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

[Christian Thalinger]

> On Dec 10, 2015, at 1:38 PM, Vladimir Ivanov <vladimir.x.ivanov at oracle.com> wrote:
> 
> Also, doesn't -XX:DisableIntrinsic=_identityHashCode,_hashCode already solve the problem?
> 
>  diagnostic(ccstrlist, DisableIntrinsic, "",      \
>         "do not expand intrinsics whose (internal) names appear here")     \

Even better!  Let’s not add more flags.

> 
> 
> Best regards,
> Vladimir Ivanov
> 
> On 12/11/15 12:03 AM, Christian Thalinger wrote:
>> 
>>> On Dec 9, 2015, at 1:30 PM, Dean Long <dean.long at oracle.com> wrote:
>>> 
>>> The new System.identityHashCode optimization can't be turned off on the command-line,
>>> because InlineObjectHash only applies to Object.hashCode.  Does it matter?
>> 
>> All these command line flags are a pain since they are all product flags.  Doesn’t Compiler Control provide a way to disable an intrinsic?
>> 
>> Actually, InlineObjectHash is a develop flag so you can’t turn it off in a release build:
>> 
>> src/share/vm/runtime/globals.hpp
>> 806:  develop(bool, InlineObjectHash, true,                                     \
>> 
>>> 
>>> dl
>>> 
>>> On 12/9/2015 1:12 AM, 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
>>> 
>>