Error handling of `RERAISE` is strange

[sobolevn]

Bug report

There's a strange pattern used in RERAISE opcode:

cpython/Python/bytecodes.c

Lines 1174 to 1189 in 4767a6e

	tier1 inst(RERAISE, (values[oparg], exc_st -- values[oparg])) {
	PyObject *exc = PyStackRef_AsPyObjectBorrow(exc_st);
	assert(oparg >= 0 && oparg <= 2);
	if (oparg) {
	PyObject *lasti = PyStackRef_AsPyObjectBorrow(values[0]);
	if (PyLong_Check(lasti)) {
	frame->instr_ptr = _PyCode_CODE(_PyFrame_GetCode(frame)) + PyLong_AsLong(lasti);
	assert(!_PyErr_Occurred(tstate));
	}
	else {
	assert(PyLong_Check(lasti));
	_PyErr_SetString(tstate, PyExc_SystemError, "lasti is not an int");
	ERROR_NO_POP();
	}
	}

Especially these lines:

cpython/Python/bytecodes.c

Lines 1180 to 1187 in 4767a6e

	if (PyLong_Check(lasti)) {
	frame->instr_ptr = _PyCode_CODE(_PyFrame_GetCode(frame)) + PyLong_AsLong(lasti);
	assert(!_PyErr_Occurred(tstate));
	}
	else {
	assert(PyLong_Check(lasti));
	_PyErr_SetString(tstate, PyExc_SystemError, "lasti is not an int");
	ERROR_NO_POP();

It looks like the assert call is not needed here:

• In debug builds it will always crash, since PyLong_Check(lasti) will always be false
• In non-debug builds it will set SystemError as it should be (at least, I think so). That's the only line that matches r'assert\(.*\);\n\s+_PyErr'

I have a PR ready.

Linked PRs

• gh-122759: Remove assert from RERAISE error handling #122760

[hugovk]

Triage: closing because the linked PR is merged, please re-open if still needed.