RFR - Avoid G1 write barriers on newly allocated objects

[Staffan Friberg]

Hi Mikael,

I updated the documentation, and uploaded a new webrev, 
http://cr.openjdk.java.net/~sfriberg/8057737/webrev.01

Thanks for agreeing to sponsor, and the good idea about pushing to hs-gc 
for extra coverage.

Thanks,
Staffan

On 09/09/2014 07:31 AM, Mikael Gerdin wrote:
> Hi Staffan,
>
> On Friday 05 September 2014 16.31.44 Staffan Friberg wrote:
>> Hi,
>>
>> Copying both the compiler and GC alias as the optimization involves both
>> groups.
>>
>> This optimization aims to avoid generating G1 barriers for newly
>> allocated objects where the compiler can prove that the object has not
>> been written to earlier and there is no safepoint between the allocation
>> and the write. The bug has some further details and microbenchmark
>> result. The new code has fairly extensive comments about the optimization.
>>
>> It would be great if the GC team can help validate that the premise of
>> the optimization is correct as well.
>>
>> webrev: http://cr.openjdk.java.net/~sfriberg/8057737/webrev/
> I mostly read through the comments since I can't decode what the IR transforms
> intend to do :)
>
> We usually stick to the terms "old generation" and "young generation" instead
> of "Old Space" and "Young Space".
>
> "G1 also requires to keep track of objects between different
> + * regions to enable evacuation of old regions"
> should probably be.
> .."to keep track of references between different regions"
>
> I leave it to the compiler team to review the actual code changes.
>
>> bug: https://bugs.openjdk.java.net/browse/JDK-8057737
>>
>> I would also need a sponsor for this change if it passes review.
> I'll push this to hs-gc after review since we have more G1 test coverage on
> hs-gc.
>
> /Mikael
>
>> Thanks,
>> Staffan