[PATCH] D93377: [Clang] Add __ibm128 type to represent ppc_fp128

[Jonathan Wakely via Phabricator via cfe-commits]

jwakely added inline comments.


================
Comment at: clang/lib/Parse/ParseExprCXX.cpp:2245
+  case tok::kw___ibm128:
+    DS.SetTypeSpecType(DeclSpec::TST_ibm128, Loc, PrevSpec, DiagID, Policy);
+    break;
----------------
hubert.reinterpretcast wrote:
> qiucf wrote:
> > hubert.reinterpretcast wrote:
> > > qiucf wrote:
> > > > hubert.reinterpretcast wrote:
> > > > > Not sure what the best method is to implement this, but `long double` and `__ibm128` are the same type for GCC when `-mabi=ibmlongdouble` is in effect.
> > > > Seems clang is also different from GCC under `-mabi=ieeelongdouble`? I saw `__float128` and `long double` are the same for GCC but not for clang.
> > > Have you checked whether the new libstdc++ for which this support is being added needs the GCC behaviour to work properly?
> > > 
> > > The GCC behaviour allows the following to be compiled without introducing novel overload resolution tiebreakers:
> > > ```
> > > void f(__float128);
> > > void f(__ibm128);
> > > void f(int);
> > > 
> > > long double ld;
> > > 
> > > int main() { f(ld); }
> > > ```
> > As I saw both GCC and clang have error for ambiguous `operator<<` for:
> > 
> > ```
> >     std::cout << "long double:\n";
> >     std::cout << std::numeric_limits<long double>::max() << std::endl;
> >     std::cout << std::numeric_limits<long double>::min() << std::endl;
> > 
> >     std::cout << "__float128:\n";
> >     std::cout << std::numeric_limits<__float128>::max() << std::endl;
> >     std::cout << std::numeric_limits<__float128>::min() << std::endl;
> > 
> >     std::cout << "__ibm128:\n";
> >     std::cout << std::numeric_limits<__ibm128>::max() << std::endl;
> >     std::cout << std::numeric_limits<__ibm128>::min() << std::endl;
> > ```
> @jwakely, are the overload resolution errors expected? @qiucf, are you sure you have a sufficiently new libstdc++?
> @jwakely, are the overload resolution errors expected? 

Yes. Iostreams support `long double` but not `__float128`, unless that happens to be the same type as `long double` (due to a `-mabi=ieeelongdouble` option).


Repository:
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  https://reviews.llvm.org/D93377/new/

https://reviews.llvm.org/D93377