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  1. JDK
  2. JDK-8261022

Fix incorrect result of Math.abs() with char type

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    • Subcomponent:
    • Introduced In Version:
      13
    • Resolved In Build:
      b09
    • CPU:
      generic
    • OS:
      generic

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        Description

        Math.abs() with char type may return incorrect result after C2 superword optimization. It can be reproduced by below Java code and commands.

        public class Bug {
            private static int SIZE = 60000;
            private static char[] a = new char[SIZE];
            private static char[] b = new char[SIZE];

            public static void main(String[] args) {
                for (int i = 0; i < SIZE; i++) {
                    a[i] = b[i] = (char) i;
                }
                for (int i = 0; i < SIZE; i++) {
                    a[i] = (char) Math.abs(a[i]);
                }
                for (int i = 0; i < SIZE; i++) {
                    if (a[i] != b[i]) {
                        throw new RuntimeException("Broken!");
                    }
                }
                System.out.println("OK");
            }
        }

        // $ java -Xint Bug
        // OK

        // $ java -Xcomp -XX:-TieredCompilation Bug
        // Exception in thread "main" java.lang.RuntimeException: Broken!
        // at Bug.main(Bug.java:15)

        This may cause loss of data (although in few cases) so I would change the priority to P2.

        Affect versions: 13, 14, 15, 16, 17 (both x86 and AArch64) and 11u (x86-only)

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                Assignee:
                pli Pengfei Li
                Reporter:
                pli Pengfei Li
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                  Created:
                  Updated:
                  Resolved: