Re: Prevent all uses of DFP when unsupported (PR c/91985)

[Joseph Myers <joseph@codesourcery.com>]

On Wed, 27 Nov 2019, Rainer Orth wrote:

> Hi Jonathan,
> 
> > On 26/11/19 00:57 +0000, Joseph Myers wrote:
> >>On Mon, 25 Nov 2019, Rainer Orth wrote:
> >>
> >>> and a few more, all DFP related.  They used to be emitted by g++ for
> >>> __fundamental_type_info in libsupc++/fundamental_type_info.cc and lived
> >>> in the CXXABI_1.3.4 version.  However, since Solaris *does* lack DFP
> >>> support, that's no longer the case.  I'm uncertain how best to deal with
> >>> this, however.
> >>
> >>As I understand it, _GLIBCXX_USE_DECIMAL_FLOAT should already have been
> >>undefined for this target, and so std::decimal::decimal32 etc. should not
> >>have been usable (both the header not working without that define, and the
> >>mode attributes in the header being rejected by the front end when DFP is
> >>unsupported).  I.e. such defines in libsupc++ would never have been usable
> >>on this target, so I think they are something it should be safe to remove
> >>from the ABI baseline.
> >
> > If it's actually impossible that any real program could have depended
> > on those symbols, then I agree.
> 
> this is exactly what I've got no way of telling, that's why I was asking
> for guidance.  Just removing the DFP symbols from the baselines works,
> of course.

I don't think any real program could have used those symbols; it would 
have required using __typeof (__builtin_fabsd32 (0)) or similar to access 
types that weren't normally available for those targets (and by accessing 
the types using builtins like that, you're getting a completely undefined 
function-calling ABI for them anyway).

-- 
Joseph S. Myers
joseph@codesourcery.com