Index Checker cannot estimate value of a variable (which is declared outside the loop) inside the loop

Consider the following code:

class tryit{
  public static void check_it(int[] a) {
 		int index = 0;
 		for(int x = 0 ; x < a.length ; x++){
 			a[index++] = 0;
 		}
    }
}

Run it by typing in the terminal:
javac -processor index tryit.java

Output:

tryit.java:6: error: [array.access.unsafe.high.range] Potentially unsafe array access: the index could be larger than the array's bound
 			a[index++] = 0;
 			       ^
  index type found: @IntRange(from=-2147483648, to=9223372036854775807) int
  array type found: @UnknownVal int @UnknownVal []
  required        : index of type @IndexFor("a") or @LTLengthOf("a"), or array of type @MinLen(-9223372036854775808)
1 error

Firstly, the checker is imprecise in estimating the value of index inside the loop.
Second, the error message @MinLen(-9223372036854775808) seem absurd.

Reproduce the report using tryit.java and javac -processor index tryit.java, then trace the Index Checker handling of the variable declared before the loop. Investigate why the loop does not refine index and why the diagnostic reports @MinLen(-9223372036854775808). Done means the example is analyzed correctly and the reported range is sensible.