GH-108035: Remove the _PyCFrame struct as it is no longer needed for performance. (GH-108036)

Author: markshannon

Include/cpython/pystate.h

@@ -29,24 +29,6 @@ typedef int (*Py_tracefunc)(PyObject *, PyFrameObject *, int, PyObject *);
 #define PyTrace_C_RETURN 6
 #define PyTrace_OPCODE 7
 
-// Internal structure: you should not use it directly, but use public functions
-// like PyThreadState_EnterTracing() and PyThreadState_LeaveTracing().
-typedef struct _PyCFrame {
-    /* This struct will be threaded through the C stack
-     * allowing fast access to per-thread state that needs
-     * to be accessed quickly by the interpreter, but can
-     * be modified outside of the interpreter.
-     *
-     * WARNING: This makes data on the C stack accessible from
-     * heap objects. Care must be taken to maintain stack
-     * discipline and make sure that instances of this struct cannot
-     * accessed outside of their lifetime.
-     */
-    /* Pointer to the currently executing frame (it can be NULL) */
-    struct _PyInterpreterFrame *current_frame;
-    struct _PyCFrame *previous;
-} _PyCFrame;
-
 typedef struct _err_stackitem {
     /* This struct represents a single execution context where we might
      * be currently handling an exception.  It is a per-coroutine state
@@ -123,9 +105,8 @@ struct _ts {
     int tracing;
     int what_event; /* The event currently being monitored, if any. */
 
-    /* Pointer to current _PyCFrame in the C stack frame of the currently,
-     * or most recently, executing _PyEval_EvalFrameDefault. */
-    _PyCFrame *cframe;
+    /* Pointer to currently executing frame. */
+    struct _PyInterpreterFrame *current_frame;
 
     Py_tracefunc c_profilefunc;
     Py_tracefunc c_tracefunc;
@@ -211,8 +192,6 @@ struct _ts {
     /* The thread's exception stack entry.  (Always the last entry.) */
     _PyErr_StackItem exc_state;
 
-    /* The bottom-most frame on the stack. */
-    _PyCFrame root_cframe;
 };
 
 /* WASI has limited call stack. Python's recursion limit depends on code

Include/internal/pycore_frame.h

@@ -196,7 +196,7 @@ _PyFrame_GetFirstComplete(_PyInterpreterFrame *frame)
 static inline _PyInterpreterFrame *
 _PyThreadState_GetFrame(PyThreadState *tstate)
 {
-    return _PyFrame_GetFirstComplete(tstate->cframe->current_frame);
+    return _PyFrame_GetFirstComplete(tstate->current_frame);
 }
 
 /* For use by _PyFrame_GetFrameObject

Include/internal/pycore_runtime.h

@@ -80,7 +80,7 @@ typedef struct _Py_DebugOffsets {
         off_t prev;
         off_t next;
         off_t interp;
-        off_t cframe;
+        off_t current_frame;
         off_t thread_id;
         off_t native_thread_id;
     } thread_state;

Include/internal/pycore_runtime_init.h

@@ -45,7 +45,7 @@ extern PyTypeObject _PyExc_MemoryError;
                 .prev = offsetof(PyThreadState, prev), \
                 .next = offsetof(PyThreadState, next), \
                 .interp = offsetof(PyThreadState, interp), \
-                .cframe = offsetof(PyThreadState, cframe), \
+                .current_frame = offsetof(PyThreadState, current_frame), \
                 .thread_id = offsetof(PyThreadState, thread_id), \
                 .native_thread_id = offsetof(PyThreadState, native_thread_id), \
             }, \
@@ -56,10 +56,6 @@ extern PyTypeObject _PyExc_MemoryError;
                 .localsplus = offsetof(_PyInterpreterFrame, localsplus), \
                 .owner = offsetof(_PyInterpreterFrame, owner), \
             }, \
-            .cframe = { \
-                .current_frame = offsetof(_PyCFrame, current_frame), \
-                .previous = offsetof(_PyCFrame, previous), \
-            }, \
             .code_object = { \
                 .filename = offsetof(PyCodeObject, co_filename), \
                 .name = offsetof(PyCodeObject, co_name), \

Misc/NEWS.d/next/Core and Builtins/2023-08-11-16-18-19.gh-issue-108035.e2msOD.rst

@@ -0,0 +1,4 @@
+Remove the ``_PyCFrame`` struct, moving the pointer to the current intepreter frame
+back to the threadstate, as it was for 3.10 and earlier. The ``_PyCFrame``
+existed as a performance optimization for tracing. Since PEP 669 has been
+implemented, this optimization no longer applies.

Modules/_xxsubinterpretersmodule.c

@@ -369,7 +369,7 @@ _is_running(PyInterpreterState *interp)
     }
 
     assert(!PyErr_Occurred());
-    struct _PyInterpreterFrame *frame = tstate->cframe->current_frame;
+    struct _PyInterpreterFrame *frame = tstate->current_frame;
     if (frame == NULL) {
         return 0;
     }

Objects/genobject.c

@@ -476,17 +476,17 @@ _gen_throw(PyGenObject *gen, int close_on_genexit,
                will be reported correctly to the user. */
             /* XXX We should probably be updating the current frame
                somewhere in ceval.c. */
-            _PyInterpreterFrame *prev = tstate->cframe->current_frame;
+            _PyInterpreterFrame *prev = tstate->current_frame;
             frame->previous = prev;
-            tstate->cframe->current_frame = frame;
+            tstate->current_frame = frame;
             /* Close the generator that we are currently iterating with
                'yield from' or awaiting on with 'await'. */
             PyFrameState state = gen->gi_frame_state;
             gen->gi_frame_state = FRAME_EXECUTING;
             ret = _gen_throw((PyGenObject *)yf, close_on_genexit,
                              typ, val, tb);
             gen->gi_frame_state = state;
-            tstate->cframe->current_frame = prev;
+            tstate->current_frame = prev;
             frame->previous = NULL;
         } else {
             /* `yf` is an iterator or a coroutine-like object. */
@@ -938,7 +938,7 @@ _Py_MakeCoro(PyFunctionObject *func)
     if (origin_depth == 0) {
         ((PyCoroObject *)coro)->cr_origin_or_finalizer = NULL;
     } else {
-        _PyInterpreterFrame *frame = tstate->cframe->current_frame;
+        _PyInterpreterFrame *frame = tstate->current_frame;
         assert(frame);
         assert(_PyFrame_IsIncomplete(frame));
         frame = _PyFrame_GetFirstComplete(frame->previous);

Objects/typevarobject.c

@@ -107,7 +107,7 @@ make_union(PyObject *self, PyObject *other)
 static PyObject *
 caller(void)
 {
-    _PyInterpreterFrame *f = _PyThreadState_GET()->cframe->current_frame;
+    _PyInterpreterFrame *f = _PyThreadState_GET()->current_frame;
     if (f == NULL) {
         Py_RETURN_NONE;
     }

Python/bytecodes.c

@@ -72,7 +72,6 @@ dummy_func(
     _PyInterpreterFrame *frame,
     unsigned char opcode,
     unsigned int oparg,
-    _PyCFrame cframe,
     _Py_CODEUNIT *next_instr,
     PyObject **stack_pointer,
     PyObject *kwnames,
@@ -134,8 +133,7 @@ dummy_func(
         }
 
         inst(RESUME, (--)) {
-            assert(tstate->cframe == &cframe);
-            assert(frame == cframe.current_frame);
+            assert(frame == tstate->current_frame);
             /* Possibly combine this with eval breaker */
             if (_PyFrame_GetCode(frame)->_co_instrumentation_version != tstate->interp->monitoring_version) {
                 int err = _Py_Instrument(_PyFrame_GetCode(frame), tstate->interp);
@@ -752,9 +750,8 @@ dummy_func(
         inst(INTERPRETER_EXIT, (retval --)) {
             assert(frame == &entry_frame);
             assert(_PyFrame_IsIncomplete(frame));
-            /* Restore previous cframe and return. */
-            tstate->cframe = cframe.previous;
-            assert(tstate->cframe->current_frame == frame->previous);
+            /* Restore previous frame and return. */
+            tstate->current_frame = frame->previous;
             assert(!_PyErr_Occurred(tstate));
             tstate->c_recursion_remaining += PY_EVAL_C_STACK_UNITS;
             return retval;
@@ -768,7 +765,7 @@ dummy_func(
             assert(frame != &entry_frame);
             // GH-99729: We need to unlink the frame *before* clearing it:
             _PyInterpreterFrame *dying = frame;
-            frame = cframe.current_frame = dying->previous;
+            frame = tstate->current_frame = dying->previous;
             _PyEvalFrameClearAndPop(tstate, dying);
             frame->prev_instr += frame->return_offset;
             _PyFrame_StackPush(frame, retval);
@@ -787,7 +784,7 @@ dummy_func(
             assert(frame != &entry_frame);
             // GH-99729: We need to unlink the frame *before* clearing it:
             _PyInterpreterFrame *dying = frame;
-            frame = cframe.current_frame = dying->previous;
+            frame = tstate->current_frame = dying->previous;
             _PyEvalFrameClearAndPop(tstate, dying);
             frame->prev_instr += frame->return_offset;
             _PyFrame_StackPush(frame, retval);
@@ -803,7 +800,7 @@ dummy_func(
             assert(frame != &entry_frame);
             // GH-99729: We need to unlink the frame *before* clearing it:
             _PyInterpreterFrame *dying = frame;
-            frame = cframe.current_frame = dying->previous;
+            frame = tstate->current_frame = dying->previous;
             _PyEvalFrameClearAndPop(tstate, dying);
             frame->prev_instr += frame->return_offset;
             _PyFrame_StackPush(frame, retval);
@@ -823,7 +820,7 @@ dummy_func(
             assert(frame != &entry_frame);
             // GH-99729: We need to unlink the frame *before* clearing it:
             _PyInterpreterFrame *dying = frame;
-            frame = cframe.current_frame = dying->previous;
+            frame = tstate->current_frame = dying->previous;
             _PyEvalFrameClearAndPop(tstate, dying);
             frame->prev_instr += frame->return_offset;
             _PyFrame_StackPush(frame, retval);
@@ -1019,7 +1016,7 @@ dummy_func(
             gen->gi_exc_state.previous_item = NULL;
             _Py_LeaveRecursiveCallPy(tstate);
             _PyInterpreterFrame *gen_frame = frame;
-            frame = cframe.current_frame = frame->previous;
+            frame = tstate->current_frame = frame->previous;
             gen_frame->previous = NULL;
             _PyFrame_StackPush(frame, retval);
             goto resume_frame;
@@ -1038,7 +1035,7 @@ dummy_func(
             gen->gi_exc_state.previous_item = NULL;
             _Py_LeaveRecursiveCallPy(tstate);
             _PyInterpreterFrame *gen_frame = frame;
-            frame = cframe.current_frame = frame->previous;
+            frame = tstate->current_frame = frame->previous;
             gen_frame->previous = NULL;
             _PyFrame_StackPush(frame, retval);
             goto resume_frame;
@@ -2207,10 +2204,10 @@ dummy_func(
                 OBJECT_STAT_INC(optimization_attempts);
                 frame = _PyOptimizer_BackEdge(frame, here, next_instr, stack_pointer);
                 if (frame == NULL) {
-                    frame = cframe.current_frame;
+                    frame = tstate->current_frame;
                     goto resume_with_error;
                 }
-                assert(frame == cframe.current_frame);
+                assert(frame == tstate->current_frame);
                 here[1].cache &= ((1 << OPTIMIZER_BITS_IN_COUNTER) -1);
                 goto resume_frame;
             }
@@ -2238,7 +2235,7 @@ dummy_func(
             Py_INCREF(executor);
             frame = executor->execute(executor, frame, stack_pointer);
             if (frame == NULL) {
-                frame = cframe.current_frame;
+                frame = tstate->current_frame;
                 goto resume_with_error;
             }
             goto resume_frame;
@@ -2993,12 +2990,11 @@ dummy_func(
             _PyFrame_SetStackPointer(frame, stack_pointer);
             new_frame->previous = frame;
             CALL_STAT_INC(inlined_py_calls);
+            frame = tstate->current_frame = new_frame;
             #if TIER_ONE
-            frame = cframe.current_frame = new_frame;
             goto start_frame;
             #endif
             #if TIER_TWO
-            frame = tstate->cframe->current_frame = new_frame;
             ERROR_IF(_Py_EnterRecursivePy(tstate), exit_unwind);
             stack_pointer = _PyFrame_GetStackPointer(frame);
             ip_offset = (_Py_CODEUNIT *)_PyFrame_GetCode(frame)->co_code_adaptive;
@@ -3135,7 +3131,7 @@ dummy_func(
             /* Link frames */
             init_frame->previous = shim;
             shim->previous = frame;
-            frame = cframe.current_frame = init_frame;
+            frame = tstate->current_frame = init_frame;
             CALL_STAT_INC(inlined_py_calls);
             /* Account for pushing the extra frame.
              * We don't check recursion depth here,
@@ -3598,7 +3594,7 @@ dummy_func(
             assert(frame != &entry_frame);
             _PyInterpreterFrame *prev = frame->previous;
             _PyThreadState_PopFrame(tstate, frame);
-            frame = cframe.current_frame = prev;
+            frame = tstate->current_frame = prev;
             _PyFrame_StackPush(frame, (PyObject *)gen);
             goto resume_frame;
         }

