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From: Jonathan Wakely <redi@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org, libstdc++-cvs@gcc.gnu.org Subject: [gcc r13-5386] libstdc++: Add returns_nonnull to non-inline std::map detail [PR108554] Date: Thu, 26 Jan 2023 13:38:36 +0000 (GMT) [thread overview] Message-ID: <20230126133836.5BF593858425@sourceware.org> (raw) https://gcc.gnu.org/g:3376467ce090aa0966d59ca3aea35db4f17a4b47 commit r13-5386-g3376467ce090aa0966d59ca3aea35db4f17a4b47 Author: Jonathan Wakely <jwakely@redhat.com> Date: Thu Jan 26 10:55:28 2023 +0000 libstdc++: Add returns_nonnull to non-inline std::map detail [PR108554] std::map uses a non-inline function to rebalance its tree and the compiler can't see that it always returns a valid pointer (assuming valid inputs, which is a precondition anyway). This can result in -Wnull-derefernce warnings for valid code, because the compiler thinks there is a path where the function returns null. Adding the returns_nonnull attribute tells the compiler that is can't happen. While we're doing that, we might as well also add a nonnull attribute to the rebalancing functions too. libstdc++-v3/ChangeLog: PR libstdc++/108554 * include/bits/stl_tree.h (_Rb_tree_insert_and_rebalance): Add nonnull attribute. (_Rb_tree_rebalance_for_erase): Add nonnull and returns_nonnull attributes. * testsuite/23_containers/map/modifiers/108554.cc: New test. Diff: --- libstdc++-v3/include/bits/stl_tree.h | 2 ++ .../testsuite/23_containers/map/modifiers/108554.cc | 19 +++++++++++++++++++ 2 files changed, 21 insertions(+) diff --git a/libstdc++-v3/include/bits/stl_tree.h b/libstdc++-v3/include/bits/stl_tree.h index 5b7a5869b14..3c331fbc952 100644 --- a/libstdc++-v3/include/bits/stl_tree.h +++ b/libstdc++-v3/include/bits/stl_tree.h @@ -405,12 +405,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION _Base_ptr _M_node; }; + __attribute__((__nonnull__)) void _Rb_tree_insert_and_rebalance(const bool __insert_left, _Rb_tree_node_base* __x, _Rb_tree_node_base* __p, _Rb_tree_node_base& __header) throw (); + __attribute__((__nonnull__,__returns_nonnull__)) _Rb_tree_node_base* _Rb_tree_rebalance_for_erase(_Rb_tree_node_base* const __z, _Rb_tree_node_base& __header) throw (); diff --git a/libstdc++-v3/testsuite/23_containers/map/modifiers/108554.cc b/libstdc++-v3/testsuite/23_containers/map/modifiers/108554.cc new file mode 100644 index 00000000000..7076682f4c9 --- /dev/null +++ b/libstdc++-v3/testsuite/23_containers/map/modifiers/108554.cc @@ -0,0 +1,19 @@ +// { dg-do compile { target c++17 } } +// { dg-options "-Wnull-dereference -O2" } + +// PR libstdc++/108554 +// Warning from -Wnull-dereference when extracting a unique_ptr from a map. + +#include <map> +#include <memory> +#include <string> + +int pop(std::map<std::string, std::unique_ptr<int>>& m) +{ + if (auto it = m.find("key"); it != m.end()) + { + auto item = std::move(m.extract(it).mapped()); + return *item; + } + return 0; +}
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