessary barrier for data transfer of needed offset,
so data transfer can be overlap with GPU kernel execution.

This patch also fixes incorrect name of slice plugin. That is, replaces
"layernorm" with "slice"

test=develop

* add serialize/deserialize to slice plugin

* add static shape slice trt plugin

* fix slice trt op convertor dynamic shape bug

* fix format by clang-format

* fix pylint format error

* fix problems commented by peiyang
Co-authored-by: NRyan Jeng <rjeng@nvidia.com>
Co-authored-by: NShang Zhizhou <shangzhizhou@baidu.com>
Co-authored-by: NRyan Jeng <rjeng@nvidia.com>

test=release/1.8

* Fix test_gast_with_compatibility.py due to the problem of gast in python3.8 (#27433)

test=develop

* fix dll load bug on windows from python3.8 (#27324)

* Support python3.8 (#26850)

* Support python3.8

test=notest

* Replace the 'spawn' start method with 'fork' start method for multiprocessing, on MacOS with python>=3.8 (#27317)

* Replace the 'spawn' start method with 'fork' start method for multiprocessing, on MacOs when python>=3.8

test=develop

* Correct the error in decorator.py (#27409)

test=develop
Co-authored-by: NZhou Wei <52485244+zhouwei25@users.noreply.github.com>

* add DISTRIBUTED_TRAINER_ENDPOINTS env for cloud

* add double grad for expand, test=develop

* add double grad to reduce sum

* add mock barrier all (#24786)

* add mock barrier all
test=develop

* fix
test=develop

* fix
test=develop

* fix
test=develop

* fix gloo error
test=develop
Co-authored-by: Nxujiaqi01 <173596896@qq.com>

* fix dataset py3 (#25012)

* fix dataset py3 error
* test=develop

* fix logger (#24682)

* fix logger of FetchHandler，which may print log twice
* test=develop

* add timeout and http store in communication (#23436)

* add timeout and http store in communication, add revert and confirm in fleet
* test=develop

* modify datanorm op test=develop (#23030)
Co-authored-by: Nxujiaqi01 <173596896@qq.com>
Co-authored-by: Nyaoxuefeng <yaoxuefeng@baidu.com>

* fix prelu for compatibility with saved model of old version

* reshape alpha

test=develop
Co-authored-by: Nchalsliu <45041955+chalsliu@users.noreply.github.com>

* fix cpuid.h not found

* fix-jetson-compile-pyramid_hash

* add more info to version.txt, test=develop (#24551)

* Fix dygraph grad bugs (#25781)

* fix double grad visitid unit; test=develop

* change name hash_pair to HashPair; test=develop

* follow comment; test=develop

* remove manual seed; test=develop

* change create_graph from True to False; test=develop

* add scale_x_y for yolo_box, test=develop

* add scale_x_y for yolo_box, test=develop

* refine eps in iou_similarity, test=develop

cherry-pick,fix optimizer.state_dict and LRScheduler.state_dict to save/load dygraph

add new API:LambdaDecay,test=develop 

* enable load_program_state run in imperative mode; test=develop

* remove useless code; test=develop

* make default_collate_fn visible. test=develop. test=release/1.8

* test=release/1.8, cherry fix fluid.embedding

test=release/1.8

* CHERR-PICK1.8,add base class of LearningRateEpochDecay, and API: MultiStepDecay, and API: StepDecay,test=release/1.8

* fix unittest to add coverage,test=develop

* test=release/1.8, add index sample

* fix bug of prelu when rank not equal 4, test=develop

* fix prelu inference, test=develop

* fix api, test=develop

* fix shape when mode is chennel, test=develop

* remove debug code, test=develop

* add unittest, test=develop

* fix beam_search infershape, test=develop

* fix beam search op unittest, test=develop

Fix the bug for elementwise_div op, when the first var is scalar; Use the shape 1 replace the -1 in shape

添加loss自适应的学习率衰减策略。

* raise index error when slice out of range; test=develop

* add uni test; test=develop

* fix format error; test=develop

* add comment for py::index_error; test=develop

* polish error message; test=develop

* polish error message; test=develop

PR types: Bug fixes
PR changes:Ops
Describe:
Fix the broadcast bug in elementwise ops, when elementwise ops do not have fast gradient calculate way，use the default way to calculate.

Enhance error message of checkpoint_notify_op, fake_init_op gen_nccl_id_op and listen_and_serv_op (#24554) (#24844)

test=develop