Clone symint on set_sizes_and_strides (#85878)
From the perspective of having valid sympy expressions for any given size/stride property, we can have tensors inherit SymInts from each other (in cases where the size expression is unchanged, which is a common case).
But we also use SymInts to let us build graph traces of our programs, and we need to be able to trace from a SymInt back to the tensor that it originated from in order to trace correct graphs. This change ensures each tensor starts with fresh SymInts.
- note: our policy has already been to use PySymIntNode objects to store pointers to proxy-tracer objects for use during tracing
- before making this change (to clone symints), sometimes we'd attempt to store more than one proxy-tracer object on the same symint and the last-stored one would clobber all the earlier ones. This would result in tracing the wrong graph in some cases.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/85878
Approved by: https://github.com/ezyang
