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