try a potentially safer way to find out if we know the tp_new slot function of a type

Cython/Compiler/Optimize.py

+from Cython.Compiler import TypeSlots
 from Cython.Compiler.ExprNodes import not_a_constant
 import cython
 cython.declare(UtilityCode=object, EncodedString=object, BytesLiteral=object,
@@ -2182,6 +2183,9 @@ class OptimizeBuiltinCalls(Visitor.MethodDispatcherTransform):
         if type_arg.type_entry:
             ext_type = type_arg.type_entry.type
             if ext_type.is_extension_type and not ext_type.is_external:
+                tp_slot = TypeSlots.ConstructorSlot("tp_new", '__new__')
+                slot_func_cname = TypeSlots.get_slot_function(ext_type.scope, tp_slot)
+                if slot_func_cname:
                     cython_scope = self.context.cython_scope
                     PyTypeObjectPtr = PyrexTypes.CPtrType(
                         cython_scope.lookup('PyTypeObject').type)
@@ -2193,7 +2197,6 @@ class OptimizeBuiltinCalls(Visitor.MethodDispatcherTransform):
                             ])
 
                     type_arg = ExprNodes.CastNode(type_arg, PyTypeObjectPtr)
-                slot_func_cname = ext_type.scope.mangle_internal("tp_new")
                     if not kwargs:
                         kwargs = ExprNodes.NullNode(node.pos, type=PyrexTypes.py_object_type)  # hack?
                     return ExprNodes.PythonCapiCallNode(

Cython/Compiler/TypeSlots.py

@@ -493,11 +493,13 @@ def get_special_method_signature(name):
     else:
         return None
 
+
 def get_property_accessor_signature(name):
     #  Return signature of accessor for an extension type
     #  property, else None.
     return property_accessor_signatures.get(name)
 
+
 def get_base_slot_function(scope, slot):
     #  Returns the function implementing this slot in the baseclass.
     #  This is useful for enabling the compiler to optimize calls
@@ -511,6 +513,18 @@ def get_base_slot_function(scope, slot):
                 return parent_slot
     return None
 
+
+def get_slot_function(scope, slot):
+    #  Returns the function implementing this slot in the baseclass.
+    #  This is useful for enabling the compiler to optimize calls
+    #  that recursively climb the class hierarchy.
+    slot_code = slot.slot_code(scope)
+    if slot_code != '0':
+        entry = scope.parent_scope.lookup_here(scope.parent_type.name)
+        if entry.visibility != 'extern':
+            return slot_code
+    return None
+
 #------------------------------------------------------------------------------------------
 #
 #  Signatures for generic Python functions and methods.