Reduce number of variables in codegen (#38369)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/38369
Seems we have a lot of variables in codegen that carry duplicate information.
This PR is removing them. It unifies all use sites to use the same instance
ghstack-source-id: 104067031
Test Plan: waitforsandcastle
Differential Revision: D21537983
fbshipit-source-id: 8d3ce3d3f712f7ba355e8c192798dfefaf847dac
