1 //! The `Visitor` responsible for actually checking a `mir::Body` for invalid operations.
3 use rustc_errors::{Applicability, Diagnostic, ErrorReported};
4 use rustc_hir::def_id::DefId;
5 use rustc_hir::{self as hir, HirId, LangItem};
6 use rustc_index::bit_set::BitSet;
7 use rustc_infer::infer::TyCtxtInferExt;
8 use rustc_infer::traits::{ImplSource, Obligation, ObligationCause};
9 use rustc_middle::mir::visit::{MutatingUseContext, NonMutatingUseContext, PlaceContext, Visitor};
10 use rustc_middle::mir::*;
11 use rustc_middle::ty::cast::CastTy;
12 use rustc_middle::ty::subst::{GenericArgKind, InternalSubsts};
13 use rustc_middle::ty::{self, adjustment::PointerCast, Instance, InstanceDef, Ty, TyCtxt};
14 use rustc_middle::ty::{Binder, TraitPredicate, TraitRef};
15 use rustc_mir_dataflow::{self, Analysis};
16 use rustc_span::{sym, Span, Symbol};
17 use rustc_trait_selection::traits::error_reporting::InferCtxtExt;
18 use rustc_trait_selection::traits::{self, SelectionContext, TraitEngine};
23 use super::ops::{self, NonConstOp, Status};
24 use super::qualifs::{self, CustomEq, HasMutInterior, NeedsDrop, NeedsNonConstDrop};
25 use super::resolver::FlowSensitiveAnalysis;
26 use super::{ConstCx, Qualif};
27 use crate::const_eval::is_unstable_const_fn;
29 type QualifResults<'mir, 'tcx, Q> =
30 rustc_mir_dataflow::ResultsCursor<'mir, 'tcx, FlowSensitiveAnalysis<'mir, 'mir, 'tcx, Q>>;
33 pub struct Qualifs<'mir, 'tcx> {
34 has_mut_interior: Option<QualifResults<'mir, 'tcx, HasMutInterior>>,
35 needs_drop: Option<QualifResults<'mir, 'tcx, NeedsDrop>>,
36 needs_non_const_drop: Option<QualifResults<'mir, 'tcx, NeedsNonConstDrop>>,
39 impl Qualifs<'mir, 'tcx> {
40 /// Returns `true` if `local` is `NeedsDrop` at the given `Location`.
42 /// Only updates the cursor if absolutely necessary
45 ccx: &'mir ConstCx<'mir, 'tcx>,
49 let ty = ccx.body.local_decls[local].ty;
50 if !NeedsDrop::in_any_value_of_ty(ccx, ty) {
54 let needs_drop = self.needs_drop.get_or_insert_with(|| {
55 let ConstCx { tcx, body, .. } = *ccx;
57 FlowSensitiveAnalysis::new(NeedsDrop, ccx)
58 .into_engine(tcx, &body)
59 .iterate_to_fixpoint()
60 .into_results_cursor(&body)
63 needs_drop.seek_before_primary_effect(location);
64 needs_drop.get().contains(local)
67 /// Returns `true` if `local` is `NeedsNonConstDrop` at the given `Location`.
69 /// Only updates the cursor if absolutely necessary
70 pub fn needs_non_const_drop(
72 ccx: &'mir ConstCx<'mir, 'tcx>,
76 let ty = ccx.body.local_decls[local].ty;
77 if !NeedsNonConstDrop::in_any_value_of_ty(ccx, ty) {
81 let needs_non_const_drop = self.needs_non_const_drop.get_or_insert_with(|| {
82 let ConstCx { tcx, body, .. } = *ccx;
84 FlowSensitiveAnalysis::new(NeedsNonConstDrop, ccx)
85 .into_engine(tcx, &body)
86 .iterate_to_fixpoint()
87 .into_results_cursor(&body)
90 needs_non_const_drop.seek_before_primary_effect(location);
91 needs_non_const_drop.get().contains(local)
94 /// Returns `true` if `local` is `HasMutInterior` at the given `Location`.
96 /// Only updates the cursor if absolutely necessary.
97 pub fn has_mut_interior(
99 ccx: &'mir ConstCx<'mir, 'tcx>,
103 let ty = ccx.body.local_decls[local].ty;
104 if !HasMutInterior::in_any_value_of_ty(ccx, ty) {
108 let has_mut_interior = self.has_mut_interior.get_or_insert_with(|| {
109 let ConstCx { tcx, body, .. } = *ccx;
111 FlowSensitiveAnalysis::new(HasMutInterior, ccx)
112 .into_engine(tcx, &body)
113 .iterate_to_fixpoint()
114 .into_results_cursor(&body)
117 has_mut_interior.seek_before_primary_effect(location);
118 has_mut_interior.get().contains(local)
123 ccx: &'mir ConstCx<'mir, 'tcx>,
124 error_occured: Option<ErrorReported>,
126 // Find the `Return` terminator if one exists.
