[Bug c/111058] __builtin_nans (and its friends for other floating-point types) compiles to an external call to __builtin_nans for unsupported tag

[xry111 at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111058

--- Comment #6 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
(In reply to jos...@codesourcery.com from comment #5)
> We should absolutely *not* generate calls to a non-existent function 
> "nans" based on a long-obsolescent standard proposal.  The modern way to 
> generate a signaling NaN with given payload, as specified in C23, is to 
> generate a signaling NaN with one of the *_SNAN macros (FLT128_SNAN in 
> this case) in <float.h>, then use the relevant setpayload function 
> (setpayloadf128 in this case) to set its payload.
> 
> I don't think there is any bug here at all.

But generating an external call to __builtin_* just does not make sense at all.

If the payload won't be supported, we should just emit a diagnostic and reject
the code.