graphite loop optimizer - "C" examples?

[Gary Funck]

I have been experimenting with the graphite optimizer, based on GCC trunk, and
cloog-isl.  I started with the attached simple "C" program, which has this
basic structure.

#define N 20000
int a[N][N], b[N], c[N];
[...]
  for (i = 0; i < N; i++)
    {
      b[i] = i;
      c[i] = i + N;
    }
  for (i = 0; i < N; i++)
    for (j = 0; j < N; j++)
      a[j][i] = b[i] + c[j];

(Attached, is the full test case.)

And compiled it with: -O3  -floop-block.

Couple of questions:
1) What option should I supply to confirm that the graphite optimizer ran and
determine (i) did it in fact perform any optimizations, and (ii) which
optimizations did it perform?
2) If -floop-block couldn't optimize this program, what is the likely reason?
3) Would you please offer pointers to example "C" programs that highlight
graphite-cloog-isl optimizations?

Thanks,
- Gary

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

#define N 20000

int a[N][N], b[N], c[N];

static double
cpu_time ()
{
  struct timespec ts;
  double t;
  if (clock_gettime (CLOCK_MONOTONIC, &ts))
    abort ();
  t = ts.tv_sec + (ts.tv_nsec * 1.0e-9);
  return t;
}

int
main (void)
{

  int i, j, k;
  double start, stop, elapsed;

  for (i = 0; i < N; i++)
    {
      b[i] = i;
      c[i] = i + N;
    }

  start = cpu_time ();
  for (i = 0; i < N; i++)
    for (j = 0; j < N; j++)
      a[j][i] = b[i] + c[j];
  stop = cpu_time ();
  elapsed = stop - start;

  printf ("elapsed time = %0.2f secs.\n", elapsed);

  return 0;
}