Where is the implementation of abi::__cxa_demangle in libstdc++

Question

GNU's libstdc++ provides the function abi::__cxa_demangle. The declaration of this function can be found in gcc / libstdc++-v3 / libsupc++ / cxxabi.h (code repository here)

I am interested in reviewing the implementation of this function but I am unable to find a definition in the aforementioned repository. There is one definition in gcc / libiberty but, from what I can gather, this library is only used in a few GNU programs and mostly decommissioned (or so claims Wikipedia).

I managed to dig up some old discussion threads from 2003 that mention replacing the libstdc++-v3 demangler with the libiberty demangler which further confused me.

Here are my questions:

1. Does a libstdc++-v3 demangler still exist (as mentioned in the thread linked to above)?
2. Is the libiberty demangler used in libstdc++-v3?
3. Where can I find the implementation of abi::__cxa_demangle