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

[Per Liden]

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.
* 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
>