[PATCH] D109751: [Clang] Support conversion between PPC double-double and IEEE float128

Hubert Tong via Phabricator via cfe-commits cfe-commits at lists.llvm.org
Fri Dec 3 20:49:05 PST 2021

hubert.reinterpretcast added inline comments.

Comment at: clang/test/Sema/float128-ld-incompatibility.cpp:13
+long double ld{qf()}; // expected-error {{non-constant-expression cannot be narrowed from type '__float128' to 'long double' in initializer list}} expected-note {{insert an explicit cast to silence this issue}}
+__float128 q{ldf()}; // expected-no-error
hubert.reinterpretcast wrote:
> Should also test `__ibm128` cases.
The C++ committee has advised that this implicit conversion should be considered ill-formed (see other comment).

Note that the //allowed// implicit conversion from `__ibm128` to `long double` (and vice versa) is still a conversion, which means that overload resolution is still a problem:
void f(__ibm128);
void f(int);
void g(long double d) { return f(d); } // okay with GCC but not Clang; https://godbolt.org/z/fonsEbbY1

Comment at: clang/test/Sema/float128-ld-incompatibility.cpp:36-37
   q / ld; // expected-error {{invalid operands to binary expression ('__float128' and 'long double')}}
-  ld = q; // expected-error {{assigning to 'long double' from incompatible type '__float128'}}
-  q = ld; // expected-error {{assigning to '__float128' from incompatible type 'long double'}}
+  ld = q; // expected-no-error {{assigning to 'long double' from incompatible type '__float128'}}
+  q = ld; // expected-no-error {{assigning to '__float128' from incompatible type 'long double'}}
   q + b ? q : ld; // expected-error {{incompatible operand types ('__float128' and 'long double')}}
The C++ committee has advised that these are not okay as implicit conversions:

Additional lines testing `static_cast` would be appropriate.

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