[aarch64-port-dev ] RFR: 8217368: AArch64: C2 recursive stack locking optimisation not triggered

[Dmitry Samersoff]

Hello Nick,

Glad to see this cleanup.


3528     __ cmp(rscratch1, zr); // Sets flags for result
3529     __ cbnz(rscratch1, cont);

Should

__ br(Assembler::NE, cont);

be at line 3529 instead of cbnz ?


-Dmitry


On 22.01.2019 12:10, Nick Gasson (Arm Technology China) wrote:
> Hi,
> 
> On 21/01/2019 20:27, Andrew Haley wrote:
>>
>> OK, if that's your position: you're writing the patch. Using cmpxhg
>> everywhere will make that rather twisted code much easier to read.
>>
> 
> Please see the updated webrev to use cmpxchg in both the lock and unlock 
> functions:
> 
> http://cr.openjdk.java.net/~ngasson/8217368/webrev.1/
> 
> Also includes Derek's cleanup suggestions (although some of them are not 
> applicable now).
> 
> Testing I've done on this:
> 
> * Ran jtreg with assertions enabled (+UseLSE)
> 
> * Ran jcstress with both +UseLSE and -UseLSE
> 
> * Ran the JMH LockUnlock benchmarks with -UseBiasedLocking to check for 
> performance regressions.
> 
> The directory below contains the the generated assembly from each webrev 
> and current hg tip for this simple method:
> 
> http://cr.openjdk.java.net/~ngasson/8217368/generated/
> 
>      private Object obj = new Object();
>      public int x;
> 
>      private void incX() {
>          synchronized (obj) {
>              x++;
>          }
>      }
> 
> The output of webrev.1 looks OK to me. Any other suggestions of things 
> to test?
> 
> Thanks,
> Nick
>