Implement duck shaping on SymInts (#85808)
Duck shaping says that when two input tensors have the same
size, we assume they are symbolically related. This follows
the same optimization done by inductor.
This optimization is not done completely because we don't
currently install guards corresponding to the duck shape
relationships we created, but overall the guard propagation
for dynamic shape tracing is incomplete at the moment.
Signed-off-by: Edward Z. Yang <ezyang@fb.com>
Pull Request resolved: https://github.com/pytorch/pytorch/pull/85808
Approved by: https://github.com/albanD