128 // If no `Return` terminator exists, this MIR is divergent. Just return the conservative
129 // qualifs for the return type.
130 let return_block = ccx
134 .find(|(_, block)| matches!(block.terminator().kind, TerminatorKind::Return))
137 let return_block = match return_block {
138 None => return qualifs::in_any_value_of_ty(ccx, ccx.body.return_ty(), error_occured),
142 let return_loc = ccx.body.terminator_loc(return_block);
144 let custom_eq = match ccx.const_kind() {
145 // We don't care whether a `const fn` returns a value that is not structurally
146 // matchable. Functions calls are opaque and always use type-based qualification, so
147 // this value should never be used.
148 hir::ConstContext::ConstFn => true,
150 // If we know that all values of the return type are structurally matchable, there's no
151 // need to run dataflow.
152 _ if !CustomEq::in_any_value_of_ty(ccx, ccx.body.return_ty()) => false,
154 hir::ConstContext::Const | hir::ConstContext::Static(_) => {
155 let mut cursor = FlowSensitiveAnalysis::new(CustomEq, ccx)
156 .into_engine(ccx.tcx, &ccx.body)
157 .iterate_to_fixpoint()
158 .into_results_cursor(&ccx.body);
160 cursor.seek_after_primary_effect(return_loc);
161 cursor.get().contains(RETURN_PLACE)
166 needs_drop: self.needs_drop(ccx, RETURN_PLACE, return_loc),
167 needs_non_const_drop: self.needs_non_const_drop(ccx, RETURN_PLACE, return_loc),
168 has_mut_interior: self.has_mut_interior(ccx, RETURN_PLACE, return_loc),
175 pub struct Checker<'mir, 'tcx> {
176 ccx: &'mir ConstCx<'mir, 'tcx>,
177 qualifs: Qualifs<'mir, 'tcx>,
179 /// The span of the current statement.
182 /// A set that stores for each local whether it has a `StorageDead` for it somewhere.
183 local_has_storage_dead: Option<BitSet<Local>>,
185 error_emitted: Option<ErrorReported>,
186 secondary_errors: Vec<Diagnostic>,
189 impl Deref for Checker<'mir, 'tcx> {
190 type Target = ConstCx<'mir, 'tcx>;
192 fn deref(&self) -> &Self::Target {
197 impl Checker<'mir, 'tcx> {
198 pub fn new(ccx: &'mir ConstCx<'mir, 'tcx>) -> Self {
202 qualifs: Default::default(),
203 local_has_storage_dead: None,
205 secondary_errors: Vec::new(),
209 pub fn check_body(&mut self) {
210 let ConstCx { tcx, body, .. } = *self.ccx;
211 let def_id = self.ccx.def_id();
213 // `async` functions cannot be `const fn`. This is checked during AST lowering, so there's
214 // no need to emit duplicate errors here.
215 if is_async_fn(self.ccx) || body.generator.is_some() {
216 tcx.sess.delay_span_bug(body.span, "`async` functions cannot be `const fn`");
220 // The local type and predicate checks are not free and only relevant for `const fn`s.
221 if self.const_kind() == hir::ConstContext::ConstFn {
222 // Prevent const trait methods from being annotated as `stable`.
223 // FIXME: Do this as part of stability checking.
224 if self.is_const_stable_const_fn() {
225 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
226 if crate::const_eval::is_parent_const_impl_raw(tcx, hir_id) {
230 .struct_span_err(self.span, "trait methods cannot be stable const fn")
235 self.check_item_predicates();
237 for (idx, local) in body.local_decls.iter_enumerated() {
238 // Handle the return place below.
239 if idx == RETURN_PLACE || local.internal {
243 self.span = local.source_info.span;
244 self.check_local_or_return_ty(local.ty, idx);
247 // impl trait is gone in MIR, so check the return type of a const fn by its signature
248 // instead of the type of the return place.
249 self.span = body.local_decls[RETURN_PLACE].source_info.span;
250 let return_ty = tcx.fn_sig(def_id).output();
251 self.check_local_or_return_ty(return_ty.skip_binder(), RETURN_PLACE);
254 if !tcx.has_attr(def_id.to_def_id(), sym::rustc_do_not_const_check) {
255 self.visit_body(&body);
258 // Ensure that the end result is `Sync` in a non-thread local `static`.
259 let should_check_for_sync = self.const_kind()
260 == hir::ConstContext::Static(hir::Mutability::Not)
261 && !tcx.is_thread_local_static(def_id.to_def_id());
263 if should_check_for_sync {
264 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
265 check_return_ty_is_sync(tcx, &body, hir_id);
268 // If we got through const-checking without emitting any "primary" errors, emit any
269 // "secondary" errors if they occurred.
