Avoid calling PySequence_Tuple() if what we have is exactly a tuple.

Cython/Compiler/ExprNodes.py

@@ -6264,6 +6264,7 @@ class AsTupleNode(ExprNode):
     #  arg    ExprNode
 
     subexprs = ['arg']
+    is_temp = 1
 
     def calculate_constant_result(self):
         self.constant_result = tuple(self.arg.constant_result)
@@ -6280,7 +6281,6 @@ class AsTupleNode(ExprNode):
         if self.arg.type is tuple_type:
             return self.arg.as_none_safe_node("'NoneType' object is not iterable")
         self.type = tuple_type
-        self.is_temp = 1
         return self
 
     def may_be_none(self):
@@ -6290,10 +6290,11 @@ class AsTupleNode(ExprNode):
     gil_message = "Constructing Python tuple"
 
     def generate_result_code(self, code):
+        cfunc = "__Pyx_PySequence_Tuple" if self.arg.type in (py_object_type, tuple_type) else "PySequence_Tuple"
         code.putln(
-            "%s = PySequence_Tuple(%s); %s" % (
+            "%s = %s(%s); %s" % (
                 self.result(),
-                self.arg.py_result(),
+                cfunc, self.arg.py_result(),
                 code.error_goto_if_null(self.result(), self.pos)))
         code.put_gotref(self.py_result())
 

Cython/Compiler/Optimize.py

@@ -2210,14 +2210,10 @@ class OptimizeBuiltinCalls(Visitor.NodeRefCleanupMixin,
             PyrexTypes.CFuncTypeArg("list", Builtin.list_type, None)
             ])
 
-    PySequence_Tuple_func_type = PyrexTypes.CFuncType(
-        Builtin.tuple_type,
-        [PyrexTypes.CFuncTypeArg("it", PyrexTypes.py_object_type, None)])
-
     def _handle_simple_function_tuple(self, node, function, pos_args):
         """Replace tuple([...]) by PyList_AsTuple or PySequence_Tuple.
         """
-        if len(pos_args) != 1:
+        if len(pos_args) != 1 or not node.is_temp:
             return node
         arg = pos_args[0]
         if arg.type is Builtin.tuple_type and not arg.may_be_none():
@@ -2230,9 +2226,7 @@ class OptimizeBuiltinCalls(Visitor.NodeRefCleanupMixin,
                 node.pos, "PyList_AsTuple", self.PyList_AsTuple_func_type,
                 args=pos_args, is_temp=node.is_temp)
         else:
-            return ExprNodes.PythonCapiCallNode(
-                node.pos, "PySequence_Tuple", self.PySequence_Tuple_func_type,
-                args=pos_args, is_temp=node.is_temp)
+            return ExprNodes.AsTupleNode(node.pos, arg=arg, type=Builtin.tuple_type)
 
     PySet_New_func_type = PyrexTypes.CFuncType(
         Builtin.set_type, [

Cython/Utility/TypeConversion.c

@@ -92,6 +92,9 @@ static CYTHON_INLINE size_t __Pyx_Py_UNICODE_strlen(const Py_UNICODE *u)
 static CYTHON_INLINE int __Pyx_PyObject_IsTrue(PyObject*);
 static CYTHON_INLINE PyObject* __Pyx_PyNumber_IntOrLong(PyObject* x);
 
+#define __Pyx_PySequence_Tuple(obj) \
+    (likely(PyTuple_CheckExact(obj)) ? __Pyx_NewRef(obj) : PySequence_Tuple(obj))
+
 static CYTHON_INLINE Py_ssize_t __Pyx_PyIndex_AsSsize_t(PyObject*);
 static CYTHON_INLINE PyObject * __Pyx_PyInt_FromSize_t(size_t);