not really? It just changes how the compiler emits the x := *(addr + idx) operation where instead of doing something like ldr x, [addr, idx] it just does

not really? It just changes how the compiler emits the x := *(addr + idx) operation where instead of doing something like ldr x, [addr, idx] it just does sub t1, idx, #1 ldr x, [addr, t1] If we're talking about C, accessing invalid/OOB indices is undefined and so if idx happens to be zero and unsigned, we'll overflow and hit something unexpected, which is fine.