[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: unassig...@gcc.gnu.org

        ReportedBy: holger.h...@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;

}