Re: [Qemu-devel] [PATCH] softfloat: rename make_float[x80|128]_init to const_float[x80|128]

[Laurent Vivier]

Le 19/09/2017 à 20:45, Laszlo Ersek a écrit :
> On 09/19/17 19:39, Eric Blake wrote:
>> On 09/19/2017 11:30 AM, Richard Henderson wrote:
>>> On 09/18/2017 05:46 AM, Laurent Vivier wrote:
>>>> Redefine make_floatx80() and make_float128() as make_float16(),
>>>> make_float32() and make_float64() using a variable and not only
>>>> a cast.
>>
>>>> -#define make_floatx80(exp, mant) ((floatx80) { mant, exp })
>>>> -#define make_floatx80_init(exp, mant) { .low = mant, .high = exp }
>>>> +#define make_floatx80(exp, mant) __extension__ \
>>>> +    ({ floatx80 f80_val = { .low = mant, .high = exp }; f80_val; })
>>>> +#define const_floatx80(exp, mant) { .low = mant, .high = exp }
>>
>>>
>>> I don't like this part -- (type){ init } is a standard C99 compound literal.
>>> There's no point using a gcc extension instead.
>>
>> The C99 compound literal is not a const initializer in all situations,
>> though :(  Here's another thread where we had a similar discussion, but
>> there, the solution was to just make the macro behave as an initializer
>> (which is C99 compliant, but loses some type safety) instead of relying
>> on a gcc extension:
>>
>> https://lists.gnu.org/archive/html/qemu-devel/2017-08/msg06566.html
>>
>> I suspect you're running into the same issues that Laszlo already helped
>> us understand regarding QLit.
>>
> 
> Thanks for the CC! I don't have much context, but the patch looks quite
> isolated.
> 
> I think I agree with Richard here -- I don't think there's any reason to
> change the replacement text of make_floatx80.
> 
> The patch names make_float64() as an earlier example (already using
> __extension__), but I don't understand why make_float64() was written
> that way. ... It seems to go back to ancient commit f090c9d4ad58 ("Add
> strict checking mode for softfp code.", 2007-11-18). Was C99 support
> (esp. compound literals) spotty in gcc back then?
> 
> Not having much background, I'd suggest the opposite change -- replace
> the statement-expression in make_float64() with a compound literal.


Okay, I'll do this way.

Thank you all for your comments.

Laurent