avoid redundant C-Py-C roundtrip for Py_UCS4 return values

Cython/Compiler/Optimize.py

@@ -2021,6 +2021,9 @@ class OptimizeBuiltinCalls(Visitor.NodeRefCleanupMixin,
                 if node.type.assignable_from(arg.arg.type):
                     # completely redundant C->Py->C coercion
                     return arg.arg.coerce_to(node.type, self.current_env())
+            elif arg.type is Builtin.unicode_type:
+                if arg.arg.type.is_unicode_char and node.type.is_unicode_char:
+                    return arg.arg.coerce_to(node.type, self.current_env())
         elif isinstance(arg, ExprNodes.SimpleCallNode):
             if node.type.is_int or node.type.is_float:
                 return self._optimise_numeric_cast_call(node, arg)

tests/run/py_ucs4_type.pyx

@@ -145,6 +145,24 @@ def unicode_methods(Py_UCS4 uchar):
         uchar.title(),
         ]
 
+
+@cython.test_assert_path_exists('//PythonCapiCallNode')
+@cython.test_fail_if_path_exists(
+    '//SimpleCallNode',
+    '//CoerceFromPyTypeNode',
+)
+def unicode_method_return_type(Py_UCS4 uchar):
+    """
+    >>> unicode_method_return_type(ord('A'))
+    [True, False]
+    >>> unicode_method_return_type(ord('a'))
+    [False, True]
+    """
+    cdef Py_UCS4 uc, ul
+    uc, ul = uchar.upper(), uchar.lower()
+    return [uc == uchar, ul == uchar]
+
+
 @cython.test_assert_path_exists('//IntNode')
 @cython.test_fail_if_path_exists('//SimpleCallNode',
                                  '//PythonCapiCallNode')