Bound checks can be an issue in Rust as well, actually. It's often worthwhile to hoist them manually out of loops, which usually enables the compiler to optimize them out within the loop and even vectorize the resulting code.
(This can't happen automatically because the default semantics generally involve a panic or exception to be triggered when the check fails; there's no way to optimize this further.)
A trick I've found to eliminate them in a few cases: pass &[T; size] instead of &[T] when dealing with statically sized arrays. The compiler will elide bounds checking a lot more aggressively with statically sized arrays since the bounds are known at compile time.
In this case none of the accesses should fail because they can all be statically observed to be in-bounds; unfortunately the Swift compiler was not able to see that.
(This can't happen automatically because the default semantics generally involve a panic or exception to be triggered when the check fails; there's no way to optimize this further.)