[patch] Fix PR52822 (stable_partition move-assigns object to itself) in trunk, 4.7, and 4.6

[patch] Fix PR52822 (stable_partition move-assigns object to itself) in trunk, 4.7, and 4.6

[Jeffrey Yasskin]

[-- Attachment #1: Type: text/plain, Size: 578 bytes --]

The attached patches fix http://gcc.gnu.org/PR52822, and have been
tested with `make check-c++` on linux-x86_64. The trunk patch applies
and tests cleanly on gcc-4_7-branch. The gcc-4_6-branch patch is
significantly simpler, as Paolo suggested on the bug.

The test is still inadequate, but given that there's no way to force
get_temporary_buffer to return a short buffer, I'm not sure how to
improve it. It might be possible to use set_memory_limits(), but that
would require a very complex test program to make sure exactly the
right operator new call fails.

Jeffrey Yasskin

[-- Attachment #2: pr52822_trunk.patch --]
[-- Type: application/octet-stream, Size: 10557 bytes --]

commit a2501c1895c154966542b98389806ce83d0a300d
Author: Jeffrey Yasskin <jyasskin@google.com>
Date:   Tue Apr 3 15:10:56 2012 -0700

    Fix PR52822 (stable_partition move-assigns object to itself) by
    scanning for the first value that doesn't match the predicate before
    starting to rearrange values.
    
    2012-04-03   Jeffrey Yasskin  <jyasskin@google.com>
    
    	* libstdc++-v3/include/bits/stl_algo.h (__find_if_not): Expose in
    	C++98 mode.
    	(__find_if_not_n): Like __find_if_not, but works on and updates a
    	counted range instead of a bounded range.
    	(stable_partition): Guarantee !__pred(*__first) in call to
    	__stable_partition_adaptive() or __inplace_stable_partition().
    	(__stable_partition_adaptive): Use new precondition to avoid
    	moving/copying objects onto themselves.  Guarantee new
    	precondition to recursive calls.
    	(__inplace_stable_partition): Use new precondition to simplify
    	base case, remove __last parameter.  Guarantee new precondition to
    	recursive calls.
    	* libstdc++-v3/testsuite/25_algorithms/stable_partition/moveable.cc (test02):
    	Test a sequence that starts with a value matching the predicate.
    	* libstdc++-v3/testsuite/25_algorithms/stable_partition/pr52822.cc:
    	Test vectors, which have a destructive self-move-assignment.

diff --git a/libstdc++-v3/include/bits/stl_algo.h b/libstdc++-v3/include/bits/stl_algo.h
index c517a19..4ed5779 100644
--- a/libstdc++-v3/include/bits/stl_algo.h
+++ b/libstdc++-v3/include/bits/stl_algo.h
@@ -244,7 +244,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	}
     }
 
-#ifdef __GXX_EXPERIMENTAL_CXX0X__
   /// This is an overload used by find_if_not() for the Input Iterator case.
   template<typename _InputIterator, typename _Predicate>
     inline _InputIterator
@@ -303,7 +302,31 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	  return __last;
 	}
     }
-#endif
+
+  /// Provided for stable_partition to use.
+  template<typename _InputIterator, typename _Predicate>
+    inline _InputIterator
+    __find_if_not(_InputIterator __first, _InputIterator __last,
+		  _Predicate __pred)
+    {
+      return std::__find_if_not(__first, __last, __pred,
+				std::__iterator_category(__first));
+    }
+
+  /// Like find_if_not(), but uses and updates a count of the
+  /// remaining range length instead of comparing against an end
+  /// iterator.
+  template<typename _InputIterator, typename _Predicate, typename _Distance>
+    _InputIterator
+    __find_if_not_n(_InputIterator __first, _Distance& __len, _Predicate __pred)
+    {
+      _Distance __local_len = __len;
+      for (; __local_len != 0; --__local_len, ++__first)
+	if (!__pred(*__first))
+	  break;
+      __len = __local_len;
+      return __first;
+    }
 
   // set_difference
   // set_intersection
@@ -789,8 +812,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       __glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
 	      typename iterator_traits<_InputIterator>::value_type>)
       __glibcxx_requires_valid_range(__first, __last);
-      return std::__find_if_not(__first, __last, __pred,
-				std::__iterator_category(__first));
+      return std::__find_if_not(__first, __last, __pred);
     }
 
   /**
@@ -1784,30 +1806,39 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   // partition
 
