compiler/rustc_mir/src/borrow_check/invalidation.rs

   1 use rustc_data_structures::graph::dominators::Dominators;
   2 use rustc_middle::mir::visit::Visitor;
   3 use rustc_middle::mir::{BasicBlock, Body, Location, Place, Rvalue};
   4 use rustc_middle::mir::{BorrowKind, Mutability, Operand};
   5 use rustc_middle::mir::{InlineAsmOperand, Terminator, TerminatorKind};
   6 use rustc_middle::mir::{Statement, StatementKind};
   7 use rustc_middle::ty::TyCtxt;
   8
   9 use crate::dataflow::indexes::BorrowIndex;
  10
  11 use crate::borrow_check::{
  12     borrow_set::BorrowSet, facts::AllFacts, location::LocationTable, path_utils::*, AccessDepth,
  13     Activation, ArtificialField, Deep, JustWrite, LocalMutationIsAllowed, MutateMode, Read,
  14     ReadKind, ReadOrWrite, Reservation, Shallow, Write, WriteAndRead, WriteKind,
  15 };
  16
  17 pub(super) fn generate_invalidates<'tcx>(
  18     tcx: TyCtxt<'tcx>,
  19     all_facts: &mut Option<AllFacts>,
  20     location_table: &LocationTable,
  21     body: &Body<'tcx>,
  22     borrow_set: &BorrowSet<'tcx>,
  23 ) {
  24     if all_facts.is_none() {
  25         // Nothing to do if we don't have any facts
  26         return;
  27     }
  28
  29     if let Some(all_facts) = all_facts {
  30         let _prof_timer = tcx.prof.generic_activity("polonius_fact_generation");
  31         let dominators = body.dominators();
  32         let mut ig = InvalidationGenerator {
  33             all_facts,
  34             borrow_set,
  35             tcx,
  36             location_table,
  37             body: &body,
  38             dominators,
  39         };
  40         ig.visit_body(body);
  41     }
  42 }
  43
  44 struct InvalidationGenerator<'cx, 'tcx> {
  45     tcx: TyCtxt<'tcx>,
  46     all_facts: &'cx mut AllFacts,
  47     location_table: &'cx LocationTable,
  48     body: &'cx Body<'tcx>,
  49     dominators: Dominators<BasicBlock>,
  50     borrow_set: &'cx BorrowSet<'tcx>,
  51 }
  52
  53 /// Visits the whole MIR and generates `invalidates()` facts.
  54 /// Most of the code implementing this was stolen from `borrow_check/mod.rs`.
  55 impl<'cx, 'tcx> Visitor<'tcx> for InvalidationGenerator<'cx, 'tcx> {
  56     fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
  57         self.check_activations(location);
  58
  59         match &statement.kind {
  60             StatementKind::Assign(box (lhs, rhs)) => {
  61                 self.consume_rvalue(location, rhs);
  62
  63                 self.mutate_place(location, *lhs, Shallow(None), JustWrite);
  64             }
  65             StatementKind::FakeRead(_, _) => {
  66                 // Only relevant for initialized/liveness/safety checks.
  67             }
  68             StatementKind::SetDiscriminant { place, variant_index: _ } => {
  69                 self.mutate_place(location, **place, Shallow(None), JustWrite);
  70             }
  71             StatementKind::LlvmInlineAsm(asm) => {
  72                 for (o, output) in asm.asm.outputs.iter().zip(asm.outputs.iter()) {
  73                     if o.is_indirect {
  74                         // FIXME(eddyb) indirect inline asm outputs should
  75                         // be encoded through MIR place derefs instead.
  76                         self.access_place(
  77                             location,
  78                             *output,
  79                             (Deep, Read(ReadKind::Copy)),
  80                             LocalMutationIsAllowed::No,
  81                         );
  82                     } else {
  83                         self.mutate_place(
  84                             location,
  85                             *output,
  86                             if o.is_rw { Deep } else { Shallow(None) },
  87                             if o.is_rw { WriteAndRead } else { JustWrite },
  88                         );
  89                     }
  90                 }
  91                 for (_, input) in asm.inputs.iter() {
  92                     self.consume_operand(location, input);
  93                 }
  94             }
  95             StatementKind::CopyNonOverlapping(box rustc_middle::mir::CopyNonOverlapping {
  96                 ref src,
  97                 ref dst,
  98                 ref count,
  99             }) => {
 100                 self.consume_operand(location, src);
 101                 self.consume_operand(location, dst);
 102                 self.consume_operand(location, count);
 103             }
 104             StatementKind::Nop
 105             | StatementKind::Coverage(..)
 106             | StatementKind::AscribeUserType(..)
