pengfei planned changes to this revision. pengfei added a comment. In D136919#3906159 <https://reviews.llvm.org/D136919#3906159>, @rjmccall wrote:
> In D136919#3906133 <https://reviews.llvm.org/D136919#3906133>, @rjmccall > wrote: > >> We talked about this on the Itanium list, and as currently specified, it is >> absolutely not correct for `__bf16` to have the same mangling as >> `std::bfloat16_t`, because `__bf16` does not have the correct semantics for >> `std::bfloat16_t` and must be a distinct type. If GCC changed `__bf16` to >> use the new mangling without also updating the semantics, it is a bug. >> >> That discussion was here: https://github.com/itanium-cxx-abi/cxx-abi/pull/147 >> >> If we want to implement `std::bfloat16_t` in Clang, we need to make it a >> normal arithmetic type, and in practice it needs to guarantee >> excess-precision arithmetic, as I discussed on that thread. Coincidentally, >> we did recently implement excess-precision arithmetic in Clang for >> `_Float16`. > > Jakub Jelinek has clarified that GCC did indeed change the semantics of > `__bf16` on i386 and x86_64 to be a proper extended floating point type. > > We could change the mangling to match GCC, but I think it would be > inappropriate to do that without also matching the semantics change. Since > the mangling change is trivial to land, I think the semantics change should > happen first. Thanks @rjmccall for pointing to the Itanium list. I'm clear about what to do now. Yes, fully agreed, we should match the semantics at the same time. In D136919#3905891 <https://reviews.llvm.org/D136919#3905891>, @tra wrote: > NVPTX has no current uses of this, so if the mangling needs to change, now > would be the good time. Thanks @tra. Per to @rjmccall's information. The mangling should be aligned with its semantics. It's fine to use `u6__bf16` if a target doesn't want to support arithmetic operations. And thanks @RKSimon, @tschuett and @aaron.ballman for your kind inputs! Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D136919/new/ https://reviews.llvm.org/D136919 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
