test/hotspot/jtreg/compiler/gcbarriers/TestG1BarrierGeneration.java does not contain negative test cases for compareAndExchange and compareAndSwap.
Adding those:
-----
diff --git a/test/hotspot/jtreg/compiler/gcbarriers/TestG1BarrierGeneration.java b/test/hotspot/jtreg/compiler/gcbarriers/TestG1BarrierGeneration.java
index 01e015d50cb..297d1b848ce 100644
+++ b/test/hotspot/jtreg/compiler/gcbarriers/TestG1BarrierGeneration.java
@@ -879,6 +879,12 @@ public void runAtomicTests() {
             Object oldVal2 = testCompareAndExchange(o, oldVal, newVal);
             Asserts.assertEquals(oldVal, oldVal2);
             Asserts.assertEquals(o.f, newVal);
+ // test failing compareAndExchange
+ Object newExpected = new Object();
+ Object newSetValue = new Object();
+ Object old = testCompareAndExchange(o, newExpected, newSetValue);
+ Asserts.assertEquals(newVal, old);
+ Asserts.assertEquals(o.f, newVal);
         }
         {
             Outer o = new Outer();
@@ -888,6 +894,13 @@ public void runAtomicTests() {
             boolean b = testCompareAndSwap(o, oldVal, newVal);
             Asserts.assertTrue(b);
             Asserts.assertEquals(o.f, newVal);
+ Object newSetValue = new Object();
+ Object old = testCompareAndExchange(o, newExpected, newSetValue);
+ Asserts.assertEquals(newVal, old);
+ Asserts.assertEquals(o.f, newVal);
         }
         {
             Outer o = new Outer();
@@ -888,6 +894,13 @@ public void runAtomicTests() {
             boolean b = testCompareAndSwap(o, oldVal, newVal);
             Asserts.assertTrue(b);
             Asserts.assertEquals(o.f, newVal);
+ // test failing compareAndSwap
+ Object newExpected = new Object();
+ Object newSetValue = new Object();
+ boolean failed = testCompareAndSwap(o, newExpected, newSetValue);
+ Asserts.assertFalse(failed);
+ Asserts.assertEquals(o.f, newVal);
+
         }
         {
----

makes the test fail on S390x platform:
----------
Test Failures (1)
-----------------
Custom Run Test: @Run: runAtomicTests - @Tests: {testCompareAndExchange,testCompareAndSwap,testGetAndSet,testCompareAndExchangeOnNewObject,testCompareAndSwapOnNewObject,testGetAndSetOnNewObject,testGetAndSetConditionallyOnNewObject,testGetAndSetOnNewObjectAfterException,testGetAndSetOnNewObjectAfterCall}:
compiler.lib.ir_framework.shared.TestRunException: There was an error while invoking @Run method public void compiler.gcbarriers.TestG1BarrierGeneration.runAtomicTests()
at compiler.lib.ir_framework.test.CustomRunTest.invokeTest(CustomRunTest.java:162)
at compiler.lib.ir_framework.test.AbstractTest.run(AbstractTest.java:105)
at compiler.lib.ir_framework.test.CustomRunTest.run(CustomRunTest.java:89)
at compiler.lib.ir_framework.test.TestVM.runTests(TestVM.java:865)
at compiler.lib.ir_framework.test.TestVM.start(TestVM.java:255)
at compiler.lib.ir_framework.test.TestVM.main(TestVM.java:168)
Caused by: java.lang.reflect.InvocationTargetException
at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:119)
at java.base/java.lang.reflect.Method.invoke(Method.java:565)
at compiler.lib.ir_framework.test.CustomRunTest.invokeTest(CustomRunTest.java:159)
... 5 more
Caused by: java.lang.RuntimeException: assertEquals expected: java.lang.Object@460f76a6 but was: java.lang.Object@55f3c410
at jdk.test.lib.Asserts.fail(Asserts.java:715)
at jdk.test.lib.Asserts.assertEquals(Asserts.java:208)
at jdk.test.lib.Asserts.assertEquals(Asserts.java:195)
at compiler.gcbarriers.TestG1BarrierGeneration.runAtomicTests(TestG1BarrierGeneration.java:886)
at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
... 7 more



at compiler.lib.ir_framework.test.TestVM.runTests(TestVM.java:901)
at compiler.lib.ir_framework.test.TestVM.start(TestVM.java:255)
at compiler.lib.ir_framework.test.TestVM.main(TestVM.java:168)

----

See attached jtr file.

The modified test passes on amd64:
==============================
Test summary
==============================
   TEST TOTAL PASS FAIL ERROR SKIP
   jtreg:test/hotspot/jtreg/compiler/gcbarriers/TestG1BarrierGeneration.java
                                                         1 1 0 0 0
==============================