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::impls::MaybeMutBorrowedLocals;
16 use rustc_mir_dataflow::{self, Analysis};
17 use rustc_span::{sym, Span, Symbol};
18 use rustc_trait_selection::traits::error_reporting::InferCtxtExt;
19 use rustc_trait_selection::traits::{self, SelectionContext, TraitEngine};
24 use super::ops::{self, NonConstOp, Status};
25 use super::qualifs::{self, CustomEq, HasMutInterior, NeedsDrop, NeedsNonConstDrop};
26 use super::resolver::FlowSensitiveAnalysis;
27 use super::{is_lang_panic_fn, is_lang_special_const_fn, ConstCx, Qualif};
28 use crate::const_eval::is_unstable_const_fn;
30 // We are using `MaybeMutBorrowedLocals` as a proxy for whether an item may have been mutated
31 // through a pointer prior to the given point. This is okay even though `MaybeMutBorrowedLocals`
32 // kills locals upon `StorageDead` because a local will never be used after a `StorageDead`.
33 type IndirectlyMutableResults<'mir, 'tcx> =
34 rustc_mir_dataflow::ResultsCursor<'mir, 'tcx, MaybeMutBorrowedLocals<'mir, 'tcx>>;
36 type QualifResults<'mir, 'tcx, Q> =
37 rustc_mir_dataflow::ResultsCursor<'mir, 'tcx, FlowSensitiveAnalysis<'mir, 'mir, 'tcx, Q>>;
40 pub struct Qualifs<'mir, 'tcx> {
41 has_mut_interior: Option<QualifResults<'mir, 'tcx, HasMutInterior>>,
42 needs_drop: Option<QualifResults<'mir, 'tcx, NeedsDrop>>,
43 needs_non_const_drop: Option<QualifResults<'mir, 'tcx, NeedsNonConstDrop>>,
44 indirectly_mutable: Option<IndirectlyMutableResults<'mir, 'tcx>>,
47 impl Qualifs<'mir, 'tcx> {
48 pub fn indirectly_mutable(
50 ccx: &'mir ConstCx<'mir, 'tcx>,
54 let indirectly_mutable = self.indirectly_mutable.get_or_insert_with(|| {
55 let ConstCx { tcx, body, param_env, .. } = *ccx;
57 // We can use `unsound_ignore_borrow_on_drop` here because custom drop impls are not
58 // allowed in a const.
60 // FIXME(ecstaticmorse): Someday we want to allow custom drop impls. How do we do this
61 // without breaking stable code?
62 MaybeMutBorrowedLocals::mut_borrows_only(tcx, &body, param_env)
63 .unsound_ignore_borrow_on_drop()
64 .into_engine(tcx, &body)
65 .pass_name("const_qualification")
66 .iterate_to_fixpoint()
67 .into_results_cursor(&body)
70 indirectly_mutable.seek_before_primary_effect(location);
71 indirectly_mutable.get().contains(local)
74 /// Returns `true` if `local` is `NeedsDrop` at the given `Location`.
76 /// Only updates the cursor if absolutely necessary
79 ccx: &'mir ConstCx<'mir, 'tcx>,
83 let ty = ccx.body.local_decls[local].ty;
84 if !NeedsDrop::in_any_value_of_ty(ccx, ty) {
88 let needs_drop = self.needs_drop.get_or_insert_with(|| {
89 let ConstCx { tcx, body, .. } = *ccx;
91 FlowSensitiveAnalysis::new(NeedsDrop, ccx)
92 .into_engine(tcx, &body)
93 .iterate_to_fixpoint()
94 .into_results_cursor(&body)
97 needs_drop.seek_before_primary_effect(location);
98 needs_drop.get().contains(local) || self.indirectly_mutable(ccx, local, location)
101 /// Returns `true` if `local` is `NeedsNonConstDrop` at the given `Location`.
103 /// Only updates the cursor if absolutely necessary
104 pub fn needs_non_const_drop(
106 ccx: &'mir ConstCx<'mir, 'tcx>,
110 let ty = ccx.body.local_decls[local].ty;
111 if !NeedsNonConstDrop::in_any_value_of_ty(ccx, ty) {
115 let needs_non_const_drop = self.needs_non_const_drop.get_or_insert_with(|| {
116 let ConstCx { tcx, body, .. } = *ccx;
118 FlowSensitiveAnalysis::new(NeedsNonConstDrop, ccx)
119 .into_engine(tcx, &body)
120 .iterate_to_fixpoint()
121 .into_results_cursor(&body)
124 needs_non_const_drop.seek_before_primary_effect(location);
125 needs_non_const_drop.get().contains(local) || self.indirectly_mutable(ccx, local, location)
128 /// Returns `true` if `local` is `HasMutInterior` at the given `Location`.
130 /// Only updates the cursor if absolutely necessary.
