GH-132508: Use tagged integers on the evaluation stack for the last instruction offset (GH-132545)

1 files changed, 24 insertions, 5 deletions

diff --git a/Python/stackrefs.c b/Python/stackrefs.c
index 1a2f66feb04..979a6b1c628 100644
--- a/Python/stackrefs.c
+++ b/Python/stackrefs.c
@@ -70,7 +70,7 @@ _Py_stackref_close(_PyStackRef ref, const char *filename, int linenumber)
 
     }
     PyObject *obj;
-    if (ref.index <= LAST_PREDEFINED_STACKREF_INDEX) {
+    if (ref.index < INITIAL_STACKREF_INDEX) {
         if (ref.index == 0) {
             _Py_FatalErrorFormat(__func__, "Passing NULL to PyStackRef_CLOSE at %s:%d\n", filename, linenumber);
         }
@@ -113,7 +113,8 @@ _Py_stackref_create(PyObject *obj, const char *filename, int linenumber)
         Py_FatalError("Cannot create a stackref for NULL");
     }
     PyInterpreterState *interp = PyInterpreterState_Get();
-    uint64_t new_id = interp->next_stackref++;
+    uint64_t new_id = interp->next_stackref;
+    interp->next_stackref = new_id + 2;
     TableEntry *entry = make_table_entry(obj, filename, linenumber);
     if (entry == NULL) {
         Py_FatalError("No memory left for stackref debug table");
@@ -127,7 +128,7 @@ _Py_stackref_create(PyObject *obj, const char *filename, int linenumber)
 void
 _Py_stackref_record_borrow(_PyStackRef ref, const char *filename, int linenumber)
 {
-    if (ref.index <= LAST_PREDEFINED_STACKREF_INDEX) {
+    if (ref.index < INITIAL_STACKREF_INDEX) {
         return;
     }
     PyInterpreterState *interp = PyInterpreterState_Get();
@@ -151,8 +152,7 @@ _Py_stackref_record_borrow(_PyStackRef ref, const char *filename, int linenumber
 void
 _Py_stackref_associate(PyInterpreterState *interp, PyObject *obj, _PyStackRef ref)
 {
-    assert(interp->next_stackref >= ref.index);
-    interp->next_stackref = ref.index+1;
+    assert(ref.index < INITIAL_STACKREF_INDEX);
     TableEntry *entry = make_table_entry(obj, "builtin-object", 0);
     if (entry == NULL) {
         Py_FatalError("No memory left for stackref debug table");
@@ -197,4 +197,23 @@ _PyStackRef_CLOSE_SPECIALIZED(_PyStackRef ref, destructor destruct, const char *
     _Py_DECREF_SPECIALIZED(obj, destruct);
 }
 
+_PyStackRef PyStackRef_TagInt(intptr_t i)
+{
+    return (_PyStackRef){ .index = (i << 1) + 1 };
+}
+
+intptr_t
+PyStackRef_UntagInt(_PyStackRef i)
+{
+    assert(PyStackRef_IsTaggedInt(i));
+    intptr_t val = (intptr_t)i.index;
+    return Py_ARITHMETIC_RIGHT_SHIFT(intptr_t, val, 1);
+}
+
+bool
+PyStackRef_IsNullOrInt(_PyStackRef ref)
+{
+    return PyStackRef_IsNull(ref) || PyStackRef_IsTaggedInt(ref);
+}
+
 #endif