PR libstdc++/83982 fix exception-safety guarantee of std::vector::resize

Construct new elements before moving existing ones, so that if a default
constructor throws, the existing elements are not left in a moved-from
state.

2018-06-14  Daniel Trebbien <dtrebbien@gmail.com>
	    Jonathan Wakely  <jwakely@redhat.com>

	PR libstdc++/83982
	* include/bits/vector.tcc (vector::_M_default_append(size_type)):
	Default-construct new elements before moving existing ones.
	* testsuite/23_containers/vector/capacity/resize/strong_guarantee.cc:
	New.

Co-Authored-By: Jonathan Wakely <jwakely@redhat.com>

From-SVN: r261585

libstdc++-v3/ChangeLog

+2018-06-14  Daniel Trebbien <dtrebbien@gmail.com>
+	    Jonathan Wakely  <jwakely@redhat.com>
+
+	PR libstdc++/83982
+	* include/bits/vector.tcc (vector::_M_default_append(size_type)):
+	Default-construct new elements before moving existing ones.
+	* testsuite/23_containers/vector/capacity/resize/strong_guarantee.cc:
+	New.
+
 2018-06-13  Jonathan Wakely  <jwakely@redhat.com>
 
 	PR libstdc++/86127

libstdc++-v3/include/bits/vector.tcc

@@ -582,7 +582,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
     {
       if (__n != 0)
 	{
-	  size_type __size = size();
+	  const size_type __size = size();
 	  size_type __navail = size_type(this->_M_impl._M_end_of_storage
 					 - this->_M_impl._M_finish);
 
@@ -601,22 +601,21 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 	    {
 	      const size_type __len =
 		_M_check_len(__n, "vector::_M_default_append");
-	      const size_type __old_size = __size;
 	      pointer __new_start(this->_M_allocate(__len));
-	      pointer __new_finish(__new_start);
+	      pointer __destroy_from = pointer();
 	      __try
 		{
-		  __new_finish
-		    = std::__uninitialized_move_if_noexcept_a
-		    (this->_M_impl._M_start, this->_M_impl._M_finish,
+		  std::__uninitialized_default_n_a(__new_start + __size,
+						   __n, _M_get_Tp_allocator());
+		  __destroy_from = __new_start + __size;
+		  std::__uninitialized_move_if_noexcept_a(
+		      this->_M_impl._M_start, this->_M_impl._M_finish,
 		      __new_start, _M_get_Tp_allocator());
-		  __new_finish =
-		    std::__uninitialized_default_n_a(__new_finish, __n,
-						     _M_get_Tp_allocator());
 		}
 	      __catch(...)
 		{
-		  std::_Destroy(__new_start, __new_finish,
+		  if (__destroy_from)
+		    std::_Destroy(__destroy_from, __destroy_from + __n,
 				  _M_get_Tp_allocator());
 		  _M_deallocate(__new_start, __len);
 		  __throw_exception_again;
@@ -628,7 +627,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 			    this->_M_impl._M_end_of_storage
 			    - this->_M_impl._M_start);
 	      this->_M_impl._M_start = __new_start;
-	      this->_M_impl._M_finish = __new_finish;
+	      this->_M_impl._M_finish = __new_start + __size + __n;
 	      this->_M_impl._M_end_of_storage = __new_start + __len;
 	    }
 	}

libstdc++-v3/testsuite/23_containers/vector/capacity/resize/strong_guarantee.cc

+// Copyright (C) 2018 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/>.
+
+#include <vector>
+#include <testsuite_hooks.h>
+
+struct X
+{
+  X() : data(1)
+  {
+    if (fail)
+      throw 1;
+  }
+
+  static bool fail;
+
+  std::vector<int> data;
+};
+
+bool X::fail = false;
+
+void
+test01()
+{
+  std::vector<X> v(2);
+  X* const addr = &v[0];
+  bool caught = false;
+  try {
+    X::fail = true;
+    v.resize(v.capacity() + 1); // force reallocation
+  } catch (int) {
+    caught = true;
+  }
+  VERIFY( caught );
+  VERIFY( v.size() == 2 );
+  VERIFY( &v[0] == addr );
+  // PR libstdc++/83982
+  VERIFY( ! v[0].data.empty() );
+  VERIFY( ! v[1].data.empty() );
+}
+
+int
+main()
+{
+  test01();
+}