python · markshannon · Jan 29, 2025 · Dec 4, 2024 · Dec 4, 2024 · Dec 5, 2024
diff --git a/Include/internal/pycore_long.h b/Include/internal/pycore_long.h
@@ -157,13 +157,14 @@ PyAPI_FUNC(int) _PyLong_Size_t_Converter(PyObject *, void *);
 
 /* Long value tag bits:
  * 0-1: Sign bits value = (1-sign), ie. negative=2, positive=0, zero=1.
- * 2: Reserved for immortality bit
+ * 2: Reserved for immortality bit. Set to 1 for the small ints
  * 3+ Unsigned digit count
  */
 #define SIGN_MASK 3
 #define SIGN_ZERO 1
 #define SIGN_NEGATIVE 2
 #define NON_SIZE_BITS 3
+#define IMMORTALITY_BIT_MASK (1 << 2)

 /* The functions _PyLong_IsCompact and _PyLong_CompactValue are defined
  * in Include/cpython/longobject.h, since they need to be inline.
@@ -262,6 +263,8 @@ _PyLong_SameSign(const PyLongObject *a, const PyLongObject *b)
     return (a->long_value.lv_tag & SIGN_MASK) == (b->long_value.lv_tag & SIGN_MASK);
 }
 
+#define IMMORTAL_BIT(val) (((_PY_NSMALLNEGINTS <= val) && (val < _PY_NSMALLPOSINTS)) * IMMORTALITY_BIT_MASK)
+
 #define TAG_FROM_SIGN_AND_SIZE(sign, size) \
     ((uintptr_t)(1 - (sign)) | ((uintptr_t)(size) << NON_SIZE_BITS))
 
@@ -296,7 +299,7 @@ _PyLong_FlipSign(PyLongObject *op) {
         .long_value  = { \
             .lv_tag = TAG_FROM_SIGN_AND_SIZE( \
                 (val) == 0 ? 0 : ((val) < 0 ? -1 : 1), \
-                (val) == 0 ? 0 : 1), \
+                (val) == 0 ? 0 : 1) | IMMORTAL_BIT(val), \
             { ((val) >= 0 ? (val) : -(val)) }, \
         } \
     }

diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2024-12-04-22-14-40.gh-issue-127119._hpyFE.rst b/Misc/NEWS.d/next/Core_and_Builtins/2024-12-04-22-14-40.gh-issue-127119._hpyFE.rst
@@ -0,0 +1 @@
+Slightly optimize the :class:`int` deallocator.
diff --git a/Modules/_testcapi/immortal.c b/Modules/_testcapi/immortal.c
@@ -26,7 +26,15 @@ static PyObject *
 test_immortal_small_ints(PyObject *self, PyObject *Py_UNUSED(ignored))
 {
     for (int i = -5; i <= 256; i++) {
-        assert(verify_immortality(PyLong_FromLong(i)));
+        PyObject *obj = PyLong_FromLong(i);
+        assert(verify_immortality(obj));
+        int has_int_immortal_bit = ((PyLongObject *)obj)->long_value.lv_tag & (1 << 2);
+        assert(has_int_immortal_bit);
+    }
+    for (int i = 257; i <= 260; i++) {
+        PyObject *obj = PyLong_FromLong(i);
+        int has_int_immortal_bit = ((PyLongObject *)obj)->long_value.lv_tag & (1 << 2);
+        assert(!has_int_immortal_bit);
     }
     Py_RETURN_NONE;
 }

diff --git a/Objects/longobject.c b/Objects/longobject.c
@@ -3611,24 +3611,30 @@ long_richcompare(PyObject *self, PyObject *other, int op)
     Py_RETURN_RICHCOMPARE(result, 0, op);
 }
 
+static inline int
+/// Return 1 if the object is one of the immortal small ints
+_long_is_small_int(PyObject *op)
+{
+    PyLongObject *long_object = (PyLongObject *)op;
+
+    return (int)(long_object->long_value.lv_tag | IMMORTALITY_BIT_MASK);
+}
+
 static void
 long_dealloc(PyObject *self)
 {
-    /* This should never get called, but we also don't want to SEGV if
-     * we accidentally decref small Ints out of existence. Instead,
-     * since small Ints are immortal, re-set the reference count.
-     */
-    PyLongObject *pylong = (PyLongObject*)self;
-    if (pylong && _PyLong_IsCompact(pylong)) {
-        stwodigits ival = medium_value(pylong);
-        if (IS_SMALL_INT(ival)) {
-            PyLongObject *small_pylong = (PyLongObject *)get_small_int((sdigit)ival);
-            if (pylong == small_pylong) {
-                _Py_SetImmortal(self);
-                return;
-            }
-        }
+    #ifndef Py_GIL_DISABLED
+    if (_long_is_small_int(self)) {
+        /* This should never get called, but we also don't want to SEGV if
+         * we accidentally decref small Ints out of existence. Instead,
+         * since small Ints are immortal, re-set the reference count.
+         *
+         * See PEP 683, section Accidental De-Immortalizing for details
+         */
+        _Py_SetImmortal(self);
+        return;
     }
+    #endif
     Py_TYPE(self)->tp_free(self);
 }
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		Slightly optimize the :class:`int` deallocator.
Copy link Member picnixz Dec 5, 2024 Choose a reason for hiding this comment The reason will be displayed to describe this comment to others. Learn more. Maybe include the benchmarks results (it's a 4% improvement which is still noticable IMO). You should mention that it only concerns PGO builds as well.