src/librustc_mir/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::Nop
  96             | StatementKind::AscribeUserType(..)
  97             | StatementKind::Retag { .. }
  98             | StatementKind::StorageLive(..) => {
  99                 // `Nop`, `AscribeUserType`, `Retag`, and `StorageLive` are irrelevant
 100                 // to borrow check.
 101             }
 102             StatementKind::StorageDead(local) => {
 103                 self.access_place(
 104                     location,
 105                     Place::from(*local),
 106                     (Shallow(None), Write(WriteKind::StorageDeadOrDrop)),
 107                     LocalMutationIsAllowed::Yes,
 108                 );
 109             }
 110         }
 111
 112         self.super_statement(statement, location);
 113     }
 114
 115     fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
 116         self.check_activations(location);
 117
 118         match &terminator.kind {
 119             TerminatorKind::SwitchInt { ref discr, switch_ty: _, values: _, targets: _ } => {
 120                 self.consume_operand(location, discr);
 121             }
 122             TerminatorKind::Drop { place: drop_place, target: _, unwind: _ } => {
 123                 self.access_place(
 124                     location,
 125                     *drop_place,
 126                     (AccessDepth::Drop, Write(WriteKind::StorageDeadOrDrop)),
 127                     LocalMutationIsAllowed::Yes,
 128                 );
 129             }
 130             TerminatorKind::DropAndReplace {
 131                 place: drop_place,
 132                 value: ref new_value,
 133                 target: _,
 134                 unwind: _,
 135             } => {
 136                 self.mutate_place(location, *drop_place, Deep, JustWrite);
 137                 self.consume_operand(location, new_value);
 138             }
 139             TerminatorKind::Call {
 140                 ref func,
 141                 ref args,
 142                 destination,
 143                 cleanup: _,
 144                 from_hir_call: _,
 145                 fn_span: _,
 146             } => {
 147                 self.consume_operand(location, func);
 148                 for arg in args {
 149                     self.consume_operand(location, arg);
 150                 }
 151                 if let Some((dest, _ /*bb*/)) = destination {
 152                     self.mutate_place(location, *dest, Deep, JustWrite);
 153                 }
 154             }
 155             TerminatorKind::Assert { ref cond, expected: _, ref msg, target: _, cleanup: _ } => {
 156                 self.consume_operand(location, cond);
 157                 use rustc_middle::mir::AssertKind;
 158                 if let AssertKind::BoundsCheck { ref len, ref index } = *msg {
 159                     self.consume_operand(location, len);
 160                     self.consume_operand(location, index);
 161                 }
 162             }
 163             TerminatorKind::Yield { ref value, resume, resume_arg, drop: _ } => {
 164                 self.consume_operand(location, value);
 165
 166                 // Invalidate all borrows of local places
 167                 let borrow_set = self.borrow_set.clone();
 168                 let resume = self.location_table.start_index(resume.start_location());
 169                 for i in borrow_set.borrows.indices() {
 170                     if borrow_of_local_data(borrow_set.borrows[i].borrowed_place) {
 171                         self.all_facts.invalidates.push((resume, i));
 172                     }
 173                 }
 174
 175                 self.mutate_place(location, *resume_arg, Deep, JustWrite);
 176             }
 177             TerminatorKind::Resume | TerminatorKind::Return | TerminatorKind::GeneratorDrop => {
 178                 // Invalidate all borrows of local places
 179                 let borrow_set = self.borrow_set.clone();
 180                 let start = self.location_table.start_index(location);
 181                 for i in borrow_set.borrows.indices() {
 182                     if borrow_of_local_data(borrow_set.borrows[i].borrowed_place) {
 183                         self.all_facts.invalidates.push((start, i));
 184                     }
 185                 }
 186             }
 187             TerminatorKind::InlineAsm {
 188                 template: _,
 189                 ref operands,
 190                 options: _,
 191                 line_spans: _,
 192                 destination: _,
 193             } => {
 194                 for op in operands {
 195                     match *op {
 196                         InlineAsmOperand::In { reg: _, ref value }
 197                         | InlineAsmOperand::Const { ref value } => {
 198                             self.consume_operand(location, value);
 199                         }
 200                         InlineAsmOperand::Out { reg: _, late: _, place, .. } => {
 201                             if let Some(place) = place {
 202                                 self.mutate_place(location, place, Shallow(None), JustWrite);
 203                             }
 204                         }
 205                         InlineAsmOperand::InOut { reg: _, late: _, ref in_value, out_place } => {
 206                             self.consume_operand(location, in_value);
 207                             if let Some(out_place) = out_place {
 208                                 self.mutate_place(location, out_place, Shallow(None), JustWrite);
 209                             }
 210                         }
 211                         InlineAsmOperand::SymFn { value: _ }
 212                         | InlineAsmOperand::SymStatic { def_id: _ } => {}
 213                     }
 214                 }
 215             }
 216             TerminatorKind::Goto { target: _ }
 217             | TerminatorKind::Abort
 218             | TerminatorKind::Unreachable
 219             | TerminatorKind::FalseEdge { real_target: _, imaginary_target: _ }
 220             | TerminatorKind::FalseUnwind { real_target: _, unwind: _ } => {
 221                 // no data used, thus irrelevant to borrowck
 222             }
 223         }
 224
 225         self.super_terminator(terminator, location);
 226     }
 227 }
 228
 229 impl<'cx, 'tcx> InvalidationGenerator<'cx, 'tcx> {
 230     /// Simulates mutation of a place.
