[llvm] unpack packed instructions overlapped by MFMAs post-RA scheduling (PR #157968)

[Jeffrey Byrnes via llvm-commits]

https://github.com/jrbyrnes commented:

@arsenm This one is urgent -- I wonder if you have any concerns?

There are still some glaring TODOs (e.g. combine the loops) , but we're going for a 90% approach and would like to propagate through branches.

https://github.com/llvm/llvm-project/pull/157968