gh-127599: Fix _Py_RefcntAdd missing calls to _Py_INCREF_STAT_INC/_Py_INCREF_IMMORTAL_STAT_INC (#127717)

Previously, `_Py_RefcntAdd` hasn't called 
`_Py_INCREF_STAT_INC/_Py_INCREF_IMMORTAL_STAT_INC` which is incorrect. 

Now it has been fixed.

3 files changed, 13 insertions, 0 deletions

diff --git a/Include/cpython/pystats.h b/Include/cpython/pystats.h
index 2ae4800..29ef0c0 100644
--- a/Include/cpython/pystats.h
+++ b/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"
diff --git a/Include/internal/pycore_object.h b/Include/internal/pycore_object.h
index 668ea47..d7d68f9 100644
--- a/Include/internal/pycore_object.h
+++ b/Include/internal/pycore_object.h
@@ -131,6 +131,7 @@ 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
@@ -159,6 +160,10 @@ 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)
 
diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2024-12-07-13-06-09.gh-issue-127599.tXCZb_.rst b/Misc/NEWS.d/next/Core_and_Builtins/2024-12-07-13-06-09.gh-issue-127599.tXCZb_.rst
new file mode 100644
index 0000000..565ecb8
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2024-12-07-13-06-09.gh-issue-127599.tXCZb_.rst
@@ -0,0 +1,2 @@
+Fix statistics for increments of object reference counts (in particular, when
+a reference count was increased by more than 1 in a single operation).