[llvm] [WIP][CodeGen] Encode liveness for COPY instructions after virtRegRewriter pass. (PR #151123)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> Do not include any links in the upstream PRs that can't be accessible to all. This internal referencing is unwanted. Instead, explain the actual problem here.

It can have the tag as a Fixes SWDEV-xxx

https://github.com/llvm/llvm-project/pull/151123