#include <stdbool.h>

#include "Python.h"
#include "opcode.h"

#include "pycore_code.h"          // _PyCodeConstructor
#include "pycore_frame.h"         // FRAME_SPECIALS_SIZE
#include "pycore_hashtable.h"     // _Py_hashtable_t
#include "pycore_index_pool.h"     // _PyIndexPool
#include "pycore_initconfig.h"    // _PyStatus_OK()
#include "pycore_interp.h"        // PyInterpreterState.co_extra_freefuncs
#include "pycore_object.h"        // _PyObject_SetDeferredRefcount
#include "pycore_object_stack.h"
#include "pycore_opcode_metadata.h" // _PyOpcode_Deopt, _PyOpcode_Caches
#include "pycore_opcode_utils.h"  // RESUME_AT_FUNC_START
#include "pycore_pymem.h"         // _PyMem_FreeDelayed
#include "pycore_pystate.h"       // _PyInterpreterState_GET()
#include "pycore_setobject.h"     // _PySet_NextEntry()
#include "pycore_tuple.h"         // _PyTuple_ITEMS()
#include "pycore_uniqueid.h"      // _PyObject_AssignUniqueId()
#include "clinic/codeobject.c.h"

#define INITIAL_SPECIALIZED_CODE_SIZE 16

static const char *
code_event_name(PyCodeEvent event) {
    switch (event) {
        #define CASE(op)                \
        case PY_CODE_EVENT_##op:         \
            return "PY_CODE_EVENT_" #op;
        PY_FOREACH_CODE_EVENT(CASE)
        #undef CASE
    }
    Py_UNREACHABLE();
}

static void
notify_code_watchers(PyCodeEvent event, PyCodeObject *co)
{
    assert(Py_REFCNT(co) > 0);
    PyInterpreterState *interp = _PyInterpreterState_GET();
    assert(interp->_initialized);
    uint8_t bits = interp->active_code_watchers;
    int i = 0;
    while (bits) {
        assert(i < CODE_MAX_WATCHERS);
        if (bits & 1) {
            PyCode_WatchCallback cb = interp->code_watchers[i];
            // callback must be non-null if the watcher bit is set
            assert(cb != NULL);
            if (cb(event, co) < 0) {
                PyErr_FormatUnraisable(
                    "Exception ignored in %s watcher callback for %R",
                    code_event_name(event), co);
            }
        }
        i++;
        bits >>= 1;
    }
}

int
PyCode_AddWatcher(PyCode_WatchCallback callback)
{
    PyInterpreterState *interp = _PyInterpreterState_GET();
    assert(interp->_initialized);

    for (int i = 0; i < CODE_MAX_WATCHERS; i++) {
        if (!interp->code_watchers[i]) {
            interp->code_watchers[i] = callback;
            interp->active_code_watchers |= (1 << i);
            return i;
        }
    }

    PyErr_SetString(PyExc_RuntimeError, "no more code watcher IDs available");
    return -1;
}

static inline int
validate_watcher_id(PyInterpreterState *interp, int watcher_id)
{
    if (watcher_id < 0 || watcher_id >= CODE_MAX_WATCHERS) {
        PyErr_Format(PyExc_ValueError, "Invalid code watcher ID %d", watcher_id);
        return -1;
    }
    if (!interp->code_watchers[watcher_id]) {
        PyErr_Format(PyExc_ValueError, "No code watcher set for ID %d", watcher_id);
        return -1;
    }
    return 0;
}

int
PyCode_ClearWatcher(int watcher_id)
{
    PyInterpreterState *interp = _PyInterpreterState_GET();
    assert(interp->_initialized);
    if (validate_watcher_id(interp, watcher_id) < 0) {
        return -1;
    }
    interp->code_watchers[watcher_id] = NULL;
    interp->active_code_watchers &= ~(1 << watcher_id);
    return 0;
}

/******************
 * generic helpers
 ******************/

#define _PyCodeObject_CAST(op)  (assert(PyCode_Check(op)), (PyCodeObject *)(op))

static int
should_intern_string(PyObject *o)
{
#ifdef Py_GIL_DISABLED
    // The free-threaded build interns (and immortalizes) all string constants
    return 1;
#else
    // compute if s matches [a-zA-Z0-9_]
    const unsigned char *s, *e;

    if (!PyUnicode_IS_ASCII(o))
        return 0;

    s = PyUnicode_1BYTE_DATA(o);
    e = s + PyUnicode_GET_LENGTH(o);
    for (; s != e; s++) {
        if (!Py_ISALNUM(*s) && *s != '_')
            return 0;
    }
    return 1;
#endif
}

#ifdef Py_GIL_DISABLED
static PyObject *intern_one_constant(PyObject *op);
#endif

static int
intern_strings(PyObject *tuple)
{
    PyInterpreterState *interp = _PyInterpreterState_GET();
    Py_ssize_t i;

    for (i = PyTuple_GET_SIZE(tuple); --i >= 0; ) {
        PyObject *v = PyTuple_GET_ITEM(tuple, i);
        if (v == NULL || !PyUnicode_CheckExact(v)) {
            PyErr_SetString(PyExc_SystemError,
                            "non-string found in code slot");
            return -1;
        }
        _PyUnicode_InternImmortal(interp, &_PyTuple_ITEMS(tuple)[i]);
    }
    return 0;
}

/* Intern constants. In the default build, this interns selected string
   constants. In the free-threaded build, this also interns non-string
   constants. */
static int
intern_constants(PyObject *tuple, int *modified)
{
    PyInterpreterState *interp = _PyInterpreterState_GET();
    for (Py_ssize_t i = PyTuple_GET_SIZE(tuple); --i >= 0; ) {
        PyObject *v = PyTuple_GET_ITEM(tuple, i);
        if (PyUnicode_CheckExact(v)) {
            if (should_intern_string(v)) {
                PyObject *w = v;
                _PyUnicode_InternMortal(interp, &v);
                if (w != v) {
                    PyTuple_SET_ITEM(tuple, i, v);
                    if (modified) {
                        *modified = 1;
                    }
                }
            }
        }
        else if (PyTuple_CheckExact(v)) {
            if (intern_constants(v, NULL) < 0) {
                return -1;
            }
        }
        else if (PyFrozenSet_CheckExact(v)) {
            PyObject *w = v;
            PyObject *tmp = PySequence_Tuple(v);
            if (tmp == NULL) {
                return -1;
            }
            int tmp_modified = 0;
            if (intern_constants(tmp, &tmp_modified) < 0) {
                Py_DECREF(tmp);
                return -1;
            }
            if (tmp_modified) {
                v = PyFrozenSet_New(tmp);
                if (v == NULL) {
                    Py_DECREF(tmp);
                    return -1;
                }

                PyTuple_SET_ITEM(tuple, i, v);
                Py_DECREF(w);
                if (modified) {
                    *modified = 1;
                }
            }
            Py_DECREF(tmp);
        }
#ifdef Py_GIL_DISABLED
        else if (PySlice_Check(v)) {
            PySliceObject *slice = (PySliceObject *)v;
            PyObject *tmp = PyTuple_New(3);
            if (tmp == NULL) {
                return -1;
            }
            PyTuple_SET_ITEM(tmp, 0, Py_NewRef(slice->start));
            PyTuple_SET_ITEM(tmp, 1, Py_NewRef(slice->stop));
            PyTuple_SET_ITEM(tmp, 2, Py_NewRef(slice->step));
            int tmp_modified = 0;
            if (intern_constants(tmp, &tmp_modified) < 0) {
                Py_DECREF(tmp);
                return -1;
            }
            if (tmp_modified) {
                v = PySlice_New(PyTuple_GET_ITEM(tmp, 0),
                                PyTuple_GET_ITEM(tmp, 1),
                                PyTuple_GET_ITEM(tmp, 2));
                if (v == NULL) {
                    Py_DECREF(tmp);
                    return -1;
                }
                PyTuple_SET_ITEM(tuple, i, v);
                Py_DECREF(slice);
                if (modified) {
                    *modified = 1;
                }
            }
            Py_DECREF(tmp);
        }

        // Intern non-string constants in the free-threaded build
        _PyThreadStateImpl *tstate = (_PyThreadStateImpl *)_PyThreadState_GET();
        if (!_Py_IsImmortal(v) && !PyCode_Check(v) &&
            !PyUnicode_CheckExact(v) && !tstate->suppress_co_const_immortalization)
        {
            PyObject *interned = intern_one_constant(v);
            if (interned == NULL) {
                return -1;
            }
            else if (interned != v) {
                PyTuple_SET_ITEM(tuple, i, interned);
                Py_SETREF(v, interned);
                if (modified) {
                    *modified = 1;
                }
            }
        }
#endif
    }
    return 0;
}

/* Return a shallow copy of a tuple that is
   guaranteed to contain exact strings, by converting string subclasses
   to exact strings and complaining if a non-string is found. */
static PyObject*
validate_and_copy_tuple(PyObject *tup)
{
    PyObject *newtuple;
    PyObject *item;
    Py_ssize_t i, len;

    len = PyTuple_GET_SIZE(tup);
    newtuple = PyTuple_New(len);
    if (newtuple == NULL)
        return NULL;

    for (i = 0; i < len; i++) {
        item = PyTuple_GET_ITEM(tup, i);
        if (PyUnicode_CheckExact(item)) {
            Py_INCREF(item);
        }
        else if (!PyUnicode_Check(item)) {
            PyErr_Format(
                PyExc_TypeError,
                "name tuples must contain only "
                "strings, not '%.500s'",
                Py_TYPE(item)->tp_name);
            Py_DECREF(newtuple);
            return NULL;
        }
        else {
            item = _PyUnicode_Copy(item);
            if (item == NULL) {
                Py_DECREF(newtuple);
                return NULL;
            }
        }
        PyTuple_SET_ITEM(newtuple, i, item);
    }

    return newtuple;
}

static int
init_co_cached(PyCodeObject *self)
{
    _PyCoCached *cached = FT_ATOMIC_LOAD_PTR(self->_co_cached);
    if (cached != NULL) {
        return 0;
    }

    Py_BEGIN_CRITICAL_SECTION(self);
    cached = self->_co_cached;
    if (cached == NULL) {
        cached = PyMem_New(_PyCoCached, 1);
        if (cached == NULL) {
            PyErr_NoMemory();
        }
        else {
            cached->_co_code = NULL;
            cached->_co_cellvars = NULL;
            cached->_co_freevars = NULL;
            cached->_co_varnames = NULL;
            FT_ATOMIC_STORE_PTR(self->_co_cached, cached);
        }
    }
    Py_END_CRITICAL_SECTION();
    return cached != NULL ? 0 : -1;
}

/******************
 * _PyCode_New()
 ******************/

// This is also used in compile.c.
void
_Py_set_localsplus_info(int offset, PyObject *name, _PyLocals_Kind kind,
                        PyObject *names, PyObject *kinds)
{
    PyTuple_SET_ITEM(names, offset, Py_NewRef(name));
    _PyLocals_SetKind(kinds, offset, kind);
}

static void
get_localsplus_counts(PyObject *names, PyObject *kinds,
                      int *pnlocals, int *pncellvars,
                      int *pnfreevars)
{
    int nlocals = 0;
    int ncellvars = 0;
    int nfreevars = 0;
    Py_ssize_t nlocalsplus = PyTuple_GET_SIZE(names);
    for (int i = 0; i < nlocalsplus; i++) {
        _PyLocals_Kind kind = _PyLocals_GetKind(kinds, i);
        if (kind & CO_FAST_LOCAL) {
            nlocals += 1;
            if (kind & CO_FAST_CELL) {
                ncellvars += 1;
            }
        }
        else if (kind & CO_FAST_CELL) {
            ncellvars += 1;
        }
        else if (kind & CO_FAST_FREE) {
            nfreevars += 1;
        }
    }
    if (pnlocals != NULL) {
        *pnlocals = nlocals;
    }
    if (pncellvars != NULL) {
        *pncellvars = ncellvars;
    }
    if (pnfreevars != NULL) {
        *pnfreevars = nfreevars;
    }
}

static PyObject *
get_localsplus_names(PyCodeObject *co, _PyLocals_Kind kind, int num)
{
    PyObject *names = PyTuple_New(num);
    if (names == NULL) {
        return NULL;
    }
    int index = 0;
    for (int offset = 0; offset < co->co_nlocalsplus; offset++) {
        _PyLocals_Kind k = _PyLocals_GetKind(co->co_localspluskinds, offset);
        if ((k & kind) == 0) {
            continue;
        }
        assert(index < num);
        PyObject *name = PyTuple_GET_ITEM(co->co_localsplusnames, offset);
        PyTuple_SET_ITEM(names, index, Py_NewRef(name));
        index += 1;
    }
    assert(index == num);
    return names;
}

int
_PyCode_Validate(struct _PyCodeConstructor *con)
{
    /* Check argument types */
    if (con->argcount < con->posonlyargcount || con->posonlyargcount < 0 ||
        con->kwonlyargcount < 0 ||
        con->stacksize < 0 || con->flags < 0 ||
        con->code == NULL || !PyBytes_Check(con->code) ||
        con->consts == NULL || !PyTuple_Check(con->consts) ||
        con->names == NULL || !PyTuple_Check(con->names) ||
        con->localsplusnames == NULL || !PyTuple_Check(con->localsplusnames) ||
        con->localspluskinds == NULL || !PyBytes_Check(con->localspluskinds) ||
        PyTuple_GET_SIZE(con->localsplusnames)
            != PyBytes_GET_SIZE(con->localspluskinds) ||
        con->name == NULL || !PyUnicode_Check(con->name) ||
        con->qualname == NULL || !PyUnicode_Check(con->qualname) ||
        con->filename == NULL || !PyUnicode_Check(con->filename) ||
        con->linetable == NULL || !PyBytes_Check(con->linetable) ||
        con->exceptiontable == NULL || !PyBytes_Check(con->exceptiontable)
        ) {
        PyErr_BadInternalCall();
        return -1;
    }

