[Bug c/16309] New: different behavior in lvalue assignment in -O0 & -O2

[Bug c/16309] New: different behavior in lvalue assignment in -O0 & -O2

[nakkore at libero dot it]

Compiling with -O2 and -O0 the following code i obtain different
result with gcc version > 3.2 ( i tryed 3.3.3,3.3.4)

unsigned char dest[10],source[10]={1,2,3,4,5,6,7,8,9,10};

int main(void)
{
  int i = 1;
  int step = 1;

  while (i < 8)
    dest[i] = source[(i++*step) % 7];


  for(i=0; i < 8; i++)
    printf("%02x ",dest[i]);

  printf("\n");


  i=1;

  while (i < 8)
    {
      dest[i] = source[(i*step) % 7];
      i++;
    }

  for(i=0; i < 8; i++)
    printf("%02x ",dest[i]);

  printf("\n");

  return(i+dest[6]);
}

the difference is how dest[i] is addressed via the index i.

-- 
           Summary: different behavior in lvalue assignment in -O0 & -O2
           Product: gcc
           Version: 3.3.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: nakkore at libero dot it
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: Reading specs from /usr/lib/gcc-lib/i686-pc-linux-
                    gnu/3.3.3/spec
  GCC host triplet: i386
GCC target triplet: i386


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16309

[Bug c/16309] different behavior in lvalue assignment in -O0 & -O2

[falk at debian dot org]

------- Additional Comments From falk at debian dot org  2004-07-01 09:08 -------
With -Wall, you get:

test.c:9: warning: operation on `i' may be undefined

and in fact it is; see documentation on -Wsequence-point.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID
            Summary|different behavior in lvalue|different behavior in lvalue
                   |assignment in -O0 & -O2     |assignment in -O0 & -O2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16309

[Bug c/16309] different behavior in lvalue assignment in -O0 & -O2

[bangerth at dealii dot org]

------- Additional Comments From bangerth at dealii dot org  2004-08-13 16:01 -------
Reopening to mark as a duplicate of... 

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |UNCONFIRMED
         Resolution|INVALID                     |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16309

[Bug c/16309] different behavior in lvalue assignment in -O0 & -O2

[bangerth at dealii dot org]

------- Additional Comments From bangerth at dealii dot org  2004-08-13 16:04 -------
...PR 11751. 

*** This bug has been marked as a duplicate of 11751 ***

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |DUPLICATE


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16309