[Bug tree-optimization/46590] New: long compile time with -O2 and many loops

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46590

           Summary: long compile time with -O2 and many loops
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Keywords: compile-time-hog
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: tkoenig@gcc.gnu.org


The attached program, which is a stress-test to test array assignment
dependencies for gfortran, compiles just about forever at -O2;
so far, it's 90 minutes and still no sign of finishing.

Compilation time without -O2 is 45 seconds.

Here is the perl script used to generate the test case.

#! /usr/bin/perl                                                         

$cnt = 0;
# @ind = (-6, -3, -1, 1, 3, 6);
@ind = (-5, -3, -1, 1, 3, 5);  
$n = 6;                        

print <<EOF;
program main
  implicit none
  integer, dimension(-100:100) :: a,b,original
  integer :: i
  original = [(15*i+2,i=-100,100)]

EOF
foreach $stride_l (@ind) {
    foreach $stride_r (@ind) {
        for ($start_l = 1; $start_l < $n; $start_l ++) {
            for ($start_r = 1; $start_r < $n; $start_r ++) {
                for ($times = 0; $times < $n; $times ++) {
                    $end_l = $start_l + ($times-1)*$stride_l;
                    $end_r = $start_r + ($times-1)*$stride_r;
                    print <<EOF;
  a = original
  b = original
  a($start_l:$end_l:$stride_l) =  a($start_r:$end_r:$stride_r)
  b($start_l:$end_l:$stride_l) = original($start_r:$end_r:$stride_r)
  if (any (a /= b)) then
    print *,$start_l, $end_l,$stride_l,$start_r,$end_r, $stride_r
    call abort
  end if

EOF
                }
            }
        }
    }
}
print "end program main\n";