From: Jonathan Wakely <jwakely@redhat.com>
To: libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org
Subject: [PATCH] Improvements to valid range checks in debug mode
Date: Thu, 27 Feb 2020 13:06:00 -0000 [thread overview]
Message-ID: <20200227130636.GV9441@redhat.com> (raw)
[-- Attachment #1: Type: text/plain, Size: 298 bytes --]
These should wait for stage 1 but I'm posting them now for comment.
With the change to __gnu_debug::__valid_range we now get a debug
assertion for:
std::string s;
std::min_element(std::string::iterator{}, s.end());
where previously it would just crash with undefined behaviour.
[-- Attachment #2: patch.txt --]
[-- Type: text/x-patch, Size: 7010 bytes --]
commit 77a610b7e88635ee7c63d82cc30fad9c80abebea
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Thu Feb 27 11:17:31 2020 +0000
libstdc++: Minor optimization for min/max/minmax
By calling the internal __min_element (or __max_element or
__minmax_element) function directly we avoid a function call and the
valid range checks that are redundant when the range is defined by an
initializer_list.
* include/bits/stl_algo.h (min(initializer_list<T>))
(min(initializer_list<T>, Compare)): Call __min_element directly to
avoid redundant debug checks for valid ranges.
(max(initializer_list<T>), max(initializer_list<T>, Compare)):
Likewise, for __max_element.
(minmax(initializer_list<T>), minmax(initializer_list<T>, Compare)):
Likewise, for __minmax_element.
diff --git a/libstdc++-v3/include/bits/stl_algo.h b/libstdc++-v3/include/bits/stl_algo.h
index 6503d1518d3..d5eed9c47f6 100644
--- a/libstdc++-v3/include/bits/stl_algo.h
+++ b/libstdc++-v3/include/bits/stl_algo.h
@@ -3543,38 +3543,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
__gnu_cxx::__ops::__iter_comp_iter(__comp));
}
- // N2722 + DR 915.
- template<typename _Tp>
- _GLIBCXX14_CONSTEXPR
- inline _Tp
- min(initializer_list<_Tp> __l)
- { return *std::min_element(__l.begin(), __l.end()); }
-
- template<typename _Tp, typename _Compare>
- _GLIBCXX14_CONSTEXPR
- inline _Tp
- min(initializer_list<_Tp> __l, _Compare __comp)
- { return *std::min_element(__l.begin(), __l.end(), __comp); }
-
- template<typename _Tp>
- _GLIBCXX14_CONSTEXPR
- inline _Tp
- max(initializer_list<_Tp> __l)
- { return *std::max_element(__l.begin(), __l.end()); }
-
- template<typename _Tp, typename _Compare>
- _GLIBCXX14_CONSTEXPR
- inline _Tp
- max(initializer_list<_Tp> __l, _Compare __comp)
- { return *std::max_element(__l.begin(), __l.end(), __comp); }
-
template<typename _Tp>
_GLIBCXX14_CONSTEXPR
inline pair<_Tp, _Tp>
minmax(initializer_list<_Tp> __l)
{
+ __glibcxx_requires_irreflexive(__l.begin(), __l.end);
pair<const _Tp*, const _Tp*> __p =
- std::minmax_element(__l.begin(), __l.end());
+ std::__minmax_element(__l.begin(), __l.end(),
+ __gnu_cxx::__ops::__iter_less_iter());
return std::make_pair(*__p.first, *__p.second);
}
@@ -3583,8 +3560,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
inline pair<_Tp, _Tp>
minmax(initializer_list<_Tp> __l, _Compare __comp)
{
+ __glibcxx_requires_irreflexive_pred(__l.begin(), __l.end, __comp);
pair<const _Tp*, const _Tp*> __p =
- std::minmax_element(__l.begin(), __l.end(), __comp);
+ std::__minmax_element(__l.begin(), __l.end(),
+ __gnu_cxx::__ops::__iter_comp_iter(__comp));
return std::make_pair(*__p.first, *__p.second);
}
@@ -3959,7 +3938,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
for (_RandomAccessIterator __i = __first + 1; __i != __last; ++__i)
std::iter_swap(__i, __first + __d(__g, __p_type(0, __i - __first)));
}
-#endif
+#endif // USE C99_STDINT
#endif // C++11
@@ -5902,6 +5881,49 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
__gnu_cxx::__ops::__iter_comp_iter(__comp));
}
+#if __cplusplus >= 201103L
+ // N2722 + DR 915.
