add test for const string multiply

Author: xuantengh

Lib/test/test_compile.py

@@ -906,6 +906,9 @@ def with_fstring():
 
             def with_const_expression():
                 "also" + " not docstring"
+
+            def with_multiplied_string():
+                "not docstring" * 4
             """)
 
         for opt in [0, 1, 2]:
@@ -922,6 +925,7 @@ def with_const_expression():
                     self.assertIsNone(ns['two_strings'].__doc__)
                 self.assertIsNone(ns['with_fstring'].__doc__)
                 self.assertIsNone(ns['with_const_expression'].__doc__)
+                self.assertIsNone(ns['with_multiplied_string'].__doc__)
 
         # Run AST parse first, then compile and run it
         for opt in [0, 1, 2]:
@@ -940,6 +944,7 @@ def with_const_expression():
                     self.assertIsNone(ns['two_strings'].__doc__)
                 self.assertIsNone(ns['with_fstring'].__doc__)
                 self.assertIsNone(ns['with_const_expression'].__doc__)
+                self.assertIsNone(ns['with_multiplied_string'].__doc__)
 
     @support.cpython_only
     def test_docstring_interactive_mode(self):

Python/ast_opt.c

@@ -500,6 +500,12 @@ fold_binop(expr_ty node, PyArena *arena, _PyASTOptimizeState *state)
         newval = PyNumber_Subtract(lv, rv);
         break;
     case Mult:
+        if ((state->optimize == 1) && (
+            (PyUnicode_CheckExact(lv) && PyLong_CheckExact(rv)) ||
+            (PyUnicode_CheckExact(rv) && PyLong_Check(lv))))
+        {
+            return 1;
+        }
         newval = safe_multiply(lv, rv);
         break;
     case Div: