Quuxplusone added inline comments.
================ Comment at: include/vector:318 + } +} + ---------------- Marshall writes: > Instead, we should be writing simple loops that the compiler can optimize > into a call to memcpy if it chooses. Having calls to memcpy in the code paths > makes it impossible to "constexp-ify" this code. Well, I have three thoughts on that. (A), "removing the calls to memcpy" sounds like you want to just call the *actual* move-constructor in a loop, and then later call the actual destructor in a loop. Which is to say, you don't want libc++ to have a codepath for this speed optimization at all. That's just leaving a ton of performance on the table, and I strongly disagree with that idea. (B), regardless, couldn't you achieve that goal simply by taking this patch almost exactly as it is except removing the overloads that take `true_type`? If you want constexpr-friendliness badly enough that you're willing to call the move-constructor and destructor even of trivially copyable types, then you can still use this framework; you just have to remove the overloads that call memcpy. That wouldn't be a major refactoring. (C), surely if you want the best of both worlds, you should be pushing someone to invent a constexpr memcpy and/or a way to [detect constexpr-context at compile time](https://quuxplusone.github.io/blog/2018/06/12/perennial-impossibilities/#detect-the-constexprness-of-the-current-context)? I don't think it makes sense to pessimize existing (non-constexpr) users in C++03-through-C++17 just because someone hypothetically might in C++2a-or-later want to mutate a std::vector in a constexpr context. Repository: rCXX libc++ https://reviews.llvm.org/D49317 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
