[PATCH] Make any_cast compare typeinfo as well as function pointers

[Jonathan Wakely]

It's possible for the function pointer comparison to fail even though
the type is correct, because the function could be defined multiple
times with different addresses when shared libraries are in use.

Retain the function pointer check for the common case where the check
succeeds, but compare typeinfo (if RTTI is enabled) if the first check
fails.

        * include/experimental/any (__any_caster): Use RTTI if comparing
        addresses fails, to support non-unique addresses in shared libraries.
        * include/std/any (__any_caster): Likewise.

Tested powerpc64le-linux, committed to trunk, backports to follow.



commit 330b70bbe09569c3d2c753e27186805977b78c8d
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Thu May 23 14:43:12 2019 +0100

    Make any_cast compare typeinfo as well as function pointers
    
    It's possible for the function pointer comparison to fail even though
    the type is correct, because the function could be defined multiple
    times with different addresses when shared libraries are in use.
    
    Retain the function pointer check for the common case where the check
    succeeds, but compare typeinfo (if RTTI is enabled) if the first check
    fails.
    
            * include/experimental/any (__any_caster): Use RTTI if comparing
            addresses fails, to support non-unique addresses in shared 
libraries.
            * include/std/any (__any_caster): Likewise.

diff --git a/libstdc++-v3/include/experimental/any 
b/libstdc++-v3/include/experimental/any
index f1d4bbf788c..f7a4c8fa394 100644
--- a/libstdc++-v3/include/experimental/any
+++ b/libstdc++-v3/include/experimental/any
@@ -432,11 +432,18 @@ inline namespace fundamentals_v1
       // is explicitly specialized and has a no-op _S_manage function.
       using _Vp = conditional_t<__and_<__does_not_decay, __is_copyable>::value,
                                _Up, any::_Op>;
-      if (__any->_M_manager != &any::_Manager<_Vp>::_S_manage)
-       return nullptr;
-      any::_Arg __arg;
-      __any->_M_manager(any::_Op_access, __any, &__arg);
-      return __arg._M_obj;
+      // First try comparing function addresses, which works without RTTI
+      if (__any->_M_manager == &any::_Manager<_Vp>::_S_manage
+#if __cpp_rtti
+         || __any->type() == typeid(_Tp)
+#endif
+         )
+       {
+         any::_Arg __arg;
+         __any->_M_manager(any::_Op_access, __any, &__arg);
+         return __arg._M_obj;
+       }
+      return nullptr;
     }
 
   // This overload exists so that std::any_cast<void(*)()>(a) is well-formed.
diff --git a/libstdc++-v3/include/std/any b/libstdc++-v3/include/std/any
index 8cbabdddd9b..229c7c6b65e 100644
--- a/libstdc++-v3/include/std/any
+++ b/libstdc++-v3/include/std/any
@@ -503,6 +503,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     }
   // @}
 
+  /// @cond undocumented
   template<typename _Tp>
     void* __any_caster(const any* __any)
     {
@@ -516,8 +517,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       // Only copy constructible types can be used for contained values:
       else if constexpr (!is_copy_constructible_v<_Up>)
        return nullptr;
-      // This check is equivalent to __any->type() == typeid(_Tp)
-      else if (__any->_M_manager == &any::_Manager<_Up>::_S_manage)
+      // First try comparing function addresses, which works without RTTI
+      else if (__any->_M_manager == &any::_Manager<_Up>::_S_manage
+#if __cpp_rtti
+         || __any->type() == typeid(_Tp)
+#endif
+         )
        {
          any::_Arg __arg;
          __any->_M_manager(any::_Op_access, __any, &__arg);
@@ -525,6 +530,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
        }
       return nullptr;
     }
+  /// @endcond
 
   /**
    * @brief Access the contained object.