Re: [PATCH, version 3], Add support for _Float<N> and _Float<N>X sqrt, fma, fmin, fmax built-in functions

[Michael Meissner <meissner@linux.vnet.ibm.com>]

On Tue, Oct 24, 2017 at 11:08:15PM +0000, Joseph Myers wrote:
> On Tue, 24 Oct 2017, Michael Meissner wrote:
> 
> > This patch adds a new switch (-fimplicit-math-floatn) that when enabled, it
> > will add implicit declarations for copysign, fabs, fma, fmax, fmin, nan, and
> > sqrt _Float<N> and _Float<N>X variants.  Like the previous patch, it adds fma,
> > fmax, fmin, and sqrt builtins to the machine independent built-in support, and
> > removed the PowerPC specific __builtin_{sqrt,fma}f128 functions.
> 
> I don't see why this new option is needed.  My expectation would be to use 
> DEF_EXT_LIB_BUILTIN, as discussed before (i.e. declare the non-__builtin_* 
> variants by default, but not if flag_iso).
> 
> That they should be declared by default is clear, in line with the normal 
> principle of enabling GNU extensions by default.  That they should not be 
> declared with existing -std=c11 etc. options is also clear.  Sometimes 
> there may be a use for an option to enable particular features of a TS 
> (e.g. -fpermitted-flt-eval-methods=ts-18661-3, 
> -fno-fp-int-builtin-inexact), I just don't see the requirement for it in 
> this particular case.  Of course, if in future TS 18661-3 gets added to 
> C2x, such built-in functions could be enabled for -std=c2x, subject to any 
> questions of the circumstances under which their names are reserved if the 
> relevant feature test macros are not defined.
> 
> (There are various issues with the documentation of the new option as 
> well.)

Ok, I misunderstood your previous comment.  I thought you were saying not to
export the normal functions (not huge_val, nan, inf) by default on the off
chance that somebody could declare a sqrtf128 function that did something
else.

I would prefer not to have the switch, but I wanted some way for fmaf128 and
sqrtf128 to automatically use the instructions.  I'll switch it to
DEF_EXT_LIB_BUILTIN, and delete the option.

-- 
Michael Meissner, IBM
IBM, M/S 2506R, 550 King Street, Littleton, MA 01460-6245, USA
email: meissner@linux.vnet.ibm.com, phone: +1 (978) 899-4797