You're right, I didn't distinguish between overall compile times and the front-end time taken, which is what you were focusing on. For the Rust toolchain, the (vast IIRC) majority of compilation time is in LLVM's backend. So, to me, front-end optimizations are interesting, but not the highest priority for Rust specifically. LMD seems to be a great thing to compare against, so here's my follow-up question: What's the proportion of front-end to back-end time in LMD?