[gcc r12-6794] libstdc++: Fix constexpr constructor for atomic<shared_ptr<T>>

[Jonathan Wakely <redi@gcc.gnu.org>]

https://gcc.gnu.org/g:7d47aae7cd4bb4dbf1e59a52c2a3f127151c8fab

commit r12-6794-g7d47aae7cd4bb4dbf1e59a52c2a3f127151c8fab
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Jan 21 11:55:22 2022 +0000

    libstdc++: Fix constexpr constructor for atomic<shared_ptr<T>>
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/shared_ptr_atomic.h (_Sp_atomic::_Atomic_count):
            Add constexpr.
            (_Sp_atomic::_M_ptr): Add default member-initializer.
            * testsuite/20_util/shared_ptr/atomic/atomic_shared_ptr.cc:
            Check constant initialization.
            * testsuite/20_util/weak_ptr/atomic_weak_ptr.cc: Likewise.

Diff:
---
 libstdc++-v3/include/bits/shared_ptr_atomic.h                         | 4 ++--
 libstdc++-v3/testsuite/20_util/shared_ptr/atomic/atomic_shared_ptr.cc | 3 +++
 libstdc++-v3/testsuite/20_util/weak_ptr/atomic_weak_ptr.cc            | 3 +++
 3 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/libstdc++-v3/include/bits/shared_ptr_atomic.h b/libstdc++-v3/include/bits/shared_ptr_atomic.h
index 35f781dc9a0..9e4df7da7f8 100644
--- a/libstdc++-v3/include/bits/shared_ptr_atomic.h
+++ b/libstdc++-v3/include/bits/shared_ptr_atomic.h
@@ -357,7 +357,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	// Ensure we can use the LSB as the lock bit.
 	static_assert(alignof(remove_pointer_t<pointer>) > 1);
 
-	_Atomic_count() : _M_val(0) { }
+	constexpr _Atomic_count() noexcept = default;
 
 	explicit
 	_Atomic_count(__count_type&& __c) noexcept
@@ -457,7 +457,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	static constexpr uintptr_t _S_lock_bit{1};
       };
 
-      typename _Tp::element_type* _M_ptr;
+      typename _Tp::element_type* _M_ptr = nullptr;
       _Atomic_count _M_refcount;
 
       static typename _Atomic_count::pointer
diff --git a/libstdc++-v3/testsuite/20_util/shared_ptr/atomic/atomic_shared_ptr.cc b/libstdc++-v3/testsuite/20_util/shared_ptr/atomic/atomic_shared_ptr.cc
index 725e7ba5031..1f97224bf6a 100644
--- a/libstdc++-v3/testsuite/20_util/shared_ptr/atomic/atomic_shared_ptr.cc
+++ b/libstdc++-v3/testsuite/20_util/shared_ptr/atomic/atomic_shared_ptr.cc
@@ -16,6 +16,9 @@
 
 #include <testsuite_hooks.h>
 
+// Check constexpr constructor.
+constinit std::atomic<std::shared_ptr<int>> a;
+
 void
 test_is_lock_free()
 {
diff --git a/libstdc++-v3/testsuite/20_util/weak_ptr/atomic_weak_ptr.cc b/libstdc++-v3/testsuite/20_util/weak_ptr/atomic_weak_ptr.cc
index e394e5562b9..b38cea768c8 100644
--- a/libstdc++-v3/testsuite/20_util/weak_ptr/atomic_weak_ptr.cc
+++ b/libstdc++-v3/testsuite/20_util/weak_ptr/atomic_weak_ptr.cc
@@ -8,6 +8,9 @@
 #include <thread>
 #include <testsuite_hooks.h>
 
+// Check constexpr constructor.
+constinit std::atomic<std::weak_ptr<int>> a;
+
 void
 test_is_lock_free()
 {