[PATCH] Fix algo constexpr tests in Debug mode

["François Dumont" <frs.dumont@gmail.com>]

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Here is what I just commited.

I try to use the asm trick in the _GLIBCXX_DEBUG_VERIFY_COND_AT but 
didn't notice any enhancement. So for now I kept my solution to just 
have a non-constexpr call compiler error.

I fix my patch to use __builtin_is_constant_evaluated rather than 
std::is_constant_evaluated in __valid_range.

     * include/bits/stl_algobase.h (__memmove): Return _Tp*.
     (__memmove): Loop as long as __n is not 0.
     (__copy_move<>::__copy_m): Likewise.
     (__copy_move_backward<>::__copy_move_b): Likewise.
     * testsuite/25_algorithms/copy/constexpr.cc: Add check on copied 
values.
     * testsuite/25_algorithms/copy_backward/constexpr.cc: Likewise.
     * testsuite/25_algorithms/copy/constexpr_neg.cc: New.
     * testsuite/25_algorithms/copy_backward/constexpr.cc: New.

     * include/debug/forward_list
(_Sequence_traits<__debug::forward_list<>>::_S_size): Returns __dp_sign
     distance when not empty.
     * include/debug/list
     (_Sequence_traits<__debug::list<>>::_S_size): Likewise.
     * include/debug/helper_functions.h (__dp_sign_max_size): New
     _Distance_precision enum entry.
     * include/debug/safe_iterator.h
     (__copy_move_a(_II, _II, const _Safe_iterator<>&)): Check for output
     iterator _M_can_advance as soon as input range distance precision is
     strictly higher than __dp_size.
     (__copy_move_a(const _Safe_iterator<>&, const _Safe_iterator<>&,
     const _Safe_iterator<>&)): Likewise.
     (__copy_move_backward_a(_II, _II, const _Safe_iterator<>&)): Likewise.
     (__copy_move_backward_a(const _Safe_iterator<>&,
     const _Safe_iterator<>&, const _Safe_iterator<>&)): Likewise.
     (__equal_aux(_II, _II, const _Safe_iterator<>&)): Likewise.
     (__equal_aux(const _Safe_iterator<>&,
     const _Safe_iterator<>&, const _Safe_iterator<>&)): Likewise.

François

On 9/27/19 6:45 PM, Jonathan Wakely wrote:
> On 27/09/19 18:24 +0200, François Dumont wrote:
>> On 9/27/19 2:11 PM, Jonathan Wakely wrote:
>>> On 19/09/19 22:27 +0200, François Dumont wrote:
>>>> Hi
>>>>
>>>>     I start working on making recently added constexpr tests to 
>>>> work in Debug mode.
>>>
>>> The attached patch seems to be necessary for that, right?
>>>
>>>
>> On my side I had done this, almost the same.
>>
>> For the moment there is a FIXME in macros.h to find out how to 
>> generate a nice compilation error when the condition is not meant.
>>
>> static_assert can't be called in this context, too bad.
>>
>> I also try to define a function with a 
>> __attribute__((__error__("because"))) attribute. But when I make it 
>> constexpr gcc complains about missing definition. When I provide a 
>> definition gcc complains that this attribute must be on a 
>> declaration. And when I split declaration and definition gcc does not 
>> produce the expected compilation error.
>
> Yes, I've tried similar things without success.
>
>> Unless you have the solution I consider that we need help from the 
>> front-end.
>>
>> For the moment if Debug mode finds a problem it will be reported as 
>> _M_error function not being constexpr !
>
> A reasonable workaround is to do:
>
> #ifdef _GLIBCXX_HAVE_BUILTIN_IS_CONSTANT_EVALUATED
>  if (__builtin_is_constant_evaluated())
>    asm("Debug Mode assertion failed");
>  else
> #endif
>  if (!(Cond))
>    __gnu_debug::_Error_formatter::...
>
> The builtin is available even for C++98, whereas
> std::is_constant_evaluated() is only available for C++20.
>
> This produces errors that include lines like:
>
> asm.cc:12:17:   in ‘constexpr’ expansion of ‘f(-1)’
> asm.cc:4:7: error: inline assembly is not a constant expression
>    4 |       asm("debug mode assertion failed");
>      |       ^~~
> asm.cc:8:3: note: in expansion of macro ‘CHECK’
>    8 |   _GLIBCXX_ASSERT(i > 0);
>      |   ^~~~~
> asm.cc:4:7: note: only unevaluated inline assembly is allowed in a 
> ‘constexpr’ function in C++2a
>    4 |       asm("debug mode assertion failed");
>      |       ^~~
> asm.cc:8:3: note: in expansion of macro ‘CHECK’
>    8 |   CHECK(i > 0);
>      |   ^~~~~
>
> It's not ideal, but it does show the failed condition and the text
> "debug mode assertion failed" (or whatever message you choose to use
> there).
>
>
>


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diff --git a/libstdc++-v3/include/bits/stl_algo.h b/libstdc++-v3/include/bits/stl_algo.h
index a672f8b2b39..f25b8b76df6 100644
--- a/libstdc++-v3/include/bits/stl_algo.h
+++ b/libstdc++-v3/include/bits/stl_algo.h
@@ -5054,8 +5054,8 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
    *  @param  __last1   Another iterator.
    *  @param  __last2   Another iterator.
    *  @param  __result  An iterator pointing to the end of the merged range.
-   *  @return         An iterator pointing to the first element <em>not less
-   *                  than</em> @e val.
+   *  @return   An output iterator equal to @p __result + (__last1 - __first1)
+   *            + (__last2 - __first2).
    *
    *  Merges the ranges @p [__first1,__last1) and @p [__first2,__last2) into
    *  the sorted range @p [__result, __result + (__last1-__first1) +
@@ -5102,8 +5102,8 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
    *  @param  __last2   Another iterator.
    *  @param  __result  An iterator pointing to the end of the merged range.
    *  @param  __comp    A functor to use for comparisons.
-   *  @return         An iterator pointing to the first element "not less
-   *                  than" @e val.
+   *  @return   An output iterator equal to @p __result + (__last1 - __first1)
+   *            + (__last2 - __first2).
    *
    *  Merges the ranges @p [__first1,__last1) and @p [__first2,__last2) into
    *  the sorted range @p [__result, __result + (__last1-__first1) +
diff --git a/libstdc++-v3/include/debug/functions.h b/libstdc++-v3/include/debug/functions.h
index f87838692c6..8c385b87244 100644
--- a/libstdc++-v3/include/debug/functions.h
+++ b/libstdc++-v3/include/debug/functions.h
@@ -219,6 +219,7 @@ namespace __gnu_debug
   // Can't check if an input iterator sequence is sorted, because we
   // can't step through the sequence.
   template<typename _InputIterator>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     __check_sorted_aux(const _InputIterator&, const _InputIterator&,
                        std::input_iterator_tag)
@@ -227,6 +228,7 @@ namespace __gnu_debug
   // Can verify if a forward iterator sequence is in fact sorted using
   // std::__is_sorted
   template<typename _ForwardIterator>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     __check_sorted_aux(_ForwardIterator __first, _ForwardIterator __last,
                        std::forward_iterator_tag)
@@ -245,6 +247,7 @@ namespace __gnu_debug
   // Can't check if an input iterator sequence is sorted, because we can't step
   // through the sequence.
   template<typename _InputIterator, typename _Predicate>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     __check_sorted_aux(const _InputIterator&, const _InputIterator&,
                        _Predicate, std::input_iterator_tag)
@@ -253,6 +256,7 @@ namespace __gnu_debug
   // Can verify if a forward iterator sequence is in fact sorted using
   // std::__is_sorted
   template<typename _ForwardIterator, typename _Predicate>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     __check_sorted_aux(_ForwardIterator __first, _ForwardIterator __last,
                        _Predicate __pred, std::forward_iterator_tag)
@@ -270,31 +274,26 @@ namespace __gnu_debug
 
