GH-126892: Reset warmup counters when JIT compiling code

Lib/test/test_capi/test_opt.py

@@ -1390,7 +1390,9 @@ def test_guard_type_version_not_removed(self):
 
         def thing(a):
             x = 0
-            for i in range(100):
+            # 90 iterations with Foo.attr == 1, then 16 to invalidate, warm up
+            # again, and re-optimize with Foo.attr == 2:
+            for i in range(90 + 16):
                 x += a.attr
                 # for the first 90 iterations we set the attribute on this dummy function which shouldn't
                 # trigger the type watcher
@@ -1410,7 +1412,7 @@ class Bar:
         opnames = list(iter_opnames(ex))
 
         self.assertIsNotNone(ex)
-        self.assertEqual(res, 219)
+        self.assertEqual(res, 243)
         guard_type_version_count = opnames.count("_GUARD_TYPE_VERSION")
         self.assertEqual(guard_type_version_count, 2)
 

Misc/NEWS.d/next/Core_and_Builtins/2024-11-15-16-39-37.gh-issue-126892.QR6Yo3.rst

@@ -0,0 +1,2 @@
+Require cold or invalidated code to "warm up" before being JIT compiled
+again.

Python/bytecodes.c

@@ -2624,15 +2624,16 @@ dummy_func(
                 }
                 _PyExecutorObject *executor;
                 int optimized = _PyOptimizer_Optimize(frame, start, stack_pointer, &executor, 0);
-                ERROR_IF(optimized < 0, error);
-                if (optimized) {
+                if (optimized <= 0) {
+                    this_instr[1].counter = restart_backoff_counter(counter);
+                    ERROR_IF(optimized < 0, error);
+                }
+                else {
+                    this_instr[1].counter = initial_jump_backoff_counter();
                     assert(tstate->previous_executor == NULL);
                     tstate->previous_executor = Py_None;
                     GOTO_TIER_TWO(executor);
                 }
-                else {
-                    this_instr[1].counter = restart_backoff_counter(counter);
-                }
             }
             else {
                 ADVANCE_ADAPTIVE_COUNTER(this_instr[1].counter);
@@ -4869,6 +4870,9 @@ dummy_func(
                         tstate->previous_executor = (PyObject *)current_executor;
                         GOTO_TIER_ONE(target);
                     }
+                    else {
+                        exit->temperature = initial_temperature_backoff_counter();
+                    }
                 }
                 exit->executor = executor;
             }