Python/ast_opt.c

/* AST Optimizer */
#include "Python.h"
#include "pycore_ast.h"           // _PyAST_GetDocString()
#include "pycore_compile.h"       // _PyASTOptimizeState
#include "pycore_pystate.h"       // _PyThreadState_GET()


static int
make_const(expr_ty node, PyObject *val, PyArena *arena)
{
    // Even if no new value was calculated, make_const may still
    // need to clear an error (e.g. for division by zero)
    if (val == NULL) {
        if (PyErr_ExceptionMatches(PyExc_KeyboardInterrupt)) {
            return 0;
        }
        PyErr_Clear();
        return 1;
    }
    if (_PyArena_AddPyObject(arena, val) < 0) {
        Py_DECREF(val);
        return 0;
    }
    node->kind = Constant_kind;
    node->v.Constant.kind = NULL;
    node->v.Constant.value = val;
    return 1;
}

#define COPY_NODE(TO, FROM) (memcpy((TO), (FROM), sizeof(struct _expr)))

static PyObject*
unary_not(PyObject *v)
{
    int r = PyObject_IsTrue(v);
    if (r < 0)
        return NULL;
    return PyBool_FromLong(!r);
}

static int
fold_unaryop(expr_ty node, PyArena *arena, _PyASTOptimizeState *state)
{
    expr_ty arg = node->v.UnaryOp.operand;

    if (arg->kind != Constant_kind) {
        /* Fold not into comparison */
        if (node->v.UnaryOp.op == Not && arg->kind == Compare_kind &&
                asdl_seq_LEN(arg->v.Compare.ops) == 1) {
            /* Eq and NotEq are often implemented in terms of one another, so
               folding not (self == other) into self != other breaks implementation
               of !=. Detecting such cases doesn't seem worthwhile.
               Python uses </> for 'is subset'/'is superset' operations on sets.
               They don't satisfy not folding laws. */
            cmpop_ty op = asdl_seq_GET(arg->v.Compare.ops, 0);
            switch (op) {
            case Is:
                op = IsNot;
                break;
            case IsNot:
                op = Is;
                break;
            case In:
                op = NotIn;
                break;
            case NotIn:
                op = In;
                break;
            // The remaining comparison operators can't be safely inverted
            case Eq:
            case NotEq:
            case Lt:
            case LtE:
            case Gt:
            case GtE:
                op = 0; // The AST enums leave "0" free as an "unused" marker
                break;
            // No default case, so the compiler will emit a warning if new
            // comparison operators are added without being handled here
            }
            if (op) {
                asdl_seq_SET(arg->v.Compare.ops, 0, op);
                COPY_NODE(node, arg);
                return 1;
            }
        }
        return 1;
    }

    typedef PyObject *(*unary_op)(PyObject*);
    static const unary_op ops[] = {
        [Invert] = PyNumber_Invert,
        [Not] = unary_not,
        [UAdd] = PyNumber_Positive,
        [USub] = PyNumber_Negative,
    };
    PyObject *newval = ops[node->v.UnaryOp.op](arg->v.Constant.value);
    return make_const(node, newval, arena);
}

/* Check whether a collection doesn't containing too much items (including
   subcollections).  This protects from creating a constant that needs
   too much time for calculating a hash.
   "limit" is the maximal number of items.
   Returns the negative number if the total number of items exceeds the
   limit.  Otherwise returns the limit minus the total number of items.
*/

static Py_ssize_t
check_complexity(PyObject *obj, Py_ssize_t limit)
{
    if (PyTuple_Check(obj)) {
        Py_ssize_t i;
        limit -= PyTuple_GET_SIZE(obj);
        for (i = 0; limit >= 0 && i < PyTuple_GET_SIZE(obj); i++) {
            limit = check_complexity(PyTuple_GET_ITEM(obj, i), limit);
        }
        return limit;
    }
    else if (PyFrozenSet_Check(obj)) {
        Py_ssize_t i = 0;
        PyObject *item;
        Py_hash_t hash;
        limit -= PySet_GET_SIZE(obj);
        while (limit >= 0 && _PySet_NextEntry(obj, &i, &item, &hash)) {
            limit = check_complexity(item, limit);
        }
    }
    return limit;
}

