[go-nuts] Elide bounds-check in range when using index for direct access

It would be nice if go can recognize the pattern below and bypass the
bounds checking:

// where l is a slice, array or pointer to an array
for i := range l {
    v := &l[i] // nice if bounds check isn't done here, as i hasn't changed
and is in range of l
    // ... work on v
}

I have no idea the difficulty in implementing this. But I do this a fair
amount in my code, and would love to see it supported.

I do it when my array/slice has value objects, which I want to be together,
but I want to check state in them.

Using for i, v := range l { ... } will return a copy of each element in the
array, which is not what I want.