   /// This is a helper function...
+  /// Requires __len != 0 and !__pred(*__first),
+  /// same as __stable_partition_adaptive.
   template<typename _ForwardIterator, typename _Predicate, typename _Distance>
     _ForwardIterator
     __inplace_stable_partition(_ForwardIterator __first,
-			       _ForwardIterator __last,
 			       _Predicate __pred, _Distance __len)
     {
       if (__len == 1)
-	return __pred(*__first) ? __last : __first;
+	return __first;
       _ForwardIterator __middle = __first;
       std::advance(__middle, __len / 2);
-      _ForwardIterator __begin = std::__inplace_stable_partition(__first,
-								 __middle,
-								 __pred,
-								 __len / 2);
-      _ForwardIterator __end = std::__inplace_stable_partition(__middle, __last,
-							       __pred,
-							       __len
-							       - __len / 2);
-      std::rotate(__begin, __middle, __end);
-      std::advance(__begin, std::distance(__middle, __end));
-      return __begin;
+      _ForwardIterator __left_split =
+	std::__inplace_stable_partition(__first, __pred, __len / 2);
+      // Advance past true-predicate values to satisfy this
+      // function's preconditions.
+      _Distance __right_len = __len - __len / 2;
+      _ForwardIterator __right_split =
+	std::__find_if_not_n(__middle, __right_len, __pred);
+      if (__right_len != 0)
+	__right_split = std::__inplace_stable_partition(__middle,
+							__pred,
+							__right_len);
+      std::rotate(__left_split, __middle, __right_split);
+      std::advance(__left_split, std::distance(__middle, __right_split));
+      return __left_split;
     }
 
   /// This is a helper function...
+  /// Requires __first != __last and !__pred(*__first)
+  /// and __len == distance(__first, __last).
+  ///
+  /// !__pred(*__first) allows us to guarantee that we don't
+  /// move-assign an element onto itself.
   template<typename _ForwardIterator, typename _Pointer, typename _Predicate,
 	   typename _Distance>
     _ForwardIterator
@@ -1821,6 +1852,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	{
 	  _ForwardIterator __result1 = __first;
 	  _Pointer __result2 = __buffer;
+	  // The precondition guarantees that !__pred(*__first), so
+	  // move that element to the buffer before starting the loop.
+	  // This ensures that we only call __pred once per element.
+	  *__result2 = _GLIBCXX_MOVE(*__first);
+	  ++__result2;
+	  ++__first;
 	  for (; __first != __last; ++__first)
 	    if (__pred(*__first))
 	      {
@@ -1839,17 +1876,23 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	{
 	  _ForwardIterator __middle = __first;
 	  std::advance(__middle, __len / 2);
-	  _ForwardIterator __begin =
+	  _ForwardIterator __left_split =
 	    std::__stable_partition_adaptive(__first, __middle, __pred,
 					     __len / 2, __buffer,
 					     __buffer_size);
-	  _ForwardIterator __end =
-	    std::__stable_partition_adaptive(__middle, __last, __pred,
-					     __len - __len / 2,
-					     __buffer, __buffer_size);
-	  std::rotate(__begin, __middle, __end);
-	  std::advance(__begin, std::distance(__middle, __end));
-	  return __begin;
+	  // Advance past true-predicate values to satisfy this
+	  // function's preconditions.
+	  _Distance __right_len = __len - __len / 2;
+	  _ForwardIterator __right_split =
+	    std::__find_if_not_n(__middle, __right_len, __pred);
+	  if (__right_len != 0)
+	    __right_split =
+	      std::__stable_partition_adaptive(__right_split, __last, __pred,
+					       __right_len,
+					       __buffer, __buffer_size);
+	  std::rotate(__left_split, __middle, __right_split);
+	  std::advance(__left_split, std::distance(__middle, __right_split));
+	  return __left_split;
 	}
     }
 
@@ -1882,6 +1925,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	    typename iterator_traits<_ForwardIterator>::value_type>)
       __glibcxx_requires_valid_range(__first, __last);
 
+      __first = std::__find_if_not(__first, __last, __pred);
+
       if (__first == __last)
 	return __first;
       else
@@ -1901,7 +1946,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 					  _DistanceType(__buf.size()));
 	else
 	  return
-	    std::__inplace_stable_partition(__first, __last, __pred,
+	    std::__inplace_stable_partition(__first, __pred,
 					 _DistanceType(__buf.requested_size()));
 	}
     }
diff --git a/libstdc++-v3/testsuite/25_algorithms/stable_partition/moveable.cc b/libstdc++-v3/testsuite/25_algorithms/stable_partition/moveable.cc
index b649b10..95d5006 100644
--- a/libstdc++-v3/testsuite/25_algorithms/stable_partition/moveable.cc
+++ b/libstdc++-v3/testsuite/25_algorithms/stable_partition/moveable.cc
@@ -35,6 +35,11 @@ const int A[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17};
 const int B[] = {2, 4, 6, 8, 10, 12, 14, 16, 1, 3, 5, 7, 9, 11, 13, 15, 17};
 const int N = sizeof(A) / sizeof(int);
 
