PR libstdc++/81476 Optimise vector insertion from input iterators

PR libstdc++/81476
	* include/bits/vector.tcc (vector::_M_range_insert<_InputIterator>):
	Only insert elements one-by-one when inserting at the end.
	* testsuite/performance/23_containers/insert/81476.cc: New.

From-SVN: r250366

libstdc++-v3/ChangeLog

@@ -1,3 +1,10 @@
+2017-07-19  Jonathan Wakely  <jwakely@redhat.com>
+
+	PR libstdc++/81476
+	* include/bits/vector.tcc (vector::_M_range_insert<_InputIterator>):
+	Only insert elements one-by-one when inserting at the end.
+	* testsuite/performance/23_containers/insert/81476.cc: New.
+
 2017-07-19  Volker Reichelt  <v.reichelt@netcologne.de>
 
 	* libsupc++/new (bad_array_new_length): Remove redundant

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

@@ -617,10 +617,17 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       _M_range_insert(iterator __pos, _InputIterator __first,
 		      _InputIterator __last, std::input_iterator_tag)
       {
-	for (; __first != __last; ++__first)
+	if (__pos == end())
 	  {
-	    __pos = insert(__pos, *__first);
-	    ++__pos;
+	    for (; __first != __last; ++__first)
+	      insert(end(), *__first);
+	  }
+	else if (__first != __last)
+	  {
+	    vector __tmp(__first, __last, _M_get_Tp_allocator());
+	    insert(__pos,
+		   _GLIBCXX_MAKE_MOVE_ITERATOR(__tmp.begin()),
+		   _GLIBCXX_MAKE_MOVE_ITERATOR(__tmp.end()));
 	  }
       }
 

libstdc++-v3/testsuite/performance/23_containers/insert/81476.cc

@@ -0,0 +1,86 @@
+// Copyright (C) 2012-2017 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 } }
+
+#include <random>
+#include <vector>
+#include <testsuite_hooks.h>
+#include <testsuite_performance.h>
+
+int main()
+{
+  using namespace __gnu_test;
+
+  std::default_random_engine eng;
+  std::uniform_int_distribution<unsigned> r(0, 127);
+
+  time_counter time;
+  resource_counter resource;
+
+  std::vector<std::vector<char>> vecs(10000);
+  for (auto& v : vecs)
+  {
+    v.resize(1000);
+    for (auto& c : v)
+      c = r(eng);
+  }
+
+  start_counters(time, resource);
+  std::vector<char> res;
+  for (auto& v : vecs)
+    res.insert(res.begin(), v.begin(), v.end());
+  stop_counters(time, resource);
+  report_performance(__FILE__, "insert pointers", time, resource);
+
+  struct input_iterator : std::vector<char>::iterator
+  {
+    using iterator_category = std::input_iterator_tag;
+    using base = std::vector<char>::iterator;
+
+    input_iterator(base it) : base(it) { }
+  };
+
+  start_counters(time, resource);
+  std::vector<char> res2;
+  for (auto& v : vecs)
+  {
+    auto begin = input_iterator(v.begin());
+    auto end = input_iterator(v.end());
+    res2.insert(res2.begin(), begin, end);
+  }
+  stop_counters(time, resource);
+  report_performance(__FILE__, "insert input iterators", time, resource);
+
+  start_counters(time, resource);
+  std::vector<char> res3;
+  for (auto rev = vecs.rbegin(); rev != vecs.rend(); ++rev)
+    res3.insert(res3.end(), rev->begin(), rev->end());
+  stop_counters(time, resource);
+  report_performance(__FILE__, "insert pointers end", time, resource);
+
+  start_counters(time, resource);
+  std::vector<char> res4;
+  for (auto rev = vecs.rbegin(); rev != vecs.rend(); ++rev)
+    res4.insert(res4.end(), rev->begin(), rev->end());
+  stop_counters(time, resource);
+  report_performance(__FILE__, "insert input iterators end", time, resource);
+
+  VERIFY(res2 == res);
+  VERIFY(res3 == res);
+  VERIFY(res4 == res);
+}