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

[Hubert Tong via Phabricator via cfe-commits]

hubert.reinterpretcast added a comment.

In D109751#3136543 <https://reviews.llvm.org/D109751#3136543>, @qiucf wrote:

> Because the piece of code will be expanded to:
>
>   long double _Complex x;
>   
>   if ((__builtin_types_compatible_p(__typeof(creall(x)), _Float128)
>            ? __isinff128(creall(x))
>            : __builtin_isinf_sign(creall(x))) ||
>       (__builtin_types_compatible_p(__typeof(cimagl(x)), _Float128)
>            ? __isinff128(cimagl(x))
>            : __builtin_isinf_sign(cimagl(x))))
>     return inf;
>
> which requires 'long double' (the same semantics to `__ibm128` by default) and '_Float128' are compatible.

Noting that the way the types are implemented in Clang, the conversion isn't the first problem with the above code. The types with the same representation are not considered "compatible" by Clang:

  extern char x[__builtin_types_compatible_p(long double, __ibm128) ? 1 : -1]; // errors
  extern char x[__builtin_types_compatible_p(long double, __ieee128) ? 1 : -1]; // errors too

Compiler Explorer link: https://godbolt.org/z/fP3MfdexM


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D109751/new/

https://reviews.llvm.org/D109751