+// Check that starting with a true predicate works too. (PR52822)
+const int A2[] = {2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17};
+const int B2[] = {2, 4, 6, 8, 10, 12, 14, 16, 3, 5, 7, 9, 11, 13, 15, 17};
+const int N2 = sizeof(A2) / sizeof(int);
+
 struct Pred
 {
   bool
@@ -42,7 +47,7 @@ struct Pred
   { return (x.val % 2) == 0; }
 };
 
-// 25.2.12 stable_partition()
+// 25.2.12 stable_partition(), starting with a false predicate.
 void
 test01()
 {
@@ -56,9 +61,24 @@ test01()
   VERIFY( std::equal(s1, s1 + N, B) );
 }
 
+// 25.2.12 stable_partition(), starting with a true predicate.
+void
+test02()
+{
+  bool test __attribute__((unused)) = true;
+
+  rvalstruct s1[N2];
+  std::copy(A2, A2 + N2, s1);
+  Container con(s1, s1 + N2);
+
+  std::stable_partition(con.begin(), con.end(), Pred());
+  VERIFY( std::equal(s1, s1 + N2, B2) );
+}
+
 int
 main()
 {
   test01();
+  test02();
   return 0;
 }
diff --git a/libstdc++-v3/testsuite/25_algorithms/stable_partition/pr52822.cc b/libstdc++-v3/testsuite/25_algorithms/stable_partition/pr52822.cc
new file mode 100644
index 0000000..c5f95f3
--- /dev/null
+++ b/libstdc++-v3/testsuite/25_algorithms/stable_partition/pr52822.cc
@@ -0,0 +1,43 @@
+// { dg-options "-std=gnu++0x" }
+
+// Copyright (C) 2012 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 Pred 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/>.
+
+// 25.2.12 [lib.alg.partitions] Partitions.
+
+#include <algorithm>
+#include <vector>
+#include <testsuite_hooks.h>
+
+bool true_vector_pred(const std::vector<int>&) { return true; }
+
+void
+test01()
+{
+  std::vector<std::vector<int> > v(1);
+  v[0].push_back(7);
+  VERIFY( v[0].size() == 1 );
+  std::stable_partition(v.begin(), v.end(), &true_vector_pred);
+  VERIFY( v[0].size() == 1 );
+}
+
+int
+main()
+{
+  test01();
+  return 0;
+}

[-- Attachment #3: pr52822_gcc46.patch --]
[-- Type: application/octet-stream, Size: 4629 bytes --]

commit d17265de7cdbef19640f99939e776440fcace8be
Author: Jeffrey Yasskin <jyasskin@google.com>
Date:   Tue Apr 3 14:36:53 2012 -0700

    Fix PR52822 by explicitly checking for object identity before
    move-assigning.  This is a simpler fix than is being committed to 4.7
    and 4.8.
    
    2012-04-02   Jeffrey Yasskin  <jyasskin@google.com>
    
    	* libstdc++-v3/include/bits/stl_algo.h (__stable_partition_adaptive):
    	Avoid move-assigning an object to itself by explicitly testing
    	for identity.
    	* libstdc++-v3/testsuite/25_algorithms/stable_partition/pr52822.cc:
    	Test vectors, which have a destructive self-move-assignment.
    	* libstdc++-v3/testsuite/25_algorithms/stable_partition/moveable.cc (test02):
    	Test with rvalstruct, which explicitly checks self-move-assignment.

diff --git a/libstdc++-v3/include/bits/stl_algo.h b/libstdc++-v3/include/bits/stl_algo.h
index 8391d3e..e2922f6 100644
--- a/libstdc++-v3/include/bits/stl_algo.h
+++ b/libstdc++-v3/include/bits/stl_algo.h
@@ -1811,7 +1811,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	  for (; __first != __last; ++__first)
 	    if (__pred(*__first))
 	      {
-		*__result1 = _GLIBCXX_MOVE(*__first);
+		if (&*__result1 != &*__first)
+		  *__result1 = _GLIBCXX_MOVE(*__first);
 		++__result1;
 	      }
 	    else
diff --git a/libstdc++-v3/testsuite/25_algorithms/stable_partition/moveable.cc b/libstdc++-v3/testsuite/25_algorithms/stable_partition/moveable.cc
index fe46463..3fca316 100644
--- a/libstdc++-v3/testsuite/25_algorithms/stable_partition/moveable.cc
+++ b/libstdc++-v3/testsuite/25_algorithms/stable_partition/moveable.cc
@@ -1,6 +1,6 @@
 // { dg-options "-std=gnu++0x" }
 
