[cfe-dev] constexpr bit_cast status?

JF Bastien via cfe-dev cfe-dev at lists.llvm.org
Mon Oct 29 13:09:31 PDT 2018


Richard recently made __builtin_memcpy constexpr in some cases: https://reviews.llvm.org/rL338941 <https://reviews.llvm.org/rL338941>
His patch currently disallows all type-puns.

Erik is looking at implementing a bit_cast intrinsic for clang, at which point libc++ can use it. ADT won’t be able to do so until we migrate to C++20 (and toolchains support it).

We also want to reach out to the RedHat maintainers of libstdc++ to make sure we don’t adopt a weirdly different builtin.



> On Oct 29, 2018, at 12:56 PM, will wray via cfe-dev <cfe-dev at lists.llvm.org> wrote:
> 
> std::bit_cast was added to the C++ 20 draft this summer:
> http://eel.is/c++draft/bit.cast <http://eel.is/c++draft/bit.cast>
> In September JFB added a header with implementation (in llvm namespace):
> llvm/include/llvm/ADT/bit.h
> 
>   // This file implements the C++20 <bit> header.
>   ...
>   // - It isn't constexpr because that requires compiler support.
> 
> What compiler support is it waiting on? What's the status?
> 
> _______________________________________________
> cfe-dev mailing list
> cfe-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/cfe-dev/attachments/20181029/cb1eaa7f/attachment.html>


More information about the cfe-dev mailing list