gh-118335: Configure Tier 2 interpreter at build time (#118339)

The code for Tier 2 is now only compiled when configured
with `--enable-experimental-jit[=yes|interpreter]`.

We drop support for `PYTHON_UOPS` and -`Xuops`,
but you can disable the interpreter or JIT
at runtime by setting `PYTHON_JIT=0`.
You can also build it without enabling it by default
using `--enable-experimental-jit=yes-off`;
enable with `PYTHON_JIT=1`.

On Windows, the `build.bat` script supports
`--experimental-jit`, `--experimental-jit-off`,
`--experimental-interpreter`.

In the C code, `_Py_JIT` is defined as before
when the JIT is enabled; the new variable
`_Py_TIER2` is defined when the JIT *or* the
interpreter is enabled. It is actually a bitmask:
1: JIT; 2: default-off; 4: interpreter.

Doc/whatsnew/3.13.rst

@@ -888,7 +888,7 @@ Experimental JIT Compiler
 =========================
 
 When CPython is configured using the ``--enable-experimental-jit`` option,
-a just-in-time compiler is added which can speed up some Python programs.
+a just-in-time compiler is added which may speed up some Python programs.
 
 The internal architecture is roughly as follows.
 
@@ -905,19 +905,35 @@ The internal architecture is roughly as follows.
   before it is interpreted or translated to machine code.
 
 * There is a Tier 2 interpreter, but it is mostly intended for debugging
-  the earlier stages of the optimization pipeline. If the JIT is not
+  the earlier stages of the optimization pipeline.
-  enabled, the Tier 2 interpreter can be invoked by passing Python the
+  The Tier 2 interpreter can be enabled by configuring Python
-  ``-X uops`` option or by setting the ``PYTHON_UOPS`` environment
+  with ``--enable-experimental-jit=interpreter``.
-  variable to ``1``.
 
-* When the ``--enable-experimental-jit`` option is used, the optimized
+* When the JIT is enabled, the optimized
   Tier 2 IR is translated to machine code, which is then executed.
-  This does not require additional runtime options.
 
 * The machine code translation process uses an architecture called
   *copy-and-patch*. It has no runtime dependencies, but there is a new
   build-time dependency on LLVM.
 
+The ``--enable-experimental-jit`` flag has the following optional values:
+
+* ``no`` (default) -- Disable the entire Tier 2 and JIT pipeline.
+
+* ``yes`` (default if the flag is present without optional value)
+  -- Enable the JIT. To disable the JIT at runtime,
+  pass the environment variable ``PYTHON_JIT=0``.
+
+* ``yes-off`` -- Build the JIT but disable it by default.
+  To enable the JIT at runtime, pass the environment variable
+  ``PYTHON_JIT=1``.
+
+* ``interpreter`` -- Enable the Tier 2 interpreter but disable the JIT.
+  The interpreter can be disabled by running with
+  ``PYTHON_JIT=0``.
+
+(On Windows, use ``PCbuild/build.bat --enable-jit`` to enable the JIT.)
+
 See :pep:`744` for more details.
 
 (JIT by Brandt Bucher, inspired by a paper by Haoran Xu and Fredrik Kjolstad.

Include/internal/pycore_opcode_metadata.h

@@ -981,7 +981,7 @@ const struct opcode_metadata _PyOpcode_opcode_metadata[268] = {
     [BUILD_SLICE] = { true, INSTR_FMT_IB, HAS_ARG_FLAG | HAS_ERROR_FLAG },
     [BUILD_STRING] = { true, INSTR_FMT_IB, HAS_ARG_FLAG | HAS_ERROR_FLAG },
     [BUILD_TUPLE] = { true, INSTR_FMT_IB, HAS_ARG_FLAG | HAS_ERROR_FLAG },
-    [CACHE] = { true, INSTR_FMT_IX, HAS_ESCAPES_FLAG },
+    [CACHE] = { true, INSTR_FMT_IX, 0 },
     [CALL] = { true, INSTR_FMT_IBC00, HAS_ARG_FLAG | HAS_EVAL_BREAK_FLAG | HAS_ERROR_FLAG | HAS_ERROR_NO_POP_FLAG | HAS_ESCAPES_FLAG },
     [CALL_ALLOC_AND_ENTER_INIT] = { true, INSTR_FMT_IBC00, HAS_ARG_FLAG | HAS_DEOPT_FLAG | HAS_ERROR_FLAG | HAS_ERROR_NO_POP_FLAG | HAS_ESCAPES_FLAG },
     [CALL_BOUND_METHOD_EXACT_ARGS] = { true, INSTR_FMT_IBC00, HAS_ARG_FLAG | HAS_DEOPT_FLAG | HAS_EXIT_FLAG },
@@ -1121,7 +1121,7 @@ const struct opcode_metadata _PyOpcode_opcode_metadata[268] = {
     [PUSH_NULL] = { true, INSTR_FMT_IX, HAS_PURE_FLAG },
     [RAISE_VARARGS] = { true, INSTR_FMT_IB, HAS_ARG_FLAG | HAS_ERROR_FLAG | HAS_ERROR_NO_POP_FLAG | HAS_ESCAPES_FLAG },
     [RERAISE] = { true, INSTR_FMT_IB, HAS_ARG_FLAG | HAS_ERROR_FLAG | HAS_ERROR_NO_POP_FLAG | HAS_ESCAPES_FLAG },
-    [RESERVED] = { true, INSTR_FMT_IX, HAS_ESCAPES_FLAG },
+    [RESERVED] = { true, INSTR_FMT_IX, 0 },
     [RESUME] = { true, INSTR_FMT_IB, HAS_ARG_FLAG | HAS_EVAL_BREAK_FLAG | HAS_ERROR_FLAG | HAS_ESCAPES_FLAG },
     [RESUME_CHECK] = { true, INSTR_FMT_IX, HAS_DEOPT_FLAG },
     [RETURN_CONST] = { true, INSTR_FMT_IB, HAS_ARG_FLAG | HAS_CONST_FLAG },