-// Copyright (C) 2009, 2010 Free Software Foundation, Inc.
+// Copyright (C) 2009, 2010, 2012 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
@@ -39,6 +39,11 @@ const int A[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17};
 const int B[] = {2, 4, 6, 8, 10, 12, 14, 16, 1, 3, 5, 7, 9, 11, 13, 15, 17};
 const int N = sizeof(A) / sizeof(int);
 
+// Check that starting with a true predicate works too. (PR52822)
+const int A2[] = {2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17};
+const int B2[] = {2, 4, 6, 8, 10, 12, 14, 16, 3, 5, 7, 9, 11, 13, 15, 17};
+const int N2 = sizeof(A2) / sizeof(int);
+
 struct Pred
 {
   bool
@@ -46,7 +51,7 @@ struct Pred
   { return (x.val % 2) == 0; }
 };
 
-// 25.2.12 stable_partition()
+// 25.2.12 stable_partition(), starting with a false predicate.
 void
 test01()
 {
@@ -60,9 +65,24 @@ test01()
   VERIFY( std::equal(s1, s1 + N, B) );
 }
 
+// 25.2.12 stable_partition(), starting with a true predicate.
+void
+test02()
+{
+  bool test __attribute__((unused)) = true;
+
+  rvalstruct s1[N2];
+  std::copy(A2, A2 + N2, s1);
+  Container con(s1, s1 + N2);
+
+  std::stable_partition(con.begin(), con.end(), Pred());
+  VERIFY( std::equal(s1, s1 + N2, B2) );
+}
+
 int
 main()
 {
   test01();
+  test02();
   return 0;
 }
diff --git a/libstdc++-v3/testsuite/25_algorithms/stable_partition/pr52822.cc b/libstdc++-v3/testsuite/25_algorithms/stable_partition/pr52822.cc
new file mode 100644
index 0000000..c5f95f3
--- /dev/null
+++ b/libstdc++-v3/testsuite/25_algorithms/stable_partition/pr52822.cc
@@ -0,0 +1,43 @@
+// { dg-options "-std=gnu++0x" }
+
+// Copyright (C) 2012 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 Pred 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/>.
+
+// 25.2.12 [lib.alg.partitions] Partitions.
+
+#include <algorithm>
+#include <vector>
+#include <testsuite_hooks.h>
+
+bool true_vector_pred(const std::vector<int>&) { return true; }
+
+void
+test01()
+{
+  std::vector<std::vector<int> > v(1);
+  v[0].push_back(7);
+  VERIFY( v[0].size() == 1 );
+  std::stable_partition(v.begin(), v.end(), &true_vector_pred);
+  VERIFY( v[0].size() == 1 );
+}
+
+int
+main()
+{
+  test01();
+  return 0;
+}

Re: [patch] Fix PR52822 (stable_partition move-assigns object to itself) in trunk, 4.7, and 4.6

[Paolo Carlini]

Hi,
> The attached patches fix http://gcc.gnu.org/PR52822, and have been
> tested with `make check-c++` on linux-x86_64. The trunk patch applies
> and tests cleanly on gcc-4_7-branch. The gcc-4_6-branch patch is
> significantly simpler, as Paolo suggested on the bug.
A few small issues.

For the 4.6 version of the patch, you want to use std::__addressof, 
instead of simply &, which may be overloaded.

For the mainline/4.7 version, you want to cast __pred to bool: 
!bool(__pred(*__first)). Also, isn't clear to me why you have 
__local_len in __find_if_not_n instead of just working on __len (and in 
any case please prefer just __local_len as condition instead of the 
redundant __local_len != 0; likewise in many other similar situations).

Also, very minor nit, you will be touching the libstdc++-v3 Changelog 
thus no libstdc++-v3 prefixes in the ChangeLog entry.

Paolo.

Re: [patch] Fix PR52822 (stable_partition move-assigns object to itself) in trunk, 4.7, and 4.6

[Paolo Carlini]

On 4/4/12 11:09 PM, Paolo Carlini wrote:
> Hi,
>> The attached patches fix http://gcc.gnu.org/PR52822, and have been
>> tested with `make check-c++` on linux-x86_64. The trunk patch applies
>> and tests cleanly on gcc-4_7-branch. The gcc-4_6-branch patch is
>> significantly simpler, as Paolo suggested on the bug.
> A few small issues.
>
> For the 4.6 version of the patch, you want to use std::__addressof, 
> instead of simply &, which may be overloaded.
And by the way what's wrong with just comparing the iterators?

Paolo.

