Pow() : Use lightweight operations for predefined scalar exponent values (#28903)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/28903
Use of predefined and less compute intensive functions instead of pow() for predefined scalar exponent values.
Test Plan: automated tests
Reviewed By: jspark1105
Differential Revision: D18227280
fbshipit-source-id: 0a443832c3ff8372e64dbe04de4f7fb4ce7c0740
