[PATCH] Use _GLIBCXX_ASSERTIONS as _GLIBCXX_DEBUG light

[François Dumont via Gcc-patches]

We have been talking for a long time of a debug mode with less impact on 
performances.

I propose to simply use the existing _GLIBCXX_ASSERTIONS macro.
    libstdc++: [_GLIBCXX_ASSERTIONS] Activate basic debug checks

    Use _GLIBCXX_ASSERTIONS as a _GLIBCXX_DEBUG light mode. When 
defined it activates
    all _GLIBCXX_DEBUG checks but skipping those requiring to loop 
through the iterator
    range unless in case of constexpr.

    libstdc++-v3/ChangeLog:

            * include/debug/debug.h [_GLIBCXX_ASSERTIONS]: Define debug 
macros non-empty.
            * include/debug/helper_functions.h: Cleanup comment about 
removed _Iter_base.
            * include/debug/functions.h (__skip_debug_runtime_check): 
New, returns false if
            _GLIBCXX_DEBUG is defined or if constant evaluated.
            (__check_sorted, __check_partitioned_lower, 
__check_partitioned_upper): Use latter.

Tested under Linux x64.

Ok to commit ?

François

diff --git a/libstdc++-v3/include/debug/debug.h b/libstdc++-v3/include/debug/debug.h
index 116f2f023e2..2e6ce1c8a93 100644
--- a/libstdc++-v3/include/debug/debug.h
+++ b/libstdc++-v3/include/debug/debug.h
@@ -61,7 +61,7 @@ namespace __gnu_debug
     struct _Safe_iterator;
 }
 
-#ifndef _GLIBCXX_DEBUG
+#ifndef _GLIBCXX_ASSERTIONS
 
 # define __glibcxx_requires_cond(_Cond,_Msg)
 # define __glibcxx_requires_valid_range(_First,_Last)
diff --git a/libstdc++-v3/include/debug/functions.h b/libstdc++-v3/include/debug/functions.h
index 6cac11f2abd..ee0eb877568 100644
--- a/libstdc++-v3/include/debug/functions.h
+++ b/libstdc++-v3/include/debug/functions.h
@@ -48,6 +48,25 @@ namespace __gnu_debug
   template<typename _Sequence>
     struct _Is_contiguous_sequence : std::__false_type { };
 
+  _GLIBCXX20_CONSTEXPR
+  inline bool
+  __skip_debug_runtime_check()
+  {
+    // We could be here while only _GLIBCXX_ASSERTIONS has been defined.
+    // In this case we skip expensive runtime checks, constexpr will still
+    // be checked.
+    return
+#ifndef _GLIBCXX_DEBUG
+# if _GLIBCXX_HAVE_BUILTIN_IS_CONSTANT_EVALUATED
+      !__builtin_is_constant_evaluated();
+# else
+      true;
+# endif
+#else
+      false;
+#endif
+  }
+
   /* Checks that [first, last) is a valid range, and then returns
    * __first. This routine is useful when we can't use a separate
    * assertion statement because, e.g., we are in a constructor.
@@ -260,8 +279,9 @@ namespace __gnu_debug
     inline bool
     __check_sorted(const _InputIterator& __first, const _InputIterator& __last)
     {
-      return __check_sorted_aux(__first, __last,
-				std::__iterator_category(__first));
+      return __skip_debug_runtime_check()
+	|| __check_sorted_aux(__first, __last,
+			      std::__iterator_category(__first));
     }
 
   template<typename _InputIterator, typename _Predicate>
@@ -270,8 +290,9 @@ namespace __gnu_debug
     __check_sorted(const _InputIterator& __first, const _InputIterator& __last,
                    _Predicate __pred)
     {
-      return __check_sorted_aux(__first, __last, __pred,
-				std::__iterator_category(__first));
+      return __skip_debug_runtime_check()
+	|| __check_sorted_aux(__first, __last, __pred,
+			      std::__iterator_category(__first));
     }
 
   template<typename _InputIterator>
@@ -351,6 +372,9 @@ namespace __gnu_debug
     __check_partitioned_lower(_ForwardIterator __first,
 			      _ForwardIterator __last, const _Tp& __value)
     {
+      if (__skip_debug_runtime_check())
+	return true;
+
       while (__first != __last && *__first < __value)
 	++__first;
       if (__first != __last)
@@ -368,6 +392,9 @@ namespace __gnu_debug
     __check_partitioned_upper(_ForwardIterator __first,
 			      _ForwardIterator __last, const _Tp& __value)
     {
+      if (__skip_debug_runtime_check())
+	return true;
+
       while (__first != __last && !(__value < *__first))
 	++__first;
       if (__first != __last)
@@ -387,6 +414,9 @@ namespace __gnu_debug
 			      _ForwardIterator __last, const _Tp& __value,
 			      _Pred __pred)
     {
+      if (__skip_debug_runtime_check())
+	return true;
+
       while (__first != __last && bool(__pred(*__first, __value)))
 	++__first;
       if (__first != __last)
@@ -405,6 +435,9 @@ namespace __gnu_debug
 			      _ForwardIterator __last, const _Tp& __value,
 			      _Pred __pred)
     {
+      if (__skip_debug_runtime_check())
+	return true;
+
       while (__first != __last && !bool(__pred(__value, *__first)))
 	++__first;
       if (__first != __last)
diff --git a/libstdc++-v3/include/debug/helper_functions.h b/libstdc++-v3/include/debug/helper_functions.h
index c0144ced979..587eba2f3e5 100644
--- a/libstdc++-v3/include/debug/helper_functions.h
+++ b/libstdc++-v3/include/debug/helper_functions.h
@@ -30,8 +30,8 @@
 #define _GLIBCXX_DEBUG_HELPER_FUNCTIONS_H 1
 
 #include <bits/move.h>				// for __addressof
-#include <bits/stl_iterator_base_types.h>	// for iterator_traits,
-						// categories and _Iter_base
+#include <bits/stl_iterator_base_types.h>	// for iterator_traits and
+						// categories
 #include <bits/cpp_type_traits.h>		// for __is_integer
 
 #include <bits/stl_pair.h>			// for pair