[llvm] [DebugInfo] Preserve line and column number when merging debug info. (PR #129960)

[Snehasish Kumar via llvm-commits]

snehasish wrote:

Thanks for taking a look @pogo59 @jmorse!

> The commit message should say "arbitrary but deterministic." If it's just arbitrary, the workload got lucky and it might not remain lucky. If it's deterministic, the luck won't change.

Yes, determinism is necessary for accurate profile attribution. Updated the PR description.

> My understanding of this is that with this flag on, a consistent but essentially arbitrary source location will be kept for merged instructions -- potentially misleading for debugging (hence it's an option), but good for PGO, yes?
> 
> I wonder how effective this is in the general case, but you've got numbers for a workload, so SGTM.

Yes, it's a net positive for PGO and not meant to be used in interactive debugging sessions. 


https://github.com/llvm/llvm-project/pull/129960