Clean weakrefs before calling user's dealloc

We must clean the weakreferences before calling the user's __dealloc__
because if the __dealloc__ releases the GIL, a weakref can be
dereferenced accessing the object in an inconsistent state or
resurrecting it.

Cython/Compiler/ModuleNode.py

@@ -1475,12 +1475,16 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
                 UtilityCode.load_cached("PyTrashcan", "ExtensionTypes.c"))
             code.putln("__Pyx_TRASHCAN_BEGIN(o, %s)" % slot_func_cname)
 
-        # call the user's __dealloc__
-        self.generate_usr_dealloc_call(scope, code)
-
         if weakref_slot:
+            # We must clean the weakreferences before calling the user's __dealloc__
+            # because if the __dealloc__ releases the GIL, a weakref can be
+            # dereferenced accessing the object in an inconsistent state or
+            # resurrecting it.
             code.putln("if (p->__weakref__) PyObject_ClearWeakRefs(o);")
 
+        # call the user's __dealloc__
+        self.generate_usr_dealloc_call(scope, code)
+
         if dict_slot:
             code.putln("if (p->__dict__) PyDict_Clear(p->__dict__);")