   // Determine if a sequence is sorted.
   template<typename _InputIterator>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     __check_sorted(const _InputIterator& __first, const _InputIterator& __last)
     {
-      // Verify that the < operator for elements in the sequence is a
-      // StrictWeakOrdering by checking that it is irreflexive.
-      __glibcxx_assert(__first == __last || !(*__first < *__first));
-
       return __check_sorted_aux(__first, __last,
 				std::__iterator_category(__first));
     }
 
   template<typename _InputIterator, typename _Predicate>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     __check_sorted(const _InputIterator& __first, const _InputIterator& __last,
                    _Predicate __pred)
     {
-      // Verify that the predicate is StrictWeakOrdering by checking that it
-      // is irreflexive.
-      __glibcxx_assert(__first == __last || !__pred(*__first, *__first));
-
       return __check_sorted_aux(__first, __last, __pred,
 				std::__iterator_category(__first));
     }
 
   template<typename _InputIterator>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     __check_sorted_set_aux(const _InputIterator& __first,
 			   const _InputIterator& __last,
@@ -302,6 +301,7 @@ namespace __gnu_debug
     { return __check_sorted(__first, __last); }
 
   template<typename _InputIterator>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     __check_sorted_set_aux(const _InputIterator&,
 			   const _InputIterator&,
@@ -309,6 +309,7 @@ namespace __gnu_debug
     { return true; }
 
   template<typename _InputIterator, typename _Predicate>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     __check_sorted_set_aux(const _InputIterator& __first,
 			   const _InputIterator& __last,
@@ -316,6 +317,7 @@ namespace __gnu_debug
     { return __check_sorted(__first, __last, __pred); }
 
   template<typename _InputIterator, typename _Predicate>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     __check_sorted_set_aux(const _InputIterator&,
 			   const _InputIterator&, _Predicate,
@@ -324,6 +326,7 @@ namespace __gnu_debug
 
   // ... special variant used in std::merge, std::includes, std::set_*.
   template<typename _InputIterator1, typename _InputIterator2>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     __check_sorted_set(const _InputIterator1& __first,
 		       const _InputIterator1& __last,
@@ -341,6 +344,7 @@ namespace __gnu_debug
 
   template<typename _InputIterator1, typename _InputIterator2,
 	   typename _Predicate>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     __check_sorted_set(const _InputIterator1& __first,
 		       const _InputIterator1& __last,
@@ -360,6 +364,7 @@ namespace __gnu_debug
   // 270. Binary search requirements overly strict
   // Determine if a sequence is partitioned w.r.t. this element.
   template<typename _ForwardIterator, typename _Tp>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     __check_partitioned_lower(_ForwardIterator __first,
 			      _ForwardIterator __last, const _Tp& __value)
@@ -376,6 +381,7 @@ namespace __gnu_debug
     }
 
   template<typename _ForwardIterator, typename _Tp>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     __check_partitioned_upper(_ForwardIterator __first,
 			      _ForwardIterator __last, const _Tp& __value)
@@ -393,6 +399,7 @@ namespace __gnu_debug
 
   // Determine if a sequence is partitioned w.r.t. this element.
   template<typename _ForwardIterator, typename _Tp, typename _Pred>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     __check_partitioned_lower(_ForwardIterator __first,
 			      _ForwardIterator __last, const _Tp& __value,
@@ -410,6 +417,7 @@ namespace __gnu_debug
     }
 
   template<typename _ForwardIterator, typename _Tp, typename _Pred>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     __check_partitioned_upper(_ForwardIterator __first,
 			      _ForwardIterator __last, const _Tp& __value,
@@ -435,35 +443,41 @@ namespace __gnu_debug
 
     template<typename _It,
 	     typename = decltype(__deref<_It>() < __deref<_It>())>
+      _GLIBCXX20_CONSTEXPR
       static bool
       _S_is_valid(_It __it)
       { return !(*__it < *__it); }
 
