Add sys._jit

Author: brandtbucher

Doc/library/sys.rst

@@ -1282,6 +1282,59 @@ always available. Unless explicitly noted otherwise, all variables are read-only
 
    .. versionadded:: 3.5
 
+.. data:: _jit
+
+   Utilities for observing just-in-time compilation.
+
+   .. impl-detail::
+
+      JIT compilation is an *experimental implementation detail* of CPython.
+      ``sys._jit`` is not guaranteed to exist or behave the same way in all
+      Python implementations, versions, or build configurations.
+
+   .. versionadded:: 3.14
+
+   .. function:: sys._jit.is_available()
+
+      Return ``True`` if the current Python executable supports JIT compilation,
+      and ``False`` otherwise.  This can be controlled by building CPython with
+      the ``--experimental-jit`` option on Windows, and the
+      :option:`--enable-experimental-jit` option on all other platforms.
+
+   .. function:: sys._jit.is_enabled()
+
+      Return ``True`` if JIT compilation is enabled for the current Python
+      process (implies ``sys._jit.is_available()``), and ``False`` otherwise.
+      If JIT compilation is available, this can be controlled by setting the
+      :envvar:`PYTHON_JIT` environment variable to ``0`` (disabled) or ``1``
+      (enabled) at interpreter startup.
+
+   .. function:: sys._jit.is_active()
+
+      Return ``True`` if the topmost Python frame is currently executing JIT
+      code, and ``False`` otherwise.
+
+      .. note::
+
+         Due to the nature of tracing JIT compilers, repeated calls to this
+         function may give surprising results. For example, branching on its
+         return value will likely lead to unexpected behavior (if doing so
+         causes JIT code to be entered or exited):
+
+         .. code-block:: pycon
+
+            >>> for warmup in range(BIG_NUMBER):
+            ...     # This line is "hot", and is eventually JIT-compiled:
+            ...     if sys._jit.is_active():
+            ...         # This line is "cold", and is run in the interpreter:
+            ...         assert sys._jit.is_active()
+            ...
+            Traceback (most recent call last):
+              File "<stdin>", line 5, in <module>
+                assert sys._jit.is_active()
+                       ~~~~~~~~~~~~~~~~~~^^
+            AssertionError
+
 .. data:: last_exc
 
    This variable is not always defined; it is set to the exception instance

Doc/using/cmdline.rst

@@ -1279,7 +1279,13 @@ conflict.
    free-threaded builds and to ``0`` otherwise.  See :option:`-X
    context_aware_warnings<-X>`.
 
-   .. versionadded:: 3.14
+.. envvar:: PYTHON_JIT
+
+   On builds where experimental just-in-time compilation is available, this
+   variable can force the JIT to be disabled (``0``) or enabled (``1``) at
+   interpreter startup.
+
+   .. versionadded:: 3.13
 
 Debug-mode variables
 ~~~~~~~~~~~~~~~~~~~~

Include/internal/pycore_interpframe.h

@@ -146,6 +146,7 @@ _PyFrame_Initialize(
     frame->return_offset = 0;
     frame->owner = FRAME_OWNED_BY_THREAD;
     frame->visited = 0;
+    frame->jit_active = false;
 #ifdef Py_DEBUG
     frame->lltrace = 0;
 #endif
@@ -327,6 +328,7 @@ _PyFrame_PushTrampolineUnchecked(PyThreadState *tstate, PyCodeObject *code, int
 #endif
     frame->owner = FRAME_OWNED_BY_THREAD;
     frame->visited = 0;
+    frame->jit_active = false;
 #ifdef Py_DEBUG
     frame->lltrace = 0;
 #endif

Include/internal/pycore_interpframe_structs.h

@@ -43,11 +43,11 @@ struct _PyInterpreterFrame {
 #endif
     uint16_t return_offset;  /* Only relevant during a function call */
     char owner;
-#ifdef Py_DEBUG
     uint8_t visited:1;
-    uint8_t lltrace:7;
-#else
-    uint8_t visited;
+    // Set on interpreter entry frames when the JIT is active:
+    uint8_t jit_active:1;
+#ifdef Py_DEBUG
+    uint8_t lltrace:6;
 #endif
     /* Locals and stack */
     _PyStackRef localsplus[1];

Lib/test/libregrtest/utils.py

@@ -335,43 +335,11 @@ def get_build_info():
             build.append('with_assert')
 
     # --enable-experimental-jit
-    tier2 = re.search('-D_Py_TIER2=([0-9]+)', cflags)
-    if tier2:
-        tier2 = int(tier2.group(1))
-
-    if not sys.flags.ignore_environment:
-        PYTHON_JIT = os.environ.get('PYTHON_JIT', None)
-        if PYTHON_JIT:
-            PYTHON_JIT = (PYTHON_JIT != '0')
-    else:
-        PYTHON_JIT = None
-
-    if tier2 == 1:  # =yes
-        if PYTHON_JIT == False:
-            jit = 'JIT=off'
-        else:
-            jit = 'JIT'
-    elif tier2 == 3:  # =yes-off
-        if PYTHON_JIT:
-            jit = 'JIT'
+    if sys._jit.is_available():
+        if sys._jit.is_enabled():
+            build.append("JIT")
         else:
-            jit = 'JIT=off'
-    elif tier2 == 4:  # =interpreter
-        if PYTHON_JIT == False:
-            jit = 'JIT-interpreter=off'
-        else:
-            jit = 'JIT-interpreter'
-    elif tier2 == 6:  # =interpreter-off (Secret option!)
-        if PYTHON_JIT:
-            jit = 'JIT-interpreter'
-        else:
-            jit = 'JIT-interpreter=off'
-    elif '-D_Py_JIT' in cflags:
-        jit = 'JIT'
-    else:
-        jit = None
-    if jit:
-        build.append(jit)
+            build.append("JIT (disabled)")
 
     # --enable-framework=name
     framework = sysconfig.get_config_var('PYTHONFRAMEWORK')

Lib/test/support/__init__.py

@@ -2648,13 +2648,9 @@ def exceeds_recursion_limit():
 
 Py_TRACE_REFS = hasattr(sys, 'getobjects')
 
-try:
-    from _testinternalcapi import jit_enabled
-except ImportError:
-    requires_jit_enabled = requires_jit_disabled = unittest.skip("requires _testinternalcapi")
-else:
-    requires_jit_enabled = unittest.skipUnless(jit_enabled(), "requires JIT enabled")
-    requires_jit_disabled = unittest.skipIf(jit_enabled(), "requires JIT disabled")
+_JIT_ENABLED = sys._jit.is_enabled()
+requires_jit_enabled = unittest.skipUnless(_JIT_ENABLED, "requires JIT enabled")
+requires_jit_disabled = unittest.skipIf(_JIT_ENABLED, "requires JIT disabled")
 
 
 _BASE_COPY_SRC_DIR_IGNORED_NAMES = frozenset({

Lib/test/test_dis.py

@@ -1336,7 +1336,7 @@ def test_loop_quicken(self):
         # Loop can trigger a quicken where the loop is located
         self.code_quicken(loop_test)
         got = self.get_disassembly(loop_test, adaptive=True)
-        jit = import_helper.import_module("_testinternalcapi").jit_enabled()
+        jit = sys._jit.is_enabled()
         expected = dis_loop_test_quickened_code.format("JIT" if jit else "NO_JIT")
         self.do_disassembly_compare(got, expected)
 

Lib/test/test_sys.py

@@ -2196,6 +2196,64 @@ def test_remote_exec_in_process_without_debug_fails_xoption(self):
         self.assertIn(b"Remote debugging is not enabled", err)
         self.assertEqual(out, b"")
 