Re: [patch] Fix PR52822 (stable_partition move-assigns object to itself) in trunk, 4.7, and 4.6

[Jeffrey Yasskin]

[-- Attachment #1: Type: text/plain, Size: 1297 bytes --]

On Wed, Apr 4, 2012 at 11:09 PM, Paolo Carlini <paolo.carlini@oracle.com> wrote:
> Hi,
>
>> The attached patches fix http://gcc.gnu.org/PR52822, and have been
>> tested with `make check-c++` on linux-x86_64. The trunk patch applies
>> and tests cleanly on gcc-4_7-branch. The gcc-4_6-branch patch is
>> significantly simpler, as Paolo suggested on the bug.
>
> A few small issues.
>
> For the 4.6 version of the patch, you want to use std::__addressof, instead
> of simply &, which may be overloaded.
> And by the way what's wrong with just comparing the iterators?

Nothing's wrong with comparing the iterators. Switched.

> For the mainline/4.7 version, you want to cast __pred to bool:
> !bool(__pred(*__first)). Also, isn't clear to me why you have __local_len in
> __find_if_not_n instead of just working on __len (and in any case please
> prefer just __local_len as condition instead of the redundant __local_len !=
> 0; likewise in many other similar situations).

I was micro-optimizing, since the compiler might think __len is
modified in __pred if it doesn't inline enough. I've removed
__local_len, casted pred results to bool, and avoided !=0.

> Also, very minor nit, you will be touching the libstdc++-v3 Changelog thus
> no libstdc++-v3 prefixes in the ChangeLog entry.

Yep, done.

[-- Attachment #2: pr52822_gcc46.patch --]
[-- Type: application/octet-stream, Size: 4614 bytes --]

commit 836a1597079591ba3c4bd0e2a72bf72d4684aa5a
Author: Jeffrey Yasskin <jyasskin@google.com>
Date:   Tue Apr 3 14:36:53 2012 -0700

    Fix PR52822 by explicitly checking for object identity before
    move-assigning.  This is a simpler fix than is being committed to 4.7
    and 4.8.
    
    libstdc++-v3/ChangeLog:
    2012-04-02   Jeffrey Yasskin  <jyasskin@google.com>
    
    	* include/bits/stl_algo.h (__stable_partition_adaptive):
    	Avoid move-assigning an object to itself by explicitly testing
    	for identity.
    	* testsuite/25_algorithms/stable_partition/pr52822.cc:
    	Test vectors, which have a destructive self-move-assignment.
    	* testsuite/25_algorithms/stable_partition/moveable.cc (test02):
    	Test with rvalstruct, which explicitly checks self-move-assignment.

diff --git a/libstdc++-v3/include/bits/stl_algo.h b/libstdc++-v3/include/bits/stl_algo.h
index 8391d3e..6e9965c 100644
--- a/libstdc++-v3/include/bits/stl_algo.h
+++ b/libstdc++-v3/include/bits/stl_algo.h
@@ -1811,7 +1811,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	  for (; __first != __last; ++__first)
 	    if (__pred(*__first))
 	      {
-		*__result1 = _GLIBCXX_MOVE(*__first);
+		if (__result1 != __first)
+		  *__result1 = _GLIBCXX_MOVE(*__first);
 		++__result1;
 	      }
 	    else
diff --git a/libstdc++-v3/testsuite/25_algorithms/stable_partition/moveable.cc b/libstdc++-v3/testsuite/25_algorithms/stable_partition/moveable.cc
index fe46463..3fca316 100644
--- a/libstdc++-v3/testsuite/25_algorithms/stable_partition/moveable.cc
+++ b/libstdc++-v3/testsuite/25_algorithms/stable_partition/moveable.cc
@@ -1,6 +1,6 @@
 // { dg-options "-std=gnu++0x" }
 
-// Copyright (C) 2009, 2010 Free Software Foundation, Inc.
+// Copyright (C) 2009, 2010, 2012 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
@@ -39,6 +39,11 @@ const int A[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17};
 const int B[] = {2, 4, 6, 8, 10, 12, 14, 16, 1, 3, 5, 7, 9, 11, 13, 15, 17};
 const int N = sizeof(A) / sizeof(int);
 
+// Check that starting with a true predicate works too. (PR52822)
+const int A2[] = {2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17};
+const int B2[] = {2, 4, 6, 8, 10, 12, 14, 16, 3, 5, 7, 9, 11, 13, 15, 17};
+const int N2 = sizeof(A2) / sizeof(int);
+
 struct Pred
 {
   bool
@@ -46,7 +51,7 @@ struct Pred
   { return (x.val % 2) == 0; }
 };
 
