revise std::vector uninit-mem hacks under libc++ #1912
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This pull request was exported from Phabricator. Differential Revision: D42459219 |
Summary: Pull Request resolved: facebook#1912 Closes: facebook#1867 The `std::__vector_base` class in libc++ is removed in libc++ 15 (llvm/llvm-project@b82da8b). So the two current implementations of the hacks - the implementation for libc++ 14 and the implementation for earlier libc++ - both fail. Even with libc++ 14, which retains `std::__vector_base`, Xcode 14 fails to compile the hacks: ``` In file included from folly/memory/test/UninitializedMemoryHacksODR.cpp:17: folly/memory/UninitializedMemoryHacks.h:461:1: error: conversion from 'std::__vector_base<char, std::allocator<char>>::pointer std::__vector_base<char, std::allocator<char>>::*' to 'char *std::vector<char>::*' is not allowed in a converted constant expression FOLLY_DECLARE_VECTOR_RESIZE_WITHOUT_INIT(char) ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ folly/memory/UninitializedMemoryHacks.h:327:7: note: expanded from macro 'FOLLY_DECLARE_VECTOR_RESIZE_WITHOUT_INIT' &std::vector<TYPE>::__end_, \ ^~~~~~~~~~~~~~~~~~~~~~~~~~ ... ``` Since libc++ is unlikely to change the internal layout of `std::vector` on a cadence which is too frequent for folly - any material change would be an ABI break -, we can use a layout struct rather than a template instance for the hacks and have it work for a range of versions of libc++ and Xcode. Reviewed By: simpkins, swolchok Differential Revision: D42459219 fbshipit-source-id: 379b86055601e5cc166a4d3364ab8d10be86f001
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This pull request was exported from Phabricator. Differential Revision: D42459219 |
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Summary: X-link: facebook/folly#1912 Closes: facebook/folly#1867 The `std::__vector_base` class in libc++ is removed in libc++ 15 (llvm/llvm-project@b82da8b). So the two current implementations of the hacks - the implementation for libc++ 14 and the implementation for earlier libc++ - both fail. Even with libc++ 14, which retains `std::__vector_base`, Xcode 14 fails to compile the hacks: ``` In file included from folly/memory/test/UninitializedMemoryHacksODR.cpp:17: folly/memory/UninitializedMemoryHacks.h:461:1: error: conversion from 'std::__vector_base<char, std::allocator<char>>::pointer std::__vector_base<char, std::allocator<char>>::*' to 'char *std::vector<char>::*' is not allowed in a converted constant expression FOLLY_DECLARE_VECTOR_RESIZE_WITHOUT_INIT(char) ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ folly/memory/UninitializedMemoryHacks.h:327:7: note: expanded from macro 'FOLLY_DECLARE_VECTOR_RESIZE_WITHOUT_INIT' &std::vector<TYPE>::__end_, \ ^~~~~~~~~~~~~~~~~~~~~~~~~~ ... ``` Since libc++ is unlikely to change the internal layout of `std::vector` on a cadence which is too frequent for folly - any material change would be an ABI break -, we can use a layout struct rather than a template instance for the hacks and have it work for a range of versions of libc++ and Xcode. Reviewed By: simpkins, swolchok Differential Revision: D42459219 fbshipit-source-id: e23ef383869681b5c81e4301114020b9089c7461
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Summary:
The
std::__vector_baseclass in libc++ is removed in libc++ 15 (llvm/llvm-project@b82da8b). So the two current implementations of the hacks - the implementation for libc++ 14 and the implementation for earlier libc++ - both fail.Even with libc++ 14, which retains
std::__vector_base, Xcode 14 fails to compile the hacks:Since libc++ is unlikely to change the internal layout of
std::vectoron a cadence which is too frequent for folly, we can use a layout struct rather than a template instance for the hacks and have it work for a range of versions of libc++ and Xcode.Closes: #1867.
Differential Revision: D42459219