[Bug c++/49321] New: Incorrect Optimization O2 and O3 on Shift Operation for 64 bit Integers

[bbli08 at yahoo dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49321

           Summary: Incorrect Optimization O2 and O3 on Shift Operation
                    for 64 bit Integers
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: bbl...@yahoo.com


// Shift operation yielded different results on different
// level of optimization for the same source. O1 is working but
// not O2 and O3

// Tested environments: Fedora 10. GCC 4.3.2.20081105 
// and Windows XP, MingGW GCC 4.5.2

// Compiler output and warning: nothing
// source file: one attached (no header file)

#include "stdio.h"
/*
 * Incorrect -O2 and -O3 optimization for 64 bit integer shift operator.
 * -O1 is working correclty
g++ -O1 main.cpp && ./a.out
i[0]=0, i[1]=8

g++ -O2 main.cpp && ./a.out 
i[0]=1, i[1]=0

g++ -O3 main.cpp && ./a.out 
i[0]=1, i[1]=0
 */
int main(int argc, char* argv[]) {
       int i[2];
        i[0] = 1;
        i[1] = 0;
        *((unsigned long long *) (&i)) <<= 35;
    /* correct result: linux test i[0]=0, i[1]=8 */
        printf ("i[0]=%d, i[1]=%d\n", i[0],i[1]);
    return 0;
}