From: Patrick Palka <ppalka@redhat.com>
To: gcc-patches@gcc.gnu.org
Cc: libstdc++@gcc.gnu.org, Patrick Palka <ppalka@redhat.com>
Subject: [PATCH] libstdc++: Avoid double-deref of __first in ranges::minmax [PR104858]
Date: Thu, 14 Apr 2022 11:21:11 -0400 [thread overview]
Message-ID: <20220414152111.229967-1-ppalka@redhat.com> (raw)
Tested on x86_64-pc-linux-gnu, does this look OK for trunk and 11/10
once the branch is unfrozen?
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.
---
libstdc++-v3/include/bits/ranges_algo.h | 2 +-
.../25_algorithms/minmax/constrained.cc | 23 +++++++++++++++++++
2 files changed, 24 insertions(+), 1 deletion(-)
diff --git a/libstdc++-v3/include/bits/ranges_algo.h b/libstdc++-v3/include/bits/ranges_algo.h
index 62dc605080a..3d30fb1428c 100644
--- 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 90882afb6d0..306c495babe 100644
--- a/libstdc++-v3/testsuite/25_algorithms/minmax/constrained.cc
+++ b/libstdc++-v3/testsuite/25_algorithms/minmax/constrained.cc
@@ -129,6 +129,28 @@ test05()
VERIFY( result.min == "a"s && result.max == "c"s );
}
+struct A {
+ A() = default;
+ A(const A&) = default;
+ A(A&&) { ++move_count; }
+ A& operator=(const A&) = default;
+ A& operator=(A&&) = default;
+ friend auto operator<=>(const A&, const A&) = default;
+ static inline int move_count = 0;
+};
+
+void
+test06()
+{
+ // PR libstdc++/104858
+ // Verify ranges::minmax doesn't dereference the iterator for the first
+ // element in the range twice.
+ A a;
+ ranges::subrange r = {std::move_iterator(&a), std::move_sentinel(&a + 1)};
+ ranges::minmax(r);
+ VERIFY( A::move_count == 1 );
+}
+
int
main()
{
@@ -137,4 +159,5 @@ main()
test03();
test04();
test05();
+ test06();
}
--
2.36.0.rc2.10.g1ac7422e39
next reply other threads:[~2022-04-14 15:21 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-14 15:21 Patrick Palka [this message]
2022-04-14 15:27 ` Jonathan Wakely
2022-04-15 18:42 ` Patrick Palka
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