commit b9546ed53b169ffb809371231342eeb63595d8bc
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Fri Sep 23 18:01:25 2016 +0100
Avoid reallocation for basic_string::clear()
PR libstdc++/56166
PR libstdc++/77582
* include/bits/basic_string.h (basic_string::clear()): Drop reference
and use empty rep.
* include/ext/rc_string_base.h (__rc_string_base::_M_clear()):
Likewise.
* testsuite/21_strings/basic_string/56166.cc: New.
* testsuite/ext/vstring/modifiers/clear/56166.cc: New.
@@ -3690,10 +3690,24 @@ _GLIBCXX_END_NAMESPACE_CXX11
/**
* Erases the string, making it empty.
*/
+#if _GLIBCXX_FULLY_DYNAMIC_STRING == 0
+ void
+ clear() _GLIBCXX_NOEXCEPT
+ {
+ if (_M_rep()->_M_is_shared())
+ {
+ _M_rep()->_M_dispose(this->get_allocator());
+ _M_data(_S_empty_rep()._M_refdata());
+ }
+ else
+ _M_rep()->_M_set_length_and_sharable(0);
+ }
+#else
// PR 56166: this should not throw.
void
clear()
{ _M_mutate(0, this->size(), 0); }
+#endif
/**
* Returns true if the %string is empty. Equivalent to
@@ -354,7 +354,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
void
_M_clear()
- { _M_erase(size_type(0), _M_length()); }
+ {
+ _M_dispose();
+ _M_data(_S_empty_rep._M_refcopy());
+ }
bool
_M_compare(const __rc_string_base&) const
new file mode 100644
@@ -0,0 +1,93 @@
+// Copyright (C) 2016 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library. This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3. If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-do run { target c++11 } }
+
+// libstdc++/56166
+
+#ifndef _GLIBCXX_USE_CXX11_ABI
+# define _GLIBCXX_USE_CXX11_ABI 0
+#endif
+#include <string>
+#include <new>
+
+static int fail_after = -1;
+
+template<typename T>
+ struct Allocator
+ {
+ using value_type = T;
+
+ // Need these typedefs because COW string doesn't use allocator_traits.
+ using pointer = T*;
+ using const_pointer = const T*;
+ using reference = T&;
+ using const_reference = const T&;
+ using difference_type = long;
+ using size_type = unsigned long;
+ template<typename U>
+ struct rebind {
+ using other = Allocator<U>;
+ };
+
+ Allocator() { }
+
+ template<typename U>
+ Allocator(const Allocator<U>&) { }
+
+ T* allocate(size_type n)
+ {
+ if (fail_after >= 0) {
+ if (fail_after-- == 0) {
+ throw std::bad_alloc();
+ }
+ }
+ return (T*)new char[n * sizeof(T)];
+ }
+
+ void deallocate(T* p, size_type)
+ {
+ delete[] (char*)p;
+ }
+ };
+
+template<typename T, typename U>
+ bool operator==(const Allocator<T>&, const Allocator<U>&) { return true; }
+template<typename T, typename U>
+ bool operator!=(const Allocator<T>&, const Allocator<U>&) { return false; }
+
+using string = std::basic_string<char, std::char_traits<char>, Allocator<char>>;
+
+string f()
+{
+ string s1("xxxxxx");
+ string s2 = s1;
+ s1.clear();
+ return s2;
+}
+
+int main()
+{
+ for (int i = 0; i < 10; i++) {
+ try {
+ fail_after = i;
+ f();
+ break;
+ } catch (std::bad_alloc) {
+ }
+ }
+}
new file mode 100644
@@ -0,0 +1,96 @@
+// Copyright (C) 2016 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library. This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3. If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-do run { target c++11 } }
+
+// libstdc++/56166
+
+#ifndef _GLIBCXX_USE_CXX11_ABI
+# define _GLIBCXX_USE_CXX11_ABI 0
+#endif
+#include <ext/vstring.h>
+#include <new>
+
+static int fail_after = -1;
+
+template<typename T>
+ struct Allocator
+ {
+ using value_type = T;
+
+ // Need these typedefs because COW string doesn't use allocator_traits.
+ using pointer = T*;
+ using const_pointer = const T*;
+ using reference = T&;
+ using const_reference = const T&;
+ using difference_type = long;
+ using size_type = unsigned long;
+ template<typename U>
+ struct rebind {
+ using other = Allocator<U>;
+ };
+
+ Allocator() { }
+
+ template<typename U>
+ Allocator(const Allocator<U>&) { }
+
+ T* allocate(size_type n)
+ {
+ if (fail_after >= 0) {
+ if (fail_after-- == 0) {
+ throw std::bad_alloc();
+ }
+ }
+ return (T*)new char[n * sizeof(T)];
+ }
+
+ void deallocate(T* p, size_type)
+ {
+ delete[] (char*)p;
+ }
+ };
+
+template<typename T, typename U>
+ bool operator==(const Allocator<T>&, const Allocator<U>&) { return true; }
+template<typename T, typename U>
+ bool operator!=(const Allocator<T>&, const Allocator<U>&) { return false; }
+
+
+using string = __gnu_cxx::__versa_string<char, std::char_traits<char>,
+ Allocator<char>,
+ __gnu_cxx::__rc_string_base>;
+
+string f()
+{
+ string s1("xxxxxx");
+ string s2 = s1;
+ s1.clear();
+ return s2;
+}
+
+int main()
+{
+ for (int i = 0; i < 10; i++) {
+ try {
+ fail_after = i;
+ f();
+ break;
+ } catch (std::bad_alloc) {
+ }
+ }
+}