Python/ceval.c

@@ -656,17 +656,10 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
     int lltrace = 0;
 #endif
 
-    _PyCFrame cframe;
     _PyInterpreterFrame  entry_frame;
     PyObject *kwnames = NULL; // Borrowed reference. Reset by CALL instructions.
 
-    /* WARNING: Because the _PyCFrame lives on the C stack,
-     * but can be accessed from a heap allocated object (tstate)
-     * strict stack discipline must be maintained.
-     */
-    _PyCFrame *prev_cframe = tstate->cframe;
-    cframe.previous = prev_cframe;
-    tstate->cframe = &cframe;
+
 
 #ifdef Py_DEBUG
     /* Set these to invalid but identifiable values for debugging. */
@@ -682,9 +675,9 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
     entry_frame.owner = FRAME_OWNED_BY_CSTACK;
     entry_frame.return_offset = 0;
     /* Push frame */
-    entry_frame.previous = prev_cframe->current_frame;
+    entry_frame.previous = tstate->current_frame;
     frame->previous = &entry_frame;
-    cframe.current_frame = frame;
+    tstate->current_frame = frame;
 
     tstate->c_recursion_remaining -= (PY_EVAL_C_STACK_UNITS - 1);
     if (_Py_EnterRecursiveCallTstate(tstate, "")) {
@@ -924,13 +917,12 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
     assert(frame != &entry_frame);
     // GH-99729: We need to unlink the frame *before* clearing it:
     _PyInterpreterFrame *dying = frame;
-    frame = cframe.current_frame = dying->previous;
+    frame = tstate->current_frame = dying->previous;
     _PyEvalFrameClearAndPop(tstate, dying);
     frame->return_offset = 0;
     if (frame == &entry_frame) {
-        /* Restore previous cframe and exit */
-        tstate->cframe = cframe.previous;
-        assert(tstate->cframe->current_frame == frame->previous);
+        /* Restore previous frame and exit */
+        tstate->current_frame = frame->previous;
         tstate->c_recursion_remaining += PY_EVAL_C_STACK_UNITS;
         return NULL;
     }
@@ -2297,7 +2289,7 @@ int
 PyEval_MergeCompilerFlags(PyCompilerFlags *cf)
 {
     PyThreadState *tstate = _PyThreadState_GET();
-    _PyInterpreterFrame *current_frame = tstate->cframe->current_frame;
+    _PyInterpreterFrame *current_frame = tstate->current_frame;
     int result = cf->cf_flags != 0;
 
     if (current_frame != NULL) {