Only populate net_pos in ssaRewrite if the op doesn't already have a net_pos argument (#21051)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/21051
In net transforms, we perform an SSARewrite where we update the 'net_pos' for all the ops in the net. The transform function also takes a unordered set of net positions for blacklisting. It's possible that SSARewrite will change the indexes of the ops so the blacklist is applied to the wrong ops. We fix this issue by having SSARewrite only assign new net_pos if the op doesn't already have one.
Reviewed By: yinghai
Differential Revision: D15532795
fbshipit-source-id: e020492a7b5196a91cdc39d0eda761b1ca612cdb
