* fix selected_rows bug
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* refine cos_sim
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* add fp16 backward support
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* add sum_op fp16 test

* disable test_dist_save_load
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* add check_grad for sum

* add unit test for softmax_grad fp16
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* add scale_op unit test

* add mul_grad_op unit test for fp16

* add cross_entropy_grad and eman_grad unit test for fp16
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* fix cross_entropy unit test

* add pool2d fp16 unit test

* refine conv2d fp16 unit test
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* refine activation unit test
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* fix ci
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* follow zhihong's comment, copy from https://github.com/PaddlePaddle/Paddle/pull/12796
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This reverts commit ce7d9b07.

* exhaustive search for cuDNN conv.
* Refine code and add unit testing.
* Clean code
* Fix model load in fluid/inference and unit testing in conv2d
* Follow comments.

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1. Non utf-8 characters within comments of OPs may lead to protobuf fail to parse_from_string
2. comment out some ops which not supported on windows
3. cuda libs may not be correctly linked to target on windows

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* Fix build error of affine grid op in mac os.
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* Make function return reference.
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* wip

* add ref_by_trainer_id op

* ready to test

* fix ref inputs

* refine rpc_op_handle

* fix merge bug

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* Add affine grid generator.

* fix ffine grid.

* Add unitest.

* Add CPU kernel and fix unitest.

* Fix CPU kernel.

* Refine code.
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* Fix python api.
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* Update python api.
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* Fix comment.
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* Rename affine_grid_generator to affine_grid and enhence unitest.
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* Fix unitest.
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* fix dim0 in _load_slice_up_vars

* fix dim0 in _load_slice_up_vars, fix innershape in delete_var_op

* Revert "fix lookuptable in reduce strategy"

This reverts commit 0e722c5e

* add unit test for dist

* add unit test for dist, test=develop

* cancel revert, test=develop

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* fix GetTensorFromVar
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* refine GetTensorFromVar
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