    /* Make sure that code is indexable with an int, this is
       a long running assumption in ceval.c and many parts of
       the interpreter. */
    if (PyBytes_GET_SIZE(con->code) > INT_MAX) {
        PyErr_SetString(PyExc_OverflowError,
                        "code: co_code larger than INT_MAX");
        return -1;
    }
    if (PyBytes_GET_SIZE(con->code) % sizeof(_Py_CODEUNIT) != 0 ||
        !_Py_IS_ALIGNED(PyBytes_AS_STRING(con->code), sizeof(_Py_CODEUNIT))
        ) {
        PyErr_SetString(PyExc_ValueError, "code: co_code is malformed");
        return -1;
    }

    /* Ensure that the co_varnames has enough names to cover the arg counts.
     * Note that totalargs = nlocals - nplainlocals.  We check nplainlocals
     * here to avoid the possibility of overflow (however remote). */
    int nlocals;
    get_localsplus_counts(con->localsplusnames, con->localspluskinds,
                          &nlocals, NULL, NULL);
    int nplainlocals = nlocals -
                       con->argcount -
                       con->kwonlyargcount -
                       ((con->flags & CO_VARARGS) != 0) -
                       ((con->flags & CO_VARKEYWORDS) != 0);
    if (nplainlocals < 0) {
        PyErr_SetString(PyExc_ValueError, "code: co_varnames is too small");
        return -1;
    }

    return 0;
}

extern void
_PyCode_Quicken(_Py_CODEUNIT *instructions, Py_ssize_t size, PyObject *consts,
                int enable_counters);

#ifdef Py_GIL_DISABLED
static _PyCodeArray * _PyCodeArray_New(Py_ssize_t size);
#endif

static int
init_code(PyCodeObject *co, struct _PyCodeConstructor *con)
{
    int nlocalsplus = (int)PyTuple_GET_SIZE(con->localsplusnames);
    int nlocals, ncellvars, nfreevars;
    get_localsplus_counts(con->localsplusnames, con->localspluskinds,
                          &nlocals, &ncellvars, &nfreevars);
    if (con->stacksize == 0) {
        con->stacksize = 1;
    }

    PyInterpreterState *interp = _PyInterpreterState_GET();
    co->co_filename = Py_NewRef(con->filename);
    co->co_name = Py_NewRef(con->name);
    co->co_qualname = Py_NewRef(con->qualname);
    _PyUnicode_InternMortal(interp, &co->co_filename);
    _PyUnicode_InternMortal(interp, &co->co_name);
    _PyUnicode_InternMortal(interp, &co->co_qualname);
    co->co_flags = con->flags;

    co->co_firstlineno = con->firstlineno;
    co->co_linetable = Py_NewRef(con->linetable);

    co->co_consts = Py_NewRef(con->consts);
    co->co_names = Py_NewRef(con->names);

    co->co_localsplusnames = Py_NewRef(con->localsplusnames);
    co->co_localspluskinds = Py_NewRef(con->localspluskinds);

    co->co_argcount = con->argcount;
    co->co_posonlyargcount = con->posonlyargcount;
    co->co_kwonlyargcount = con->kwonlyargcount;

    co->co_stacksize = con->stacksize;

    co->co_exceptiontable = Py_NewRef(con->exceptiontable);

    /* derived values */
    co->co_nlocalsplus = nlocalsplus;
    co->co_nlocals = nlocals;
    co->co_framesize = nlocalsplus + con->stacksize + FRAME_SPECIALS_SIZE;
    co->co_ncellvars = ncellvars;
    co->co_nfreevars = nfreevars;
#ifdef Py_GIL_DISABLED
    PyMutex_Lock(&interp->func_state.mutex);
#endif
    co->co_version = interp->func_state.next_version;
    if (interp->func_state.next_version != 0) {
        interp->func_state.next_version++;
    }
#ifdef Py_GIL_DISABLED
    PyMutex_Unlock(&interp->func_state.mutex);
#endif
    co->_co_monitoring = NULL;
    co->_co_instrumentation_version = 0;
    /* not set */
    co->co_weakreflist = NULL;
    co->co_extra = NULL;
    co->_co_cached = NULL;
    co->co_executors = NULL;

    memcpy(_PyCode_CODE(co), PyBytes_AS_STRING(con->code),
           PyBytes_GET_SIZE(con->code));
#ifdef Py_GIL_DISABLED
    co->co_tlbc = _PyCodeArray_New(INITIAL_SPECIALIZED_CODE_SIZE);
    if (co->co_tlbc == NULL) {
        return -1;
    }
    co->co_tlbc->entries[0] = co->co_code_adaptive;
#endif
    int entry_point = 0;
    while (entry_point < Py_SIZE(co) &&
        _PyCode_CODE(co)[entry_point].op.code != RESUME) {
        entry_point++;
    }
    co->_co_firsttraceable = entry_point;
#ifdef Py_GIL_DISABLED
    _PyCode_Quicken(_PyCode_CODE(co), Py_SIZE(co), co->co_consts,
                    interp->config.tlbc_enabled);
#else
    _PyCode_Quicken(_PyCode_CODE(co), Py_SIZE(co), co->co_consts, 1);
#endif
    notify_code_watchers(PY_CODE_EVENT_CREATE, co);
    return 0;
}

static int
scan_varint(const uint8_t *ptr)
{
    unsigned int read = *ptr++;
    unsigned int val = read & 63;
    unsigned int shift = 0;
    while (read & 64) {
        read = *ptr++;
        shift += 6;
        val |= (read & 63) << shift;
    }
    return val;
}

static int
scan_signed_varint(const uint8_t *ptr)
{
    unsigned int uval = scan_varint(ptr);
    if (uval & 1) {
        return -(int)(uval >> 1);
    }
    else {
        return uval >> 1;
    }
}

static int
get_line_delta(const uint8_t *ptr)
{
    int code = ((*ptr) >> 3) & 15;
    switch (code) {
        case PY_CODE_LOCATION_INFO_NONE:
            return 0;
        case PY_CODE_LOCATION_INFO_NO_COLUMNS:
        case PY_CODE_LOCATION_INFO_LONG:
            return scan_signed_varint(ptr+1);
        case PY_CODE_LOCATION_INFO_ONE_LINE0:
            return 0;
        case PY_CODE_LOCATION_INFO_ONE_LINE1:
            return 1;
        case PY_CODE_LOCATION_INFO_ONE_LINE2:
            return 2;
        default:
            /* Same line */
            return 0;
    }
}

static PyObject *
remove_column_info(PyObject *locations)
{
    Py_ssize_t offset = 0;
    const uint8_t *data = (const uint8_t *)PyBytes_AS_STRING(locations);
    PyObject *res = PyBytes_FromStringAndSize(NULL, 32);
    if (res == NULL) {
        PyErr_NoMemory();
        return NULL;
    }
    uint8_t *output = (uint8_t *)PyBytes_AS_STRING(res);
    while (offset < PyBytes_GET_SIZE(locations)) {
        Py_ssize_t write_offset = output - (uint8_t *)PyBytes_AS_STRING(res);
        if (write_offset + 16 >= PyBytes_GET_SIZE(res)) {
            if (_PyBytes_Resize(&res, PyBytes_GET_SIZE(res) * 2) < 0) {
                return NULL;
            }
            output = (uint8_t *)PyBytes_AS_STRING(res) + write_offset;
        }
        int code = (data[offset] >> 3) & 15;
        if (code == PY_CODE_LOCATION_INFO_NONE) {
            *output++ = data[offset];
        }
        else {
            int blength = (data[offset] & 7)+1;
            output += write_location_entry_start(
                output, PY_CODE_LOCATION_INFO_NO_COLUMNS, blength);
            int ldelta = get_line_delta(&data[offset]);
            output += write_signed_varint(output, ldelta);
        }
        offset++;
        while (offset < PyBytes_GET_SIZE(locations) &&
            (data[offset] & 128) == 0) {
            offset++;
        }
    }
    Py_ssize_t write_offset = output - (uint8_t *)PyBytes_AS_STRING(res);
    if (_PyBytes_Resize(&res, write_offset)) {
        return NULL;
    }
    return res;
}

static int
intern_code_constants(struct _PyCodeConstructor *con)
{
#ifdef Py_GIL_DISABLED
    PyInterpreterState *interp = _PyInterpreterState_GET();
    struct _py_code_state *state = &interp->code_state;
    PyMutex_Lock(&state->mutex);
#endif
    if (intern_strings(con->names) < 0) {
        goto error;
    }
    if (intern_constants(con->consts, NULL) < 0) {
        goto error;
    }
    if (intern_strings(con->localsplusnames) < 0) {
        goto error;
    }
#ifdef Py_GIL_DISABLED
    PyMutex_Unlock(&state->mutex);
#endif
    return 0;

error:
#ifdef Py_GIL_DISABLED
    PyMutex_Unlock(&state->mutex);
#endif
    return -1;
}

/* The caller is responsible for ensuring that the given data is valid. */

PyCodeObject *
_PyCode_New(struct _PyCodeConstructor *con)
{
    if (intern_code_constants(con) < 0) {
        return NULL;
    }

    PyObject *replacement_locations = NULL;
    // Compact the linetable if we are opted out of debug
    // ranges.
    if (!_Py_GetConfig()->code_debug_ranges) {
        replacement_locations = remove_column_info(con->linetable);
        if (replacement_locations == NULL) {
            return NULL;
        }
        con->linetable = replacement_locations;
    }

    Py_ssize_t size = PyBytes_GET_SIZE(con->code) / sizeof(_Py_CODEUNIT);
    PyCodeObject *co;
#ifdef Py_GIL_DISABLED
    co = PyObject_GC_NewVar(PyCodeObject, &PyCode_Type, size);
#else
    co = PyObject_NewVar(PyCodeObject, &PyCode_Type, size);
#endif
    if (co == NULL) {
        Py_XDECREF(replacement_locations);
        PyErr_NoMemory();
        return NULL;
    }

    if (init_code(co, con) < 0) {
        Py_DECREF(co);
        return NULL;
    }

#ifdef Py_GIL_DISABLED
    co->_co_unique_id = _PyObject_AssignUniqueId((PyObject *)co);
    _PyObject_GC_TRACK(co);
#endif
    Py_XDECREF(replacement_locations);
    return co;
}


/******************
 * the legacy "constructors"
 ******************/

PyCodeObject *
PyUnstable_Code_NewWithPosOnlyArgs(
                          int argcount, int posonlyargcount, int kwonlyargcount,
                          int nlocals, int stacksize, int flags,
                          PyObject *code, PyObject *consts, PyObject *names,
                          PyObject *varnames, PyObject *freevars, PyObject *cellvars,
                          PyObject *filename, PyObject *name,
                          PyObject *qualname, int firstlineno,
                          PyObject *linetable,
                          PyObject *exceptiontable)
{
    PyCodeObject *co = NULL;
    PyObject *localsplusnames = NULL;
    PyObject *localspluskinds = NULL;

    if (varnames == NULL || !PyTuple_Check(varnames) ||
        cellvars == NULL || !PyTuple_Check(cellvars) ||
        freevars == NULL || !PyTuple_Check(freevars)
        ) {
        PyErr_BadInternalCall();
        return NULL;
    }

    // Set the "fast locals plus" info.
    int nvarnames = (int)PyTuple_GET_SIZE(varnames);
    int ncellvars = (int)PyTuple_GET_SIZE(cellvars);
    int nfreevars = (int)PyTuple_GET_SIZE(freevars);
    int nlocalsplus = nvarnames + ncellvars + nfreevars;
    localsplusnames = PyTuple_New(nlocalsplus);
    if (localsplusnames == NULL) {
        goto error;
    }
    localspluskinds = PyBytes_FromStringAndSize(NULL, nlocalsplus);
    if (localspluskinds == NULL) {
        goto error;
    }
    int  offset = 0;
    for (int i = 0; i < nvarnames; i++, offset++) {
        PyObject *name = PyTuple_GET_ITEM(varnames, i);
        _Py_set_localsplus_info(offset, name, CO_FAST_LOCAL,
                               localsplusnames, localspluskinds);
    }
    for (int i = 0; i < ncellvars; i++, offset++) {
        PyObject *name = PyTuple_GET_ITEM(cellvars, i);
        int argoffset = -1;
        for (int j = 0; j < nvarnames; j++) {
            int cmp = PyUnicode_Compare(PyTuple_GET_ITEM(varnames, j),
                                        name);
            assert(!PyErr_Occurred());
            if (cmp == 0) {
                argoffset = j;
                break;
            }
        }
        if (argoffset >= 0) {
            // Merge the localsplus indices.
            nlocalsplus -= 1;
            offset -= 1;
            _PyLocals_Kind kind = _PyLocals_GetKind(localspluskinds, argoffset);
            _PyLocals_SetKind(localspluskinds, argoffset, kind | CO_FAST_CELL);
            continue;
        }
        _Py_set_localsplus_info(offset, name, CO_FAST_CELL,
                               localsplusnames, localspluskinds);
    }
    for (int i = 0; i < nfreevars; i++, offset++) {
        PyObject *name = PyTuple_GET_ITEM(freevars, i);
        _Py_set_localsplus_info(offset, name, CO_FAST_FREE,
                               localsplusnames, localspluskinds);
    }

    // gh-110543: Make sure the CO_FAST_HIDDEN flag is set correctly.
    if (!(flags & CO_OPTIMIZED)) {
        Py_ssize_t code_len = PyBytes_GET_SIZE(code);
        _Py_CODEUNIT *code_data = (_Py_CODEUNIT *)PyBytes_AS_STRING(code);
        Py_ssize_t num_code_units = code_len / sizeof(_Py_CODEUNIT);
        int extended_arg = 0;
        for (int i = 0; i < num_code_units; i += 1 + _PyOpcode_Caches[code_data[i].op.code]) {
            _Py_CODEUNIT *instr = &code_data[i];
            uint8_t opcode = instr->op.code;
            if (opcode == EXTENDED_ARG) {
                extended_arg = extended_arg << 8 | instr->op.arg;
                continue;
            }
            if (opcode == LOAD_FAST_AND_CLEAR) {
                int oparg = extended_arg << 8 | instr->op.arg;
                if (oparg >= nlocalsplus) {
                    PyErr_Format(PyExc_ValueError,
                                "code: LOAD_FAST_AND_CLEAR oparg %d out of range",
                                oparg);
                    goto error;
                }
                _PyLocals_Kind kind = _PyLocals_GetKind(localspluskinds, oparg);
                _PyLocals_SetKind(localspluskinds, oparg, kind | CO_FAST_HIDDEN);
            }
            extended_arg = 0;
        }
    }

    // If any cells were args then nlocalsplus will have shrunk.
    if (nlocalsplus != PyTuple_GET_SIZE(localsplusnames)) {
        if (_PyTuple_Resize(&localsplusnames, nlocalsplus) < 0
                || _PyBytes_Resize(&localspluskinds, nlocalsplus) < 0) {
            goto error;
        }
    }

    struct _PyCodeConstructor con = {
        .filename = filename,
        .name = name,
        .qualname = qualname,
        .flags = flags,

        .code = code,
        .firstlineno = firstlineno,
        .linetable = linetable,

        .consts = consts,
        .names = names,

        .localsplusnames = localsplusnames,
        .localspluskinds = localspluskinds,

        .argcount = argcount,
        .posonlyargcount = posonlyargcount,
        .kwonlyargcount = kwonlyargcount,

        .stacksize = stacksize,

        .exceptiontable = exceptiontable,
    };

    if (_PyCode_Validate(&con) < 0) {
        goto error;
    }
    assert(PyBytes_GET_SIZE(code) % sizeof(_Py_CODEUNIT) == 0);
    assert(_Py_IS_ALIGNED(PyBytes_AS_STRING(code), sizeof(_Py_CODEUNIT)));
    if (nlocals != PyTuple_GET_SIZE(varnames)) {
        PyErr_SetString(PyExc_ValueError,
                        "code: co_nlocals != len(co_varnames)");
        goto error;
    }

    co = _PyCode_New(&con);
    if (co == NULL) {
        goto error;
    }

error:
    Py_XDECREF(localsplusnames);
    Py_XDECREF(localspluskinds);
    return co;
}

PyCodeObject *
PyUnstable_Code_New(int argcount, int kwonlyargcount,
           int nlocals, int stacksize, int flags,
           PyObject *code, PyObject *consts, PyObject *names,
           PyObject *varnames, PyObject *freevars, PyObject *cellvars,
           PyObject *filename, PyObject *name, PyObject *qualname,
           int firstlineno,
           PyObject *linetable,
           PyObject *exceptiontable)
{
    return PyCode_NewWithPosOnlyArgs(argcount, 0, kwonlyargcount, nlocals,
                                     stacksize, flags, code, consts, names,
                                     varnames, freevars, cellvars, filename,
                                     name, qualname, firstlineno,
                                     linetable,
                                     exceptiontable);
}

// NOTE: When modifying the construction of PyCode_NewEmpty, please also change
// test.test_code.CodeLocationTest.test_code_new_empty to keep it in sync!

static const uint8_t assert0[6] = {
    RESUME, RESUME_AT_FUNC_START,
    LOAD_COMMON_CONSTANT, CONSTANT_ASSERTIONERROR,
    RAISE_VARARGS, 1
};

static const uint8_t linetable[2] = {
    (1 << 7)  // New entry.
    | (PY_CODE_LOCATION_INFO_NO_COLUMNS << 3)
    | (3 - 1),  // Three code units.
    0,  // Offset from co_firstlineno.
};

PyCodeObject *
PyCode_NewEmpty(const char *filename, const char *funcname, int firstlineno)
{
    PyObject *nulltuple = NULL;
    PyObject *filename_ob = NULL;
    PyObject *funcname_ob = NULL;
    PyObject *code_ob = NULL;
    PyObject *linetable_ob = NULL;
    PyCodeObject *result = NULL;

    nulltuple = PyTuple_New(0);
    if (nulltuple == NULL) {
        goto failed;
    }
    funcname_ob = PyUnicode_FromString(funcname);
    if (funcname_ob == NULL) {
        goto failed;
    }
    filename_ob = PyUnicode_DecodeFSDefault(filename);
    if (filename_ob == NULL) {
        goto failed;
    }
    code_ob = PyBytes_FromStringAndSize((const char *)assert0, 6);
    if (code_ob == NULL) {
        goto failed;
    }
    linetable_ob = PyBytes_FromStringAndSize((const char *)linetable, 2);
    if (linetable_ob == NULL) {
        goto failed;
    }

#define emptystring (PyObject *)&_Py_SINGLETON(bytes_empty)
    struct _PyCodeConstructor con = {
        .filename = filename_ob,
        .name = funcname_ob,
        .qualname = funcname_ob,
        .code = code_ob,
        .firstlineno = firstlineno,
        .linetable = linetable_ob,
        .consts = nulltuple,
        .names = nulltuple,
        .localsplusnames = nulltuple,
        .localspluskinds = emptystring,
        .exceptiontable = emptystring,
        .stacksize = 1,
    };
    result = _PyCode_New(&con);

failed:
    Py_XDECREF(nulltuple);
    Py_XDECREF(funcname_ob);
    Py_XDECREF(filename_ob);
    Py_XDECREF(code_ob);
    Py_XDECREF(linetable_ob);
    return result;
}


/******************
 * source location tracking (co_lines/co_positions)
 ******************/

int
PyCode_Addr2Line(PyCodeObject *co, int addrq)
{
    if (addrq < 0) {
        return co->co_firstlineno;
    }
    assert(addrq >= 0 && addrq < _PyCode_NBYTES(co));
    PyCodeAddressRange bounds;
    _PyCode_InitAddressRange(co, &bounds);
    return _PyCode_CheckLineNumber(addrq, &bounds);
}

void
_PyLineTable_InitAddressRange(const char *linetable, Py_ssize_t length, int firstlineno, PyCodeAddressRange *range)
{
    range->opaque.lo_next = (const uint8_t *)linetable;
    range->opaque.limit = range->opaque.lo_next + length;
    range->ar_start = -1;
    range->ar_end = 0;
    range->opaque.computed_line = firstlineno;
    range->ar_line = -1;
}

int
_PyCode_InitAddressRange(PyCodeObject* co, PyCodeAddressRange *bounds)
{
    assert(co->co_linetable != NULL);
    const char *linetable = PyBytes_AS_STRING(co->co_linetable);
    Py_ssize_t length = PyBytes_GET_SIZE(co->co_linetable);
    _PyLineTable_InitAddressRange(linetable, length, co->co_firstlineno, bounds);
    return bounds->ar_line;
}

/* Update *bounds to describe the first and one-past-the-last instructions in
   the same line as lasti.  Return the number of that line, or -1 if lasti is out of bounds. */
int
_PyCode_CheckLineNumber(int lasti, PyCodeAddressRange *bounds)
{
    while (bounds->ar_end <= lasti) {
        if (!_PyLineTable_NextAddressRange(bounds)) {
            return -1;
        }
    }
    while (bounds->ar_start > lasti) {
        if (!_PyLineTable_PreviousAddressRange(bounds)) {
            return -1;
        }
    }
    return bounds->ar_line;
}

static int
is_no_line_marker(uint8_t b)
{
    return (b >> 3) == 0x1f;
}


#define ASSERT_VALID_BOUNDS(bounds) \
    assert(bounds->opaque.lo_next <=  bounds->opaque.limit && \
        (bounds->ar_line == -1 || bounds->ar_line == bounds->opaque.computed_line) && \
        (bounds->opaque.lo_next == bounds->opaque.limit || \
        (*bounds->opaque.lo_next) & 128))

static int
next_code_delta(PyCodeAddressRange *bounds)
{
    assert((*bounds->opaque.lo_next) & 128);
    return (((*bounds->opaque.lo_next) & 7) + 1) * sizeof(_Py_CODEUNIT);
}

static int
previous_code_delta(PyCodeAddressRange *bounds)
{
    if (bounds->ar_start == 0) {
        // If we looking at the first entry, the
        // "previous" entry has an implicit length of 1.
        return 1;
    }
    const uint8_t *ptr = bounds->opaque.lo_next-1;
    while (((*ptr) & 128) == 0) {
        ptr--;
    }
    return (((*ptr) & 7) + 1) * sizeof(_Py_CODEUNIT);
}

static int
read_byte(PyCodeAddressRange *bounds)
{
    return *bounds->opaque.lo_next++;
}

static int
read_varint(PyCodeAddressRange *bounds)
{
    unsigned int read = read_byte(bounds);
    unsigned int val = read & 63;
    unsigned int shift = 0;
    while (read & 64) {
        read = read_byte(bounds);
        shift += 6;
        val |= (read & 63) << shift;
    }
    return val;
}

static int
read_signed_varint(PyCodeAddressRange *bounds)
{
    unsigned int uval = read_varint(bounds);
    if (uval & 1) {
        return -(int)(uval >> 1);
    }
    else {
        return uval >> 1;
    }
}

static void
retreat(PyCodeAddressRange *bounds)
{
    ASSERT_VALID_BOUNDS(bounds);
    assert(bounds->ar_start >= 0);
    do {
        bounds->opaque.lo_next--;
    } while (((*bounds->opaque.lo_next) & 128) == 0);
    bounds->opaque.computed_line -= get_line_delta(bounds->opaque.lo_next);
    bounds->ar_end = bounds->ar_start;
    bounds->ar_start -= previous_code_delta(bounds);
    if (is_no_line_marker(bounds->opaque.lo_next[-1])) {
        bounds->ar_line = -1;
    }
    else {
        bounds->ar_line = bounds->opaque.computed_line;
    }
    ASSERT_VALID_BOUNDS(bounds);
}

static void
advance(PyCodeAddressRange *bounds)
{
    ASSERT_VALID_BOUNDS(bounds);
    bounds->opaque.computed_line += get_line_delta(bounds->opaque.lo_next);
    if (is_no_line_marker(*bounds->opaque.lo_next)) {
        bounds->ar_line = -1;
    }
    else {
        bounds->ar_line = bounds->opaque.computed_line;
    }
    bounds->ar_start = bounds->ar_end;
    bounds->ar_end += next_code_delta(bounds);
    do {
        bounds->opaque.lo_next++;
    } while (bounds->opaque.lo_next < bounds->opaque.limit &&
        ((*bounds->opaque.lo_next) & 128) == 0);
    ASSERT_VALID_BOUNDS(bounds);
}

static void
advance_with_locations(PyCodeAddressRange *bounds, int *endline, int *column, int *endcolumn)
{
    ASSERT_VALID_BOUNDS(bounds);
    int first_byte = read_byte(bounds);
    int code = (first_byte >> 3) & 15;
    bounds->ar_start = bounds->ar_end;
    bounds->ar_end = bounds->ar_start + ((first_byte & 7) + 1) * sizeof(_Py_CODEUNIT);
    switch(code) {
        case PY_CODE_LOCATION_INFO_NONE:
            bounds->ar_line = *endline = -1;
            *column =  *endcolumn = -1;
            break;
        case PY_CODE_LOCATION_INFO_LONG:
        {
            bounds->opaque.computed_line += read_signed_varint(bounds);
            bounds->ar_line = bounds->opaque.computed_line;
            *endline = bounds->ar_line + read_varint(bounds);
            *column = read_varint(bounds)-1;
            *endcolumn = read_varint(bounds)-1;
            break;
        }
        case PY_CODE_LOCATION_INFO_NO_COLUMNS:
        {
            /* No column */
            bounds->opaque.computed_line += read_signed_varint(bounds);
            *endline = bounds->ar_line = bounds->opaque.computed_line;
            *column = *endcolumn = -1;
            break;
        }
        case PY_CODE_LOCATION_INFO_ONE_LINE0:
        case PY_CODE_LOCATION_INFO_ONE_LINE1:
        case PY_CODE_LOCATION_INFO_ONE_LINE2:
        {
            /* one line form */
            int line_delta = code - 10;
            bounds->opaque.computed_line += line_delta;
            *endline = bounds->ar_line = bounds->opaque.computed_line;
            *column = read_byte(bounds);
            *endcolumn = read_byte(bounds);
            break;
        }
        default:
        {
            /* Short forms */
            int second_byte = read_byte(bounds);
            assert((second_byte & 128) == 0);
            *endline = bounds->ar_line = bounds->opaque.computed_line;
            *column = code << 3 | (second_byte >> 4);
            *endcolumn = *column + (second_byte & 15);
        }
    }
    ASSERT_VALID_BOUNDS(bounds);
}
int
PyCode_Addr2Location(PyCodeObject *co, int addrq,
                     int *start_line, int *start_column,
                     int *end_line, int *end_column)
{
    if (addrq < 0) {
        *start_line = *end_line = co->co_firstlineno;
        *start_column = *end_column = 0;
        return 1;
    }
    assert(addrq >= 0 && addrq < _PyCode_NBYTES(co));
    PyCodeAddressRange bounds;
    _PyCode_InitAddressRange(co, &bounds);
    _PyCode_CheckLineNumber(addrq, &bounds);
    retreat(&bounds);
    advance_with_locations(&bounds, end_line, start_column, end_column);
    *start_line = bounds.ar_line;
    return 1;
}


static inline int
at_end(PyCodeAddressRange *bounds) {
    return bounds->opaque.lo_next >= bounds->opaque.limit;
}

int
_PyLineTable_PreviousAddressRange(PyCodeAddressRange *range)
{
    if (range->ar_start <= 0) {
        return 0;
    }
    retreat(range);
    assert(range->ar_end > range->ar_start);
    return 1;
}

int
_PyLineTable_NextAddressRange(PyCodeAddressRange *range)
{
    if (at_end(range)) {
        return 0;
    }
    advance(range);
    assert(range->ar_end > range->ar_start);
    return 1;
}

static int
emit_pair(PyObject **bytes, int *offset, int a, int b)
{
    Py_ssize_t len = PyBytes_GET_SIZE(*bytes);
    if (*offset + 2 >= len) {
        if (_PyBytes_Resize(bytes, len * 2) < 0)
            return 0;
    }
    unsigned char *lnotab = (unsigned char *) PyBytes_AS_STRING(*bytes);
    lnotab += *offset;
    *lnotab++ = a;
    *lnotab++ = b;
    *offset += 2;
    return 1;
}

static int
emit_delta(PyObject **bytes, int bdelta, int ldelta, int *offset)
{
    while (bdelta > 255) {
        if (!emit_pair(bytes, offset, 255, 0)) {
            return 0;
        }
        bdelta -= 255;
    }
    while (ldelta > 127) {
        if (!emit_pair(bytes, offset, bdelta, 127)) {
            return 0;
        }
        bdelta = 0;
        ldelta -= 127;
    }
    while (ldelta < -128) {
        if (!emit_pair(bytes, offset, bdelta, -128)) {
            return 0;
        }
        bdelta = 0;
        ldelta += 128;
    }
    return emit_pair(bytes, offset, bdelta, ldelta);
}

static PyObject *
decode_linetable(PyCodeObject *code)
{
    PyCodeAddressRange bounds;
    PyObject *bytes;
    int table_offset = 0;
    int code_offset = 0;
    int line = code->co_firstlineno;
    bytes = PyBytes_FromStringAndSize(NULL, 64);
    if (bytes == NULL) {
        return NULL;
    }
    _PyCode_InitAddressRange(code, &bounds);
    while (_PyLineTable_NextAddressRange(&bounds)) {
        if (bounds.opaque.computed_line != line) {
            int bdelta = bounds.ar_start - code_offset;
            int ldelta = bounds.opaque.computed_line - line;
            if (!emit_delta(&bytes, bdelta, ldelta, &table_offset)) {
                Py_DECREF(bytes);
                return NULL;
            }
            code_offset = bounds.ar_start;
            line = bounds.opaque.computed_line;
        }
    }
    _PyBytes_Resize(&bytes, table_offset);
    return bytes;
}


typedef struct {
    PyObject_HEAD
    PyCodeObject *li_code;
    PyCodeAddressRange li_line;
} lineiterator;


static void
lineiter_dealloc(PyObject *self)
{
    lineiterator *li = (lineiterator*)self;
    Py_DECREF(li->li_code);
    Py_TYPE(li)->tp_free(li);
}

static PyObject *
_source_offset_converter(int *value) {
    if (*value == -1) {
        Py_RETURN_NONE;
    }
    return PyLong_FromLong(*value);
}

static PyObject *
lineiter_next(PyObject *self)
{
    lineiterator *li = (lineiterator*)self;
    PyCodeAddressRange *bounds = &li->li_line;
    if (!_PyLineTable_NextAddressRange(bounds)) {
        return NULL;
    }
    int start = bounds->ar_start;
    int line = bounds->ar_line;
    // Merge overlapping entries:
    while (_PyLineTable_NextAddressRange(bounds)) {
        if (bounds->ar_line != line) {
            _PyLineTable_PreviousAddressRange(bounds);
            break;
        }
    }
    return Py_BuildValue("iiO&", start, bounds->ar_end,
                         _source_offset_converter, &line);
}

PyTypeObject _PyLineIterator = {
    PyVarObject_HEAD_INIT(&PyType_Type, 0)
    "line_iterator",                    /* tp_name */
    sizeof(lineiterator),               /* tp_basicsize */
    0,                                  /* tp_itemsize */
    /* methods */
    lineiter_dealloc,                   /* tp_dealloc */
    0,                                  /* tp_vectorcall_offset */
    0,                                  /* tp_getattr */
    0,                                  /* tp_setattr */
    0,                                  /* tp_as_async */
    0,                                  /* tp_repr */
    0,                                  /* tp_as_number */
    0,                                  /* tp_as_sequence */
    0,                                  /* tp_as_mapping */
    0,                                  /* tp_hash */
    0,                                  /* tp_call */
    0,                                  /* tp_str */
    0,                                  /* tp_getattro */
    0,                                  /* tp_setattro */
    0,                                  /* tp_as_buffer */
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,       /* tp_flags */
    0,                                  /* tp_doc */
    0,                                  /* tp_traverse */
    0,                                  /* tp_clear */
    0,                                  /* tp_richcompare */
    0,                                  /* tp_weaklistoffset */
    PyObject_SelfIter,                  /* tp_iter */
    lineiter_next,                      /* tp_iternext */
    0,                                  /* tp_methods */
    0,                                  /* tp_members */
    0,                                  /* tp_getset */
    0,                                  /* tp_base */
    0,                                  /* tp_dict */
    0,                                  /* tp_descr_get */
    0,                                  /* tp_descr_set */
    0,                                  /* tp_dictoffset */
    0,                                  /* tp_init */
    0,                                  /* tp_alloc */
    0,                                  /* tp_new */
    PyObject_Free,                      /* tp_free */
};

static lineiterator *
new_linesiterator(PyCodeObject *code)
{
    lineiterator *li = (lineiterator *)PyType_GenericAlloc(&_PyLineIterator, 0);
    if (li == NULL) {
        return NULL;
    }
    li->li_code = (PyCodeObject*)Py_NewRef(code);
    _PyCode_InitAddressRange(code, &li->li_line);
    return li;
}

/* co_positions iterator object. */
typedef struct {
    PyObject_HEAD
    PyCodeObject* pi_code;
    PyCodeAddressRange pi_range;
    int pi_offset;
    int pi_endline;
    int pi_column;
    int pi_endcolumn;
} positionsiterator;

static void
positionsiter_dealloc(PyObject *self)
{
    positionsiterator *pi = (positionsiterator*)self;
    Py_DECREF(pi->pi_code);
    Py_TYPE(pi)->tp_free(pi);
}

static PyObject*
positionsiter_next(PyObject *self)
{
    positionsiterator *pi = (positionsiterator*)self;
    if (pi->pi_offset >= pi->pi_range.ar_end) {
        assert(pi->pi_offset == pi->pi_range.ar_end);
        if (at_end(&pi->pi_range)) {
            return NULL;
        }
        advance_with_locations(&pi->pi_range, &pi->pi_endline, &pi->pi_column, &pi->pi_endcolumn);
    }
    pi->pi_offset += 2;
    return Py_BuildValue("(O&O&O&O&)",
        _source_offset_converter, &pi->pi_range.ar_line,
        _source_offset_converter, &pi->pi_endline,
        _source_offset_converter, &pi->pi_column,
        _source_offset_converter, &pi->pi_endcolumn);
}

PyTypeObject _PyPositionsIterator = {
    PyVarObject_HEAD_INIT(&PyType_Type, 0)
    "positions_iterator",               /* tp_name */
    sizeof(positionsiterator),          /* tp_basicsize */
    0,                                  /* tp_itemsize */
    /* methods */
    positionsiter_dealloc,              /* tp_dealloc */
    0,                                  /* tp_vectorcall_offset */
    0,                                  /* tp_getattr */
    0,                                  /* tp_setattr */
    0,                                  /* tp_as_async */
    0,                                  /* tp_repr */
    0,                                  /* tp_as_number */
    0,                                  /* tp_as_sequence */
    0,                                  /* tp_as_mapping */
    0,                                  /* tp_hash */
    0,                                  /* tp_call */
    0,                                  /* tp_str */
    0,                                  /* tp_getattro */
    0,                                  /* tp_setattro */
    0,                                  /* tp_as_buffer */
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,       /* tp_flags */
    0,                                  /* tp_doc */
    0,                                  /* tp_traverse */
    0,                                  /* tp_clear */
    0,                                  /* tp_richcompare */
    0,                                  /* tp_weaklistoffset */
    PyObject_SelfIter,                  /* tp_iter */
    positionsiter_next,                 /* tp_iternext */
    0,                                  /* tp_methods */
    0,                                  /* tp_members */
    0,                                  /* tp_getset */
    0,                                  /* tp_base */
    0,                                  /* tp_dict */
    0,                                  /* tp_descr_get */
    0,                                  /* tp_descr_set */
    0,                                  /* tp_dictoffset */
    0,                                  /* tp_init */
    0,                                  /* tp_alloc */
    0,                                  /* tp_new */
    PyObject_Free,                      /* tp_free */
};

static PyObject*
code_positionsiterator(PyObject *self, PyObject* Py_UNUSED(args))
{
    PyCodeObject *code = (PyCodeObject*)self;
    positionsiterator* pi = (positionsiterator*)PyType_GenericAlloc(&_PyPositionsIterator, 0);
    if (pi == NULL) {
        return NULL;
    }
    pi->pi_code = (PyCodeObject*)Py_NewRef(code);
    _PyCode_InitAddressRange(code, &pi->pi_range);
    pi->pi_offset = pi->pi_range.ar_end;
    return (PyObject*)pi;
}


/******************
 * "extra" frame eval info (see PEP 523)
 ******************/

/* Holder for co_extra information */
typedef struct {
    Py_ssize_t ce_size;
    void *ce_extras[1];
} _PyCodeObjectExtra;


int
PyUnstable_Code_GetExtra(PyObject *code, Py_ssize_t index, void **extra)
{
    if (!PyCode_Check(code)) {
        PyErr_BadInternalCall();
        return -1;
    }

    PyCodeObject *o = (PyCodeObject*) code;
    _PyCodeObjectExtra *co_extra = (_PyCodeObjectExtra*) o->co_extra;

    if (co_extra == NULL || index < 0 || co_extra->ce_size <= index) {
        *extra = NULL;
        return 0;
    }

    *extra = co_extra->ce_extras[index];
    return 0;
}


int
PyUnstable_Code_SetExtra(PyObject *code, Py_ssize_t index, void *extra)
{
    PyInterpreterState *interp = _PyInterpreterState_GET();

    if (!PyCode_Check(code) || index < 0 ||
            index >= interp->co_extra_user_count) {
        PyErr_BadInternalCall();
        return -1;
    }