131 pub fn has_mut_interior(
133 ccx: &'mir ConstCx<'mir, 'tcx>,
137 let ty = ccx.body.local_decls[local].ty;
138 if !HasMutInterior::in_any_value_of_ty(ccx, ty) {
142 let has_mut_interior = self.has_mut_interior.get_or_insert_with(|| {
143 let ConstCx { tcx, body, .. } = *ccx;
145 FlowSensitiveAnalysis::new(HasMutInterior, ccx)
146 .into_engine(tcx, &body)
147 .iterate_to_fixpoint()
148 .into_results_cursor(&body)
151 has_mut_interior.seek_before_primary_effect(location);
152 has_mut_interior.get().contains(local) || self.indirectly_mutable(ccx, local, location)
157 ccx: &'mir ConstCx<'mir, 'tcx>,
158 error_occured: Option<ErrorReported>,
160 // Find the `Return` terminator if one exists.
162 // If no `Return` terminator exists, this MIR is divergent. Just return the conservative
163 // qualifs for the return type.
164 let return_block = ccx
168 .find(|(_, block)| match block.terminator().kind {
169 TerminatorKind::Return => true,
174 let return_block = match return_block {
175 None => return qualifs::in_any_value_of_ty(ccx, ccx.body.return_ty(), error_occured),
179 let return_loc = ccx.body.terminator_loc(return_block);
181 let custom_eq = match ccx.const_kind() {
182 // We don't care whether a `const fn` returns a value that is not structurally
183 // matchable. Functions calls are opaque and always use type-based qualification, so
184 // this value should never be used.
185 hir::ConstContext::ConstFn => true,
187 // If we know that all values of the return type are structurally matchable, there's no
188 // need to run dataflow.
189 _ if !CustomEq::in_any_value_of_ty(ccx, ccx.body.return_ty()) => false,
191 hir::ConstContext::Const | hir::ConstContext::Static(_) => {
192 let mut cursor = FlowSensitiveAnalysis::new(CustomEq, ccx)
193 .into_engine(ccx.tcx, &ccx.body)
194 .iterate_to_fixpoint()
195 .into_results_cursor(&ccx.body);
197 cursor.seek_after_primary_effect(return_loc);
198 cursor.contains(RETURN_PLACE)
203 needs_drop: self.needs_drop(ccx, RETURN_PLACE, return_loc),
204 needs_non_const_drop: self.needs_non_const_drop(ccx, RETURN_PLACE, return_loc),
205 has_mut_interior: self.has_mut_interior(ccx, RETURN_PLACE, return_loc),
212 pub struct Checker<'mir, 'tcx> {
213 ccx: &'mir ConstCx<'mir, 'tcx>,
214 qualifs: Qualifs<'mir, 'tcx>,
216 /// The span of the current statement.
219 /// A set that stores for each local whether it has a `StorageDead` for it somewhere.
220 local_has_storage_dead: Option<BitSet<Local>>,
222 error_emitted: Option<ErrorReported>,
223 secondary_errors: Vec<Diagnostic>,
226 impl Deref for Checker<'mir, 'tcx> {
227 type Target = ConstCx<'mir, 'tcx>;
229 fn deref(&self) -> &Self::Target {
234 impl Checker<'mir, 'tcx> {
235 pub fn new(ccx: &'mir ConstCx<'mir, 'tcx>) -> Self {
239 qualifs: Default::default(),
240 local_has_storage_dead: None,
242 secondary_errors: Vec::new(),
246 pub fn check_body(&mut self) {
247 let ConstCx { tcx, body, .. } = *self.ccx;
248 let def_id = self.ccx.def_id();
250 // `async` functions cannot be `const fn`. This is checked during AST lowering, so there's
251 // no need to emit duplicate errors here.
252 if is_async_fn(self.ccx) || body.generator.is_some() {
253 tcx.sess.delay_span_bug(body.span, "`async` functions cannot be `const fn`");
257 // The local type and predicate checks are not free and only relevant for `const fn`s.
258 if self.const_kind() == hir::ConstContext::ConstFn {
259 // Prevent const trait methods from being annotated as `stable`.
260 // FIXME: Do this as part of stability checking.
261 if self.is_const_stable_const_fn() {
262 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
263 if crate::const_eval::is_parent_const_impl_raw(tcx, hir_id) {
267 .struct_span_err(self.span, "trait methods cannot be stable const fn")
272 self.check_item_predicates();
274 for (idx, local) in body.local_decls.iter_enumerated() {
275 // Handle the return place below.
276 if idx == RETURN_PLACE || local.internal {
280 self.span = local.source_info.span;
281 self.check_local_or_return_ty(local.ty, idx);
284 // impl trait is gone in MIR, so check the return type of a const fn by its signature
285 // instead of the type of the return place.
286 self.span = body.local_decls[RETURN_PLACE].source_info.span;
287 let return_ty = tcx.fn_sig(def_id).output();
288 self.check_local_or_return_ty(return_ty.skip_binder(), RETURN_PLACE);
291 if !tcx.has_attr(def_id.to_def_id(), sym::rustc_do_not_const_check) {
292 self.visit_body(&body);
295 // Ensure that the end result is `Sync` in a non-thread local `static`.
