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* [gcc r12-2995] libstdc++: Minor optimization for min/max/minmax
@ 2021-08-18 14:36 Jonathan Wakely
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From: Jonathan Wakely @ 2021-08-18 14:36 UTC (permalink / raw)
To: gcc-cvs, libstdc++-cvs
https://gcc.gnu.org/g:de44eee5d52f5980b6b2b2120940f70cc2fa007e
commit r12-2995-gde44eee5d52f5980b6b2b2120940f70cc2fa007e
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Wed Aug 18 12:24:12 2021 +0100
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:
---
libstdc++-v3/include/bits/stl_algo.h | 78 +++++++++++++++++++++++-------------
1 file changed, 50 insertions(+), 28 deletions(-)
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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