[llvm] [MergeFunctions] Add debug locations to redirected calls (PR #225625)

[Jeremy Morse via llvm-commits]

jmorse wrote:

Hmm -- a nearby instruction is reasonably likely to have an inappropriate inlining context/scope after a few rounds of optimisation. We typically favour the absence of information over any potential risk of false information, to avoid people losing trust in their debuggers, so IMHO missing frames is better than the possibility of false frames.

Is there really no possibility of preserving any scope or source information for these merged call sites? Given that is merging functions, is this similar to linker ICF (identical code folding)? That's well understood to require linker/debugger support to identify scenarios where ICF makes the callstack incorrect, it's possible that we need an in-compiler way of expressing that.

https://github.com/llvm/llvm-project/pull/225625