JIT: Remove guard for slicing known type tuple

Author: fluhus

Lib/test/test_capi/test_opt.py

@@ -2233,6 +2233,18 @@ def f(n):
         self.assertIn("_TO_BOOL_LIST", uops)
         self.assertNotIn("_GUARD_TOS_LIST", uops)
 
+    def test_remove_guard_for_slice_tuple(self):
+        def f(n):
+            for i in range(n):
+                false = i == TIER2_THRESHOLD
+                a, b = (1, 2, 3)[: false + 2]
+
+        _, ex = self._run_with_optimizer(f, TIER2_THRESHOLD)
+        self.assertIsNotNone(ex)
+        uops = get_opnames(ex)
+        self.assertIn("_UNPACK_SEQUENCE_TWO_TUPLE", uops)
+        self.assertNotIn("_GUARD_TOS_TUPLE", uops)
+
 
 def global_identity(x):
     return x

Python/optimizer_bytecodes.c

@@ -1217,10 +1217,11 @@ dummy_func(void) {
     }
 
     op(_BINARY_SLICE, (container, start, stop -- res)) {
-        // Slicing a string/list always returns the same type.
+        // Slicing a string/list/tuple always returns the same type.
         PyTypeObject *type = sym_get_type(container);
         if (type == &PyUnicode_Type ||
-            type == &PyList_Type) {
+            type == &PyList_Type ||
+            type == &PyTuple_Type) {
             res = sym_new_type(ctx, type);
         } else {
             res = sym_new_not_null(ctx);