gh-131798: Add _IS_NONE to the JIT optimizer (GH-148369)

Author: Wulian233

Lib/test/test_capi/test_opt.py

@@ -4662,6 +4662,24 @@ def return_true():
         # v + 1 should be constant folded
         self.assertNotIn("_BINARY_OP", uops)
 
+    def test_is_none_narrows_to_constant(self):
+        def testfunc(n):
+            value = None
+            hits = 0
+            for _ in range(n):
+                if value is None:
+                    hits += 1
+            return hits
+
+        res, ex = self._run_with_optimizer(testfunc, TIER2_THRESHOLD)
+        self.assertEqual(res, TIER2_THRESHOLD)
+        self.assertIsNotNone(ex)
+        uops = get_opnames(ex)
+
+        self.assertNotIn("_IS_NONE", uops)
+        self.assertIn("_GUARD_IS_NONE_POP", uops)
+        self.assertIn("_POP_TOP_NOP", uops)
+
     def test_is_false_narrows_to_constant(self):
         def f(n):
             def return_false():

Python/optimizer_bytecodes.c

@@ -724,6 +724,16 @@ dummy_func(void) {
         r = right;
     }
 
+    op(_IS_NONE, (value -- b)) {
+        if (sym_is_const(ctx, value)) {
+            PyObject *value_o = sym_get_const(ctx, value);
+            b = sym_new_const(ctx, Py_IsNone(value_o) ? Py_True : Py_False);
+        }
+        else {
+            b = sym_new_type(ctx, &PyBool_Type);
+        }
+    }
+
     op(_CONTAINS_OP, (left, right -- b, l, r)) {
         b = sym_new_type(ctx, &PyBool_Type);
         l = left;