Re: Poor performance with GNAT-GPL-2017

[alkhimey@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?