fix type inference for names of builtin functions

Cython/Compiler/ExprNodes.py

@@ -1349,6 +1349,10 @@ class NameNode(AtomicExprNode):
             # is used for the pointer to the type they represent.
             return type_type
         elif self.entry.type.is_cfunction:
+            if self.entry.scope.is_builtin_scope:
+                # special case: optimised builtin functions must be treated as Python objects
+                return py_object_type
+            else:
                 # special case: referring to a C function must return its pointer
                 return PyrexTypes.CPtrType(self.entry.type)
         else:

tests/run/builtin_abs.pyx

@@ -12,6 +12,15 @@ max_long_long = 2 ** (sizeof(long long) * 8 - 1) - 1
 
 cimport cython
 
+def abs_as_name():
+    """
+    >>> _abs = abs_as_name()
+    >>> _abs(-5)
+    5
+    """
+    x = abs
+    return x
+
 def py_abs(a):
     """
     >>> py_abs(-5)

tests/run/type_inference.pyx

@@ -221,6 +221,24 @@ def c_functions():
     assert typeof(f) == 'int (*)(int)', typeof(f)
     assert 2 == f(1)
 
+def builtin_functions():
+    """
+    >>> _abs, _getattr = builtin_functions()
+    Python object
+    Python object
+    >>> _abs(-1)
+    1
+    >>> class o(object): pass
+    >>> o.x = 1
+    >>> _getattr(o, 'x')
+    1
+    """
+    _abs = abs
+    print(typeof(_abs))
+    _getattr = getattr
+    print(typeof(_getattr))
+    return _abs, _getattr
+
 def cascade():
     """
     >>> cascade()