You can see the impact on Rust here: https://perf.rust-lang.org/compare.html?start=2d0a7def330ed90f416a3429dbb44c5ee2a914e5&end=4a04d086cac54a41517d5657b59d5fe2

You can see the impact on Rust here: https://perf.rust-lang.org/compare.html?start=2d0a7def330ed90f416a3429dbb44c5ee2a914e5&end=4a04d086cac54a41517d5657b59d5fe2caca2d71&stat=instructions%3Au https://perf.rust-lang.org/compare.html?start=2d0a7def330ed9... The tl;dr is that check builds are faster (i.e. optimization quality has improved) while debug/opt builds are mixed, but slightly slower when averaged over everything.