* standard_api

* add hardtanh

* first commit

* clarify the quotes

* change code style format

* support bfloat16

* Fix bug of reduce_sum op. When input.numel() > INT32_MAX, its result
is wrong.

* Fix some problems.
1. Change fluid head files to phi files.
2. Delete useless code.
3. Fix code style problems.

* Fix some code style problems.

* Fix some code style problems.

* move elementwise test=kunlun

* move add/sub/mul/div kernel to elementwise_kernel, test=kunlun

* fix ci bugs,test=kunlun

* fix ci bugs

* test=kunlun

* [OpAttr]Adapt tensor axis for reduce_min/max/mean/sum/prod

* first commit

* add fp16 ctest files for compare op

* add cpu register of float16 for compare ops

* move grad_add

* fix unittest bugs

* fix compile bugs

* Create elementwise_heaviside_op.cc

* add ElementwiseHeavisideFunctor

* Create test_elementwise_heaviside_op.py

* 增加heaviside的python接口

* add heaviside in white list

* 增加heaviside的签名

* 增加heaviside的核函数

* 增加heaviside梯度的核函数

* 增加heaviside梯度的注册

* 调整代码格式

* Update elementwise_sig.cc

* add heaviside in __all__

* Update heaviside docs

* Update math.py

* Update math.py

* Update math.py

* optimize the performanece of sum api

* optimize IsDenseTensorInput

* remove debug log

[Phi]Separate AddKernel/DivideKernel/SubtractKernel/MultiplyKernel from ElementwiseKernel（Part1） (#41806)

* seperate add/div/sub/mul from elementwise

* delete code

* fix compile bugs

* deal with conflict

* fix bugs when compile

* fix windows unit test bug

* fix ci converage bugs

* regist elementwise_xxx

* init commit no push

* collect comile errors

* bitwise UT

* fix compile problem

* cancel comments

* restore miss deletion

* fix compilation

* fix UT

* NO stash in multiple branch at the same times

* fix error

* combine .cu from gpu and kps

* replace gpu by kps

* fix by Chen-weihang

* Revert "Fix kps compile error in Junhui logic compare bitwise"

* fix backend test

* rm comments
Co-authored-by: NChen Weihang <chenweihang@baidu.com>