Re: _LIBCXX_DEBUG value initialized singular iterators assert failures in std algorithms [PR104316]

[François Dumont]

OK for trunk, thanks!

I think this is OK to backport to 13 too.

Maybe after this we can define the __cpp_lib_null_itetators macro for 
debug mode?

After this fix of local_iterator I think we can indeed.

In fact the added 11316.cc was already passing for 
unordered_set<>::local_iterator but simply because we were missing the 
singular check. Both issues solved with this patch.

I found the version.def file to cleanup but no idea how to regenerate 
version.h from it so I'll let you do it, ok ?

    libstdc++: Fix _Safe_local_iterator<>::_M_valid_range

    Unordered container local_iterator range shall not contain any singular
    iterator unless both iterators are value-initialized.

    libstdc++-v3/ChangeLog:

            * include/debug/safe_local_iterator.tcc
            (_Safe_local_iterator::_M_valid_range): Add 
_M_value_initialized and
            _M_singular checks.
            * testsuite/23_containers/unordered_set/debug/114316.cc: 
New test case.


Ok to commit ?

François
diff --git a/libstdc++-v3/include/debug/safe_local_iterator.tcc 
b/libstdc++-v3/include/debug/safe_local_iterator.tcc
index 90e60e37c32..6d546ec040c 100644
--- a/libstdc++-v3/include/debug/safe_local_iterator.tcc
+++ b/libstdc++-v3/include/debug/safe_local_iterator.tcc
@@ -78,7 +78,13 @@ namespace __gnu_debug
     _M_valid_range(const _Safe_local_iterator& __rhs,
                std::pair<difference_type, _Distance_precision>& __dist) const
     {
-      if (!_M_can_compare(__rhs))
+      if (_M_value_initialized() && __rhs._M_value_initialized())
+       {
+         __dist = { 0, __dp_exact };
+         return true;
+       }
+
+      if (_M_singular() || __rhs._M_singular() || !_M_can_compare(__rhs))
        return false;
 
       if (bucket() != __rhs.bucket())
diff --git a/libstdc++-v3/testsuite/23_containers/unordered_set/debug/114316.cc 
b/libstdc++-v3/testsuite/23_containers/unordered_set/debug/114316.cc
new file mode 100644
index 00000000000..41b649a9cbd
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/unordered_set/debug/114316.cc
@@ -0,0 +1,28 @@
+// { dg-do run { target c++11 } }
+// { dg-require-debug-mode "" }
+
+// PR libstdc++/114316
+
+#include <unordered_set>
+#include <algorithm>
+
+#include <testsuite_hooks.h>
+
+void test01()
+{
+  std::unordered_set<int>::iterator it{};
+  VERIFY( std::find(it, it, 0) == it );
+}
+
+void test02()
+{
+  std::unordered_set<int>::local_iterator it{};
+  VERIFY( std::find(it, it, 0) == it );
+}
+
+int main()
+{
+  test01();
+  test02();
+  return 0;
+}