src/librustc_mir/transform/check_consts/validation.rs

   1 //! The `Visitor` responsible for actually checking a `mir::Body` for invalid operations.
   2
   3 use rustc::middle::lang_items;
   4 use rustc::mir::visit::{MutatingUseContext, NonMutatingUseContext, PlaceContext, Visitor};
   5 use rustc::mir::*;
   6 use rustc::traits::{self, TraitEngine};
   7 use rustc::ty::cast::CastTy;
   8 use rustc::ty::{self, TyCtxt};
   9 use rustc_error_codes::*;
  10 use rustc_errors::struct_span_err;
  11 use rustc_hir::{def_id::DefId, HirId};
  12 use rustc_index::bit_set::BitSet;
  13 use rustc_span::symbol::sym;
  14 use rustc_span::Span;
  15
  16 use std::borrow::Cow;
  17 use std::ops::Deref;
  18
  19 use self::old_dataflow::IndirectlyMutableLocals;
  20 use super::ops::{self, NonConstOp};
  21 use super::qualifs::{self, HasMutInterior, NeedsDrop};
  22 use super::resolver::FlowSensitiveAnalysis;
  23 use super::{is_lang_panic_fn, ConstKind, Item, Qualif};
  24 use crate::const_eval::{is_const_fn, is_unstable_const_fn};
  25 use crate::dataflow::{self as old_dataflow, generic as dataflow};
  26
  27 pub type IndirectlyMutableResults<'mir, 'tcx> =
  28     old_dataflow::DataflowResultsCursor<'mir, 'tcx, IndirectlyMutableLocals<'mir, 'tcx>>;
  29
  30 struct QualifCursor<'a, 'mir, 'tcx, Q: Qualif> {
  31     cursor: dataflow::ResultsCursor<'mir, 'tcx, FlowSensitiveAnalysis<'a, 'mir, 'tcx, Q>>,
  32     in_any_value_of_ty: BitSet<Local>,
  33 }
  34
  35 impl<Q: Qualif> QualifCursor<'a, 'mir, 'tcx, Q> {
  36     pub fn new(q: Q, item: &'a Item<'mir, 'tcx>, dead_unwinds: &BitSet<BasicBlock>) -> Self {
  37         let analysis = FlowSensitiveAnalysis::new(q, item);
  38         let results =
  39             dataflow::Engine::new(item.tcx, &item.body, item.def_id, dead_unwinds, analysis)
  40                 .iterate_to_fixpoint();
  41         let cursor = dataflow::ResultsCursor::new(*item.body, results);
  42
  43         let mut in_any_value_of_ty = BitSet::new_empty(item.body.local_decls.len());
  44         for (local, decl) in item.body.local_decls.iter_enumerated() {
  45             if Q::in_any_value_of_ty(item, decl.ty) {
  46                 in_any_value_of_ty.insert(local);
  47             }
  48         }
  49
  50         QualifCursor { cursor, in_any_value_of_ty }
  51     }
  52 }
  53
  54 pub struct Qualifs<'a, 'mir, 'tcx> {
  55     has_mut_interior: QualifCursor<'a, 'mir, 'tcx, HasMutInterior>,
  56     needs_drop: QualifCursor<'a, 'mir, 'tcx, NeedsDrop>,
  57     indirectly_mutable: IndirectlyMutableResults<'mir, 'tcx>,
  58 }
  59
  60 impl Qualifs<'a, 'mir, 'tcx> {
  61     fn indirectly_mutable(&mut self, local: Local, location: Location) -> bool {
  62         self.indirectly_mutable.seek(location);
  63         self.indirectly_mutable.get().contains(local)
  64     }
  65
  66     /// Returns `true` if `local` is `NeedsDrop` at the given `Location`.
  67     ///
  68     /// Only updates the cursor if absolutely necessary
  69     fn needs_drop_lazy_seek(&mut self, local: Local, location: Location) -> bool {
  70         if !self.needs_drop.in_any_value_of_ty.contains(local) {
  71             return false;
  72         }
  73
  74         self.needs_drop.cursor.seek_before(location);
  75         self.needs_drop.cursor.get().contains(local) || self.indirectly_mutable(local, location)
  76     }
  77
  78     /// Returns `true` if `local` is `HasMutInterior` at the given `Location`.
