Re: [PATCH] Implement __builtin_issignaling

[Jakub Jelinek <jakub@redhat.com>]

On Tue, Aug 16, 2022 at 11:41:06AM +0000, Richard Biener wrote:
> Can you also amend the extend.texi documentation?  I think the
> behavior will be special enough to worth mentioning it (I don't see
> any of -ffinite-math-only effect on isnan/isinf mentioned though).

Like this?

--- gcc/doc/extend.texi.jj	2022-08-16 13:23:04.227103773 +0200
+++ gcc/doc/extend.texi	2022-08-16 13:56:01.250769807 +0200
@@ -13557,6 +13557,8 @@ In the same fashion, GCC provides @code{
 @code{isinf_sign}, @code{isnormal} and @code{signbit} built-ins used with
 @code{__builtin_} prefixed.  The @code{isinf} and @code{isnan}
 built-in functions appear both with and without the @code{__builtin_} prefix.
+With @code{-ffinite-math-only} option the @code{isinf} and @code{isnan}
+built-in functions will always return 0.
 
 GCC provides built-in versions of the ISO C99 floating-point rounding and
 exceptions handling functions @code{fegetround}, @code{feclearexcept} and
@@ -14496,6 +14498,12 @@ Note while the parameter list is an
 ellipsis, this function only accepts exactly one floating-point
 argument.  GCC treats this parameter as type-generic, which means it
 does not do default promotion from float to double.
+This built-in function can work even without the non-default
+@code{-fsignaling-nans} option, although if a signaling NaN is computed,
+stored or passed as argument to some function other than this built-in
+in the current translation unit, it is safer to use @code{-fsignaling-nans}.
+With @code{-ffinite-math-only} option this built-in function will always
+return 0.
 @end deftypefn
 
 @deftypefn {Built-in Function} int __builtin_ffs (int x)

	Jakub