Move _EXIT_TRACE logic to a separate label

Using `GOTO_TIER_ONE()` macro. This should make things simpler
for Justin.

Python/bytecodes.c

@@ -4024,10 +4024,7 @@ dummy_func(
 
         op(_EXIT_TRACE, (--)) {
             TIER_TWO_ONLY
-            _PyFrame_SetStackPointer(frame, stack_pointer);
-            Py_DECREF(current_executor);
-            OPT_HIST(trace_uop_execution_counter, trace_run_length_hist);
-            goto enter_tier_one;
+            GOTO_TIER_ONE();
         }
 
         op(_INSERT, (unused[oparg], top -- top, unused[oparg])) {

Python/ceval.c

@@ -1027,13 +1027,15 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
         }
     }
 
+// Jump here from ERROR_IF(..., unbound_local_error)
 unbound_local_error_tier_two:
     _PyEval_FormatExcCheckArg(tstate, PyExc_UnboundLocalError,
         UNBOUNDLOCAL_ERROR_MSG,
         PyTuple_GetItem(_PyFrame_GetCode(frame)->co_localsplusnames, oparg)
     );
     goto error_tier_two;
 
+// JUMP to any of these from ERROR_IF(..., error)
 pop_4_error_tier_two:
     STACK_SHRINK(1);
 pop_3_error_tier_two:
@@ -1050,6 +1052,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
     Py_DECREF(current_executor);
     goto resume_with_error;
 
+// Jump here from DEOPT_IF()
 deoptimize:
     // On DEOPT_IF we just repeat the last instruction.
     // This presumes nothing was popped from the stack (nor pushed).
@@ -1058,10 +1061,18 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
     frame->return_offset = 0;  // Dispatch to frame->instr_ptr
     _PyFrame_SetStackPointer(frame, stack_pointer);
     Py_DECREF(current_executor);
+    // Fall through
+// Jump here from ENTER_EXECUTOR
 enter_tier_one:
     next_instr = frame->instr_ptr;
     goto resume_frame;
 
+// Jump here from _EXIT_TRACE
+exit_trace:
+    _PyFrame_SetStackPointer(frame, stack_pointer);
+    Py_DECREF(current_executor);
+    OPT_HIST(trace_uop_execution_counter, trace_run_length_hist);
+    goto enter_tier_one;
 }
 #if defined(__GNUC__)
 #  pragma GCC diagnostic pop

Python/ceval_macros.h

@@ -395,3 +395,5 @@ stack_pointer = _PyFrame_GetStackPointer(frame);
 /* Tier-switching macros. */
 
 #define GOTO_TIER_TWO() goto enter_tier_two;
+
+#define GOTO_TIER_ONE() goto exit_trace;