[llvm] [AArch64] Do adc(s) machine instruction combine (PR #113663)

[David Green via llvm-commits]

https://github.com/davemgreen commented:

Hi - sounds like a decent addition. Can you add a .ll files where this comes from, to test end-to-end?

As a high level comment - can you give reasons why this was done in MachineCombiner? As opposed to doing it always.  I like machine combiner, other than it being a bit more difficult than it should be to add patterns (It should ideally be table-gen'd). Is it to do with the scheduling info / critical path length, or that it comes up from cross-basic block patterns?

https://github.com/llvm/llvm-project/pull/113663