RE: enabling float128 support in clang?

Brooks Davis <brooks_at_freebsd.org> wrote on
Date: Mon, 03 Oct 2022 18:43:10 UTC :

> TL;DR: Is there a reason not to enable float128 support in clang for
> x86?
> 
> Due to a build breakage with the flang runtime, I recently noticed that 
> unlike most other OSes we don't support float128 in clang.  It's enable
> in modern GCC and other OSes have it enable in clang:
>  - Hakiu 2018: https://reviews.llvm.org/D54901
>  - Solaris 2018: https://reviews.llvm.org/D41240
>  - WASM 2019: https://reviews.llvm.org/D57154
>  - Dragonfly 2021: https://reviews.llvm.org/D111760
>  - OpenBSD (history hard to find...)
> 
> Is there a known reason not to enable this?
> 
> Patch to enable below (I'm a bit skeptical of the __FLOAT128__ part as
> GCC doesn't define it...)
> 
> -- Brooks
> 
> diff --git a/clang/lib/Basic/Targets/OSTargets.h b/clang/lib/Basic/Targets/OSTargets.h
> index c75f7d9fbafe..ea95f40e81a0 100644
> --- a/clang/lib/Basic/Targets/OSTargets.h
> +++ b/clang/lib/Basic/Targets/OSTargets.h
> @@ -232,6 +232,9 @@ protected:
>      // setting this to 1 is conforming even if all the basic source
>      // character literals have the same encoding as char and wchar_t.
>      Builder.defineMacro("__STDC_MB_MIGHT_NEQ_WC__", "1");
> +
> +    if (this->HasFloat128)
> +      Builder.defineMacro("__FLOAT128__");
>    }
>  
>  public:
> @@ -241,6 +244,7 @@ public:
>      default:
>      case llvm::Triple::x86:
>      case llvm::Triple::x86_64:
> +      this->HasFloat128 = true;
>        this->MCountName = ".mcount";
>        break;
>      case llvm::Triple::mips:
> 
> 


See:

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=238129

for some past exchanges on this. From comment #3:

QUOTE of Dimitry Andric:
As mentioned on the mailing list, it is not a matter of just "enabling" float128. Somebody has to step up and write a BSD licensed quadmath.h, to start with.
END QUOTE

===
Mark Millard
marklmi at yahoo.com