2 use rustc_hir::def::DefKind;
3 use rustc_index::bit_set::BitSet;
4 use rustc_index::vec::IndexVec;
5 use rustc_infer::infer::InferCtxt;
6 use rustc_middle::mir::abstract_const::{Node, NodeId};
7 use rustc_middle::mir::interpret::ErrorHandled;
8 use rustc_middle::mir::visit::Visitor;
9 use rustc_middle::mir::{self, Rvalue, StatementKind, TerminatorKind};
10 use rustc_middle::ty::subst::Subst;
11 use rustc_middle::ty::subst::SubstsRef;
12 use rustc_middle::ty::{self, TyCtxt, TypeFoldable};
13 use rustc_session::lint;
14 use rustc_span::def_id::{DefId, LocalDefId};
17 pub fn is_const_evaluatable<'cx, 'tcx>(
18 infcx: &InferCtxt<'cx, 'tcx>,
19 def: ty::WithOptConstParam<DefId>,
20 substs: SubstsRef<'tcx>,
21 param_env: ty::ParamEnv<'tcx>,
23 ) -> Result<(), ErrorHandled> {
24 debug!("is_const_evaluatable({:?}, {:?})", def, substs);
25 if infcx.tcx.features().const_evaluatable_checked {
26 if let Some(ct) = AbstractConst::new(infcx.tcx, def, substs) {
27 for pred in param_env.caller_bounds() {
28 match pred.skip_binders() {
29 ty::PredicateAtom::ConstEvaluatable(b_def, b_substs) => {
30 debug!("is_const_evaluatable: caller_bound={:?}, {:?}", b_def, b_substs);
31 if b_def == def && b_substs == substs {
32 debug!("is_const_evaluatable: caller_bound ~~> ok");
34 } else if AbstractConst::new(infcx.tcx, b_def, b_substs)
35 .map_or(false, |b_ct| try_unify(infcx.tcx, ct, b_ct))
37 debug!("is_const_evaluatable: abstract_const ~~> ok");
47 let future_compat_lint = || {
48 if let Some(local_def_id) = def.did.as_local() {
49 infcx.tcx.struct_span_lint_hir(
50 lint::builtin::CONST_EVALUATABLE_UNCHECKED,
51 infcx.tcx.hir().local_def_id_to_hir_id(local_def_id),
54 err.build("cannot use constants which depend on generic parameters in types")
61 // FIXME: We should only try to evaluate a given constant here if it is fully concrete
62 // as we don't want to allow things like `[u8; std::mem::size_of::<*mut T>()]`.
64 // We previously did not check this, so we only emit a future compat warning if
65 // const evaluation succeeds and the given constant is still polymorphic for now
66 // and hopefully soon change this to an error.
68 // See #74595 for more details about this.
69 let concrete = infcx.const_eval_resolve(param_env, def, substs, None, Some(span));
71 if concrete.is_ok() && substs.has_param_types_or_consts() {
72 match infcx.tcx.def_kind(def.did) {
73 DefKind::AnonConst => {
74 let mir_body = if let Some(def) = def.as_const_arg() {
75 infcx.tcx.optimized_mir_of_const_arg(def)
77 infcx.tcx.optimized_mir(def.did)
80 if mir_body.is_polymorphic {
84 _ => future_compat_lint(),
88 debug!(?concrete, "is_const_evaluatable");
92 /// A tree representing an anonymous constant.
94 /// This is only able to represent a subset of `MIR`,
95 /// and should not leak any information about desugarings.
96 #[derive(Clone, Copy)]
97 pub struct AbstractConst<'tcx> {
98 // FIXME: Consider adding something like `IndexSlice`
100 inner: &'tcx [Node<'tcx>],
101 substs: SubstsRef<'tcx>,
104 impl AbstractConst<'tcx> {
107 def: ty::WithOptConstParam<DefId>,
108 substs: SubstsRef<'tcx>,
109 ) -> Option<AbstractConst<'tcx>> {
110 let inner = match (def.did.as_local(), def.const_param_did) {
111 (Some(did), Some(param_did)) => {
112 tcx.mir_abstract_const_of_const_arg((did, param_did))?