270 let secondary_errors = mem::take(&mut self.secondary_errors);
271 if self.error_emitted.is_none() {
272 for error in secondary_errors {
273 self.tcx.sess.diagnostic().emit_diagnostic(&error);
276 assert!(self.tcx.sess.has_errors());
280 fn local_has_storage_dead(&mut self, local: Local) -> bool {
282 self.local_has_storage_dead
283 .get_or_insert_with(|| {
284 struct StorageDeads {
285 locals: BitSet<Local>,
287 impl Visitor<'tcx> for StorageDeads {
288 fn visit_statement(&mut self, stmt: &Statement<'tcx>, _: Location) {
289 if let StatementKind::StorageDead(l) = stmt.kind {
290 self.locals.insert(l);
294 let mut v = StorageDeads { locals: BitSet::new_empty(ccx.body.local_decls.len()) };
295 v.visit_body(ccx.body);
301 pub fn qualifs_in_return_place(&mut self) -> ConstQualifs {
302 self.qualifs.in_return_place(self.ccx, self.error_emitted)
305 /// Emits an error if an expression cannot be evaluated in the current context.
306 pub fn check_op(&mut self, op: impl NonConstOp) {
307 self.check_op_spanned(op, self.span);
310 /// Emits an error at the given `span` if an expression cannot be evaluated in the current
312 pub fn check_op_spanned<O: NonConstOp>(&mut self, op: O, span: Span) {
313 let gate = match op.status_in_item(self.ccx) {
314 Status::Allowed => return,
316 Status::Unstable(gate) if self.tcx.features().enabled(gate) => {
317 let unstable_in_stable = self.ccx.is_const_stable_const_fn()
318 && !super::rustc_allow_const_fn_unstable(
320 self.def_id().to_def_id(),
323 if unstable_in_stable {
324 emit_unstable_in_stable_error(self.ccx, span, gate);
330 Status::Unstable(gate) => Some(gate),
331 Status::Forbidden => None,
334 if self.tcx.sess.opts.debugging_opts.unleash_the_miri_inside_of_you {
335 self.tcx.sess.miri_unleashed_feature(span, gate);
339 let mut err = op.build_error(self.ccx, span);
340 assert!(err.is_error());
342 match op.importance() {
343 ops::DiagnosticImportance::Primary => {
344 self.error_emitted = Some(ErrorReported);
348 ops::DiagnosticImportance::Secondary => err.buffer(&mut self.secondary_errors),
352 fn check_static(&mut self, def_id: DefId, span: Span) {
353 if self.tcx.is_thread_local_static(def_id) {
354 self.tcx.sess.delay_span_bug(span, "tls access is checked in `Rvalue::ThreadLocalRef");
356 self.check_op_spanned(ops::StaticAccess, span)
359 fn check_local_or_return_ty(&mut self, ty: Ty<'tcx>, local: Local) {
360 let kind = self.body.local_kind(local);
362 for ty in ty.walk(self.tcx) {
363 let ty = match ty.unpack() {
364 GenericArgKind::Type(ty) => ty,
366 // No constraints on lifetimes or constants, except potentially
367 // constants' types, but `walk` will get to them as well.
368 GenericArgKind::Lifetime(_) | GenericArgKind::Const(_) => continue,
372 ty::Ref(_, _, hir::Mutability::Mut) => self.check_op(ops::ty::MutRef(kind)),
373 ty::Opaque(..) => self.check_op(ops::ty::ImplTrait),
374 ty::FnPtr(..) => self.check_op(ops::ty::FnPtr(kind)),
376 ty::Dynamic(preds, _) => {
377 for pred in preds.iter() {
378 match pred.skip_binder() {
379 ty::ExistentialPredicate::AutoTrait(_)
380 | ty::ExistentialPredicate::Projection(_) => {
381 self.check_op(ops::ty::DynTrait(kind))
383 ty::ExistentialPredicate::Trait(trait_ref) => {
384 if Some(trait_ref.def_id) != self.tcx.lang_items().sized_trait() {
385 self.check_op(ops::ty::DynTrait(kind))
396 fn check_item_predicates(&mut self) {
397 let ConstCx { tcx, .. } = *self.ccx;
399 let mut current = self.def_id().to_def_id();
401 let predicates = tcx.predicates_of(current);
402 for (predicate, _) in predicates.predicates {
403 match predicate.kind().skip_binder() {
404 ty::PredicateKind::RegionOutlives(_)
405 | ty::PredicateKind::TypeOutlives(_)
406 | ty::PredicateKind::WellFormed(_)
407 | ty::PredicateKind::Projection(_)
408 | ty::PredicateKind::ConstEvaluatable(..)
409 | ty::PredicateKind::ConstEquate(..)
