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libstdc++: Minor optimization for min/max/minmax

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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.
This commit is contained in:
Jonathan Wakely
2021-08-18 12:24:12 +01:00
parent 085c2f8f0e
commit de44eee5d5
1 changed files with 50 additions and 28 deletions
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libstdc++-v3/include/bits/stl_algo.h
+50 -28
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@@ -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,