gh-90667: Add specializations of Py_DECREF when types are known (GH-30872)

Author: sweeneyde

Include/internal/pycore_floatobject.h

@@ -38,6 +38,8 @@ struct _Py_float_state {
 #endif
 };
 
+void _PyFloat_ExactDealloc(PyObject *op);
+
 
 PyAPI_FUNC(void) _PyFloat_DebugMallocStats(FILE* out);
 

Include/internal/pycore_object.h

@@ -14,7 +14,6 @@ extern "C" {
 #include "pycore_pystate.h"       // _PyInterpreterState_GET()
 #include "pycore_runtime.h"       // _PyRuntime
 
-
 #define _PyObject_IMMORTAL_INIT(type) \
     { \
         .ob_refcnt = 999999999, \
@@ -26,6 +25,42 @@ extern "C" {
         .ob_size = size, \
     }
 
+PyAPI_FUNC(void) _Py_NO_RETURN _Py_FatalRefcountErrorFunc(
+    const char *func,
+    const char *message);
+
+#define _Py_FatalRefcountError(message) _Py_FatalRefcountErrorFunc(__func__, message)
+
+static inline void
+_Py_DECREF_SPECIALIZED(PyObject *op, const destructor destruct)
+{
+#ifdef Py_REF_DEBUG
+    _Py_RefTotal--;
+#endif
+    if (--op->ob_refcnt != 0) {
+        assert(op->ob_refcnt > 0);
+    }
+    else {
+#ifdef Py_TRACE_REFS
+        _Py_ForgetReference(op);
+#endif
+        destruct(op);
+    }
+}
+
+static inline void
+_Py_DECREF_NO_DEALLOC(PyObject *op)
+{
+#ifdef Py_REF_DEBUG
+    _Py_RefTotal--;
+#endif
+    op->ob_refcnt--;
+#ifdef Py_DEBUG
+    if (op->ob_refcnt <= 0) {
+        _Py_FatalRefcountError("Expected a positive remaining refcount");
+    }
+#endif
+}
 
 PyAPI_FUNC(int) _PyType_CheckConsistency(PyTypeObject *type);
 PyAPI_FUNC(int) _PyDict_CheckConsistency(PyObject *mp, int check_content);

Include/internal/pycore_pyerrors.h

@@ -100,13 +100,6 @@ extern PyObject* _Py_Offer_Suggestions(PyObject* exception);
 PyAPI_FUNC(Py_ssize_t) _Py_UTF8_Edit_Cost(PyObject *str_a, PyObject *str_b,
                                           Py_ssize_t max_cost);
 
-PyAPI_FUNC(void) _Py_NO_RETURN _Py_FatalRefcountErrorFunc(
-    const char *func,
-    const char *message);
-
-#define _Py_FatalRefcountError(message) _Py_FatalRefcountErrorFunc(__func__, message)
-
-
 #ifdef __cplusplus
 }
 #endif

Include/internal/pycore_unicodeobject.h

@@ -10,6 +10,7 @@ extern "C" {
 
 #include "pycore_fileutils.h"     // _Py_error_handler
 
+void _PyUnicode_ExactDealloc(PyObject *op);
 
 /* runtime lifecycle */
 

Misc/NEWS.d/next/Core and Builtins/2022-01-25-05-39-38.bpo-46509.ljrqrc.rst

@@ -0,0 +1 @@
+Add type-specialized versions of the ``Py_DECREF()``, and use them for ``float``, ``int``, ``str``, ``bool``, and ``None`` to avoid pointer-chasing at runtime where types are known at C compile time.

Objects/boolobject.c

@@ -1,8 +1,8 @@
 /* Boolean type, a subtype of int */
 
 #include "Python.h"
+#include "pycore_object.h"      // _Py_FatalRefcountError()
 #include "pycore_runtime.h"       // _Py_ID()
-#include "pycore_pyerrors.h"      // _Py_FatalRefcountError()
 
