[llvm] [CodeGen] Mark read_register of allocatable physreg as live-in (PR #200825)

[Adhemerval Zanella via llvm-commits]

zatrazz wrote:

Right, I am testing a fix that uses the non-liveness-tracked operand. It ended not being as large as I expected.

https://github.com/llvm/llvm-project/pull/200825