src/librustc/mir/visit.rs

   1 use crate::ty::subst::SubstsRef;
   2 use crate::ty::{CanonicalUserTypeAnnotation, ClosureSubsts, GeneratorSubsts, Ty};
   3 use crate::mir::*;
   4 use syntax_pos::Span;
   5
   6 // # The MIR Visitor
   7 //
   8 // ## Overview
   9 //
  10 // There are two visitors, one for immutable and one for mutable references,
  11 // but both are generated by the following macro. The code is written according
  12 // to the following conventions:
  13 //
  14 // - introduce a `visit_foo` and a `super_foo` method for every MIR type
  15 // - `visit_foo`, by default, calls `super_foo`
  16 // - `super_foo`, by default, destructures the `foo` and calls `visit_foo`
  17 //
  18 // This allows you as a user to override `visit_foo` for types are
  19 // interested in, and invoke (within that method) call
  20 // `self.super_foo` to get the default behavior. Just as in an OO
  21 // language, you should never call `super` methods ordinarily except
  22 // in that circumstance.
  23 //
  24 // For the most part, we do not destructure things external to the
  25 // MIR, e.g., types, spans, etc, but simply visit them and stop. This
  26 // avoids duplication with other visitors like `TypeFoldable`.
  27 //
  28 // ## Updating
  29 //
  30 // The code is written in a very deliberate style intended to minimize
  31 // the chance of things being overlooked. You'll notice that we always
  32 // use pattern matching to reference fields and we ensure that all
  33 // matches are exhaustive.
  34 //
  35 // For example, the `super_basic_block_data` method begins like this:
  36 //
  37 // ```rust
  38 // fn super_basic_block_data(&mut self,
  39 //                           block: BasicBlock,
  40 //                           data: & $($mutability)? BasicBlockData<'tcx>) {
  41 //     let BasicBlockData {
  42 //         statements,
  43 //         terminator,
  44 //         is_cleanup: _
  45 //     } = *data;
  46 //
  47 //     for statement in statements {
  48 //         self.visit_statement(block, statement);
  49 //     }
  50 //
  51 //     ...
  52 // }
  53 // ```
  54 //
  55 // Here we used `let BasicBlockData { <fields> } = *data` deliberately,
  56 // rather than writing `data.statements` in the body. This is because if one
  57 // adds a new field to `BasicBlockData`, one will be forced to revise this code,
  58 // and hence one will (hopefully) invoke the correct visit methods (if any).
  59 //
  60 // For this to work, ALL MATCHES MUST BE EXHAUSTIVE IN FIELDS AND VARIANTS.
  61 // That means you never write `..` to skip over fields, nor do you write `_`
  62 // to skip over variants in a `match`.
  63 //
  64 // The only place that `_` is acceptable is to match a field (or
  65 // variant argument) that does not require visiting, as in
  66 // `is_cleanup` above.
  67
  68 macro_rules! make_mir_visitor {
  69     ($visitor_trait_name:ident, $($mutability:ident)?) => {
  70         pub trait $visitor_trait_name<'tcx> {
  71             // Override these, and call `self.super_xxx` to revert back to the
  72             // default behavior.
  73
  74             fn visit_body(&mut self, body: & $($mutability)? Body<'tcx>) {
  75                 self.super_body(body);
  76             }
  77
  78             fn visit_basic_block_data(&mut self,
  79                                       block: BasicBlock,
  80                                       data: & $($mutability)? BasicBlockData<'tcx>) {
  81                 self.super_basic_block_data(block, data);
  82             }
  83
  84             fn visit_source_scope_data(&mut self,
  85                                            scope_data: & $($mutability)? SourceScopeData) {
  86                 self.super_source_scope_data(scope_data);
  87             }
  88
  89             fn visit_statement(&mut self,
  90                                statement: & $($mutability)? Statement<'tcx>,
  91                                location: Location) {
  92                 self.super_statement(statement, location);
  93             }
  94
  95             fn visit_assign(&mut self,
  96                             place: & $($mutability)? Place<'tcx>,
  97                             rvalue: & $($mutability)? Rvalue<'tcx>,
  98                             location: Location) {
  99                 self.super_assign(place, rvalue, location);
 100             }
 101
 102             fn visit_terminator(&mut self,
 103                                 terminator: & $($mutability)? Terminator<'tcx>,
 104                                 location: Location) {
 105                 self.super_terminator(terminator, location);
 106             }
 107
 108             fn visit_terminator_kind(&mut self,
 109                                      kind: & $($mutability)? TerminatorKind<'tcx>,
 110                                      location: Location) {
 111                 self.super_terminator_kind(kind, location);
 112             }
 113
 114             fn visit_assert_message(&mut self,
 115                                     msg: & $($mutability)? AssertMessage<'tcx>,
 116                                     location: Location) {
 117                 self.super_assert_message(msg, location);
 118             }
 119
 120             fn visit_rvalue(&mut self,
 121                             rvalue: & $($mutability)? Rvalue<'tcx>,
 122                             location: Location) {
 123                 self.super_rvalue(rvalue, location);
 124             }
 125
 126             fn visit_operand(&mut self,
 127                              operand: & $($mutability)? Operand<'tcx>,
 128                              location: Location) {
 129                 self.super_operand(operand, location);
 130             }
 131
 132             fn visit_ascribe_user_ty(&mut self,
 133                                      place: & $($mutability)? Place<'tcx>,
 134                                      variance: & $($mutability)? ty::Variance,
 135                                      user_ty: & $($mutability)? UserTypeProjection,
 136                                      location: Location) {
 137                 self.super_ascribe_user_ty(place, variance, user_ty, location);
 138             }
 139
 140             fn visit_retag(&mut self,
 141                            kind: & $($mutability)? RetagKind,
 142                            place: & $($mutability)? Place<'tcx>,
 143                            location: Location) {
 144                 self.super_retag(kind, place, location);
 145             }
 146
 147             fn visit_place(&mut self,
 148                             place: & $($mutability)? Place<'tcx>,
 149                             context: PlaceContext,
 150                             location: Location) {
 151                 self.super_place(place, context, location);
 152             }
 153
 154             fn visit_place_base(&mut self,
 155                                 place_base: & $($mutability)? PlaceBase<'tcx>,
 156                                 context: PlaceContext,
 157                                 location: Location) {
 158                 self.super_place_base(place_base, context, location);
 159             }
 160
 161             fn visit_projection(&mut self,
 162                                 place_base: & $($mutability)? PlaceBase<'tcx>,
 163                                 place: & $($mutability)? Projection<'tcx>,
 164                                 context: PlaceContext,
 165                                 location: Location) {
 166                 self.super_projection(place_base, place, context, location);
 167             }
 168
 169             fn visit_constant(&mut self,
 170                               constant: & $($mutability)? Constant<'tcx>,
 171                               location: Location) {
 172                 self.super_constant(constant, location);
 173             }
 174
 175             fn visit_span(&mut self,
 176                           span: & $($mutability)? Span) {
 177                 self.super_span(span);
 178             }
 179
 180             fn visit_source_info(&mut self,
 181                                  source_info: & $($mutability)? SourceInfo) {
 182                 self.super_source_info(source_info);
 183             }
 184
 185             fn visit_ty(&mut self,
 186                         ty: $(& $mutability)? Ty<'tcx>,
 187                         _: TyContext) {
 188                 self.super_ty(ty);
 189             }
 190
 191             fn visit_user_type_projection(
 192                 &mut self,
 193                 ty: & $($mutability)? UserTypeProjection,
 194             ) {
 195                 self.super_user_type_projection(ty);
 196             }
 197
 198             fn visit_user_type_annotation(
 199                 &mut self,
 200                 index: UserTypeAnnotationIndex,
 201                 ty: & $($mutability)? CanonicalUserTypeAnnotation<'tcx>,
 202             ) {
 203                 self.super_user_type_annotation(index, ty);
 204             }
 205
 206             fn visit_region(&mut self,
 207                             region: & $($mutability)? ty::Region<'tcx>,
 208                             _: Location) {
 209                 self.super_region(region);
 210             }
 211
 212             fn visit_const(&mut self,
 213                            constant: & $($mutability)? &'tcx ty::Const<'tcx>,
 214                            _: Location) {
 215                 self.super_const(constant);
 216             }
 217
 218             fn visit_substs(&mut self,
 219                             substs: & $($mutability)? SubstsRef<'tcx>,
 220                             _: Location) {
 221                 self.super_substs(substs);
 222             }
 223
 224             fn visit_closure_substs(&mut self,
 225                                     substs: & $($mutability)? ClosureSubsts<'tcx>,
 226                                     _: Location) {
 227                 self.super_closure_substs(substs);
 228             }
 229
 230             fn visit_generator_substs(&mut self,
 231                                       substs: & $($mutability)? GeneratorSubsts<'tcx>,
 232                                     _: Location) {
 233                 self.super_generator_substs(substs);
 234             }
 235
 236             fn visit_local_decl(&mut self,
 237                                 local: Local,
 238                                 local_decl: & $($mutability)? LocalDecl<'tcx>) {
 239                 self.super_local_decl(local, local_decl);
 240             }
 241
 242             fn visit_local(&mut self,
 243                             _local: & $($mutability)? Local,
 244                             _context: PlaceContext,
 245                             _location: Location) {
 246             }
 247
 248             fn visit_source_scope(&mut self,
 249                                       scope: & $($mutability)? SourceScope) {
 250                 self.super_source_scope(scope);
 251             }
 252
 253             // The `super_xxx` methods comprise the default behavior and are
 254             // not meant to be overridden.
 255
 256             fn super_body(&mut self,
 257                          body: & $($mutability)? Body<'tcx>) {
 258                 if let Some(yield_ty) = &$($mutability)? body.yield_ty {
 259                     self.visit_ty(yield_ty, TyContext::YieldTy(SourceInfo {
 260                         span: body.span,
 261                         scope: OUTERMOST_SOURCE_SCOPE,
 262                     }));
 263                 }
 264
 265                 // for best performance, we want to use an iterator rather
 266                 // than a for-loop, to avoid calling `body::Body::invalidate` for
 267                 // each basic block.
