On Sep 7, 2012, at 2:02 PM, Andrew Pinski wrote:
> On Fri, Sep 7, 2012 at 10:57 AM, <paul_kon...@dell.com> wrote:
>> This seems to be a bug:
>>
>> struct bug
>> {
>> int f1:1;
>> unsigned long long f2:31;
>> };
>>
>> struct bug test = { 1, 0x8000ULL };
>>
>> int main (int c, char **v)
>> {
>> unsigned long long tf2;
>>
>> tf2 = test.f2 << 16;
>> if (tf2 == 0x80000000ULL)
>> return 0;
>> return 1;
>> }
>>
>> Since the underlying type of field f2 is unsigned long long, I would not
>> expect the expression "test.f2 << 16" to do sign extending of a 32 bit
>> intermediate result. But that is in fact what GCC produces, for
>> x86_64-linux (gcc 4.7.0).
>>
>> If I explicitly cast test.f2 to unsigned long long before the shift, the
>> expected result appears. But I shouldn't have to do that cast, given that
>> the type of f2 is already unsigned long long, correct?
>
> The type of "test.f2" is a 31 bit unsigned integer (the declared type
> is used for alignment) and that fits in a 32bit signed integer so when
> doing test.f2 << 16, it is promoted to only an 32bit signed integer.
>
> Thanks,
> Andrew
Ok, thanks.
GDB doesn't do things this way, so I guess I have to tell them.
paul