410 | ty::PredicateKind::TypeWellFormedFromEnv(..) => continue,
411 ty::PredicateKind::ObjectSafe(_) => {
412 bug!("object safe predicate on function: {:#?}", predicate)
414 ty::PredicateKind::ClosureKind(..) => {
415 bug!("closure kind predicate on function: {:#?}", predicate)
417 ty::PredicateKind::Subtype(_) | ty::PredicateKind::Coerce(_) => {
418 bug!("subtype/coerce predicate on function: {:#?}", predicate)
420 ty::PredicateKind::Trait(pred) => {
421 if Some(pred.def_id()) == tcx.lang_items().sized_trait() {
424 match pred.self_ty().kind() {
426 let generics = tcx.generics_of(current);
427 let def = generics.type_param(p, tcx);
428 let span = tcx.def_span(def.def_id);
430 // These are part of the function signature, so treat them like
431 // arguments when determining importance.
432 let kind = LocalKind::Arg;
434 self.check_op_spanned(ops::ty::TraitBound(kind), span);
436 // other kinds of bounds are either tautologies
437 // or cause errors in other passes
443 match predicates.parent {
444 Some(parent) => current = parent,
450 fn check_mut_borrow(&mut self, local: Local, kind: hir::BorrowKind) {
451 match self.const_kind() {
452 // In a const fn all borrows are transient or point to the places given via
453 // references in the arguments (so we already checked them with
454 // TransientMutBorrow/MutBorrow as appropriate).
455 // The borrow checker guarantees that no new non-transient borrows are created.
456 // NOTE: Once we have heap allocations during CTFE we need to figure out
457 // how to prevent `const fn` to create long-lived allocations that point
458 // to mutable memory.
459 hir::ConstContext::ConstFn => self.check_op(ops::TransientMutBorrow(kind)),
461 // Locals with StorageDead do not live beyond the evaluation and can
462 // thus safely be borrowed without being able to be leaked to the final
463 // value of the constant.
464 if self.local_has_storage_dead(local) {
465 self.check_op(ops::TransientMutBorrow(kind));
467 self.check_op(ops::MutBorrow(kind));
474 impl Visitor<'tcx> for Checker<'mir, 'tcx> {
475 fn visit_basic_block_data(&mut self, bb: BasicBlock, block: &BasicBlockData<'tcx>) {
476 trace!("visit_basic_block_data: bb={:?} is_cleanup={:?}", bb, block.is_cleanup);
478 // We don't const-check basic blocks on the cleanup path since we never unwind during
479 // const-eval: a panic causes an immediate compile error. In other words, cleanup blocks
480 // are unreachable during const-eval.
482 // We can't be more conservative (e.g., by const-checking cleanup blocks anyways) because
483 // locals that would never be dropped during normal execution are sometimes dropped during
484 // unwinding, which means backwards-incompatible live-drop errors.
485 if block.is_cleanup {
489 self.super_basic_block_data(bb, block);
492 fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
493 trace!("visit_rvalue: rvalue={:?} location={:?}", rvalue, location);
495 // Special-case reborrows to be more like a copy of a reference.
497 Rvalue::Ref(_, kind, place) => {
498 if let Some(reborrowed_place_ref) = place_as_reborrow(self.tcx, self.body, place) {
499 let ctx = match kind {
500 BorrowKind::Shared => {
501 PlaceContext::NonMutatingUse(NonMutatingUseContext::SharedBorrow)
503 BorrowKind::Shallow => {
504 PlaceContext::NonMutatingUse(NonMutatingUseContext::ShallowBorrow)
506 BorrowKind::Unique => {
507 PlaceContext::NonMutatingUse(NonMutatingUseContext::UniqueBorrow)
509 BorrowKind::Mut { .. } => {
510 PlaceContext::MutatingUse(MutatingUseContext::Borrow)
513 self.visit_local(&reborrowed_place_ref.local, ctx, location);
514 self.visit_projection(reborrowed_place_ref, ctx, location);
518 Rvalue::AddressOf(mutbl, place) => {
519 if let Some(reborrowed_place_ref) = place_as_reborrow(self.tcx, self.body, place) {
520 let ctx = match mutbl {
522 PlaceContext::NonMutatingUse(NonMutatingUseContext::AddressOf)
524 Mutability::Mut => PlaceContext::MutatingUse(MutatingUseContext::AddressOf),
526 self.visit_local(&reborrowed_place_ref.local, ctx, location);
527 self.visit_projection(reborrowed_place_ref, ctx, location);
534 self.super_rvalue(rvalue, location);
537 Rvalue::ThreadLocalRef(_) => self.check_op(ops::ThreadLocalAccess),
541 | Rvalue::Discriminant(..)
543 | Rvalue::Aggregate(..) => {}
545 Rvalue::Ref(_, kind @ BorrowKind::Mut { .. }, ref place)
546 | Rvalue::Ref(_, kind @ BorrowKind::Unique, ref place) => {
547 let ty = place.ty(self.body, self.tcx).ty;
548 let is_allowed = match ty.kind() {
549 // Inside a `static mut`, `&mut [...]` is allowed.
