bpo-29469: Move constant folding to AST optimizer (GH-2858)

1 files changed, 649 insertions, 0 deletions

diff --git a/Python/ast_opt.c b/Python/ast_opt.c
new file mode 100644
index 0000000..80531cc
--- /dev/null
+++ b/Python/ast_opt.c
@@ -0,0 +1,649 @@
+/* AST Optimizer */
+#include "Python.h"
+#include "Python-ast.h"
+
+
+/* TODO: is_const and get_const_value are copied from Python/compile.c.
+   It should be deduped in the future.  Maybe, we can include this file
+   from compile.c?
+*/
+static int
+is_const(expr_ty e)
+{
+    switch (e->kind) {
+    case Constant_kind:
+    case Num_kind:
+    case Str_kind:
+    case Bytes_kind:
+    case Ellipsis_kind:
+    case NameConstant_kind:
+        return 1;
+    default:
+        return 0;
+    }
+}
+
+static PyObject *
+get_const_value(expr_ty e)
+{
+    switch (e->kind) {
+    case Constant_kind:
+        return e->v.Constant.value;
+    case Num_kind:
+        return e->v.Num.n;
+    case Str_kind:
+        return e->v.Str.s;
+    case Bytes_kind:
+        return e->v.Bytes.s;
+    case Ellipsis_kind:
+        return Py_Ellipsis;
+    case NameConstant_kind:
+        return e->v.NameConstant.value;
+    default:
+        Py_UNREACHABLE();
+    }
+}
+
+static int
+make_const(expr_ty node, PyObject *val, PyArena *arena)
+{
+    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.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)
+{
+    expr_ty arg = node->v.UnaryOp.operand;
+
+    if (!is_const(arg)) {
+        /* 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. */
+            int 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;
+            default:
+                op = 0;
+            }
+            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](get_const_value(arg));
+    return make_const(node, newval, arena);
+}
+
+static int
+fold_binop(expr_ty node, PyArena *arena)
+{
+    expr_ty lhs, rhs;
+    lhs = node->v.BinOp.left;
+    rhs = node->v.BinOp.right;
+    if (!is_const(lhs) || !is_const(rhs)) {
+        return 1;
+    }
+
+    PyObject *lv = get_const_value(lhs);
+    PyObject *rv = get_const_value(rhs);
+    PyObject *newval;
+
+    switch (node->v.BinOp.op) {
+    case Add:
+        newval = PyNumber_Add(lv, rv);
+        break;
+    case Sub:
+        newval = PyNumber_Subtract(lv, rv);
+        break;
+    case Mult:
+        newval = PyNumber_Multiply(lv, rv);
+        break;
+    case Div:
+        newval = PyNumber_TrueDivide(lv, rv);
+        break;
+    case FloorDiv:
+        newval = PyNumber_FloorDivide(lv, rv);
+        break;
+    case Mod:
+        newval = PyNumber_Remainder(lv, rv);
+        break;
+    case Pow:
+        newval = PyNumber_Power(lv, rv, Py_None);
+        break;
+    case LShift:
+        newval = PyNumber_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;
+    default: // Unknown operator
+        return 1;
+    }
+
+    if (newval == NULL) {
+        if (PyErr_ExceptionMatches(PyExc_KeyboardInterrupt)) {
+            return 0;
+        }
+        PyErr_Clear();
+        return 1;
+    }
+
+    /* Avoid creating large constants. */
+    Py_ssize_t size = PyObject_Size(newval);
+    if (size == -1) {
+        if (PyErr_ExceptionMatches(PyExc_KeyboardInterrupt)) {
+            Py_DECREF(newval);
+            return 0;
+        }
+        PyErr_Clear();
+    }
+    else if (size > 20) {
+        Py_DECREF(newval);
+        return 1;
+    }
+    return make_const(node, newval, arena);
+}
+
+static PyObject*
+make_const_tuple(asdl_seq *elts, int make_set)
