RFR: JDK-8246751 Mac OS build settings should use -O3

[Magnus Ihse Bursie]

On 2020-06-08 19:31, Sergey Bylokhov wrote:
> One of the reasons why -0s was used from the beginning is the 
> performance of the client related libraries, especially java2d.
> Does anybody run or plan to run performance tests to check that we do 
> not have performance there?
As Claes say in the bug report, hopefully any potential performance 
regression will show up in the  general performance testing.

The idea here is, after all, that we will *increase* performance. :-)

Is there some specific library/behavior/test that you are worried about 
that should show performance regression when we increase the 
optimization level?

/Magnus
>
> On 6/8/20 8:55 am, Magnus Ihse Bursie wrote:
>>  From Jim's bug report:
>>
>> "Mac OS X should use -O3 optimization level to be consistent with 
>> other platforms and benefit Mac OS X java with the same performance 
>> levels as other platforms.
>>
>> Mac OS X has used -Os level optimization since management of the 
>> platform JDK was handed over from Apple. This level of optimization 
>> was Apple's policy, not OpenJDK's. The policy was established in a 
>> time when memory was tight (I was there at the time.) Since then 
>> other platforms have moved on, making the decision to target speed 
>> over disk space. Specifically, using -O3 level optimization.
>>
>> I've personally seen 20-30% improvement in performance in C/C++ 
>> applications using -O3 over -Os. But, of course, the performance team 
>> should verify the affect on the JDK.
>>
>> A 11% real time improvement can be seen with a rough HelloWord 
>> compile/run."
>>
>> I discussed this with Claes, our performance guru, and he agreed that 
>> it is low risk enough that we can push this for JDK 15.
>>
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8246751
>> WebRev: 
>> http://cr.openjdk.java.net/~ihse/JDK-8246751-macos-optimize-O3/webrev.01
>>
>> /Magnus
>
>