* [committed] libstdc++: Fix self-move for std::weak_ptr [PR108118]
@ 2022-12-16 14:31 Jonathan Wakely
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From: Jonathan Wakely @ 2022-12-16 14:31 UTC (permalink / raw)
To: libstdc++, gcc-patches
Tested x86_64-lixnu. Pushed to trunk. I'll backport this too.
-- >8 --
I think an alternative fix would be something like:
_M_ptr = std::exchange(rhs._M_ptr, nullptr);
_M_refcount = std::move(rhs._M_refcount);
The standard's move-and-swap implementation generates smaller code at
all levels except -O0 and -Og, so it seems simplest to just do what the
standard says.
libstdc++-v3/ChangeLog:
PR libstdc++/108118
* include/bits/shared_ptr_base.h (weak_ptr::operator=):
Implement as move-and-swap exactly as specified in the standard.
* testsuite/20_util/weak_ptr/cons/self_move.cc: New test.
---
libstdc++-v3/include/bits/shared_ptr_base.h | 4 +---
.../20_util/weak_ptr/cons/self_move.cc | 19 +++++++++++++++++++
2 files changed, 20 insertions(+), 3 deletions(-)
create mode 100644 libstdc++-v3/testsuite/20_util/weak_ptr/cons/self_move.cc
diff --git a/libstdc++-v3/include/bits/shared_ptr_base.h b/libstdc++-v3/include/bits/shared_ptr_base.h
index d9230b72203..c22b397a194 100644
--- a/libstdc++-v3/include/bits/shared_ptr_base.h
+++ b/libstdc++-v3/include/bits/shared_ptr_base.h
@@ -2049,9 +2049,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
__weak_ptr&
operator=(__weak_ptr&& __r) noexcept
{
- _M_ptr = __r._M_ptr;
- _M_refcount = std::move(__r._M_refcount);
- __r._M_ptr = nullptr;
+ __weak_ptr(std::move(__r)).swap(*this);
return *this;
}
diff --git a/libstdc++-v3/testsuite/20_util/weak_ptr/cons/self_move.cc b/libstdc++-v3/testsuite/20_util/weak_ptr/cons/self_move.cc
new file mode 100644
index 00000000000..c890d2ba94d
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/weak_ptr/cons/self_move.cc
@@ -0,0 +1,19 @@
+// { dg-do run { target c++11 } }
+
+#include <memory>
+#include <testsuite_hooks.h>
+
+void
+test_self_move()
+{
+ std::shared_ptr<int> sp(new int(66));
+ std::weak_ptr<int> wp(sp);
+ wp = std::move(wp); // PR libstdc++/108118
+ std::shared_ptr<int> sp2(wp);
+ VERIFY(sp2 == sp);
+}
+
+int main()
+{
+ test_self_move();
+}
--
2.38.1
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2022-12-16 14:31 [committed] libstdc++: Fix self-move for std::weak_ptr [PR108118] Jonathan Wakely
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