Re: Poor performance with GNAT-GPL-2017

[stephane.carrez@gmail.com]

Le jeudi 15 juin 2017 18:31:52 UTC+2, Charly a écrit :
> 
> 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.

The best choice is different for each program.

As far as I'm concerned, I observe a 5% improvement in speed
and 8% reduction in code size. The -O2 or -O3 give better
performance for me.

If you look at gcc bug list at https://gcc.gnu.org/bugzilla/ you will
find some performance regressions for some very particular cases between
gcc 4.9 and gcc 6.3.  Fortunatly it does not affect the majority of
programs.

It might be interesting that you publish your program so that
further investigations can be conducted.

Stephane