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