Include/internal/pycore_uop_metadata.h

@@ -249,7 +249,7 @@ const uint16_t _PyUop_Flags[MAX_UOP_ID+1] = {
     [_COLD_EXIT] = HAS_ARG_FLAG | HAS_ESCAPES_FLAG,
     [_DYNAMIC_EXIT] = HAS_ARG_FLAG | HAS_ESCAPES_FLAG,
     [_START_EXECUTOR] = HAS_DEOPT_FLAG,
-    [_FATAL_ERROR] = HAS_ESCAPES_FLAG,
+    [_FATAL_ERROR] = 0,
     [_CHECK_VALIDITY_AND_SET_IP] = HAS_DEOPT_FLAG,
     [_DEOPT] = 0,
     [_SIDE_EXIT] = 0,

Lib/dis.py

@@ -216,7 +216,7 @@ def _get_code_array(co, adaptive):
             if op == ENTER_EXECUTOR:
                 try:
                     ex = get_executor(co, i)
-                except ValueError:
+                except (ValueError, RuntimeError):
                     ex = None
 
                 if ex:

Lib/test/support/__init__.py

@@ -2539,17 +2539,17 @@ Py_TRACE_REFS = hasattr(sys, 'getobjects')
 # Decorator to disable optimizer while a function run
 def without_optimizer(func):
     try:
-        import _testinternalcapi
+        from _testinternalcapi import get_optimizer, set_optimizer
     except ImportError:
         return func
     @functools.wraps(func)
     def wrapper(*args, **kwargs):
-        save_opt = _testinternalcapi.get_optimizer()
+        save_opt = get_optimizer()
         try:
-            _testinternalcapi.set_optimizer(None)
+            set_optimizer(None)
             return func(*args, **kwargs)
         finally:
-            _testinternalcapi.set_optimizer(save_opt)
+            set_optimizer(save_opt)
     return wrapper
 
 

Lib/test/test_capi/test_opt.py

@@ -34,6 +34,8 @@ def clear_executors(func):
 
 
 @requires_specialization
+@unittest.skipUnless(hasattr(_testinternalcapi, "get_optimizer"),
+                     "Requires optimizer infrastructure")
 class TestOptimizerAPI(unittest.TestCase):
 
     def test_new_counter_optimizer_dealloc(self):
@@ -136,6 +138,8 @@ def get_opnames(ex):
 
 
 @requires_specialization
+@unittest.skipUnless(hasattr(_testinternalcapi, "get_optimizer"),
+                     "Requires optimizer infrastructure")
 class TestExecutorInvalidation(unittest.TestCase):
 
     def setUp(self):
@@ -215,6 +219,8 @@ class TestExecutorInvalidation(unittest.TestCase):
 
 
 @requires_specialization
+@unittest.skipUnless(hasattr(_testinternalcapi, "get_optimizer"),
+                     "Requires optimizer infrastructure")
 @unittest.skipIf(os.getenv("PYTHON_UOPS_OPTIMIZE") == "0", "Needs uop optimizer to run.")
 class TestUops(unittest.TestCase):
 
@@ -579,6 +585,8 @@ class TestUops(unittest.TestCase):
 
 
 @requires_specialization
+@unittest.skipUnless(hasattr(_testinternalcapi, "get_optimizer"),
+                     "Requires optimizer infrastructure")
 @unittest.skipIf(os.getenv("PYTHON_UOPS_OPTIMIZE") == "0", "Needs uop optimizer to run.")
 class TestUopsOptimization(unittest.TestCase):
 

