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Date: Sat, 21 Oct 2006 17:22:05 -0400
From: Jeffrey Creem <jeff@thecreems.com>
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Subject: Re: GNAT compiler switches and optimization
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Date: 2006-10-21T17:22:05-04:00
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Pascal Obry wrote:
> Jeffrey Creem a �crit :
> 
> 
>>I'd certainly be willing to run a few benchmarks but the important thing
>>here is that rather innocent looking code is running 2-4x slower than it
>> "should".
> 
> 
> The first thing is to be sure that we are running the same program.
> 
> Running your program with the following changes (as done in Fortran):
> 
> 1. Using Sum tmp var for the computation
> 
>    for I in A'range (1) loop
>       for J in A'range (2) loop
>          Sum := 0.0;
>          for R in A'range (2) loop
>             Sum := Sum + A (I, R) * B (R, J);
>          end loop;
>          C (I, J) := Sum;
>       end loop;
>    end loop;
> 
> 2. Using Long_Float instead of Float (I think Fortran float is a
> Long_Float, to be checked).
> 
> I went from 7.8s to 4.8s (with 1) and to 4.2s (with 2).
> 
> Pascal.
> 

Actually, the original poster's Ada program had the temp var and all of 
my comparisons of programs that I have asserted were "the same" used the 
temporary.

As for Long_Float v.s. Short_Float, gfortran is using 32 bit floats (as 
verified by dumping the tree representation and assembly language).

Since we are all getting a bit confused by specific versions and numbers 
I thought I'd post a summary and create a way of tracking more global 
performance issues at the gnuada.sf.net wiki.

The direct link to these test results are here:

http://gnuada.sourceforge.net/pmwiki.php/Main/Oct2006CLAGFORTRANComparison