RFR: jsr166 jdk9 integration wave 9

[Aleksey Shipilev]

On 08/11/2016 09:59 PM, Martin Buchholz wrote:
> On Thu, Aug 11, 2016 at 10:40 AM, Aleksey Shipilev
>> Why doesn't AtomicBoolean.getAndSet use VarHandle.getAndSet, which is
>> hopefully intrinsified completely?
> 
> Good question.  This optimization originated in a suggestion for jdk8,
> where there are no VarHandles.
> VarHandle.getAndSet does not know there are only two values for the int,
> so it is not obvious which one wins.  I can imagine getAndSet being
> compiled to a weak cas loop. 

getAndSet/getAndAdd have a nice rationale for x86: they compile to
xchg/xadd, respectively. This is what I meant about "intrinsified
completely".

>> Any benchmarks backing up this optimization?
> 
> I measured a reduction in bytecode!  Does that count? 

I measured x86 instructions count, and you would not believe what it
told me!
  http://cr.openjdk.java.net/~shade/8162805/BooleanGetAndSet.java

Thanks,
-Aleksey