[Bug c/37067] New: gcc creating wrong code with -O2

[stefan dot bruens at rwth-aachen dot de]

The following code is producing false results with -O2 optimization (-O1 and O3
are correct):
-------
#include <stdio.h>
#define BLOCK_SIZE 100000

int main()
{
  int i;
  float block_f[BLOCK_SIZE];
  int d_phase = 0;
  int d_phase_inc = 0x100000;

  for (i = 0; i < BLOCK_SIZE; i++){
      block_f[i] = (float)(d_phase);
      d_phase += d_phase_inc;
    }

  printf ("%x %x\n", (int)block_f[1695], (int)block_f[1696]);
  return 0;
}
-----
With -O2, the loop is run only 0x6a0 times, instead of 0x186a0 times.

gcc is from openSUSE 11.0 (4.3.1 20080507 (prerelease) [gcc-4_3-branch revision
135036] (SUSE Linux)), but fc9 is most probably affected as well.

Failing code is a very simplified test case from gnuradio
(http://www.ruby-forum.com/topic/156807)


-- 
           Summary: gcc creating wrong code with -O2
           Product: gcc
           Version: 4.3.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: stefan dot bruens at rwth-aachen dot de


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37067