Fix FallbackKernel behavior on mutable ops (#118649)
FallbackKernel wasn't handing mutable ops correctly: it would not report
them in get_mutation_names or get_alias_names. This would lead to silent
incorrectness -- Inductor would incorrectly reorder the mutable op with other
mutable ops.
This PR fixes that:
- we only support mutable operations that are "auto_functionalizable".
That is, they mutate inputs and do not return aliases of any inputs.
- Following the Triton kernel work, any mutated inputs must be specified
in get_alias_names and processed via mark_node_as_mutating
- We also do some minor cleanup by killing dead code (FallbackKernel no
longer processes OpOverloadPacket) and adding some handling around
HOPs.
Test Plan:
- new tests
Pull Request resolved: https://github.com/pytorch/pytorch/pull/118649
Approved by: https://github.com/eellison, https://github.com/oulgen
