[Bug c/47670] New: Gcc 4.5.1 inconsistent optimisation of loop with mixed 32bit and 64bit arithmetic

[argondsgn at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47670

           Summary: Gcc 4.5.1 inconsistent optimisation of loop with mixed
                    32bit and 64bit arithmetic
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: argondsgn@gmail.com


Created attachment 23290
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=23290
Output of gcc -v save-temps -O2 bug.c

int main(int argc, char *argv[]) 
{ 
    int i;
    long long count=0;
    int ret;
    for (i=0;i<9;i++)
    {
        count+=i*0x40000000;      
    }
    ret=count>>32;
    return ret;
}

produces different answers when compiled with 
gcc -O1 bug.c      (returns -1)
or
gcc -O2 bug.c      (returns 9)

Judging from the assembler output with -S, this loop is optimised to a
different constant expression in the two cases.

It works with gcc 3.4.4, but not with gcc 4.5.1 (I haven't tested any other
versions yet)

(First time I've attempted to submit a bug report to an open source project, so
many apologies if this is already fixed, an issue with my understanding of C,
or in the wrong category!)