550 ty::Array(..) | ty::Slice(_)
551 if self.const_kind() == hir::ConstContext::Static(hir::Mutability::Mut) =>
556 // FIXME(ecstaticmorse): We could allow `&mut []` inside a const context given
557 // that this is merely a ZST and it is already eligible for promotion.
558 // This may require an RFC?
560 ty::Array(_, len) if len.try_eval_usize(cx.tcx, cx.param_env) == Some(0)
567 if let BorrowKind::Mut { .. } = kind {
568 self.check_mut_borrow(place.local, hir::BorrowKind::Ref)
570 self.check_op(ops::CellBorrow);
575 Rvalue::AddressOf(Mutability::Mut, ref place) => {
576 self.check_mut_borrow(place.local, hir::BorrowKind::Raw)
579 Rvalue::Ref(_, BorrowKind::Shared | BorrowKind::Shallow, ref place)
580 | Rvalue::AddressOf(Mutability::Not, ref place) => {
581 let borrowed_place_has_mut_interior = qualifs::in_place::<HasMutInterior, _>(
583 &mut |local| self.qualifs.has_mut_interior(self.ccx, local, location),
587 if borrowed_place_has_mut_interior {
588 match self.const_kind() {
589 // In a const fn all borrows are transient or point to the places given via
590 // references in the arguments (so we already checked them with
591 // TransientCellBorrow/CellBorrow as appropriate).
592 // The borrow checker guarantees that no new non-transient borrows are created.
593 // NOTE: Once we have heap allocations during CTFE we need to figure out
594 // how to prevent `const fn` to create long-lived allocations that point
595 // to (interior) mutable memory.
596 hir::ConstContext::ConstFn => self.check_op(ops::TransientCellBorrow),
598 // Locals with StorageDead are definitely not part of the final constant value, and
599 // it is thus inherently safe to permit such locals to have their
600 // address taken as we can't end up with a reference to them in the
602 // Note: This is only sound if every local that has a `StorageDead` has a
603 // `StorageDead` in every control flow path leading to a `return` terminator.
604 if self.local_has_storage_dead(place.local) {
605 self.check_op(ops::TransientCellBorrow);
607 self.check_op(ops::CellBorrow);
615 CastKind::Pointer(PointerCast::MutToConstPointer | PointerCast::ArrayToPointer),
622 PointerCast::UnsafeFnPointer
623 | PointerCast::ClosureFnPointer(_)
624 | PointerCast::ReifyFnPointer,
628 ) => self.check_op(ops::FnPtrCast),
630 Rvalue::Cast(CastKind::Pointer(PointerCast::Unsize), _, _) => {
631 // Nothing to check here (`check_local_or_return_ty` ensures no trait objects occur
632 // in the type of any local, which also excludes casts).
635 Rvalue::Cast(CastKind::Misc, ref operand, cast_ty) => {
636 let operand_ty = operand.ty(self.body, self.tcx);
637 let cast_in = CastTy::from_ty(operand_ty).expect("bad input type for cast");
638 let cast_out = CastTy::from_ty(cast_ty).expect("bad output type for cast");
640 if let (CastTy::Ptr(_) | CastTy::FnPtr, CastTy::Int(_)) = (cast_in, cast_out) {
641 self.check_op(ops::RawPtrToIntCast);
645 Rvalue::NullaryOp(NullOp::SizeOf | NullOp::AlignOf, _) => {}
646 Rvalue::NullaryOp(NullOp::Box, _) => self.check_op(ops::HeapAllocation),
647 Rvalue::ShallowInitBox(_, _) => {}
649 Rvalue::UnaryOp(_, ref operand) => {
650 let ty = operand.ty(self.body, self.tcx);
651 if is_int_bool_or_char(ty) {
652 // Int, bool, and char operations are fine.
653 } else if ty.is_floating_point() {
654 self.check_op(ops::FloatingPointOp);
656 span_bug!(self.span, "non-primitive type in `Rvalue::UnaryOp`: {:?}", ty);
660 Rvalue::BinaryOp(op, box (ref lhs, ref rhs))
661 | Rvalue::CheckedBinaryOp(op, box (ref lhs, ref rhs)) => {
662 let lhs_ty = lhs.ty(self.body, self.tcx);
663 let rhs_ty = rhs.ty(self.body, self.tcx);
665 if is_int_bool_or_char(lhs_ty) && is_int_bool_or_char(rhs_ty) {
666 // Int, bool, and char operations are fine.
