Why isn't the overflow flag set?

[Simen Kjærås]

On Thu, 10 Nov 2011 18:56:37 +0100, Steven Schveighoffer  
<schveiguy at yahoo.com> wrote:

> On Thu, 10 Nov 2011 12:24:30 -0500, Simen Kjærås  
> <simen.kjaras at gmail.com> wrote:
>
>> I'm creating a Checked!T struct for integral values. The version  
>> attached
>> works
>> for the most part, but some parts confuse me, namely that the following
>> operations do not set the overflow flag:
>>
>> uint.max + 1
>> ulong.max + 1
>>
>> int.min - 1
>> uint.min - 1
>> long.min - 1
>> ulong.min - 1
>>
>> uint.max << 1
>> long.max << 1
>> ulong.max << 1
>>
>> int.min << 1
>> long.min << 1
>
> These are likely folded into a single constant.  I think it would be  
> inappropriate for these to set the flag (it would be something unnatural  
> anyways).

Sorry, my example was simplified. These are all on the form

uint a = uint.max;
a = a + 1;

It works for all integral types not mentioned here.


>> int a = int.max; a *= 2
>> long a = long.max; a *= 2
>
> These I would think could set the overflow flag, but not necessarily  
> when optimized.

No optimizations are on, and -debug is passed. I find it unlikely the
compiler is doing much magic here. If it does, I am more than willing
to call it a bug.