[FX] change dynamic control flow example to a *more* dynamic version (#53250)
Summary:
This is a more fundamental example, as we may support some amount of shape specialization in the future.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/53250
Reviewed By: navahgar
Differential Revision: D26841272
Pulled By: Chillee
fbshipit-source-id: 027c719afafc03828a657e40859cbfbf135e05c9
