Optimize boolean expressions & unwraps (#18259)
Summary:
Simplify or eliminate boolean and/or expressions, optimize unwrapping a value that cannot be None, and optimize using `is` with a None and a non-None value
Since peephole optimize is now introducing constants, i added another constant propagation pass after running it.
Previously i had a PR that did this & optimized shape ops - i will add the shape optimizations in a separate PR.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/18259
Differential Revision: D14602749
Pulled By: eellison
fbshipit-source-id: 1c3f5a67067d8dfdf55d7b78dcb616472ea8a267