#define MAX_INT_SIZE           128  /* bits */
#define MAX_COLLECTION_SIZE    256  /* items */
#define MAX_STR_SIZE          4096  /* characters */
#define MAX_TOTAL_ITEMS       1024  /* including nested collections */

static PyObject *
safe_multiply(PyObject *v, PyObject *w)
{
    if (PyLong_Check(v) && PyLong_Check(w) && Py_SIZE(v) && Py_SIZE(w)) {
        size_t vbits = _PyLong_NumBits(v);
        size_t wbits = _PyLong_NumBits(w);
        if (vbits == (size_t)-1 || wbits == (size_t)-1) {
            return NULL;
        }
        if (vbits + wbits > MAX_INT_SIZE) {
            return NULL;
        }
    }
    else if (PyLong_Check(v) && (PyTuple_Check(w) || PyFrozenSet_Check(w))) {
        Py_ssize_t size = PyTuple_Check(w) ? PyTuple_GET_SIZE(w) :
                                             PySet_GET_SIZE(w);
        if (size) {
            long n = PyLong_AsLong(v);
            if (n < 0 || n > MAX_COLLECTION_SIZE / size) {
                return NULL;
            }
            if (n && check_complexity(w, MAX_TOTAL_ITEMS / n) < 0) {
                return NULL;
            }
        }
    }
    else if (PyLong_Check(v) && (PyUnicode_Check(w) || PyBytes_Check(w))) {
        Py_ssize_t size = PyUnicode_Check(w) ? PyUnicode_GET_LENGTH(w) :
                                               PyBytes_GET_SIZE(w);
        if (size) {
            long n = PyLong_AsLong(v);
            if (n < 0 || n > MAX_STR_SIZE / size) {
                return NULL;
            }
        }
    }
    else if (PyLong_Check(w) &&
             (PyTuple_Check(v) || PyFrozenSet_Check(v) ||
              PyUnicode_Check(v) || PyBytes_Check(v)))
    {
        return safe_multiply(w, v);
    }

    return PyNumber_Multiply(v, w);
}

static PyObject *
safe_power(PyObject *v, PyObject *w)
{
    if (PyLong_Check(v) && PyLong_Check(w) && Py_SIZE(v) && Py_SIZE(w) > 0) {
        size_t vbits = _PyLong_NumBits(v);
        size_t wbits = PyLong_AsSize_t(w);
        if (vbits == (size_t)-1 || wbits == (size_t)-1) {
            return NULL;
        }
        if (vbits > MAX_INT_SIZE / wbits) {
            return NULL;
        }
    }

    return PyNumber_Power(v, w, Py_None);
}

static PyObject *
safe_lshift(PyObject *v, PyObject *w)
{
    if (PyLong_Check(v) && PyLong_Check(w) && Py_SIZE(v) && Py_SIZE(w)) {
        size_t vbits = _PyLong_NumBits(v);
        size_t wbits = PyLong_AsSize_t(w);
        if (vbits == (size_t)-1 || wbits == (size_t)-1) {
            return NULL;
        }
        if (wbits > MAX_INT_SIZE || vbits > MAX_INT_SIZE - wbits) {
            return NULL;
        }
    }

    return PyNumber_Lshift(v, w);
}

static PyObject *
safe_mod(PyObject *v, PyObject *w)
{
    if (PyUnicode_Check(v) || PyBytes_Check(v)) {
        return NULL;
    }

    return PyNumber_Remainder(v, w);
}

static int
fold_binop(expr_ty node, PyArena *arena, _PyASTOptimizeState *state)
{
    expr_ty lhs, rhs;
    lhs = node->v.BinOp.left;
    rhs = node->v.BinOp.right;
    if (lhs->kind != Constant_kind || rhs->kind != Constant_kind) {
        return 1;
    }

    PyObject *lv = lhs->v.Constant.value;
    PyObject *rv = rhs->v.Constant.value;
    PyObject *newval = NULL;

    switch (node->v.BinOp.op) {
    case Add:
        newval = PyNumber_Add(lv, rv);
        break;
    case Sub:
        newval = PyNumber_Subtract(lv, rv);
        break;
    case Mult:
        newval = safe_multiply(lv, rv);
        break;
    case Div:
        newval = PyNumber_TrueDivide(lv, rv);
        break;
    case FloorDiv:
        newval = PyNumber_FloorDivide(lv, rv);
        break;
    case Mod:
        newval = safe_mod(lv, rv);
        break;
    case Pow:
        newval = safe_power(lv, rv);
        break;
    case LShift:
        newval = safe_lshift(lv, rv);
        break;
    case RShift:
        newval = PyNumber_Rshift(lv, rv);
        break;
    case BitOr:
        newval = PyNumber_Or(lv, rv);
        break;
    case BitXor:
        newval = PyNumber_Xor(lv, rv);
        break;
    case BitAnd:
        newval = PyNumber_And(lv, rv);
        break;
    // No builtin constants implement the following operators
    case MatMult:
        return 1;
    // No default case, so the compiler will emit a warning if new binary
    // operators are added without being handled here
    }

    return make_const(node, newval, arena);
}

static PyObject*
make_const_tuple(asdl_expr_seq *elts)
{
    for (int i = 0; i < asdl_seq_LEN(elts); i++) {
        expr_ty e = (expr_ty)asdl_seq_GET(elts, i);
        if (e->kind != Constant_kind) {
            return NULL;
        }
    }

    PyObject *newval = PyTuple_New(asdl_seq_LEN(elts));
    if (newval == NULL) {
        return NULL;
    }

    for (int i = 0; i < asdl_seq_LEN(elts); i++) {
        expr_ty e = (expr_ty)asdl_seq_GET(elts, i);
        PyObject *v = e->v.Constant.value;
        Py_INCREF(v);
        PyTuple_SET_ITEM(newval, i, v);
    }
    return newval;
}

static int
fold_tuple(expr_ty node, PyArena *arena, _PyASTOptimizeState *state)
{
    PyObject *newval;

    if (node->v.Tuple.ctx != Load)
        return 1;

    newval = make_const_tuple(node->v.Tuple.elts);
    return make_const(node, newval, arena);
}

static int
fold_subscr(expr_ty node, PyArena *arena, _PyASTOptimizeState *state)
{
    PyObject *newval;
    expr_ty arg, idx;

    arg = node->v.Subscript.value;
    idx = node->v.Subscript.slice;
    if (node->v.Subscript.ctx != Load ||
            arg->kind != Constant_kind ||
            idx->kind != Constant_kind)
    {
        return 1;
    }

    newval = PyObject_GetItem(arg->v.Constant.value, idx->v.Constant.value);
    return make_const(node, newval, arena);
}

/* Change literal list or set of constants into constant
   tuple or frozenset respectively.  Change literal list of
   non-constants into tuple.
   Used for right operand of "in" and "not in" tests and for iterable
   in "for" loop and comprehensions.
*/
static int
fold_iter(expr_ty arg, PyArena *arena, _PyASTOptimizeState *state)
{
    PyObject *newval;
    if (arg->kind == List_kind) {
        /* First change a list into tuple. */
        asdl_expr_seq *elts = arg->v.List.elts;
        Py_ssize_t n = asdl_seq_LEN(elts);
        for (Py_ssize_t i = 0; i < n; i++) {
            expr_ty e = (expr_ty)asdl_seq_GET(elts, i);
            if (e->kind == Starred_kind) {
                return 1;
            }
        }
        expr_context_ty ctx = arg->v.List.ctx;
        arg->kind = Tuple_kind;
        arg->v.Tuple.elts = elts;
        arg->v.Tuple.ctx = ctx;
        /* Try to create a constant tuple. */
        newval = make_const_tuple(elts);
    }
    else if (arg->kind == Set_kind) {
        newval = make_const_tuple(arg->v.Set.elts);
        if (newval) {
            Py_SETREF(newval, PyFrozenSet_New(newval));
        }
    }
    else {
        return 1;
    }
    return make_const(arg, newval, arena);
}

static int
fold_compare(expr_ty node, PyArena *arena, _PyASTOptimizeState *state)
{
    asdl_int_seq *ops;
    asdl_expr_seq *args;
    Py_ssize_t i;

    ops = node->v.Compare.ops;
    args = node->v.Compare.comparators;
    /* TODO: optimize cases with literal arguments. */
    /* Change literal list or set in 'in' or 'not in' into
       tuple or frozenset respectively. */
    i = asdl_seq_LEN(ops) - 1;
    int op = asdl_seq_GET(ops, i);
    if (op == In || op == NotIn) {
        if (!fold_iter((expr_ty)asdl_seq_GET(args, i), arena, state)) {
            return 0;
        }
    }
    return 1;
}

static int astfold_mod(mod_ty node_, PyArena *ctx_, _PyASTOptimizeState *state);
static int astfold_stmt(stmt_ty node_, PyArena *ctx_, _PyASTOptimizeState *state);
static int astfold_expr(expr_ty node_, PyArena *ctx_, _PyASTOptimizeState *state);
static int astfold_arguments(arguments_ty node_, PyArena *ctx_, _PyASTOptimizeState *state);
static int astfold_comprehension(comprehension_ty node_, PyArena *ctx_, _PyASTOptimizeState *state);
static int astfold_keyword(keyword_ty node_, PyArena *ctx_, _PyASTOptimizeState *state);
static int astfold_arg(arg_ty node_, PyArena *ctx_, _PyASTOptimizeState *state);
static int astfold_withitem(withitem_ty node_, PyArena *ctx_, _PyASTOptimizeState *state);
static int astfold_excepthandler(excepthandler_ty node_, PyArena *ctx_, _PyASTOptimizeState *state);
static int astfold_match_case(match_case_ty node_, PyArena *ctx_, _PyASTOptimizeState *state);
static int astfold_pattern(expr_ty node_, PyArena *ctx_, _PyASTOptimizeState *state);

#define CALL(FUNC, TYPE, ARG) \
    if (!FUNC((ARG), ctx_, state)) \
        return 0;

#define CALL_OPT(FUNC, TYPE, ARG) \
    if ((ARG) != NULL && !FUNC((ARG), ctx_, state)) \
        return 0;

#define CALL_SEQ(FUNC, TYPE, ARG) { \
    int i; \
    asdl_ ## TYPE ## _seq *seq = (ARG); /* avoid variable capture */ \
    for (i = 0; i < asdl_seq_LEN(seq); i++) { \
        TYPE ## _ty elt = (TYPE ## _ty)asdl_seq_GET(seq, i); \
        if (elt != NULL && !FUNC(elt, ctx_, state)) \
            return 0; \
    } \
}

#define CALL_INT_SEQ(FUNC, TYPE, ARG) { \
    int i; \
    asdl_int_seq *seq = (ARG); /* avoid variable capture */ \
    for (i = 0; i < asdl_seq_LEN(seq); i++) { \
        TYPE elt = (TYPE)asdl_seq_GET(seq, i); \
        if (!FUNC(elt, ctx_, state)) \
            return 0; \
    } \
}

static int
astfold_body(asdl_stmt_seq *stmts, PyArena *ctx_, _PyASTOptimizeState *state)
{
    int docstring = _PyAST_GetDocString(stmts) != NULL;
    CALL_SEQ(astfold_stmt, stmt, stmts);
    if (!docstring && _PyAST_GetDocString(stmts) != NULL) {
        stmt_ty st = (stmt_ty)asdl_seq_GET(stmts, 0);
        asdl_expr_seq *values = _Py_asdl_expr_seq_new(1, ctx_);
        if (!values) {
            return 0;
        }
        asdl_seq_SET(values, 0, st->v.Expr.value);
        expr_ty expr = _PyAST_JoinedStr(values, st->lineno, st->col_offset,
                                        st->end_lineno, st->end_col_offset,
                                        ctx_);
        if (!expr) {
            return 0;
        }
        st->v.Expr.value = expr;
    }
    return 1;
}

static int
astfold_mod(mod_ty node_, PyArena *ctx_, _PyASTOptimizeState *state)
{
    switch (node_->kind) {
    case Module_kind:
        CALL(astfold_body, asdl_seq, node_->v.Module.body);
        break;
    case Interactive_kind:
        CALL_SEQ(astfold_stmt, stmt, node_->v.Interactive.body);
        break;
    case Expression_kind:
        CALL(astfold_expr, expr_ty, node_->v.Expression.body);
        break;
    // The following top level nodes don't participate in constant folding
    case FunctionType_kind:
        break;
    // No default case, so the compiler will emit a warning if new top level
    // compilation nodes are added without being handled here
    }
    return 1;
}

static int
astfold_expr(expr_ty node_, PyArena *ctx_, _PyASTOptimizeState *state)
{
    if (++state->recursion_depth > state->recursion_limit) {
        PyErr_SetString(PyExc_RecursionError,
                        "maximum recursion depth exceeded during compilation");
        return 0;
    }
    switch (node_->kind) {
    case BoolOp_kind:
        CALL_SEQ(astfold_expr, expr, node_->v.BoolOp.values);
        break;
    case BinOp_kind:
        CALL(astfold_expr, expr_ty, node_->v.BinOp.left);
        CALL(astfold_expr, expr_ty, node_->v.BinOp.right);
        CALL(fold_binop, expr_ty, node_);
        break;
    case UnaryOp_kind:
        CALL(astfold_expr, expr_ty, node_->v.UnaryOp.operand);
        CALL(fold_unaryop, expr_ty, node_);
        break;
    case Lambda_kind:
        CALL(astfold_arguments, arguments_ty, node_->v.Lambda.args);
        CALL(astfold_expr, expr_ty, node_->v.Lambda.body);
        break;
    case IfExp_kind:
        CALL(astfold_expr, expr_ty, node_->v.IfExp.test);
        CALL(astfold_expr, expr_ty, node_->v.IfExp.body);
        CALL(astfold_expr, expr_ty, node_->v.IfExp.orelse);
        break;
    case Dict_kind:
        CALL_SEQ(astfold_expr, expr, node_->v.Dict.keys);
        CALL_SEQ(astfold_expr, expr, node_->v.Dict.values);
        break;
    case Set_kind:
        CALL_SEQ(astfold_expr, expr, node_->v.Set.elts);
        break;
    case ListComp_kind:
        CALL(astfold_expr, expr_ty, node_->v.ListComp.elt);
        CALL_SEQ(astfold_comprehension, comprehension, node_->v.ListComp.generators);
        break;
    case SetComp_kind:
        CALL(astfold_expr, expr_ty, node_->v.SetComp.elt);
        CALL_SEQ(astfold_comprehension, comprehension, node_->v.SetComp.generators);
        break;
    case DictComp_kind:
        CALL(astfold_expr, expr_ty, node_->v.DictComp.key);
        CALL(astfold_expr, expr_ty, node_->v.DictComp.value);
        CALL_SEQ(astfold_comprehension, comprehension, node_->v.DictComp.generators);
        break;
    case GeneratorExp_kind:
        CALL(astfold_expr, expr_ty, node_->v.GeneratorExp.elt);
        CALL_SEQ(astfold_comprehension, comprehension, node_->v.GeneratorExp.generators);
        break;
    case Await_kind:
        CALL(astfold_expr, expr_ty, node_->v.Await.value);
        break;
    case Yield_kind:
        CALL_OPT(astfold_expr, expr_ty, node_->v.Yield.value);
        break;
    case YieldFrom_kind:
        CALL(astfold_expr, expr_ty, node_->v.YieldFrom.value);
        break;
    case Compare_kind:
        CALL(astfold_expr, expr_ty, node_->v.Compare.left);
        CALL_SEQ(astfold_expr, expr, node_->v.Compare.comparators);
        CALL(fold_compare, expr_ty, node_);
        break;
    case Call_kind:
        CALL(astfold_expr, expr_ty, node_->v.Call.func);
        CALL_SEQ(astfold_expr, expr, node_->v.Call.args);
        CALL_SEQ(astfold_keyword, keyword, node_->v.Call.keywords);
        break;
    case FormattedValue_kind:
        CALL(astfold_expr, expr_ty, node_->v.FormattedValue.value);
        CALL_OPT(astfold_expr, expr_ty, node_->v.FormattedValue.format_spec);
        break;
    case JoinedStr_kind:
        CALL_SEQ(astfold_expr, expr, node_->v.JoinedStr.values);
        break;
    case Attribute_kind:
        CALL(astfold_expr, expr_ty, node_->v.Attribute.value);
        break;
    case Subscript_kind:
        CALL(astfold_expr, expr_ty, node_->v.Subscript.value);
        CALL(astfold_expr, expr_ty, node_->v.Subscript.slice);
        CALL(fold_subscr, expr_ty, node_);
        break;
    case Starred_kind:
        CALL(astfold_expr, expr_ty, node_->v.Starred.value);
        break;
    case Slice_kind:
        CALL_OPT(astfold_expr, expr_ty, node_->v.Slice.lower);
        CALL_OPT(astfold_expr, expr_ty, node_->v.Slice.upper);
        CALL_OPT(astfold_expr, expr_ty, node_->v.Slice.step);
        break;
    case List_kind:
        CALL_SEQ(astfold_expr, expr, node_->v.List.elts);
        break;
    case Tuple_kind:
        CALL_SEQ(astfold_expr, expr, node_->v.Tuple.elts);
        CALL(fold_tuple, expr_ty, node_);
        break;
    case Name_kind:
        if (node_->v.Name.ctx == Load &&
                _PyUnicode_EqualToASCIIString(node_->v.Name.id, "__debug__")) {
            state->recursion_depth--;
            return make_const(node_, PyBool_FromLong(!state->optimize), ctx_);
        }
        break;
    case NamedExpr_kind:
        CALL(astfold_expr, expr_ty, node_->v.NamedExpr.value);
        break;
    case Constant_kind:
        // Already a constant, nothing further to do
        break;
    case MatchAs_kind:
    case MatchOr_kind:
        // These can't occur outside of patterns.
        Py_UNREACHABLE();
    // No default case, so the compiler will emit a warning if new expression
    // kinds are added without being handled here
    }
    state->recursion_depth--;
    return 1;
}

static int
astfold_keyword(keyword_ty node_, PyArena *ctx_, _PyASTOptimizeState *state)
{
    CALL(astfold_expr, expr_ty, node_->value);
    return 1;
}

static int
astfold_comprehension(comprehension_ty node_, PyArena *ctx_, _PyASTOptimizeState *state)
{
    CALL(astfold_expr, expr_ty, node_->target);
    CALL(astfold_expr, expr_ty, node_->iter);
    CALL_SEQ(astfold_expr, expr, node_->ifs);

    CALL(fold_iter, expr_ty, node_->iter);
    return 1;
}

static int
astfold_arguments(arguments_ty node_, PyArena *ctx_, _PyASTOptimizeState *state)
{
    CALL_SEQ(astfold_arg, arg, node_->posonlyargs);
    CALL_SEQ(astfold_arg, arg, node_->args);
    CALL_OPT(astfold_arg, arg_ty, node_->vararg);
    CALL_SEQ(astfold_arg, arg, node_->kwonlyargs);
    CALL_SEQ(astfold_expr, expr, node_->kw_defaults);
    CALL_OPT(astfold_arg, arg_ty, node_->kwarg);
    CALL_SEQ(astfold_expr, expr, node_->defaults);
    return 1;
}

static int
astfold_arg(arg_ty node_, PyArena *ctx_, _PyASTOptimizeState *state)
{
    if (!(state->ff_features & CO_FUTURE_ANNOTATIONS)) {
        CALL_OPT(astfold_expr, expr_ty, node_->annotation);
    }
    return 1;
}

static int
astfold_stmt(stmt_ty node_, PyArena *ctx_, _PyASTOptimizeState *state)
{
    if (++state->recursion_depth > state->recursion_limit) {
        PyErr_SetString(PyExc_RecursionError,
                        "maximum recursion depth exceeded during compilation");
        return 0;
    }
    switch (node_->kind) {
    case FunctionDef_kind:
        CALL(astfold_arguments, arguments_ty, node_->v.FunctionDef.args);
        CALL(astfold_body, asdl_seq, node_->v.FunctionDef.body);
        CALL_SEQ(astfold_expr, expr, node_->v.FunctionDef.decorator_list);
        if (!(state->ff_features & CO_FUTURE_ANNOTATIONS)) {
            CALL_OPT(astfold_expr, expr_ty, node_->v.FunctionDef.returns);
        }
        break;
    case AsyncFunctionDef_kind:
        CALL(astfold_arguments, arguments_ty, node_->v.AsyncFunctionDef.args);
        CALL(astfold_body, asdl_seq, node_->v.AsyncFunctionDef.body);
        CALL_SEQ(astfold_expr, expr, node_->v.AsyncFunctionDef.decorator_list);
        if (!(state->ff_features & CO_FUTURE_ANNOTATIONS)) {
            CALL_OPT(astfold_expr, expr_ty, node_->v.AsyncFunctionDef.returns);
        }
        break;
    case ClassDef_kind:
        CALL_SEQ(astfold_expr, expr, node_->v.ClassDef.bases);
        CALL_SEQ(astfold_keyword, keyword, node_->v.ClassDef.keywords);
        CALL(astfold_body, asdl_seq, node_->v.ClassDef.body);
        CALL_SEQ(astfold_expr, expr, node_->v.ClassDef.decorator_list);
        break;
    case Return_kind:
        CALL_OPT(astfold_expr, expr_ty, node_->v.Return.value);
        break;
    case Delete_kind:
        CALL_SEQ(astfold_expr, expr, node_->v.Delete.targets);
        break;
    case Assign_kind:
        CALL_SEQ(astfold_expr, expr, node_->v.Assign.targets);
        CALL(astfold_expr, expr_ty, node_->v.Assign.value);
        break;
    case AugAssign_kind:
        CALL(astfold_expr, expr_ty, node_->v.AugAssign.target);
        CALL(astfold_expr, expr_ty, node_->v.AugAssign.value);
        break;
    case AnnAssign_kind:
        CALL(astfold_expr, expr_ty, node_->v.AnnAssign.target);
        if (!(state->ff_features & CO_FUTURE_ANNOTATIONS)) {
            CALL(astfold_expr, expr_ty, node_->v.AnnAssign.annotation);
        }
        CALL_OPT(astfold_expr, expr_ty, node_->v.AnnAssign.value);
        break;
    case For_kind:
        CALL(astfold_expr, expr_ty, node_->v.For.target);
        CALL(astfold_expr, expr_ty, node_->v.For.iter);
        CALL_SEQ(astfold_stmt, stmt, node_->v.For.body);
        CALL_SEQ(astfold_stmt, stmt, node_->v.For.orelse);

        CALL(fold_iter, expr_ty, node_->v.For.iter);
        break;
    case AsyncFor_kind:
        CALL(astfold_expr, expr_ty, node_->v.AsyncFor.target);
        CALL(astfold_expr, expr_ty, node_->v.AsyncFor.iter);
        CALL_SEQ(astfold_stmt, stmt, node_->v.AsyncFor.body);
        CALL_SEQ(astfold_stmt, stmt, node_->v.AsyncFor.orelse);
        break;
    case While_kind:
        CALL(astfold_expr, expr_ty, node_->v.While.test);
        CALL_SEQ(astfold_stmt, stmt, node_->v.While.body);
        CALL_SEQ(astfold_stmt, stmt, node_->v.While.orelse);
        break;
    case If_kind:
        CALL(astfold_expr, expr_ty, node_->v.If.test);
        CALL_SEQ(astfold_stmt, stmt, node_->v.If.body);
        CALL_SEQ(astfold_stmt, stmt, node_->v.If.orelse);
        break;
    case With_kind:
        CALL_SEQ(astfold_withitem, withitem, node_->v.With.items);
        CALL_SEQ(astfold_stmt, stmt, node_->v.With.body);
        break;
    case AsyncWith_kind:
        CALL_SEQ(astfold_withitem, withitem, node_->v.AsyncWith.items);
        CALL_SEQ(astfold_stmt, stmt, node_->v.AsyncWith.body);
        break;
    case Raise_kind:
        CALL_OPT(astfold_expr, expr_ty, node_->v.Raise.exc);
        CALL_OPT(astfold_expr, expr_ty, node_->v.Raise.cause);
        break;
    case Try_kind:
        CALL_SEQ(astfold_stmt, stmt, node_->v.Try.body);
        CALL_SEQ(astfold_excepthandler, excepthandler, node_->v.Try.handlers);
        CALL_SEQ(astfold_stmt, stmt, node_->v.Try.orelse);
        CALL_SEQ(astfold_stmt, stmt, node_->v.Try.finalbody);
        break;
    case Assert_kind:
        CALL(astfold_expr, expr_ty, node_->v.Assert.test);
        CALL_OPT(astfold_expr, expr_ty, node_->v.Assert.msg);
        break;
    case Expr_kind:
        CALL(astfold_expr, expr_ty, node_->v.Expr.value);
        break;
    case Match_kind:
        CALL(astfold_expr, expr_ty, node_->v.Match.subject);
        CALL_SEQ(astfold_match_case, match_case, node_->v.Match.cases);
        break;
    // The following statements don't contain any subexpressions to be folded
    case Import_kind:
    case ImportFrom_kind:
    case Global_kind:
    case Nonlocal_kind:
    case Pass_kind:
    case Break_kind:
    case Continue_kind:
        break;
    // No default case, so the compiler will emit a warning if new statement
    // kinds are added without being handled here
    }
    state->recursion_depth--;
    return 1;
}

static int
astfold_excepthandler(excepthandler_ty node_, PyArena *ctx_, _PyASTOptimizeState *state)
{
    switch (node_->kind) {
    case ExceptHandler_kind:
        CALL_OPT(astfold_expr, expr_ty, node_->v.ExceptHandler.type);
        CALL_SEQ(astfold_stmt, stmt, node_->v.ExceptHandler.body);
        break;
    // No default case, so the compiler will emit a warning if new handler
    // kinds are added without being handled here
    }
    return 1;
}

static int
astfold_withitem(withitem_ty node_, PyArena *ctx_, _PyASTOptimizeState *state)
{
    CALL(astfold_expr, expr_ty, node_->context_expr);
    CALL_OPT(astfold_expr, expr_ty, node_->optional_vars);
    return 1;
}

static int
astfold_pattern_negative(expr_ty node_, PyArena *ctx_, _PyASTOptimizeState *state)
{
    assert(node_->kind == UnaryOp_kind);
    assert(node_->v.UnaryOp.op == USub);
    assert(node_->v.UnaryOp.operand->kind == Constant_kind);
    PyObject *value = node_->v.UnaryOp.operand->v.Constant.value;
    assert(PyComplex_CheckExact(value) ||
           PyFloat_CheckExact(value) ||
           PyLong_CheckExact(value));
    PyObject *negated = PyNumber_Negative(value);
    if (negated == NULL) {
        return 0;
    }
    assert(PyComplex_CheckExact(negated) ||
           PyFloat_CheckExact(negated) ||
           PyLong_CheckExact(negated));
    return make_const(node_, negated, ctx_);
}

