RFR: 8244550: Unsafe::allocateInstance does redundant transitions

[David Holmes]

Looks good!

Thanks,
David

On 7/05/2020 9:09 am, Claes Redestad wrote:
> Hi,
> 
> Unsafe::allocateInstance transitions from VM to native only to call
> jni_AllocObject, transitioning back into VM.
> 
> This contributes measurably to overhead when run in interpreter and C1,
> so improving this helps startup/warmup. (C2 replaces with an intrinsic.)
> 
> Patch moves code to allocate instance into InstanceKlass, so that it
> can be shared between jni.cpp and unsafe.cpp, and changes to the unsafe
> call doesn't go via jni_AllocObject.
> 
> Patch: http://cr.openjdk.java.net/~redestad/8244550/open.00/
> Bug:   https://bugs.openjdk.java.net/browse/JDK-8244550
> 
> Testing: tier1-3, reduces U::allocateInstance overhead per call from
> ~100ns to ~60ns
> 
> Thanks!
> 
> /Claes