So there's this guy you may have heard of called Ryan Fleury who makes the RAD debugger for Epic. The whole thing is made with 278k lines of C and is built as a unity build (all the code is included into one file that is compiled as a single translation unit). On a decent windows machine it takes 1.5 seconds to do a clean compile. This seems like a clear case-study that compilation can be incredibly fast and makes me wonder why other languages like Rust and Swift can't just do something similar to achieve similar speeds.
Because Russt and Swift are doing much more work than a C compiler would? The analysis necessary for the borrow checker is not free, likewise with a lot of other compile-time checks in both languages. C can be fast because it effectively does no compile-time checking of things beyond basic syntax so you can call foo(char) with foo(int) and other unholy things.
This explanation gets repeated over and over again in discussions about the speed of the Rust compiler, but apart from rare pathological cases, the majority of time in a release build is not spent doing compile-time checks, but in LLVM. Rust has zero-cost abstractions, but the zero-cost refers to runtime, sadly there's a lot of junk generated at compile-time that LLVM has to work to remove. Which is does, very well, but at cost of slower compilation.
Is it possible to generate less junk? Sounds like compiler developers took a shortcuts, which could be improved over time.