ldionne added inline comments.
================ Comment at: clang/include/clang/Basic/TokenKinds.def:528 +TYPE_TRAIT_1(__is_nothrow_copy_constructible, IsNothrowCopyConstructible, KEYCXX) +TYPE_TRAIT_1(__is_trivially_copy_constructible, IsTriviallyCopyConstructible, KEYCXX) TYPE_TRAIT_2(__reference_binds_to_temporary, ReferenceBindsToTemporary, KEYCXX) ---------------- cjdb wrote: > erichkeane wrote: > > royjacobson wrote: > > > erichkeane wrote: > > > > cjdb wrote: > > > > > erichkeane wrote: > > > > > > So this one is a whole 'thing'. The Clang definition of 'trivially > > > > > > copy constructible' is a few DRs behind. We should probably > > > > > > discuss this with libcxx to make sure use of this wouldn't be > > > > > > broken. > > > > > I'd prefer to get those DRs in before finalising D135238 and > > > > > subsequent ones. Do you know the DR numbers I should be looking at, > > > > > or should I just poke npaperbot? > > > > Not off the top of my head, Aaron and I both poked at it at one point > > > > trying to get trivially constructible right at one point, but I think > > > > we both gave up due to the ABI/versioning concerns. > > > Maybe DR1734? Although it's about the trivially copyable trait, not > > > trivially copy constructible. > > > > > Yeah, I think that was the DR, that number sounds familiar. > The `__is_trivially_*` traits were, in part, what inspired the Great Split of > D116208. I could remove them for now and revisit once I rip my hair out over > these DRs, if that would substantially improve the chances of these commits > landing (other commentary notwithstanding). I am not sure I see a problem with the "triviality" part of this -- we already use a compiler builtin for `std::is_trivially_constructible`, so I would expect either this patch is fine, or we already have a latent bug in libc++. I think I can echo @philnik's comment about this not necessarily providing the biggest benefit since our implementation of `std::is_trivially_copy_constructible` is a fairly trivial wrapper on top of `__is_trivially_constructible`, but I wouldn't object to the patch on that basis. I think it would probably be possible to instead provide a set of basis builtin operations that we can then build all of the library type traits on top of -- that would provide the highest bang-for-our-buck ratio. At the same time, there's something kind of enticing in the consistency of defining every single type trait as a builtin, without exception. If that's the end goal, I think that would also be neat and we'd likely regroup all of our type traits under a single header, since each of them would literally be a one liner. There's also the question of whether GCC provides these builtins -- if they don't and if they don't have plans to, then we'd actually need to add complexity in libc++ to support both, which we would be unlikely to do given that there's probably not a huge compile-time performance benefit. TLDR, I think the two questions that can help gauge how much interest there will be from libc++ to use this are: 1. Is the plan to provide *all* the type traits as builtins? 2. Will GCC implement them? That being said, libc++ might not be the only potential user of these builtins, so I wouldn't necessarily make it a hard requirement to satisfy us. Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D135238/new/ https://reviews.llvm.org/D135238 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
