BUG: Fix reference count issues (GH-3022)

Cython/Utility/ObjectHandling.c

@@ -432,8 +432,11 @@ static CYTHON_INLINE PyObject *__Pyx_GetItemInt_Fast(PyObject *o, Py_ssize_t i,
         PyMappingMethods *mm = Py_TYPE(o)->tp_as_mapping;
         PySequenceMethods *sm = Py_TYPE(o)->tp_as_sequence;
         if (mm && mm->mp_subscript) {
-            PyObject *key = PyInt_FromSsize_t(i);
-            return likely(key) ? mm->mp_subscript(o, key) : NULL;
+            PyObject *r, *key = PyInt_FromSsize_t(i);
+            if (unlikely(!key)) return NULL;
+            r = mm->mp_subscript(o, key);
+            Py_DECREF(key);
+            return r;
         }
         if (likely(sm && sm->sq_item)) {
             if (wraparound && unlikely(i < 0) && likely(sm->sq_length)) {
@@ -497,8 +500,12 @@ static CYTHON_INLINE int __Pyx_SetItemInt_Fast(PyObject *o, Py_ssize_t i, PyObje
         PyMappingMethods *mm = Py_TYPE(o)->tp_as_mapping;
         PySequenceMethods *sm = Py_TYPE(o)->tp_as_sequence;
         if (mm && mm->mp_ass_subscript) {
+            int r;
             PyObject *key = PyInt_FromSsize_t(i);
-            return likely(key) ? mm->mp_ass_subscript(o, key, v) : -1;
+            if (unlikely(!key)) return -1;
+            mm->mp_ass_subscript(o, key, v);
+            Py_DECREF(key);
+            return r;
         }
         if (likely(sm && sm->sq_ass_item)) {
             if (wraparound && unlikely(i < 0) && likely(sm->sq_length)) {

Cython/Utility/Optimize.c

@@ -685,9 +685,11 @@ static PyObject* __Pyx__PyNumber_PowerOf2(PyObject *two, PyObject *exp, PyObject
             return PyLong_FromUnsignedLongLong(value);
 #endif
         } else {
-            PyObject *one = PyInt_FromLong(1L);
+            PyObject *result, *one = PyInt_FromLong(1L);
             if (unlikely(!one)) return NULL;
-            return PyNumber_Lshift(one, exp);
+            result = PyNumber_Lshift(one, exp);
+            Py_DECREF(one);
+            return result;
         }
     } else if (shiftby == -1 && PyErr_Occurred()) {
         PyErr_Clear();