Compilation in Cargo has been split into metadata pass and code generation pass. Metadata part has interdependencies, but is relatively fast (it's roughly like

Compilation in Cargo has been split into metadata pass and code generation pass. Metadata part has interdependencies, but is relatively fast (it's roughly like a C header generation). This allowed more codegen to be done in parallel. To be honest, it was a modest improvement, because compilation has been decently parallelized already (compiler uses incremental builds, parallel codegen, and ThinLTO even within a single crate)