On 9/06/2020 8:26 am, Claes Redestad wrote:
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.
On the third hand "if ain't broke ..."
Seems to me that any change to build flags should be backed up by
a-priori evidence that it is a worthwhile change.
David
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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
