[libc++] Always initialize __tree::{,const_}iterator

[philnik777]

This was probably added to support https://wg21.link/n3644 but there's no reason not to initialize the pointer in all standard modes. This is technically an extension since n3644 only required value-initialized iterators to be comparable, but supporting this as an extension should be uncontroversial since it avoids potential reads of uninitialized memory in C++03/C++11 without doing any harm.

[llvmbot]

@llvm/pr-subscribers-libcxx

Author: Nikolas Klauser (philnik777)

Changes

There doesn't seem to be much of a reason to not initialize the iterator types in all standard modes. This avoids potential reads of uninitialized memory in C++03/C++11 without any harm I can see.

---

Full diff: https://github.com/llvm/llvm-project/pull/147167.diff

3 Files Affected:

• (modified) libcxx/include/__tree (+2-12)
• (added) libcxx/test/libcxx/containers/associative/map/initialize_iterator.pass.cpp (+26)
• (added) libcxx/test/libcxx/containers/associative/set/initialize_iterator.pass.cpp (+26)

diff --git a/libcxx/include/__tree b/libcxx/include/__tree
index 9d4ba3ad0639c..5dee314b847f2 100644
--- a/libcxx/include/__tree
+++ b/libcxx/include/__tree
@@ -646,12 +646,7 @@ public:
   using reference         = value_type&;
   using pointer           = __rebind_pointer_t<_NodePtr, value_type>;
 
-  _LIBCPP_HIDE_FROM_ABI __tree_iterator() _NOEXCEPT
-#if _LIBCPP_STD_VER >= 14
-      : __ptr_(nullptr)
-#endif
-  {
-  }
+  _LIBCPP_HIDE_FROM_ABI __tree_iterator() _NOEXCEPT : __ptr_(nullptr) {}
 
   _LIBCPP_HIDE_FROM_ABI reference operator*() const { return __get_np()->__value_; }
   _LIBCPP_HIDE_FROM_ABI pointer operator->() const { return pointer_traits<pointer>::pointer_to(__get_np()->__value_); }
@@ -720,12 +715,7 @@ public:
   using reference         = const value_type&;
   using pointer           = __rebind_pointer_t<_NodePtr, const value_type>;
 
-  _LIBCPP_HIDE_FROM_ABI __tree_const_iterator() _NOEXCEPT
-#if _LIBCPP_STD_VER >= 14
-      : __ptr_(nullptr)
-#endif
-  {
-  }
+  _LIBCPP_HIDE_FROM_ABI __tree_const_iterator() _NOEXCEPT : __ptr_(nullptr) {}
 
 private:
   typedef __tree_iterator<_Tp, __node_pointer, difference_type> __non_const_iterator;
diff --git a/libcxx/test/libcxx/containers/associative/map/initialize_iterator.pass.cpp b/libcxx/test/libcxx/containers/associative/map/initialize_iterator.pass.cpp
new file mode 100644
index 0000000000000..cfa8e72e98e51
--- /dev/null
+++ b/libcxx/test/libcxx/containers/associative/map/initialize_iterator.pass.cpp
@@ -0,0 +1,26 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03
+
+// Check that map::iterator is initialized when default constructed
+
+#include <cassert>
+#include <map>
+
+template <class Iter>
+void test() {
+  Iter iter;
+  Iter iter2 = Iter();
+  assert(iter == iter2);
+}
+
+int main() {
+  test<std::map<int, int>::iterator>();
+  test<std::map<int, int>::const_iterator>();
+}
diff --git a/libcxx/test/libcxx/containers/associative/set/initialize_iterator.pass.cpp b/libcxx/test/libcxx/containers/associative/set/initialize_iterator.pass.cpp
new file mode 100644
index 0000000000000..c919e5c3680c3
--- /dev/null
+++ b/libcxx/test/libcxx/containers/associative/set/initialize_iterator.pass.cpp
@@ -0,0 +1,26 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03
+
+// Check that set::iterator is initialized when default constructed
+
+#include <cassert>
+#include <set>
+
+template <class Iter>
+void test() {
+  Iter iter;
+  Iter iter2 = Iter();
+  assert(iter == iter2);
+}
+
+int main() {
+  test<std::set<int>::iterator>();
+  test<std::set<int>::const_iterator>();
+}

[ldionne]

LGTM with comments applied.

[ldionne]

This is effectively testing an extension since https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3644.pdf mentions value-initialized iterators and this extension makes it work with default initialized iterators. Let's move it under test/extensions and adjust the test comment to mention that this is an extension.

[ldionne]

We're missing a similar test for multiset and multimap.

[ldionne]

Suggested change

	int main() {
	int main(int, char**) {

[ldionne]

return 0;

[ldionne]

While we're at it, let's test the following combinations:

{
  Iter iter1, iter2;
  assert(iter1 == iter2);
}
{
  Iter iter1;
  Iter iter2{};
  assert(iter1 == iter2);  
}
{
  Iter iter1{};
  Iter iter2;
  assert(iter1 == iter2);  
}