Lib/test/test_monitoring.py

@@ -1831,15 +1831,17 @@ class TestOptimizer(MonitoringTestBase, unittest.TestCase):
 
     def setUp(self):
         _testinternalcapi = import_module("_testinternalcapi")
-        self.old_opt = _testinternalcapi.get_optimizer()
+        if hasattr(_testinternalcapi, "get_optimizer"):
-        opt = _testinternalcapi.new_counter_optimizer()
+            self.old_opt = _testinternalcapi.get_optimizer()
-        _testinternalcapi.set_optimizer(opt)
+            opt = _testinternalcapi.new_counter_optimizer()
+            _testinternalcapi.set_optimizer(opt)
         super(TestOptimizer, self).setUp()
 
     def tearDown(self):
         super(TestOptimizer, self).tearDown()
         import _testinternalcapi
-        _testinternalcapi.set_optimizer(self.old_opt)
+        if hasattr(_testinternalcapi, "get_optimizer"):
+            _testinternalcapi.set_optimizer(self.old_opt)
 
     def test_for_loop(self):
         def test_func(x):

Lib/test/test_opcache.py

@@ -16,6 +16,8 @@ _testinternalcapi = import_module("_testinternalcapi")
 
 def disabling_optimizer(func):
     def wrapper(*args, **kwargs):
+        if not hasattr(_testinternalcapi, "get_optimizer"):
+            return func(*args, **kwargs)
         old_opt = _testinternalcapi.get_optimizer()
         _testinternalcapi.set_optimizer(None)
         try:

Lib/test/test_optimizer.py

@@ -80,6 +80,8 @@ class TestRareEventCounters(unittest.TestCase):
 
 class TestOptimizerSymbols(unittest.TestCase):
 
+    @unittest.skipUnless(hasattr(_testinternalcapi, "uop_symbols_test"),
+                "requires _testinternalcapi.uop_symbols_test")
     def test_optimizer_symbols(self):
         _testinternalcapi.uop_symbols_test()
 

Lib/test/test_weakref.py

@@ -17,6 +17,7 @@ from test.support import script_helper, ALWAYS_EQ, suppress_immortalization
 from test.support import gc_collect
 from test.support import import_helper
 from test.support import threading_helper
+from test.support import is_wasi, Py_DEBUG
 
 # Used in ReferencesTestCase.test_ref_created_during_del() .
 ref_from_del = None
@@ -960,6 +961,7 @@ class ReferencesTestCase(TestBase):
         self.assertEqual(hash(a), hash(42))
         self.assertRaises(TypeError, hash, b)
 
+    @unittest.skipIf(is_wasi and Py_DEBUG, "requires deep stack")
     def test_trashcan_16602(self):
         # Issue #16602: when a weakref's target was part of a long
         # deallocation chain, the trashcan mechanism could delay clearing

Misc/NEWS.d/next/Core and Builtins/2024-04-26-14-06-18.gh-issue-118335.SRFsxO.rst

@@ -0,0 +1,4 @@
+Change how to use the tier 2 interpreter. Instead of running Python with
+``-X uops`` or setting the environment variable ``PYTHON_UOPS=1``, this
+choice is now made at build time by configuring with
+``--enable-experimental-jit=interpreter``.

Modules/_opcode.c

@@ -367,7 +367,13 @@ _opcode_get_executor_impl(PyObject *module, PyObject *code, int offset)
                      Py_TYPE(code)->tp_name);
         return NULL;
     }
+#ifdef _Py_TIER2
     return (PyObject *)PyUnstable_GetExecutor((PyCodeObject *)code, offset);
+#else
+    PyErr_Format(PyExc_RuntimeError,
+                 "Executors are not available in this build");
+    return NULL;
+#endif
 }
 
 static PyMethodDef

Modules/_testinternalcapi.c

@@ -985,6 +985,8 @@ get_co_framesize(PyObject *self, PyObject *arg)
     return PyLong_FromLong(code->co_framesize);
 }
 
+#ifdef _Py_TIER2
+
 static PyObject *
 new_counter_optimizer(PyObject *self, PyObject *arg)
 {
@@ -1012,7 +1014,10 @@ set_optimizer(PyObject *self, PyObject *opt)
 static PyObject *
 get_optimizer(PyObject *self, PyObject *Py_UNUSED(ignored))
 {
-    PyObject *opt = (PyObject *)PyUnstable_GetOptimizer();
+    PyObject *opt = NULL;
+#ifdef _Py_TIER2
+    opt = (PyObject *)PyUnstable_GetOptimizer();
+#endif
     if (opt == NULL) {
         Py_RETURN_NONE;
     }
@@ -1045,6 +1050,8 @@ invalidate_executors(PyObject *self, PyObject *obj)
     Py_RETURN_NONE;
 }
 
+#endif
+
 static int _pending_callback(void *arg)
 {
     /* we assume the argument is callable object to which we own a reference */
@@ -2020,12 +2027,14 @@ static PyMethodDef module_functions[] = {
     {"iframe_getline", iframe_getline, METH_O, NULL},
     {"iframe_getlasti", iframe_getlasti, METH_O, NULL},
     {"get_co_framesize", get_co_framesize, METH_O, NULL},
+#ifdef _Py_TIER2
     {"get_optimizer", get_optimizer,  METH_NOARGS, NULL},
     {"set_optimizer", set_optimizer,  METH_O, NULL},
     {"new_counter_optimizer", new_counter_optimizer, METH_NOARGS, NULL},
     {"new_uop_optimizer", new_uop_optimizer, METH_NOARGS, NULL},
     {"add_executor_dependency", add_executor_dependency, METH_VARARGS, NULL},
     {"invalidate_executors", invalidate_executors, METH_O, NULL},
+#endif
     {"pending_threadfunc", _PyCFunction_CAST(pending_threadfunc),
      METH_VARARGS | METH_KEYWORDS},
     {"pending_identify", pending_identify, METH_VARARGS, NULL},
@@ -2072,7 +2081,9 @@ static PyMethodDef module_functions[] = {
     {"py_thread_id", get_py_thread_id, METH_NOARGS},
 #endif
     {"set_immortalize_deferred", set_immortalize_deferred, METH_VARARGS},
+#ifdef _Py_TIER2
     {"uop_symbols_test", _Py_uop_symbols_test, METH_NOARGS},
+#endif
     {NULL, NULL} /* sentinel */
 };
 

Objects/codeobject.c

@@ -1496,6 +1496,8 @@ PyCode_GetFreevars(PyCodeObject *code)
     return _PyCode_GetFreevars(code);
 }
 
+#ifdef _Py_TIER2
+
 static void
 clear_executors(PyCodeObject *co)
 {
@@ -1515,6 +1517,8 @@ _PyCode_Clear_Executors(PyCodeObject *code)
     clear_executors(code);
 }
 
+#endif
+
 static void
 deopt_code(PyCodeObject *code, _Py_CODEUNIT *instructions)
 {
@@ -1739,9 +1743,11 @@ code_dealloc(PyCodeObject *co)
 
         PyMem_Free(co_extra);
     }
+#ifdef _Py_TIER2
     if (co->co_executors != NULL) {
         clear_executors(co);
     }
+#endif
 
     Py_XDECREF(co->co_consts);
     Py_XDECREF(co->co_names);

Objects/object.c

@@ -2281,9 +2281,11 @@ static PyTypeObject* static_types[] = {
     &_PyBufferWrapper_Type,
     &_PyContextTokenMissing_Type,
     &_PyCoroWrapper_Type,
+#ifdef _Py_TIER2
     &_PyCounterExecutor_Type,
     &_PyCounterOptimizer_Type,
     &_PyDefaultOptimizer_Type,
+#endif
     &_Py_GenericAliasIterType,
     &_PyHamtItems_Type,
     &_PyHamtKeys_Type,
@@ -2304,8 +2306,10 @@ static PyTypeObject* static_types[] = {
     &_PyPositionsIterator,
     &_PyUnicodeASCIIIter_Type,
     &_PyUnion_Type,
+#ifdef _Py_TIER2
     &_PyUOpExecutor_Type,
     &_PyUOpOptimizer_Type,
+#endif
     &_PyWeakref_CallableProxyType,
     &_PyWeakref_ProxyType,
     &_PyWeakref_RefType,

PCbuild/_testinternalcapi.vcxproj

@@ -108,6 +108,12 @@
       <ReferenceOutputAssembly>false</ReferenceOutputAssembly>
     </ProjectReference>
   </ItemGroup>
+  <ItemDefinitionGroup>
+    <ClCompile>
+      <PreprocessorDefinitions Condition="'$(UseJIT)' == 'true'">_Py_JIT;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <PreprocessorDefinitions Condition="'$(UseTIER2)' != '0'">_Py_TIER2=$(UseTIER2);%(PreprocessorDefinitions)</PreprocessorDefinitions>
+    </ClCompile>
+  </ItemDefinitionGroup>
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />
   <ImportGroup Label="ExtensionTargets">
   </ImportGroup>

PCbuild/build.bat

@@ -36,7 +36,9 @@ echo.                 overrides -c and -d
 echo.  --disable-gil  Enable experimental support for running without the GIL.
 echo.  --test-marker  Enable the test marker within the build.
 echo.  --regen        Regenerate all opcodes, grammar and tokens.
-echo.  --experimental-jit  Enable the experimental just-in-time compiler.
+echo.  --experimental-jit          Enable the experimental just-in-time compiler.
+echo.  --experimental-jit-off      Ditto but off by default (PYTHON_JIT=1 enables).
+echo.  --experimental-interpreter  Enable the experimental Tier 2 interpreter.
 echo.
 echo.Available flags to avoid building certain modules.
 echo.These flags have no effect if '-e' is not given:
@@ -66,6 +68,7 @@ set verbose=/nologo /v:m /clp:summary
 set kill=
 set do_pgo=
 set pgo_job=-m test --pgo
+set UseTIER2=0
 
