native-image leads to wrong execution / code

[ptrd]

Given this simple sample

package sample;

public class Simple {

    public static void main(String[] args) {
        byte ca = (byte) 0xca;
        System.out.println("Result: " + checkType(ca));
    }

    static boolean checkType(byte type) {
        byte masked = (byte) (type & 0xf0);
        boolean result = (masked == (byte) 0xc0);
        return result;
    }
}

When compiled and run with java, it returns true (which it obviously should).

When compiled with native-image however, it returns false.

GraalVM Version 19.3.0 CE
MacOS Catalina 10.15.2
Using -H:Optimize=0 doesn't make any difference.

[olpaw]

@dougxc this looks like a compiler bug. If I run checkType in a hot loop if get to the point where it returns false. On Stock JDK I do not ever get to that point.

[olpaw]

public class Simple {

    public static void main(String[] args) {
        byte ca = (byte) 0xca;
        int x = 0;
        while(x++ < 2 << 20) {
            boolean res = checkType(ca);
            assert res : "Fails after " + x + " iterations.";
            System.out.print(res ? "X" : "x");
        }
    }

    static boolean checkType(byte type) {
        byte masked = (byte) (type & 0xf0);
        boolean result = (masked == (byte) 0xc0);
        return result;
    }

}

Passes java -ea Simple with stock JDK but not when run on GraalVM 19.3.0.

[olpaw]

@ptrd thanks a lot for this bug report!

[ptrd]

You're welcome. Can't wait to experiment with kwik.tech compiled to native....

[dougxc]

Hi @ptrd , thanks for reporting. This is related to #1995 and is fixed in master (276ff2b). It will be in GraalVM CE 19.3.1.

[ptrd]

Ok, cool. Made a note in my agenda for Jan 14. ;-)