[OpenJDK Rasterizer] Marlin #4

[Jim Graham]

We should also be wary of compiler options that are a win on one 
processor family and a loss on another.  Anything that schedules 
instructions may be specific to a particular generation of CPUs, for 
instance.  Or for i5 vs i7 vs M(obile)...

			...jim

On 10/2/15 9:10 AM, Laurent Bourgès wrote:
> Sergey,
>
> thanks for the information:
>
>         I tried your gcc options on my ubuntu 14.4 (v4.8.4) and it is
>         actually
>         slightly faster: 10% on my fill ellipse test (450ms vs 490ms).
>
>
>     I tested by your jmh test, and the difference became bigger on 1400
>     size.
>
>
> Interesting; I will try too.
>
>
>
>         Do you know which gcc compiler and options are used to build
>         JavaSE EA?
>
>     I guess that compiler options in makefile are the same.
>
>     plus some default gcc options:
>     jdk8:
>     gcc (GCC) 4.3.0 20080428 (Red Hat-8) C compiler version 4.3.0-8)
>
>     jdk9:
>     gcc-4.8.2 - OEL5.5
>
>
> However the gcc compiler are different: 4.3 vs 4.8.2 !
>
> So it may be worth comparing their different optimization options; I
> guess somebody already looked at that !
>
>
>         Moreover, the linux distrib may define default options.
>
>         I will try to figure out all compiler options (command line +
>         defaults)
>         on my machine.
>
>
>     It is not simple to find an option, which will help for everyone.
>     Two options suggested by me is a minimum number from -O3 to get the
>     maximum performance, both seems reasonable. Actually if I change the
>     -O2 to -O3(OPTIMIZATION := LOW =>> OPTIMIZATION := HIGHEST)
>     performance became worse.
>
>
> It is often the case with O3, but your patch seems a good win with only
> 2 enabled options.
>
>
>         What is your build environment ?
>
>
>     Ubuntu 14.04 gcc 4.8.4
>
>
> I have the same and I got finally my gcc options:
> gcc -c -Q -O2 --help=common
>
> Here are the difference between O2 vs O3 with gcc 4.8.4:
>
> gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts
> gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts
> diff /tmp/O2-opts /tmp/O3-opts | grep enabled
>
> *>   -fgcse-after-reload                 [enabled]
> *>   -finline-functions                  [enabled]
>>   -fipa-cp-clone                      [enabled]
>>   -fpredictive-commoning              [enabled]
>>   -ftree-loop-distribute-patterns     [enabled]
>>   -ftree-partial-pre                  [enabled]
> *>   -ftree-vectorize                    [enabled]
> *>   -funswitch-loops                    [enabled]
>>   -fvect-cost-model                   [enabled]
>
> So we could evaluate some of these options and see what is the best
> compromise for libawt on gcc 4.8 !
>
> Regards,
> Laurent