+{
+    for (int i = 0; i < asdl_seq_LEN(elts); i++) {
+        expr_ty e = (expr_ty)asdl_seq_GET(elts, i);
+        if (!is_const(e)) {
+            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 = get_const_value(e);
+        Py_INCREF(v);
+        PyTuple_SET_ITEM(newval, i, v);
+    }
+
+    /* Need to create frozen_set instead. */
+    if (make_set) {
+        Py_SETREF(newval, PyFrozenSet_New(newval));
+    }
+    return newval;
+}
+
+static int
+fold_tuple(expr_ty node, PyArena *arena)
+{
+    PyObject *newval;
+
+    if (node->v.Tuple.ctx != Load)
+        return 1;
+
+    newval = make_const_tuple(node->v.Tuple.elts, 0);
+    return make_const(node, newval, arena);
+}
+
+static int
+fold_subscr(expr_ty node, PyArena *arena)
+{
+    PyObject *newval;
+    expr_ty arg, idx;
+    slice_ty slice;
+
+    arg = node->v.Subscript.value;
+    slice = node->v.Subscript.slice;
+    if (node->v.Subscript.ctx != Load ||
+            !is_const(arg) ||
+            /* TODO: handle other types of slices */
+            slice->kind != Index_kind ||
+            !is_const(slice->v.Index.value))
+    {
+        return 1;
+    }
+
+    idx = slice->v.Index.value;
+    newval = PyObject_GetItem(get_const_value(arg), get_const_value(idx));
+    return make_const(node, newval, arena);
+}
+
+static int
+fold_compare(expr_ty node, PyArena *arena)
+{
+    asdl_int_seq *ops;
+    asdl_seq *args;
+    PyObject *newval;
+    int i;
+
+    ops = node->v.Compare.ops;
+    args = node->v.Compare.comparators;
+    /* TODO: optimize cases with literal arguments. */
+    for (i = 0; i < asdl_seq_LEN(ops); i++) {
+        int op;
+        expr_ty arg;
+        asdl_seq *elts;
+
+        op = asdl_seq_GET(ops, i);
+        arg = (expr_ty)asdl_seq_GET(args, i);
+        /* Change literal list or set in 'in' or 'not in' into
+           tuple or frozenset respectively. */
+        /* TODO: do the same when list or set is used as iterable
+           in for loop and comprehensions? */
+        if (op != In && op != NotIn)
+            continue;
+        if (arg->kind == List_kind)
+            elts = arg->v.List.elts;
+        else if (arg->kind == Set_kind)
+            elts = arg->v.Set.elts;
+        else continue;
+
+        newval = make_const_tuple(elts, arg->kind == Set_kind);
+        make_const(arg, newval, arena);
+    }
+    return 1;
+}
+
+static int astfold_mod(mod_ty node_, PyArena* ctx_);
+static int astfold_stmt(stmt_ty node_, PyArena* ctx_);
+static int astfold_expr(expr_ty node_, PyArena* ctx_);
+static int astfold_arguments(arguments_ty node_, PyArena* ctx_);
+static int astfold_comprehension(comprehension_ty node_, PyArena* ctx_);
+static int astfold_keyword(keyword_ty node_, PyArena* ctx_);
+static int astfold_slice(slice_ty node_, PyArena* ctx_);
+static int astfold_arg(arg_ty node_, PyArena* ctx_);
+static int astfold_withitem(withitem_ty node_, PyArena* ctx_);
+static int astfold_excepthandler(excepthandler_ty node_, PyArena* ctx_);
+#define CALL(FUNC, TYPE, ARG) \
+    if (!FUNC((ARG), ctx_)) \
+        return 0;
+
+#define CALL_OPT(FUNC, TYPE, ARG) \
+    if ((ARG) != NULL && !FUNC((ARG), ctx_)) \
+        return 0;
+
+#define CALL_SEQ(FUNC, TYPE, ARG) { \
+    int i; \
+    asdl_seq *seq = (ARG); /* avoid variable capture */ \
+    for (i = 0; i < asdl_seq_LEN(seq); i++) { \
+        TYPE elt = (TYPE)asdl_seq_GET(seq, i); \
+        if (elt != NULL && !FUNC(elt, ctx_)) \
+            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_)) \
+            return 0; \
+    } \
+}
+
+static int
+astfold_mod(mod_ty node_, PyArena* ctx_)
+{
+    switch (node_->kind) {
+    case Module_kind:
+        CALL_SEQ(astfold_stmt, stmt_ty, node_->v.Module.body);
+        break;
+    case Interactive_kind:
+        CALL_SEQ(astfold_stmt, stmt_ty, node_->v.Interactive.body);
+        break;
+    case Expression_kind:
+        CALL(astfold_expr, expr_ty, node_->v.Expression.body);
+        break;
+    case Suite_kind:
+        CALL_SEQ(astfold_stmt, stmt_ty, node_->v.Suite.body);
+        break;
+    default:
+        break;
+    }
+    return 1;
+}
+
+static int
+astfold_expr(expr_ty node_, PyArena* ctx_)
+{
+    switch (node_->kind) {
+    case BoolOp_kind:
+        CALL_SEQ(astfold_expr, expr_ty, 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_ty, node_->v.Dict.keys);
+        CALL_SEQ(astfold_expr, expr_ty, node_->v.Dict.values);
+        break;
+    case Set_kind:
+        CALL_SEQ(astfold_expr, expr_ty, node_->v.Set.elts);
+        break;
+    case ListComp_kind:
+        CALL(astfold_expr, expr_ty, node_->v.ListComp.elt);
+        CALL_SEQ(astfold_comprehension, comprehension_ty, node_->v.ListComp.generators);
+        break;
+    case SetComp_kind:
+        CALL(astfold_expr, expr_ty, node_->v.SetComp.elt);
+        CALL_SEQ(astfold_comprehension, comprehension_ty, 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_ty, node_->v.DictComp.generators);
+        break;
+    case GeneratorExp_kind:
+        CALL(astfold_expr, expr_ty, node_->v.GeneratorExp.elt);
+        CALL_SEQ(astfold_comprehension, comprehension_ty, 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_ty, 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_ty, node_->v.Call.args);
+        CALL_SEQ(astfold_keyword, keyword_ty, 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_ty, 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_slice, slice_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 List_kind:
+        CALL_SEQ(astfold_expr, expr_ty, node_->v.List.elts);
+        break;
+    case Tuple_kind:
+        CALL_SEQ(astfold_expr, expr_ty, node_->v.Tuple.elts);
+        CALL(fold_tuple, expr_ty, node_);
+        break;
+    default:
+        break;
+    }
+    return 1;
+}
+
+static int
+astfold_slice(slice_ty node_, PyArena* ctx_)
+{
+    switch (node_->kind) {
+    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 ExtSlice_kind:
+        CALL_SEQ(astfold_slice, slice_ty, node_->v.ExtSlice.dims);
+        break;
+    case Index_kind:
+        CALL(astfold_expr, expr_ty, node_->v.Index.value);
+        break;
+    default:
+        break;
+    }
+    return 1;
+}
+
+static int
+astfold_keyword(keyword_ty node_, PyArena* ctx_)
+{
+    CALL(astfold_expr, expr_ty, node_->value);
+    return 1;
+}
+
+static int
+astfold_comprehension(comprehension_ty node_, PyArena* ctx_)
+{
+    CALL(astfold_expr, expr_ty, node_->target);
+    CALL(astfold_expr, expr_ty, node_->iter);
+    CALL_SEQ(astfold_expr, expr_ty, node_->ifs);
+    return 1;
+}
+
+static int
+astfold_arguments(arguments_ty node_, PyArena* ctx_)
+{
+    CALL_SEQ(astfold_arg, arg_ty, node_->args);
+    CALL_OPT(astfold_arg, arg_ty, node_->vararg);
+    CALL_SEQ(astfold_arg, arg_ty, node_->kwonlyargs);
+    CALL_SEQ(astfold_expr, expr_ty, node_->kw_defaults);
+    CALL_OPT(astfold_arg, arg_ty, node_->kwarg);
+    CALL_SEQ(astfold_expr, expr_ty, node_->defaults);
+    return 1;
+}
+
+static int
+astfold_arg(arg_ty node_, PyArena* ctx_)
+{
+    CALL_OPT(astfold_expr, expr_ty, node_->annotation);
