RFR(M): 8232896: ZGC: Enable C2 clone intrinsic

[Nils Eliasson]

On 2019-11-01 12:50, Per Liden wrote:
> Hi Nils,
>
> On 10/31/19 5:37 PM, Nils Eliasson wrote:
>> Hi,
>>
>> This patch fixes and enables the clone intrinsic for C2 with ZGC.
>>
>> The main thing added is an implementation of the 
>> ZBarrierSetC2::clone_at_expansion method. This method handles clone 
>> expansion for regular objects and primitive arrays that hasn't 
>> already been reduced by optimizations. (Oop array clones doesn't go 
>> through this path.)
>>
>> The code switches on the type of the source to either make a leaf 
>> call to a runtime clone for regular objects, or delegate to 
>> BarrierSetC2::clone_at_expansion for primitive arrays.
>>
>> Updated micro benchmark shows great gains, especially for small 
>> objects that now will be reduced to inlined move-store sequences.
>
> Sweet! The speedup of micro:Clone is impressive!
>
>>
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8232896
>>
>> Webrev: http://cr.openjdk.java.net/~neliasso/8232896/webrev.02/
>
> My review comments summarized in a patch on top of yours. Let me know 
> if there's something you don't agree with. The changes are:
> * Changed the type of the runtime function's size arguments from 
> TypeInt::INT to TypeLong::LONG, to make it 64 bits, rather than 32.
> * Changed the new runtime function to call HeapAccess::clone() rather 
> than ZBarrier::clone_oop(), since ZBarrier is the backend for the 
> access layer, not the frontend.
> * Renamed clone_oop() to clone(), as we're cloning an object rather 
> than an oop.

Overall, I like your suggestions.

One problem with using "clone" is that is suggest that it will create a 
new Object too (like how java.lang.Object.clone does). But this function 
only copies the contents. I am open to suggestions, and even keeping the 
clone name, but feel a slight bit of unease.

Thanks!

/Nils

> * Added const where applicable.
> * Adjusted an include line.
> * Moved the clone_at_expansion() function up in the file.
>
> http://cr.openjdk.java.net/~pliden/8232896/webrev.pliden_review.0
>
> I ran micro:Clone to verify my changes.
>
> cheers,
> Per
>
>>
>>
>> Please review,
>>
>> Nils Eliasson
>>