Citation needed, since all evidence points to the contrary.
Could you please point us to a Rust application (there are hundreds of thousands at this point) that gets noticeably faster when disabling bound checks?
In servo, a whole web browser written in Rust, the cost of doing this was negligible, to the point that it was barely measurable (1-3%, noise levels for such a big app).
Same for Firefox which has a substantial amount of Rust.
Go ahead and give Fuchsia a try. You can enable bound checks for a substantial part of Android's user space and not really notice it.
Same for Redox, or any operating system kernel written in Rust.
You have many large applications to choose from, so please, just point us to 1 for which this is the case.
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Compared with other mitigations already in the kernel, that can cost you up to 50% perf, and that people seem to be ok with, bound checking all the array accesses seems like a no brainer, given that ~70% of CVE are caused by memory issues.
When most people think about bound checking all array accesses, they think, for some "i can only think inside the box" reason, that this happens on hardware, for every memory access.
But that is not how Rust works. Rust adds bound checks "in Rust", and the Rust compiler and LLVM are really good at removing duplicates, hoisting many bound checks out of a loop into a single bound check at the beginning of the loop, etc.
People also think that this is an all or nothing approach, but Rust allows you to manually access without bound checks and do the hoisting manually. So if you find a function in which this makes a big difference, you can just fix the performance issue there manually.