114 _ => tcx.mir_abstract_const(def.did)?,
117 Some(AbstractConst { inner, substs })
121 pub fn subtree(self, node: NodeId) -> AbstractConst<'tcx> {
122 AbstractConst { inner: &self.inner[..=node.index()], substs: self.substs }
126 pub fn root(self) -> Node<'tcx> {
127 self.inner.last().copied().unwrap()
131 struct AbstractConstBuilder<'a, 'tcx> {
133 body: &'a mir::Body<'tcx>,
134 nodes: IndexVec<NodeId, Node<'tcx>>,
135 locals: IndexVec<mir::Local, NodeId>,
136 checked_op_locals: BitSet<mir::Local>,
139 impl<'a, 'tcx> AbstractConstBuilder<'a, 'tcx> {
140 fn new(tcx: TyCtxt<'tcx>, body: &'a mir::Body<'tcx>) -> Option<AbstractConstBuilder<'a, 'tcx>> {
141 if body.is_cfg_cyclic() {
145 Some(AbstractConstBuilder {
148 nodes: IndexVec::new(),
149 locals: IndexVec::from_elem(NodeId::MAX, &body.local_decls),
150 checked_op_locals: BitSet::new_empty(body.local_decls.len()),
154 fn operand_to_node(&mut self, op: &mir::Operand<'tcx>) -> Option<NodeId> {
155 debug!("operand_to_node: op={:?}", op);
156 const ZERO_FIELD: mir::Field = mir::Field::from_usize(0);
158 mir::Operand::Copy(p) | mir::Operand::Move(p) => {
159 if let Some(p) = p.as_local() {
160 debug_assert!(!self.checked_op_locals.contains(p));
162 } else if let &[mir::ProjectionElem::Field(ZERO_FIELD, _)] = p.projection.as_ref() {
163 // Only allow field accesses on the result of checked operations.
164 if self.checked_op_locals.contains(p.local) {
165 Some(self.locals[p.local])
173 mir::Operand::Constant(ct) => Some(self.nodes.push(Node::Leaf(ct.literal))),
177 /// We do not allow all binary operations in abstract consts, so filter disallowed ones.
178 fn check_binop(op: mir::BinOp) -> bool {
181 Add | Sub | Mul | Div | Rem | BitXor | BitAnd | BitOr | Shl | Shr | Eq | Lt | Le
182 | Ne | Ge | Gt => true,
187 /// While we currently allow all unary operations, we still want to explicitly guard against
188 /// future changes here.
189 fn check_unop(op: mir::UnOp) -> bool {
196 fn build_statement(&mut self, stmt: &mir::Statement<'tcx>) -> Option<()> {
197 debug!("AbstractConstBuilder: stmt={:?}", stmt);
199 StatementKind::Assign(box (ref place, ref rvalue)) => {
200 let local = place.as_local()?;
202 Rvalue::Use(ref operand) => {
203 self.locals[local] = self.operand_to_node(operand)?;
206 Rvalue::BinaryOp(op, ref lhs, ref rhs) if Self::check_binop(op) => {
207 let lhs = self.operand_to_node(lhs)?;
208 let rhs = self.operand_to_node(rhs)?;
209 self.locals[local] = self.nodes.push(Node::Binop(op, lhs, rhs));
210 if op.is_checkable() {
211 bug!("unexpected unchecked checkable binary operation");
216 Rvalue::CheckedBinaryOp(op, ref lhs, ref rhs) if Self::check_binop(op) => {
217 let lhs = self.operand_to_node(lhs)?;
218 let rhs = self.operand_to_node(rhs)?;
219 self.locals[local] = self.nodes.push(Node::Binop(op, lhs, rhs));
220 self.checked_op_locals.insert(local);
223 Rvalue::UnaryOp(op, ref operand) if Self::check_unop(op) => {
224 let operand = self.operand_to_node(operand)?;
225 self.locals[local] = self.nodes.push(Node::UnaryOp(op, operand));
231 // These are not actually relevant for us here, so we can ignore them.