 107             | StatementKind::Retag { .. }
 108             | StatementKind::StorageLive(..) => {
 109                 // `Nop`, `AscribeUserType`, `Retag`, and `StorageLive` are irrelevant
 110                 // to borrow check.
 111             }
 112             StatementKind::StorageDead(local) => {
 113                 self.access_place(
 114                     location,
 115                     Place::from(*local),
 116                     (Shallow(None), Write(WriteKind::StorageDeadOrDrop)),
 117                     LocalMutationIsAllowed::Yes,
 118                 );
 119             }
 120         }
 121
 122         self.super_statement(statement, location);
 123     }
 124
 125     fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
 126         self.check_activations(location);
 127
 128         match &terminator.kind {
 129             TerminatorKind::SwitchInt { ref discr, switch_ty: _, targets: _ } => {
 130                 self.consume_operand(location, discr);
 131             }
 132             TerminatorKind::Drop { place: drop_place, target: _, unwind: _ } => {
 133                 self.access_place(
 134                     location,
 135                     *drop_place,
 136                     (AccessDepth::Drop, Write(WriteKind::StorageDeadOrDrop)),
 137                     LocalMutationIsAllowed::Yes,
 138                 );
 139             }
 140             TerminatorKind::DropAndReplace {
 141                 place: drop_place,
 142                 value: ref new_value,
 143                 target: _,
 144                 unwind: _,
 145             } => {
 146                 self.mutate_place(location, *drop_place, Deep, JustWrite);
 147                 self.consume_operand(location, new_value);
 148             }
 149             TerminatorKind::Call {
 150                 ref func,
 151                 ref args,
 152                 destination,
 153                 cleanup: _,
 154                 from_hir_call: _,
 155                 fn_span: _,
 156             } => {
 157                 self.consume_operand(location, func);
 158                 for arg in args {
 159                     self.consume_operand(location, arg);
 160                 }
 161                 if let Some((dest, _ /*bb*/)) = destination {
 162                     self.mutate_place(location, *dest, Deep, JustWrite);
 163                 }
 164             }
 165             TerminatorKind::Assert { ref cond, expected: _, ref msg, target: _, cleanup: _ } => {
 166                 self.consume_operand(location, cond);
 167                 use rustc_middle::mir::AssertKind;
 168                 if let AssertKind::BoundsCheck { ref len, ref index } = *msg {
 169                     self.consume_operand(location, len);
 170                     self.consume_operand(location, index);
 171                 }
 172             }
 173             TerminatorKind::Yield { ref value, resume, resume_arg, drop: _ } => {
 174                 self.consume_operand(location, value);
 175
 176                 // Invalidate all borrows of local places
 177                 let borrow_set = self.borrow_set;
 178                 let resume = self.location_table.start_index(resume.start_location());
 179                 for (i, data) in borrow_set.iter_enumerated() {
 180                     if borrow_of_local_data(data.borrowed_place) {
 181                         self.all_facts.invalidates.push((resume, i));
 182                     }
 183                 }
 184
 185                 self.mutate_place(location, *resume_arg, Deep, JustWrite);
 186             }
 187             TerminatorKind::Resume | TerminatorKind::Return | TerminatorKind::GeneratorDrop => {
 188                 // Invalidate all borrows of local places
 189                 let borrow_set = self.borrow_set;
 190                 let start = self.location_table.start_index(location);
 191                 for (i, data) in borrow_set.iter_enumerated() {
 192                     if borrow_of_local_data(data.borrowed_place) {
 193                         self.all_facts.invalidates.push((start, i));
 194                     }
 195                 }
 196             }
 197             TerminatorKind::InlineAsm {
 198                 template: _,
 199                 ref operands,
 200                 options: _,
 201                 line_spans: _,
 202                 destination: _,
 203             } => {
 204                 for op in operands {
 205                     match *op {
 206                         InlineAsmOperand::In { reg: _, ref value }
 207                         | InlineAsmOperand::Const { ref value } => {
 208                             self.consume_operand(location, value);
 209                         }
 210                         InlineAsmOperand::Out { reg: _, late: _, place, .. } => {
 211                             if let Some(place) = place {
 212                                 self.mutate_place(location, place, Shallow(None), JustWrite);
 213                             }
 214                         }
 215                         InlineAsmOperand::InOut { reg: _, late: _, ref in_value, out_place } => {
 216                             self.consume_operand(location, in_value);
 217                             if let Some(out_place) = out_place {
 218                                 self.mutate_place(location, out_place, Shallow(None), JustWrite);
 219                             }
 220                         }
 221                         InlineAsmOperand::SymFn { value: _ }
 222                         | InlineAsmOperand::SymStatic { def_id: _ } => {}
 223                     }
 224                 }
 225             }
 226             TerminatorKind::Goto { target: _ }
 227             | TerminatorKind::Abort
 228             | TerminatorKind::Unreachable
 229             | TerminatorKind::FalseEdge { real_target: _, imaginary_target: _ }
 230             | TerminatorKind::FalseUnwind { real_target: _, unwind: _ } => {
 231                 // no data used, thus irrelevant to borrowck
 232             }
 233         }
 234
 235         self.super_terminator(terminator, location);
 236     }
 237 }
 238
 239 impl<'cx, 'tcx> InvalidationGenerator<'cx, 'tcx> {
 240     /// Simulates mutation of a place.
