[9] RFR (XS): C2: Broken cmpxchgb encoding on x86

[Vladimir Ivanov]

Aleksey, Paul, Vladimir, thanks for the reviews.

Best regards,
Vladimir Ivanov

On 8/17/16 10:03 PM, Vladimir Kozlov wrote:
> Good.
>
> Thanks,
> Vladimir
>
> On 8/17/16 9:56 AM, Vladimir Ivanov wrote:
>> http://cr.openjdk.java.net/~vlivanov/8164103/webrev.00/
>> https://bugs.openjdk.java.net/browse/JDK-8164103
>>
>> Newly introduced compareAndSwapB/compareAndExchangeB rules on x64
>> incorrectly encodes cmpxchgb instruction when new value is in DIL
>> (RDI) register.
>>
>> What was missing is REX prefix. The fix is to use REX_breg_mem which
>> takes care of that case [1].
>>
>> The bug was found by new VarHandle tests on bitwise atomics [2]. So, I
>> decided not to duplicate the failing test in hotspot repository.
>> 8161444 will be integrated after the fix is in.
>>
>> Testing: failing test, VarHandle tests (existing and new), RBT
>> (hs-tier0-comp, in progress).
>>
>> Thanks!
>>
>> Best regards,
>> Vladimir Ivanov
>>
>> [1]
>> http://hg.openjdk.java.net/jdk9/hs-comp/hotspot/file/031f53ef620a/src/cpu/x86/vm/x86_64.ad#l2375
>>
>>
>> [2] https://jbs.oracle.com/browse/JDK-8161444