--- Comment #4 from Chris Green <greenc at fnal dot gov> ---
(In reply to Jakub Jelinek from comment #3)
> Ah, maybe I'm wrong what S6_ stands for. Anyway:
> has more details. So NOTABUG?
See particularly https://llvm.org/bugs/show_bug.cgi?id=30401#c1. While the
c++filt provided with binutils on Ubuntu 16.04 demangles both symbols to the
same (correct) function, LLVM's libc++abi demangler demonstrates an apparent
erroneous backreference in LLVM's mangled symbol name. Until new evidence
suggests otherwise, I'd be willing to accept a determination that this is
LLVM's bug, not GCC's.