Avoid branch for known mortal objects

Author: markshannon

Include/internal/pycore_stackref.h

@@ -370,6 +370,7 @@ PyStackRef_AsStrongReference(_PyStackRef stackref)
         } \
     } while (0)
 
+#define PyStackRef_FromPyObjectNewMortal PyStackRef_FromPyObjectNew
 
 #else // Py_GIL_DISABLED
 
@@ -508,6 +509,17 @@ _PyStackRef_FromPyObjectNew(PyObject *obj)
 }
 #define PyStackRef_FromPyObjectNew(obj) _PyStackRef_FromPyObjectNew(_PyObject_CAST(obj))
 
+static inline _PyStackRef
+_PyStackRef_FromPyObjectNewMortal(PyObject *obj)
+{
+    assert(obj != NULL);
+    Py_INCREF_MORTAL(obj);
+    _PyStackRef ref = (_PyStackRef){ .bits = (uintptr_t)obj };
+    PyStackRef_CheckValid(ref);
+    return ref;
+}
+#define PyStackRef_FromPyObjectNewMortal(obj) _PyStackRef_FromPyObjectNewMortal(_PyObject_CAST(obj))
+
 /* Create a new reference from an object with an embedded reference count */
 static inline _PyStackRef
 PyStackRef_FromPyObjectImmortal(PyObject *obj)

Python/bytecodes.c

@@ -311,7 +311,7 @@ dummy_func(
 
         inst(LOAD_CONST_MORTAL, (-- value)) {
             PyObject *obj = GETITEM(FRAME_CO_CONSTS, oparg);
-            value = PyStackRef_FromPyObjectNew(obj);
+            value = PyStackRef_FromPyObjectNewMortal(obj);
         }
 
         inst(LOAD_CONST_IMMORTAL, (-- value)) {

Python/executor_cases.c.h

@@ -583,6 +583,7 @@ def has_error_without_pop(op: parser.CodeDef) -> bool:
     "PySlice_New",
     "PyStackRef_AsPyObjectBorrow",
     "PyStackRef_AsPyObjectNew",
+    "PyStackRef_FromPyObjectNewMortal",
     "PyStackRef_AsPyObjectSteal",
     "PyStackRef_CLEAR",
     "PyStackRef_CLOSE_SPECIALIZED",