RFR: 8217747: ZGC: Minor optimization of ZLoadBarrierStubC1

[Per Liden]

On 01/29/2019 10:24 AM, Erik Österlund wrote:
> Hi Per,
> 
> While I think this optimization is going to be completely invisible in 
> all profiles, I don't mind it either. Looks good.

Thanks for reviewing, Erik. I agree, I mostly just found it annoying to 
see those push/pop when inspecting the generated code.

/Per

> 
> Thanks,
> /Erik
> 
> On 2019-01-28 09:56, Per Liden wrote:
>> In the C1 load barrier stub for ZGC we currently save/restore rax 
>> unless it's the stub result register. However, we can also avoid this 
>> save/restore of rax if it's the tmp register. Avoiding a push/pop in 
>> the stub isn't really an important optimization, but since we already 
>> do it for the result register we can just as well do it for the tmp 
>> register too, without making the code more complex.
>>
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8217747
>> Webrev: http://cr.openjdk.java.net/~pliden/8217747/webrev.0
>>
>> /Per