     // Fallback method if operator doesn't exist.
     template<typename... _Args>
+      _GLIBCXX20_CONSTEXPR
       static bool
       _S_is_valid(_Args...)
       { return true; }
 
     template<typename _It, typename _Pred, typename
 	= decltype(std::declval<_Pred>()(__deref<_It>(), __deref<_It>()))>
+      _GLIBCXX20_CONSTEXPR
       static bool
       _S_is_valid_pred(_It __it, _Pred __pred)
       { return !__pred(*__it, *__it); }
 
     // Fallback method if predicate can't be invoked.
     template<typename... _Args>
+      _GLIBCXX20_CONSTEXPR
       static bool
       _S_is_valid_pred(_Args...)
       { return true; }
   };
 
   template<typename _Iterator>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     __is_irreflexive(_Iterator __it)
     { return _Irreflexive_checker::_S_is_valid(__it); }
 
   template<typename _Iterator, typename _Pred>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     __is_irreflexive_pred(_Iterator __it, _Pred __pred)
     { return _Irreflexive_checker::_S_is_valid_pred(__it, __pred); }
diff --git a/libstdc++-v3/include/debug/helper_functions.h b/libstdc++-v3/include/debug/helper_functions.h
index 9429bb90a55..5a920bb9a6f 100644
--- a/libstdc++-v3/include/debug/helper_functions.h
+++ b/libstdc++-v3/include/debug/helper_functions.h
@@ -88,12 +88,14 @@ namespace __gnu_debug
    *	precision.
   */
   template<typename _Iterator>
+    _GLIBCXX_CONSTEXPR
     inline typename _Distance_traits<_Iterator>::__type
     __get_distance(_Iterator __lhs, _Iterator __rhs,
 		   std::random_access_iterator_tag)
     { return std::make_pair(__rhs - __lhs, __dp_exact); }
 
   template<typename _Iterator>
+    _GLIBCXX_CONSTEXPR
     inline typename _Distance_traits<_Iterator>::__type
     __get_distance(_Iterator __lhs, _Iterator __rhs,
 		   std::input_iterator_tag)
@@ -105,6 +107,7 @@ namespace __gnu_debug
     }
 
   template<typename _Iterator>
+    _GLIBCXX_CONSTEXPR
     inline typename _Distance_traits<_Iterator>::__type
     __get_distance(_Iterator __lhs, _Iterator __rhs)
     { return __get_distance(__lhs, __rhs, std::__iterator_category(__lhs)); }
@@ -114,6 +117,13 @@ namespace __gnu_debug
    *  iterators.
   */
   template<typename _Integral>
+    _GLIBCXX_CONSTEXPR
+    inline bool
+    __valid_range_aux(_Integral, _Integral, std::__true_type)
+    { return true; }
+
+  template<typename _Integral>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     __valid_range_aux(_Integral, _Integral,
 		      typename _Distance_traits<_Integral>::__type& __dist,
@@ -123,10 +133,35 @@ namespace __gnu_debug
       return true;
     }
 
+  template<typename _InputIterator>
+    _GLIBCXX_CONSTEXPR
+    inline bool
+    __valid_range_aux(_InputIterator __first, _InputIterator __last,
+		      std::input_iterator_tag)
+    { return true; }
+
+  template<typename _InputIterator>
+    _GLIBCXX_CONSTEXPR
+    inline bool
+    __valid_range_aux(_InputIterator __first, _InputIterator __last,
+		      std::random_access_iterator_tag)
+    { return __first <= __last; }
+
   /** We have iterators, so figure out what kind of iterators they are
    *  to see if we can check the range ahead of time.
   */
   template<typename _InputIterator>
+    _GLIBCXX_CONSTEXPR
+    inline bool
+    __valid_range_aux(_InputIterator __first, _InputIterator __last,
+		      std::__false_type)
+    {
+      return __valid_range_aux(__first, __last,
+			       std::__iterator_category(__first));
+    }
+
+  template<typename _InputIterator>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     __valid_range_aux(_InputIterator __first, _InputIterator __last,
 		      typename _Distance_traits<_InputIterator>::__type& __dist,
@@ -157,10 +192,16 @@ namespace __gnu_debug
    *  otherwise.
   */
   template<typename _InputIterator>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     __valid_range(_InputIterator __first, _InputIterator __last,
 		  typename _Distance_traits<_InputIterator>::__type& __dist)
     {
+#ifdef __cpp_lib_is_constant_evaluated
+      if (std::is_constant_evaluated())
+	// Detected by the compiler directly.
+	return true;
+#endif
       typedef typename std::__is_integer<_InputIterator>::__type _Integral;
       return __valid_range_aux(__first, __last, __dist, _Integral());
     }
@@ -180,11 +221,17 @@ namespace __gnu_debug
 #endif
 
   template<typename _InputIterator>
+    _GLIBCXX_CONSTEXPR
     inline bool
     __valid_range(_InputIterator __first, _InputIterator __last)
     {
-      typename _Distance_traits<_InputIterator>::__type __dist;
-      return __valid_range(__first, __last, __dist);
+#ifdef _GLIBCXX_HAVE_BUILTIN_IS_CONSTANT_EVALUATED
+      if (__builtin_is_constant_evaluated())
+	// Detected by the compiler directly.
+	return true;
+#endif
+      typedef typename std::__is_integer<_InputIterator>::__type _Integral;
+      return __valid_range_aux(__first, __last, _Integral());
     }
 
   template<typename _Iterator, typename _Sequence, typename _Category>
@@ -201,6 +248,7 @@ namespace __gnu_debug
 
   // Fallback method, always ok.
   template<typename _InputIterator, typename _Size>
+    _GLIBCXX_CONSTEXPR
     inline bool
     __can_advance(_InputIterator, _Size)
     { return true; }
@@ -218,6 +266,7 @@ namespace __gnu_debug
    *  thanks to the < operator.
    */
   template<typename _Iterator>
+    _GLIBCXX_CONSTEXPR
     inline _Iterator
     __base(_Iterator __it)
     { return __it; }
diff --git a/libstdc++-v3/include/debug/macros.h b/libstdc++-v3/include/debug/macros.h
index b598192cb3e..97e54fd8390 100644
--- a/libstdc++-v3/include/debug/macros.h
+++ b/libstdc++-v3/include/debug/macros.h
@@ -38,10 +38,20 @@
  * the user error and where the error is reported.
  *
  */
-#define _GLIBCXX_DEBUG_VERIFY_COND_AT(_Cond,_ErrMsg,_File,_Line,_Func)	\
+#if 0 /* defined _GLIBCXX_HAVE_BUILTIN_IS_CONSTANT_EVALUATED */
+# define _GLIBCXX_DEBUG_VERIFY_COND_AT(_Cond,_ErrMsg,_File,_Line,_Func)	\
+  if (__builtin_is_constant_evaluated())				\
+    /* FIXME: Compilation error here when !_Cond. */			\
+    break;								\
   if (! (_Cond))							\
     __gnu_debug::_Error_formatter::_S_at(_File, _Line, _Func)		\
       ._ErrMsg._M_error()
+#else
+# define _GLIBCXX_DEBUG_VERIFY_COND_AT(_Cond,_ErrMsg,_File,_Line,_Func)	\
+  if (! (_Cond))							\
+    __gnu_debug::_Error_formatter::_S_at(_File, _Line, _Func)		\
+      ._ErrMsg._M_error()
+#endif
 
 #define _GLIBCXX_DEBUG_VERIFY_AT_F(_Cond,_ErrMsg,_File,_Line,_Func)	\
   do									\
@@ -291,9 +301,43 @@ _GLIBCXX_DEBUG_VERIFY(! this->empty(),					\
 		      _M_message(__gnu_debug::__msg_empty)	        \
                       ._M_sequence(*this, "this"))
 
