[llvm] [AArch64][SME] Enable subreg liveness tracking when SME is available (PR #92142)

[David Green via llvm-commits]

https://github.com/davemgreen commented:

> I suspect this may not be enabled by default for compile-time reasons. It's worth doing some measurements on what the impact is and decide based on that whether we want to enable it for more cases.

Do you have any evidence or this? My understanding was that it was not enabled as it can cause mis-compiles (for example in https://reviews.llvm.org/D129646). I would strong advise against making this SME only. The testing it will get will not be enough to be sure it doesn't cause mis-compiles elsewhere.

https://github.com/llvm/llvm-project/pull/92142