I recently uploaded a patch that adds an infrastructure for implementing reaching definitions for C++: https://reviews.llvm.org/D76287. Though there is much to be done still, I'm comfortable enough to publish and gather feedback on the current state of the code.
I'm not terribly experienced with the development of dataflow algorithms (this is my first!) so I'm not sure who would be most interested in it. If you are, and have some comments about my initial work, you can find the revision here: