gh-116968: Reimplement Tier 2 counters (#117144)

Introduce a unified 16-bit backoff counter type (``_Py_BackoffCounter``),
shared between the Tier 1 adaptive specializer and the Tier 2 optimizer. The
API used for adaptive specialization counters is changed but the behavior is
(supposed to be) identical.

The behavior of the Tier 2 counters is changed:
- There are no longer dynamic thresholds (we never varied these).
- All counters now use the same exponential backoff.
- The counter for ``JUMP_BACKWARD`` starts counting down from 16.
- The ``temperature`` in side exits starts counting down from 64.

1 files changed, 9 insertions, 7 deletions

diff --git a/Lib/test/test_capi/test_opt.py b/Lib/test/test_capi/test_opt.py
index ceb49c3c712..7ca0f6927fe 100644
--- a/Lib/test/test_capi/test_opt.py
+++ b/Lib/test/test_capi/test_opt.py
@@ -10,6 +10,7 @@ import _testinternalcapi
 
 from test.support import script_helper, requires_specialization
 
+from _testinternalcapi import TIER2_THRESHOLD
 
 @contextlib.contextmanager
 def temporary_optimizer(opt):
@@ -69,7 +70,8 @@ class TestOptimizerAPI(unittest.TestCase):
                 self.assertEqual(opt.get_count(), 0)
                 with clear_executors(loop):
                     loop()
-                self.assertEqual(opt.get_count(), 1000)
+                # Subtract because optimizer doesn't kick in sooner
+                self.assertEqual(opt.get_count(), 1000 - TIER2_THRESHOLD)
 
     def test_long_loop(self):
         "Check that we aren't confused by EXTENDED_ARG"
@@ -81,7 +83,7 @@ class TestOptimizerAPI(unittest.TestCase):
                 pass
 
             def long_loop():
-                for _ in range(10):
+                for _ in range(20):
                     nop(); nop(); nop(); nop(); nop(); nop(); nop(); nop();
                     nop(); nop(); nop(); nop(); nop(); nop(); nop(); nop();
                     nop(); nop(); nop(); nop(); nop(); nop(); nop(); nop();
@@ -96,7 +98,7 @@ class TestOptimizerAPI(unittest.TestCase):
         with temporary_optimizer(opt):
             self.assertEqual(opt.get_count(), 0)
             long_loop()
-            self.assertEqual(opt.get_count(), 10)
+            self.assertEqual(opt.get_count(), 20 - TIER2_THRESHOLD)  # Need iterations to warm up
 
     def test_code_restore_for_ENTER_EXECUTOR(self):
         def testfunc(x):
@@ -932,10 +934,10 @@ class TestUopsOptimization(unittest.TestCase):
         exec(src, ns, ns)
         testfunc = ns['testfunc']
         ns['_test_global'] = 0
-        _, ex = self._run_with_optimizer(testfunc, 16)
+        _, ex = self._run_with_optimizer(testfunc, TIER2_THRESHOLD)
         self.assertIsNone(ex)
         ns['_test_global'] = 1
-        _, ex = self._run_with_optimizer(testfunc, 16)
+        _, ex = self._run_with_optimizer(testfunc, TIER2_THRESHOLD)
         self.assertIsNotNone(ex)
         uops = get_opnames(ex)
         self.assertNotIn("_GUARD_BOTH_INT", uops)
@@ -946,10 +948,10 @@ class TestUopsOptimization(unittest.TestCase):
         exec(src, ns, ns)
         testfunc = ns['testfunc']
         ns['_test_global'] = 0
-        _, ex = self._run_with_optimizer(testfunc, 16)
+        _, ex = self._run_with_optimizer(testfunc, TIER2_THRESHOLD)
         self.assertIsNone(ex)
         ns['_test_global'] = 3.14
-        _, ex = self._run_with_optimizer(testfunc, 16)
+        _, ex = self._run_with_optimizer(testfunc, TIER2_THRESHOLD)
         self.assertIsNone(ex)
 
     def test_combine_stack_space_checks_sequential(self):