 :CheckOpts
 if "%~1"=="-h" goto Usage
@@ -86,7 +89,10 @@ if "%~1"=="--disable-gil" (set UseDisableGil=true) & shift & goto CheckOpts
 if "%~1"=="--test-marker" (set UseTestMarker=true) & shift & goto CheckOpts
 if "%~1"=="-V" shift & goto Version
 if "%~1"=="--regen" (set Regen=true) & shift & goto CheckOpts
-if "%~1"=="--experimental-jit" (set UseJIT=true) & shift & goto CheckOpts
+if "%~1"=="--experimental-jit" (set UseJIT=true) & (set UseTIER2=1) & shift & goto CheckOpts
+if "%~1"=="--experimental-jit-off" (set UseJIT=true) & (set UseTIER2=3) & shift & goto CheckOpts
+if "%~1"=="--experimental-interpreter" (set UseTIER2=4) & shift & goto CheckOpts
+if "%~1"=="--experimental-interpreter-off" (set UseTIER2=6) & shift & goto CheckOpts
 rem These use the actual property names used by MSBuild.  We could just let
 rem them in through the environment, but we specify them on the command line
 rem anyway for visibility so set defaults after this
@@ -179,6 +185,7 @@ echo on
  /p:DisableGil=%UseDisableGil%^
  /p:UseTestMarker=%UseTestMarker% %GITProperty%^
  /p:UseJIT=%UseJIT%^
+ /p:UseTIER2=%UseTIER2%^
  %1 %2 %3 %4 %5 %6 %7 %8 %9
 
 @echo off

PCbuild/pythoncore.vcxproj

@@ -105,6 +105,7 @@
       <PreprocessorDefinitions>_USRDLL;Py_BUILD_CORE;Py_BUILD_CORE_BUILTIN;Py_ENABLE_SHARED;MS_DLL_ID="$(SysWinVer)";%(PreprocessorDefinitions)</PreprocessorDefinitions>
       <PreprocessorDefinitions Condition="$(IncludeExternals)">_Py_HAVE_ZLIB;%(PreprocessorDefinitions)</PreprocessorDefinitions>
       <PreprocessorDefinitions Condition="'$(UseJIT)' == 'true'">_Py_JIT;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <PreprocessorDefinitions Condition="'$(UseTIER2)' != '0'">_Py_TIER2=$(UseTIER2);%(PreprocessorDefinitions)</PreprocessorDefinitions>
     </ClCompile>
     <Link>
       <AdditionalDependencies>version.lib;ws2_32.lib;pathcch.lib;bcrypt.lib;%(AdditionalDependencies)</AdditionalDependencies>

Python/bytecodes.c

@@ -2363,6 +2363,7 @@ dummy_func(
             CHECK_EVAL_BREAKER();
             assert(oparg <= INSTR_OFFSET());
             JUMPBY(-oparg);
+            #ifdef _Py_TIER2
             #if ENABLE_SPECIALIZATION
             _Py_BackoffCounter counter = this_instr[1].counter;
             if (backoff_counter_triggers(counter) && this_instr->op.code == JUMP_BACKWARD) {
@@ -2388,6 +2389,7 @@ dummy_func(
                 ADVANCE_ADAPTIVE_COUNTER(this_instr[1].counter);
             }
             #endif  /* ENABLE_SPECIALIZATION */
+            #endif /* _Py_TIER2 */
         }
 
         pseudo(JUMP) = {
@@ -2401,6 +2403,7 @@ dummy_func(
         };
 
         tier1 inst(ENTER_EXECUTOR, (--)) {
+            #ifdef _Py_TIER2
             int prevoparg = oparg;
             CHECK_EVAL_BREAKER();
             if (this_instr->op.code != ENTER_EXECUTOR ||
@@ -2418,6 +2421,9 @@ dummy_func(
             tstate->previous_executor = Py_None;
             Py_INCREF(executor);
             GOTO_TIER_TWO(executor);
+            #else
+            Py_FatalError("ENTER_EXECUTOR is not supported in this build");
+            #endif /* _Py_TIER2 */
         }
 
         replaced op(_POP_JUMP_IF_FALSE, (cond -- )) {

Python/ceval.c

@@ -755,7 +755,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
     _Py_CODEUNIT *next_instr;
     PyObject **stack_pointer;
 
-#ifndef _Py_JIT
+#if defined(_Py_TIER2) && !defined(_Py_JIT)
     /* Tier 2 interpreter state */
     _PyExecutorObject *current_executor = NULL;
     const _PyUOpInstruction *next_uop = NULL;
@@ -959,6 +959,7 @@ resume_with_error:
     goto error;
 
 
+#ifdef _Py_TIER2
 
 // Tier 2 is also here!
 enter_tier_two:
@@ -1113,6 +1114,8 @@ exit_to_trace:
 
 #endif  // _Py_JIT
 
+#endif // _Py_TIER2
+
 }
 
 #if defined(__GNUC__)

Python/generated_cases.c.h

@@ -2492,6 +2492,7 @@
             (void)this_instr;
             next_instr += 1;
             INSTRUCTION_STATS(ENTER_EXECUTOR);
+            #ifdef _Py_TIER2
             int prevoparg = oparg;
             CHECK_EVAL_BREAKER();
             if (this_instr->op.code != ENTER_EXECUTOR ||
@@ -2508,6 +2509,9 @@
             tstate->previous_executor = Py_None;
             Py_INCREF(executor);
             GOTO_TIER_TWO(executor);
+            #else
+            Py_FatalError("ENTER_EXECUTOR is not supported in this build");
+            #endif /* _Py_TIER2 */
             DISPATCH();
         }
 
@@ -3432,6 +3436,7 @@
             CHECK_EVAL_BREAKER();
             assert(oparg <= INSTR_OFFSET());
             JUMPBY(-oparg);
+            #ifdef _Py_TIER2
             #if ENABLE_SPECIALIZATION
             _Py_BackoffCounter counter = this_instr[1].counter;
             if (backoff_counter_triggers(counter) && this_instr->op.code == JUMP_BACKWARD) {
@@ -3457,6 +3462,7 @@
                 ADVANCE_ADAPTIVE_COUNTER(this_instr[1].counter);
             }
             #endif  /* ENABLE_SPECIALIZATION */
+            #endif /* _Py_TIER2 */
             DISPATCH();
         }
 

Python/instrumentation.c

@@ -1705,10 +1705,12 @@ instrument_lock_held(PyCodeObject *code, PyInterpreterState *interp)
         );
         return 0;
     }
+#ifdef _Py_TIER2
     if (code->co_executors != NULL) {
         _PyCode_Clear_Executors(code);
     }
     _Py_Executors_InvalidateDependency(interp, code, 1);
+#endif
     int code_len = (int)Py_SIZE(code);
     /* Exit early to avoid creating instrumentation
      * data for potential statically allocated code
@@ -1946,7 +1948,9 @@ _PyMonitoring_SetEvents(int tool_id, _PyMonitoringEventSet events)
         goto done;
     }
     set_global_version(tstate, new_version);
+#ifdef _Py_TIER2
     _Py_Executors_InvalidateAll(interp, 1);
+#endif
     res = instrument_all_executing_code_objects(interp);
 done:
     _PyEval_StartTheWorld(interp);
@@ -1986,7 +1990,9 @@ _PyMonitoring_SetLocalEvents(PyCodeObject *code, int tool_id, _PyMonitoringEvent
         code->_co_instrumentation_version -= MONITORING_VERSION_INCREMENT;
     }
 
+#ifdef _Py_TIER2
     _Py_Executors_InvalidateDependency(interp, code, 1);
+#endif
 
     res = instrument_lock_held(code, interp);
 

Python/optimizer.c

@@ -1,3 +1,5 @@
+#ifdef _Py_TIER2
+
 #include "Python.h"
 #include "opcode.h"
 #include "pycore_interp.h"
@@ -1622,3 +1624,5 @@ _Py_Executors_InvalidateAll(PyInterpreterState *interp, int is_invalidation)
         }
     }
 }
+
+#endif /* _Py_TIER2 */

Python/optimizer_analysis.c

@@ -1,3 +1,5 @@
+#ifdef _Py_TIER2
+
 /*
  * This file contains the support code for CPython's uops optimizer.
  * It also performs some simple optimizations.
@@ -603,3 +605,5 @@ _Py_uop_analyze_and_optimize(
     OPT_STAT_INC(optimizer_successes);
     return length;
 }
+
+#endif /* _Py_TIER2 */

Python/optimizer_symbols.c

@@ -1,3 +1,4 @@
+#ifdef _Py_TIER2
 
 #include "Python.h"
 
@@ -506,3 +507,5 @@ fail:
     Py_XDECREF(val_43);
     return NULL;
 }
+
+#endif /* _Py_TIER2 */

