On 1/14/16 06:54, Al Viro wrote:
> On Thu, Jan 14, 2016 at 06:39:53AM +0800, Chen Gang wrote:
>
>>> As for the inlines... frankly, if gcc generates a different code from having
>>> replaced int with bool in those, it's time to do something very nasty to
>>> gcc developers.
>>>
>>
>> Could you provide the related proof?
>
> static inline _Bool f(.....)
> {
> return <int expression>;
> }
>
> ...
> if (f(.....))
>
For me, your case above isn't suitable for using bool. Please check this
patch, there is no any cases like you said above.
- For d_unhashed() which return hlist_bl_unhashed(), it seems like your
case, but in fact hlist_bl_unhashed() also need return bool (which I
shall send another patch for, next).
- And all the other changes of this patch are all for real, pure bool
functions.
Thanks.
> should generate the code identical to
> if ((_Bool)<int expression>)
> which, in turn, should generate the code identical to
> if (<int expression> != 0)
> and
> if (<int expression>)
>
> Neither explicit nor implicit conversion to _Bool (the former by the explicit
> cast, the latter - by declaring f() to return _Bool) matters at all when the
> damn thing is inlined in a condition context. Conversion to _Bool is
> equivalent to comparison with 0, and so is the use in condition of if() and
> friends.
>
> For something not inlined you might get different code generated due to a
> difference in calling sequences of _Bool(...) and int(...); for inlined
> case having one of those variants produce a better code means that compiler
> has managed to miss some trivial optimization in all other variants.
>
> And I'm yet to see any proof that gcc *does* fuck up in that fashion. It
> might - dumb bugs happen to everyone, but I would not assume that they'd
> managed to do something that bogys without experimental evidence.
>
For your cases, what you said sounds OK to me (although I am not quite
sure what you said above whether precise or not).
Thanks.
--
Chen Gang (陈刚)
Open, share, and attitude like air, water, and life which God blessed
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