RFR: 8316186: RISC-V: Remove PlatformCmpxchg<4>

[Robbin Ehn]

On Fri, 15 Sep 2023 10:14:38 GMT, Fei Yang <fyang at openjdk.org> wrote:

> Try this test: `make test TEST="test/hotspot/jtreg/gc/shenandoah/compiler/TestReferenceCAS.java"` It fails with this change:
> 
> ```
> java.lang.RuntimeException: a (foo) != b (bar): success compareAndSet Object value
>         at TestReferenceCAS.assertEquals(TestReferenceCAS.java:93)
>         at TestReferenceCAS.testAccess(TestReferenceCAS.java:115)
>         at TestReferenceCAS.main(TestReferenceCAS.java:100)
>         at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
>         at java.base/java.lang.reflect.Method.invoke(Method.java:580)
>         at com.sun.javatest.regtest.agent.MainWrapper$MainTask.run(MainWrapper.java:138)
>         at java.base/java.lang.Thread.run(Thread.java:1570)
> ```

But that test should be using MacroAssembler::cmpxchg_ ?

Testing whats wrong....

-------------

PR Comment: https://git.openjdk.org/jdk/pull/15715#issuecomment-1721039242