RFR(S): 6378256: Performance problem with System.identityHashCode in client compiler

[Tobias Hartmann]

Hi Rahul,

looks good to me (not a reviewer).

Best,
Tobias

On 09.12.2015 10:12, Rahul Raghavan wrote:
> Hello, 
> 
> Please review the following patch for JDK-6378256.
> 
> webrev: http://cr.openjdk.java.net/~thartmann/6378256/webrev.00/ .
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-6378256  .
> Performance problem with System.identityHashCode, compared to Object.hashCode, with client compiler (at least seven times slower).
> Issue reproducible for x86_32, SPARC (with -client / -XX:TieredStopAtLevel=1 , 2, 3 options).
> 
> sample unit test:
>    public class Jdk6378256Test
>    {
>       public static void main(String[] args) 
>       {
>          Object obj = new Object();
>          long time = System.nanoTime();
>          for(int i = 0 ; i < 1000000 ; i++)
>             System.identityHashCode(obj);  //compare to obj.hashCode();
>          System.out.println ("Result = " + (System.nanoTime() - time));
>       }
>    }
> 
> Fix: Enabled the C1 optimization which was done only for Object.hashCode, now for System.identityHashCode() also.
> (looks in the header for the hashCode before calling into the VM).
> Unlike for Object.hashCode, System.identityHashCode is static method and gets object as argument instead of the receiver.
> So also added required additional null check for System.identityHashCode case.
> 
> Testing:
>    - successful JPRT run (-testset hotspot).
>    - JTREG testing (hotspot/test, jdk/test - java/util, java/io, java/lang/System).
>        (with -client / -XX:TieredStopAtLevel=1 etc. options).
>    - Added 'noreg-perf' label for this performance bug.
>       Manual testing done and confirmed expected performance values for unit tests with fix.
> 
> Thanks,
> Rahul
>