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bpo-44878: Remove loop from interpreter. All dispatching is done by gotos. #27727

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Aug 12, 2021
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bpo-44878: Remove loop from interpreter. All dispatching is done by gotos. #27727

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5e5ab9e
Remove loop from interpreter. All dispatching is done by gotos.
markshannon Aug 12, 2021
e7d16af
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markshannon Aug 11, 2021
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2021-08-11-14-12-41.bpo-44878.pAbBfc.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Remove the loop from the bytecode interpreter. All instructions end with a
DISPATCH macro, so the loop is now redundant.
31 changes: 17 additions & 14 deletions Python/ceval.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1280,7 +1280,7 @@ eval_frame_handle_pending(PyThreadState *tstate)

#define CHECK_EVAL_BREAKER() \
if (_Py_atomic_load_relaxed(eval_breaker)) { \
continue; \
goto check_eval_breaker; \
}


Expand Down Expand Up @@ -1584,7 +1584,8 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, InterpreterFrame *frame, int thr
assert(!_PyErr_Occurred(tstate));
#endif

for (;;) {
check_eval_breaker:
{
assert(STACK_LEVEL() >= 0); /* else underflow */
assert(STACK_LEVEL() <= co->co_stacksize); /* else overflow */
assert(!_PyErr_Occurred(tstate));
Expand Down Expand Up @@ -4292,6 +4293,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, InterpreterFrame *frame, int thr
CHECK_EVAL_BREAKER();
DISPATCH();
}

TARGET(CALL_METHOD_KW): {
/* Designed to work in tandem with LOAD_METHOD. Same as CALL_METHOD
but pops TOS to get a tuple of keyword names. */
Expand All @@ -4315,6 +4317,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, InterpreterFrame *frame, int thr
CHECK_EVAL_BREAKER();
DISPATCH();
}

TARGET(CALL_FUNCTION): {
PREDICTED(CALL_FUNCTION);
PyObject **sp, *res;
Expand Down Expand Up @@ -4621,7 +4624,17 @@ MISS_WITH_OPARG_COUNTER(BINARY_SUBSCR)
int level, handler, lasti;
if (get_exception_handler(co, offset, &level, &handler, &lasti) == 0) {
// No handlers, so exit.
break;
assert(retval == NULL);
assert(_PyErr_Occurred(tstate));

/* Pop remaining stack entries. */
while (!EMPTY()) {
PyObject *o = POP();
Py_XDECREF(o);
}
frame->stackdepth = 0;
frame->f_state = FRAME_RAISED;
goto exiting;
}

assert(STACK_LEVEL() >= level);
Expand Down Expand Up @@ -4661,18 +4674,8 @@ MISS_WITH_OPARG_COUNTER(BINARY_SUBSCR)
NEXTOPARG();
PRE_DISPATCH_GOTO();
DISPATCH_GOTO();
} /* main loop */

assert(retval == NULL);
assert(_PyErr_Occurred(tstate));

/* Pop remaining stack entries. */
while (!EMPTY()) {
PyObject *o = POP();
Py_XDECREF(o);
}
frame->stackdepth = 0;
frame->f_state = FRAME_RAISED;

exiting:
if (cframe.use_tracing) {
if (tstate->c_tracefunc) {
Expand Down