+// Verify that a predicate is irreflexive
+#define __glibcxx_check_irreflexive(_First,_Last)			\
+  _GLIBCXX_DEBUG_VERIFY(_First == _Last || !(*_First < *_First),	\
+			_M_message(__gnu_debug::__msg_irreflexive_ordering) \
+			._M_iterator_value_type(_First, "< operator type"))
+
+#if __cplusplus >= 201103L
+# define __glibcxx_check_irreflexive2(_First,_Last)			\
+  _GLIBCXX_DEBUG_VERIFY(_First == _Last					\
+			|| __gnu_debug::__is_irreflexive(_First),	\
+			_M_message(__gnu_debug::__msg_irreflexive_ordering) \
+			._M_iterator_value_type(_First, "< operator type"))
+#else
+# define __glibcxx_check_irreflexive2(_First,_Last)
+#endif
+
+#define __glibcxx_check_irreflexive_pred(_First,_Last,_Pred)		\
+  _GLIBCXX_DEBUG_VERIFY(_First == _Last || !_Pred(*_First, *_First),	\
+			_M_message(__gnu_debug::__msg_irreflexive_ordering) \
+			._M_instance(_Pred, "functor")			\
+			._M_iterator_value_type(_First, "ordered type"))
+
+#if __cplusplus >= 201103L
+# define __glibcxx_check_irreflexive_pred2(_First,_Last,_Pred)		\
+  _GLIBCXX_DEBUG_VERIFY(_First == _Last					\
+			||__gnu_debug::__is_irreflexive_pred(_First, _Pred), \
+			_M_message(__gnu_debug::__msg_irreflexive_ordering) \
+			._M_instance(_Pred, "functor")			\
+			._M_iterator_value_type(_First, "ordered type"))
+#else
+# define __glibcxx_check_irreflexive_pred2(_First,_Last,_Pred)
+#endif
+
 // Verify that the iterator range [_First, _Last) is sorted
 #define __glibcxx_check_sorted(_First,_Last)				\
 __glibcxx_check_valid_range(_First,_Last);				\
+__glibcxx_check_irreflexive(_First,_Last);				\
  _GLIBCXX_DEBUG_VERIFY(__gnu_debug::__check_sorted(			\
 			__gnu_debug::__base(_First),			\
 			__gnu_debug::__base(_Last)),			\
@@ -305,6 +349,7 @@ __glibcxx_check_valid_range(_First,_Last);				\
     predicate _Pred. */
 #define __glibcxx_check_sorted_pred(_First,_Last,_Pred)			\
 __glibcxx_check_valid_range(_First,_Last);				\
+__glibcxx_check_irreflexive_pred(_First,_Last,_Pred);			\
 _GLIBCXX_DEBUG_VERIFY(__gnu_debug::__check_sorted(			\
 			__gnu_debug::__base(_First),			\
 			__gnu_debug::__base(_Last), _Pred),		\
@@ -423,37 +468,4 @@ _GLIBCXX_DEBUG_VERIFY(_This.get_allocator() == _Other.get_allocator(),	\
 #define __glibcxx_check_string_len(_String,_Len) \
   _GLIBCXX_DEBUG_PEDASSERT(_String != 0 || _Len == 0)
 
