Re: smbfs bug introduced at smbfs_vnops.c:1.58

On 2005-04-10 at 13:45:50 Daniel Ellard wrote:

>> int main(void) {
>>   int a;
>>   a+=1;
>>   return (0);
>> }
[snip]
> If you change the -O to -g, then the code for "a" is not
> removed -- but there's still no warning.  I think this is
> a bug, because if the expression wasn't an innocuous a+=1
> it could be a real problem if the variable wasn't removed.

The idea here is that gcc sees that the value of a is never used, and
therefore it doesn't have to warn.  (Whether you agree with this, or
not, is more of a political or philosophical question. ;)  But as soon
as you actually *do* something with a's value afterwards, it will
start to complain.  IOW, if you change main into:

    int main(void)
    {
        int a;
        a += 1;
        a++;
        //...bunch of other operations on a...
        ++a;
        a *= 3;
        return 0;
    }

and gcc will still issue no warning.  However, add one actual *use*
of a:

    extern void f(int i);

    int main(void)
    {
        int a;
        a += 1;
        f(a);
        return 0;
    }

and you'll get the warning you want... :)