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

[Nick Gasson (Arm Technology China)]

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