[llvm] [CorrelatedValuePropagation] Drop stale debug records on context-only rewrites (PR #218498)

[Jeremy Morse via llvm-commits]

https://github.com/jmorse commented:

I agree with @MrEven132 that dropping the records isn't great, as it makes variable assignments disappear. Setting them to undef/kill is strictly better as it specifically means "this has been optimised away", or indeed perhaps there's a way to represent the values in DIExpressions.

(I haven't read the rest of this patch yet, have commented on an initial concern instead)

https://github.com/llvm/llvm-project/pull/218498