-// 25.2.12 stable_partition()
+// 25.2.12 stable_partition(), starting with a false predicate.
 void
 test01()
 {
@@ -60,9 +65,24 @@ test01()
   VERIFY( std::equal(s1, s1 + N, B) );
 }
 
+// 25.2.12 stable_partition(), starting with a true predicate.
+void
+test02()
+{
+  bool test __attribute__((unused)) = true;
+
+  rvalstruct s1[N2];
+  std::copy(A2, A2 + N2, s1);
+  Container con(s1, s1 + N2);
+
+  std::stable_partition(con.begin(), con.end(), Pred());
+  VERIFY( std::equal(s1, s1 + N2, B2) );
+}
+
 int
 main()
 {
   test01();
+  test02();
   return 0;
 }
diff --git a/libstdc++-v3/testsuite/25_algorithms/stable_partition/pr52822.cc b/libstdc++-v3/testsuite/25_algorithms/stable_partition/pr52822.cc
new file mode 100644
index 0000000..c5f95f3
--- /dev/null
+++ b/libstdc++-v3/testsuite/25_algorithms/stable_partition/pr52822.cc
@@ -0,0 +1,43 @@
+// { dg-options "-std=gnu++0x" }
+
+// Copyright (C) 2012 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 Pred 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/>.
+
+// 25.2.12 [lib.alg.partitions] Partitions.
+
+#include <algorithm>
+#include <vector>
+#include <testsuite_hooks.h>
+
+bool true_vector_pred(const std::vector<int>&) { return true; }
+
+void
+test01()
+{
+  std::vector<std::vector<int> > v(1);
+  v[0].push_back(7);
+  VERIFY( v[0].size() == 1 );
+  std::stable_partition(v.begin(), v.end(), &true_vector_pred);
+  VERIFY( v[0].size() == 1 );
+}
+
+int
+main()
+{
+  test01();
+  return 0;
+}

[-- Attachment #3: pr52822_trunk.patch --]
[-- Type: application/octet-stream, Size: 10459 bytes --]

commit c43736b064cba82af572bbb78c10432cf5178dad
Author: Jeffrey Yasskin <jyasskin@google.com>
Date:   Tue Apr 3 15:10:56 2012 -0700

    Fix PR52822 (stable_partition move-assigns object to itself) by
    scanning for the first value that doesn't match the predicate before
    starting to rearrange values.
    
    libstdc++-v3/Changelog:
    2012-04-03   Jeffrey Yasskin  <jyasskin@google.com>
    
    	* include/bits/stl_algo.h (__find_if_not): Expose in
    	C++98 mode.
    	(__find_if_not_n): Like __find_if_not, but works on and updates a
    	counted range instead of a bounded range.
    	(stable_partition): Guarantee !__pred(*__first) in call to
    	__stable_partition_adaptive() or __inplace_stable_partition().
    	(__stable_partition_adaptive): Use new precondition to avoid
    	moving/copying objects onto themselves.  Guarantee new
    	precondition to recursive calls.
    	(__inplace_stable_partition): Use new precondition to simplify
    	base case, remove __last parameter.  Guarantee new precondition to
    	recursive calls.
    	* testsuite/25_algorithms/stable_partition/moveable.cc (test02):
    	Test a sequence that starts with a value matching the predicate.
    	* testsuite/25_algorithms/stable_partition/pr52822.cc:
    	Test vectors, which have a destructive self-move-assignment.

diff --git a/libstdc++-v3/include/bits/stl_algo.h b/libstdc++-v3/include/bits/stl_algo.h
index c517a19..f337e0c 100644
--- a/libstdc++-v3/include/bits/stl_algo.h
+++ b/libstdc++-v3/include/bits/stl_algo.h
@@ -244,7 +244,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	}
     }
 
-#ifdef __GXX_EXPERIMENTAL_CXX0X__
   /// This is an overload used by find_if_not() for the Input Iterator case.
   template<typename _InputIterator, typename _Predicate>
     inline _InputIterator
@@ -303,7 +302,29 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	  return __last;
 	}
     }
-#endif
+
+  /// Provided for stable_partition to use.
+  template<typename _InputIterator, typename _Predicate>
+    inline _InputIterator
+    __find_if_not(_InputIterator __first, _InputIterator __last,
+		  _Predicate __pred)
+    {
+      return std::__find_if_not(__first, __last, __pred,
+				std::__iterator_category(__first));
+    }
+
+  /// Like find_if_not(), but uses and updates a count of the
+  /// remaining range length instead of comparing against an end
+  /// iterator.
+  template<typename _InputIterator, typename _Predicate, typename _Distance>
+    _InputIterator
+    __find_if_not_n(_InputIterator __first, _Distance& __len, _Predicate __pred)
+    {
+      for (; __len; --__len, ++__first)
+	if (!bool(__pred(*__first)))
+	  break;
+      return __first;
+    }
 
