Comment by philzook

A very interesting application of constraint programming is the Unison compiler https://unison-code.github.io/, which uses constraint models to solve compiler backend problems for llvm. As a simple example, register allocation can be modeled as a graph coloring problem for which there is an edge between every variable which must be live at the same time and colors represent registers, but he unison model is sophisticated beyond this. We use a simpler related model in our project VIBES https://github.com/draperlaboratory/VIBES which is a micropatching compiler (it uses the constraints to compile code in such a way it can fit in place, has the right stuff in the right registers, etc.)