[llvm] [CodeGen] Expose the extensibility of PassConfig to plugins (PR #139059)

[Stefan Gränitz via llvm-commits]

https://github.com/weliveindetail commented:

Hi all, I am no expert for the legacy pass manager, so let's wait for the others to add their thoughts. Overall this patch LGTM.

While most folks focus on porting MachineIR passes to the NewPM these days, this patch still seems like a reasonable addition. IIUC the legacy PM is still the default infra for codegen and will likely stay around for a while.

Unfortunately, we don't have good end-to-end testing for plugins in general. The proposed unittests repeat what we have in other places. Good enough. Could we use them for drafting similar functionality in the NewPM in a follow-up step? Might be good timing since the NewPM work is in progress right now.

https://github.com/llvm/llvm-project/pull/139059