On Tue, Oct 24, 2017 at 3:24 PM, Richard Sandiford
<[email protected]> wrote:
> Richard Biener <[email protected]> writes:
>> On Tue, Oct 24, 2017 at 2:48 PM, Richard Sandiford
>> <[email protected]> wrote:
>>> Richard Biener <[email protected]> writes:
>>>> On Tue, Oct 24, 2017 at 1:23 PM, Richard Sandiford
>>>> <[email protected]> wrote:
>>>>> Eric Botcazou <[email protected]> writes:
>>>>>>> Yeah. E.g. for ==, the two options would be:
>>>>>>>
>>>>>>> a) must_eq (a, b) -> a == b
>>>>>>> must_ne (a, b) -> a != b
>>>>>>>
>>>>>>> which has the weird property that (a == b) != (!(a != b))
>>>>>>>
>>>>>>> b) must_eq (a, b) -> a == b
>>>>>>> may_ne (a, b) -> a != b
>>>>>>>
>>>>>>> which has the weird property that a can be equal to b when a != b
>>>>>>
>>>>>> Yes, a) was the one I had in mind, i.e. the traditional operators are
>>>>>> the must
>>>>>> variants and you use an outer ! in order to express the may. Of
>>>>>> course this
>>>>>> would require a bit of discipline but, on the other hand, if most of
>>>>>> the cases
>>>>>> fall in the must category, that could be less ugly.
>>>>>
>>>>> I just think that discipline is going to be hard to maintain in practice,
>>>>> since it's so natural to assume (a == b || a != b) == true. With the
>>>>> may/must approach, static type checking forces the issue.
>>>>>
>>>>>>> Sorry about that. It's the best I could come up with without losing
>>>>>>> the may/must distinction.
>>>>>>
>>>>>> Which variant is known_zero though? Must or may?
>>>>>
>>>>> must. maybe_nonzero is the may version.
>>>>
>>>> Can you rename known_zero to must_be_zero then?
>>>
>>> That'd be OK with me.
>>>
>>> Another alternative I wondered about was must_eq_0 / may_ne_0.
>>>
>>>> What's wrong with must_eq (X, 0) / may_eq (X, 0) btw?
>>>
>>> must_eq (X, 0) generated a warning if X is unsigned, so sometimes you'd
>>> need must_eq (X, 0) and sometimes must_eq (X, 0U).
>>
>> Is that because they are templates? Maybe providing a partial specialization
>> would help?
>
> I don't think it's templates specifically. We end up with something like:
>
> int f (unsigned int x, const int y)
> {
> return x != y;
> }
>
> int g (unsigned int x) { return f (x, 0); }
>
> which generates a warning too.
>
>> I'd be fine with must_eq_p and may_eq_0.
>
> OK, I'll switch to that if there are no objections.
Hum. But then we still warn for must_eq_p (x, 1), no?
So why does
int f (unsigned int x)
{
return x != 0;
}
not warn? Probably because of promotion of the arg.
Shouldn't we then simply never have a may/must_*_p (T1, T2)
with T1 and T2 being not compatible? That is, force promotion
rules on them with template magic?
Richard.
> Thanks,
> Richard
