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

	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.

diff --git a/libstdc++-v3/include/bits/ranges_algo.h b/libstdc++-v3/include/bits/ranges_algo.h
index 62dc605..3d30fb1 100644 (file)
--- a/libstdc++-v3/include/bits/ranges_algo.h
+++ b/libstdc++-v3/include/bits/ranges_algo.h
@@ -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

diff --git a/libstdc++-v3/testsuite/25_algorithms/minmax/constrained.cc b/libstdc++-v3/testsuite/25_algorithms/minmax/constrained.cc
index 90882af..5986404 100644 (file)
--- a/libstdc++-v3/testsuite/25_algorithms/minmax/constrained.cc
+++ b/libstdc++-v3/testsuite/25_algorithms/minmax/constrained.cc
@@ -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();
 }