   // set_difference
   // set_intersection
@@ -789,8 +810,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       __glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
 	      typename iterator_traits<_InputIterator>::value_type>)
       __glibcxx_requires_valid_range(__first, __last);
-      return std::__find_if_not(__first, __last, __pred,
-				std::__iterator_category(__first));
+      return std::__find_if_not(__first, __last, __pred);
     }
 
   /**
@@ -1784,30 +1804,39 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   // partition
 
   /// This is a helper function...
+  /// Requires __len != 0 and !__pred(*__first),
+  /// same as __stable_partition_adaptive.
   template<typename _ForwardIterator, typename _Predicate, typename _Distance>
     _ForwardIterator
     __inplace_stable_partition(_ForwardIterator __first,
-			       _ForwardIterator __last,
 			       _Predicate __pred, _Distance __len)
     {
       if (__len == 1)
-	return __pred(*__first) ? __last : __first;
+	return __first;
       _ForwardIterator __middle = __first;
       std::advance(__middle, __len / 2);
-      _ForwardIterator __begin = std::__inplace_stable_partition(__first,
-								 __middle,
-								 __pred,
-								 __len / 2);
-      _ForwardIterator __end = std::__inplace_stable_partition(__middle, __last,
-							       __pred,
-							       __len
-							       - __len / 2);
-      std::rotate(__begin, __middle, __end);
-      std::advance(__begin, std::distance(__middle, __end));
-      return __begin;
+      _ForwardIterator __left_split =
+	std::__inplace_stable_partition(__first, __pred, __len / 2);
+      // Advance past true-predicate values to satisfy this
+      // function's preconditions.
+      _Distance __right_len = __len - __len / 2;
+      _ForwardIterator __right_split =
+	std::__find_if_not_n(__middle, __right_len, __pred);
+      if (__right_len)
+	__right_split = std::__inplace_stable_partition(__middle,
+							__pred,
+							__right_len);
+      std::rotate(__left_split, __middle, __right_split);
+      std::advance(__left_split, std::distance(__middle, __right_split));
+      return __left_split;
     }
 
   /// This is a helper function...
+  /// Requires __first != __last and !__pred(*__first)
+  /// and __len == distance(__first, __last).
+  ///
+  /// !__pred(*__first) allows us to guarantee that we don't
+  /// move-assign an element onto itself.
   template<typename _ForwardIterator, typename _Pointer, typename _Predicate,
 	   typename _Distance>
     _ForwardIterator
@@ -1821,6 +1850,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	{
 	  _ForwardIterator __result1 = __first;
 	  _Pointer __result2 = __buffer;
+	  // The precondition guarantees that !__pred(*__first), so
+	  // move that element to the buffer before starting the loop.
+	  // This ensures that we only call __pred once per element.
+	  *__result2 = _GLIBCXX_MOVE(*__first);
+	  ++__result2;
+	  ++__first;
 	  for (; __first != __last; ++__first)
 	    if (__pred(*__first))
 	      {
@@ -1839,17 +1874,23 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	{
 	  _ForwardIterator __middle = __first;
 	  std::advance(__middle, __len / 2);
-	  _ForwardIterator __begin =
+	  _ForwardIterator __left_split =
 	    std::__stable_partition_adaptive(__first, __middle, __pred,
 					     __len / 2, __buffer,
 					     __buffer_size);
-	  _ForwardIterator __end =
-	    std::__stable_partition_adaptive(__middle, __last, __pred,
-					     __len - __len / 2,
-					     __buffer, __buffer_size);
-	  std::rotate(__begin, __middle, __end);
-	  std::advance(__begin, std::distance(__middle, __end));
-	  return __begin;
+	  // Advance past true-predicate values to satisfy this
+	  // function's preconditions.
+	  _Distance __right_len = __len - __len / 2;
+	  _ForwardIterator __right_split =
+	    std::__find_if_not_n(__middle, __right_len, __pred);
+	  if (__right_len)
+	    __right_split =
+	      std::__stable_partition_adaptive(__right_split, __last, __pred,
+					       __right_len,
+					       __buffer, __buffer_size);
+	  std::rotate(__left_split, __middle, __right_split);
+	  std::advance(__left_split, std::distance(__middle, __right_split));
+	  return __left_split;
 	}
     }
 
@@ -1882,6 +1923,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	    typename iterator_traits<_ForwardIterator>::value_type>)
       __glibcxx_requires_valid_range(__first, __last);
 