 /* We define bool_repr to return "False" or "True" */
 

Objects/floatobject.c

@@ -238,28 +238,41 @@ PyFloat_FromString(PyObject *v)
     return result;
 }
 
-static void
-float_dealloc(PyFloatObject *op)
+void
+_PyFloat_ExactDealloc(PyObject *obj)
 {
+    assert(PyFloat_CheckExact(obj));
+    PyFloatObject *op = (PyFloatObject *)obj;
 #if PyFloat_MAXFREELIST > 0
-    if (PyFloat_CheckExact(op)) {
-        struct _Py_float_state *state = get_float_state();
+    struct _Py_float_state *state = get_float_state();
 #ifdef Py_DEBUG
-        // float_dealloc() must not be called after _PyFloat_Fini()
-        assert(state->numfree != -1);
+    // float_dealloc() must not be called after _PyFloat_Fini()
+    assert(state->numfree != -1);
 #endif
-        if (state->numfree >= PyFloat_MAXFREELIST)  {
-            PyObject_Free(op);
-            return;
-        }
-        state->numfree++;
-        Py_SET_TYPE(op, (PyTypeObject *)state->free_list);
-        state->free_list = op;
+    if (state->numfree >= PyFloat_MAXFREELIST)  {
+        PyObject_Free(op);
+        return;
+    }
+    state->numfree++;
+    Py_SET_TYPE(op, (PyTypeObject *)state->free_list);
+    state->free_list = op;
+#else
+    PyObject_Free(op);
+#endif
+}
+
+static void
+float_dealloc(PyObject *op)
+{
+    assert(PyFloat_Check(op));
+#if PyFloat_MAXFREELIST > 0
+    if (PyFloat_CheckExact(op)) {
+        _PyFloat_ExactDealloc(op);
     }
     else
 #endif
     {
-        Py_TYPE(op)->tp_free((PyObject *)op);
+        Py_TYPE(op)->tp_free(op);
     }
 }
 

Objects/longobject.c

@@ -36,7 +36,15 @@ medium_value(PyLongObject *x)
 #define IS_SMALL_INT(ival) (-_PY_NSMALLNEGINTS <= (ival) && (ival) < _PY_NSMALLPOSINTS)
 #define IS_SMALL_UINT(ival) ((ival) < _PY_NSMALLPOSINTS)
 
-static inline int is_medium_int(stwodigits x)
+static inline void
+_Py_DECREF_INT(PyLongObject *op)
+{
+    assert(PyLong_CheckExact(op));
+    _Py_DECREF_SPECIALIZED((PyObject *)op, PyObject_Free);
+}
+
+static inline int
+is_medium_int(stwodigits x)
 {
     /* Take care that we are comparing unsigned values. */
     twodigits x_plus_mask = ((twodigits)x) + PyLong_MASK;
@@ -58,7 +66,7 @@ maybe_small_long(PyLongObject *v)
     if (v && IS_MEDIUM_VALUE(v)) {
         stwodigits ival = medium_value(v);
         if (IS_SMALL_INT(ival)) {
-            Py_DECREF(v);
+            _Py_DECREF_INT(v);
             return (PyLongObject *)get_small_int((sdigit)ival);
         }
     }
@@ -1856,7 +1864,7 @@ long_to_decimal_string_internal(PyObject *aa,
 #undef WRITE_DIGITS
 #undef WRITE_UNICODE_DIGITS
 
-    Py_DECREF(scratch);
+    _Py_DECREF_INT(scratch);
     if (writer) {
         writer->pos += strlen;
     }
@@ -3561,15 +3569,15 @@ k_mul(PyLongObject *a, PyLongObject *b)
      */
     i = Py_SIZE(ret) - shift;  /* # digits after shift */
     (void)v_isub(ret->ob_digit + shift, i, t2->ob_digit, Py_SIZE(t2));
-    Py_DECREF(t2);
+    _Py_DECREF_INT(t2);
 
     (void)v_isub(ret->ob_digit + shift, i, t1->ob_digit, Py_SIZE(t1));
-    Py_DECREF(t1);
+    _Py_DECREF_INT(t1);
 
     /* 6. t3 <- (ah+al)(bh+bl), and add into result. */
     if ((t1 = x_add(ah, al)) == NULL) goto fail;
-    Py_DECREF(ah);
-    Py_DECREF(al);
+    _Py_DECREF_INT(ah);
+    _Py_DECREF_INT(al);
     ah = al = NULL;
 
     if (a == b) {
@@ -3580,21 +3588,21 @@ k_mul(PyLongObject *a, PyLongObject *b)
         Py_DECREF(t1);
         goto fail;
     }
-    Py_DECREF(bh);
-    Py_DECREF(bl);
+    _Py_DECREF_INT(bh);
+    _Py_DECREF_INT(bl);
     bh = bl = NULL;
 
     t3 = k_mul(t1, t2);
-    Py_DECREF(t1);
-    Py_DECREF(t2);
+    _Py_DECREF_INT(t1);
+    _Py_DECREF_INT(t2);
     if (t3 == NULL) goto fail;
     assert(Py_SIZE(t3) >= 0);
 
