Fast dealloc of immortal tuples

Author: mdboom

Include/cpython/tupleobject.h

@@ -6,6 +6,7 @@ typedef struct {
     PyObject_VAR_HEAD
     /* Cached hash.  Initially set to -1. */
     Py_hash_t ob_hash;
+    int contains_mortal;
     /* ob_item contains space for 'ob_size' elements.
        Items must normally not be NULL, except during construction when
        the tuple is not yet visible outside the function that builds it. */
@@ -35,6 +36,7 @@ PyTuple_SET_ITEM(PyObject *op, Py_ssize_t index, PyObject *value) {
     assert(0 <= index);
     assert(index < Py_SIZE(tuple));
     tuple->ob_item[index] = value;
+    tuple->contains_mortal |= !_Py_IsImmortal(value);
 }
 #define PyTuple_SET_ITEM(op, index, value) \
     PyTuple_SET_ITEM(_PyObject_CAST(op), (index), _PyObject_CAST(value))

Include/internal/pycore_runtime_init.h

@@ -108,6 +108,7 @@ extern PyTypeObject _PyExc_MemoryError;
                 .tuple_empty = { \
                     .ob_base = _PyVarObject_HEAD_INIT(&PyTuple_Type, 0), \
                     .ob_hash = _PyTuple_HASH_EMPTY, \
+                    .contains_mortal = 0, \
                 }, \
                 .hamt_bitmap_node_empty = { \
                     .ob_base = _PyVarObject_HEAD_INIT(&_PyHamt_BitmapNode_Type, 0), \

Include/internal/pycore_tuple.h

@@ -44,6 +44,7 @@ typedef struct {
 static inline void
 _PyTuple_Recycle(PyObject *op)
 {
+    ((PyTupleObject *)op)->contains_mortal = 0;
     _PyTuple_RESET_HASH_CACHE(op);
     if (!_PyObject_GC_IS_TRACKED(op)) {
         _PyObject_GC_TRACK(op);