Re: compiler settings in AdaGIDE

[jonathan <johnscpg@googlemail.com>]

On Jul 25, 2:29 pm, Ada novice <po...@gmx.us> wrote:
> Many thanks for all these precious information. The settings
>
> -gnatnp -O2 -march=native -ffast-math -funroll-loops
>
> was only 1 s faster (1537 s) as compared to using
>
> -gnatVa -O3 -gnatn -funroll-loops -gnatf -gnato

Interesting result. I repeated the 100 calls to
COMPLEX_EIGENVALUES.Eigen ( P, W, V, FAIL) test on a
121 x 121 sized matrix.
I still get the same big decrease in running time from the
-ffast-math switch. Generic_Complex_Eigenvalues
seems sensitive to -ffast-math, but I've never seen any other
program care much about it.

> 1. I see that you use -gnatnp. Is this safe to do so i.e. to suppress
> all checks?

If I remove the -gnatp  then running time goes from 3.61 to 6.1 sec.
If I remove the -gnatnp then running time goes from 3.61 to 6.7 sec.
(I suspect that you know that -gnatnp is really -gnatn -gnatp).

On a high percentage of ordinary problems (usually data
analysis) I would not care at all about the increased
running time, and I would not remove the checks. There
is another class of program I write and these run for days
or weeks. These I never stop optimizing and testing, and
all checks are removed!

> 2. In the specification -march="machine architecture here", you use
> native for the machine architecture. Does this apply to Intel
> processors as well?

I just checked the gcc man pages and found nothing at all about
-march=native.  It helps a little on all the machines I've
used and occasionally in the past it has helped enormously.  Just
now I removed -march=native from the Generic_Complex_Eigenvalues
test and running time went from 3.61 sec to 3.58 sec. When
I remove it from the Jacobi benchmark, the program slows down
slightly. So the switch seems to do something on my intel machine,
but all I can say now is that the difference is very small and
unpredictable.

J.