Immediately compile backwards graph in AOTAutograd if dynamic shapes (#104971)
Previously, we made backwards graph compilation lazy to avoid paying
for compilation if the user didn't actually end up using the backwards
graph. This was useful in the old days when a lot of things in Inductor
didn't work and we could bypass errors this way.
However, this has a bad implication for dynamic shapes: the backwards
graph compilation can trigger extra guards, which are too late to
install in the Dynamo context if we wait until backwards is being run.
So in this PR I move us back to compiling backwards graph immediately
if we capture any SymInts for backwards.
Signed-off-by: Edward Z. Yang <ezyang@meta.com>
Pull Request resolved: https://github.com/pytorch/pytorch/pull/104971
Approved by: https://github.com/Chillee