static int
astfold_pattern_complex(expr_ty node_, PyArena *ctx_, _PyASTOptimizeState *state)
{
    expr_ty left = node_->v.BinOp.left;
    expr_ty right = node_->v.BinOp.right;
    if (left->kind == UnaryOp_kind) {
        CALL(astfold_pattern_negative, expr_ty, left);
    }
    assert(left->kind = Constant_kind);
    assert(right->kind = Constant_kind);
    // LHS must be real, RHS must be imaginary:
    if (!(PyFloat_CheckExact(left->v.Constant.value) ||
          PyLong_CheckExact(left->v.Constant.value)) ||
        !PyComplex_CheckExact(right->v.Constant.value))
    {
        // Not actually valid, but it's the compiler's job to complain:
        return 1;
    }
    PyObject *new;
    if (node_->v.BinOp.op == Add) {
        new = PyNumber_Add(left->v.Constant.value, right->v.Constant.value);
    }
    else {
        assert(node_->v.BinOp.op == Sub);
        new = PyNumber_Subtract(left->v.Constant.value, right->v.Constant.value);
    }
    if (new == NULL) {
        return 0;
    }
    assert(PyComplex_CheckExact(new));
    return make_const(node_, new, ctx_);
}

static int
astfold_pattern_keyword(keyword_ty node_, PyArena *ctx_, _PyASTOptimizeState *state)
{
    CALL(astfold_pattern, expr_ty, node_->value);
    return 1;
}

static int
astfold_pattern(expr_ty node_, PyArena *ctx_, _PyASTOptimizeState *state)
{
    // Don't blindly optimize the pattern as an expr; it plays by its own rules!
    // Currently, this is only used to form complex/negative numeric constants.
    switch (node_->kind) {
        case Attribute_kind:
            break;
        case BinOp_kind:
            CALL(astfold_pattern_complex, expr_ty, node_);
            break;
        case Call_kind:
            CALL_SEQ(astfold_pattern, expr, node_->v.Call.args);
            CALL_SEQ(astfold_pattern_keyword, keyword, node_->v.Call.keywords);
            break;
        case Constant_kind:
            break;
        case Dict_kind:
            CALL_SEQ(astfold_pattern, expr, node_->v.Dict.keys);
            CALL_SEQ(astfold_pattern, expr, node_->v.Dict.values);
            break;
        // Not actually valid, but it's the compiler's job to complain:
        case JoinedStr_kind:
            break;
        case List_kind:
            CALL_SEQ(astfold_pattern, expr, node_->v.List.elts);
            break;
        case MatchAs_kind:
            CALL(astfold_pattern, expr_ty, node_->v.MatchAs.pattern);
            break;
        case MatchOr_kind:
            CALL_SEQ(astfold_pattern, expr, node_->v.MatchOr.patterns);
            break;
        case Name_kind:
            break;
        case Starred_kind:
            CALL(astfold_pattern, expr_ty, node_->v.Starred.value);
            break;
        case Tuple_kind:
            CALL_SEQ(astfold_pattern, expr, node_->v.Tuple.elts);
            break;
        case UnaryOp_kind:
            CALL(astfold_pattern_negative, expr_ty, node_);
            break;
        default:
            Py_UNREACHABLE();
    }
    return 1;
}

static int
astfold_match_case(match_case_ty node_, PyArena *ctx_, _PyASTOptimizeState *state)
{
    CALL(astfold_pattern, expr_ty, node_->pattern);
    CALL_OPT(astfold_expr, expr_ty, node_->guard);
    CALL_SEQ(astfold_stmt, stmt, node_->body);
    return 1;
}

#undef CALL
#undef CALL_OPT
#undef CALL_SEQ
#undef CALL_INT_SEQ

/* See comments in symtable.c. */
#define COMPILER_STACK_FRAME_SCALE 3

int
_PyAST_Optimize(mod_ty mod, PyArena *arena, _PyASTOptimizeState *state)
{
    PyThreadState *tstate;
    int recursion_limit = Py_GetRecursionLimit();
    int starting_recursion_depth;

    /* Setup recursion depth check counters */
    tstate = _PyThreadState_GET();
    if (!tstate) {
        return 0;
    }
    /* Be careful here to prevent overflow. */
    starting_recursion_depth = (tstate->recursion_depth < INT_MAX / COMPILER_STACK_FRAME_SCALE) ?
        tstate->recursion_depth * COMPILER_STACK_FRAME_SCALE : tstate->recursion_depth;
    state->recursion_depth = starting_recursion_depth;
    state->recursion_limit = (recursion_limit < INT_MAX / COMPILER_STACK_FRAME_SCALE) ?
        recursion_limit * COMPILER_STACK_FRAME_SCALE : recursion_limit;

    int ret = astfold_mod(mod, arena, state);
    assert(ret || PyErr_Occurred());

    /* Check that the recursion depth counting balanced correctly */
    if (ret && state->recursion_depth != starting_recursion_depth) {
        PyErr_Format(PyExc_SystemError,
            "AST optimizer recursion depth mismatch (before=%d, after=%d)",
            starting_recursion_depth, state->recursion_depth);
        return 0;
    }

    return ret;
}