Richard Biener <richard.guent...@gmail.com> writes:
> On Tue, Oct 24, 2017 at 2:48 PM, Richard Sandiford
> <richard.sandif...@linaro.org> wrote:
>> Richard Biener <richard.guent...@gmail.com> writes:
>>> On Tue, Oct 24, 2017 at 1:23 PM, Richard Sandiford
>>> <richard.sandif...@linaro.org> wrote:
>>>> Eric Botcazou <ebotca...@adacore.com> 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.
Thanks,
Richard
