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From: Jonathan Wakely <redi@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org, libstdc++-cvs@gcc.gnu.org Subject: [gcc r13-3814] libstdc++: Refactor implementation of operator+ for std::string Date: Tue, 8 Nov 2022 17:35:52 +0000 (GMT) [thread overview] Message-ID: <20221108173552.062743858C56@sourceware.org> (raw) https://gcc.gnu.org/g:c93baa93df2d454f329a38686affcfe1a1339766 commit r13-3814-gc93baa93df2d454f329a38686affcfe1a1339766 Author: Will Hawkins <whh8b@obs.cr> Date: Wed Oct 19 20:05:59 2022 -0400 libstdc++: Refactor implementation of operator+ for std::string Until now operator+(char*, string) and operator+(string, char*) had different performance characteristics. The former required a single memory allocation and the latter required two. This patch makes the performance equal. After consultation with Jonathan, it seemed like a good idea to create a single function that performed one-allocation string concatenation that could be used by various different version of operator+. This patch adds such a function and calls it from the relevant implementations. Co-authored-by: Jonathan Wakely <jwakely@redhat.com> libstdc++-v3/ChangeLog: * include/bits/basic_string.h (__str_cat): Add common function that performs single-allocation string concatenation. (operator+): Use __str_cat. * include/bits/basic_string.tcc (operator+): Move to .h and define inline using __str_cat. Signed-off-by: Will Hawkins <whh8b@obs.cr> Diff: --- libstdc++-v3/include/bits/basic_string.h | 66 ++++++++++++++++++++++-------- libstdc++-v3/include/bits/basic_string.tcc | 41 ------------------- 2 files changed, 49 insertions(+), 58 deletions(-) diff --git a/libstdc++-v3/include/bits/basic_string.h b/libstdc++-v3/include/bits/basic_string.h index cd244191df4..9c2b57f5a1d 100644 --- a/libstdc++-v3/include/bits/basic_string.h +++ b/libstdc++-v3/include/bits/basic_string.h @@ -3485,6 +3485,24 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 _GLIBCXX_END_NAMESPACE_CXX11 #endif + template<typename _Str> + _GLIBCXX20_CONSTEXPR + inline _Str + __str_concat(typename _Str::value_type const* __lhs, + typename _Str::size_type __lhs_len, + typename _Str::value_type const* __rhs, + typename _Str::size_type __rhs_len, + typename _Str::allocator_type const& __a) + { + typedef typename _Str::allocator_type allocator_type; + typedef __gnu_cxx::__alloc_traits<allocator_type> _Alloc_traits; + _Str __str(_Alloc_traits::_S_select_on_copy(__a)); + __str.reserve(__lhs_len + __rhs_len); + __str.append(__lhs, __lhs_len); + __str.append(__rhs, __rhs_len); + return __str; + } + // operator+ /** * @brief Concatenate two strings. @@ -3494,13 +3512,14 @@ _GLIBCXX_END_NAMESPACE_CXX11 */ template<typename _CharT, typename _Traits, typename _Alloc> _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR - basic_string<_CharT, _Traits, _Alloc> + inline basic_string<_CharT, _Traits, _Alloc> operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs, const basic_string<_CharT, _Traits, _Alloc>& __rhs) { - basic_string<_CharT, _Traits, _Alloc> __str(__lhs); - __str.append(__rhs); - return __str; + typedef basic_string<_CharT, _Traits, _Alloc> _Str; + return std::__str_concat<_Str>(__lhs.c_str(), __lhs.size(), + __rhs.c_str(), __rhs.size(), + __lhs.get_allocator()); } /** @@ -3511,9 +3530,16 @@ _GLIBCXX_END_NAMESPACE_CXX11 */ template<typename _CharT, typename _Traits, typename _Alloc> _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR - basic_string<_CharT,_Traits,_Alloc> + inline basic_string<_CharT,_Traits,_Alloc> operator+(const _CharT* __lhs, - const