Mobile backward compatibility (#42413)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/42413
When a default argument is added, it does not break backward compatibility (BC) for full-jit, but does break BC for mobile bytecode. For example, https://github.com/pytorch/pytorch/pull/40737. To make bytecode BC in this case, we
1. Introduce kMinSupportedBytecodeVersion. The loaded model version should be between kMinSupportedBytecodeVersion and kProducedBytecodeVersion.
2. If an operator is updated, and we can handle BC, bump the kProducedBytecodeVersion (for example, from 3 to 4).
3. If model version is at the older version of the operator, add an adapter function at loading. For the added default arg, we push this default arg to stack before calling the actual operator function.
Test Plan: Imported from OSS
Reviewed By: xcheng16
Differential Revision: D22898314
Pulled By: iseeyuan
fbshipit-source-id: 90d339f8e1365f4bb178db8db7c147390173372b
