gh-99537: Use Py_SETREF() function in C code (#99657)

Fix potential race condition in code patterns:

* Replace "Py_DECREF(var); var = new;" with "Py_SETREF(var, new);"
* Replace "Py_XDECREF(var); var = new;" with "Py_XSETREF(var, new);"
* Replace "Py_CLEAR(var); var = new;" with "Py_XSETREF(var, new);"

Other changes:

* Replace "old = var; var = new; Py_DECREF(var)"
  with "Py_SETREF(var, new);"
* Replace "old = var; var = new; Py_XDECREF(var)"
  with "Py_XSETREF(var, new);"
* And remove the "old" variable.

1 files changed, 3 insertions, 6 deletions

diff --git a/Objects/floatobject.c b/Objects/floatobject.c
index 46016e946a..912b742f79 100644
--- a/Objects/floatobject.c
+++ b/Objects/floatobject.c
@@ -531,20 +531,17 @@ float_richcompare(PyObject *v, PyObject *w, int op)
                 temp = _PyLong_Lshift(ww, 1);
                 if (temp == NULL)
                     goto Error;
-                Py_DECREF(ww);
-                ww = temp;
+                Py_SETREF(ww, temp);
 
                 temp = _PyLong_Lshift(vv, 1);
                 if (temp == NULL)
                     goto Error;
-                Py_DECREF(vv);
-                vv = temp;
+                Py_SETREF(vv, temp);
 
                 temp = PyNumber_Or(vv, _PyLong_GetOne());
                 if (temp == NULL)
                     goto Error;
-                Py_DECREF(vv);
-                vv = temp;
+                Py_SETREF(vv, temp);
             }
 
             r = PyObject_RichCompareBool(vv, ww, op);