fix isinstance() check against a tuple of extension types

Cython/Compiler/Optimize.py

@@ -1994,14 +1994,15 @@ class OptimizeBuiltinCalls(Visitor.EnvTransform):
                         builtin_type = entry.type
             if builtin_type and builtin_type is not Builtin.type_type:
                 type_check_function = entry.type.type_check_function(exact=False)
+                if type_check_function in tests:
+                    continue
+                tests.append(type_check_function)
                 type_check_args = [arg]
             elif test_type_node.type is Builtin.type_type:
                 type_check_function = '__Pyx_TypeCheck'
                 type_check_args = [arg, test_type_node]
             else:
                 return node
-            if type_check_function not in tests:
-                tests.append(type_check_function)
             test_nodes.append(
                 ExprNodes.PythonCapiCallNode(
                     test_type_node.pos, type_check_function, self.Py_type_check_func_type,

tests/run/isinstance.pyx

@@ -77,6 +77,23 @@ def test_custom():
     assert isinstance(A(), A)
     return True
 
+cdef class B:
+    pass
+
+cdef class C:
+    pass
+
+def test_custom_tuple(obj):
+    """
+    >>> test_custom_tuple(A())
+    True
+    >>> test_custom_tuple(B())
+    True
+    >>> test_custom_tuple(C())
+    False
+    """
+    return isinstance(obj, (A,B))
+
 def test_nested(x):
     """
     >>> test_nested(1)