[mypyc] Optimize str.rsplit (#18673)

Use `PyUnicode_RSplit` to optimize `str.rsplit` calls. Although not
present in the documentation, it's has actually part of the stable API
since Python 3.2.

https://github.com/python/cpython/blob/v3.13.2/Doc/data/stable_abi.dat#L799

https://github.com/python/cpython/blob/main/Include/unicodeobject.h#L841-L858

Author: cdce8p

mypyc/doc/str_operations.rst

@@ -36,6 +36,9 @@ Methods
 * ``s.removesuffix(suffix: str)``
 * ``s.replace(old: str, new: str)``
 * ``s.replace(old: str, new: str, count: int)``
+* ``s.rsplit()``
+* ``s.rsplit(sep: str)``
+* ``s.rsplit(sep: str, maxsplit: int)``
 * ``s.split()``
 * ``s.split(sep: str)``
 * ``s.split(sep: str, maxsplit: int)``

mypyc/lib-rt/CPy.h

@@ -721,6 +721,7 @@ static inline char CPyDict_CheckSize(PyObject *dict, CPyTagged size) {
 PyObject *CPyStr_Build(Py_ssize_t len, ...);
 PyObject *CPyStr_GetItem(PyObject *str, CPyTagged index);
 PyObject *CPyStr_Split(PyObject *str, PyObject *sep, CPyTagged max_split);
+PyObject *CPyStr_RSplit(PyObject *str, PyObject *sep, CPyTagged max_split);
 PyObject *CPyStr_Replace(PyObject *str, PyObject *old_substr, PyObject *new_substr, CPyTagged max_replace);
 PyObject *CPyStr_Append(PyObject *o1, PyObject *o2);
 PyObject *CPyStr_GetSlice(PyObject *obj, CPyTagged start, CPyTagged end);

mypyc/lib-rt/str_ops.c

@@ -142,6 +142,15 @@ PyObject *CPyStr_Split(PyObject *str, PyObject *sep, CPyTagged max_split) {
     return PyUnicode_Split(str, sep, temp_max_split);
 }
 
+PyObject *CPyStr_RSplit(PyObject *str, PyObject *sep, CPyTagged max_split) {
+    Py_ssize_t temp_max_split = CPyTagged_AsSsize_t(max_split);
+    if (temp_max_split == -1 && PyErr_Occurred()) {
+        PyErr_SetString(PyExc_OverflowError, CPYTHON_LARGE_INT_ERRMSG);
+        return NULL;
+    }
+    return PyUnicode_RSplit(str, sep, temp_max_split);
+}
+
 PyObject *CPyStr_Replace(PyObject *str, PyObject *old_substr,
                          PyObject *new_substr, CPyTagged max_replace) {
     Py_ssize_t temp_max_replace = CPyTagged_AsSsize_t(max_replace);

mypyc/primitives/str_ops.py

@@ -136,9 +136,10 @@
     error_kind=ERR_NEVER,
 )
 
-# str.split(...)
+# str.split(...) and str.rsplit(...)
 str_split_types: list[RType] = [str_rprimitive, str_rprimitive, int_rprimitive]
 str_split_functions = ["PyUnicode_Split", "PyUnicode_Split", "CPyStr_Split"]
+str_rsplit_functions = ["PyUnicode_RSplit", "PyUnicode_RSplit", "CPyStr_RSplit"]
 str_split_constants: list[list[tuple[int, RType]]] = [
     [(0, pointer_rprimitive), (-1, c_int_rprimitive)],
     [(-1, c_int_rprimitive)],
@@ -153,6 +154,14 @@
         extra_int_constants=str_split_constants[i],
         error_kind=ERR_MAGIC,
     )
+    method_op(
+        name="rsplit",
+        arg_types=str_split_types[0 : i + 1],
+        return_type=list_rprimitive,
+        c_function_name=str_rsplit_functions[i],
+        extra_int_constants=str_split_constants[i],
+        error_kind=ERR_MAGIC,
+    )
 
 # str.replace(old, new)
 method_op(

mypyc/test-data/fixtures/ir.py

@@ -102,7 +102,8 @@ def __getitem__(self, i: int) -> str: pass
     def __getitem__(self, i: slice) -> str: pass
     def __contains__(self, item: str) -> bool: pass
     def __iter__(self) -> Iterator[str]: ...
-    def split(self, sep: Optional[str] = None, max: Optional[int] = None) -> List[str]: pass
+    def split(self, sep: Optional[str] = None, maxsplit: int = -1) -> List[str]: pass
+    def rsplit(self, sep: Optional[str] = None, maxsplit: int = -1) -> List[str]: pass
     def strip (self, item: str) -> str: pass
     def join(self, x: Iterable[str]) -> str: pass
     def format(self, *args: Any, **kwargs: Any) -> str: ...

mypyc/test-data/run-strings.test

@@ -61,6 +61,14 @@ def do_split(s: str, sep: Optional[str] = None, max_split: Optional[int] = None)
             return s.split(sep)
     return s.split()
 
+def do_rsplit(s: str, sep: Optional[str] = None, max_split: Optional[int] = None) -> List[str]:
+    if sep is not None:
+        if max_split is not None:
+            return s.rsplit(sep, max_split)
+        else:
+            return s.rsplit(sep)
+    return s.rsplit()
+
 ss = "abc abcd abcde abcdef"
 
 def test_split() -> None:
@@ -72,6 +80,15 @@ def test_split() -> None:
     assert do_split(ss, " ", 1) == ["abc", "abcd abcde abcdef"]
     assert do_split(ss, " ", 2) == ["abc", "abcd", "abcde abcdef"]
 
+def test_rsplit() -> None:
+    assert do_rsplit(ss) == ["abc", "abcd", "abcde", "abcdef"]
+    assert do_rsplit(ss, " ") == ["abc", "abcd", "abcde", "abcdef"]
+    assert do_rsplit(ss, "-") == ["abc abcd abcde abcdef"]
+    assert do_rsplit(ss, " ", -1) == ["abc", "abcd", "abcde", "abcdef"]
+    assert do_rsplit(ss, " ", 0) == ["abc abcd abcde abcdef"]
+    assert do_rsplit(ss, " ", 1) == ["abc abcd abcde", "abcdef"]  # different to do_split
+    assert do_rsplit(ss, " ", 2) == ["abc abcd", "abcde", "abcdef"]  # different to do_split
+
 def getitem(s: str, index: int) -> str:
     return s[index]