296 let should_check_for_sync = self.const_kind()
297 == hir::ConstContext::Static(hir::Mutability::Not)
298 && !tcx.is_thread_local_static(def_id.to_def_id());
300 if should_check_for_sync {
301 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
302 check_return_ty_is_sync(tcx, &body, hir_id);
305 // If we got through const-checking without emitting any "primary" errors, emit any
306 // "secondary" errors if they occurred.
307 let secondary_errors = mem::take(&mut self.secondary_errors);
308 if self.error_emitted.is_none() {
309 for error in secondary_errors {
310 self.tcx.sess.diagnostic().emit_diagnostic(&error);
313 assert!(self.tcx.sess.has_errors());
317 fn local_has_storage_dead(&mut self, local: Local) -> bool {
319 self.local_has_storage_dead
320 .get_or_insert_with(|| {
321 struct StorageDeads {
322 locals: BitSet<Local>,
324 impl Visitor<'tcx> for StorageDeads {
325 fn visit_statement(&mut self, stmt: &Statement<'tcx>, _: Location) {
326 if let StatementKind::StorageDead(l) = stmt.kind {
327 self.locals.insert(l);
331 let mut v = StorageDeads { locals: BitSet::new_empty(ccx.body.local_decls.len()) };
332 v.visit_body(ccx.body);
338 pub fn qualifs_in_return_place(&mut self) -> ConstQualifs {
339 self.qualifs.in_return_place(self.ccx, self.error_emitted)
342 /// Emits an error if an expression cannot be evaluated in the current context.
343 pub fn check_op(&mut self, op: impl NonConstOp) {
344 self.check_op_spanned(op, self.span);
347 /// Emits an error at the given `span` if an expression cannot be evaluated in the current
349 pub fn check_op_spanned<O: NonConstOp>(&mut self, op: O, span: Span) {
350 let gate = match op.status_in_item(self.ccx) {
351 Status::Allowed => return,
353 Status::Unstable(gate) if self.tcx.features().enabled(gate) => {
354 let unstable_in_stable = self.ccx.is_const_stable_const_fn()
355 && !super::rustc_allow_const_fn_unstable(
357 self.def_id().to_def_id(),
360 if unstable_in_stable {
361 emit_unstable_in_stable_error(self.ccx, span, gate);
367 Status::Unstable(gate) => Some(gate),
368 Status::Forbidden => None,
371 if self.tcx.sess.opts.debugging_opts.unleash_the_miri_inside_of_you {
372 self.tcx.sess.miri_unleashed_feature(span, gate);
376 let mut err = op.build_error(self.ccx, span);
377 assert!(err.is_error());
379 match op.importance() {
380 ops::DiagnosticImportance::Primary => {
381 self.error_emitted = Some(ErrorReported);
385 ops::DiagnosticImportance::Secondary => err.buffer(&mut self.secondary_errors),
389 fn check_static(&mut self, def_id: DefId, span: Span) {
390 if self.tcx.is_thread_local_static(def_id) {
391 self.tcx.sess.delay_span_bug(span, "tls access is checked in `Rvalue::ThreadLocalRef");
393 self.check_op_spanned(ops::StaticAccess, span)
396 fn check_local_or_return_ty(&mut self, ty: Ty<'tcx>, local: Local) {
397 let kind = self.body.local_kind(local);
399 for ty in ty.walk(self.tcx) {
400 let ty = match ty.unpack() {
401 GenericArgKind::Type(ty) => ty,
403 // No constraints on lifetimes or constants, except potentially
404 // constants' types, but `walk` will get to them as well.
405 GenericArgKind::Lifetime(_) | GenericArgKind::Const(_) => continue,
409 ty::Ref(_, _, hir::Mutability::Mut) => self.check_op(ops::ty::MutRef(kind)),
410 ty::Opaque(..) => self.check_op(ops::ty::ImplTrait),
411 ty::FnPtr(..) => self.check_op(ops::ty::FnPtr(kind)),
413 ty::Dynamic(preds, _) => {
414 for pred in preds.iter() {
415 match pred.skip_binder() {
416 ty::ExistentialPredicate::AutoTrait(_)
417 | ty::ExistentialPredicate::Projection(_) => {
418 self.check_op(ops::ty::DynTrait(kind))
420 ty::ExistentialPredicate::Trait(trait_ref) => {
421 if Some(trait_ref.def_id) != self.tcx.lang_items().sized_trait() {
422 self.check_op(ops::ty::DynTrait(kind))
433 fn check_item_predicates(&mut self) {
434 let ConstCx { tcx, .. } = *self.ccx;
436 let mut current = self.def_id().to_def_id();
438 let predicates = tcx.predicates_of(current);
439 for (predicate, _) in predicates.predicates {
440 match predicate.kind().skip_binder() {
441 ty::PredicateKind::RegionOutlives(_)
442 | ty::PredicateKind::TypeOutlives(_)
443 | ty::PredicateKind::WellFormed(_)
444 | ty::PredicateKind::Projection(_)
445 | ty::PredicateKind::ConstEvaluatable(..)
