* follow comments. test=develop

* Fix typo

* fix compile error. test=develop

* merge develop branch. test=develop

* Remove set_equal

* Polish code

* Delete unused functions

test=develop

* polish code. test=develop

* follow comment

* polish code.

* fix windows compile error. test=develop

* fix op handle.

* rerun ci. test=develop

* rerun ci. test=develop

* rerun macci. test=develop

* polish code. test=develop

* rewrite sort code. test=develop

* remove unused code. test=develop

* fix tests. test=develop

* fix conflict. test=develop

* follow comment. test=develop

* merge develop branch. test=develop

* fix tests. test=develop

* remove ToTypeIndex. test=develop

* rerun ci. test=develop

test=develop

* Enable ngraph tests for a ngraph engine
test=develop

* Move the test structure to other place
test=develop

* Add USE_NGRAPH flag, simple structure
test=develop

* Add psroi_pool operator.

* add l2 unit test
test=develop

* code refine
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* fix nccl dist test acc test=develop

* fix test=develop

test=develop

* random failed. rerun ci. test=develop

* windows failed. rerun ci. test=develop

* add more log for dist test for ci test=develop

* increase deadline test=develop

Revert "Merge pull request #14798 from PaddlePaddle/revert-14786-revert-14782-revert-14398-imperative"

This reverts commit b1d3a1c8, reversing
changes made to f1fb64b1.

fix cmake
test=develop

add unittest model containing while_op
remove unnecessary codes
test=develop

* enable test_gradient_clip in mac
test=develop

* refine test_gradient_clip
test=develop

* add nccl2 dist tests test=develop

* fix dist_base test=develop

* fix tests test=develop

* fix test on mac test=develop

* Refine conv_fusion_op for identity activation.
* Fix unit testing.
test=develop

test=develop

* test dist ut fixes test=develop

* fix cmake

* for test

* expose square
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* fix activation
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* Add square API
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* add necessary op

* code refine

* fix API.spec
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* fix unit test
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* add unit test sparse_grad_clip
test=develop

* fix API.spec
test=develop

* remove mac test for test_gradient_clip
test=develop

* remove selectedrows_mul_tensor
test=develop

test=develop

test=develop

test=develop

test=develop

add unittest
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add unittest
test=develop

test=develop

test=develop