optimise set(it) into a call to PySet_New(it)

Cython/Compiler/Optimize.py

@@ -1993,9 +1993,14 @@ class OptimizeBuiltinCalls(Visitor.MethodDispatcherTransform):
         exception_value = "((double)-1)",
         exception_check = True)
 
+    PySet_New_func_type = PyrexTypes.CFuncType(
+        Builtin.set_type, [
+            PyrexTypes.CFuncTypeArg("it", PyrexTypes.py_object_type, None)
+        ])
+
     def _handle_simple_function_set(self, node, function, pos_args):
-        if len(pos_args) == 1 and isinstance(pos_args[0], (ExprNodes.ListNode,
-                                                           ExprNodes.TupleNode)):
+        if len(pos_args) == 1:
+            if pos_args[0].is_sequence_constructor:
                 # We can optimise set([x,y,z]) safely into a set literal,
                 # but only if we create all items before adding them -
                 # adding an item may raise an exception if it is not
@@ -2012,6 +2017,15 @@ class OptimizeBuiltinCalls(Visitor.MethodDispatcherTransform):
                 for temp in temps[::-1]:
                     result = UtilNodes.EvalWithTempExprNode(temp, result)
                 return result
+            else:
+                # PySet_New(it) is better than a generic Python call to set(it)
+                return ExprNodes.PythonCapiCallNode(
+                    node.pos, "PySet_New",
+                    self.PySet_New_func_type,
+                    args=pos_args,
+                    is_temp=node.is_temp,
+                    utility_code=UtilityCode.load_cached('pyset_compat', 'Builtins.c'),
+                    py_name="set")
         return node
 
     def _handle_simple_function_float(self, node, function, pos_args):