Re: enabling float128 support in clang?
- Reply: Brooks Davis : "Re: enabling float128 support in clang?"
- In reply to: Brooks Davis : "enabling float128 support in clang?"
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Date: Tue, 04 Oct 2022 15:02:05 UTC
On Mon, 3 Oct 2022 at 19:43, Brooks Davis <email@example.com> wrote: > > 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: > I think this makes sense and may even motivate me to try and get the necessary library calls merged to compiler-rt (https://reviews.llvm.org/D98261). One thing to note is that your current patch will also enable float128 for AArch64 (and other targets), which I don't believe any other OS does. I think it makes sense to restrict it to just x86 to avoid executing code in the compiler that has not been well tested. I believe for all other supported architectures long double is the same as float128 so it probably doesn't make too much sense to enable it there anyway. Alex