667 } else if lhs_ty.is_fn_ptr() || lhs_ty.is_unsafe_ptr() {
668 assert_eq!(lhs_ty, rhs_ty);
676 || op == BinOp::Offset
679 self.check_op(ops::RawPtrComparison);
680 } else if lhs_ty.is_floating_point() || rhs_ty.is_floating_point() {
681 self.check_op(ops::FloatingPointOp);
685 "non-primitive type in `Rvalue::BinaryOp`: {:?} ⚬ {:?}",
694 fn visit_operand(&mut self, op: &Operand<'tcx>, location: Location) {
695 self.super_operand(op, location);
696 if let Operand::Constant(c) = op {
697 if let Some(def_id) = c.check_static_ptr(self.tcx) {
698 self.check_static(def_id, self.span);
702 fn visit_projection_elem(
705 proj_base: &[PlaceElem<'tcx>],
706 elem: PlaceElem<'tcx>,
707 context: PlaceContext,
711 "visit_projection_elem: place_local={:?} proj_base={:?} elem={:?} \
712 context={:?} location={:?}",
720 self.super_projection_elem(place_local, proj_base, elem, context, location);
723 ProjectionElem::Deref => {
724 let base_ty = Place::ty_from(place_local, proj_base, self.body, self.tcx).ty;
725 if base_ty.is_unsafe_ptr() {
726 if proj_base.is_empty() {
727 let decl = &self.body.local_decls[place_local];
728 if let Some(box LocalInfo::StaticRef { def_id, .. }) = decl.local_info {
729 let span = decl.source_info.span;
730 self.check_static(def_id, span);
735 // `*const T` is stable, `*mut T` is not
736 if !base_ty.is_mutable_ptr() {
740 self.check_op(ops::RawMutPtrDeref);
743 if context.is_mutating_use() {
744 self.check_op(ops::MutDeref);
748 ProjectionElem::ConstantIndex { .. }
749 | ProjectionElem::Downcast(..)
750 | ProjectionElem::Subslice { .. }
751 | ProjectionElem::Field(..)
752 | ProjectionElem::Index(_) => {}
756 fn visit_source_info(&mut self, source_info: &SourceInfo) {
757 trace!("visit_source_info: source_info={:?}", source_info);
758 self.span = source_info.span;
761 fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
762 trace!("visit_statement: statement={:?} location={:?}", statement, location);
764 self.super_statement(statement, location);
766 match statement.kind {
767 StatementKind::LlvmInlineAsm { .. } => {
768 self.check_op(ops::InlineAsm);
771 StatementKind::Assign(..)
772 | StatementKind::SetDiscriminant { .. }
773 | StatementKind::FakeRead(..)
774 | StatementKind::StorageLive(_)
775 | StatementKind::StorageDead(_)
776 | StatementKind::Retag { .. }
777 | StatementKind::AscribeUserType(..)
778 | StatementKind::Coverage(..)
779 | StatementKind::CopyNonOverlapping(..)
780 | StatementKind::Nop => {}
784 #[instrument(level = "debug", skip(self))]
785 fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
786 use rustc_target::spec::abi::Abi::RustIntrinsic;
788 self.super_terminator(terminator, location);
790 match &terminator.kind {
791 TerminatorKind::Call { func, args, .. } => {
792 let ConstCx { tcx, body, param_env, .. } = *self.ccx;
793 let caller = self.def_id().to_def_id();
795 let fn_ty = func.ty(body, tcx);
797 let (mut callee, mut substs) = match *fn_ty.kind() {
798 ty::FnDef(def_id, substs) => (def_id, substs),
801 self.check_op(ops::FnCallIndirect);
805 span_bug!(terminator.source_info.span, "invalid callee of type {:?}", fn_ty)
809 let mut nonconst_call_permission = false;
811 // Attempting to call a trait method?
812 if let Some(trait_id) = tcx.trait_of_item(callee) {
813 trace!("attempting to call a trait method");
814 if !self.tcx.features().const_trait_impl {
815 self.check_op(ops::FnCallNonConst);
819 let trait_ref = TraitRef::from_method(tcx, trait_id, substs);
820 let obligation = Obligation::new(
821 ObligationCause::dummy(),
823 Binder::dummy(TraitPredicate {
825 constness: ty::BoundConstness::ConstIfConst,
826 polarity: ty::ImplPolarity::Positive,
830 let implsrc = tcx.infer_ctxt().enter(|infcx| {
832 SelectionContext::with_constness(&infcx, hir::Constness::Const);
833 selcx.select(&obligation)
837 Ok(Some(ImplSource::Param(_, ty::BoundConstness::ConstIfConst))) => {
839 "const_trait_impl: provided {:?} via where-clause in {:?}",
844 Ok(Some(ImplSource::UserDefined(data))) => {
845 let callee_name = tcx.item_name(callee);
846 if let Some(&did) = tcx
847 .associated_item_def_ids(data.impl_def_id)
849 .find(|did| tcx.item_name(**did) == callee_name)
851 // using internal substs is ok here, since this is only
852 // used for the `resolve` call below
853 substs = InternalSubsts::identity_for_item(tcx, did);
857 _ if !tcx.is_const_fn_raw(callee) => {
858 // At this point, it is only legal when the caller is marked with
859 // #[default_method_body_is_const], and the callee is in the same
861 let callee_trait = tcx.trait_of_item(callee);
862 if callee_trait.is_some() {
863 if tcx.has_attr(caller, sym::default_method_body_is_const) {
864 if tcx.trait_of_item(caller) == callee_trait {
865 nonconst_call_permission = true;
870 if !nonconst_call_permission {
871 self.check_op(ops::FnCallNonConst);
878 // Resolve a trait method call to its concrete implementation, which may be in a
879 // `const` trait impl.
