Re: GNAT compiler switches and optimization

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On 20 Oct 2006 03:47:44 -0700, 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.
> 
> I'm using GNAT (GPL 2006) and GFortran (4.2.0) and the following
> compile options:
> 
> gnat make -O3 -gnatp tst_array
> gfortran -O3 tst_array.f95
> 
> Running them on 800x800 matrices (on my 2GHz laptop)
> 
> for Ada: "tst_array 800" runs in 18 seconds
> for Fortran "tst_array 800" runs in 6 seconds
> 
> (if I use the fortran "matmul" intrinsic the fortran time drops to
> 2.5 seconds)
> 
> Note, I tried reordering the loops, removing the random calls, etc.
> none of which made huge changes.  There is something killing
> performance
> and/or a switch or two that I'm missing, but I can't seem to find it.
> Any thoughts?
> 
> Here is the code:
[...]

Pointers + index checks I'd say. Try this:

with Ada.Numerics.Float_Random;      use 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_2 is
   package F_IO is new Ada.Text_IO.Float_IO(Float);
   package D_IO is new Ada.Text_Io.Fixed_Io(Duration);
   type Real_Matrix is array(Integer range <>,Integer range <>) of Float;

   N    : Positive;
   G    : Ada.Numerics.Float_Random.Generator;

   Start, Finish : Ada.Calendar.Time;
   Sum : Float := 0.0;
begin
   N := Positive'Value (Argument (1));
   declare
      subtype Matrix is Real_Matrix (1..N, 1..N);
      A, B, C : Matrix;
   begin
      for I in A'range(1) loop
         for J in A'range(2) loop
            A(I,J) := Ada.Numerics.Float_Random.Random(G);
            B(I,J) := Ada.Numerics.Float_Random.Random(G);
         end loop;
      end loop;

      Start := Ada.Calendar.Clock;

      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;

      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;
   end;
   Put ("Time: "); D_IO.Put(Finish-Start); New_Line;New_Line;
end tst_array_2;

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de