Python/pylifecycle.c

@@ -624,9 +624,11 @@ static int
 builtins_dict_watcher(PyDict_WatchEvent event, PyObject *dict, PyObject *key, PyObject *new_value)
 {
     PyInterpreterState *interp = _PyInterpreterState_GET();
+#ifdef _Py_TIER2
     if (interp->rare_events.builtin_dict < _Py_MAX_ALLOWED_BUILTINS_MODIFICATIONS) {
         _Py_Executors_InvalidateAll(interp, 1);
     }
+#endif
     RARE_EVENT_INTERP_INC(interp, builtin_dict);
     return 0;
 }
@@ -1272,30 +1274,30 @@ init_interp_main(PyThreadState *tstate)
     }
 
     // Turn on experimental tier 2 (uops-based) optimizer
+    // This is also needed when the JIT is enabled
+#ifdef _Py_TIER2
     if (is_main_interp) {
-#ifndef _Py_JIT
+        int enabled = 1;
-        // No JIT, maybe use the tier two interpreter:
+#if _Py_TIER2 & 2
-        char *envvar = Py_GETENV("PYTHON_UOPS");
+        enabled = 0;
-        int enabled = envvar != NULL && *envvar > '0';
+#endif
-        if (_Py_get_xoption(&config->xoptions, L"uops") != NULL) {
+        char *env = Py_GETENV("PYTHON_JIT");
-            enabled = 1;
+        if (env && *env != '\0') {
+            // PYTHON_JIT=0|1 overrides the default
+            enabled = *env != '0';
         }
         if (enabled) {
-#else
-        // Always enable tier two for JIT builds (ignoring the environment
-        // variable and command-line option above):
-        if (true) {
-#endif
             PyObject *opt = PyUnstable_Optimizer_NewUOpOptimizer();
             if (opt == NULL) {
                 return _PyStatus_ERR("can't initialize optimizer");
             }
             if (PyUnstable_SetOptimizer((_PyOptimizerObject *)opt)) {
-                return _PyStatus_ERR("can't initialize optimizer");
+                return _PyStatus_ERR("can't install optimizer");
             }
             Py_DECREF(opt);
         }
     }
+#endif
 
     if (!is_main_interp) {
         // The main interpreter is handled in Py_Main(), for now.
@@ -1655,10 +1657,12 @@ finalize_modules(PyThreadState *tstate)
 {
     PyInterpreterState *interp = tstate->interp;
 
+#ifdef _Py_TIER2
     // Invalidate all executors and turn off tier 2 optimizer
     _Py_Executors_InvalidateAll(interp, 0);
     _PyOptimizerObject *old = _Py_SetOptimizer(interp, NULL);
     Py_XDECREF(old);
+#endif
 
     // Stop watching __builtin__ modifications
     PyDict_Unwatch(0, interp->builtins);

Python/pystate.c

@@ -653,8 +653,10 @@ init_interpreter(PyInterpreterState *interp,
     }
     interp->sys_profile_initialized = false;
     interp->sys_trace_initialized = false;
+#ifdef _Py_TIER2
     (void)_Py_SetOptimizer(interp, NULL);
     interp->executor_list_head = NULL;
+#endif
     if (interp != &runtime->_main_interpreter) {
         /* Fix the self-referential, statically initialized fields. */
         interp->dtoa = (struct _dtoa_state)_dtoa_state_INIT(interp);
@@ -806,9 +808,11 @@ interpreter_clear(PyInterpreterState *interp, PyThreadState *tstate)
         tstate->_status.cleared = 0;
     }
 
+#ifdef _Py_TIER2
     _PyOptimizerObject *old = _Py_SetOptimizer(interp, NULL);
     assert(old != NULL);
     Py_DECREF(old);
+#endif
 
     /* It is possible that any of the objects below have a finalizer
        that runs Python code or otherwise relies on a thread state
@@ -2821,9 +2825,11 @@ _PyInterpreterState_SetEvalFrameFunc(PyInterpreterState *interp,
     if (eval_frame == interp->eval_frame) {
         return;
     }
+#ifdef _Py_TIER2
     if (eval_frame != NULL) {
         _Py_Executors_InvalidateAll(interp, 1);
     }
+#endif
     RARE_EVENT_INC(set_eval_frame_func);
     interp->eval_frame = eval_frame;
 }

Python/sysmodule.c

@@ -2165,8 +2165,10 @@ static PyObject *
 sys__clear_internal_caches_impl(PyObject *module)
 /*[clinic end generated code: output=0ee128670a4966d6 input=253e741ca744f6e8]*/
 {
+#ifdef _Py_TIER2
     PyInterpreterState *interp = _PyInterpreterState_GET();
     _Py_Executors_InvalidateAll(interp, 0);
+#endif
     PyType_ClearCache();
     Py_RETURN_NONE;
 }

Tools/cases_generator/analyzer.py

@@ -411,6 +411,7 @@ NON_ESCAPING_FUNCTIONS = (
     "PyCell_New",
     "PyFloat_AS_DOUBLE",
     "_PyFrame_PushUnchecked",
+    "Py_FatalError",
 )
 
 ESCAPING_FUNCTIONS = (

Tools/jit/README.md

@@ -7,18 +7,18 @@ This version of CPython can be built with an experimental just-in-time compiler.
 
