[llvm] [CodeGen] Utilizing register units based liveIns tracking in MBB (PR #129847)

[Jay Foad via llvm-commits]

jayfoad wrote:

Before we can switch the liveins representation to regunits I think we need a proper fix for #96146. Without that, regunits cannot distinguish AArch64 Qn and Dn registers, because there is no regunit corresponding to the not-directly-addressable high bits of those registers.

https://github.com/llvm/llvm-project/pull/129847