I'm not sure anybody was using it as the implementation would always assert (as the PR https://bugs.llvm.org/show_bug.cgi?id=34098 shows).
Couple of notes:
- If nobody is using this code, we might as well consider removing it from the tree (as it seems unmaintained, and partly untested).
- I'm nowhere near an expert in floating point arithmetic, so the amended implementation might be wrong. Comments appreciated.