 The JIT compiler does not require end users to install any third-party dependencies, but part of it must be *built* using LLVM[^why-llvm]. You are *not* required to build the rest of CPython using LLVM, or even the same version of LLVM (in fact, this is uncommon).
 
-LLVM version 16 is required. Both `clang` and `llvm-readobj` need to be installed and discoverable (version suffixes, like `clang-16`, are okay). It's highly recommended that you also have `llvm-objdump` available, since this allows the build script to dump human-readable assembly for the generated code.
+LLVM version 18 is required. Both `clang` and `llvm-readobj` need to be installed and discoverable (version suffixes, like `clang-18`, are okay). It's highly recommended that you also have `llvm-objdump` available, since this allows the build script to dump human-readable assembly for the generated code.
 
 It's easy to install all of the required tools:
 
 ### Linux
 
-Install LLVM 16 on Ubuntu/Debian:
+Install LLVM 18 on Ubuntu/Debian:
 
 ```sh
 wget https://apt.llvm.org/llvm.sh
 chmod +x llvm.sh
-sudo ./llvm.sh 16
+sudo ./llvm.sh 18
 ```
 
 ### macOS

configure

@@ -1818,7 +1818,7 @@ Optional Features:
   --disable-gil           enable experimental support for running without the
                           GIL (default is no)
   --enable-pystats        enable internal statistics gathering (default is no)
-  --enable-experimental-jit
+  --enable-experimental-jit[=no|yes|yes-off|interpreter]
                           build the experimental just-in-time compiler
                           (default is no)
   --enable-optimizations  enable expensive, stable optimizations (PGO, etc.)
@@ -8229,11 +8229,19 @@ else $as_nop
   enable_experimental_jit=no
 fi
 
+case $enable_experimental_jit in
+  no) enable_experimental_jit=no ;;
+  yes) enable_experimental_jit="-D_Py_JIT -D_Py_TIER2=1" ;;
+  yes-off) enable_experimental_jit="-D_Py_JIT -D_Py_TIER2=3" ;;
+  interpreter) enable_experimental_jit="-D_Py_TIER2=4" ;;
+  interpreter-off) enable_experimental_jit="-D_Py_TIER2=6" ;;  # Secret option
+  *) as_fn_error $? "invalid argument: --enable-experimental-jit=$enable_experimental_jit; expected no|yes|yes-off|interpreter" "$LINENO" 5 ;;
+esac
 if test "x$enable_experimental_jit" = xno
 then :
 
 else $as_nop
-  as_fn_append CFLAGS_NODIST " -D_Py_JIT"
+  as_fn_append CFLAGS_NODIST " $enable_experimental_jit"
            REGEN_JIT_COMMAND="\$(PYTHON_FOR_REGEN) \$(srcdir)/Tools/jit/build.py $host"
            JIT_STENCILS_H="jit_stencils.h"
            if test "x$Py_DEBUG" = xtrue

configure.ac

@@ -1768,14 +1768,23 @@ fi
 # Check for --enable-experimental-jit:
 AC_MSG_CHECKING([for --enable-experimental-jit])
 AC_ARG_ENABLE([experimental-jit],
-              [AS_HELP_STRING([--enable-experimental-jit],
+              [AS_HELP_STRING([--enable-experimental-jit@<:@=no|yes|yes-off|interpreter@:>@],
                               [build the experimental just-in-time compiler (default is no)])],
               [],
               [enable_experimental_jit=no])
+case $enable_experimental_jit in
+  no) enable_experimental_jit=no ;;
+  yes) enable_experimental_jit="-D_Py_JIT -D_Py_TIER2=1" ;;
+  yes-off) enable_experimental_jit="-D_Py_JIT -D_Py_TIER2=3" ;;
+  interpreter) enable_experimental_jit="-D_Py_TIER2=4" ;;
+  interpreter-off) enable_experimental_jit="-D_Py_TIER2=6" ;;  # Secret option
+  *) AC_MSG_ERROR(
+      [invalid argument: --enable-experimental-jit=$enable_experimental_jit; expected no|yes|yes-off|interpreter]) ;;
+esac
 AS_VAR_IF([enable_experimental_jit],
           [no],
           [],
-          [AS_VAR_APPEND([CFLAGS_NODIST], [" -D_Py_JIT"])
+          [AS_VAR_APPEND([CFLAGS_NODIST], [" $enable_experimental_jit"])
            AS_VAR_SET([REGEN_JIT_COMMAND],
                       ["\$(PYTHON_FOR_REGEN) \$(srcdir)/Tools/jit/build.py $host"])
            AS_VAR_SET([JIT_STENCILS_H], ["jit_stencils.h"])