Optimize checks; add bytearray tests

Author: esarp

mypyc/lib-rt/bytes_ops.c

@@ -178,20 +178,19 @@ int CPyBytes_Startswith(PyObject *self, PyObject *subobj) {
             return 1;
         }
 
-        Py_ssize_t self_len = PyBytes_GET_SIZE(self);
         Py_ssize_t subobj_len = PyBytes_GET_SIZE(subobj);
+        if (subobj_len == 0) {
+            return 1;
+        }
 
+        Py_ssize_t self_len = PyBytes_GET_SIZE(self);
         if (subobj_len > self_len) {
             return 0;
         }
 
         const char *self_buf = PyBytes_AS_STRING(self);
         const char *subobj_buf = PyBytes_AS_STRING(subobj);
 
-        if (subobj_len == 0) {
-            return 1;
-        }
-
         return memcmp(self_buf, subobj_buf, (size_t)subobj_len) == 0 ? 1 : 0;
     }
     _Py_IDENTIFIER(startswith);

mypyc/test-data/fixtures/ir.py

@@ -193,6 +193,7 @@ def __add__(self, s: bytes) -> bytearray: ...
     def __setitem__(self, i: int, o: int) -> None: ...
     def __getitem__(self, i: int) -> int: ...
     def decode(self, x: str = ..., y: str = ...) -> str: ...
+    def startswith(self, t: bytes) -> bool: ...
 
 class bool(int):
     def __init__(self, o: object = ...) -> None: ...

mypyc/test-data/run-bytes.test

@@ -213,6 +213,14 @@ def test_startswith() -> None:
     assert b''.startswith(b'')
     assert not b''.startswith(test)
 
+    # Test bytearray to verify slow paths
+    assert test.startswith(bytearray(b'some'))
+    assert not test.startswith(bytearray(b'other'))
+
+    test = bytearray(b'some string')
+    assert test.startswith(b'some')
+    assert not test.startswith(b'other')
+
 [case testBytesSlicing]
 def test_bytes_slicing() -> None:
     b = b'abcdefg'