[Bug tree-optimization/14741] graphite with loop blocking and interchanging doesn't optimize a matrix multiplication loop

["spop at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14741

--- Comment #18 from Sebastian Pop <spop at gcc dot gnu.org> ---
On my laptop ARM Exynos5 at 1.6GHz I get this:

gfortran -ffast-math -O3 t.f90
./a.out
   192.75000000000000        10.239999999999826     

gfortran -ffast-math -O3 -fgraphite -floop-interchange -floop-block t.f90
./a.out
   193.77500000000001        10.239999999999826     

gfortran -ffast-math -O3 -floop-nest-optimize t.f90
t.f90: In function âMAIN__â:
t.f90:5:0: warning: iteration 31 invokes undefined behavior
[-Waggressive-loop-optimizations]
 B=0.1D0
 ^
f951: note: containing loop
t.f90:4:0: warning: iteration 31 invokes undefined behavior
[-Waggressive-loop-optimizations]
 A=0.1D0
 ^
f951: note: containing loop
./a.out
./a.out: No such file or directory

I don't know why the compiler does not produce an executable: -S does produce a
.s file.

Adding -fdump-tree-graphite-all produces a file t.f90.106t.graphite containing
the information about what graphite has done: I see that we do loop block the
loop nest like this:

gfortran -ffast-math -O3 -floop-nest-optimize -fdump-tree-graphite-all t.f90

CLAST generated by CLooG: 
for (scat_0=0;scat_0<=1023;scat_0+=32) {
  for (scat_1=0;scat_1<=1023;scat_1+=32) {
    for (scat_2=scat_0;scat_2<=scat_0+31;scat_2++) {
      for (scat_3=scat_1;scat_3<=scat_1+31;scat_3++) {
        (scat_2,scat_3);
      }
    }
  }
}

I see that the tile size is hard coded as a constant in graphite-optimize-isl.c

  TileMap = getTileMap(ctx, *Dimensions, 32);

that should be replaced by a param and tuned.