gh-126204: Add a sys._jit_enabled helper

Doc/library/sys.rst

@@ -1236,6 +1236,16 @@ always available.
  .. versionadded:: 3.13
 
 
+.. function:: _jit_enabled()
+
+ Return :const:`True` if the :ref:`JIT compiler <whatsnew313-jit-compiler>` is active,
+ and :const:`False` otherwise.
+
+ Available only in JIT builds; tier 2 interpreter does not count here.
+
+ .. versionadded:: next
+
+
 .. function:: is_finalizing()
 
  Return :const:`True` if the main Python interpreter is

Doc/whatsnew/3.14.rst

@@ -443,6 +443,9 @@ sys
  which only exists in specialized builds of Python, may now return objects
  from other interpreters than the one it's called in.
 
+* Add :func:`sys._jit_enabled` to determine at runtime if the
+ :ref:`JIT compiler <whatsnew313-jit-compiler>` is active.
+
 
 unicodedata
 -----------

Include/internal/pycore_sysmodule.h

@@ -22,6 +22,10 @@ extern int _PySys_ClearAttrString(PyInterpreterState *interp,
 extern int _PySys_SetFlagObj(Py_ssize_t pos, PyObject *new_value);
 extern int _PySys_SetIntMaxStrDigits(int maxdigits);
 
+#if defined(_Py_TIER2) && (_Py_TIER2 % 2 != 0)
+extern int _PySys_JITEnabled(void);
+#endif
+
 #ifdef __cplusplus
 }
 #endif

Lib/test/test_embed.py

@@ -1782,10 +1782,8 @@ def test_initconfig_api(self):
  'perf_profiling': 2,
  }
  config_dev_mode(preconfig, config)
- # Temporarily enable ignore_stderr=True to ignore warnings on JIT builds
- # See gh-126255 for more information
  self.check_all_configs("test_initconfig_api", config, preconfig,
- api=API_ISOLATED, ignore_stderr=True)
+ api=API_ISOLATED, env={'PYTHON_JIT': '0'})
 
  def test_initconfig_get_api(self):
  self.run_embedded_interpreter("test_initconfig_get_api")

Misc/NEWS.d/next/Core_and_Builtins/2024-11-10-04-59-43.gh-issue-126204.ASKDL1.rst

@@ -0,0 +1 @@
+Allow to determine whether the JIT is enabled at runtime via :func:`sys._jit_enabled`.

Python/pylifecycle.c

@@ -1296,43 +1296,34 @@ init_interp_main(PyThreadState *tstate)
 #endif
  }
 
-// Turn on experimental tier 2 (uops-based) optimizer
-// This is also needed when the JIT is enabled
+// Turn on experimental tier 2 (uops-based) optimizer
+// This is also needed when the JIT is enabled
 #ifdef _Py_TIER2
  if (is_main_interp) {
- int enabled = 1;
-#if _Py_TIER2 & 2
- enabled = 0;
-#endif
-char *env = Py_GETENV("PYTHON_JIT");
-if (env && *env != '\0') {
-// PYTHON_JIT=0|1 overrides the default
-enabled = *env != '0';
+// perf profiler works fine with tier 2 interpreter, so
+// only checking for a "real JIT".
+#if _Py_TIER % 2 != 0
+ if (_PySys_JITEnabled() && config->perf_profiling > 0) {
+ (void)PyErr_WarnEx(
+ PyExc_RuntimeWarning,
+"JIT deactivated as perf profiling support is active",
+0);
  }
- if (enabled) {
-#ifdef _Py_JIT
- // perf profiler works fine with tier 2 interpreter, so
- // only checking for a "real JIT".
- if (config->perf_profiling > 0) {
- (void)PyErr_WarnEx(
- PyExc_RuntimeWarning,
- "JIT deactivated as perf profiling support is active",
- 0);
- } else
+ else
 #endif
- {
- PyObject *opt = _PyOptimizer_NewUOpOptimizer();
- if (opt == NULL) {
- return _PyStatus_ERR("can't initialize optimizer");
- }
- if (_Py_SetTier2Optimizer((_PyOptimizerObject *)opt)) {
- return _PyStatus_ERR("can't install optimizer");
- }
+ {
+ PyObject *opt = _PyOptimizer_NewUOpOptimizer();
+ if (opt == NULL) {
+ return _PyStatus_ERR("can't initialize optimizer");
+ }
+ if (_Py_SetTier2Optimizer((_PyOptimizerObject *)opt)) {
  Py_DECREF(opt);
+ return _PyStatus_ERR("can't install optimizer");
  }
+ Py_DECREF(opt);
  }
  }
-#endif
+#endif // Py_TIER2
 
  if (!is_main_interp) {
  // The main interpreter is handled in Py_Main(), for now.

Python/sysmodule.c

@@ -2264,12 +2264,14 @@ sys_activate_stack_trampoline_impl(PyObject *module, const char *backend)
 /*[clinic end generated code: output=5783cdeb51874b43 input=a12df928758a82b4]*/
 {
 #ifdef PY_HAVE_PERF_TRAMPOLINE
-#ifdef _Py_JIT
- _PyOptimizerObject* optimizer = _Py_GetOptimizer();
- if (optimizer != NULL) {
- Py_DECREF(optimizer);
- PyErr_SetString(PyExc_ValueError, "Cannot activate the perf trampoline if the JIT is active");
- return NULL;
+#if defined(_Py_TIER2) && (_Py_TIER2 % 2 != 0)
+ if (_PySys_JITEnabled()) {
+ _PyOptimizerObject *optimizer = _Py_GetOptimizer();
+ if (optimizer != NULL) {
+ Py_DECREF(optimizer);
+ PyErr_SetString(PyExc_ValueError, "Cannot activate the perf trampoline if the JIT is active");
+ return NULL;
+ }
  }
 #endif
 
@@ -2533,6 +2535,46 @@ PyAPI_FUNC(int) PyUnstable_CopyPerfMapFile(const char* parent_filename) {
 }
 
 
+#ifdef _Py_TIER2
+// _Py_TIER2 is set to 4 or 6 in tier 2 builds.
+#if _Py_TIER2 % 2 != 0
+int
+_PySys_JITEnabled(void)
+{
+ const char *env = Py_GETENV("PYTHON_JIT");
+ if (_Py_TIER2 == 1) {
+ // Interpreter was built with enabled jit, but it can be disabled via PYTHON_JIT=0
+ if (env && *env != '\0') {
+ return *env != '0';
+ }
+ return 1;
+ }
+ else if (_Py_TIER2 == 3) {
+ // Interpreter was built with disabled jit, but it can be enabled via PYTHON_JIT=1
+ if (env && *env != '\0') {
+ return *env == '1';
+ }
+ return 0;
+ }
+ Py_UNREACHABLE();
+}
+
+/*[clinic input]
+sys._jit_enabled -> bool
+
+Returns True if JIT is enabled, False otherwise.
+[clinic start generated code]*/
+
+static int
+sys__jit_enabled_impl(PyObject *module)
+/*[clinic end generated code: output=e8adca3fa5011880 input=f2bdfa820c11f65b]*/
+{
+ return _PySys_JITEnabled();
+}
+#endif
+#endif // _Py_TIER2
+
+
 static PyMethodDef sys_methods[] = {
  /* Might as well keep this in alphabetic order */
  SYS_ADDAUDITHOOK_METHODDEF
@@ -2603,6 +2645,7 @@ static PyMethodDef sys_methods[] = {
 #endif
  SYS__GET_CPU_COUNT_CONFIG_METHODDEF
  SYS__IS_GIL_ENABLED_METHODDEF
+ SYS__JIT_ENABLED_METHODDEF
  {NULL, NULL} // sentinel
 };