This patch fixes PR66754 by reverting an earlier unintended change.
We now generate a much simpler AST for interchange-1.c:

ISL AST generated by ISL:
{
  for (int c1 = 0; c1 <= 1334; c1 += 1) {
    S_7(c1);
    for (int c3 = 0; c3 <= 1334; c3 += 1)
      S_4(c1, c3);
    S_5(c1);
  }
  for (int c1 = 0; c1 <= 1334; c1 += 1)
    S_10(c1);
  S_8();
}

Bootstrap and check pass on x86_64-linux with isl-0.14.1

          PR tree-optimization/67754
          * graphite-optimize-isl.c (optimize_isl): Call
          isl_options_set_schedule_fuse with ISL_SCHEDULE_FUSE_MIN for ISL-14.

Co-Authored-By: Aditya Kumar <aditya.k7@samsung.com>

From-SVN: r228268