fix: _Py_RefcntAdd missing calls to _Py_INCREF_STAT_INC/_Py_INCREF_IMMORTAL_STAT_INC.

Author: EdNutting

Include/cpython/pystats.h

@@ -18,6 +18,12 @@
 //
 // Define _PY_INTERPRETER macro to increment interpreter_increfs and
 // interpreter_decrefs. Otherwise, increment increfs and decrefs.
+//
+// The number of incref operations counted by `incref` and
+// `interpreter_incref` is the number of increment operations, which is
+// not equal to the total of all reference counts. A single increment
+// operation may increase the reference count of an object by more than
+// one. For example, see `_Py_RefcntAdd`.
 
 #ifndef Py_CPYTHON_PYSTATS_H
 #  error "this header file must not be included directly"

Include/internal/pycore_object.h

@@ -121,6 +121,7 @@ extern void _Py_DecRefTotal(PyThreadState *);
 static inline void _Py_RefcntAdd(PyObject* op, Py_ssize_t n)
 {
     if (_Py_IsImmortal(op)) {
+        _Py_INCREF_IMMORTAL_STAT_INC();
         return;
     }
 #ifdef Py_REF_DEBUG
@@ -145,6 +146,10 @@ static inline void _Py_RefcntAdd(PyObject* op, Py_ssize_t n)
         _Py_atomic_add_ssize(&op->ob_ref_shared, (n << _Py_REF_SHARED_SHIFT));
     }
 #endif
+    // Although the ref count was increased by `n` (which may be greater than 1)
+    // it is only a single increment (i.e. addition) operation, so only 1 refcnt
+    // increment operation is counted.
+    _Py_INCREF_STAT_INC();
 }
 #define _Py_RefcntAdd(op, n) _Py_RefcntAdd(_PyObject_CAST(op), n)