[llvm] IRBuilder: avoid crash when seeking to start of a BasicBlock with only DebugInfo (PR #66266)

[Jeremy Morse via llvm-commits]

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

LGTM; on closer examination it's impossible to return an empty debugloc here because it's returning an lvalue reference, and we would be returning a temporary. It's not too important to have this behaviour as it only becomes important when comparing normal debug-info with non-intrinsic-based debug-info. That's something we can push back for now.

Thanks for putting the patch together!

https://github.com/llvm/llvm-project/pull/66266