[llvm] [Thumb] Resolve FIXME: We can trust live-in information from successor blocks now (PR #84111)

[Craig Topper via llvm-commits]

topperc wrote:

> Also by the thing that changed I was actually referring to the changes that resulted from moving from livephysregs to liveregunits.
> 
> R6 is reserved anyway, so it is always "live"

Then you should explain that in your description. I was going off the text of the FIXME.

https://github.com/llvm/llvm-project/pull/84111