[felixangell1024]

Depends what you compile to. Writing a register allocator may be a little tricky (if you compile to a VM/Assembly/..), though if you compile to something like C, it's very easy. LLVM is another alternative which is also relatively simple to learn.

[andars]

Spilling every variable to memory isn't too bad if you just want it to work and aren't worried about performance.

[sklogic]

Linear scan register allocation is "good enough" in most cases and it is trivial if you're doing it on top of an SSA.