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* [gcc r13-3814] libstdc++: Refactor implementation of operator+ for std::string
@ 2022-11-08 17:35 Jonathan Wakely
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From: Jonathan Wakely @ 2022-11-08 17:35 UTC (permalink / raw)
To: gcc-cvs, libstdc++-cvs
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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