  79     ///
  80     /// Only updates the cursor if absolutely necessary.
  81     fn has_mut_interior_lazy_seek(&mut self, local: Local, location: Location) -> bool {
  82         if !self.has_mut_interior.in_any_value_of_ty.contains(local) {
  83             return false;
  84         }
  85
  86         self.has_mut_interior.cursor.seek_before(location);
  87         self.has_mut_interior.cursor.get().contains(local)
  88             || self.indirectly_mutable(local, location)
  89     }
  90
  91     /// Returns `true` if `local` is `HasMutInterior`, but requires the `has_mut_interior` and
  92     /// `indirectly_mutable` cursors to be updated beforehand.
  93     fn has_mut_interior_eager_seek(&self, local: Local) -> bool {
  94         if !self.has_mut_interior.in_any_value_of_ty.contains(local) {
  95             return false;
  96         }
  97
  98         self.has_mut_interior.cursor.get().contains(local)
  99             || self.indirectly_mutable.get().contains(local)
 100     }
 101
 102     fn in_return_place(&mut self, item: &Item<'_, 'tcx>) -> ConstQualifs {
 103         // Find the `Return` terminator if one exists.
 104         //
 105         // If no `Return` terminator exists, this MIR is divergent. Just return the conservative
 106         // qualifs for the return type.
 107         let return_block = item
 108             .body
 109             .basic_blocks()
 110             .iter_enumerated()
 111             .find(|(_, block)| match block.terminator().kind {
 112                 TerminatorKind::Return => true,
 113                 _ => false,
 114             })
 115             .map(|(bb, _)| bb);
 116
 117         let return_block = match return_block {
 118             None => return qualifs::in_any_value_of_ty(item, item.body.return_ty()),
 119             Some(bb) => bb,
 120         };
 121
 122         let return_loc = item.body.terminator_loc(return_block);
 123
 124         ConstQualifs {
 125             needs_drop: self.needs_drop_lazy_seek(RETURN_PLACE, return_loc),
 126             has_mut_interior: self.has_mut_interior_lazy_seek(RETURN_PLACE, return_loc),
 127         }
 128     }
 129 }
 130
 131 pub struct Validator<'a, 'mir, 'tcx> {
 132     item: &'a Item<'mir, 'tcx>,
 133     qualifs: Qualifs<'a, 'mir, 'tcx>,
 134
 135     /// The span of the current statement.
 136     span: Span,
 137 }
 138
 139 impl Deref for Validator<'_, 'mir, 'tcx> {
 140     type Target = Item<'mir, 'tcx>;
 141
 142     fn deref(&self) -> &Self::Target {
 143         &self.item
 144     }
 145 }
 146
 147 impl Validator<'a, 'mir, 'tcx> {
 148     pub fn new(item: &'a Item<'mir, 'tcx>) -> Self {
 149         let dead_unwinds = BitSet::new_empty(item.body.basic_blocks().len());
 150
 151         let needs_drop = QualifCursor::new(NeedsDrop, item, &dead_unwinds);
 152
 153         let has_mut_interior = QualifCursor::new(HasMutInterior, item, &dead_unwinds);
 154
 155         let indirectly_mutable = old_dataflow::do_dataflow(
 156             item.tcx,
 157             &*item.body,
 158             item.def_id,
 159             &item.tcx.get_attrs(item.def_id),
 160             &dead_unwinds,
 161             old_dataflow::IndirectlyMutableLocals::new(item.tcx, *item.body, item.param_env),
 162             |_, local| old_dataflow::DebugFormatted::new(&local),
 163         );
 164
 165         let indirectly_mutable =
 166             old_dataflow::DataflowResultsCursor::new(indirectly_mutable, *item.body);
 167
 168         let qualifs = Qualifs { needs_drop, has_mut_interior, indirectly_mutable };
 169
 170         Validator { span: item.body.span, item, qualifs }
 171     }
 172
 173     pub fn check_body(&mut self) {
 174         let Item { tcx, body, def_id, const_kind, .. } = *self.item;
 175
 176         let use_min_const_fn_checks = (const_kind == Some(ConstKind::ConstFn)
 177             && crate::const_eval::is_min_const_fn(tcx, def_id))
 178             && !tcx.sess.opts.debugging_opts.unleash_the_miri_inside_of_you;
 179
 180         if use_min_const_fn_checks {
 181             // Enforce `min_const_fn` for stable `const fn`s.
 182             use crate::transform::qualify_min_const_fn::is_min_const_fn;
 183             if let Err((span, err)) = is_min_const_fn(tcx, def_id, &body) {
 184                 error_min_const_fn_violation(tcx, span, err);
 185                 return;
 186             }
 187         }
 188
 189         check_short_circuiting_in_const_local(self.item);
 190
 191         if body.is_cfg_cyclic() {
 192             // We can't provide a good span for the error here, but this should be caught by the
 193             // HIR const-checker anyways.
 194             self.check_op_spanned(ops::Loop, body.span);
 195         }
 196
 197         self.visit_body(body);
 198
 199         // Ensure that the end result is `Sync` in a non-thread local `static`.
 200         let should_check_for_sync =
 201             const_kind == Some(ConstKind::Static) && !tcx.has_attr(def_id, sym::thread_local);
 202
 203         if should_check_for_sync {
 204             let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
 205             check_return_ty_is_sync(tcx, &body, hir_id);
 206         }
 207     }
 208
 209     pub fn qualifs_in_return_place(&mut self) -> ConstQualifs {
 210         self.qualifs.in_return_place(self.item)
 211     }
 212
 213     /// Emits an error at the given `span` if an expression cannot be evaluated in the current
 214     /// context.
 215     pub fn check_op_spanned<O>(&mut self, op: O, span: Span)
 216     where
 217         O: NonConstOp,
 218     {
 219         trace!("check_op: op={:?}", op);
 220
 221         if op.is_allowed_in_item(self) {
 222             return;
 223         }
 224
 225         // If an operation is supported in miri (and is not already controlled by a feature gate) it
 226         // can be turned on with `-Zunleash-the-miri-inside-of-you`.
 227         let is_unleashable = O::IS_SUPPORTED_IN_MIRI && O::feature_gate(self.tcx).is_none();
 228
 229         if is_unleashable && self.tcx.sess.opts.debugging_opts.unleash_the_miri_inside_of_you {
 230             self.tcx.sess.span_warn(span, "skipping const checks");
 231             return;
 232         }
 233
 234         op.emit_error(self, span);
 235     }
 236
 237     /// Emits an error if an expression cannot be evaluated in the current context.
 238     pub fn check_op(&mut self, op: impl NonConstOp) {
 239         let span = self.span;
 240         self.check_op_spanned(op, span)
 241     }
 242
 243     fn check_static(&mut self, def_id: DefId, span: Span) {
 244         let is_thread_local = self.tcx.has_attr(def_id, sym::thread_local);
 245         if is_thread_local {
 246             self.check_op_spanned(ops::ThreadLocalAccess, span)
 247         } else {
 248             self.check_op_spanned(ops::StaticAccess, span)
 249         }
 250     }
 251
 252     fn check_immutable_borrow_like(&mut self, location: Location, place: &Place<'tcx>) {
 253         // FIXME: Change the `in_*` methods to take a `FnMut` so we don't have to manually
 254         // seek the cursors beforehand.
 255         self.qualifs.has_mut_interior.cursor.seek_before(location);
 256         self.qualifs.indirectly_mutable.seek(location);
 257
 258         let borrowed_place_has_mut_interior = HasMutInterior::in_place(
 259             &self.item,
 260             &|local| self.qualifs.has_mut_interior_eager_seek(local),
 261             place.as_ref(),
 262         );
 263
 264         if borrowed_place_has_mut_interior {
 265             self.check_op(ops::CellBorrow);
 266         }
 267     }
 268 }
 269
 270 impl Visitor<'tcx> for Validator<'_, 'mir, 'tcx> {
 271     fn visit_basic_block_data(&mut self, bb: BasicBlock, block: &BasicBlockData<'tcx>) {
 272         trace!("visit_basic_block_data: bb={:?} is_cleanup={:?}", bb, block.is_cleanup);
 273
 274         // Just as the old checker did, we skip const-checking basic blocks on the unwind path.
