* optimize performance of dygraph

* optimize performance of dygraph and elementwise_add

* optimize the trace op

* fix bug

* fix bug

* fix unittest bug

* fix code format

* change sequential logic

* change some quotes

* add some notations

* change wrong note style.

* move elementwise_div grad

* change mutable_data to alloc

* fix compile bugs

* clean distribution_helper, index_impl, aligned_vector code in fluid

* fix conflicts

* move elementwise function to funcs directory

* fix compile bugs

* modify according to comment

* [KP] Add elementwise add xpu, test=develop

* modify the File Permissions

* modify the copyright time

* modify code style

* modify code style

* rename pten dir to phi

* rename namespace to phi

* rename infrt pten dir to phi

* resolve conflict

* rename pten to phi in cmake

* revert all infrt change

* change needed files

* fix infrt failed

* fix inference failed