Fix type unification With Specialized Tensor Shapes (#31076)
Summary:
Fix for https://github.com/pytorch/pytorch/issues/30015
We had a model that failed in shape propagation because we could not unify `Tensor` and `Optional[BoolTensor]`. Tensor not subtyping Optional[BoolTensor] was correct, but we should have unified those two types to `Optional[Tensor]`.
The fix here is that for immutable types containers (Optional, Tuple Type), we should be attempting to unify with complete shape information, and if that fails, then try to unify those types with unshaped types.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/31076
Differential Revision: D18921802
Pulled By: eellison
fbshipit-source-id: aa6890277470c60b349ed1da4d81cc5d71d377f6
