gh-145860: Eliminate unnecessary refcount ops in BUILD_INTERPOLATION/BUILD_TEMPLATE

Make _PyInterpolation_Build and _PyTemplate_Build steal references to
their arguments instead of borrowing and incref'ing them. This avoids
redundant incref/decref pairs in the bytecode handlers, matching the
pattern already used by all other BUILD instructions.

Author: aleksandr.tseluyko

Misc/NEWS.d/next/Core_and_Builtins/2026-04-07-12-00-00.gh-issue-145860.pgec7ElZ.rst

@@ -0,0 +1,4 @@
+Eliminate unnecessary reference count operations in ``BUILD_INTERPOLATION``
+and ``BUILD_TEMPLATE`` bytecode instructions by making
+:c:func:`!_PyInterpolation_Build` and :c:func:`!_PyTemplate_Build` steal
+references to their arguments.

Modules/_testinternalcapi/test_cases.c.h

@@ -190,12 +190,15 @@ _PyInterpolation_Build(PyObject *value, PyObject *str, int conversion, PyObject
 {
     interpolationobject *interpolation = PyObject_GC_New(interpolationobject, &_PyInterpolation_Type);
     if (!interpolation) {
+        Py_DECREF(value);
+        Py_DECREF(str);
+        Py_DECREF(format_spec);
         return NULL;
     }
 
-    interpolation->value = Py_NewRef(value);
-    interpolation->expression = Py_NewRef(str);
-    interpolation->format_spec = Py_NewRef(format_spec);
+    interpolation->value = value;
+    interpolation->expression = str;
+    interpolation->format_spec = format_spec;
     interpolation->conversion = NULL;
 
     if (conversion == 0) {

Objects/interpolationobject.c

@@ -176,10 +176,7 @@ template_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
         PyTuple_SET_ITEM(strings, stringsidx++, &_Py_STR(empty));
     }
 
-    PyObject *template = _PyTemplate_Build(strings, interpolations);
-    Py_DECREF(strings);
-    Py_DECREF(interpolations);
-    return template;
+    return _PyTemplate_Build(strings, interpolations);
 }
 
 static void
@@ -292,10 +289,7 @@ template_concat_templates(templateobject *self, templateobject *other)
         return NULL;
     }
 
-    PyObject *newtemplate = _PyTemplate_Build(newstrings, newinterpolations);
-    Py_DECREF(newstrings);
-    Py_DECREF(newinterpolations);
-    return newtemplate;
+    return _PyTemplate_Build(newstrings, newinterpolations);
 }
 
 PyObject *
@@ -402,11 +396,13 @@ _PyTemplate_Build(PyObject *strings, PyObject *interpolations)
 {
     templateobject *template = PyObject_GC_New(templateobject, &_PyTemplate_Type);
     if (template == NULL) {
+        Py_DECREF(strings);
+        Py_DECREF(interpolations);
         return NULL;
     }
 
-    template->strings = Py_NewRef(strings);
-    template->interpolations = Py_NewRef(interpolations);
+    template->strings = strings;
+    template->interpolations = interpolations;
     PyObject_GC_Track(template);
     return (PyObject *) template;
 }

Objects/templateobject.c

@@ -2329,35 +2329,31 @@ dummy_func(
         }
 
         inst(BUILD_INTERPOLATION, (value, str, format[oparg & 1] -- interpolation)) {
-            PyObject *value_o = PyStackRef_AsPyObjectBorrow(value);
-            PyObject *str_o = PyStackRef_AsPyObjectBorrow(str);
+            PyObject *value_o = PyStackRef_AsPyObjectSteal(value);
+            DEAD(value);
+            PyObject *str_o = PyStackRef_AsPyObjectSteal(str);
+            DEAD(str);
             int conversion = oparg >> 2;
             PyObject *format_o;
             if (oparg & 1) {
-                format_o = PyStackRef_AsPyObjectBorrow(format[0]);
-            }
-            else {
-                format_o = &_Py_STR(empty);
-            }
-            PyObject *interpolation_o = _PyInterpolation_Build(value_o, str_o, conversion, format_o);
-            if (oparg & 1) {
-                PyStackRef_CLOSE(format[0]);
+                format_o = PyStackRef_AsPyObjectSteal(format[0]);
+                DEAD(format);
             }
             else {
+                format_o = Py_NewRef(&_Py_STR(empty));
                 DEAD(format);
             }
-            PyStackRef_CLOSE(str);
-            PyStackRef_CLOSE(value);
+            PyObject *interpolation_o = _PyInterpolation_Build(value_o, str_o, conversion, format_o);
             ERROR_IF(interpolation_o == NULL);
             interpolation = PyStackRef_FromPyObjectSteal(interpolation_o);
         }
 
         inst(BUILD_TEMPLATE, (strings, interpolations -- template)) {
-            PyObject *strings_o = PyStackRef_AsPyObjectBorrow(strings);
-            PyObject *interpolations_o = PyStackRef_AsPyObjectBorrow(interpolations);
+            PyObject *strings_o = PyStackRef_AsPyObjectSteal(strings);
+            DEAD(strings);
+            PyObject *interpolations_o = PyStackRef_AsPyObjectSteal(interpolations);
+            DEAD(interpolations);
             PyObject *template_o = _PyTemplate_Build(strings_o, interpolations_o);
-            PyStackRef_CLOSE(interpolations);
-            PyStackRef_CLOSE(strings);
             ERROR_IF(template_o == NULL);
             template = PyStackRef_FromPyObjectSteal(template_o);
         }