[ridiculous_fish]

Branches add control flow which can inhibit other optimizations, such as vectorization. Compare the codegen of these two functions to double the first 64 elements in a u8 slice: https://rust.godbolt.org/z/hccWGv889

The unchecked version is fully unrolled and vectorized using multiple registers. The checked version must use a loop.

Part of what's going on here is that panics are "recoverable." If the out-of-bounds write occurs at index 61, this will panic, but the writes to lower indexes must have gone through. This means the panic cannot be hoisted out of the loop.