 231     fn mutate_place(
 232         &mut self,
 233         location: Location,
 234         place: Place<'tcx>,
 235         kind: AccessDepth,
 236         _mode: MutateMode,
 237     ) {
 238         self.access_place(
 239             location,
 240             place,
 241             (kind, Write(WriteKind::Mutate)),
 242             LocalMutationIsAllowed::ExceptUpvars,
 243         );
 244     }
 245
 246     /// Simulates consumption of an operand.
 247     fn consume_operand(&mut self, location: Location, operand: &Operand<'tcx>) {
 248         match *operand {
 249             Operand::Copy(place) => {
 250                 self.access_place(
 251                     location,
 252                     place,
 253                     (Deep, Read(ReadKind::Copy)),
 254                     LocalMutationIsAllowed::No,
 255                 );
 256             }
 257             Operand::Move(place) => {
 258                 self.access_place(
 259                     location,
 260                     place,
 261                     (Deep, Write(WriteKind::Move)),
 262                     LocalMutationIsAllowed::Yes,
 263                 );
 264             }
 265             Operand::Constant(_) => {}
 266         }
 267     }
 268
 269     // Simulates consumption of an rvalue
 270     fn consume_rvalue(&mut self, location: Location, rvalue: &Rvalue<'tcx>) {
 271         match *rvalue {
 272             Rvalue::Ref(_ /*rgn*/, bk, place) => {
 273                 let access_kind = match bk {
 274                     BorrowKind::Shallow => {
 275                         (Shallow(Some(ArtificialField::ShallowBorrow)), Read(ReadKind::Borrow(bk)))
 276                     }
 277                     BorrowKind::Shared => (Deep, Read(ReadKind::Borrow(bk))),
 278                     BorrowKind::Unique | BorrowKind::Mut { .. } => {
 279                         let wk = WriteKind::MutableBorrow(bk);
 280                         if allow_two_phase_borrow(bk) {
 281                             (Deep, Reservation(wk))
 282                         } else {
 283                             (Deep, Write(wk))
 284                         }
 285                     }
 286                 };
 287
 288                 self.access_place(location, place, access_kind, LocalMutationIsAllowed::No);
 289             }
 290
 291             Rvalue::AddressOf(mutability, place) => {
 292                 let access_kind = match mutability {
 293                     Mutability::Mut => (
 294                         Deep,
 295                         Write(WriteKind::MutableBorrow(BorrowKind::Mut {
 296                             allow_two_phase_borrow: false,
 297                         })),
 298                     ),
 299                     Mutability::Not => (Deep, Read(ReadKind::Borrow(BorrowKind::Shared))),
 300                 };
 301
 302                 self.access_place(location, place, access_kind, LocalMutationIsAllowed::No);
 303             }
 304
 305             Rvalue::ThreadLocalRef(_) => {}
 306
 307             Rvalue::Use(ref operand)
 308             | Rvalue::Repeat(ref operand, _)
 309             | Rvalue::UnaryOp(_ /*un_op*/, ref operand)
 310             | Rvalue::Cast(_ /*cast_kind*/, ref operand, _ /*ty*/) => {
 311                 self.consume_operand(location, operand)
 312             }
 313
 314             Rvalue::Len(place) | Rvalue::Discriminant(place) => {
 315                 let af = match *rvalue {
 316                     Rvalue::Len(..) => Some(ArtificialField::ArrayLength),
 317                     Rvalue::Discriminant(..) => None,
 318                     _ => unreachable!(),
 319                 };
 320                 self.access_place(
 321                     location,
 322                     place,
 323                     (Shallow(af), Read(ReadKind::Copy)),
 324                     LocalMutationIsAllowed::No,
 325                 );
 326             }
 327
 328             Rvalue::BinaryOp(_bin_op, ref operand1, ref operand2)
 329             | Rvalue::CheckedBinaryOp(_bin_op, ref operand1, ref operand2) => {
 330                 self.consume_operand(location, operand1);
 331                 self.consume_operand(location, operand2);
 332             }
 333
 334             Rvalue::NullaryOp(_op, _ty) => {}
 335
 336             Rvalue::Aggregate(_, ref operands) => {
 337                 for operand in operands {
 338                     self.consume_operand(location, operand);
 339                 }
 340             }
 341         }
 342     }
 343
 344     /// Simulates an access to a place.
 345     fn access_place(
 346         &mut self,
 347         location: Location,
 348         place: Place<'tcx>,
 349         kind: (AccessDepth, ReadOrWrite),
 350         _is_local_mutation_allowed: LocalMutationIsAllowed,
 351     ) {
 352         let (sd, rw) = kind;
 353         // note: not doing check_access_permissions checks because they don't generate invalidates
 354         self.check_access_for_conflict(location, place, sd, rw);
 355     }
 356
 357     fn check_access_for_conflict(
 358         &mut self,
 359         location: Location,
 360         place: Place<'tcx>,
 361         sd: AccessDepth,
 362         rw: ReadOrWrite,
 363     ) {
 364         debug!(
 365             "invalidation::check_access_for_conflict(location={:?}, place={:?}, sd={:?}, \
 366              rw={:?})",
 367             location, place, sd, rw,
 368         );
 369         let tcx = self.tcx;
 370         let body = self.body;
 371         let borrow_set = self.borrow_set.clone();
 372         let indices = self.borrow_set.borrows.indices();
 373         each_borrow_involving_path(
 374             self,
 375             tcx,
 376             body,
 377             location,
 378             (sd, place),
 379             &borrow_set.clone(),
 380             indices,
 381             |this, borrow_index, borrow| {
 382                 match (rw, borrow.kind) {
 383                     // Obviously an activation is compatible with its own
 384                     // reservation (or even prior activating uses of same
 385                     // borrow); so don't check if they interfere.
 386                     //
 387                     // NOTE: *reservations* do conflict with themselves;
 388                     // thus aren't injecting unsoundenss w/ this check.)
 389                     (Activation(_, activating), _) if activating == borrow_index => {
 390                         // Activating a borrow doesn't generate any invalidations, since we
 391                         // have already taken the reservation
 392                     }
 393
 394                     (Read(_), BorrowKind::Shallow | BorrowKind::Shared)
 395                     | (
 396                         Read(ReadKind::Borrow(BorrowKind::Shallow)),
 397                         BorrowKind::Unique | BorrowKind::Mut { .. },
 398                     ) => {
 399                         // Reads don't invalidate shared or shallow borrows
 400                     }
 401
 402                     (Read(_), BorrowKind::Unique | BorrowKind::Mut { .. }) => {
 403                         // Reading from mere reservations of mutable-borrows is OK.
 404                         if !is_active(&this.dominators, borrow, location) {
 405                             // If the borrow isn't active yet, reads don't invalidate it
 406                             assert!(allow_two_phase_borrow(borrow.kind));
 407                             return Control::Continue;
 408                         }
 409
 410                         // Unique and mutable borrows are invalidated by reads from any
 411                         // involved path
 412                         this.generate_invalidates(borrow_index, location);
 413                     }
 414
 415                     (Reservation(_) | Activation(_, _) | Write(_), _) => {
 416                         // unique or mutable borrows are invalidated by writes.
 417                         // Reservations count as writes since we need to check
 418                         // that activating the borrow will be OK
 419                         // FIXME(bob_twinkles) is this actually the right thing to do?
 420                         this.generate_invalidates(borrow_index, location);
 421                     }
 422                 }
 423                 Control::Continue
 424             },
 425         );
 426     }
 427
 428     /// Generates a new `invalidates(L, B)` fact.
 429     fn generate_invalidates(&mut self, b: BorrowIndex, l: Location) {
 430         let lidx = self.location_table.start_index(l);
 431         self.all_facts.invalidates.push((lidx, b));
 432     }
 433
 434     fn check_activations(&mut self, location: Location) {
 435         // Two-phase borrow support: For each activation that is newly
 436         // generated at this statement, check if it interferes with
 437         // another borrow.
 438         for &borrow_index in self.borrow_set.activations_at_location(location) {
 439             let borrow = &self.borrow_set[borrow_index];
 440
 441             // only mutable borrows should be 2-phase
 442             assert!(match borrow.kind {
 443                 BorrowKind::Shared | BorrowKind::Shallow => false,
 444                 BorrowKind::Unique | BorrowKind::Mut { .. } => true,
 445             });
 446
 447             self.access_place(
 448                 location,
 449                 borrow.borrowed_place,
 450                 (Deep, Activation(WriteKind::MutableBorrow(borrow.kind), borrow_index)),
 451                 LocalMutationIsAllowed::No,
 452             );
 453
 454             // We do not need to call `check_if_path_or_subpath_is_moved`
 455             // again, as we already called it when we made the
 456             // initial reservation.
 457         }
 458     }
 459 }