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