RemoveNeverExecutedCode

[Deneau, Tom]

Doug --

Yes, for the bytecode in question this tells me that the branchProbability is 1.0 but I was trying to understand why.

For instance, 10000 elements in array, the first 10 should all not take the branch, but I see...

executionCount at 13: 9488; branchProbability at 13: 1.000000; exceptionSeen at 13: FALSE;

It looks like maybe the profiling only kicks in after the first 512 times a bytecode is executed (since executionCount above is 9488)?   Also if I move the location of the differing elements to past 512, I see that it gets recorded. Is there some logic like that in the hotspot profiling interpreter?

-- Tom



-----Original Message-----
From: Doug Simon [mailto:doug.simon at oracle.com] 
Sent: Friday, August 22, 2014 7:39 AM
To: Deneau, Tom
Cc: Tom Rodriguez; graal-dev at openjdk.java.net
Subject: Re: RemoveNeverExecutedCode

You should get all the info you need with ResolvedJavaMethod.getProfilingInfo().toString().

On Aug 22, 2014, at 2:34 PM, Deneau, Tom <tom.deneau at amd.com> wrote:

> I don't know the details of how the profile is collected but...
> In my case with 2000000 elements and 1 different, in the profile, the branchTakenProbability is showing up as 1.0.
> For other combinations of elements and differs I saw this:
>     Elems    Differs      BTP 
>    1000000    1000        < 1.0
>    1000000      10        1.0
>     100000      10        1.0
>      10000      10        1.0
>       1000      10        < 1.0
> 
> -- Tom
> 
> 
> -----Original Message-----
> From: Tom Rodriguez [mailto:tom.rodriguez at oracle.com] 
> Sent: Thursday, August 21, 2014 7:12 PM
> To: Deneau, Tom
> Cc: graal-dev at openjdk.java.net
> Subject: Re: RemoveNeverExecutedCode
> 
> 
> On Aug 21, 2014, at 4:39 PM, Deneau, Tom <tom.deneau at amd.com> wrote:
> 
>> I am trying to benchmark an HSAIL kernel that is implementing the following lambda
>>    n -> {
>>      if (a1[n] != a2[n]) {
>>        isEqual = false;
>>     }
>> 
>> where a1 and a2 are arrays of doubles.   So it is basically doing an Arrays.equals.
>> 
>> I set up the test to have 2,000,000 elements in the arrays and one of them does not match.
>> Before I compile for HSAIL, I enable some profiling by running the above lambda on the cpu in non-parallel mode (IntStream.range().forEach()) so the lambda gets executed 2000000 times (and takes the false branch once).
>> 
>> But even though one of the elements does not match, when I compile thru graal with the default -G:+RemoveNeverExecutedCode, I see that the isEqual = false path has been considered "not executed" and has been removed.
>> 
>> Is taking a branch once out of 2,000,000 times considered "not executed"?
>> Or is there some other flaw here?
> 
> Remember this means never executed according to the profile, so if it doesn't show up in the profile then it didn't happen.  Did the profile include the taken branch?
> 
> tom
> 
>> 
>> Of course I can work around this  in this case by forcing -G:-RemoveNeverExecutedCode but I'd like to understand this.
>> This is running in -server mode.
>> 
>> -- Tom
>> 
>