[Bug target/84829] -mieee-fp causes to link with -lieee but that is no longer available

[carlos at redhat dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84829

--- Comment #8 from Carlos O'Donell <carlos at redhat dot com> ---
(In reply to Florian Weimer from comment #6)
> (In reply to Jakub Jelinek from comment #5)
> > -mieee-fp does affect code generation on x86 and m68k, but I don't see how
> > it is related to any changes in glibc.
> > And besides code generation changes it affects whether -lieee is linked in
> > or not.
> 
> It matters from the users' point of view.  I think it's better to give them
> a build error when they use unsupported functionality, rather than giving
> the wrong results at run time.  The overloaded nature of -mieee-fp makes
> this difficult to achieve, though.

I agree.

My own opinion is that I would rather see a link-time failure for user
applications that use any interfaces that are no longer supported for building
new programs.

Therefore it is that -mieee-fp is no longer supported with glibc 2.27, you
cannot use it, and it will not work. You must XFAIL any such tests if you are
using a glibc with the obsoleted matherr, _LIB_VERSION, and libieee.a
functionality.

Opinions vary though, since -mieee-fp is intended to require IEEE semantics,
and that is now the default in glibc, we could just keep silently supporting
-mieee-fp as the default.

I think that Joseph will need to comment on thoughts about the behaviour of
using deprecated interfaces.