diff mbox

[libstdc++/61347] std::distance(list.first(),list.end()) in O(1)

Message ID alpine.DEB.2.02.1504140951460.27632@stedding.saclay.inria.fr
State New
Headers show

Commit Message

Marc Glisse April 14, 2015, 8:24 a.m. UTC
On Mon, 13 Apr 2015, Jonathan Wakely wrote:

> I don't have a preference, but I think the forward declarations should
> work without problems. <list> includes bits/stl_iterator_base_funcs.h
> so if the forward declarations didn't match the definitions for some
> reason we'd know right away.

Here is a new version that also passes the tests. I guess we will have 
plenty of time during stage1 to notice if it causes problems. We could 
probably move the new definitions of __distance to 
bits/stl_iterator_base_funcs.h, I don't have a clear preference.

2015-04-14  Marc Glisse  <marc.glisse@inria.fr>

 	PR libstdc++/61347
 	* include/bits/stl_iterator_base_funcs.h (_List_iterator,
 	_List_const_iterator): Declare.
 	(__distance): Declare new overloads for _List_iterator and
 	_List_const_iterator.
 	* include/bits/stl_list.h (__distance): New overloads for
 	_List_iterator and _List_const_iterator.
 	* testsuite/23_containers/list/61347.cc: New testcase.

Comments

Jonathan Wakely April 14, 2015, 9:32 a.m. UTC | #1
On 14/04/15 10:24 +0200, Marc Glisse wrote:
>On Mon, 13 Apr 2015, Jonathan Wakely wrote:
>
>>I don't have a preference, but I think the forward declarations should
>>work without problems. <list> includes bits/stl_iterator_base_funcs.h
>>so if the forward declarations didn't match the definitions for some
>>reason we'd know right away.
>
>Here is a new version that also passes the tests. I guess we will have 
>plenty of time during stage1 to notice if it causes problems. We could 
>probably move the new definitions of __distance to 
>bits/stl_iterator_base_funcs.h, I don't have a clear preference.

Seems like a great start and we can improve it later if needed.

OK for trunk, thanks.

We should also look into applying the same optimisation for
__gnu_debug::list, as long as we don't lose the ability to detect
errors like std::distance(l1.begin(), l2.end()) where &l1 != &l2.
diff mbox

Patch

Index: include/bits/stl_iterator_base_funcs.h
===================================================================
--- include/bits/stl_iterator_base_funcs.h	(revision 222076)
+++ include/bits/stl_iterator_base_funcs.h	(working copy)
@@ -59,20 +59,26 @@ 
 #ifndef _STL_ITERATOR_BASE_FUNCS_H
 #define _STL_ITERATOR_BASE_FUNCS_H 1
 
 #pragma GCC system_header
 
 #include <bits/concept_check.h>
 #include <debug/debug.h>
 
 namespace std _GLIBCXX_VISIBILITY(default)
 {
+_GLIBCXX_BEGIN_NAMESPACE_CONTAINER
+  // Forward declaration for the overloads of __distance.
+  template <typename> struct _List_iterator;
+  template <typename> struct _List_const_iterator;
+_GLIBCXX_END_NAMESPACE_CONTAINER
+
 _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   template<typename _InputIterator>
     inline typename iterator_traits<_InputIterator>::difference_type
     __distance(_InputIterator __first, _InputIterator __last,
                input_iterator_tag)
     {
       // concept requirements
       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
 
@@ -89,20 +95,35 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
     inline typename iterator_traits<_RandomAccessIterator>::difference_type
     __distance(_RandomAccessIterator __first, _RandomAccessIterator __last,
                random_access_iterator_tag)
     {
       // concept requirements
       __glibcxx_function_requires(_RandomAccessIteratorConcept<
 				  _RandomAccessIterator>)
       return __last - __first;
     }
 
