Hello,
there's freearray() at end of setarrvalue(). It can be replaced with
free() if ownership of all strings will be given away:

        for (r = val; *r;)
           *p++ = ztrdup(*r++);

becomes:

        for (r = val; *r;)
           *p++ = *r++;

and freearray(val) -> free(val).

It is very provable that this is correct: `val` must have data of the
same kind as ztrdup() produces, as it is simply passed to freearray(),
where zsfree() is called on each string.

Test function:

test_fun() {
    local -a arr
    arr=( "a" )
    repeat 20; do
        arr+=( $arr )
    done
}

Runs 2189 ms when no optimization, 1653 ms when optimized (when ran 3
times, test script attached). This is a mild optimization as most often
short arrays are being assigned, not long like in the test function, but
still, this can save one's day in certain situations.

-- 
  Sebastian Gniazdowski
  psprint@fastmail.com