 241     fn mutate_place(
 242         &mut self,
 243         location: Location,
 244         place: Place<'tcx>,
 245         kind: AccessDepth,
 246         _mode: MutateMode,
 247     ) {
 248         self.access_place(
 249             location,
 250             place,
 251             (kind, Write(WriteKind::Mutate)),
 252             LocalMutationIsAllowed::ExceptUpvars,
 253         );
 254     }
 255
 256     /// Simulates consumption of an operand.
 257     fn consume_operand(&mut self, location: Location, operand: &Operand<'tcx>) {
 258         match *operand {
 259             Operand::Copy(place) => {
 260                 self.access_place(
 261                     location,
 262                     place,
 263                     (Deep, Read(ReadKind::Copy)),
 264                     LocalMutationIsAllowed::No,
 265                 );
 266             }
 267             Operand::Move(place) => {
 268                 self.access_place(
 269                     location,
 270                     place,
 271                     (Deep, Write(WriteKind::Move)),
 272                     LocalMutationIsAllowed::Yes,
 273                 );
 274             }
 275             Operand::Constant(_) => {}
 276         }
 277     }
 278
 279     // Simulates consumption of an rvalue
 280     fn consume_rvalue(&mut self, location: Location, rvalue: &Rvalue<'tcx>) {
 281         match *rvalue {
 282             Rvalue::Ref(_ /*rgn*/, bk, place) => {
 283                 let access_kind = match bk {
 284                     BorrowKind::Shallow => {
 285                         (Shallow(Some(ArtificialField::ShallowBorrow)), Read(ReadKind::Borrow(bk)))
 286                     }
 287                     BorrowKind::Shared => (Deep, Read(ReadKind::Borrow(bk))),
 288                     BorrowKind::Unique | BorrowKind::Mut { .. } => {
 289                         let wk = WriteKind::MutableBorrow(bk);
 290                         if allow_two_phase_borrow(bk) {
 291                             (Deep, Reservation(wk))
 292                         } else {
 293                             (Deep, Write(wk))
 294                         }
 295                     }
 296                 };
 297
 298                 self.access_place(location, place, access_kind, LocalMutationIsAllowed::No);
 299             }
 300
 301             Rvalue::AddressOf(mutability, place) => {
 302                 let access_kind = match mutability {
 303                     Mutability::Mut => (
 304                         Deep,
 305                         Write(WriteKind::MutableBorrow(BorrowKind::Mut {
 306                             allow_two_phase_borrow: false,
 307                         })),
 308                     ),
 309                     Mutability::Not => (Deep, Read(ReadKind::Borrow(BorrowKind::Shared))),
 310                 };
 311
 312                 self.access_place(location, place, access_kind, LocalMutationIsAllowed::No);
 313             }
 314
 315             Rvalue::ThreadLocalRef(_) => {}
 316
 317             Rvalue::Use(ref operand)
 318             | Rvalue::Repeat(ref operand, _)
 319             | Rvalue::UnaryOp(_ /*un_op*/, ref operand)
 320             | Rvalue::Cast(_ /*cast_kind*/, ref operand, _ /*ty*/) => {
 321                 self.consume_operand(location, operand)
 322             }
 323
 324             Rvalue::Len(place) | Rvalue::Discriminant(place) => {
 325                 let af = match *rvalue {
 326                     Rvalue::Len(..) => Some(ArtificialField::ArrayLength),
 327                     Rvalue::Discriminant(..) => None,
 328                     _ => unreachable!(),
 329                 };
 330                 self.access_place(
 331                     location,
 332                     place,
 333                     (Shallow(af), Read(ReadKind::Copy)),
 334                     LocalMutationIsAllowed::No,
 335                 );
 336             }
 337
 338             Rvalue::BinaryOp(_bin_op, box (ref operand1, ref operand2))
 339             | Rvalue::CheckedBinaryOp(_bin_op, box (ref operand1, ref operand2)) => {
 340                 self.consume_operand(location, operand1);
 341                 self.consume_operand(location, operand2);
 342             }
 343
 344             Rvalue::NullaryOp(_op, _ty) => {}
 345
 346             Rvalue::Aggregate(_, ref operands) => {
 347                 for operand in operands {
 348                     self.consume_operand(location, operand);
 349                 }
 350             }
 351         }
 352     }
 353
 354     /// Simulates an access to a place.