    PyCodeObject *o = (PyCodeObject*) code;
    _PyCodeObjectExtra *co_extra = (_PyCodeObjectExtra *) o->co_extra;

    if (co_extra == NULL || co_extra->ce_size <= index) {
        Py_ssize_t i = (co_extra == NULL ? 0 : co_extra->ce_size);
        co_extra = PyMem_Realloc(
                co_extra,
                sizeof(_PyCodeObjectExtra) +
                (interp->co_extra_user_count-1) * sizeof(void*));
        if (co_extra == NULL) {
            return -1;
        }
        for (; i < interp->co_extra_user_count; i++) {
            co_extra->ce_extras[i] = NULL;
        }
        co_extra->ce_size = interp->co_extra_user_count;
        o->co_extra = co_extra;
    }

    if (co_extra->ce_extras[index] != NULL) {
        freefunc free = interp->co_extra_freefuncs[index];
        if (free != NULL) {
            free(co_extra->ce_extras[index]);
        }
    }

    co_extra->ce_extras[index] = extra;
    return 0;
}


/******************
 * other PyCodeObject accessor functions
 ******************/

static PyObject *
get_cached_locals(PyCodeObject *co, PyObject **cached_field,
    _PyLocals_Kind kind, int num)
{
    assert(cached_field != NULL);
    assert(co->_co_cached != NULL);
    PyObject *varnames = FT_ATOMIC_LOAD_PTR(*cached_field);
    if (varnames != NULL) {
        return Py_NewRef(varnames);
    }

    Py_BEGIN_CRITICAL_SECTION(co);
    varnames = *cached_field;
    if (varnames == NULL) {
        varnames = get_localsplus_names(co, kind, num);
        if (varnames != NULL) {
            FT_ATOMIC_STORE_PTR(*cached_field, varnames);
        }
    }
    Py_END_CRITICAL_SECTION();
    return Py_XNewRef(varnames);
}

PyObject *
_PyCode_GetVarnames(PyCodeObject *co)
{
    if (init_co_cached(co)) {
        return NULL;
    }
    return get_cached_locals(co, &co->_co_cached->_co_varnames, CO_FAST_LOCAL, co->co_nlocals);
}

PyObject *
PyCode_GetVarnames(PyCodeObject *code)
{
    return _PyCode_GetVarnames(code);
}

PyObject *
_PyCode_GetCellvars(PyCodeObject *co)
{
    if (init_co_cached(co)) {
        return NULL;
    }
    return get_cached_locals(co, &co->_co_cached->_co_cellvars, CO_FAST_CELL, co->co_ncellvars);
}

PyObject *
PyCode_GetCellvars(PyCodeObject *code)
{
    return _PyCode_GetCellvars(code);
}

PyObject *
_PyCode_GetFreevars(PyCodeObject *co)
{
    if (init_co_cached(co)) {
        return NULL;
    }
    return get_cached_locals(co, &co->_co_cached->_co_freevars, CO_FAST_FREE, co->co_nfreevars);
}

PyObject *
PyCode_GetFreevars(PyCodeObject *code)
{
    return _PyCode_GetFreevars(code);
}

#ifdef _Py_TIER2

static void
clear_executors(PyCodeObject *co)
{
    assert(co->co_executors);
    for (int i = 0; i < co->co_executors->size; i++) {
        if (co->co_executors->executors[i]) {
            _Py_ExecutorDetach(co->co_executors->executors[i]);
            assert(co->co_executors->executors[i] == NULL);
        }
    }
    PyMem_Free(co->co_executors);
    co->co_executors = NULL;
}

void
_PyCode_Clear_Executors(PyCodeObject *code)
{
    clear_executors(code);
}

#endif

static void
deopt_code(PyCodeObject *code, _Py_CODEUNIT *instructions)
{
    Py_ssize_t len = Py_SIZE(code);
    for (int i = 0; i < len; i++) {
        _Py_CODEUNIT inst = _Py_GetBaseCodeUnit(code, i);
        assert(inst.op.code < MIN_SPECIALIZED_OPCODE);
        int caches = _PyOpcode_Caches[inst.op.code];
        instructions[i] = inst;
        for (int j = 1; j <= caches; j++) {
            instructions[i+j].cache = 0;
        }
        i += caches;
    }
}

PyObject *
_PyCode_GetCode(PyCodeObject *co)
{
    if (init_co_cached(co)) {
        return NULL;
    }

    _PyCoCached *cached = co->_co_cached;
    PyObject *code = FT_ATOMIC_LOAD_PTR(cached->_co_code);
    if (code != NULL) {
        return Py_NewRef(code);
    }

    Py_BEGIN_CRITICAL_SECTION(co);
    code = cached->_co_code;
    if (code == NULL) {
        code = PyBytes_FromStringAndSize((const char *)_PyCode_CODE(co),
                                         _PyCode_NBYTES(co));
        if (code != NULL) {
            deopt_code(co, (_Py_CODEUNIT *)PyBytes_AS_STRING(code));
            assert(cached->_co_code == NULL);
            FT_ATOMIC_STORE_PTR(cached->_co_code, code);
        }
    }
    Py_END_CRITICAL_SECTION();
    return Py_XNewRef(code);
}

PyObject *
PyCode_GetCode(PyCodeObject *co)
{
    return _PyCode_GetCode(co);
}

/******************
 * PyCode_Type
 ******************/

/*[clinic input]
class code "PyCodeObject *" "&PyCode_Type"
[clinic start generated code]*/
/*[clinic end generated code: output=da39a3ee5e6b4b0d input=78aa5d576683bb4b]*/

/*[clinic input]
@classmethod
code.__new__ as code_new

    argcount: int
    posonlyargcount: int
    kwonlyargcount: int
    nlocals: int
    stacksize: int
    flags: int
    codestring as code: object(subclass_of="&PyBytes_Type")
    constants as consts: object(subclass_of="&PyTuple_Type")
    names: object(subclass_of="&PyTuple_Type")
    varnames: object(subclass_of="&PyTuple_Type")
    filename: unicode
    name: unicode
    qualname: unicode
    firstlineno: int
    linetable: object(subclass_of="&PyBytes_Type")
    exceptiontable: object(subclass_of="&PyBytes_Type")
    freevars: object(subclass_of="&PyTuple_Type", c_default="NULL") = ()
    cellvars: object(subclass_of="&PyTuple_Type", c_default="NULL") = ()
    /

Create a code object.  Not for the faint of heart.
[clinic start generated code]*/

static PyObject *
code_new_impl(PyTypeObject *type, int argcount, int posonlyargcount,
              int kwonlyargcount, int nlocals, int stacksize, int flags,
              PyObject *code, PyObject *consts, PyObject *names,
              PyObject *varnames, PyObject *filename, PyObject *name,
              PyObject *qualname, int firstlineno, PyObject *linetable,
              PyObject *exceptiontable, PyObject *freevars,
              PyObject *cellvars)
/*[clinic end generated code: output=069fa20d299f9dda input=e31da3c41ad8064a]*/
{
    PyObject *co = NULL;
    PyObject *ournames = NULL;
    PyObject *ourvarnames = NULL;
    PyObject *ourfreevars = NULL;
    PyObject *ourcellvars = NULL;

    if (PySys_Audit("code.__new__", "OOOiiiiii",
                    code, filename, name, argcount, posonlyargcount,
                    kwonlyargcount, nlocals, stacksize, flags) < 0) {
        goto cleanup;
    }

    if (argcount < 0) {
        PyErr_SetString(
            PyExc_ValueError,
            "code: argcount must not be negative");
        goto cleanup;
    }

    if (posonlyargcount < 0) {
        PyErr_SetString(
            PyExc_ValueError,
            "code: posonlyargcount must not be negative");
        goto cleanup;
    }

    if (kwonlyargcount < 0) {
        PyErr_SetString(
            PyExc_ValueError,
            "code: kwonlyargcount must not be negative");
        goto cleanup;
    }
    if (nlocals < 0) {
        PyErr_SetString(
            PyExc_ValueError,
            "code: nlocals must not be negative");
        goto cleanup;
    }

    ournames = validate_and_copy_tuple(names);
    if (ournames == NULL)
        goto cleanup;
    ourvarnames = validate_and_copy_tuple(varnames);
    if (ourvarnames == NULL)
        goto cleanup;
    if (freevars)
        ourfreevars = validate_and_copy_tuple(freevars);
    else
        ourfreevars = PyTuple_New(0);
    if (ourfreevars == NULL)
        goto cleanup;
    if (cellvars)
        ourcellvars = validate_and_copy_tuple(cellvars);
    else
        ourcellvars = PyTuple_New(0);
    if (ourcellvars == NULL)
        goto cleanup;

    co = (PyObject *)PyCode_NewWithPosOnlyArgs(argcount, posonlyargcount,
                                               kwonlyargcount,
                                               nlocals, stacksize, flags,
                                               code, consts, ournames,
                                               ourvarnames, ourfreevars,
                                               ourcellvars, filename,
                                               name, qualname, firstlineno,
                                               linetable,
                                               exceptiontable
                                              );
  cleanup:
    Py_XDECREF(ournames);
    Py_XDECREF(ourvarnames);
    Py_XDECREF(ourfreevars);
    Py_XDECREF(ourcellvars);
    return co;
}

static void
free_monitoring_data(_PyCoMonitoringData *data)
{
    if (data == NULL) {
        return;
    }
    if (data->tools) {
        PyMem_Free(data->tools);
    }
    if (data->lines) {
        PyMem_Free(data->lines);
    }
    if (data->line_tools) {
        PyMem_Free(data->line_tools);
    }
    if (data->per_instruction_opcodes) {
        PyMem_Free(data->per_instruction_opcodes);
    }
    if (data->per_instruction_tools) {
        PyMem_Free(data->per_instruction_tools);
    }
    PyMem_Free(data);
}

static void
code_dealloc(PyObject *self)
{
    PyCodeObject *co = _PyCodeObject_CAST(self);
    _PyObject_ResurrectStart(self);
    notify_code_watchers(PY_CODE_EVENT_DESTROY, co);
    if (_PyObject_ResurrectEnd(self)) {
        return;
    }

#ifdef Py_GIL_DISABLED
    PyObject_GC_UnTrack(co);
#endif

    _PyFunction_ClearCodeByVersion(co->co_version);
    if (co->co_extra != NULL) {
        PyInterpreterState *interp = _PyInterpreterState_GET();
        _PyCodeObjectExtra *co_extra = co->co_extra;

        for (Py_ssize_t i = 0; i < co_extra->ce_size; i++) {
            freefunc free_extra = interp->co_extra_freefuncs[i];

            if (free_extra != NULL) {
                free_extra(co_extra->ce_extras[i]);
            }
        }

        PyMem_Free(co_extra);
    }
#ifdef _Py_TIER2
    if (co->co_executors != NULL) {
        clear_executors(co);
    }
#endif

    Py_XDECREF(co->co_consts);
    Py_XDECREF(co->co_names);
    Py_XDECREF(co->co_localsplusnames);
    Py_XDECREF(co->co_localspluskinds);
    Py_XDECREF(co->co_filename);
    Py_XDECREF(co->co_name);
    Py_XDECREF(co->co_qualname);
    Py_XDECREF(co->co_linetable);
    Py_XDECREF(co->co_exceptiontable);
#ifdef Py_GIL_DISABLED
    assert(co->_co_unique_id == _Py_INVALID_UNIQUE_ID);
#endif
    if (co->_co_cached != NULL) {
        Py_XDECREF(co->_co_cached->_co_code);
        Py_XDECREF(co->_co_cached->_co_cellvars);
        Py_XDECREF(co->_co_cached->_co_freevars);
        Py_XDECREF(co->_co_cached->_co_varnames);
        PyMem_Free(co->_co_cached);
    }
    if (co->co_weakreflist != NULL) {
        PyObject_ClearWeakRefs(self);
    }
    free_monitoring_data(co->_co_monitoring);
#ifdef Py_GIL_DISABLED
    // The first element always points to the mutable bytecode at the end of
    // the code object, which will be freed when the code object is freed.
    for (Py_ssize_t i = 1; i < co->co_tlbc->size; i++) {
        char *entry = co->co_tlbc->entries[i];
        if (entry != NULL) {
            PyMem_Free(entry);
        }
    }
    PyMem_Free(co->co_tlbc);
#endif
    PyObject_Free(co);
}

#ifdef Py_GIL_DISABLED
static int
code_traverse(PyObject *self, visitproc visit, void *arg)
{
    PyCodeObject *co = _PyCodeObject_CAST(self);
    Py_VISIT(co->co_consts);
    return 0;
}
#endif

static PyObject *
code_repr(PyObject *self)
{
    PyCodeObject *co = _PyCodeObject_CAST(self);
    int lineno;
    if (co->co_firstlineno != 0)
        lineno = co->co_firstlineno;
    else
        lineno = -1;
    if (co->co_filename && PyUnicode_Check(co->co_filename)) {
        return PyUnicode_FromFormat(
            "<code object %U at %p, file \"%U\", line %d>",
            co->co_name, co, co->co_filename, lineno);
    } else {
        return PyUnicode_FromFormat(
            "<code object %U at %p, file ???, line %d>",
            co->co_name, co, lineno);
    }
}

static PyObject *
code_richcompare(PyObject *self, PyObject *other, int op)
{
    PyCodeObject *co, *cp;
    int eq;
    PyObject *consts1, *consts2;
    PyObject *res;

    if ((op != Py_EQ && op != Py_NE) ||
        !PyCode_Check(self) ||
        !PyCode_Check(other)) {
        Py_RETURN_NOTIMPLEMENTED;
    }

    co = (PyCodeObject *)self;
    cp = (PyCodeObject *)other;

    eq = PyObject_RichCompareBool(co->co_name, cp->co_name, Py_EQ);
    if (!eq) goto unequal;
    eq = co->co_argcount == cp->co_argcount;
    if (!eq) goto unequal;
    eq = co->co_posonlyargcount == cp->co_posonlyargcount;
    if (!eq) goto unequal;
    eq = co->co_kwonlyargcount == cp->co_kwonlyargcount;
    if (!eq) goto unequal;
    eq = co->co_flags == cp->co_flags;
    if (!eq) goto unequal;
    eq = co->co_firstlineno == cp->co_firstlineno;
    if (!eq) goto unequal;
    eq = Py_SIZE(co) == Py_SIZE(cp);
    if (!eq) {
        goto unequal;
    }
    for (int i = 0; i < Py_SIZE(co); i++) {
        _Py_CODEUNIT co_instr = _Py_GetBaseCodeUnit(co, i);
        _Py_CODEUNIT cp_instr = _Py_GetBaseCodeUnit(cp, i);
        if (co_instr.cache != cp_instr.cache) {
            goto unequal;
        }
        i += _PyOpcode_Caches[co_instr.op.code];
    }

    /* compare constants */
    consts1 = _PyCode_ConstantKey(co->co_consts);
    if (!consts1)
        return NULL;
    consts2 = _PyCode_ConstantKey(cp->co_consts);
    if (!consts2) {
        Py_DECREF(consts1);
        return NULL;
    }
    eq = PyObject_RichCompareBool(consts1, consts2, Py_EQ);
    Py_DECREF(consts1);
    Py_DECREF(consts2);
    if (eq <= 0) goto unequal;

    eq = PyObject_RichCompareBool(co->co_names, cp->co_names, Py_EQ);
    if (eq <= 0) goto unequal;
    eq = PyObject_RichCompareBool(co->co_localsplusnames,
                                  cp->co_localsplusnames, Py_EQ);
    if (eq <= 0) goto unequal;
    eq = PyObject_RichCompareBool(co->co_linetable, cp->co_linetable, Py_EQ);
    if (eq <= 0) {
        goto unequal;
    }
    eq = PyObject_RichCompareBool(co->co_exceptiontable,
                                  cp->co_exceptiontable, Py_EQ);
    if (eq <= 0) {
        goto unequal;
    }

    if (op == Py_EQ)
        res = Py_True;
    else
        res = Py_False;
    goto done;

  unequal:
    if (eq < 0)
        return NULL;
    if (op == Py_NE)
        res = Py_True;
    else
        res = Py_False;

  done:
    return Py_NewRef(res);
}

static Py_hash_t
code_hash(PyObject *self)
{
    PyCodeObject *co = _PyCodeObject_CAST(self);
    Py_uhash_t uhash = 20221211;
    #define SCRAMBLE_IN(H) do {       \
        uhash ^= (Py_uhash_t)(H);     \
        uhash *= PyHASH_MULTIPLIER;  \
    } while (0)
    #define SCRAMBLE_IN_HASH(EXPR) do {     \
        Py_hash_t h = PyObject_Hash(EXPR);  \
        if (h == -1) {                      \
            return -1;                      \
        }                                   \
        SCRAMBLE_IN(h);                     \
    } while (0)

    SCRAMBLE_IN_HASH(co->co_name);
    SCRAMBLE_IN_HASH(co->co_consts);
    SCRAMBLE_IN_HASH(co->co_names);
    SCRAMBLE_IN_HASH(co->co_localsplusnames);
    SCRAMBLE_IN_HASH(co->co_linetable);
    SCRAMBLE_IN_HASH(co->co_exceptiontable);
    SCRAMBLE_IN(co->co_argcount);
    SCRAMBLE_IN(co->co_posonlyargcount);
    SCRAMBLE_IN(co->co_kwonlyargcount);
    SCRAMBLE_IN(co->co_flags);
    SCRAMBLE_IN(co->co_firstlineno);
    SCRAMBLE_IN(Py_SIZE(co));
    for (int i = 0; i < Py_SIZE(co); i++) {
        _Py_CODEUNIT co_instr = _Py_GetBaseCodeUnit(co, i);
        SCRAMBLE_IN(co_instr.op.code);
        SCRAMBLE_IN(co_instr.op.arg);
        i += _PyOpcode_Caches[co_instr.op.code];
    }
    if ((Py_hash_t)uhash == -1) {
        return -2;
    }
    return (Py_hash_t)uhash;
}


#define OFF(x) offsetof(PyCodeObject, x)

static PyMemberDef code_memberlist[] = {
    {"co_argcount",        Py_T_INT,     OFF(co_argcount),        Py_READONLY},
    {"co_posonlyargcount", Py_T_INT,     OFF(co_posonlyargcount), Py_READONLY},
    {"co_kwonlyargcount",  Py_T_INT,     OFF(co_kwonlyargcount),  Py_READONLY},
    {"co_stacksize",       Py_T_INT,     OFF(co_stacksize),       Py_READONLY},
    {"co_flags",           Py_T_INT,     OFF(co_flags),           Py_READONLY},
    {"co_nlocals",         Py_T_INT,     OFF(co_nlocals),         Py_READONLY},
    {"co_consts",          _Py_T_OBJECT, OFF(co_consts),          Py_READONLY},
    {"co_names",           _Py_T_OBJECT, OFF(co_names),           Py_READONLY},
    {"co_filename",        _Py_T_OBJECT, OFF(co_filename),        Py_READONLY},
    {"co_name",            _Py_T_OBJECT, OFF(co_name),            Py_READONLY},
    {"co_qualname",        _Py_T_OBJECT, OFF(co_qualname),        Py_READONLY},
    {"co_firstlineno",     Py_T_INT,     OFF(co_firstlineno),     Py_READONLY},
    {"co_linetable",       _Py_T_OBJECT, OFF(co_linetable),       Py_READONLY},
    {"co_exceptiontable",  _Py_T_OBJECT, OFF(co_exceptiontable),  Py_READONLY},
    {NULL}      /* Sentinel */
};


static PyObject *
code_getlnotab(PyObject *self, void *closure)
{
    PyCodeObject *code = _PyCodeObject_CAST(self);
    if (PyErr_WarnEx(PyExc_DeprecationWarning,
                     "co_lnotab is deprecated, use co_lines instead.",
                     1) < 0) {
        return NULL;
    }
    return decode_linetable(code);
}

static PyObject *
code_getvarnames(PyObject *self, void *closure)
{
    PyCodeObject *code = _PyCodeObject_CAST(self);
    return _PyCode_GetVarnames(code);
}

static PyObject *
code_getcellvars(PyObject *self, void *closure)
{
    PyCodeObject *code = _PyCodeObject_CAST(self);
    return _PyCode_GetCellvars(code);
}

static PyObject *
code_getfreevars(PyObject *self, void *closure)
{
    PyCodeObject *code = _PyCodeObject_CAST(self);
    return _PyCode_GetFreevars(code);
}

static PyObject *
code_getcodeadaptive(PyObject *self, void *closure)
{
    PyCodeObject *code = _PyCodeObject_CAST(self);
    return PyBytes_FromStringAndSize(code->co_code_adaptive,
                                     _PyCode_NBYTES(code));
}

static PyObject *
code_getcode(PyObject *self, void *closure)
{
    PyCodeObject *code = _PyCodeObject_CAST(self);
    return _PyCode_GetCode(code);
}

static PyGetSetDef code_getsetlist[] = {
    {"co_lnotab",         code_getlnotab,       NULL, NULL},
    {"_co_code_adaptive", code_getcodeadaptive, NULL, NULL},
    // The following old names are kept for backward compatibility.
    {"co_varnames",       code_getvarnames,     NULL, NULL},
    {"co_cellvars",       code_getcellvars,     NULL, NULL},
    {"co_freevars",       code_getfreevars,     NULL, NULL},
    {"co_code",           code_getcode,         NULL, NULL},
    {0}
};


static PyObject *
code_sizeof(PyObject *self, PyObject *Py_UNUSED(args))
{
    PyCodeObject *co = _PyCodeObject_CAST(self);
    size_t res = _PyObject_VAR_SIZE(Py_TYPE(co), Py_SIZE(co));
    _PyCodeObjectExtra *co_extra = (_PyCodeObjectExtra*) co->co_extra;
    if (co_extra != NULL) {
        res += sizeof(_PyCodeObjectExtra);
        res += ((size_t)co_extra->ce_size - 1) * sizeof(co_extra->ce_extras[0]);
    }
    return PyLong_FromSize_t(res);
}

static PyObject *
code_linesiterator(PyObject *self, PyObject *Py_UNUSED(args))
{
    PyCodeObject *code = _PyCodeObject_CAST(self);
    return (PyObject *)new_linesiterator(code);
}

static PyObject *
code_branchesiterator(PyObject *self, PyObject *Py_UNUSED(args))
{
    PyCodeObject *code = _PyCodeObject_CAST(self);
    return _PyInstrumentation_BranchesIterator(code);
}

/*[clinic input]
@text_signature "($self, /, **changes)"
code.replace

    *
    co_argcount: int(c_default="((PyCodeObject *)self)->co_argcount") = unchanged
    co_posonlyargcount: int(c_default="((PyCodeObject *)self)->co_posonlyargcount") = unchanged
    co_kwonlyargcount: int(c_default="((PyCodeObject *)self)->co_kwonlyargcount") = unchanged
    co_nlocals: int(c_default="((PyCodeObject *)self)->co_nlocals") = unchanged
    co_stacksize: int(c_default="((PyCodeObject *)self)->co_stacksize") = unchanged
    co_flags: int(c_default="((PyCodeObject *)self)->co_flags") = unchanged
    co_firstlineno: int(c_default="((PyCodeObject *)self)->co_firstlineno") = unchanged
    co_code: object(subclass_of="&PyBytes_Type", c_default="NULL") = unchanged
    co_consts: object(subclass_of="&PyTuple_Type", c_default="((PyCodeObject *)self)->co_consts") = unchanged
    co_names: object(subclass_of="&PyTuple_Type", c_default="((PyCodeObject *)self)->co_names") = unchanged
    co_varnames: object(subclass_of="&PyTuple_Type", c_default="NULL") = unchanged
    co_freevars: object(subclass_of="&PyTuple_Type", c_default="NULL") = unchanged
    co_cellvars: object(subclass_of="&PyTuple_Type", c_default="NULL") = unchanged
    co_filename: unicode(c_default="((PyCodeObject *)self)->co_filename") = unchanged
    co_name: unicode(c_default="((PyCodeObject *)self)->co_name") = unchanged
    co_qualname: unicode(c_default="((PyCodeObject *)self)->co_qualname") = unchanged
    co_linetable: object(subclass_of="&PyBytes_Type", c_default="((PyCodeObject *)self)->co_linetable") = unchanged
    co_exceptiontable: object(subclass_of="&PyBytes_Type", c_default="((PyCodeObject *)self)->co_exceptiontable") = unchanged

Return a copy of the code object with new values for the specified fields.
[clinic start generated code]*/

static PyObject *
code_replace_impl(PyCodeObject *self, int co_argcount,
                  int co_posonlyargcount, int co_kwonlyargcount,
                  int co_nlocals, int co_stacksize, int co_flags,
                  int co_firstlineno, PyObject *co_code, PyObject *co_consts,
                  PyObject *co_names, PyObject *co_varnames,
                  PyObject *co_freevars, PyObject *co_cellvars,
                  PyObject *co_filename, PyObject *co_name,
                  PyObject *co_qualname, PyObject *co_linetable,
                  PyObject *co_exceptiontable)
/*[clinic end generated code: output=e75c48a15def18b9 input=a455a89c57ac9d42]*/
{
#define CHECK_INT_ARG(ARG) \
        if (ARG < 0) { \
            PyErr_SetString(PyExc_ValueError, \
                            #ARG " must be a positive integer"); \
            return NULL; \
        }

    CHECK_INT_ARG(co_argcount);
    CHECK_INT_ARG(co_posonlyargcount);
    CHECK_INT_ARG(co_kwonlyargcount);
    CHECK_INT_ARG(co_nlocals);
    CHECK_INT_ARG(co_stacksize);
    CHECK_INT_ARG(co_flags);
    CHECK_INT_ARG(co_firstlineno);

#undef CHECK_INT_ARG

    PyObject *code = NULL;
    if (co_code == NULL) {
        code = _PyCode_GetCode(self);
        if (code == NULL) {
            return NULL;
        }
        co_code = code;
    }

    if (PySys_Audit("code.__new__", "OOOiiiiii",
                    co_code, co_filename, co_name, co_argcount,
                    co_posonlyargcount, co_kwonlyargcount, co_nlocals,
                    co_stacksize, co_flags) < 0) {
        Py_XDECREF(code);
        return NULL;
    }

    PyCodeObject *co = NULL;
    PyObject *varnames = NULL;
    PyObject *cellvars = NULL;
    PyObject *freevars = NULL;
    if (co_varnames == NULL) {
        varnames = get_localsplus_names(self, CO_FAST_LOCAL, self->co_nlocals);
        if (varnames == NULL) {
            goto error;
        }
        co_varnames = varnames;
    }
    if (co_cellvars == NULL) {
        cellvars = get_localsplus_names(self, CO_FAST_CELL, self->co_ncellvars);
        if (cellvars == NULL) {
            goto error;
        }
        co_cellvars = cellvars;
    }
    if (co_freevars == NULL) {
        freevars = get_localsplus_names(self, CO_FAST_FREE, self->co_nfreevars);
        if (freevars == NULL) {
            goto error;
        }
        co_freevars = freevars;
    }

    co = PyCode_NewWithPosOnlyArgs(
        co_argcount, co_posonlyargcount, co_kwonlyargcount, co_nlocals,
        co_stacksize, co_flags, co_code, co_consts, co_names,
        co_varnames, co_freevars, co_cellvars, co_filename, co_name,
        co_qualname, co_firstlineno,
        co_linetable, co_exceptiontable);

error:
    Py_XDECREF(code);
    Py_XDECREF(varnames);
    Py_XDECREF(cellvars);
    Py_XDECREF(freevars);
    return (PyObject *)co;
}

/*[clinic input]
code._varname_from_oparg

    oparg: int

(internal-only) Return the local variable name for the given oparg.

WARNING: this method is for internal use only and may change or go away.
[clinic start generated code]*/

static PyObject *
code__varname_from_oparg_impl(PyCodeObject *self, int oparg)
/*[clinic end generated code: output=1fd1130413184206 input=c5fa3ee9bac7d4ca]*/
{
    PyObject *name = PyTuple_GetItem(self->co_localsplusnames, oparg);
    if (name == NULL) {
        return NULL;
    }
    return Py_NewRef(name);
}

/* XXX code objects need to participate in GC? */

static struct PyMethodDef code_methods[] = {
    {"__sizeof__", code_sizeof, METH_NOARGS},
    {"co_lines", code_linesiterator, METH_NOARGS},
    {"co_branches", code_branchesiterator, METH_NOARGS},
    {"co_positions", code_positionsiterator, METH_NOARGS},
    CODE_REPLACE_METHODDEF
    CODE__VARNAME_FROM_OPARG_METHODDEF
    {"__replace__", _PyCFunction_CAST(code_replace), METH_FASTCALL|METH_KEYWORDS,
     PyDoc_STR("__replace__($self, /, **changes)\n--\n\nThe same as replace().")},
    {NULL, NULL}                /* sentinel */
};


PyTypeObject PyCode_Type = {
    PyVarObject_HEAD_INIT(&PyType_Type, 0)
    "code",
    offsetof(PyCodeObject, co_code_adaptive),
    sizeof(_Py_CODEUNIT),
    code_dealloc,                       /* tp_dealloc */
    0,                                  /* tp_vectorcall_offset */
    0,                                  /* tp_getattr */
    0,                                  /* tp_setattr */
    0,                                  /* tp_as_async */
    code_repr,                          /* tp_repr */
    0,                                  /* tp_as_number */
    0,                                  /* tp_as_sequence */
    0,                                  /* tp_as_mapping */
    code_hash,                          /* tp_hash */
    0,                                  /* tp_call */
    0,                                  /* tp_str */
    PyObject_GenericGetAttr,            /* tp_getattro */
    0,                                  /* tp_setattro */
    0,                                  /* tp_as_buffer */
#ifdef Py_GIL_DISABLED
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC, /* tp_flags */
#else
    Py_TPFLAGS_DEFAULT,                 /* tp_flags */
#endif
    code_new__doc__,                    /* tp_doc */
#ifdef Py_GIL_DISABLED
    code_traverse,                      /* tp_traverse */
#else
    0,                                  /* tp_traverse */
#endif
    0,                                  /* tp_clear */
    code_richcompare,                   /* tp_richcompare */
    offsetof(PyCodeObject, co_weakreflist),     /* tp_weaklistoffset */
    0,                                  /* tp_iter */
    0,                                  /* tp_iternext */
    code_methods,                       /* tp_methods */
    code_memberlist,                    /* tp_members */
    code_getsetlist,                    /* tp_getset */
    0,                                  /* tp_base */
    0,                                  /* tp_dict */
    0,                                  /* tp_descr_get */
    0,                                  /* tp_descr_set */
    0,                                  /* tp_dictoffset */
    0,                                  /* tp_init */
    0,                                  /* tp_alloc */
    code_new,                           /* tp_new */
};


/******************
 * other API
 ******************/

PyObject*
_PyCode_ConstantKey(PyObject *op)
{
    PyObject *key;

    /* Py_None and Py_Ellipsis are singletons. */
    if (op == Py_None || op == Py_Ellipsis
       || PyLong_CheckExact(op)
       || PyUnicode_CheckExact(op)
          /* code_richcompare() uses _PyCode_ConstantKey() internally */
       || PyCode_Check(op))
    {
        /* Objects of these types are always different from object of other
         * type and from tuples. */
        key = Py_NewRef(op);
    }
    else if (PyBool_Check(op) || PyBytes_CheckExact(op)) {
        /* Make booleans different from integers 0 and 1.
         * Avoid BytesWarning from comparing bytes with strings. */
        key = PyTuple_Pack(2, Py_TYPE(op), op);
    }
    else if (PyFloat_CheckExact(op)) {
        double d = PyFloat_AS_DOUBLE(op);
        /* all we need is to make the tuple different in either the 0.0
         * or -0.0 case from all others, just to avoid the "coercion".
         */
        if (d == 0.0 && copysign(1.0, d) < 0.0)
            key = PyTuple_Pack(3, Py_TYPE(op), op, Py_None);
        else
            key = PyTuple_Pack(2, Py_TYPE(op), op);
    }
    else if (PyComplex_CheckExact(op)) {
        Py_complex z;
        int real_negzero, imag_negzero;
        /* For the complex case we must make complex(x, 0.)
           different from complex(x, -0.) and complex(0., y)
           different from complex(-0., y), for any x and y.
           All four complex zeros must be distinguished.*/
        z = PyComplex_AsCComplex(op);
        real_negzero = z.real == 0.0 && copysign(1.0, z.real) < 0.0;
        imag_negzero = z.imag == 0.0 && copysign(1.0, z.imag) < 0.0;
        /* use True, False and None singleton as tags for the real and imag
         * sign, to make tuples different */
        if (real_negzero && imag_negzero) {
            key = PyTuple_Pack(3, Py_TYPE(op), op, Py_True);
        }
        else if (imag_negzero) {
            key = PyTuple_Pack(3, Py_TYPE(op), op, Py_False);
        }
        else if (real_negzero) {
            key = PyTuple_Pack(3, Py_TYPE(op), op, Py_None);
        }
        else {
            key = PyTuple_Pack(2, Py_TYPE(op), op);
        }
    }
    else if (PyTuple_CheckExact(op)) {
        Py_ssize_t i, len;
        PyObject *tuple;

        len = PyTuple_GET_SIZE(op);
        tuple = PyTuple_New(len);
        if (tuple == NULL)
            return NULL;

        for (i=0; i < len; i++) {
            PyObject *item, *item_key;

            item = PyTuple_GET_ITEM(op, i);
            item_key = _PyCode_ConstantKey(item);
            if (item_key == NULL) {
                Py_DECREF(tuple);
                return NULL;
            }

            PyTuple_SET_ITEM(tuple, i, item_key);
        }

        key = PyTuple_Pack(2, tuple, op);
        Py_DECREF(tuple);
    }
    else if (PyFrozenSet_CheckExact(op)) {
        Py_ssize_t pos = 0;
        PyObject *item;
        Py_hash_t hash;
        Py_ssize_t i, len;
        PyObject *tuple, *set;

        len = PySet_GET_SIZE(op);
        tuple = PyTuple_New(len);
        if (tuple == NULL)
            return NULL;

        i = 0;
        while (_PySet_NextEntry(op, &pos, &item, &hash)) {
            PyObject *item_key;

            item_key = _PyCode_ConstantKey(item);
            if (item_key == NULL) {
                Py_DECREF(tuple);
                return NULL;
            }

            assert(i < len);
            PyTuple_SET_ITEM(tuple, i, item_key);
            i++;
        }
        set = PyFrozenSet_New(tuple);
        Py_DECREF(tuple);
        if (set == NULL)
            return NULL;

        key = PyTuple_Pack(2, set, op);
        Py_DECREF(set);
        return key;
    }
    else if (PySlice_Check(op)) {
        PySliceObject *slice = (PySliceObject *)op;
        PyObject *start_key = NULL;
        PyObject *stop_key = NULL;
        PyObject *step_key = NULL;
        key = NULL;

        start_key = _PyCode_ConstantKey(slice->start);
        if (start_key == NULL) {
            goto slice_exit;
        }

        stop_key = _PyCode_ConstantKey(slice->stop);
        if (stop_key == NULL) {
            goto slice_exit;
        }

        step_key = _PyCode_ConstantKey(slice->step);
        if (step_key == NULL) {
            goto slice_exit;
        }

        PyObject *slice_key = PySlice_New(start_key, stop_key, step_key);
        if (slice_key == NULL) {
            goto slice_exit;
        }

        key = PyTuple_Pack(2, slice_key, op);
        Py_DECREF(slice_key);
    slice_exit:
        Py_XDECREF(start_key);
        Py_XDECREF(stop_key);
        Py_XDECREF(step_key);
    }
    else {
        /* for other types, use the object identifier as a unique identifier
         * to ensure that they are seen as unequal. */
        PyObject *obj_id = PyLong_FromVoidPtr(op);
        if (obj_id == NULL)
            return NULL;

        key = PyTuple_Pack(2, obj_id, op);
        Py_DECREF(obj_id);
    }
    return key;
}

#ifdef Py_GIL_DISABLED
static PyObject *
intern_one_constant(PyObject *op)
{
    PyInterpreterState *interp = _PyInterpreterState_GET();
    _Py_hashtable_t *consts = interp->code_state.constants;

    assert(!PyUnicode_CheckExact(op));  // strings are interned separately

    _Py_hashtable_entry_t *entry = _Py_hashtable_get_entry(consts, op);
    if (entry == NULL) {
        if (_Py_hashtable_set(consts, op, op) != 0) {
            return NULL;
        }

#ifdef Py_REF_DEBUG
        Py_ssize_t refcnt = Py_REFCNT(op);
        if (refcnt != 1) {
            // Adjust the reftotal to account for the fact that we only
            // restore a single reference in _PyCode_Fini.
            _Py_AddRefTotal(_PyThreadState_GET(), -(refcnt - 1));
        }
#endif

