On 12/3/19 5:50 PM, Joseph Myers wrote:
> On Tue, 3 Dec 2019, Stefan Liebler wrote:
> 
>> On 12/2/19 10:00 PM, Joseph Myers wrote:
>>> On Mon, 2 Dec 2019, Stefan Liebler wrote:
>>>
>>>> This patch is using the corresponding GCC builtin for copysignf, copysign,
>>>> copysignl and copysignf128 if the USE_FUNCTION_BUILTIN macros are defined
>>>> to one
>>>> in math-use-builtins.h.
>>>
>>> I believe this is always safe for these implementations (the only case
>>> where GCC might not expand copysign functions inline is copysignl for IBM
>>> long double, in the soft-float case).
>>>
>> Thus you mean we can do the following preset in
>> sysdeps/generic/math-use-builtins.h?
>> #define USE_COPYSIGN_BUILTIN 1
>> #define USE_COPYSIGNF_BUILTIN 1
>> #define USE_COPYSIGNL_BUILTIN 0
>> #define USE_COPYSIGNF128_BUILTIN 0
>>
>> Or even also set USE_COPYSIGNL_BUILTIN to one as IBM long double has its own
>> implementation in ./sysdeps/ieee754/ldbl-128ibm/s_copysignl.c.
> 
> I think they can all be 1, given that IBM long double has its own
> implementation.  Except that you shouldn't need the indirection through
> these macros at all.  Just use __builtin_copysign etc. directly in the
> implementations (other than IBM long double), unconditionally, the same
> way that sysdeps/ieee754/dbl-64/s_fabs.c uses __builtin_fabs directly
> without such macros being needed.
> 

Okay. I've set them to 1 and also used build-many-glibcs.py and had a 
look into the s_copysign*.os files. There is no function call to 
copysign* itself.

If one architecture encounters issues with those builtins, an 
architecture specific math-use-builtins.sh file can set the macros to zero.

Bye,
Stefan