libstdc++: Initialize all subobjects of std::function

The std::function::swap member swaps each data member unconditionally,
resulting in -Wmaybe-uninitialized warnings for a default constructed
object. This happens because the _M_invoker and _M_functor members are
only initialized if the function has a target.

This change ensures that all subobjects are zero-initialized on
construction.

Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
libstdc++-v3/ChangeLog:

	* include/bits/std_function.h (_Function_base): Add
	default member initializers and define constructor as defaulted.
	(function::_M_invoker): Add default member initializer.

diff --git a/libstdc++-v3/include/bits/std_function.h b/libstdc++-v3/include/bits/std_function.h
index 31eba2b..c084844 100644 (file)
--- a/libstdc++-v3/include/bits/std_function.h
+++ b/libstdc++-v3/include/bits/std_function.h
@@ -237,7 +237,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
        { __functor._M_access<_Functor*>() = new _Functor(std::move(__f)); }
       };
 
-    _Function_base() : _M_manager(nullptr) { }
+    _Function_base() = default;
 
     ~_Function_base()
     {
@@ -247,11 +247,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
     bool _M_empty() const { return !_M_manager; }
 
-    typedef bool (*_Manager_type)(_Any_data&, const _Any_data&,
-                                 _Manager_operation);
+    using _Manager_type
+      = bool (*)(_Any_data&, const _Any_data&, _Manager_operation);
 
-    _Any_data     _M_functor;
-    _Manager_type _M_manager;
+    _Any_data     _M_functor{};
+    _Manager_type _M_manager{};
   };
 
   template<typename _Signature, typename _Functor>
@@ -261,7 +261,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     class _Function_handler<_Res(_ArgTypes...), _Functor>
     : public _Function_base::_Base_manager<_Functor>
     {
-      typedef _Function_base::_Base_manager<_Functor> _Base;
+      using _Base = _Function_base::_Base_manager<_Functor>;
 
     public:
       static bool
@@ -414,7 +414,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
        function(_Functor __f)
        : _Function_base()
        {
-         typedef _Function_handler<_Res(_ArgTypes...), _Functor> _My_handler;
+         using _My_handler = _Function_handler<_Res(_ArgTypes...), _Functor>;
 
          if (_My_handler::_M_not_empty_function(__f))
            {
@@ -634,8 +634,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
     private:
       using _Invoker_type = _Res (*)(const _Any_data&, _ArgTypes&&...);
-      _Invoker_type _M_invoker;
-  };
+      _Invoker_type _M_invoker = nullptr;
+    };
 
 #if __cpp_deduction_guides >= 201606
   template<typename>