Python/ceval.c (part 46)

Source:

cpython 3.14 @ ab2d84fe1023/Python/ceval.c ↗

This annotation covers tuple subscript specialization and stack manipulation opcodes. See python_ceval45_detail for list/dict subscript specializations.

Map

Lines	Symbol	Role
1-80	BINARY_SUBSCR_TUPLE_INT	Specialized tuple index with int key
81-160	STORE_SUBSCR_DICT	Specialized dict item assignment
161-240	COPY	Duplicate a stack slot
241-320	SWAP	Exchange two stack slots
321-500	PUSH_EXC_INFO / POP_EXCEPT	Exception state on the stack

Reading

BINARY_SUBSCR_TUPLE_INT

// CPython: Python/ceval.c:2780 BINARY_SUBSCR_TUPLE_INT
inst(BINARY_SUBSCR_TUPLE_INT, (unused/1, tuple, sub -- res)) {
    DEOPT_IF(!PyTuple_CheckExact(tuple));
    DEOPT_IF(!PyLong_CheckExact(sub));
    Py_ssize_t index = PyLong_AsSSizeT(sub);
    DEOPT_IF(index < 0 || index >= PyTuple_GET_SIZE(tuple));
    res = Py_NewRef(PyTuple_GET_ITEM(tuple, index));
    DECREF_INPUTS();
    DISPATCH();
}

Specialization guard: tuple type exact, int type exact, non-negative index in range. Falls back to BINARY_SUBSCR on any mismatch. Hot path avoids the full sq_item slot dispatch.

STORE_SUBSCR_DICT

// CPython: Python/ceval.c:2860 STORE_SUBSCR_DICT
inst(STORE_SUBSCR_DICT, (unused/1, dict, sub, value --)) {
    DEOPT_IF(!PyDict_CheckExact(dict));
    int err = PyDict_SetItem(dict, sub, value);
    DECREF_INPUTS();
    ERROR_IF(err != 0, error);
    DISPATCH();
}

d[key] = val when d is a plain dict. Skips the mp_ass_subscript slot overhead. Uses PyDict_SetItem which handles hash computation and collision resolution.

COPY

// CPython: Python/ceval.c:3020 COPY
inst(COPY, (bottom, unused[oparg-1] -- bottom, unused[oparg-1], top)) {
    assert(oparg > 0);
    top = Py_NewRef(bottom);
    DISPATCH();
}

COPY i pushes a reference to the ith item from the top. COPY 1 duplicates the top of stack. Used in assignments like x = y = expr and augmented assignments where the target must be preserved.

SWAP

// CPython: Python/ceval.c:3040 SWAP
inst(SWAP, (bottom, unused[oparg-2], top --
            top, unused[oparg-2], bottom)) {
    assert(oparg >= 2);
    /* Exchange TOS with the item oparg positions down */
    PyObject *temp = bottom;
    bottom = top;
    top = temp;
    DISPATCH();
}

SWAP 2 exchanges TOS and TOS1. Used extensively by the compiler for multi-target assignments and exception cleanup without introducing temporary names.

PUSH_EXC_INFO

// CPython: Python/ceval.c:3100 PUSH_EXC_INFO
inst(PUSH_EXC_INFO, (new_exc -- prev_exc, new_exc)) {
    _PyErr_StackItem *exc_info = tstate->exc_info;
    if (exc_info->previous_item == NULL) {
        prev_exc = Py_NewRef(Py_None);
    } else {
        prev_exc = Py_NewRef(exc_info->exc_value);
    }
    exc_info->exc_value = Py_NewRef(new_exc);
    DISPATCH();
}

PUSH_EXC_INFO is emitted at the start of every except block. It saves the current active exception and installs the new one. POP_EXCEPT restores the saved exception when the except block exits.

gopy notes

BINARY_SUBSCR_TUPLE_INT is in vm/eval_simple.go as a specialization guard. STORE_SUBSCR_DICT calls objects.DictSetItem. COPY and SWAP manipulate vm.stack directly by index. PUSH_EXC_INFO / POP_EXCEPT manage vm.excStack in vm/eval_unwind.go.