Re: [Bug libstdc++/112477] [13/14 Regression] Assignment of value-initialized iterators differs from value-initialization

["François Dumont" <frs.dumont@gmail.com>]

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libstdc++: [_GLIBCXX_DEBUG] Fix assignment of value-initialized iterator 
[PR112477]

Now that _M_Detach do not reset iterator _M_version value we need to 
reset it when
the iterator is attached to a new sequence. Even if this sequencer is 
null like when
assigning a value-initialized iterator. In this case _M_version shall be 
reset to 0.

libstdc++-v3/ChangeLog:

     PR libstdc++/112477
     * src/c++11/debug.cc
     (_Safe_iterator_base::_M_attach): Reset _M_version to 0 if 
attaching to null
     sequence.
     (_Safe_iterator_base::_M_attach_single): Likewise.
     (_Safe_local_iterator_base::_M_attach): Likewise.
     (_Safe_local_iterator_base::_M_attach_single): Likewise.
     * testsuite/23_containers/map/debug/112477.cc: New test case.

Tested under Linux x64 _GLIBCXX_DEBUG mode.

Ok to commit and backport to gcc 13 ?

François

On 09/01/2024 22:47, fdumont at gcc dot gnu.org wrote:
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112477
>
> François Dumont <fdumont at gcc dot gnu.org> changed:
>
>             What    |Removed                     |Added
> ----------------------------------------------------------------------------
>             Assignee|unassigned at gcc dot gnu.org      |fdumont at gcc dot gnu.org
>
> --- Comment #8 from François Dumont <fdumont at gcc dot gnu.org> ---
> Hi
> I'm going to have a look but if you wish to contribute do not hesitate.
> Thanks for the report.
>

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diff --git a/libstdc++-v3/src/c++11/debug.cc b/libstdc++-v3/src/c++11/debug.cc
index bb0d0db6679..cb2cbf9d312 100644
--- a/libstdc++-v3/src/c++11/debug.cc
+++ b/libstdc++-v3/src/c++11/debug.cc
@@ -437,6 +437,8 @@ namespace __gnu_debug
 	_M_version = _M_sequence->_M_version;
 	_M_sequence->_M_attach(this, __constant);
       }
+    else
+      _M_version = 0;
   }
 
   void
@@ -452,6 +454,8 @@ namespace __gnu_debug
 	_M_version = _M_sequence->_M_version;
 	_M_sequence->_M_attach_single(this, __constant);
       }
+    else
+      _M_version = 0;
   }
 
   void
@@ -528,6 +532,8 @@ namespace __gnu_debug
 	_M_version = _M_sequence->_M_version;
 	_M_get_container()->_M_attach_local(this, __constant);
       }
+    else
+      _M_version = 0;
   }
 
   void
@@ -543,6 +549,8 @@ namespace __gnu_debug
 	_M_version = _M_sequence->_M_version;
 	_M_get_container()->_M_attach_local_single(this, __constant);
       }
+    else
+      _M_version = 0;
   }
 
   void
diff --git a/libstdc++-v3/testsuite/23_containers/map/debug/112477.cc b/libstdc++-v3/testsuite/23_containers/map/debug/112477.cc
new file mode 100644
index 00000000000..bde613b8905
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/map/debug/112477.cc
@@ -0,0 +1,20 @@
+// { dg-do run { target c++11 } }
+// { dg-require-debug-mode "" }
+
+// PR libstdc++/112477
+
+#include <map>
+
+int main()
+{
+  using M = std::map<int, int>;
+  using I = M::iterator;
+
+  M map{ {1, 1}, {2, 2} };
+
+  I it1 = map.begin();
+  it1 = I{};
+
+  I it2{};
+  (void)(it1 == it2);
+}