Traits.h: Use std::is_trivially_relocatable if P1144 is available #2216
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Summary: Well, llvm/llvm-project#84621 isn't going anywhere in Clang, therefore facebook/folly#2159 will presumably never be mergeable (in the foreseeable future, anyway). So here's an alternative approach, for your consideration: If [P1144's feature-test macro](https://open-std.org/jtc1/sc22/wg21/docs/papers/2024/p1144r10.html#wording) is set, then use `std::is_trivially_relocatable<T>` in place of `std::is_trivially_copyable<T>`. This will produce improved codegen for e.g. `fbvector<std::vector<int>>::erase`, when compiled on a compiler supporting P1144 semantics. https://godbolt.org/z/s6sa313h3 Compare https://github.com/charles-salvia/std_error/blob/3abc272/all_in_one.hpp#L180-L196 X-link: facebook/folly#2216 Reviewed By: Gownta Differential Revision: D58147899 Pulled By: Orvid fbshipit-source-id: 671ed21eeb6080f583e6966e776d243c99c9c17f
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Oct 12, 2024
Well, this is awkward. facebook#2216 added this `#if` check, but with the wrong macro: `__cpp_lib_is_trivially_relocatable` should have been `__cpp_lib_trivially_relocatable`.
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Well, llvm/llvm-project#84621 isn't going anywhere in Clang, therefore #2159 will presumably never be mergeable (in the foreseeable future, anyway).
So here's an alternative approach, for your consideration: If P1144's feature-test macro is set, then use
std::is_trivially_relocatable<T>in place ofstd::is_trivially_copyable<T>.This will produce improved codegen for e.g.
fbvector<std::vector<int>>::erase, when compiled on a compiler supporting P1144 semantics. https://godbolt.org/z/s6sa313h3Compare https://github.com/charles-salvia/std_error/blob/3abc272/all_in_one.hpp#L180-L196