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libstdc++: Avoid double-deref of __first in ranges::minmax [PR104858]

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PR libstdc++/104858

libstdc++-v3/ChangeLog:

	* include/bits/ranges_algo.h (__minmax_fn): Avoid dereferencing
	__first twice at the start.
	* testsuite/25_algorithms/minmax/constrained.cc (test06): New test.
This commit is contained in:
Patrick Palka 2022-04-15 14:41:14 -04:00
parent eb3f2e9348
commit 7e76cef873
2 changed files with 31 additions and 1 deletions
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2
libstdc++-v3/include/bits/ranges_algo.h
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@ -3084,7 +3084,7 @@ namespace ranges
auto __last = ranges::end(__r);
__glibcxx_assert(__first != __last);
auto __comp_proj = __detail::__make_comp_proj(__comp, __proj);
minmax_result<range_value_t<_Range>> __result = {*__first, *__first};
minmax_result<range_value_t<_Range>> __result = {*__first, __result.min};
if (++__first == __last)
return __result;
else

30
libstdc++-v3/testsuite/25_algorithms/minmax/constrained.cc
View file

@ -20,6 +20,7 @@
#include <algorithm>
#include <string>
#include <utility>
#include <vector>
#include <testsuite_hooks.h>
#include <testsuite_iterators.h>
@ -129,6 +130,34 @@ test05()
VERIFY( result.min == "a"s && result.max == "c"s );
}
struct A {
A() = delete;
A(int i) : i(i) { }
A(const A&) = default;
A(A&& other) : A(std::as_const(other)) { ++move_count; }
A& operator=(const A&) = default;
A& operator=(A&& other) {
++move_count;
return *this = std::as_const(other);
};
friend auto operator<=>(const A&, const A&) = default;
static inline int move_count = 0;
int i;
};
void
test06()
{
// PR libstdc++/104858
// Verify ranges::minmax doesn't dereference the iterator for the first
// element in the range twice.
A a(42);
ranges::subrange r = {std::move_iterator(&a), std::move_sentinel(&a + 1)};
auto result = ranges::minmax(r);
VERIFY( A::move_count == 1 );
VERIFY( result.min.i == 42 && result.max.i == 42 );
}
int
main()
{
@ -137,4 +166,5 @@ main()
test03();
test04();
test05();
test06();
}