[llvm] [RegisterCoalescer]: Try inflated RC for coalescing (PR #130870)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

I was working on the same thing a few weeks ago, and I think we need more targeted handling. This is too aggressively trying to recompute the register classes. In terms of patch splitting, I also think we should take each of these cases one at a time. I think the subregister insert case is the most likely to be profitable piece, so I think we should start there.

However, in terms of the AGPR-or-VGPR to AV_* class case, it will soon only be relevant for gfx908. I'm actively working on avoiding using AGPRs until the actual allocation forces it. I was also wondering if instead we should just be using the AV_* classes for all values in the first place.

I'll try to polish my patch into something postable.

https://github.com/llvm/llvm-project/pull/130870