Re: GNAT compiler switches and optimization

["Jeffrey R. Carter" <spam.not.jrcarter@acm.not.spam.org>]

tkrauss wrote:
> I'm a bit stuck trying to figure out how to coax more performance
> out of some Ada code.  I suspect there is something simple (like
> compiler switches) but I'm missing it.  As an example I'm using
> a simple matrix multiply and comparing it to similar code in
> Fortran.  Unfortunately the Ada code takes 3-4 times as long.

1st, make sure you're timing the same thing. How does Ada matrix 
multiplication compare to FORTRAN? You don't know, because you're also 
timing the random number generators and I/O. Ada.Text_IO, especially, is 
quite heavy-weight compared to other languages.

Here's my version of your program:

with Ada.Numerics.Float_Random;
with Ada.Command_Line;          use Ada.Command_Line;
with Ada.Text_IO;               use Ada.Text_IO;
with Ada.Calendar;              use Ada.Calendar;

procedure Tst_Array is
    package F_IO is new Ada.Text_IO.Float_IO (Float);
    package D_IO is new Ada.Text_Io.Fixed_Io (Duration);

    N : constant Positive := Integer'Value (Argument (1) );

    type Real_Matrix is array (1 .. N, 1 .. N) of Float;
    pragma Convention (FORTRAN, Real_Matrix);

    G : Ada.Numerics.Float_Random.Generator;

    A,B : Real_Matrix :=
       (others => (others => Ada.Numerics.Float_Random.Random (G) ) );
    C : Real_Matrix := (others => (others => 0.0) );
    Start, Finish : Ada.Calendar.Time;
begin
    Start := Ada.Calendar.Clock;

    for I in A'range (1) loop
       for J in A'range (2) loop
          for R in A'range (2) loop
             C (I, J) := C (I, J) + A (I, R) * B (R, J);
          end loop;
       end loop;
    end loop;

    Finish := Ada.Calendar.Clock;

    F_IO.Put (C (1, 1) );
    F_IO.Put (C (1, 2) );
    New_Line;
    F_IO.Put (C (2, 1) );
    F_IO.Put (C (2, 2) );
    New_Line;

    Put ("Time: ");
    D_IO.Put (Finish - Start);
    New_Line;
end Tst_Array;

I compiled as

gnatmake -O3 -gnatnp -fomit-frame-pointer tst_array

With MinGW GNAT 3.4.2, Windows XP, and a 3.2 GHz Pentium 4 HT processor, 
I get

C:\Documents and Settings\All Users\Documents\Code>tst_array 800
  2.05839E+02 2.01230E+02
  2.00866E+02 1.94039E+02
Time:           5.821082831

I don't have a FORTRAN compiler for comparison. FORTRAN will probably do 
better, but I wouldn't expect the difference to be as great as your values.

-- 
Jeff Carter
"I was hobbling along, minding my own business, all of a
sudden, up he comes, cures me! One minute I'm a leper with
a trade, next minute my livelihood's gone! Not so much as a
'by your leave!' You're cured, mate. Bloody do-gooder!"
Monty Python's Life of Brian
76