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From: whh8b@obs.cr
To: libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org
Cc: Will Hawkins <whh8b@obs.cr>
Subject: [PATCH] libstdc++: Optimize operator+(string/char*, string/char*) equally
Date: Wed, 24 Aug 2022 02:16:48 -0400	[thread overview]
Message-ID: <20220824061648.1119635-2-whh8b@obs.cr> (raw)
Message-ID: <20220824061648.Smx5F3kEnoTR_F7id9HbBHz5tNPpQ2H-V98WQWc-9kc@z> (raw)
In-Reply-To: <20220824061648.1119635-1-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.

Signed-off-by: Will Hawkins <whh8b@obs.cr>
---
 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
-- 
2.34.1


  reply	other threads:[~2022-08-24  6:16 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
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     ` whh8b [this message]
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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