446 | ty::PredicateKind::ConstEquate(..)
447 | ty::PredicateKind::TypeWellFormedFromEnv(..) => continue,
448 ty::PredicateKind::ObjectSafe(_) => {
449 bug!("object safe predicate on function: {:#?}", predicate)
451 ty::PredicateKind::ClosureKind(..) => {
452 bug!("closure kind predicate on function: {:#?}", predicate)
454 ty::PredicateKind::Subtype(_) | ty::PredicateKind::Coerce(_) => {
455 bug!("subtype/coerce predicate on function: {:#?}", predicate)
457 ty::PredicateKind::Trait(pred) => {
458 if Some(pred.def_id()) == tcx.lang_items().sized_trait() {
461 match pred.self_ty().kind() {
463 let generics = tcx.generics_of(current);
464 let def = generics.type_param(p, tcx);
465 let span = tcx.def_span(def.def_id);
467 // These are part of the function signature, so treat them like
468 // arguments when determining importance.
469 let kind = LocalKind::Arg;
471 self.check_op_spanned(ops::ty::TraitBound(kind), span);
473 // other kinds of bounds are either tautologies
474 // or cause errors in other passes
480 match predicates.parent {
481 Some(parent) => current = parent,
487 fn check_mut_borrow(&mut self, local: Local, kind: hir::BorrowKind) {
488 match self.const_kind() {
489 // In a const fn all borrows are transient or point to the places given via
490 // references in the arguments (so we already checked them with
491 // TransientMutBorrow/MutBorrow as appropriate).
492 // The borrow checker guarantees that no new non-transient borrows are created.
493 // NOTE: Once we have heap allocations during CTFE we need to figure out
494 // how to prevent `const fn` to create long-lived allocations that point
495 // to mutable memory.
496 hir::ConstContext::ConstFn => self.check_op(ops::TransientMutBorrow(kind)),
498 // Locals with StorageDead do not live beyond the evaluation and can
499 // thus safely be borrowed without being able to be leaked to the final
500 // value of the constant.
501 if self.local_has_storage_dead(local) {
502 self.check_op(ops::TransientMutBorrow(kind));
504 self.check_op(ops::MutBorrow(kind));
511 impl Visitor<'tcx> for Checker<'mir, 'tcx> {
512 fn visit_basic_block_data(&mut self, bb: BasicBlock, block: &BasicBlockData<'tcx>) {
513 trace!("visit_basic_block_data: bb={:?} is_cleanup={:?}", bb, block.is_cleanup);
515 // We don't const-check basic blocks on the cleanup path since we never unwind during
516 // const-eval: a panic causes an immediate compile error. In other words, cleanup blocks
517 // are unreachable during const-eval.
519 // We can't be more conservative (e.g., by const-checking cleanup blocks anyways) because
520 // locals that would never be dropped during normal execution are sometimes dropped during
521 // unwinding, which means backwards-incompatible live-drop errors.
522 if block.is_cleanup {
526 self.super_basic_block_data(bb, block);
529 fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
530 trace!("visit_rvalue: rvalue={:?} location={:?}", rvalue, location);
532 // Special-case reborrows to be more like a copy of a reference.
534 Rvalue::Ref(_, kind, place) => {
535 if let Some(reborrowed_place_ref) = place_as_reborrow(self.tcx, self.body, place) {
536 let ctx = match kind {
537 BorrowKind::Shared => {
538 PlaceContext::NonMutatingUse(NonMutatingUseContext::SharedBorrow)
540 BorrowKind::Shallow => {
541 PlaceContext::NonMutatingUse(NonMutatingUseContext::ShallowBorrow)
543 BorrowKind::Unique => {
544 PlaceContext::NonMutatingUse(NonMutatingUseContext::UniqueBorrow)
546 BorrowKind::Mut { .. } => {
547 PlaceContext::MutatingUse(MutatingUseContext::Borrow)
550 self.visit_local(&reborrowed_place_ref.local, ctx, location);
551 self.visit_projection(reborrowed_place_ref, ctx, location);
555 Rvalue::AddressOf(mutbl, place) => {
556 if let Some(reborrowed_place_ref) = place_as_reborrow(self.tcx, self.body, place) {
557 let ctx = match mutbl {
559 PlaceContext::NonMutatingUse(NonMutatingUseContext::AddressOf)
561 Mutability::Mut => PlaceContext::MutatingUse(MutatingUseContext::AddressOf),
563 self.visit_local(&reborrowed_place_ref.local, ctx, location);
564 self.visit_projection(reborrowed_place_ref, ctx, location);
571 self.super_rvalue(rvalue, location);
574 Rvalue::ThreadLocalRef(_) => self.check_op(ops::ThreadLocalAccess),
578 | Rvalue::Discriminant(..)
580 | Rvalue::Aggregate(..) => {}
582 Rvalue::Ref(_, kind @ BorrowKind::Mut { .. }, ref place)
583 | Rvalue::Ref(_, kind @ BorrowKind::Unique, ref place) => {
584 let ty = place.ty(self.body, self.tcx).ty;
585 let is_allowed = match ty.kind() {
586 // Inside a `static mut`, `&mut [...]` is allowed.
587 ty::Array(..) | ty::Slice(_)
588 if self.const_kind() == hir::ConstContext::Static(hir::Mutability::Mut) =>
593 // FIXME(ecstaticmorse): We could allow `&mut []` inside a const context given
594 // that this is merely a ZST and it is already eligible for promotion.
595 // This may require an RFC?
597 ty::Array(_, len) if len.try_eval_usize(cx.tcx, cx.param_env) == Some(0)
604 if let BorrowKind::Mut { .. } = kind {
605 self.check_mut_borrow(place.local, hir::BorrowKind::Ref)
607 self.check_op(ops::CellBorrow);
612 Rvalue::AddressOf(Mutability::Mut, ref place) => {
613 self.check_mut_borrow(place.local, hir::BorrowKind::Raw)
616 Rvalue::Ref(_, BorrowKind::Shared | BorrowKind::Shallow, ref place)
617 | Rvalue::AddressOf(Mutability::Not, ref place) => {
618 let borrowed_place_has_mut_interior = qualifs::in_place::<HasMutInterior, _>(
620 &mut |local| self.qualifs.has_mut_interior(self.ccx, local, location),
624 if borrowed_place_has_mut_interior {
625 match self.const_kind() {
626 // In a const fn all borrows are transient or point to the places given via
627 // references in the arguments (so we already checked them with
628 // TransientCellBorrow/CellBorrow as appropriate).
629 // The borrow checker guarantees that no new non-transient borrows are created.
630 // NOTE: Once we have heap allocations during CTFE we need to figure out
631 // how to prevent `const fn` to create long-lived allocations that point
632 // to (interior) mutable memory.
633 hir::ConstContext::ConstFn => self.check_op(ops::TransientCellBorrow),
635 // Locals with StorageDead are definitely not part of the final constant value, and
636 // it is thus inherently safe to permit such locals to have their
637 // address taken as we can't end up with a reference to them in the
639 // Note: This is only sound if every local that has a `StorageDead` has a
640 // `StorageDead` in every control flow path leading to a `return` terminator.
641 if self.local_has_storage_dead(place.local) {
642 self.check_op(ops::TransientCellBorrow);
644 self.check_op(ops::CellBorrow);
652 CastKind::Pointer(PointerCast::MutToConstPointer | PointerCast::ArrayToPointer),
659 PointerCast::UnsafeFnPointer
660 | PointerCast::ClosureFnPointer(_)
661 | PointerCast::ReifyFnPointer,
665 ) => self.check_op(ops::FnPtrCast),
667 Rvalue::Cast(CastKind::Pointer(PointerCast::Unsize), _, _) => {
668 // Nothing to check here (`check_local_or_return_ty` ensures no trait objects occur
669 // in the type of any local, which also excludes casts).
672 Rvalue::Cast(CastKind::Misc, ref operand, cast_ty) => {
673 let operand_ty = operand.ty(self.body, self.tcx);
674 let cast_in = CastTy::from_ty(operand_ty).expect("bad input type for cast");
675 let cast_out = CastTy::from_ty(cast_ty).expect("bad output type for cast");
677 if let (CastTy::Ptr(_) | CastTy::FnPtr, CastTy::Int(_)) = (cast_in, cast_out) {
678 self.check_op(ops::RawPtrToIntCast);
682 Rvalue::NullaryOp(NullOp::SizeOf | NullOp::AlignOf, _) => {}
683 Rvalue::NullaryOp(NullOp::Box, _) => self.check_op(ops::HeapAllocation),
684 Rvalue::ShallowInitBox(_, _) => {}
686 Rvalue::UnaryOp(_, ref operand) => {
687 let ty = operand.ty(self.body, self.tcx);
688 if is_int_bool_or_char(ty) {
689 // Int, bool, and char operations are fine.
690 } else if ty.is_floating_point() {
691 self.check_op(ops::FloatingPointOp);
693 span_bug!(self.span, "non-primitive type in `Rvalue::UnaryOp`: {:?}", ty);
697 Rvalue::BinaryOp(op, box (ref lhs, ref rhs))
698 | Rvalue::CheckedBinaryOp(op, box (ref lhs, ref rhs)) => {
699 let lhs_ty = lhs.ty(self.body, self.tcx);
700 let rhs_ty = rhs.ty(self.body, self.tcx);
702 if is_int_bool_or_char(lhs_ty) && is_int_bool_or_char(rhs_ty) {
703 // Int, bool, and char operations are fine.
704 } else if lhs_ty.is_fn_ptr() || lhs_ty.is_unsafe_ptr() {
705 assert_eq!(lhs_ty, rhs_ty);
713 || op == BinOp::Offset
716 self.check_op(ops::RawPtrComparison);
717 } else if lhs_ty.is_floating_point() || rhs_ty.is_floating_point() {
718 self.check_op(ops::FloatingPointOp);
722 "non-primitive type in `Rvalue::BinaryOp`: {:?} ⚬ {:?}",
731 fn visit_operand(&mut self, op: &Operand<'tcx>, location: Location) {
732 self.super_operand(op, location);
733 if let Operand::Constant(c) = op {
734 if let Some(def_id) = c.check_static_ptr(self.tcx) {
735 self.check_static(def_id, self.span);
739 fn visit_projection_elem(
742 proj_base: &[PlaceElem<'tcx>],
743 elem: PlaceElem<'tcx>,
744 context: PlaceContext,
748 "visit_projection_elem: place_local={:?} proj_base={:?} elem={:?} \
749 context={:?} location={:?}",
757 self.super_projection_elem(place_local, proj_base, elem, context, location);
760 ProjectionElem::Deref => {
761 let base_ty = Place::ty_from(place_local, proj_base, self.body, self.tcx).ty;
762 if let ty::RawPtr(_) = base_ty.kind() {
763 if proj_base.is_empty() {
764 let decl = &self.body.local_decls[place_local];
765 if let Some(box LocalInfo::StaticRef { def_id, .. }) = decl.local_info {
766 let span = decl.source_info.span;
767 self.check_static(def_id, span);
771 self.check_op(ops::RawPtrDeref);
774 if context.is_mutating_use() {
775 self.check_op(ops::MutDeref);
779 ProjectionElem::ConstantIndex { .. }
780 | ProjectionElem::Downcast(..)
781 | ProjectionElem::Subslice { .. }
782 | ProjectionElem::Field(..)
783 | ProjectionElem::Index(_) => {}
787 fn visit_source_info(&mut self, source_info: &SourceInfo) {
788 trace!("visit_source_info: source_info={:?}", source_info);
789 self.span = source_info.span;
792 fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
793 trace!("visit_statement: statement={:?} location={:?}", statement, location);
795 self.super_statement(statement, location);
797 match statement.kind {
798 StatementKind::LlvmInlineAsm { .. } => {
799 self.check_op(ops::InlineAsm);
802 StatementKind::Assign(..)
803 | StatementKind::SetDiscriminant { .. }
804 | StatementKind::FakeRead(..)
805 | StatementKind::StorageLive(_)
806 | StatementKind::StorageDead(_)
807 | StatementKind::Retag { .. }
808 | StatementKind::AscribeUserType(..)
809 | StatementKind::Coverage(..)
810 | StatementKind::CopyNonOverlapping(..)
811 | StatementKind::Nop => {}
815 #[instrument(level = "debug", skip(self))]
816 fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
817 use rustc_target::spec::abi::Abi::RustIntrinsic;
819 self.super_terminator(terminator, location);
821 match &terminator.kind {
822 TerminatorKind::Call { func, args, .. } => {
823 let ConstCx { tcx, body, param_env, .. } = *self.ccx;
824 let caller = self.def_id().to_def_id();
826 let fn_ty = func.ty(body, tcx);
828 let (mut callee, mut substs) = match *fn_ty.kind() {
829 ty::FnDef(def_id, substs) => (def_id, substs),
832 self.check_op(ops::FnCallIndirect);
836 span_bug!(terminator.source_info.span, "invalid callee of type {:?}", fn_ty)
840 let mut nonconst_call_permission = false;
842 // Attempting to call a trait method?
843 if let Some(trait_id) = tcx.trait_of_item(callee) {
844 trace!("attempting to call a trait method");
845 if !self.tcx.features().const_trait_impl {
846 self.check_op(ops::FnCallNonConst);
850 let trait_ref = TraitRef::from_method(tcx, trait_id, substs);
851 let obligation = Obligation::new(
852 ObligationCause::dummy(),
854 Binder::dummy(TraitPredicate {
856 constness: ty::BoundConstness::ConstIfConst,
860 let implsrc = tcx.infer_ctxt().enter(|infcx| {
862 SelectionContext::with_constness(&infcx, hir::Constness::Const);
863 selcx.select(&obligation)
867 Ok(Some(ImplSource::Param(_, ty::BoundConstness::ConstIfConst))) => {
869 "const_trait_impl: provided {:?} via where-clause in {:?}",
874 Ok(Some(ImplSource::UserDefined(data))) => {
875 let callee_name = tcx.item_name(callee);
876 if let Some(&did) = tcx
877 .associated_item_def_ids(data.impl_def_id)
879 .find(|did| tcx.item_name(**did) == callee_name)
881 // using internal substs is ok here, since this is only
882 // used for the `resolve` call below
883 substs = InternalSubsts::identity_for_item(tcx, did);
887 _ if !tcx.is_const_fn_raw(callee) => {
888 // At this point, it is only legal when the caller is marked with
889 // #[default_method_body_is_const], and the callee is in the same
891 let callee_trait = tcx.trait_of_item(callee);
892 if callee_trait.is_some() {
893 if tcx.has_attr(caller, sym::default_method_body_is_const) {
894 if tcx.trait_of_item(caller) == callee_trait {
895 nonconst_call_permission = true;
900 if !nonconst_call_permission {
901 self.check_op(ops::FnCallNonConst);
908 // Resolve a trait method call to its concrete implementation, which may be in a
909 // `const` trait impl.
910 let instance = Instance::resolve(tcx, param_env, callee, substs);
911 debug!("Resolving ({:?}) -> {:?}", callee, instance);
912 if let Ok(Some(func)) = instance {
913 if let InstanceDef::Item(def) = func.def {
919 // At this point, we are calling a function, `callee`, whose `DefId` is known...
920 if is_lang_special_const_fn(tcx, callee) {
921 // `begin_panic` and `panic_display` are generic functions that accept
922 // types other than str. Check to enforce that only str can be used in
925 // const-eval of the `begin_panic` fn assumes the argument is `&str`
926 if Some(callee) == tcx.lang_items().begin_panic_fn() {
927 match args[0].ty(&self.ccx.body.local_decls, tcx).kind() {
928 ty::Ref(_, ty, _) if ty.is_str() => (),
929 _ => self.check_op(ops::PanicNonStr),
933 // const-eval of the `panic_display` fn assumes the argument is `&&str`
934 if Some(callee) == tcx.lang_items().panic_display() {
935 match args[0].ty(&self.ccx.body.local_decls, tcx).kind() {
936 ty::Ref(_, ty, _) if matches!(ty.kind(), ty::Ref(_, ty, _) if ty.is_str()) =>
938 _ => self.check_op(ops::PanicNonStr),
942 if is_lang_panic_fn(tcx, callee) {
943 // run stability check on non-panic special const fns.
948 if Some(callee) == tcx.lang_items().exchange_malloc_fn() {
949 self.check_op(ops::HeapAllocation);
953 // `async` blocks get lowered to `std::future::from_generator(/* a closure */)`.
954 let is_async_block = Some(callee) == tcx.lang_items().from_generator_fn();
956 let kind = hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Block);
957 self.check_op(ops::Generator(kind));
961 let is_intrinsic = tcx.fn_sig(callee).abi() == RustIntrinsic;
963 if !tcx.is_const_fn_raw(callee) {
964 if tcx.trait_of_item(callee).is_some() {
965 if tcx.has_attr(callee, sym::default_method_body_is_const) {
966 // To get to here we must have already found a const impl for the
967 // trait, but for it to still be non-const can be that the impl is
968 // using default method bodies.
969 nonconst_call_permission = true;
973 if !nonconst_call_permission {
974 self.check_op(ops::FnCallNonConst);
979 // If the `const fn` we are trying to call is not const-stable, ensure that we have
980 // the proper feature gate enabled.
981 if let Some(gate) = is_unstable_const_fn(tcx, callee) {
982 trace!(?gate, "calling unstable const fn");
983 if self.span.allows_unstable(gate) {
987 // Calling an unstable function *always* requires that the corresponding gate
988 // be enabled, even if the function has `#[rustc_allow_const_fn_unstable(the_gate)]`.
989 if !tcx.features().declared_lib_features.iter().any(|&(sym, _)| sym == gate) {
990 self.check_op(ops::FnCallUnstable(callee, Some(gate)));
994 // If this crate is not using stability attributes, or the caller is not claiming to be a
995 // stable `const fn`, that is all that is required.
996 if !self.ccx.is_const_stable_const_fn() {
997 trace!("crate not using stability attributes or caller not stably const");
1001 // Otherwise, we are something const-stable calling a const-unstable fn.
1003 if super::rustc_allow_const_fn_unstable(tcx, caller, gate) {
1004 trace!("rustc_allow_const_fn_unstable gate active");
1008 self.check_op(ops::FnCallUnstable(callee, Some(gate)));
1012 // FIXME(ecstaticmorse); For compatibility, we consider `unstable` callees that
1013 // have no `rustc_const_stable` attributes to be const-unstable as well. This
1014 // should be fixed later.
1015 let callee_is_unstable_unmarked = tcx.lookup_const_stability(callee).is_none()
1016 && tcx.lookup_stability(callee).map_or(false, |s| s.level.is_unstable());
1017 if callee_is_unstable_unmarked {
1018 trace!("callee_is_unstable_unmarked");
1019 // We do not use `const` modifiers for intrinsic "functions", as intrinsics are
1020 // `extern` funtions, and these have no way to get marked `const`. So instead we
1021 // use `rustc_const_(un)stable` attributes to mean that the intrinsic is `const`
1022 if self.ccx.is_const_stable_const_fn() || is_intrinsic {
1023 self.check_op(ops::FnCallUnstable(callee, None));
1027 trace!("permitting call");
1030 // Forbid all `Drop` terminators unless the place being dropped is a local with no
1031 // projections that cannot be `NeedsNonConstDrop`.
