[Bug tree-optimization/29543] Poor code generated for arrays with variable bounds

["laurent at guerby dot net" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #9 from laurent at guerby dot net  2006-10-22 16:13 -------
Eric, build is "i686-pc-linux-gnu" I don't understand why you speak of
generalization :).

Anyway, I changed the code to match more likely use, that is by using a
subprogram:

   procedure Compute (A, B : in Real_Matrix; C : out Real_Matrix) is
      Sum : Float := 0.0;
   begin
      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;
   end Compute;

...

   Start := Ada.Calendar.Clock;
   Compute (A.all, B.all, C.all);
   Finish := Ada.Calendar.Clock;

On my x86_64 box at -O2 (-gnatp) Ada is still three times slower

cd ada ; ./tst_array 600
 1.65129E+02 1.47839E+02
 1.57425E+02 1.40635E+02
Time:           1.541291000

cd fortran ; ./tst_array 600
   146.0253       145.0025       149.3322       150.8924
 Time:   0.5400340

I don't know how to write the equivalent fortran code, but it's likely better
to concentrate on the subprogram version for optimization purpose.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29543