 275         // These blocks often drop locals that would otherwise be returned from the function.
 276         //
 277         // FIXME: This shouldn't be unsound since a panic at compile time will cause a compiler
 278         // error anyway, but maybe we should do more here?
 279         if block.is_cleanup {
 280             return;
 281         }
 282
 283         self.super_basic_block_data(bb, block);
 284     }
 285
 286     fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
 287         trace!("visit_rvalue: rvalue={:?} location={:?}", rvalue, location);
 288
 289         // Special-case reborrows to be more like a copy of a reference.
 290         match *rvalue {
 291             Rvalue::Ref(_, kind, ref place) => {
 292                 if let Some(reborrowed_proj) = place_as_reborrow(self.tcx, *self.body, place) {
 293                     let ctx = match kind {
 294                         BorrowKind::Shared => {
 295                             PlaceContext::NonMutatingUse(NonMutatingUseContext::SharedBorrow)
 296                         }
 297                         BorrowKind::Shallow => {
 298                             PlaceContext::NonMutatingUse(NonMutatingUseContext::ShallowBorrow)
 299                         }
 300                         BorrowKind::Unique => {
 301                             PlaceContext::NonMutatingUse(NonMutatingUseContext::UniqueBorrow)
 302                         }
 303                         BorrowKind::Mut { .. } => {
 304                             PlaceContext::MutatingUse(MutatingUseContext::Borrow)
 305                         }
 306                     };
 307                     self.visit_place_base(&place.base, ctx, location);
 308                     self.visit_projection(&place.base, reborrowed_proj, ctx, location);
 309                     return;
 310                 }
 311             }
 312             Rvalue::AddressOf(mutbl, ref place) => {
 313                 if let Some(reborrowed_proj) = place_as_reborrow(self.tcx, *self.body, place) {
 314                     let ctx = match mutbl {
 315                         Mutability::Not => {
 316                             PlaceContext::NonMutatingUse(NonMutatingUseContext::AddressOf)
 317                         }
 318                         Mutability::Mut => PlaceContext::MutatingUse(MutatingUseContext::AddressOf),
 319                     };
 320                     self.visit_place_base(&place.base, ctx, location);
 321                     self.visit_projection(&place.base, reborrowed_proj, ctx, location);
 322                     return;
 323                 }
 324             }
 325             _ => {}
 326         }
 327
 328         self.super_rvalue(rvalue, location);
 329
 330         match *rvalue {
 331             Rvalue::Use(_)
 332             | Rvalue::Repeat(..)
 333             | Rvalue::UnaryOp(UnOp::Neg, _)
 334             | Rvalue::UnaryOp(UnOp::Not, _)
 335             | Rvalue::NullaryOp(NullOp::SizeOf, _)
 336             | Rvalue::CheckedBinaryOp(..)
 337             | Rvalue::Cast(CastKind::Pointer(_), ..)
 338             | Rvalue::Discriminant(..)
 339             | Rvalue::Len(_)
 340             | Rvalue::Aggregate(..) => {}
 341
 342             Rvalue::Ref(_, kind @ BorrowKind::Mut { .. }, ref place)
 343             | Rvalue::Ref(_, kind @ BorrowKind::Unique, ref place) => {
 344                 let ty = place.ty(*self.body, self.tcx).ty;
 345                 let is_allowed = match ty.kind {
 346                     // Inside a `static mut`, `&mut [...]` is allowed.
 347                     ty::Array(..) | ty::Slice(_) if self.const_kind() == ConstKind::StaticMut => {
 348                         true
 349                     }
 350
 351                     // FIXME(ecstaticmorse): We could allow `&mut []` inside a const context given
 352                     // that this is merely a ZST and it is already eligible for promotion.
 353                     // This may require an RFC?
