I even convinced a C++ compiler (don't recall whether it was g++ or clang++; it might have been during a FreeBSD fling) to do TCO at one point, but I don't reme

I even convinced a C++ compiler (don't recall whether it was g++ or clang++; it might have been during a FreeBSD fling) to do TCO at one point, but I don't remember exactly how I did it and don't think the requirements are documented anywhere. It probably involved functions declared "static" (i.e. internal linkage) and with the same signature.