bpo-43760: Speed up check for tracing in interpreter dispatch (#25276)
* Remove redundant tracing_possible field from interpreter state.
* Move 'use_tracing' from tstate onto C stack, for fastest possible checking in dispatch logic.
* Add comments stressing the importance stack discipline when dealing with CFrames.
* Add NEWS
diff --git a/Python/pystate.c b/Python/pystate.c
index c8b2530..436f874 100644
--- a/Python/pystate.c
+++ b/Python/pystate.c
@@ -624,7 +624,8 @@ new_threadstate(PyInterpreterState *interp, int init)
tstate->recursion_headroom = 0;
tstate->stackcheck_counter = 0;
tstate->tracing = 0;
- tstate->use_tracing = 0;
+ tstate->root_cframe.use_tracing = 0;
+ tstate->cframe = &tstate->root_cframe;
tstate->gilstate_counter = 0;
tstate->async_exc = NULL;
tstate->thread_id = PyThread_get_thread_ident();