 355     fn access_place(
 356         &mut self,
 357         location: Location,
 358         place: Place<'tcx>,
 359         kind: (AccessDepth, ReadOrWrite),
 360         _is_local_mutation_allowed: LocalMutationIsAllowed,
 361     ) {
 362         let (sd, rw) = kind;
 363         // note: not doing check_access_permissions checks because they don't generate invalidates
 364         self.check_access_for_conflict(location, place, sd, rw);
 365     }
 366
 367     fn check_access_for_conflict(
 368         &mut self,
 369         location: Location,
 370         place: Place<'tcx>,
 371         sd: AccessDepth,
 372         rw: ReadOrWrite,
 373     ) {
 374         debug!(
 375             "invalidation::check_access_for_conflict(location={:?}, place={:?}, sd={:?}, \
 376              rw={:?})",
 377             location, place, sd, rw,
 378         );
 379         let tcx = self.tcx;
 380         let body = self.body;
 381         let borrow_set = self.borrow_set;
 382         let indices = self.borrow_set.indices();
 383         each_borrow_involving_path(
 384             self,
 385             tcx,
 386             body,
 387             location,
 388             (sd, place),
 389             borrow_set,
 390             indices,
 391             |this, borrow_index, borrow| {
 392                 match (rw, borrow.kind) {
 393                     // Obviously an activation is compatible with its own
 394                     // reservation (or even prior activating uses of same
 395                     // borrow); so don't check if they interfere.
 396                     //
 397                     // NOTE: *reservations* do conflict with themselves;
 398                     // thus aren't injecting unsoundenss w/ this check.)
 399                     (Activation(_, activating), _) if activating == borrow_index => {
 400                         // Activating a borrow doesn't generate any invalidations, since we
 401                         // have already taken the reservation
 402                     }
 403
 404                     (Read(_), BorrowKind::Shallow | BorrowKind::Shared)
 405                     | (
 406                         Read(ReadKind::Borrow(BorrowKind::Shallow)),
 407                         BorrowKind::Unique | BorrowKind::Mut { .. },
 408                     ) => {
 409                         // Reads don't invalidate shared or shallow borrows
 410                     }
 411
 412                     (Read(_), BorrowKind::Unique | BorrowKind::Mut { .. }) => {
 413                         // Reading from mere reservations of mutable-borrows is OK.
 414                         if !is_active(&this.dominators, borrow, location) {
 415                             // If the borrow isn't active yet, reads don't invalidate it
 416                             assert!(allow_two_phase_borrow(borrow.kind));
 417                             return Control::Continue;
 418                         }
 419
 420                         // Unique and mutable borrows are invalidated by reads from any
 421                         // involved path
 422                         this.generate_invalidates(borrow_index, location);
 423                     }
 424
 425                     (Reservation(_) | Activation(_, _) | Write(_), _) => {
 426                         // unique or mutable borrows are invalidated by writes.
 427                         // Reservations count as writes since we need to check
 428                         // that activating the borrow will be OK
 429                         // FIXME(bob_twinkles) is this actually the right thing to do?
 430                         this.generate_invalidates(borrow_index, location);
 431                     }
 432                 }
 433                 Control::Continue
 434             },
 435         );
 436     }
 437
 438     /// Generates a new `invalidates(L, B)` fact.
 439     fn generate_invalidates(&mut self, b: BorrowIndex, l: Location) {
 440         let lidx = self.location_table.start_index(l);
 441         self.all_facts.invalidates.push((lidx, b));
 442     }
 443
 444     fn check_activations(&mut self, location: Location) {
 445         // Two-phase borrow support: For each activation that is newly
 446         // generated at this statement, check if it interferes with
 447         // another borrow.
 448         for &borrow_index in self.borrow_set.activations_at_location(location) {
 449             let borrow = &self.borrow_set[borrow_index];
 450
 451             // only mutable borrows should be 2-phase
 452             assert!(match borrow.kind {
 453                 BorrowKind::Shared | BorrowKind::Shallow => false,
 454                 BorrowKind::Unique | BorrowKind::Mut { .. } => true,
 455             });
 456
 457             self.access_place(
 458                 location,
 459                 borrow.borrowed_place,
 460                 (Deep, Activation(WriteKind::MutableBorrow(borrow.kind), borrow_index)),
 461                 LocalMutationIsAllowed::No,
 462             );
 463
 464             // We do not need to call `check_if_path_or_subpath_is_moved`
 465             // again, as we already called it when we made the
 466             // initial reservation.
 467         }
 468     }
 469 }