[PATCH] D15120: Add support for __float128 type to be used by targets that support it

[John McCall via cfe-commits]

rjmccall added a comment.

In http://reviews.llvm.org/D15120#337975, @hubert.reinterpretcast wrote:

> In http://reviews.llvm.org/D15120#337654, @rjmccall wrote:
>
> > In http://reviews.llvm.org/D15120#337552, @hubert.reinterpretcast wrote:
> >
> > > It remains that the present standardization effort (as `_Float128`) does not imbue the "interchange" type with inherently higher rank than `long double`. In a parallel to the treatment of extended integer types, the "standard" type has higher rank when the set of values are equivalent between the two. This is consistent with the GCC implementation (online compiler: http://melpon.org/wandbox/permlink/tM3PyGWC5WTWIdKP).
> >
> >
> > Do we have anyone involved in this standardization effort?  It seems like a really poor idea to having type ranking be target-dependent.
>
>
> I can reach out to someone who is involved.


Thank you.  If they have a strong motivation here, that's fine, but this feels like it would block and complicate future standardization efforts, as well as impair portability.

> > > As I have mentioned before, for `__float128` and `-mlong-double-128` on x86-64, GCC ends up with an undesirable situation of treating the types as distinct, but mangling them the same.

> 

> > 

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> > 

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> > Does Clang currently support that option?

> 

> 

> It appears that Clang does not currently support that option


Ok.  It would be better if we can avoid that, I think.

> ; however, there are platforms where `long double` is already IEEE quad, e.g., s390x-ibm-linux-gnu (where I have not found a GCC providing `__float128`).


Sure, that's a legitimate platform ABI choice.

> It appears that we can defer the issue as long as we do not provide `__float128` when `long double` is already IEEE quad.


Sounds good.


Repository:
  rL LLVM

http://reviews.llvm.org/D15120