[llvm] Add DebugSSAUpdater class to track debug value liveness (PR #135349)

[Stephen Tozer via llvm-commits]

SLTozer wrote:

Rebased the patch onto main and addressed review comments; also split out functionality from the DbgValueRangeTable that isn't related to variable location ranges. The line and name tracking features are used by the debug info analyzer's IR reader, but they don't need to be part of this class - however, I have moved the name tracking feature to a separate class, `SSAValueNameMap`, and added comments to describe its purpose. Since it's not strictly related to the liveness analysis it could be moved out of this file and review, but it's a utility class that is useful to the only consumer of this patch, so I think we could reasonably keep it around - happy to adjust the patch if not.

https://github.com/llvm/llvm-project/pull/135349