But it can't go to zero, that was the point -- at some level you have to pay for what you get. I'm not saying the compile times couldn't be better, but Rust can't be Go in terms of compile times if it wants to offer the guarantees and options it does. Meanwhile if Go wants to offer more options and stronger guarantees, it won't be able to preserve the short compile times everyone points to.
The Cranelift backend is extremely fast. Most of the slowness is all the crazy optimizations that LLVM does + other things (generating debug info etc).