Re: Poor performance with GNAT-GPL-2017

[Charly <carl.weierstrass@googlemail.com>]

Am Donnerstag, 15. Juni 2017 17:19:20 UTC+2 schrieb Charly:
> Am Dienstag, 13. Juni 2017 21:46:13 UTC+2 schrieb alkh...@gmail.com:
> > On Monday, June 12, 2017 at 6:28:17 PM UTC+3, Mark Lorenzen wrote:
> > > On Saturday, June 10, 2017 at 1:23:34 PM UTC+2, Charly wrote:
> > > > Hi,
> > > > 
> > > > when I found the new GNAT-GPL-2017 this morning I was happy and installed it at once.
> > > > But I was rather disappointed about the poor performance.
> > > > To be more precise:
> > > > 
> > > > When I switch to new hard- or software I allways check the performance with my private tool:
> > > > It solves Rubics Tabgle https://www.jaapsch.net/puzzles/tangle.htm with an ada programm, using one task per core.
> > > > 
> > > > With GNAT-GPL-2016 (gcc 4.9.4) it took about 0,4 sec to find both solutions,
> > > > with GNAT-GPL-2017 (gcc 6.3.1) it takes about 0,8 sec to find both solutions,
> > > > which means the program is slower by a factor of 2.
> > > > 
> > > > In both cases I use the following options: 
> > > > -O3 -gnatA -gnatn -funroll-loops -fPIC -gnatp -g -gnatW8 -gnatVn -mtune=amdfam10 -gnat12
> > > > 
> > > > Any ideas??
> > > 
> > > Previous versions of GNAT did not have overflow check (-gnato) enabled by default, whereas newer versions have. Maybe this is what you are seeing.
> > > 
> > > Regards,
> > > 
> > > Mark L
> > 
> > I see Charly is compiling with '-gnatp'. Does it suppress the overflow checks as well?
> > 
> > Charly, it can be an interesting experiment to trace the source of this anomaly. This is strange that the compiler is emitting a code that is twice as slow. It can compile a specific language feature to be slower, but this one needs to be run frequently enough in your program. Can you guess what this feature can be? Maybe a profiler can help.
> > 
> > Can you try to compile your benchmark without tasking at all (remove the tasking code, rather than create 1 task)?
> > 
> > Can you use a different run time for the 2017 compiler?
> 
> -----
Some aditional strange results, all without any tasking (new option -t 0)

gnat-gpl-2016 -O
duration 3485 ms

gnat-gpl-2016 -O2
duration 4713 ms

gnat-gpl-2016 -O3
duration 2772 ms

gnat-gpl-2017 -O
duration 3375 ms

gnat-gpl-2017 -O2
duration 4480 ms

gnat-gpl-2017 -O3
duration 4823 ms

To summarize I draw two conclusions
This year optimization level -O is the best choice,
Try several optimization levels next year when gnat-gpl-2018 is out.