880 let instance = Instance::resolve(tcx, param_env, callee, substs);
881 debug!("Resolving ({:?}) -> {:?}", callee, instance);
882 if let Ok(Some(func)) = instance {
883 if let InstanceDef::Item(def) = func.def {
889 // At this point, we are calling a function, `callee`, whose `DefId` is known...
891 // `begin_panic` and `panic_display` are generic functions that accept
892 // types other than str. Check to enforce that only str can be used in
895 // const-eval of the `begin_panic` fn assumes the argument is `&str`
896 if Some(callee) == tcx.lang_items().begin_panic_fn() {
897 match args[0].ty(&self.ccx.body.local_decls, tcx).kind() {
898 ty::Ref(_, ty, _) if ty.is_str() => return,
899 _ => self.check_op(ops::PanicNonStr),
903 // const-eval of the `panic_display` fn assumes the argument is `&&str`
904 if Some(callee) == tcx.lang_items().panic_display() {
905 match args[0].ty(&self.ccx.body.local_decls, tcx).kind() {
906 ty::Ref(_, ty, _) if matches!(ty.kind(), ty::Ref(_, ty, _) if ty.is_str()) =>
910 _ => self.check_op(ops::PanicNonStr),
914 if Some(callee) == tcx.lang_items().exchange_malloc_fn() {
915 self.check_op(ops::HeapAllocation);
919 // `async` blocks get lowered to `std::future::from_generator(/* a closure */)`.
920 let is_async_block = Some(callee) == tcx.lang_items().from_generator_fn();
922 let kind = hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Block);
923 self.check_op(ops::Generator(kind));
927 let is_intrinsic = tcx.fn_sig(callee).abi() == RustIntrinsic;
929 if !tcx.is_const_fn_raw(callee) {
930 if tcx.trait_of_item(callee).is_some() {
931 if tcx.has_attr(callee, sym::default_method_body_is_const) {
932 // To get to here we must have already found a const impl for the
933 // trait, but for it to still be non-const can be that the impl is
934 // using default method bodies.
935 nonconst_call_permission = true;
939 if !nonconst_call_permission {
940 self.check_op(ops::FnCallNonConst);
945 // If the `const fn` we are trying to call is not const-stable, ensure that we have
946 // the proper feature gate enabled.
947 if let Some(gate) = is_unstable_const_fn(tcx, callee) {
948 trace!(?gate, "calling unstable const fn");
949 if self.span.allows_unstable(gate) {
953 // Calling an unstable function *always* requires that the corresponding gate
954 // be enabled, even if the function has `#[rustc_allow_const_fn_unstable(the_gate)]`.
955 if !tcx.features().declared_lib_features.iter().any(|&(sym, _)| sym == gate) {
956 self.check_op(ops::FnCallUnstable(callee, Some(gate)));
960 // If this crate is not using stability attributes, or the caller is not claiming to be a
961 // stable `const fn`, that is all that is required.
962 if !self.ccx.is_const_stable_const_fn() {
963 trace!("crate not using stability attributes or caller not stably const");
967 // Otherwise, we are something const-stable calling a const-unstable fn.
969 if super::rustc_allow_const_fn_unstable(tcx, caller, gate) {
970 trace!("rustc_allow_const_fn_unstable gate active");
974 self.check_op(ops::FnCallUnstable(callee, Some(gate)));
978 // FIXME(ecstaticmorse); For compatibility, we consider `unstable` callees that
979 // have no `rustc_const_stable` attributes to be const-unstable as well. This
980 // should be fixed later.
981 let callee_is_unstable_unmarked = tcx.lookup_const_stability(callee).is_none()
982 && tcx.lookup_stability(callee).map_or(false, |s| s.level.is_unstable());
983 if callee_is_unstable_unmarked {
984 trace!("callee_is_unstable_unmarked");
985 // We do not use `const` modifiers for intrinsic "functions", as intrinsics are
986 // `extern` funtions, and these have no way to get marked `const`. So instead we
987 // use `rustc_const_(un)stable` attributes to mean that the intrinsic is `const`
988 if self.ccx.is_const_stable_const_fn() || is_intrinsic {
989 self.check_op(ops::FnCallUnstable(callee, None));
993 trace!("permitting call");
996 // Forbid all `Drop` terminators unless the place being dropped is a local with no
997 // projections that cannot be `NeedsNonConstDrop`.
