gh-131798: JIT: Narrow the return type of _CONTAINS_OP_SET to bool

Lib/test/test_capi/test_opt.py

@@ -1603,6 +1603,32 @@ def testfunc(n):
         self.assertNotIn("_COMPARE_OP_INT", uops)
         self.assertIn("_POP_TWO_LOAD_CONST_INLINE_BORROW", uops)
 
+    def test_to_bool_bool_contains_op_set(self):
+        """
+        Test that _TO_BOOL_BOOL is removed from code like:
+
+        res = foo in some_set
+        if res:
+            ....
+
+        """
+        def testfunc(n):
+            x = 0
+            s = {1, 2, 3}
+            for _ in range(n):
+                a = 2
+                in_set = a in s
+                if in_set:
+                    x += 1
+            return x
+
+        res, ex = self._run_with_optimizer(testfunc, TIER2_THRESHOLD)
+        self.assertEqual(res, TIER2_THRESHOLD)
+        self.assertIsNotNone(ex)
+        uops = get_opnames(ex)
+        self.assertIn("_CONTAINS_OP_SET", uops)
+        self.assertNotIn("_TO_BOOL_BOOL", uops)
+
     def test_remove_guard_for_known_type_str(self):
         def f(n):
             for i in range(n):

Misc/NEWS.d/next/Core_and_Builtins/2025-04-03-20-11-02.gh-issue-131798.yhdUKW.rst

@@ -0,0 +1,2 @@
+Allow the JIT to remove an extra ``_TO_BOOL_BOOL`` instruction after
+``_CONTAINS_OP_SET`` by setting the return type to bool.

Python/optimizer_bytecodes.c

@@ -477,6 +477,10 @@ dummy_func(void) {
         res = sym_new_type(ctx, &PyBool_Type);
     }
 
+    op(_CONTAINS_OP_SET, (left, right -- res)) {
+        res = sym_new_type(ctx, &PyBool_Type);
+    }
+
     op(_LOAD_CONST, (-- value)) {
         PyObject *val = PyTuple_GET_ITEM(co->co_consts, this_instr->oparg);
         int opcode = _Py_IsImmortal(val) ? _LOAD_CONST_INLINE_BORROW : _LOAD_CONST_INLINE;