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  1. JDK
  2. JDK-8321039

[lworld] Substitutability code must recognize new annotations




      The substitutability code currently doesn't recognize the @NullRestricted annotation added by JDK-8320437, which causes some failures when comparing some annotated value classes:

      import jdk.internal.misc.VM;
      import jdk.internal.vm.annotation.ImplicitlyConstructible;
      import jdk.internal.vm.annotation.LooselyConsistentValue;
      import jdk.internal.vm.annotation.NullRestricted;

      public class Test {

          static value class MyValueEmpty {


          static value class EmptyContainer {
              MyValueEmpty empty = new MyValueEmpty();

          public static void main(String[] args) {
              if (new EmptyContainer() != EmptyContainer.default) {
                  throw new RuntimeException("Failed");

      This test fails when run with -XX:InlineFieldMaxFlatSize=0.

      The newly created EmptyContainer has been created by a constructor which explicitly initialized the empty field with a reference to an instance of MyEmptyValue. The EmptyContainer.default value is the default value created by the VM, and the VM is lazy on null-free non-flat fields. The whole default value is initialized will zeroes, which is equivalent to initializing non-flat fields with a null reference, but on read, the VM substitute this null reference with the default value of the field's type. The Java code used for the substitutability test, called from if_acmpeq when two values of the same type are compared, is aware of the VM lazy initialization of null-free non-flat fields and usually recognizes this situation and perform the same substitution. The problem here is that the substitutability code doesn't recognize the field as a null-free non-flat field, because it isn't aware that the @NullRestricited annotation has the same effect as a Q-descriptor in the field signature. So, the substitutability code performs a simple comparison between the reference from the initialized field and the null reference of the default value, finds them different and returns a value indicating that the two arguments are different.


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              mchung Mandy Chung
              fparain Frederic Parain
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