* fix amp

* fix amp

* make logic consistent with torch.autocast

* support multiple device

* fix as comment

* fix as comment

* avoid circle import

* fix unit test of autocast

* fix compatiblity of unit test of optimizerwrapper

* clean code

* fix as comment

* fix docstring

* add autocast wrapper

* fix docstring

* fix docstring

* fix compare version

* fix unit test

* fix incompatible arguments

* fix as comment

* fix unit test

* rename auto_cast to autocast