basic_string<_CharT,_Traits,_Alloc>& __rhs); + const basic_string<_CharT,_Traits,_Alloc>& __rhs) + { + __glibcxx_requires_string(__lhs); + typedef basic_string<_CharT, _Traits, _Alloc> _Str; + return std::__str_concat<_Str>(__lhs, _Traits::length(__lhs), + __rhs.c_str(), __rhs.size(), + __rhs.get_allocator()); + } /** * @brief Concatenate character and string. @@ -3523,8 +3549,14 @@ _GLIBCXX_END_NAMESPACE_CXX11 */ template<typename _CharT, typename _Traits, typename _Alloc> _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR - basic_string<_CharT,_Traits,_Alloc> - operator+(_CharT __lhs, const basic_string<_CharT,_Traits,_Alloc>& __rhs); + inline basic_string<_CharT,_Traits,_Alloc> + operator+(_CharT __lhs, const basic_string<_CharT,_Traits,_Alloc>& __rhs) + { + typedef basic_string<_CharT, _Traits, _Alloc> _Str; + return std::__str_concat<_Str>(__builtin_addressof(__lhs), 1, + __rhs.c_str(), __rhs.size(), + __rhs.get_allocator()); + } /** * @brief Concatenate string and C string. @@ -3538,11 +3570,12 @@ _GLIBCXX_END_NAMESPACE_CXX11 operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs, const _CharT* __rhs) { - basic_string<_CharT, _Traits, _Alloc> __str(__lhs); - __str.append(__rhs); - return __str; + __glibcxx_requires_string(__rhs); + typedef basic_string<_CharT, _Traits, _Alloc> _Str; + return std::__str_concat<_Str>(__lhs.c_str(), __lhs.size(), + __rhs, _Traits::length(__rhs), + __lhs.get_allocator()); } - /** * @brief Concatenate string and character. * @param __lhs First string. @@ -3554,11 +3587,10 @@ _GLIBCXX_END_NAMESPACE_CXX11 inline basic_string<_CharT, _Traits, _Alloc> operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs, _CharT __rhs) { - typedef basic_string<_CharT, _Traits, _Alloc> __string_type; - typedef typename __string_type::size_type __size_type; - __string_type __str(__lhs); - __str.append(__size_type(1), __rhs); - return __str; + typedef basic_string<_CharT, _Traits, _Alloc> _Str; + return std::__str_concat<_Str>(__lhs.c_str(), __lhs.size(), + __builtin_addressof(__rhs), 1, + __lhs.get_allocator()); } #if __cplusplus >= 201103L diff --git a/libstdc++-v3/include/bits/basic_string.tcc b/libstdc++-v3/include/bits/basic_string.tcc index 710c2dfe030..56114f120ba 100644 --- a/libstdc++-v3/include/bits/basic_string.tcc +++ b/libstdc++-v3/include/bits/basic_string.tcc @@ -605,47 +605,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION #else # define _GLIBCXX_STRING_CONSTEXPR #endif - - template<typename _CharT, typename _Traits, typename _Alloc> - _GLIBCXX20_CONSTEXPR - basic_string<_CharT, _Traits, _Alloc> - operator+(const _CharT* __lhs, - const basic_string<_CharT, _Traits, _Alloc>& __rhs) - { - __glibcxx_requires_string(__lhs); - 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(__lhs); - __string_type __str(_Alloc_traits::_S_select_on_copy( - __rhs.get_allocator())); - __str.reserve(__len + __rhs.size()); - __str.append(__lhs, __len); - __str.append(__rhs); - return __str; - } - - template<typename _CharT, typename _Traits, typename _Alloc> - _GLIBCXX20_CONSTEXPR - basic_string<_CharT, _Traits, _Alloc> - operator+(_CharT __lhs, const basic_string<_CharT, _Traits, _Alloc>& __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; - __string_type __str(_Alloc_traits::_S_select_on_copy( - __rhs.get_allocator())); - const __size_type __len = __rhs.size(); - __str.reserve(__len + 1); - __str.append(__size_type(1), __lhs); - __str.append(__rhs); - return __str; - } - template<typename _CharT, typename _Traits, typename _Alloc> _GLIBCXX_STRING_CONSTEXPR typename basic_string<_CharT, _Traits, _Alloc>::size_type
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