IEEE Interchange floating point and extended floating point for C++

[Joseph Myers]

On Fri, 12 Mar 2021, Jonathan Wakely wrote:

> On Fri, 12 Mar 2021 at 12:26, Sjoerd Meijer via Gcc <gcc@gcc.gnu.org> wrote:
> > So here's finally my concrete question: what do we think about making _Float16 available in C++ mode?
> 
> I think GCC should do it.

What about types with the same format as an existing type (but which are 
nevertheless distinct types in C), such as _Float64 (typically same format 
as double) or _Float32 (typically same format as float, but not promoted 
when passed in variable arguments)?

When those types escape into C++ code, they cause an ICE in name mangling; 
see bug 85518.

(Incidental note on _Float16: various architectures have some hardware 
support for that format that don't have support for the type in GCC, 
although they may well have GCC built-in functions corresponding to the 
hardware support; also library support in glibc hasn't yet been 
implemented.  In the case of x86_64 (F16C hardware conversion instructions 
from Ivy Bridge onwards), the psABI document defines an ABI for _Float16 
and the corresponding complex type; in general such an ABI should be 
agreed with interested parties when adding _Float16 support for an 
architecture.)

-- 
Joseph S. Myers
joseph@codesourcery.com