[PATCH] Improvements to valid range checks in debug mode
Jonathan Wakely
jwakely@redhat.com
Wed Aug 18 14:40:33 GMT 2021
On Mon, 16 Aug 2021 at 20:26, Jonathan Wakely via Libstdc++
<libstdc++@gcc.gnu.org> wrote:
>
> On Fri, 13 Aug 2021 at 18:10, François Dumont via Libstdc++
> <libstdc++@gcc.gnu.org> wrote:
> >
> > I just come back to this email and it sounds like the right moment to
> > commit it.
>
> Ah yes, thanks for the reminder!
>
> I'll push it tomorrow.
>
> >
> > On 27/02/20 2:06 pm, Jonathan Wakely wrote:
> > > 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.
Actually, that change doesn't work. Some of our container iterators
use a value-initialized iterator as the past-the-end value, so the
check in the new __valid_range_aux function incorrectly rejects some
valid ranges. Maybe I can make it work for bidirectional iterators,
which must be attached to a container to be valid.
For now I've only pushed the second half of the patch, optimizing the
std::min/max/minmax overloads taking an initializer_list (as
attached).
Tested powerpc64le-linux, pushed to trunk.
-------------- next part --------------
commit de44eee5d52f5980b6b2b2120940f70cc2fa007e
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Wed Aug 18 12:24:12 2021
libstdc++: Minor optimization for min/max/minmax
The debug mode checks for a valid range are redundant when we have an
initializer_list argument, because we know it's a valid range already.
By making std::min(initialier_list<T>) call the internal __min_element
function directly we avoid a function call and skip those checks. The
same can be done for the overload taking a comparison function, and also
for the std::max and std::minmax overloads for initializer_list
arguments.
Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
libstdc++-v3/ChangeLog:
* 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 54ad383711f..ac4f2d0f721 100644
--- a/libstdc++-v3/include/bits/stl_algo.h
+++ b/libstdc++-v3/include/bits/stl_algo.h
@@ -3445,38 +3445,15 @@ _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);
}
@@ -3485,8 +3462,10 @@ _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);
}
@@ -3793,7 +3772,7 @@ _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
@@ -5746,6 +5725,49 @@ _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,
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