Comment by almostgotcaught

A compiler is a combinatorial optimizer (think bin-packing). In general, optimizers/solvers basically search for the best solution. Most production compilers don't have solvers in them, they use heuristics instead, but even the best solvers use tons of heuristics. Naturally a computer will search/try heuristics faster and more thoroughly than you but sometimes you can do better because performant searching is all about "knowing where to look".