Comment by gue5t

Personally I've been inspired by nnethercote's logs (https://nnethercote.github.io/) of incremental single-digit percentage performance improvements to rustc over the past several years. The serial portion of compilers is still quite significant and efforts to e.g. parallelize the entire rustc frontend are heroic slogs that have run into subtle semantic problems (deadlocks and races) that have made it very hard to land them. Not to disparage those working on that approach, but it is really difficult! Meanwhile, dozens of small speedups accumulate to really significant performance improvements over time.