This challenge covers much of compilers research. Many heuristics and techniques that are used in practice in compilers (certainly in ours and GHC and ocaml and other research ones I've talked with) have solutions we've all verbally shared with one another on how to solve these problems. But we're all convinced we couldn't get a paper out of it (novel enough, but it's too hard to meet the "evaluation bar"), so it remains stuff we talk about during breaks at conferences and in "Limited" circles on G+...