+    return 1;
+}
+
+static int
+astfold_stmt(stmt_ty node_, PyArena* ctx_)
+{
+    switch (node_->kind) {
+    case FunctionDef_kind:
+        CALL(astfold_arguments, arguments_ty, node_->v.FunctionDef.args);
+        CALL_SEQ(astfold_stmt, stmt_ty, node_->v.FunctionDef.body);
+        CALL_SEQ(astfold_expr, expr_ty, node_->v.FunctionDef.decorator_list);
+        CALL_OPT(astfold_expr, expr_ty, node_->v.FunctionDef.returns);
+        break;
+    case AsyncFunctionDef_kind:
+        CALL(astfold_arguments, arguments_ty, node_->v.AsyncFunctionDef.args);
+        CALL_SEQ(astfold_stmt, stmt_ty, node_->v.AsyncFunctionDef.body);
+        CALL_SEQ(astfold_expr, expr_ty, node_->v.AsyncFunctionDef.decorator_list);
+        CALL_OPT(astfold_expr, expr_ty, node_->v.AsyncFunctionDef.returns);
+        break;
+    case ClassDef_kind:
+        CALL_SEQ(astfold_expr, expr_ty, node_->v.ClassDef.bases);
+        CALL_SEQ(astfold_keyword, keyword_ty, node_->v.ClassDef.keywords);
+        CALL_SEQ(astfold_stmt, stmt_ty, node_->v.ClassDef.body);
+        CALL_SEQ(astfold_expr, expr_ty, 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_ty, node_->v.Delete.targets);
+        break;
+    case Assign_kind:
+        CALL_SEQ(astfold_expr, expr_ty, 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);
+        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_ty, node_->v.For.body);
+        CALL_SEQ(astfold_stmt, stmt_ty, node_->v.For.orelse);
+        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_ty, node_->v.AsyncFor.body);
+        CALL_SEQ(astfold_stmt, stmt_ty, node_->v.AsyncFor.orelse);
+        break;
+    case While_kind:
+        CALL(astfold_expr, expr_ty, node_->v.While.test);
+        CALL_SEQ(astfold_stmt, stmt_ty, node_->v.While.body);
+        CALL_SEQ(astfold_stmt, stmt_ty, node_->v.While.orelse);
+        break;
+    case If_kind:
+        CALL(astfold_expr, expr_ty, node_->v.If.test);
+        CALL_SEQ(astfold_stmt, stmt_ty, node_->v.If.body);
+        CALL_SEQ(astfold_stmt, stmt_ty, node_->v.If.orelse);
+        break;
+    case With_kind:
+        CALL_SEQ(astfold_withitem, withitem_ty, node_->v.With.items);
+        CALL_SEQ(astfold_stmt, stmt_ty, node_->v.With.body);
+        break;
+    case AsyncWith_kind:
+        CALL_SEQ(astfold_withitem, withitem_ty, node_->v.AsyncWith.items);
+        CALL_SEQ(astfold_stmt, stmt_ty, 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_ty, node_->v.Try.body);
+        CALL_SEQ(astfold_excepthandler, excepthandler_ty, node_->v.Try.handlers);
+        CALL_SEQ(astfold_stmt, stmt_ty, node_->v.Try.orelse);
+        CALL_SEQ(astfold_stmt, stmt_ty, 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;
+    default:
+        break;
+    }
+    return 1;
+}
+
+static int
+astfold_excepthandler(excepthandler_ty node_, PyArena* ctx_)
+{
+    switch (node_->kind) {
+    case ExceptHandler_kind:
+        CALL_OPT(astfold_expr, expr_ty, node_->v.ExceptHandler.type);
+        CALL_SEQ(astfold_stmt, stmt_ty, node_->v.ExceptHandler.body);
+        break;
+    default:
+        break;
+    }
+    return 1;
+}
+
+static int
+astfold_withitem(withitem_ty node_, PyArena* ctx_)
+{
+    CALL(astfold_expr, expr_ty, node_->context_expr);
+    CALL_OPT(astfold_expr, expr_ty, node_->optional_vars);
+    return 1;
+}
+
+#undef CALL
+#undef CALL_OPT
+#undef CALL_SEQ
+#undef CALL_INT_SEQ
+
+int
+_PyAST_Optimize(mod_ty mod, PyArena *arena)
+{
+    int ret = astfold_mod(mod, arena);
+    assert(ret || PyErr_Occurred());
+    return ret;
+}