From: whh8b@obs.cr
To: libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org
Subject: [PATCH] libstdc++: Optimize operator+(string/char*, string/char*) equally
Date: Mon, 22 Aug 2022 14:15:09 -0400 [thread overview]
Message-ID: <20220822181509.1032874-2-whh8b@obs.cr> (raw)
In-Reply-To: <20220822181509.1032874-1-whh8b@obs.cr>
From: Will Hawkins <whh8b@obs.cr>
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.
libstdc++-v3/ChangeLog:
* libstdc++-v3/include/bits/basic_string.h (operator+(string, char*)):
Remove naive implementation.
* libstdc++-v3/include/bits/basic_string.tcc (operator+(string, char*)):
Add single-allocation implementation.
---
libstdc++-v3/include/bits/basic_string.h | 7 +------
libstdc++-v3/include/bits/basic_string.tcc | 21 +++++++++++++++++++++
2 files changed, 22 insertions(+), 6 deletions(-)
diff --git a/libstdc++-v3/include/bits/basic_string.h b/libstdc++-v3/include/bits/basic_string.h
index b04fba95678..bc048fc0689 100644
--- a/libstdc++-v3/include/bits/basic_string.h
+++ b/libstdc++-v3/include/bits/basic_string.h
@@ -3523,12 +3523,7 @@ _GLIBCXX_END_NAMESPACE_CXX11
_GLIBCXX20_CONSTEXPR
inline 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
--
2.34.1
next prev parent reply other threads:[~2022-08-22 18:15 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-22 18:15 whh8b
2022-08-22 18:15 ` whh8b [this message]
2022-08-23 16:33 ` Jonathan Wakely
2022-08-24 6:18 ` Will Hawkins
2022-08-24 9:49 ` Jonathan Wakely
2022-08-24 6:16 ` [PATCH v2] libstdc++: Optimize operator+(string/char*,string/char*) whh8b
2022-08-24 6:16 ` [PATCH] libstdc++: Optimize operator+(string/char*,string/char*) equally whh8b
2022-08-24 6:16 ` [PATCH] libstdc++: Optimize operator+(string/char*, string/char*) equally whh8b
2022-08-24 14:24 ` Jonathan Wakely
2022-08-24 22:39 ` Alexandre Oliva
2022-08-24 22:47 ` Jonathan Wakely
2022-08-24 23:02 ` Jonathan Wakely
2022-08-25 5:52 ` Will Hawkins
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