[JIT] Frozen Graph Conv-BN fusion (#50074)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/50074
Adds Conv-BN fusion for models that have been frozen. I haven't explicitly tested perf yet but it should be equivalent to the results from Chillee's PR [here](https://github.com/pytorch/pytorch/pull/476570) and [here](https://github.com/pytorch/pytorch/pull/47657#issuecomment-725752765). Click on the PR for details but it's a good speed up.
In a later PR in the stack I plan on making this optimization on by default as part of `torch.jit.freeze`. I will also in a later PR add a peephole so that there is not conv->batchnorm2d doesn't generate a conditional checking # dims.
Zino was working on freezing and left the team, so not really sure who should be reviewing this, but I dont care too much so long as I get a review �
Test Plan: Imported from OSS
Reviewed By: tugsbayasgalan
Differential Revision: D25856261
Pulled By: eellison
fbshipit-source-id: da58c4ad97506a09a5c3a15e41aa92bdd7e9a197