+ template<typename _Tp>
+ _GLIBCXX14_CONSTEXPR
+ inline _Tp
+ min(initializer_list<_Tp> __l)
+ {
+ __glibcxx_requires_irreflexive(__l.begin(), __l.end);
+ return *_GLIBCXX_STD_A::__min_element(__l.begin(), __l.end(),
+ __gnu_cxx::__ops::__iter_less_iter());
+ }
+
+ template<typename _Tp, typename _Compare>
+ _GLIBCXX14_CONSTEXPR
+ inline _Tp
+ min(initializer_list<_Tp> __l, _Compare __comp)
+ {
+ __glibcxx_requires_irreflexive_pred(__l.begin(), __l.end, __comp);
+ return *_GLIBCXX_STD_A::__min_element(__l.begin(), __l.end(),
+ __gnu_cxx::__ops::__iter_comp_iter(__comp));
+ }
+
+ template<typename _Tp>
+ _GLIBCXX14_CONSTEXPR
+ inline _Tp
+ max(initializer_list<_Tp> __l)
+ {
+ __glibcxx_requires_irreflexive(__l.begin(), __l.end);
+ return *_GLIBCXX_STD_A::__max_element(__l.begin(), __l.end(),
+ __gnu_cxx::__ops::__iter_less_iter());
+ }
+
+ template<typename _Tp, typename _Compare>
+ _GLIBCXX14_CONSTEXPR
+ inline _Tp
+ max(initializer_list<_Tp> __l, _Compare __comp)
+ {
+ __glibcxx_requires_irreflexive_pred(__l.begin(), __l.end, __comp);
+ return *_GLIBCXX_STD_A::__max_element(__l.begin(), __l.end(),
+ __gnu_cxx::__ops::__iter_comp_iter(__comp));
+ }
+#endif // C++11
+
#if __cplusplus >= 201402L
/// Reservoir sampling algorithm.
template<typename _InputIterator, typename _RandomAccessIterator,
commit b183bd10b7ac1f20cc4ec60ebe621c3177297d52
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Thu Feb 27 11:20:54 2020 +0000
libstdc++: Improve check for valid forward iterator range
Since C++14 we can assume that value-initialized forward iterators are
not part of a valid range (except the special case of an empty range
defined by two value-initialized iterators).
This covers the case of null pointers which was checked by the overload
for input iterators, but also handles non-pointers.
* include/debug/helper_functions.h (__valid_range_aux): Add overload
for forward iterators that checks for value-initialized iterators.
diff --git a/libstdc++-v3/include/debug/helper_functions.h b/libstdc++-v3/include/debug/helper_functions.h
index 251582d5922..3e016c7643e 100644
--- a/libstdc++-v3/include/debug/helper_functions.h
+++ b/libstdc++-v3/include/debug/helper_functions.h
@@ -161,6 +161,28 @@ namespace __gnu_debug
|| (!__check_singular(__first) && !__check_singular(__last));
}
+#if __cplusplus >= 201402L
+ template<typename _ForwardIterator>
+ constexpr bool
+ __valid_range_aux(_ForwardIterator __first, _ForwardIterator __last,
+ std::forward_iterator_tag)
+ {
+ if (__first == __last)
+ return true;
+
+ // Value-initialized forward iterators cannot form a non-empty range.
+ if (__first == _ForwardIterator() || __last == _ForwardIterator())
+ return false;
+
+ // Hook for checking if safe iterators are singular.
+ if (__check_singular_aux(std::__addressof(__first))
+ || __check_singular_aux(std::__addressof(__last)))
+ return false;
+
+ return true;
+ }
+#endif
+
template<typename _InputIterator>
_GLIBCXX_CONSTEXPR
inline bool
@@ -168,7 +190,7 @@ namespace __gnu_debug
std::random_access_iterator_tag)
{
return
- __valid_range_aux(__first, __last, std::input_iterator_tag())
+ __valid_range_aux(__first, __last, std::forward_iterator_tag())
&& __first <= __last;
}
next reply other threads:[~2020-02-27 13:06 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-27 13:06 Jonathan Wakely [this message]
2021-08-13 17:09 ` François Dumont
2021-08-16 19:25 ` Jonathan Wakely
2021-08-18 14:40 ` Jonathan Wakely
2021-08-18 15:55 ` Jonathan Wakely
2021-08-23 5:03 ` François Dumont
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