[llvm] [DebugInfo][RemoveDIs] Don't allocate one DPMarker per instruction (PR #79345)

[Stephen Tozer via llvm-commits]

https://github.com/SLTozer approved this pull request.

Looks broadly good - though I feel like (YMMV) there are a lot of different places where we're doing mostly similar but slightly different things with debug ranges, and it's not easy to intuit what's happening in each case and what the difference is without really digging into it; I reckon it might be worth looking to see if there's more that can be done to extract common behaviour out to other functions, but that's a separate patch imo since this patch has a clear functional benefit.

https://github.com/llvm/llvm-project/pull/79345