[Bug regression/56844] New: Loop condition wrongly optimized from < to !=

[holger.hopp at sap dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56844

             Bug #: 56844
           Summary: Loop condition wrongly optimized from < to !=
    Classification: Unclassified
           Product: gcc
           Version: 4.8.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: regression
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: holger.hopp@sap.com


Following code is optimized  wrong with gcc-4.8 -O2.
It works correct with gcc-4.8 -O1 and gcc-4.7 -O2.
Somehow the 'i < 16' condition of the second loop is optimized to 'i != 16'
(runs second loop until segfault / stack overflow).

[gcc-4_8-branch revision 197479, x86_64]

int printf (const char *format, ...);
char* strncpy (char * dest, const char * src, unsigned long n);

int main()
{
  int i;
  char str[16];

  strncpy( str, "abcdefghijklmnop", 16 );
  for( i = 0; ( str[i] != '\0' ) && ( i < 16 ); i++ );
  for( ; i < 16; i++ ) str[i] = ' ';
  printf ("str = \"%s\"\n", str);
  return 0;
}