     /* Add t3.  It's not obvious why we can't run out of room here.
      * See the (*) comment after this function.
      */
     (void)v_iadd(ret->ob_digit + shift, i, t3->ob_digit, Py_SIZE(t3));
-    Py_DECREF(t3);
+    _Py_DECREF_INT(t3);
 
     return long_normalize(ret);
 
@@ -3699,13 +3707,13 @@ k_lopsided_mul(PyLongObject *a, PyLongObject *b)
         /* Add into result. */
         (void)v_iadd(ret->ob_digit + nbdone, Py_SIZE(ret) - nbdone,
                      product->ob_digit, Py_SIZE(product));
-        Py_DECREF(product);
+        _Py_DECREF_INT(product);
 
         bsize -= nbtouse;
         nbdone += nbtouse;
     }
 
-    Py_DECREF(bslice);
+    _Py_DECREF_INT(bslice);
     return long_normalize(ret);
 
   fail:
@@ -5993,7 +6001,7 @@ PyTypeObject PyLong_Type = {
     0,                                          /* tp_init */
     0,                                          /* tp_alloc */
     long_new,                                   /* tp_new */
-    PyObject_Del,                               /* tp_free */
+    PyObject_Free,                              /* tp_free */
 };
 
 static PyTypeObject Int_InfoType;

Objects/object.c

@@ -9,7 +9,7 @@
 #include "pycore_floatobject.h"   // _PyFloat_DebugMallocStats()
 #include "pycore_initconfig.h"    // _PyStatus_EXCEPTION()
 #include "pycore_namespace.h"     // _PyNamespace_Type
-#include "pycore_object.h"        // _PyType_CheckConsistency()
+#include "pycore_object.h"        // _PyType_CheckConsistency(), _Py_FatalRefcountError()
 #include "pycore_pyerrors.h"      // _PyErr_Occurred()
 #include "pycore_pymem.h"         // _PyMem_IsPtrFreed()
 #include "pycore_pystate.h"       // _PyThreadState_GET()

Objects/tupleobject.c

@@ -5,8 +5,7 @@
 #include "pycore_abstract.h"      // _PyIndex_Check()
 #include "pycore_gc.h"            // _PyObject_GC_IS_TRACKED()
 #include "pycore_initconfig.h"    // _PyStatus_OK()
-#include "pycore_object.h"        // _PyObject_GC_TRACK()
-#include "pycore_pyerrors.h"      // _Py_FatalRefcountError()
+#include "pycore_object.h"        // _PyObject_GC_TRACK(), _Py_FatalRefcountError()
 
 /*[clinic input]
 class tuple "PyTupleObject *" "&PyTuple_Type"

Objects/unicodeobject.c

@@ -48,9 +48,8 @@ OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 #include "pycore_initconfig.h"    // _PyStatus_OK()
 #include "pycore_interp.h"        // PyInterpreterState.fs_codec
 #include "pycore_long.h"          // _PyLong_FormatWriter()
-#include "pycore_object.h"        // _PyObject_GC_TRACK()
+#include "pycore_object.h"        // _PyObject_GC_TRACK(), _Py_FatalRefcountError()
 #include "pycore_pathconfig.h"    // _Py_DumpPathConfig()
-#include "pycore_pyerrors.h"      // _Py_FatalRefcountError()
 #include "pycore_pylifecycle.h"   // _Py_SetFileSystemEncoding()
 #include "pycore_pystate.h"       // _PyInterpreterState_GET()
 #include "pycore_ucnhash.h"       // _PyUnicode_Name_CAPI
@@ -15369,6 +15368,13 @@ unicode_subtype_new(PyTypeObject *type, PyObject *unicode)
     return NULL;
 }
 
+void
+_PyUnicode_ExactDealloc(PyObject *op)
+{
+    assert(PyUnicode_CheckExact(op));
+    unicode_dealloc(op);
+}
+
 PyDoc_STRVAR(unicode_doc,
 "str(object='') -> str\n\
 str(bytes_or_buffer[, encoding[, errors]]) -> str\n\

Python/bltinmodule.c

@@ -2511,7 +2511,7 @@ builtin_sum_impl(PyObject *module, PyObject *iterable, PyObject *start)
             }
             if (PyFloat_CheckExact(item)) {
                 f_result += PyFloat_AS_DOUBLE(item);
-                Py_DECREF(item);
+                _Py_DECREF_SPECIALIZED(item, _PyFloat_ExactDealloc);
                 continue;
             }
             if (PyLong_Check(item)) {