The headline feature of rustc memory management is the use of arenas: https://github.com/rust-lang/rust/blob/10f4ce324baf7cfb7ce2b2096662b82b79204944/compiler/r

The headline feature of rustc memory management is the use of arenas: https://github.com/rust-lang/rust/blob/10f4ce324baf7cfb7ce2b2096662b82b79204944/compiler/rustc_arena/src/lib.rs https://github.com/rust-lang/rust/blob/10f4ce324baf7cfb7ce2b... //! The arena, a fast but limited type of allocator. //! //! Arenas are a type of allocator that destroy the objects within, all at //! once, once the arena itself is destroyed. They do not support deallocation //! of individual objects while the arena itself is still alive. The benefit //! of an arena is very fast allocation; just a pointer bump. The other thing (not specifically mentioned in this comment, but mentioned elsewhere, and important to understanding why it work the way it does) is that if everything in the arena gets freed at once, it implies that you can soundly treat everything in the arena as having exactly the same lifetime. You can see an example of how every ty::Ty<'tcx> in rustc winds up with the same lifetime, and an entry point for understanding it more, here in the dev guide: https://rustc-dev-guide.rust-lang.org/memory.html https://rustc-dev-guide.rust-lang.org/memory.html However, arena allocation doesn't cover all of the dynamic allocation in rustc. Rustc uses a mixed strategy: there's both RAII and lots of arena allocated context that only gets destroyed at the end of a particular phase.