+      __first = std::__find_if_not(__first, __last, __pred);
+
       if (__first == __last)
 	return __first;
       else
@@ -1901,7 +1944,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 					  _DistanceType(__buf.size()));
 	else
 	  return
-	    std::__inplace_stable_partition(__first, __last, __pred,
+	    std::__inplace_stable_partition(__first, __pred,
 					 _DistanceType(__buf.requested_size()));
 	}
     }
diff --git a/libstdc++-v3/testsuite/25_algorithms/stable_partition/moveable.cc b/libstdc++-v3/testsuite/25_algorithms/stable_partition/moveable.cc
index b649b10..95d5006 100644
--- a/libstdc++-v3/testsuite/25_algorithms/stable_partition/moveable.cc
+++ b/libstdc++-v3/testsuite/25_algorithms/stable_partition/moveable.cc
@@ -35,6 +35,11 @@ const int A[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17};
 const int B[] = {2, 4, 6, 8, 10, 12, 14, 16, 1, 3, 5, 7, 9, 11, 13, 15, 17};
 const int N = sizeof(A) / sizeof(int);
 
+// Check that starting with a true predicate works too. (PR52822)
+const int A2[] = {2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17};
+const int B2[] = {2, 4, 6, 8, 10, 12, 14, 16, 3, 5, 7, 9, 11, 13, 15, 17};
+const int N2 = sizeof(A2) / sizeof(int);
+
 struct Pred
 {
   bool
@@ -42,7 +47,7 @@ struct Pred
   { return (x.val % 2) == 0; }
 };
 
-// 25.2.12 stable_partition()
+// 25.2.12 stable_partition(), starting with a false predicate.
 void
 test01()
 {
@@ -56,9 +61,24 @@ test01()
   VERIFY( std::equal(s1, s1 + N, B) );
 }
 
+// 25.2.12 stable_partition(), starting with a true predicate.
+void
+test02()
+{
+  bool test __attribute__((unused)) = true;
+
+  rvalstruct s1[N2];
+  std::copy(A2, A2 + N2, s1);
+  Container con(s1, s1 + N2);
+
+  std::stable_partition(con.begin(), con.end(), Pred());
+  VERIFY( std::equal(s1, s1 + N2, B2) );
+}
+
 int
 main()
 {
   test01();
+  test02();
   return 0;
 }
diff --git a/libstdc++-v3/testsuite/25_algorithms/stable_partition/pr52822.cc b/libstdc++-v3/testsuite/25_algorithms/stable_partition/pr52822.cc
new file mode 100644
index 0000000..c5f95f3
--- /dev/null
+++ b/libstdc++-v3/testsuite/25_algorithms/stable_partition/pr52822.cc
@@ -0,0 +1,43 @@
+// { dg-options "-std=gnu++0x" }
+
+// Copyright (C) 2012 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 Pred 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/>.
+
+// 25.2.12 [lib.alg.partitions] Partitions.
+
+#include <algorithm>
+#include <vector>
+#include <testsuite_hooks.h>
+
+bool true_vector_pred(const std::vector<int>&) { return true; }
+
+void
+test01()
+{
+  std::vector<std::vector<int> > v(1);
+  v[0].push_back(7);
+  VERIFY( v[0].size() == 1 );
+  std::stable_partition(v.begin(), v.end(), &true_vector_pred);
+  VERIFY( v[0].size() == 1 );
+}
+
+int
+main()
+{
+  test01();
+  return 0;
+}

Re: [patch] Fix PR52822 (stable_partition move-assigns object to itself) in trunk, 4.7, and 4.6

[Paolo Carlini]

Hi,
>> For the mainline/4.7 version, you want to cast __pred to bool:
>> !bool(__pred(*__first)). Also, isn't clear to me why you have __local_len in
>> __find_if_not_n instead of just working on __len (and in any case please
>> prefer just __local_len as condition instead of the redundant __local_len !=
>> 0; likewise in many other similar situations).
> I was micro-optimizing, since the compiler might think __len is
> modified in __pred if it doesn't inline enough. I've removed
> __local_len, casted pred results to bool, and avoided !=0.
>
>> Also, very minor nit, you will be touching the libstdc++-v3 Changelog thus
>> no libstdc++-v3 prefixes in the ChangeLog entry.
> Yep, done.
Great, patches are Ok and thanks a lot again for working on this. 
Please, keep an eye to any user code exercising the new bits in 
mainline/4_7-branch.

Thanks,
Paolo.

Re: [patch] Fix PR52822 (stable_partition move-assigns object to itself) in trunk, 4.7, and 4.6

[Paolo Carlini]

.. ah: remember to add "PR libstdc++/52822" at the beginning of the 
ChangeLog entry, otherwise Bugzilla will not pick your commit!

Thanks,
Paolo.