Jonathan Wakely 2b83bc6097 libstdc++: Optimize ref-count updates in COW std::string ... Most ref-count updates in the COW string are done via the functions in <ext/atomicity.h>, which will use non-atomic ops when the program is known to be single-threaded. The _M_is_leaked() and _M_is_shared() functions use __atomic_load_n directly, because <ext/atomicity.h> doesn't provide a load operation. Those functions can check the __is_single_threaded() predicate to avoid using __atomic_load_n when not needed. The move constructor for the fully-dynamic-string increments the ref-count by either 2 or 1, for leaked or non-leaked strings respectively. That can be changed to use a non-atomic store of 1 for all non-shared strings. It can be non-atomic because even if the program is multi-threaded, conflicting access to the rvalue object while it's being moved from would be data race anyway. It can store 1 directly for all non-shared strings because it doesn't matter whether the initial refcount was -1 or 0, it should be 1 after the move constructor creates a second owner. libstdc++-v3/ChangeLog: * include/bits/cow_string.h (basic_string::_M_is_leaked): Use non-atomic load when __is_single_threaded() is true. (basic_string::_M_is_shared): Likewise. (basic_string::(basic_string&&)) [_GLIBCXX_FULLY_DYNAMIC_STRING]: Use non-atomic store when rvalue is not shared.		2021-12-01 15:00:33 +00:00
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backward
bits	libstdc++: Optimize ref-count updates in COW std::string	2021-12-01 15:00:33 +00:00
c
c_compatibility
c_global	libstdc++: Enable type traits for wchar_t unconditionally [PR98725]	2021-10-09 00:57:49 +01:00
c_std
debug	libstdc++: [_GLIBCXX_DEBUG] Reduce performance impact on std::erase_if	2021-11-20 16:11:22 +01:00
decimal
experimental	libstdc++: [_GLIBCXX_DEBUG] Reduce performance impact on std::erase_if	2021-11-20 16:11:22 +01:00
ext	libstdc++: Fix circular dependency for bitmap_allocator [PR103381]	2021-11-23 12:30:57 +00:00
parallel
precompiled	libstdc++: Implement std::spanstream for C++23	2021-11-13 11:45:31 +00:00
pstl
std	libstdc++: Add [[nodiscard]] to std::byteswap	2021-11-30 13:30:27 +01:00
tr1	libstdc++: Enable type traits for wchar_t unconditionally [PR98725]	2021-10-09 00:57:49 +01:00
tr2
Makefile.am	libstdc++: Implement std::spanstream for C++23	2021-11-13 11:45:31 +00:00
Makefile.in	libstdc++: Implement std::spanstream for C++23	2021-11-13 11:45:31 +00:00