Issue #26200: The SETREF macro adds unnecessary work in some cases.

rhettinger · rhettinger · commit 38418662e033 · 2016-02-08T20:34:49.000-08:00
diff --git a/Modules/_collectionsmodule.c b/Modules/_collectionsmodule.c
@@ -1218,6 +1218,7 @@ deque_del_item(dequeobject *deque, Py_ssize_t i)
 static int
 deque_ass_item(dequeobject *deque, Py_ssize_t i, PyObject *v)
 {
+    PyObject *old_value;
     block *b;
     Py_ssize_t n, len=Py_SIZE(deque), halflen=(len+1)>>1, index=i;
 
@@ -1246,7 +1247,9 @@ deque_ass_item(dequeobject *deque, Py_ssize_t i, PyObject *v)
             b = b->leftlink;
     }
     Py_INCREF(v);
-    Py_SETREF(b->data[i], v);
+    old_value = b->data[i];
+    b->data[i] = v;
+    Py_DECREF(old_value);
     return 0;
 }
 

Original file line number	Diff line number	Diff line change
`@@ -1218,6 +1218,7 @@ deque_del_item(dequeobject *deque, Py_ssize_t i)`
`1218`	`1218`	`static int`
`1219`	`1219`	`deque_ass_item(dequeobject deque, Py_ssize_t i, PyObject v)`
`1220`	`1220`	`{`
	`1221`	`+ PyObject *old_value;`
`1221`	`1222`	`block *b;`
`1222`	`1223`	`Py_ssize_t n, len=Py_SIZE(deque), halflen=(len+1)>>1, index=i;`
`1223`	`1224`
`@@ -1246,7 +1247,9 @@ deque_ass_item(dequeobject deque, Py_ssize_t i, PyObject v)`
`1246`	`1247`	`b = b->leftlink;`
`1247`	`1248`	`}`
`1248`	`1249`	`Py_INCREF(v);`
`1249`		`- Py_SETREF(b->data[i], v);`
	`1250`	`+ old_value = b->data[i];`
	`1251`	`+ b->data[i] = v;`
	`1252`	`+ Py_DECREF(old_value);`
`1250`	`1253`	`return 0;`
`1251`	`1254`	`}`
`1252`	`1255`