GH-155728: Untrack const tuples

Lib/test/test_tuple.py

@@ -294,6 +294,9 @@ def test_repr(self):
     def _not_tracked_instantly(self, t):
         self.assertFalse(gc.is_tracked(t), t)
 
+    def _tracked_instantly(self, t):
+        self.assertTrue(gc.is_tracked(t), t)
+
     # Checks that t is not tracked after GC collection.
     def _not_tracked(self, t):
         # Nested tuples can take several collections to untrack
@@ -319,10 +322,19 @@ def test_track_literals(self):
         self._not_tracked_instantly((1,))
         self._not_tracked_instantly((1, 2))
         self._not_tracked_instantly((1, 2, "a"))
-        self._not_tracked_instantly((1, 2) * 5)
         self._not_tracked_instantly((12, 10**10, 'a_' * 100))
         self._not_tracked_instantly((object(),))
 
+        # Test for _PyTuple_Concat
+        self._not_tracked_instantly((1, 2) + (2, 3, 4))
+        self._not_tracked_instantly((x, y,) + (2, 3))
+        self._tracked_instantly((3, 4, 5, [],) + (2, 3))
+
+        # Test for _PyTuple_Repeat
+        self._not_tracked_instantly((1, 2) * 5)
+        self._not_tracked_instantly((1, x) * 5)
+        self._tracked_instantly((1, []) * 5)
+
         self._not_tracked(((1, x), y, (2, 3)))
         self._not_tracked((1, 2, (None, True, False, ()), int))
         self._not_tracked((object(), ()))

Misc/NEWS.d/next/Core_and_Builtins/2026-08-26-19-28-49.gh-issue-155728.LJIPeZ.rst

@@ -0,0 +1,2 @@
+The flowgraph optimizer now untracks tuples from the GC when possible. Patch
+by Sergey Miryanov.

Objects/tupleobject.c

@@ -593,7 +593,10 @@ _PyTuple_Concat(PyObject *aa, PyObject *bb)
         dest[i] = Py_NewRef(v);
     }
 
-    _PyObject_GC_TRACK(np);
+    if (_PyObject_GC_IS_TRACKED(aa) || _PyObject_GC_IS_TRACKED(bb))
+    {
+        _PyObject_GC_TRACK(np);
+    }
     return (PyObject *)np;
 }
 
@@ -642,7 +645,10 @@ _PyTuple_Repeat(PyObject *self, Py_ssize_t n)
         _Py_memory_repeat((char *)np->ob_item, sizeof(PyObject *)*output_size,
                           sizeof(PyObject *)*input_size);
     }
-    _PyObject_GC_TRACK(np);
+    if (_PyObject_GC_IS_TRACKED(self))
+    {
+        _PyObject_GC_TRACK(np);
+    }
     return (PyObject *) np;
 }
 

Python/flowgraph.c

@@ -1552,6 +1552,8 @@ fold_tuple_of_constants(basicblock *bb, int i, PyObject *consts,
     if (const_tuple == NULL) {
         return ERROR;
     }
+    PyObject_GC_UnTrack(const_tuple);
+    bool track_tuple = false;
 
     for (int i = 0; i < seq_size; i++) {
         cfg_instr *inst = const_instrs[i];
@@ -1562,6 +1564,12 @@ fold_tuple_of_constants(basicblock *bb, int i, PyObject *consts,
             return ERROR;
         }
         PyTuple_SET_ITEM(const_tuple, i, element);
+        if (!track_tuple && PyObject_GC_IsTracked(element)) {
+            track_tuple = true;
+        }
+    }
+    if (track_tuple) {
+        _PyObject_GC_TRACK(const_tuple);
     }
 
     nop_out(const_instrs, seq_size);
@@ -1632,6 +1640,8 @@ fold_constant_seq_into_load_const(basicblock *bb, int i,
             if (newconst == NULL) {
                 return ERROR;
             }
+            PyObject_GC_UnTrack(newconst);
+            bool track_tuple = false;
 
             int newpos_start = expected_append ? i - 1 : i;
             for (int newpos = newpos_start; newpos >= pos; newpos--) {
@@ -1647,9 +1657,15 @@ fold_constant_seq_into_load_const(basicblock *bb, int i,
                     }
                     assert(consts_found > 0);
                     PyTuple_SET_ITEM(newconst, --consts_found, constant);
+                    if (!track_tuple && PyObject_GC_IsTracked(constant)) {
+                        track_tuple = true;
+                    }
                 }
                 nop_out(&instr, 1);
             }
+            if (track_tuple) {
+                _PyObject_GC_TRACK(newconst);
+            }
             assert(consts_found == 0);
 
             if (build_op == BUILD_SET) {
@@ -1726,6 +1742,8 @@ optimize_lists_and_sets(basicblock *bb, int i, int nextop,
     if (const_result == NULL) {
         return ERROR;
     }
+    PyObject_GC_UnTrack(const_result);
+    bool track_tuple = false;
 
     for (int i = 0; i < seq_size; i++) {
         cfg_instr *inst = const_instrs[i];
@@ -1736,6 +1754,12 @@ optimize_lists_and_sets(basicblock *bb, int i, int nextop,
             return ERROR;
         }
         PyTuple_SET_ITEM(const_result, i, element);
+        if (!track_tuple && PyObject_GC_IsTracked(element)) {
+            track_tuple = true;
+        }
+    }
+    if (track_tuple) {
+        _PyObject_GC_TRACK(const_result);
     }
 
     if (instr->i_opcode == BUILD_SET) {