I once heard (and don't know if it's still true) that the biggest compile-time sinks are macros and codegen.

Both are kind of outside the Rust compiler's influence. Macros can be almost arbitrarily complex: you pay for what you order. Codegen is LLVM, and that's a fixed choice. You can use Cranelift to get around it, but then you pay elsewhere.

Also, generics and monomorphization regularly come up in these discussion, while common wisdom seems to be that cost for the additional static analysis over other languages like C++ is no a major contributor.

Regardless, it's nice to see performance improvements in the compiler, even if you have to cooperate to benefit from them (e.g. by keeping your macros light and use less generics).