1032 TerminatorKind::Drop { place: dropped_place, .. }
1033 | TerminatorKind::DropAndReplace { place: dropped_place, .. } => {
1034 // If we are checking live drops after drop-elaboration, don't emit duplicate
1036 if super::post_drop_elaboration::checking_enabled(self.ccx) {
1040 let mut err_span = self.span;
1042 let ty_needs_non_const_drop = qualifs::NeedsNonConstDrop::in_any_value_of_ty(
1044 dropped_place.ty(self.body, self.tcx).ty,
1047 if !ty_needs_non_const_drop {
1051 let needs_non_const_drop = if let Some(local) = dropped_place.as_local() {
1052 // Use the span where the local was declared as the span of the drop error.
1053 err_span = self.body.local_decls[local].source_info.span;
1054 self.qualifs.needs_non_const_drop(self.ccx, local, location)
1059 if needs_non_const_drop {
1060 self.check_op_spanned(
1061 ops::LiveDrop { dropped_at: Some(terminator.source_info.span) },
1067 TerminatorKind::InlineAsm { .. } => self.check_op(ops::InlineAsm),
1069 TerminatorKind::GeneratorDrop | TerminatorKind::Yield { .. } => {
1070 self.check_op(ops::Generator(hir::GeneratorKind::Gen))
1073 TerminatorKind::Abort => {
1074 // Cleanup blocks are skipped for const checking (see `visit_basic_block_data`).
1075 span_bug!(self.span, "`Abort` terminator outside of cleanup block")
1078 TerminatorKind::Assert { .. }
1079 | TerminatorKind::FalseEdge { .. }
1080 | TerminatorKind::FalseUnwind { .. }
1081 | TerminatorKind::Goto { .. }
1082 | TerminatorKind::Resume
1083 | TerminatorKind::Return
1084 | TerminatorKind::SwitchInt { .. }
1085 | TerminatorKind::Unreachable => {}
1090 fn check_return_ty_is_sync(tcx: TyCtxt<'tcx>, body: &Body<'tcx>, hir_id: HirId) {
1091 let ty = body.return_ty();
1092 tcx.infer_ctxt().enter(|infcx| {
1093 let cause = traits::ObligationCause::new(body.span, hir_id, traits::SharedStatic);
1094 let mut fulfillment_cx = traits::FulfillmentContext::new();
1095 let sync_def_id = tcx.require_lang_item(LangItem::Sync, Some(body.span));
1096 fulfillment_cx.register_bound(&infcx, ty::ParamEnv::empty(), ty, sync_def_id, cause);
1097 if let Err(err) = fulfillment_cx.select_all_or_error(&infcx) {
1098 infcx.report_fulfillment_errors(&err, None, false);
1103 fn place_as_reborrow(
1107 ) -> Option<PlaceRef<'tcx>> {
1108 match place.as_ref().last_projection() {
1109 Some((place_base, ProjectionElem::Deref)) => {
1110 // A borrow of a `static` also looks like `&(*_1)` in the MIR, but `_1` is a `const`
1111 // that points to the allocation for the static. Don't treat these as reborrows.
1112 if body.local_decls[place_base.local].is_ref_to_static() {
1115 // Ensure the type being derefed is a reference and not a raw pointer.
1116 // This is sufficient to prevent an access to a `static mut` from being marked as a
1117 // reborrow, even if the check above were to disappear.
1118 let inner_ty = place_base.ty(body, tcx).ty;
1120 if let ty::Ref(..) = inner_ty.kind() {
1121 return Some(place_base);
1131 fn is_int_bool_or_char(ty: Ty<'_>) -> bool {
1132 ty.is_bool() || ty.is_integral() || ty.is_char()
1135 fn is_async_fn(ccx: &ConstCx<'_, '_>) -> bool {
1136 ccx.fn_sig().map_or(false, |sig| sig.header.asyncness == hir::IsAsync::Async)
1139 fn emit_unstable_in_stable_error(ccx: &ConstCx<'_, '_>, span: Span, gate: Symbol) {
1140 let attr_span = ccx.fn_sig().map_or(ccx.body.span, |sig| sig.span.shrink_to_lo());
1146 &format!("const-stable function cannot use `#[feature({})]`", gate.as_str()),
1150 "if it is not part of the public API, make this function unstably const",
1151 concat!(r#"#[rustc_const_unstable(feature = "...", issue = "...")]"#, '\n').to_owned(),
1152 Applicability::HasPlaceholders,
1156 "otherwise `#[rustc_allow_const_fn_unstable]` can be used to bypass stability checks",
1157 format!("#[rustc_allow_const_fn_unstable({})]\n", gate),
1158 Applicability::MaybeIncorrect,