pythongh-110481: Fix Py_SET_REFCNT() integer overflow

If Py_NOGIL is defined and Py_SET_REFCNT() is called with a reference
count larger than UINT32_MAX, make the object immortal.

Set _Py_IMMORTAL_REFCNT constant type to Py_ssize_t to fix the
following compiler warning:

Include/internal/pycore_global_objects_fini_generated.h:14:24:
warning: comparison of integers of different signs: 'Py_ssize_t'
(aka 'long') and 'unsigned int' [-Wsign-compare]

    if (Py_REFCNT(obj) < _Py_IMMORTAL_REFCNT) {
        ~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~

Author: vstinner

Include/object.h

@@ -88,7 +88,7 @@ having all the lower 32 bits set, which will avoid the reference count to go
 beyond the refcount limit. Immortality checks for reference count decreases will
 be done by checking the bit sign flag in the lower 32 bits.
 */
-#define _Py_IMMORTAL_REFCNT UINT_MAX
+#define _Py_IMMORTAL_REFCNT (Py_ssize_t)UINT_MAX
 
 #else
 /*
@@ -103,7 +103,7 @@ immortality, but the execution would still be correct.
 Reference count increases and decreases will first go through an immortality
 check by comparing the reference count field to the immortality reference count.
 */
-#define _Py_IMMORTAL_REFCNT (UINT_MAX >> 2)
+#define _Py_IMMORTAL_REFCNT (Py_ssize_t)(UINT_MAX >> 2)
 #endif
 
 // Py_NOGIL builds indicate immortal objects using `ob_ref_local`, which is
@@ -317,11 +317,11 @@ static inline Py_ssize_t Py_SIZE(PyObject *ob) {
 static inline Py_ALWAYS_INLINE int _Py_IsImmortal(PyObject *op)
 {
 #if defined(Py_NOGIL)
-    return op->ob_ref_local == _Py_IMMORTAL_REFCNT_LOCAL;
+    return (op->ob_ref_local == _Py_IMMORTAL_REFCNT_LOCAL);
 #elif SIZEOF_VOID_P > 4
-    return _Py_CAST(PY_INT32_T, op->ob_refcnt) < 0;
+    return (_Py_CAST(PY_INT32_T, op->ob_refcnt) < 0);
 #else
-    return op->ob_refcnt == _Py_IMMORTAL_REFCNT;
+    return (op->ob_refcnt == _Py_IMMORTAL_REFCNT);
 #endif
 }
 #define _Py_IsImmortal(op) _Py_IsImmortal(_PyObject_CAST(op))
@@ -350,15 +350,23 @@ static inline void Py_SET_REFCNT(PyObject *ob, Py_ssize_t refcnt) {
     if (_Py_IsImmortal(ob)) {
         return;
     }
+
 #ifndef Py_NOGIL
     ob->ob_refcnt = refcnt;
 #else
     if (_Py_IsOwnedByCurrentThread(ob)) {
-        // Set local refcount to desired refcount and shared refcount to zero,
-        // but preserve the shared refcount flags.
-        assert(refcnt < UINT32_MAX);
-        ob->ob_ref_local = _Py_STATIC_CAST(uint32_t, refcnt);
-        ob->ob_ref_shared &= _Py_REF_SHARED_FLAG_MASK;
+        if ((size_t)refcnt > (size_t)UINT32_MAX) {
+            // On overflow, make the object immortal
+            op->ob_tid = _Py_UNOWNED_TID;
+            op->ob_ref_local = _Py_IMMORTAL_REFCNT_LOCAL;
+            op->ob_ref_shared = 0;
+        }
+        else {
+            // Set local refcount to desired refcount and shared refcount
+            // to zero, but preserve the shared refcount flags.
+            ob->ob_ref_local = _Py_STATIC_CAST(uint32_t, refcnt);
+            ob->ob_ref_shared &= _Py_REF_SHARED_FLAG_MASK;
+        }
     }
     else {
         // Set local refcount to zero and shared refcount to desired refcount.