[PATCH 13/13] Use GCC builtins for copysign functions if desired.

[Joseph Myers]

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.

-- 
Joseph S. Myers
joseph@codesourcery.com