GH-107596: Specialize str[int] (GH-107597)

1 files changed, 23 insertions, 0 deletions

diff --git a/Python/executor_cases.c.h b/Python/executor_cases.c.h
index 9363b49..27be8a3 100644
--- a/Python/executor_cases.c.h
+++ b/Python/executor_cases.c.h
@@ -462,6 +462,29 @@
             break;
         }
 
+        case BINARY_SUBSCR_STR_INT: {
+            PyObject *sub;
+            PyObject *str;
+            PyObject *res;
+            sub = stack_pointer[-1];
+            str = stack_pointer[-2];
+            DEOPT_IF(!PyLong_CheckExact(sub), BINARY_SUBSCR);
+            DEOPT_IF(!PyUnicode_CheckExact(str), BINARY_SUBSCR);
+            DEOPT_IF(!_PyLong_IsNonNegativeCompact((PyLongObject *)sub), BINARY_SUBSCR);
+            Py_ssize_t index = ((PyLongObject*)sub)->long_value.ob_digit[0];
+            DEOPT_IF(PyUnicode_GET_LENGTH(str) <= index, BINARY_SUBSCR);
+            // Specialize for reading an ASCII character from any string:
+            Py_UCS4 c = PyUnicode_READ_CHAR(str, index);
+            DEOPT_IF(Py_ARRAY_LENGTH(_Py_SINGLETON(strings).ascii) <= c, BINARY_SUBSCR);
+            STAT_INC(BINARY_SUBSCR, hit);
+            res = (PyObject*)&_Py_SINGLETON(strings).ascii[c];
+            _Py_DECREF_SPECIALIZED(sub, (destructor)PyObject_Free);
+            Py_DECREF(str);
+            STACK_SHRINK(1);
+            stack_pointer[-1] = res;
+            break;
+        }
+
         case BINARY_SUBSCR_TUPLE_INT: {
             PyObject *sub;
             PyObject *tuple;