Have been seen only in aarch64 so far.

Please find workdir and .jtr files attached. The stacktrace (though it looks not very informative):

java.lang.RuntimeException: Method fail6(), Rule 1 with "failOn" should have failed at Regex 2: expected true, was false
        at jdk.test.lib.Asserts.fail(Asserts.java:594)
        at jdk.test.lib.Asserts.assertTrue(Asserts.java:486)
        at ir_framework.tests.RegexConstraint.checkIRRule(TestIRMatching.java:1535)
        at ir_framework.tests.Constraint.checkConstraint(TestIRMatching.java:1399)
        at ir_framework.tests.TestIRMatching.checkConstraints(TestIRMatching.java:279)
        at ir_framework.tests.TestIRMatching.runCheck(TestIRMatching.java:271)
        at ir_framework.tests.TestIRMatching.main(TestIRMatching.java:59)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.base/java.lang.reflect.Method.invoke(Method.java:568)
        at com.sun.javatest.regtest.agent.MainWrapper$MainThread.run(MainWrapper.java:127)
        at java.base/java.lang.Thread.run(Thread.java:833)

JavaTest Message: Test threw exception: java.lang.RuntimeException: Method fail6(), Rule 1 with "failOn" should have failed at Regex 2: expected true, was false