All the input files are bitcode. Due to our arcane build methodology the bitcode files end up with ".o’. Yes, this drives me nuts.
I renamed them to “.bc” for the posting, but obviously missed one.
My guess is that the debug information in the bitcode is sometimes not updated correctly when some of the modules are combined and coalesced. Some redundancy is detected and eliminated, but the debug info is left with dangling references. It is just a guess at this point and probably wrong, but that is what I will look for as I debug this.