Exactly. You as the programmer know that the loop counter won't overflow, and in general, essentially nobody would actually write it that way. But if you don't assume it can't happen, the possibility for signed overflow is everywhere in address computations.
This is also a major blocker for auto-vectorization. Can't coalesce a load of a[i], a[i+1], a[i+2], a[i+3] into a load of a[i:i+3] if there's a possibility that `i+1`, `i+2` or `i+3` wrapped around (thus causing your "contiguous" load to be non-contiguous). This is a big reason why you shouldn't use `unsigned` for loop counters, especially if they're going to be used as an index into an address calculation.
This is also a major blocker for auto-vectorization. Can't coalesce a load of a[i], a[i+1], a[i+2], a[i+3] into a load of a[i:i+3] if there's a possibility that `i+1`, `i+2` or `i+3` wrapped around (thus causing your "contiguous" load to be non-contiguous). This is a big reason why you shouldn't use `unsigned` for loop counters, especially if they're going to be used as an index into an address calculation.