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

[Claes Redestad]

On 2020-06-09 00:12, Sergey Bylokhov wrote:
> On 6/8/20 3:06 pm, Claes Redestad wrote:
>> Right, -O3 is now likely the default for most files.
>>
>> I'm not sure you suggest the reported ~2% difference between -Os and
>> -O2/-O3 as an argument against changing to -O3 by default. It might be
>> statistically significant - or just noise - but we should at any rate
>> be wary of overfitting to a particular (micro-)benchmark.
> 
> I guess that should be the opposite way round. Some good numbers other than
> noise should be used as an argument of changing -0s to -03 by default.

I think if the differences are all in the noise then that could just as
well be used as an argument for _harmonizing_ the build optimization
strategy with the other platforms. While not easy to quantify,
harmonizing theoretically reduces risk of obscure platform specific
issues, since, while different, different platforms will use similar
optimizations schemes at -O3.

> 
>>
>> It'd also be good to re-run with the new default: when most compilation
>> units change to -O3, which optimization level is ideal for an individual
>> compilation unit (such as unsafe.cpp) might very well change, since
>> what optimizations are available through the build chain can shift
>> considerably.
> 
> Hope we will get some good improvements, otherwise it is better to use -0s.
> 

I hope so too!

/Claes