998 TerminatorKind::Drop { place: dropped_place, .. }
999 | TerminatorKind::DropAndReplace { place: dropped_place, .. } => {
1000 // If we are checking live drops after drop-elaboration, don't emit duplicate
1002 if super::post_drop_elaboration::checking_enabled(self.ccx) {
1006 let mut err_span = self.span;
1008 let ty_needs_non_const_drop = qualifs::NeedsNonConstDrop::in_any_value_of_ty(
1010 dropped_place.ty(self.body, self.tcx).ty,
1013 if !ty_needs_non_const_drop {
1017 let needs_non_const_drop = if let Some(local) = dropped_place.as_local() {
1018 // Use the span where the local was declared as the span of the drop error.
1019 err_span = self.body.local_decls[local].source_info.span;
1020 self.qualifs.needs_non_const_drop(self.ccx, local, location)
1025 if needs_non_const_drop {
1026 self.check_op_spanned(
1027 ops::LiveDrop { dropped_at: Some(terminator.source_info.span) },
1033 TerminatorKind::InlineAsm { .. } => self.check_op(ops::InlineAsm),
1035 TerminatorKind::GeneratorDrop | TerminatorKind::Yield { .. } => {
1036 self.check_op(ops::Generator(hir::GeneratorKind::Gen))
1039 TerminatorKind::Abort => {
1040 // Cleanup blocks are skipped for const checking (see `visit_basic_block_data`).
1041 span_bug!(self.span, "`Abort` terminator outside of cleanup block")
1044 TerminatorKind::Assert { .. }
1045 | TerminatorKind::FalseEdge { .. }
1046 | TerminatorKind::FalseUnwind { .. }
1047 | TerminatorKind::Goto { .. }
1048 | TerminatorKind::Resume
1049 | TerminatorKind::Return
1050 | TerminatorKind::SwitchInt { .. }
1051 | TerminatorKind::Unreachable => {}
1056 fn check_return_ty_is_sync(tcx: TyCtxt<'tcx>, body: &Body<'tcx>, hir_id: HirId) {
1057 let ty = body.return_ty();
1058 tcx.infer_ctxt().enter(|infcx| {
1059 let cause = traits::ObligationCause::new(body.span, hir_id, traits::SharedStatic);
1060 let mut fulfillment_cx = traits::FulfillmentContext::new();
1061 let sync_def_id = tcx.require_lang_item(LangItem::Sync, Some(body.span));
1062 fulfillment_cx.register_bound(&infcx, ty::ParamEnv::empty(), ty, sync_def_id, cause);
1063 let errors = fulfillment_cx.select_all_or_error(&infcx);
1064 if !errors.is_empty() {
1065 infcx.report_fulfillment_errors(&errors, None, false);
1070 fn place_as_reborrow(
1074 ) -> Option<PlaceRef<'tcx>> {
1075 match place.as_ref().last_projection() {
1076 Some((place_base, ProjectionElem::Deref)) => {
1077 // A borrow of a `static` also looks like `&(*_1)` in the MIR, but `_1` is a `const`
1078 // that points to the allocation for the static. Don't treat these as reborrows.
1079 if body.local_decls[place_base.local].is_ref_to_static() {
1082 // Ensure the type being derefed is a reference and not a raw pointer.
1083 // This is sufficient to prevent an access to a `static mut` from being marked as a
1084 // reborrow, even if the check above were to disappear.
1085 let inner_ty = place_base.ty(body, tcx).ty;
1087 if let ty::Ref(..) = inner_ty.kind() {
1088 return Some(place_base);
1098 fn is_int_bool_or_char(ty: Ty<'_>) -> bool {
1099 ty.is_bool() || ty.is_integral() || ty.is_char()
1102 fn is_async_fn(ccx: &ConstCx<'_, '_>) -> bool {
1103 ccx.fn_sig().map_or(false, |sig| sig.header.asyncness == hir::IsAsync::Async)
1106 fn emit_unstable_in_stable_error(ccx: &ConstCx<'_, '_>, span: Span, gate: Symbol) {
1107 let attr_span = ccx.fn_sig().map_or(ccx.body.span, |sig| sig.span.shrink_to_lo());
1113 &format!("const-stable function cannot use `#[feature({})]`", gate.as_str()),
1117 "if it is not part of the public API, make this function unstably const",
1118 concat!(r#"#[rustc_const_unstable(feature = "...", issue = "...")]"#, '\n').to_owned(),
1119 Applicability::HasPlaceholders,
1123 "otherwise `#[rustc_allow_const_fn_unstable]` can be used to bypass stability checks",
1124 format!("#[rustc_allow_const_fn_unstable({})]\n", gate),
1125 Applicability::MaybeIncorrect,