-// Verify that a predicate is irreflexive
-#define __glibcxx_check_irreflexive(_First,_Last)			\
-  _GLIBCXX_DEBUG_VERIFY(_First == _Last || !(*_First < *_First),	\
-			_M_message(__gnu_debug::__msg_irreflexive_ordering) \
-			._M_iterator_value_type(_First, "< operator type"))
-
-#if __cplusplus >= 201103L
-# define __glibcxx_check_irreflexive2(_First,_Last)			\
-  _GLIBCXX_DEBUG_VERIFY(_First == _Last					\
-			|| __gnu_debug::__is_irreflexive(_First),	\
-			_M_message(__gnu_debug::__msg_irreflexive_ordering) \
-			._M_iterator_value_type(_First, "< operator type"))
-#else
-# define __glibcxx_check_irreflexive2(_First,_Last)
-#endif
-
-#define __glibcxx_check_irreflexive_pred(_First,_Last,_Pred)		\
-  _GLIBCXX_DEBUG_VERIFY(_First == _Last	|| !_Pred(*_First, *_First),		\
-			_M_message(__gnu_debug::__msg_irreflexive_ordering) \
-			._M_instance(_Pred, "functor")			\
-			._M_iterator_value_type(_First, "ordered type"))
-
-#if __cplusplus >= 201103L
-# define __glibcxx_check_irreflexive_pred2(_First,_Last,_Pred)		\
-  _GLIBCXX_DEBUG_VERIFY(_First == _Last					\
-			||__gnu_debug::__is_irreflexive_pred(_First, _Pred), \
-			_M_message(__gnu_debug::__msg_irreflexive_ordering) \
-			._M_instance(_Pred, "functor")			\
-			._M_iterator_value_type(_First, "ordered type"))
-#else
-# define __glibcxx_check_irreflexive_pred2(_First,_Last,_Pred)
-#endif
-
 #endif
diff --git a/libstdc++-v3/testsuite/25_algorithms/binary_search/constexpr.cc b/libstdc++-v3/testsuite/25_algorithms/binary_search/constexpr.cc
index 8406b3d147f..205a96a223b 100644
--- a/libstdc++-v3/testsuite/25_algorithms/binary_search/constexpr.cc
+++ b/libstdc++-v3/testsuite/25_algorithms/binary_search/constexpr.cc
@@ -29,7 +29,7 @@ test()
   const auto out4 = std::binary_search(ca0.begin(), ca0.end(), 5);
 
   const auto out5 = std::binary_search(ca0.begin(), ca0.end(), 5,
-				       std::equal_to<int>());
+				       std::less<int>());
 
   return true;
 }
diff --git a/libstdc++-v3/testsuite/25_algorithms/is_sorted/constexpr.cc b/libstdc++-v3/testsuite/25_algorithms/is_sorted/constexpr.cc
index 0be2f5fed62..f549b3d9307 100644
--- a/libstdc++-v3/testsuite/25_algorithms/is_sorted/constexpr.cc
+++ b/libstdc++-v3/testsuite/25_algorithms/is_sorted/constexpr.cc
@@ -26,7 +26,7 @@ constexpr std::array<int, 12> ca0{{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11}};
 constexpr auto outv = std::is_sorted(ca0.begin(), ca0.end());
 
 constexpr auto outw = std::is_sorted(ca0.begin(), ca0.end(),
-				     std::equal_to<int>());
+				     std::less<int>());
 
 constexpr bool
 test()
diff --git a/libstdc++-v3/testsuite/25_algorithms/merge/constexpr.cc b/libstdc++-v3/testsuite/25_algorithms/merge/constexpr.cc
index cc8d3755da4..794453dd50c 100644
--- a/libstdc++-v3/testsuite/25_algorithms/merge/constexpr.cc
+++ b/libstdc++-v3/testsuite/25_algorithms/merge/constexpr.cc
@@ -26,7 +26,7 @@ test()
 {
   constexpr std::array<int, 12> ca0{{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11}};
   constexpr std::array<int, 12> cas{{3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}};
-  constexpr std::array<int, 3> camm{{-4, -5, -6}};
+  constexpr std::array<int, 3> camm{{-6, -5, -4}};
   std::array<int, 24> out0{{0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0}};
 
   const auto outdd = std::merge(ca0.begin(), ca0.end(),
@@ -34,7 +34,7 @@ test()
 
   const auto outee = std::merge(ca0.begin(), ca0.end(),
 				camm.begin(), camm.end(), out0.begin(),
-				[](int i, int j){ return i < -j; });
+				[](int i, int j){ return i < j; });
 
   return true;
 }