+#if _GLIBCXX_USE_CXX11_ABI
+  // Forward declaration because of the qualified call in distance.
+  template<typename _Tp>
+    ptrdiff_t
+    __distance(_GLIBCXX_STD_C::_List_iterator<_Tp>,
+	       _GLIBCXX_STD_C::_List_iterator<_Tp>,
+	       input_iterator_tag);
+
+  template<typename _Tp>
+    ptrdiff_t
+    __distance(_GLIBCXX_STD_C::_List_const_iterator<_Tp>,
+	       _GLIBCXX_STD_C::_List_const_iterator<_Tp>,
+	       input_iterator_tag);
+#endif
+
   /**
    *  @brief A generalization of pointer arithmetic.
    *  @param  __first  An input iterator.
    *  @param  __last  An input iterator.
    *  @return  The distance between them.
    *
    *  Returns @c n such that __first + n == __last.  This requires
    *  that @p __last must be reachable from @p __first.  Note that @c
    *  n may be negative.
    *
Index: include/bits/stl_list.h
===================================================================
--- include/bits/stl_list.h	(revision 222076)
+++ include/bits/stl_list.h	(working copy)
@@ -1861,13 +1861,52 @@  _GLIBCXX_END_NAMESPACE_CXX11
     operator>=(const list<_Tp, _Alloc>& __x, const list<_Tp, _Alloc>& __y)
     { return !(__x < __y); }
 
   /// See std::list::swap().
   template<typename _Tp, typename _Alloc>
     inline void
     swap(list<_Tp, _Alloc>& __x, list<_Tp, _Alloc>& __y)
     { __x.swap(__y); }
 
 _GLIBCXX_END_NAMESPACE_CONTAINER
+
+#if _GLIBCXX_USE_CXX11_ABI
+_GLIBCXX_BEGIN_NAMESPACE_VERSION
+
+  // Detect when distance is used to compute the size of the whole list.
+  template<typename _Tp>
+    inline ptrdiff_t
+    __distance(_GLIBCXX_STD_C::_List_iterator<_Tp> __first,
+	       _GLIBCXX_STD_C::_List_iterator<_Tp> __last,
+	       input_iterator_tag __tag)
+    {
+      typedef _GLIBCXX_STD_C::_List_const_iterator<_Tp> _CIter;
+      return std::__distance(_CIter(__first), _CIter(__last), __tag);
+    }
+
+  template<typename _Tp>
+    inline ptrdiff_t
+    __distance(_GLIBCXX_STD_C::_List_const_iterator<_Tp> __first,
+	       _GLIBCXX_STD_C::_List_const_iterator<_Tp> __last,
+	       input_iterator_tag)
+    {
+      typedef _GLIBCXX_STD_C::_List_node<size_t> _Sentinel;
+      _GLIBCXX_STD_C::_List_const_iterator<_Tp> __beyond = __last;
+      ++__beyond;
+      bool __whole = __first == __beyond;
+      if (__builtin_constant_p (__whole) && __whole)
+	return static_cast<const _Sentinel*>(__last._M_node)->_M_data;
+
+      ptrdiff_t __n = 0;
+      while (__first != __last)
+	{
+	  ++__first;
+	  ++__n;
+	}
+      return __n;
+    }
+
+_GLIBCXX_END_NAMESPACE_VERSION
+#endif
 } // namespace std
 
 #endif /* _STL_LIST_H */
Index: testsuite/23_containers/list/61347.cc
===================================================================
--- testsuite/23_containers/list/61347.cc	(revision 0)
+++ testsuite/23_containers/list/61347.cc	(working copy)
@@ -0,0 +1,49 @@ 
+// { dg-options "-std=gnu++11 -O2 -D_GLIBCXX_USE_CXX11_ABI" }
+
+// Copyright (C) 2015 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 <list>
+#include <iterator>
+#include <testsuite_hooks.h>
+
+__attribute__((__noinline__, __noclone__))
+void testm(std::list<short>& l)
+{
+  bool b = std::distance(l.begin(), l.end()) == l.size();
+  VERIFY( __builtin_constant_p(b) );
+  VERIFY( b );
+}
+
+__attribute__((__noinline__, __noclone__))
+void testc(const std::list<short>& l)
+{
+  bool b = std::distance(l.begin(), l.end()) == l.size();
+  VERIFY( __builtin_constant_p(b) );
+  VERIFY( b );
+}
+
+int main()
+{
+  bool test __attribute__((unused)) = true;
+
+#if _GLIBCXX_USE_DUAL_ABI
+  std::list<short> l;
+  testm(l);
+  testc(l);
+#endif
+}