← Back to context

Comment by lsuresh

3 days ago

Hard agree. Practically all the bottlenecks we run into with Rust compilation have to do with the LLVM passes. The frontend doesn't even come close. (e.g. https://www.feldera.com/blog/cutting-down-rust-compile-times...)

5 comments

lsuresh

Reply
edflsafoiewq  2 days ago

The point was language design influences compiler performance. Rust is heavily designed around "zero-cost abstraction", ie. generate tons of IR and let the backend sort it out. Spending all the time in LLVM passes is what you would expect from this.

  • littlestymaar  2 days ago

    Had you read the linked blog post, you'd have seen that here this isn't so much an issue with LLVM having too much work, but rustc being currently unable to split the work into parallelizable chunks before sending it to LLVM, and as such it takes a very long time not because LLVM has too much things to do, but because it does it in a single-threaded fashion, leaving tons of performance on the table.

    > Rust is heavily designed around "zero-cost abstraction", ie. generate tons of IR and let the backend sort it out.

    Those two aren't equivalent: Rust is indeed designed around zero-cost abstraction, and it currently generates tons of IR for the backend to optimize, but it doesn't have to, it could run some optimizations in the front-end so it generates less IR. In fact there has been ongoing work to do exactly this to improve compiler performance. But this required rearchitecturing the compiler in depth (IIRC Rust's MIR has been introduced for that very reason).