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

[Joseph Myers <joseph@codesourcery.com>]

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.)

-- 
Joseph S. Myers
joseph@codesourcery.com