[aarch64-port-dev ] RFR(S): 8239914: AArch64: Combine add/sub with comparison against zero

[Pengfei Li]

Hi Andrew Haley,

> I am not sure you're thought about this clearly enough. Try this
> program:
> 
> public class DifferenceTest {
> 
>     static int theTest(int x, int y) {
>         int sum = 0;
>         while (x - y > 0) {
>             sum++;
>             y--;
>         }
>         return sum;
>     }
> 
>     static int n = -0x7000_0000;
>     static int m = +0x7000_0000;
> 
>     void trial() {
>         int prev = theTest(n, m);
>         for (int i = 0; i < 10_000_000; i++) {
>             int result = theTest(n, m);
>             if (prev != result) {
>                 throw new RuntimeException("last sum was " + prev + ", is now " +
> result);
>             }
>             prev = result;
>         }
>     }
> 
>     public static void main(String[] args) {
>         new DifferenceTest().trial();
>     }
> }

Thanks for reporting this. I just tested the program and found the exception also exists with AArch64 JDK master build (without my patch).

Apologize that I will be on leave and unable to create patches in the following days. But I've reported this to my colleagues. I think someone else will reply you soon.

--
Thanks,
Pengfei