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From: Jonathan Wakely <redi@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org, libstdc++-cvs@gcc.gnu.org Subject: [gcc r13-2175] libstdc++: Optimize operator+(string/char*, char*/string) equally Date: Wed, 24 Aug 2022 14:23:23 +0000 (GMT) [thread overview] Message-ID: <20220824142323.8E9ED385C32C@sourceware.org> (raw) https://gcc.gnu.org/g:0b7c9254998b3fb2c39f6b86b5b196f415530205 commit r13-2175-g0b7c9254998b3fb2c39f6b86b5b196f415530205 Author: Will Hawkins <whh8b@obs.cr> Date: Wed Aug 24 02:16:48 2022 -0400 libstdc++: Optimize operator+(string/char*, char*/string) equally Until now operator+(char*, const string&) and operator+(const string&, char*) had different performance characteristics. The former required a single memory allocation and the latter required two. This patch makes the performance equal. libstdc++-v3/ChangeLog: * include/bits/basic_string.h (operator+(const string&, const char*)): Remove naive implementation. * include/bits/basic_string.tcc (operator+(const string&, const char*)): Add single-allocation implementation. Signed-off-by: Will Hawkins <whh8b@obs.cr> Diff: --- libstdc++-v3/include/bits/basic_string.h | 9 ++------- libstdc++-v3/include/bits/basic_string.tcc | 21 +++++++++++++++++++++ 2 files changed, 23 insertions(+), 7 deletions(-) diff --git a/libstdc++-v3/include/bits/basic_string.h b/libstdc++-v3/include/bits/basic_string.h index b04fba95678..fa6738925bb 100644 --- a/libstdc++-v3/include/bits/basic_string.h +++ b/libstdc++-v3/include/bits/basic_string.h @@ -3521,14 +3521,9 @@ _GLIBCXX_END_NAMESPACE_CXX11 */ template<typename _CharT, typename _Traits, typename _Alloc> _GLIBCXX20_CONSTEXPR - inline basic_string<_CharT, _Traits, _Alloc> + basic_string<_CharT, _Traits, _Alloc> operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs, - const _CharT* __rhs) - { - basic_string<_CharT, _Traits, _Alloc> __str(__lhs); - __str.append(__rhs); - return __str; - } + const _CharT* __rhs); /** * @brief Concatenate string and character. diff --git a/libstdc++-v3/include/bits/basic_string.tcc b/libstdc++-v3/include/bits/basic_string.tcc index 4563c61429a..95ba8e503e9 100644 --- a/libstdc++-v3/include/bits/basic_string.tcc +++ b/libstdc++-v3/include/bits/basic_string.tcc @@ -640,6 +640,27 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION return __str; } + template<typename _CharT, typename _Traits, typename _Alloc> + _GLIBCXX20_CONSTEXPR + basic_string<_CharT, _Traits, _Alloc> + operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs, + const _CharT* __rhs) + { + __glibcxx_requires_string(__rhs); + typedef basic_string<_CharT, _Traits, _Alloc> __string_type; + typedef typename __string_type::size_type __size_type; + typedef typename __gnu_cxx::__alloc_traits<_Alloc>::template + rebind<_CharT>::other _Char_alloc_type; + typedef __gnu_cxx::__alloc_traits<_Char_alloc_type> _Alloc_traits; + const __size_type __len = _Traits::length(__rhs); + __string_type __str(_Alloc_traits::_S_select_on_copy( + __lhs.get_allocator())); + __str.reserve(__len + __lhs.size()); + __str.append(__lhs); + __str.append(__rhs, __len); + return __str; + } + template<typename _CharT, typename _Traits, typename _Alloc> _GLIBCXX_STRING_CONSTEXPR typename basic_string<_CharT, _Traits, _Alloc>::size_type
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