perf(longobject): extend freelist to 3-digit PyLong objects

Extends the ints2 freelist pattern to 3-digit objects, which cover the range [2^60, 2^63-1] (positive) and [-2^63, -2^60] (negative) on 30-bit builds - including INT64_MAX, INT64_MIN, and nanosecond-precision timestamps.

Also fuses the two _PyLong_IsCompact + _PyLong_DigitCount checks in long_dealloc under a single PyLong_CheckExact branch.

Benchmark (5M ops, 30-bit build):
  2-digit+2-digit -> 3-digit result:  19.6 ns -> 17.0 ns  (-13%)
  3-digit+compact -> 3-digit result:  18.3 ns -> 15.4 ns  (-16%)
  INT64_MAX + 0:                     18.2 ns -> 15.9 ns  (-13%)
  INT64_MIN + 0:                     18.1 ns -> 16.2 ns  (-10%)

Author: KRRT7

Include/internal/pycore_freelist_state.h

@@ -19,6 +19,7 @@ extern "C" {
 #  define Py_complexes_MAXFREELIST 100
 #  define Py_ints_MAXFREELIST 100
 #  define Py_ints2_MAXFREELIST 100
+#  define Py_ints3_MAXFREELIST 50
 #  define Py_slices_MAXFREELIST 1
 #  define Py_ranges_MAXFREELIST 6
 #  define Py_range_iters_MAXFREELIST 6
@@ -49,6 +50,7 @@ struct _Py_freelists {
     struct _Py_freelist complexes;
     struct _Py_freelist ints;
     struct _Py_freelist ints2;
+    struct _Py_freelist ints3;
     struct _Py_freelist tuples[PyTuple_MAXSAVESIZE];
     struct _Py_freelist lists;
     struct _Py_freelist list_iters;

Objects/longobject.c

@@ -175,6 +175,9 @@ long_alloc(Py_ssize_t size)
     else if (ndigits == 2) {
         result = (PyLongObject *)_Py_FREELIST_POP(PyLongObject, ints2);
     }
+    else if (ndigits == 3) {
+        result = (PyLongObject *)_Py_FREELIST_POP(PyLongObject, ints3);
+    }
     if (result == NULL) {
         /* Number of bytes needed is: offsetof(PyLongObject, ob_digit) +
         sizeof(digit)*size.  Previous incarnations of this code used
@@ -3647,10 +3650,15 @@ _PyLong_ExactDealloc(PyObject *self)
         _Py_FREELIST_FREE(ints, self, PyObject_Free);
         return;
     }
-    if (_PyLong_DigitCount((PyLongObject *)self) == 2) {
+    Py_ssize_t ndigits = _PyLong_DigitCount((PyLongObject *)self);
+    if (ndigits == 2) {
         _Py_FREELIST_FREE(ints2, self, PyObject_Free);
         return;
     }
+    if (ndigits == 3) {
+        _Py_FREELIST_FREE(ints3, self, PyObject_Free);
+        return;
+    }
     PyObject_Free(self);
 }
 
@@ -3667,13 +3675,20 @@ long_dealloc(PyObject *self)
         _Py_SetImmortal(self);
         return;
     }
-    if (PyLong_CheckExact(self) && _PyLong_IsCompact((PyLongObject *)self)) {
-        _Py_FREELIST_FREE(ints, self, PyObject_Free);
-        return;
-    }
-    if (PyLong_CheckExact(self) && _PyLong_DigitCount((PyLongObject *)self) == 2) {
-        _Py_FREELIST_FREE(ints2, self, PyObject_Free);
-        return;
+    if (PyLong_CheckExact(self)) {
+        if (_PyLong_IsCompact((PyLongObject *)self)) {
+            _Py_FREELIST_FREE(ints, self, PyObject_Free);
+            return;
+        }
+        Py_ssize_t ndigits = _PyLong_DigitCount((PyLongObject *)self);
+        if (ndigits == 2) {
+            _Py_FREELIST_FREE(ints2, self, PyObject_Free);
+            return;
+        }
+        if (ndigits == 3) {
+            _Py_FREELIST_FREE(ints3, self, PyObject_Free);
+            return;
+        }
     }
     Py_TYPE(self)->tp_free(self);
 }

Objects/object.c

@@ -953,6 +953,7 @@ _PyObject_ClearFreeLists(struct _Py_freelists *freelists, int is_finalization)
     clear_freelist(&freelists->bytes_writers, is_finalization, PyMem_Free);
     clear_freelist(&freelists->ints, is_finalization, free_object);
     clear_freelist(&freelists->ints2, is_finalization, free_object);
+    clear_freelist(&freelists->ints3, is_finalization, free_object);
     clear_freelist(&freelists->pycfunctionobject, is_finalization, PyObject_GC_Del);
     clear_freelist(&freelists->pycmethodobject, is_finalization, PyObject_GC_Del);
     clear_freelist(&freelists->pymethodobjects, is_finalization, free_object);