I am a Rust fan, but 10% degradation in performance (29ms to 33ms) is not "a pretty small change" nor "within noise threshold". If the accuracy of the tests are +/- 10% then that needs to be proven and then fixed. I didn't see any evidence in the article that there is, in fact, a 10% error, and it looks like there is a genuine 10% drop in performance.
To be clear, removing the bounds checks led to the observed performance degradation. Your statement beginning with "I am a Rust fan, but..." suggests that you might have interpreted it as the other way around
Unsafe accesses do not act that way, they compile to exactly the same code as array accesses in C.
The tests aren't bunk. There are a variety of reasons why the assertions generated by array index checks can be useful for LLVM, and there is also a fair amount of noise in any end to end test like this. The main point is that it clearly isn't a primary bottleneck (which should be pretty obvious in a test that takes 30 ms and performs under 2000 bounds checks).