232 StatementKind::StorageLive(_) | StatementKind::StorageDead(_) => Some(()),
239 terminator: &mir::Terminator<'tcx>,
240 ) -> Option<Option<mir::BasicBlock>> {
241 debug!("AbstractConstBuilder: terminator={:?}", terminator);
242 match terminator.kind {
243 TerminatorKind::Goto { target } => Some(Some(target)),
244 TerminatorKind::Return => Some(None),
245 TerminatorKind::Assert { ref cond, expected: false, target, .. } => {
247 mir::Operand::Copy(p) | mir::Operand::Move(p) => p,
248 mir::Operand::Constant(_) => bug!("Unexpected assert"),
251 const ONE_FIELD: mir::Field = mir::Field::from_usize(1);
252 debug!("proj: {:?}", p.projection);
253 if let &[mir::ProjectionElem::Field(ONE_FIELD, _)] = p.projection.as_ref() {
254 // Only allow asserts checking the result of a checked operation.
255 if self.checked_op_locals.contains(p.local) {
256 return Some(Some(target));
266 fn build(mut self) -> Option<&'tcx [Node<'tcx>]> {
267 let mut block = &self.body.basic_blocks()[mir::START_BLOCK];
269 debug!("AbstractConstBuilder: block={:?}", block);
270 for stmt in block.statements.iter() {
271 self.build_statement(stmt)?;
274 if let Some(next) = self.build_terminator(block.terminator())? {
275 block = &self.body.basic_blocks()[next];
277 return Some(self.tcx.arena.alloc_from_iter(self.nodes));
283 /// Builds an abstract const, do not use this directly, but use `AbstractConst::new` instead.
284 pub(super) fn mir_abstract_const<'tcx>(
286 def: ty::WithOptConstParam<LocalDefId>,
287 ) -> Option<&'tcx [Node<'tcx>]> {
288 if tcx.features().const_evaluatable_checked {
289 let body = tcx.mir_const(def).borrow();
290 AbstractConstBuilder::new(tcx, &body)?.build()
296 pub(super) fn try_unify_abstract_consts<'tcx>(
298 ((a, a_substs), (b, b_substs)): (
299 (ty::WithOptConstParam<DefId>, SubstsRef<'tcx>),
300 (ty::WithOptConstParam<DefId>, SubstsRef<'tcx>),
303 if let Some(a) = AbstractConst::new(tcx, a, a_substs) {
304 if let Some(b) = AbstractConst::new(tcx, b, b_substs) {
305 return try_unify(tcx, a, b);
312 pub(super) fn try_unify<'tcx>(
314 a: AbstractConst<'tcx>,
315 b: AbstractConst<'tcx>,
317 match (a.root(), b.root()) {
318 (Node::Leaf(a_ct), Node::Leaf(b_ct)) => {
319 let a_ct = a_ct.subst(tcx, a.substs);
320 let b_ct = b_ct.subst(tcx, b.substs);
321 match (a_ct.val, b_ct.val) {
322 (ty::ConstKind::Param(a_param), ty::ConstKind::Param(b_param)) => {
325 (ty::ConstKind::Value(a_val), ty::ConstKind::Value(b_val)) => a_val == b_val,
326 // If we have `fn a<const N: usize>() -> [u8; N + 1]` and `fn b<const M: usize>() -> [u8; 1 + M]`
327 // we do not want to use `assert_eq!(a(), b())` to infer that `N` and `M` have to be `1`. This
328 // means that we can't do anything with inference variables here.
329 (ty::ConstKind::Infer(_), _) | (_, ty::ConstKind::Infer(_)) => false,
330 // FIXME(const_evaluatable_checked): We may want to either actually try
331 // to evaluate `a_ct` and `b_ct` if they are are fully concrete or something like
332 // this, for now we just return false here.
336 (Node::Binop(a_op, al, ar), Node::Binop(b_op, bl, br)) if a_op == b_op => {
337 try_unify(tcx, a.subtree(al), b.subtree(bl))
338 && try_unify(tcx, a.subtree(ar), b.subtree(br))
340 (Node::UnaryOp(a_op, av), Node::UnaryOp(b_op, bv)) if a_op == b_op => {
341 try_unify(tcx, a.subtree(av), b.subtree(bv))
343 (Node::FunctionCall(a_f, a_args), Node::FunctionCall(b_f, b_args))
344 if a_args.len() == b_args.len() =>
346 try_unify(tcx, a.subtree(a_f), b.subtree(b_f))
350 .all(|(&an, &bn)| try_unify(tcx, a.subtree(an), b.subtree(bn)))