 354                     /*
 355                     ty::Array(_, len) if len.try_eval_usize(cx.tcx, cx.param_env) == Some(0)
 356                         => true,
 357                     */
 358                     _ => false,
 359                 };
 360
 361                 if !is_allowed {
 362                     if let BorrowKind::Mut { .. } = kind {
 363                         self.check_op(ops::MutBorrow);
 364                     } else {
 365                         self.check_op(ops::CellBorrow);
 366                     }
 367                 }
 368             }
 369
 370             Rvalue::AddressOf(Mutability::Mut, _) => self.check_op(ops::MutAddressOf),
 371
 372             Rvalue::Ref(_, BorrowKind::Shared, ref place)
 373             | Rvalue::Ref(_, BorrowKind::Shallow, ref place) => {
 374                 self.check_immutable_borrow_like(location, place)
 375             }
 376
 377             Rvalue::AddressOf(Mutability::Not, ref place) => {
 378                 self.check_immutable_borrow_like(location, place)
 379             }
 380
 381             Rvalue::Cast(CastKind::Misc, ref operand, cast_ty) => {
 382                 let operand_ty = operand.ty(*self.body, self.tcx);
 383                 let cast_in = CastTy::from_ty(operand_ty).expect("bad input type for cast");
 384                 let cast_out = CastTy::from_ty(cast_ty).expect("bad output type for cast");
 385
 386                 if let (CastTy::Ptr(_), CastTy::Int(_)) | (CastTy::FnPtr, CastTy::Int(_)) =
 387                     (cast_in, cast_out)
 388                 {
 389                     self.check_op(ops::RawPtrToIntCast);
 390                 }
 391             }
 392
 393             Rvalue::BinaryOp(op, ref lhs, _) => {
 394                 if let ty::RawPtr(_) | ty::FnPtr(..) = lhs.ty(*self.body, self.tcx).kind {
 395                     assert!(
 396                         op == BinOp::Eq
 397                             || op == BinOp::Ne
 398                             || op == BinOp::Le
 399                             || op == BinOp::Lt
 400                             || op == BinOp::Ge
 401                             || op == BinOp::Gt
 402                             || op == BinOp::Offset
 403                     );
 404
 405                     self.check_op(ops::RawPtrComparison);
 406                 }
 407             }
 408
 409             Rvalue::NullaryOp(NullOp::Box, _) => {
 410                 self.check_op(ops::HeapAllocation);
 411             }
 412         }
 413     }
 414
 415     fn visit_place_base(
 416         &mut self,
 417         place_base: &PlaceBase,
 418         context: PlaceContext,
 419         location: Location,
 420     ) {
 421         trace!(
 422             "visit_place_base: place_base={:?} context={:?} location={:?}",
 423             place_base,
 424             context,
 425             location,
 426         );
 427         self.super_place_base(place_base, context, location);
 428
 429         match place_base {
 430             PlaceBase::Local(_) => {}
 431         }
 432     }
 433
 434     fn visit_operand(&mut self, op: &Operand<'tcx>, location: Location) {
 435         self.super_operand(op, location);
 436         if let Operand::Constant(c) = op {
 437             if let Some(def_id) = c.check_static_ptr(self.tcx) {
 438                 self.check_static(def_id, self.span);
 439             }
 440         }
 441     }
 442     fn visit_projection_elem(
 443         &mut self,
 444         place_base: &PlaceBase,
 445         proj_base: &[PlaceElem<'tcx>],
 446         elem: &PlaceElem<'tcx>,
 447         context: PlaceContext,
 448         location: Location,
 449     ) {
 450         trace!(
 451             "visit_projection_elem: place_base={:?} proj_base={:?} elem={:?} \
 452             context={:?} location={:?}",
 453             place_base,
 454             proj_base,
 455             elem,
 456             context,
 457             location,
 458         );
 459
 460         self.super_projection_elem(place_base, proj_base, elem, context, location);
 461
 462         match elem {
 463             ProjectionElem::Deref => {
 464                 let base_ty = Place::ty_from(place_base, proj_base, *self.body, self.tcx).ty;
 465                 if let ty::RawPtr(_) = base_ty.kind {
 466                     if proj_base.is_empty() {
 467                         if let (PlaceBase::Local(local), []) = (place_base, proj_base) {
 468                             let decl = &self.body.local_decls[*local];
 469                             if let LocalInfo::StaticRef { def_id, .. } = decl.local_info {
 470                                 let span = decl.source_info.span;
 471                                 self.check_static(def_id, span);
 472                                 return;
 473                             }
 474                         }
 475                     }
 476                     self.check_op(ops::RawPtrDeref);
 477                 }
 478
 479                 if context.is_mutating_use() {
 480                     self.check_op(ops::MutDeref);
 481                 }
 482             }
 483
 484             ProjectionElem::ConstantIndex { .. }
 485             | ProjectionElem::Subslice { .. }
 486             | ProjectionElem::Field(..)
 487             | ProjectionElem::Index(_) => {
 488                 let base_ty = Place::ty_from(place_base, proj_base, *self.body, self.tcx).ty;
 489                 match base_ty.ty_adt_def() {
 490                     Some(def) if def.is_union() => {
 491                         self.check_op(ops::UnionAccess);
 492                     }
 493
 494                     _ => {}
 495                 }
 496             }
 497
 498             ProjectionElem::Downcast(..) => {
 499                 self.check_op(ops::Downcast);
 500             }
 501         }
 502     }
 503
 504     fn visit_source_info(&mut self, source_info: &SourceInfo) {
 505         trace!("visit_source_info: source_info={:?}", source_info);
 506         self.span = source_info.span;
 507     }
 508
 509     fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
 510         trace!("visit_statement: statement={:?} location={:?}", statement, location);
 511
 512         match statement.kind {
 513             StatementKind::Assign(..) | StatementKind::SetDiscriminant { .. } => {
 514                 self.super_statement(statement, location);
 515             }
 516             StatementKind::FakeRead(FakeReadCause::ForMatchedPlace, _) => {
 517                 self.check_op(ops::IfOrMatch);
 518             }
 519             // FIXME(eddyb) should these really do nothing?
 520             StatementKind::FakeRead(..)
 521             | StatementKind::StorageLive(_)
 522             | StatementKind::StorageDead(_)
 523             | StatementKind::InlineAsm { .. }
 524             | StatementKind::Retag { .. }
 525             | StatementKind::AscribeUserType(..)
 526             | StatementKind::Nop => {}
 527         }
 528     }
 529
 530     fn visit_terminator_kind(&mut self, kind: &TerminatorKind<'tcx>, location: Location) {
 531         trace!("visit_terminator_kind: kind={:?} location={:?}", kind, location);
 532         self.super_terminator_kind(kind, location);
 533
 534         match kind {
 535             TerminatorKind::Call { func, .. } => {
 536                 let fn_ty = func.ty(*self.body, self.tcx);
 537
 538                 let def_id = match fn_ty.kind {
 539                     ty::FnDef(def_id, _) => def_id,
 540
 541                     ty::FnPtr(_) => {
 542                         self.check_op(ops::FnCallIndirect);
 543                         return;
 544                     }
 545                     _ => {
 546                         self.check_op(ops::FnCallOther);
 547                         return;
 548                     }
 549                 };
 550
 551                 // At this point, we are calling a function whose `DefId` is known...
 552                 if is_const_fn(self.tcx, def_id) {
 553                     return;
 554                 }
 555
 556                 if is_lang_panic_fn(self.tcx, def_id) {
 557                     self.check_op(ops::Panic);
 558                 } else if let Some(feature) = is_unstable_const_fn(self.tcx, def_id) {
 559                     // Exempt unstable const fns inside of macros with
 560                     // `#[allow_internal_unstable]`.
 561                     if !self.span.allows_unstable(feature) {
 562                         self.check_op(ops::FnCallUnstable(def_id, feature));
 563                     }
 564                 } else {
 565                     self.check_op(ops::FnCallNonConst(def_id));
 566                 }
 567             }
 568
 569             // Forbid all `Drop` terminators unless the place being dropped is a local with no
 570             // projections that cannot be `NeedsDrop`.
 571             TerminatorKind::Drop { location: dropped_place, .. }
 572             | TerminatorKind::DropAndReplace { location: dropped_place, .. } => {
 573                 let mut err_span = self.span;
 574
 575                 // Check to see if the type of this place can ever have a drop impl. If not, this
 576                 // `Drop` terminator is frivolous.
 577                 let ty_needs_drop =
 578                     dropped_place.ty(*self.body, self.tcx).ty.needs_drop(self.tcx, self.param_env);
 579
 580                 if !ty_needs_drop {
 581                     return;
 582                 }
 583
 584                 let needs_drop = if let Some(local) = dropped_place.as_local() {
 585                     // Use the span where the local was declared as the span of the drop error.
 586                     err_span = self.body.local_decls[local].source_info.span;
 587                     self.qualifs.needs_drop_lazy_seek(local, location)
 588                 } else {
 589                     true
 590                 };
 591
 592                 if needs_drop {
 593                     self.check_op_spanned(ops::LiveDrop, err_span);
 594                 }
 595             }
 596
 597             _ => {}
 598         }
 599     }
 600 }
 601
 602 fn error_min_const_fn_violation(tcx: TyCtxt<'_>, span: Span, msg: Cow<'_, str>) {
 603     struct_span_err!(tcx.sess, span, E0723, "{}", msg)
 604         .note("for more information, see issue https://github.com/rust-lang/rust/issues/57563")
 605         .help("add `#![feature(const_fn)]` to the crate attributes to enable")
 606         .emit();
 607 }
 608
 609 fn check_short_circuiting_in_const_local(item: &Item<'_, 'tcx>) {
 610     let body = item.body;
 611
 612     if body.control_flow_destroyed.is_empty() {
 613         return;
 614     }
 615
 616     let mut locals = body.vars_iter();
 617     if let Some(local) = locals.next() {
 618         let span = body.local_decls[local].source_info.span;
 619         let mut error = item.tcx.sess.struct_span_err(
 620             span,
 621             &format!(
 622                 "new features like let bindings are not permitted in {}s \
 623                 which also use short circuiting operators",
 624                 item.const_kind(),
 625             ),
 626         );
 627         for (span, kind) in body.control_flow_destroyed.iter() {
 628             error.span_note(
 629                 *span,
 630                 &format!(
 631                     "use of {} here does not actually short circuit due to \
 632                 the const evaluator presently not being able to do control flow. \
 633                 See https://github.com/rust-lang/rust/issues/49146 for more \
 634                 information.",
 635                     kind
 636                 ),
 637             );
 638         }
 639         for local in locals {
 640             let span = body.local_decls[local].source_info.span;
 641             error.span_note(span, "more locals defined here");
 642         }
 643         error.emit();
 644     }
 645 }
 646
 647 fn check_return_ty_is_sync(tcx: TyCtxt<'tcx>, body: &Body<'tcx>, hir_id: HirId) {
 648     let ty = body.return_ty();
 649     tcx.infer_ctxt().enter(|infcx| {
 650         let cause = traits::ObligationCause::new(body.span, hir_id, traits::SharedStatic);
 651         let mut fulfillment_cx = traits::FulfillmentContext::new();
 652         let sync_def_id = tcx.require_lang_item(lang_items::SyncTraitLangItem, Some(body.span));
 653         fulfillment_cx.register_bound(&infcx, ty::ParamEnv::empty(), ty, sync_def_id, cause);
 654         if let Err(err) = fulfillment_cx.select_all_or_error(&infcx) {
 655             infcx.report_fulfillment_errors(&err, None, false);
 656         }
 657     });
 658 }
 659
 660 fn place_as_reborrow(
 661     tcx: TyCtxt<'tcx>,
 662     body: &Body<'tcx>,
 663     place: &'a Place<'tcx>,
 664 ) -> Option<&'a [PlaceElem<'tcx>]> {
 665     place.projection.split_last().and_then(|(outermost, inner)| {
 666         if outermost != &ProjectionElem::Deref {
 667             return None;
 668         }
 669
 670         // A borrow of a `static` also looks like `&(*_1)` in the MIR, but `_1` is a `const`
 671         // that points to the allocation for the static. Don't treat these as reborrows.
 672         match place.base {
 673             PlaceBase::Local(local) => {
 674                 if body.local_decls[local].is_ref_to_static() {
 675                     return None;
 676                 }
 677             }
 678         }
 679
 680         // Ensure the type being derefed is a reference and not a raw pointer.
 681         //
 682         // This is sufficient to prevent an access to a `static mut` from being marked as a
 683         // reborrow, even if the check above were to disappear.
 684         let inner_ty = Place::ty_from(&place.base, inner, body, tcx).ty;
 685         match inner_ty.kind {
 686             ty::Ref(..) => Some(inner),
 687             _ => None,
 688         }
 689     })
 690 }