        _Py_SetImmortal(op);
        return op;
    }

    assert(_Py_IsImmortal(entry->value));
    return (PyObject *)entry->value;
}

static int
compare_constants(const void *key1, const void *key2) {
    PyObject *op1 = (PyObject *)key1;
    PyObject *op2 = (PyObject *)key2;
    if (op1 == op2) {
        return 1;
    }
    if (Py_TYPE(op1) != Py_TYPE(op2)) {
        return 0;
    }
    // We compare container contents by identity because we have already
    // internalized the items.
    if (PyTuple_CheckExact(op1)) {
        Py_ssize_t size = PyTuple_GET_SIZE(op1);
        if (size != PyTuple_GET_SIZE(op2)) {
            return 0;
        }
        for (Py_ssize_t i = 0; i < size; i++) {
            if (PyTuple_GET_ITEM(op1, i) != PyTuple_GET_ITEM(op2, i)) {
                return 0;
            }
        }
        return 1;
    }
    else if (PyFrozenSet_CheckExact(op1)) {
        if (PySet_GET_SIZE(op1) != PySet_GET_SIZE(op2)) {
            return 0;
        }
        Py_ssize_t pos1 = 0, pos2 = 0;
        PyObject *obj1, *obj2;
        Py_hash_t hash1, hash2;
        while ((_PySet_NextEntry(op1, &pos1, &obj1, &hash1)) &&
               (_PySet_NextEntry(op2, &pos2, &obj2, &hash2)))
        {
            if (obj1 != obj2) {
                return 0;
            }
        }
        return 1;
    }
    else if (PySlice_Check(op1)) {
        PySliceObject *s1 = (PySliceObject *)op1;
        PySliceObject *s2 = (PySliceObject *)op2;
        return (s1->start == s2->start &&
                s1->stop  == s2->stop  &&
                s1->step  == s2->step);
    }
    else if (PyBytes_CheckExact(op1) || PyLong_CheckExact(op1)) {
        return PyObject_RichCompareBool(op1, op2, Py_EQ);
    }
    else if (PyFloat_CheckExact(op1)) {
        // Ensure that, for example, +0.0 and -0.0 are distinct
        double f1 = PyFloat_AS_DOUBLE(op1);
        double f2 = PyFloat_AS_DOUBLE(op2);
        return memcmp(&f1, &f2, sizeof(double)) == 0;
    }
    else if (PyComplex_CheckExact(op1)) {
        Py_complex c1 = ((PyComplexObject *)op1)->cval;
        Py_complex c2 = ((PyComplexObject *)op2)->cval;
        return memcmp(&c1, &c2, sizeof(Py_complex)) == 0;
    }
    _Py_FatalErrorFormat("unexpected type in compare_constants: %s",
                         Py_TYPE(op1)->tp_name);
    return 0;
}

static Py_uhash_t
hash_const(const void *key)
{
    PyObject *op = (PyObject *)key;
    if (PySlice_Check(op)) {
        PySliceObject *s = (PySliceObject *)op;
        PyObject *data[3] = { s->start, s->stop, s->step };
        return Py_HashBuffer(&data, sizeof(data));
    }
    else if (PyTuple_CheckExact(op)) {
        Py_ssize_t size = PyTuple_GET_SIZE(op);
        PyObject **data = _PyTuple_ITEMS(op);
        return Py_HashBuffer(data, sizeof(PyObject *) * size);
    }
    Py_hash_t h = PyObject_Hash(op);
    if (h == -1) {
        // This should never happen: all the constants we support have
        // infallible hash functions.
        Py_FatalError("code: hash failed");
    }
    return (Py_uhash_t)h;
}

static int
clear_containers(_Py_hashtable_t *ht, const void *key, const void *value,
                 void *user_data)
{
    // First clear containers to avoid recursive deallocation later on in
    // destroy_key.
    PyObject *op = (PyObject *)key;
    if (PyTuple_CheckExact(op)) {
        for (Py_ssize_t i = 0; i < PyTuple_GET_SIZE(op); i++) {
            Py_CLEAR(_PyTuple_ITEMS(op)[i]);
        }
    }
    else if (PySlice_Check(op)) {
        PySliceObject *slice = (PySliceObject *)op;
        Py_SETREF(slice->start, Py_None);
        Py_SETREF(slice->stop, Py_None);
        Py_SETREF(slice->step, Py_None);
    }
    else if (PyFrozenSet_CheckExact(op)) {
        _PySet_ClearInternal((PySetObject *)op);
    }
    return 0;
}

static void
destroy_key(void *key)
{
    _Py_ClearImmortal(key);
}
#endif

PyStatus
_PyCode_Init(PyInterpreterState *interp)
{
#ifdef Py_GIL_DISABLED
    struct _py_code_state *state = &interp->code_state;
    state->constants = _Py_hashtable_new_full(&hash_const, &compare_constants,
                                              &destroy_key, NULL, NULL);
    if (state->constants == NULL) {
        return _PyStatus_NO_MEMORY();
    }
#endif
    return _PyStatus_OK();
}

void
_PyCode_Fini(PyInterpreterState *interp)
{
#ifdef Py_GIL_DISABLED
    // Free interned constants
    struct _py_code_state *state = &interp->code_state;
    if (state->constants) {
        _Py_hashtable_foreach(state->constants, &clear_containers, NULL);
        _Py_hashtable_destroy(state->constants);
        state->constants = NULL;
    }
    _PyIndexPool_Fini(&interp->tlbc_indices);
#endif
}

#ifdef Py_GIL_DISABLED

// Thread-local bytecode (TLBC)
//
// Each thread specializes a thread-local copy of the bytecode, created on the
// first RESUME, in free-threaded builds. All copies of the bytecode for a code
// object are stored in the `co_tlbc` array. Threads reserve a globally unique
// index identifying its copy of the bytecode in all `co_tlbc` arrays at thread
// creation and release the index at thread destruction. The first entry in
// every `co_tlbc` array always points to the "main" copy of the bytecode that
// is stored at the end of the code object. This ensures that no bytecode is
// copied for programs that do not use threads.
//
// Thread-local bytecode can be disabled at runtime by providing either `-X
// tlbc=0` or `PYTHON_TLBC=0`. Disabling thread-local bytecode also disables
// specialization. All threads share the main copy of the bytecode when
// thread-local bytecode is disabled.
//
// Concurrent modifications to the bytecode made by the specializing
// interpreter and instrumentation use atomics, with specialization taking care
// not to overwrite an instruction that was instrumented concurrently.

int32_t
_Py_ReserveTLBCIndex(PyInterpreterState *interp)
{
    if (interp->config.tlbc_enabled) {
        return _PyIndexPool_AllocIndex(&interp->tlbc_indices);
    }
    // All threads share the main copy of the bytecode when TLBC is disabled
    return 0;
}

void
_Py_ClearTLBCIndex(_PyThreadStateImpl *tstate)
{
    PyInterpreterState *interp = ((PyThreadState *)tstate)->interp;
    if (interp->config.tlbc_enabled) {
        _PyIndexPool_FreeIndex(&interp->tlbc_indices, tstate->tlbc_index);
    }
}

static _PyCodeArray *
_PyCodeArray_New(Py_ssize_t size)
{
    _PyCodeArray *arr = PyMem_Calloc(
        1, offsetof(_PyCodeArray, entries) + sizeof(void *) * size);
    if (arr == NULL) {
        PyErr_NoMemory();
        return NULL;
    }
    arr->size = size;
    return arr;
}

static void
copy_code(_Py_CODEUNIT *dst, PyCodeObject *co)
{
    int code_len = (int) Py_SIZE(co);
    for (int i = 0; i < code_len; i += _PyInstruction_GetLength(co, i)) {
        dst[i] = _Py_GetBaseCodeUnit(co, i);
    }
    _PyCode_Quicken(dst, code_len, co->co_consts, 1);
}

static Py_ssize_t
get_pow2_greater(Py_ssize_t initial, Py_ssize_t limit)
{
    // initial must be a power of two
    assert(!(initial & (initial - 1)));
    Py_ssize_t res = initial;
    while (res && res < limit) {
        res <<= 1;
    }
    return res;
}

static _Py_CODEUNIT *
create_tlbc_lock_held(PyCodeObject *co, Py_ssize_t idx)
{
    _PyCodeArray *tlbc = co->co_tlbc;
    if (idx >= tlbc->size) {
        Py_ssize_t new_size = get_pow2_greater(tlbc->size, idx + 1);
        if (!new_size) {
            PyErr_NoMemory();
            return NULL;
        }
        _PyCodeArray *new_tlbc = _PyCodeArray_New(new_size);
        if (new_tlbc == NULL) {
            return NULL;
        }
        memcpy(new_tlbc->entries, tlbc->entries, tlbc->size * sizeof(void *));
        _Py_atomic_store_ptr_release(&co->co_tlbc, new_tlbc);
        _PyMem_FreeDelayed(tlbc);
        tlbc = new_tlbc;
    }
    char *bc = PyMem_Calloc(1, _PyCode_NBYTES(co));
    if (bc == NULL) {
        PyErr_NoMemory();
        return NULL;
    }
    copy_code((_Py_CODEUNIT *) bc, co);
    assert(tlbc->entries[idx] == NULL);
    tlbc->entries[idx] = bc;
    return (_Py_CODEUNIT *) bc;
}

static _Py_CODEUNIT *
get_tlbc_lock_held(PyCodeObject *co)
{
    _PyCodeArray *tlbc = co->co_tlbc;
    _PyThreadStateImpl *tstate = (_PyThreadStateImpl *)PyThreadState_GET();
    int32_t idx = tstate->tlbc_index;
    if (idx < tlbc->size && tlbc->entries[idx] != NULL) {
        return (_Py_CODEUNIT *)tlbc->entries[idx];
    }
    return create_tlbc_lock_held(co, idx);
}

_Py_CODEUNIT *
_PyCode_GetTLBC(PyCodeObject *co)
{
    _Py_CODEUNIT *result;
    Py_BEGIN_CRITICAL_SECTION(co);
    result = get_tlbc_lock_held(co);
    Py_END_CRITICAL_SECTION();
    return result;
}

// My kingdom for a bitset
struct flag_set {
    uint8_t *flags;
    Py_ssize_t size;
};

static inline int
flag_is_set(struct flag_set *flags, Py_ssize_t idx)
{
    assert(idx >= 0);
    return (idx < flags->size) && flags->flags[idx];
}

// Set the flag for each tlbc index in use
static int
get_indices_in_use(PyInterpreterState *interp, struct flag_set *in_use)
{
    assert(interp->stoptheworld.world_stopped);
    assert(in_use->flags == NULL);
    int32_t max_index = 0;
    _Py_FOR_EACH_TSTATE_BEGIN(interp, p) {
        int32_t idx = ((_PyThreadStateImpl *) p)->tlbc_index;
        if (idx > max_index) {
            max_index = idx;
        }
    }
    _Py_FOR_EACH_TSTATE_END(interp);
    in_use->size = (size_t) max_index + 1;
    in_use->flags = PyMem_Calloc(in_use->size, sizeof(*in_use->flags));
    if (in_use->flags == NULL) {
        return -1;
    }
    _Py_FOR_EACH_TSTATE_BEGIN(interp, p) {
        in_use->flags[((_PyThreadStateImpl *) p)->tlbc_index] = 1;
    }
    _Py_FOR_EACH_TSTATE_END(interp);
    return 0;
}

struct get_code_args {
    _PyObjectStack code_objs;
    struct flag_set indices_in_use;
    int err;
};

static void
clear_get_code_args(struct get_code_args *args)
{
    if (args->indices_in_use.flags != NULL) {
        PyMem_Free(args->indices_in_use.flags);
        args->indices_in_use.flags = NULL;
    }
    _PyObjectStack_Clear(&args->code_objs);
}

static inline int
is_bytecode_unused(_PyCodeArray *tlbc, Py_ssize_t idx,
                   struct flag_set *indices_in_use)
{
    assert(idx > 0 && idx < tlbc->size);
    return tlbc->entries[idx] != NULL && !flag_is_set(indices_in_use, idx);
}

static int
get_code_with_unused_tlbc(PyObject *obj, struct get_code_args *args)
{
    if (!PyCode_Check(obj)) {
        return 1;
    }
    PyCodeObject *co = (PyCodeObject *) obj;
    _PyCodeArray *tlbc = co->co_tlbc;
    // The first index always points at the main copy of the bytecode embedded
    // in the code object.
    for (Py_ssize_t i = 1; i < tlbc->size; i++) {
        if (is_bytecode_unused(tlbc, i, &args->indices_in_use)) {
            if (_PyObjectStack_Push(&args->code_objs, obj) < 0) {
                args->err = -1;
                return 0;
            }
            return 1;
        }
    }
    return 1;
}

static void
free_unused_bytecode(PyCodeObject *co, struct flag_set *indices_in_use)
{
    _PyCodeArray *tlbc = co->co_tlbc;
    // The first index always points at the main copy of the bytecode embedded
    // in the code object.
    for (Py_ssize_t i = 1; i < tlbc->size; i++) {
        if (is_bytecode_unused(tlbc, i, indices_in_use)) {
            PyMem_Free(tlbc->entries[i]);
            tlbc->entries[i] = NULL;
        }
    }
}

int
_Py_ClearUnusedTLBC(PyInterpreterState *interp)
{
    struct get_code_args args = {
        .code_objs = {NULL},
        .indices_in_use = {NULL, 0},
        .err = 0,
    };
    _PyEval_StopTheWorld(interp);
    // Collect in-use tlbc indices
    if (get_indices_in_use(interp, &args.indices_in_use) < 0) {
        goto err;
    }
    // Collect code objects that have bytecode not in use by any thread
    _PyGC_VisitObjectsWorldStopped(
        interp, (gcvisitobjects_t)get_code_with_unused_tlbc, &args);
    if (args.err < 0) {
        goto err;
    }
    // Free unused bytecode. This must happen outside of gc_visit_heaps; it is
    // unsafe to allocate or free any mimalloc managed memory when it's
    // running.
    PyObject *obj;
    while ((obj = _PyObjectStack_Pop(&args.code_objs)) != NULL) {
        free_unused_bytecode((PyCodeObject*) obj, &args.indices_in_use);
    }
    _PyEval_StartTheWorld(interp);
    clear_get_code_args(&args);
    return 0;

err:
    _PyEval_StartTheWorld(interp);
    clear_get_code_args(&args);
    PyErr_NoMemory();
    return -1;
}

#endif