[Bug c/37569] New: Loop incorrectly optimized to endless loop with -Os/-O2/-O3

[ppr at melexis dot com]

The loop in the example is incorrectly replaced with endless loop when
compiling with -Os, -O2 or -O3. It is compiled correctly with -O0 or -O1.

    uint16 sum=0;
    uint16 *i;

    /*sum all words in inspected area*/
    i = (uint16 *)0x0FFE;
    do
    {
        --i;
        sum = sum + *(i);
    } while ( i != 0 );

(see the full source in the attachment)

Target: i686-pc-cygwin
Configured with: ../gcc-4.3.2/configure
Thread model: single
gcc version 4.3.2 (GCC) 

(the same problem occurs with earlier versions of GCC (e.g. 3.4.3) and G++ )


-- 
           Summary: Loop incorrectly optimized to endless loop with -Os/-
                    O2/-O3
           Product: gcc
           Version: 4.3.2
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: ppr at melexis dot com
  GCC host triplet: i686-pc-cygwin


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37569