+class TestSysJIT(unittest.TestCase):
+
+    def test_jit_is_available(self):
+        available = sys._jit.is_available()
+        script = f"import sys; assert sys._jit.is_available() is {available}"
+        assert_python_ok("-c", script, PYTHON_JIT="0")
+        assert_python_ok("-c", script, PYTHON_JIT="1")
+
+    def test_jit_is_enabled(self):
+        available = sys._jit.is_available()
+        script = "import sys; assert sys._jit.is_enabled() is {enabled}"
+        assert_python_ok("-c", script.format(enabled=False), PYTHON_JIT="0")
+        assert_python_ok("-c", script.format(enabled=available), PYTHON_JIT="1")
+
+    def test_jit_is_active(self):
+        available = sys._jit.is_available()
+        script = textwrap.dedent(
+            """
+            import _testinternalcapi
+            import operator
+            import sys
+
+            def frame_0_interpreter() -> None:
+                assert sys._jit.is_active() is False
+
+            def frame_1_interpreter() -> None:
+                assert sys._jit.is_active() is False
+                frame_0_interpreter()
+                assert sys._jit.is_active() is False
+
+            def frame_2_jit(expected: bool) -> None:
+                # Inlined into the last loop of frame_3_jit:
+                assert sys._jit.is_active() is expected
+                # Insert C frame:
+                operator.call(frame_1_interpreter)
+                assert sys._jit.is_active() is expected
+
+            def frame_3_jit() -> None:
+                # JITs just before the last loop:
+                for i in range(_testinternalcapi.TIER2_THRESHOLD + 1):
+                    # Careful, doing this in the reverse order breaks tracing:
+                    expected = {enabled} and i == _testinternalcapi.TIER2_THRESHOLD
+                    assert sys._jit.is_active() is expected
+                    frame_2_jit(expected)
+                    assert sys._jit.is_active() is expected
+
+            def frame_4_interpreter() -> None:
+                assert sys._jit.is_active() is False
+                frame_3_jit()
+                assert sys._jit.is_active() is False
+
+            assert sys._jit.is_active() is False
+            frame_4_interpreter()
+            assert sys._jit.is_active() is False
+            """
+        )
+        assert_python_ok("-c", script.format(enabled=False), PYTHON_JIT="0")
+        assert_python_ok("-c", script.format(enabled=available), PYTHON_JIT="1")
 
 
 if __name__ == "__main__":

Modules/_testinternalcapi.c

@@ -1165,12 +1165,6 @@ get_code_var_counts(PyObject *self, PyObject *_args, PyObject *_kwargs)
     return NULL;
 }
 
-static PyObject *
-jit_enabled(PyObject *self, PyObject *arg)
-{
-    return PyBool_FromLong(_PyInterpreterState_GET()->jit);
-}
-
 #ifdef _Py_TIER2
 
 static PyObject *
@@ -2093,13 +2087,10 @@ reset_rare_event_counters(PyObject *self, PyObject *Py_UNUSED(type))
 
     interp->rare_events.set_class = 0;
     interp->rare_events.set_bases = 0;
-    interp->rare_events.set_eval_frame_func = 0;
     interp->rare_events.builtin_dict = 0;
     interp->rare_events.func_modification = 0;
 
     return Py_None;
-}
-
 
 #ifdef Py_GIL_DISABLED
 static PyObject *
@@ -2293,7 +2284,6 @@ static PyMethodDef module_functions[] = {
     {"get_co_localskinds", get_co_localskinds, METH_O, NULL},
     {"get_code_var_counts", _PyCFunction_CAST(get_code_var_counts),
      METH_VARARGS | METH_KEYWORDS, NULL},
-    {"jit_enabled", jit_enabled,  METH_NOARGS, NULL},
 #ifdef _Py_TIER2
     {"add_executor_dependency", add_executor_dependency, METH_VARARGS, NULL},
     {"invalidate_executors", invalidate_executors, METH_O, NULL},

Python/ceval.c

@@ -1036,9 +1036,10 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
     entry_frame.f_executable = PyStackRef_None;
     entry_frame.instr_ptr = (_Py_CODEUNIT *)_Py_INTERPRETER_TRAMPOLINE_INSTRUCTIONS + 1;
     entry_frame.stackpointer = entry_frame.localsplus;
+    entry_frame.return_offset = 0;
     entry_frame.owner = FRAME_OWNED_BY_INTERPRETER;
     entry_frame.visited = 0;
-    entry_frame.return_offset = 0;
+    entry_frame.jit_active = false;
 #ifdef Py_DEBUG
     entry_frame.lltrace = 0;
 #endif