[aarch64-port-dev ] RFR: 8139042: AARCH64: Correct regression introduced by 8080293

[Andrew Dinn]

Thanks, Andrew and Vladimir for the reviews.

Since this has had two reviews and is aarch64 only I have exercised my
newly granted Committer status to push it to hs-comp! (yes, a whole 1
character got changed! :-)

regards,


Andrew Dinn
-----------
Senior Principal Software Engineer
Red Hat UK Ltd
Registered in UK and Wales under Company Registration No. 3798903
Directors: Michael Cunningham (USA), Matt Parson (USA), Charlie Peters
(USA), Michael O'Neill (Ireland)


On 07/10/15 15:31, Vladimir Kozlov wrote:
> Good.
> 
> Thanks,
> Vladimir
> 
> On 10/7/15 7:25 PM, Andrew Dinn wrote:
>> Could two reviewers please review this AArch64 only patch.
>>
>>    http://cr.openjdk.java.net/~adinn/8139042/webrev.00/
>>
>> The fix for issue JDK-8080293 (AARCH64: Remove unnecessary dmbs from
>> generated CAS code) inadvertently disabled one step of the optimization
>> process for unsafe volatile object gets. The result is that unsafe
>> volatile get is successfully translated to ldar but generation of the
>> trailing dmb ishld instruction is not inhibited.
>>
>> The patch for 8080293 extended predicate unnecessary_acquire to check
>> for a MemBarAcquire associated with a CompareAndSwapX node. In doing so
>> it changed the logic of a sanity check for MemBarAcquire introdcued as
>> part of an unsafe volatile get. The patch modified the code to
>> conditionally return true instead of return false. However the condition
>> retained the original != where it should have employed ==.
>>
>> regards,
>>
>>
>> Andrew Dinn
>> -----------
>> Senior Principal Software Engineer
>> Red Hat UK Ltd
>> Registered in UK and Wales under Company Registration No. 3798903
>> Directors: Michael Cunningham (USA), Matt Parson (USA), Charlie Peters
>> (USA), Michael O'Neill (Ireland)
>>
>