 268                 macro_rules! basic_blocks {
 269                     (mut) => (body.basic_blocks_mut().iter_enumerated_mut());
 270                     () => (body.basic_blocks().iter_enumerated());
 271                 };
 272                 for (bb, data) in basic_blocks!($($mutability)?) {
 273                     self.visit_basic_block_data(bb, data);
 274                 }
 275
 276                 for scope in &$($mutability)? body.source_scopes {
 277                     self.visit_source_scope_data(scope);
 278                 }
 279
 280                 self.visit_ty(&$($mutability)? body.return_ty(), TyContext::ReturnTy(SourceInfo {
 281                     span: body.span,
 282                     scope: OUTERMOST_SOURCE_SCOPE,
 283                 }));
 284
 285                 for local in body.local_decls.indices() {
 286                     self.visit_local_decl(local, & $($mutability)? body.local_decls[local]);
 287                 }
 288
 289                 macro_rules! type_annotations {
 290                     (mut) => (body.user_type_annotations.iter_enumerated_mut());
 291                     () => (body.user_type_annotations.iter_enumerated());
 292                 };
 293
 294                 for (index, annotation) in type_annotations!($($mutability)?) {
 295                     self.visit_user_type_annotation(
 296                         index, annotation
 297                     );
 298                 }
 299
 300                 self.visit_span(&$($mutability)? body.span);
 301             }
 302
 303             fn super_basic_block_data(&mut self,
 304                                       block: BasicBlock,
 305                                       data: & $($mutability)? BasicBlockData<'tcx>) {
 306                 let BasicBlockData {
 307                     statements,
 308                     terminator,
 309                     is_cleanup: _
 310                 } = data;
 311
 312                 let mut index = 0;
 313                 for statement in statements {
 314                     let location = Location { block: block, statement_index: index };
 315                     self.visit_statement(statement, location);
 316                     index += 1;
 317                 }
 318
 319                 if let Some(terminator) = terminator {
 320                     let location = Location { block: block, statement_index: index };
 321                     self.visit_terminator(terminator, location);
 322                 }
 323             }
 324
 325             fn super_source_scope_data(&mut self, scope_data: & $($mutability)? SourceScopeData) {
 326                 let SourceScopeData {
 327                     span,
 328                     parent_scope,
 329                 } = scope_data;
 330
 331                 self.visit_span(span);
 332                 if let Some(parent_scope) = parent_scope {
 333                     self.visit_source_scope(parent_scope);
 334                 }
 335             }
 336
 337             fn super_statement(&mut self,
 338                                statement: & $($mutability)? Statement<'tcx>,
 339                                location: Location) {
 340                 let Statement {
 341                     source_info,
 342                     kind,
 343                 } = statement;
 344
 345                 self.visit_source_info(source_info);
 346                 match kind {
 347                     StatementKind::Assign(place, rvalue) => {
 348                         self.visit_assign(place, rvalue, location);
 349                     }
 350                     StatementKind::FakeRead(_, place) => {
 351                         self.visit_place(
 352                             place,
 353                             PlaceContext::NonMutatingUse(NonMutatingUseContext::Inspect),
 354                             location
 355                         );
 356                     }
 357                     StatementKind::SetDiscriminant { place, .. } => {
 358                         self.visit_place(
 359                             place,
 360                             PlaceContext::MutatingUse(MutatingUseContext::Store),
 361                             location
 362                         );
 363                     }
 364                     StatementKind::StorageLive(local) => {
 365                         self.visit_local(
 366                             local,
 367                             PlaceContext::NonUse(NonUseContext::StorageLive),
 368                             location
 369                         );
 370                     }
 371                     StatementKind::StorageDead(local) => {
 372                         self.visit_local(
 373                             local,
 374                             PlaceContext::NonUse(NonUseContext::StorageDead),
 375                             location
 376                         );
 377                     }
 378                     StatementKind::InlineAsm(asm) => {
 379                         for output in & $($mutability)? asm.outputs[..] {
 380                             self.visit_place(
 381                                 output,
 382                                 PlaceContext::MutatingUse(MutatingUseContext::AsmOutput),
 383                                 location
 384                             );
 385                         }
 386                         for (span, input) in & $($mutability)? asm.inputs[..] {
 387                             self.visit_span(span);
 388                             self.visit_operand(input, location);
 389                         }
 390                     }
 391                     StatementKind::Retag(kind, place) => {
 392                         self.visit_retag(kind, place, location);
 393                     }
 394                     StatementKind::AscribeUserType(place, variance, user_ty) => {
 395                         self.visit_ascribe_user_ty(place, variance, user_ty, location);
 396                     }
 397                     StatementKind::Nop => {}
 398                 }
 399             }
 400
 401             fn super_assign(&mut self,
 402                             place: &$($mutability)? Place<'tcx>,
 403                             rvalue: &$($mutability)? Rvalue<'tcx>,
 404                             location: Location) {
 405                 self.visit_place(
 406                     place,
 407                     PlaceContext::MutatingUse(MutatingUseContext::Store),
 408                     location
 409                 );
 410                 self.visit_rvalue(rvalue, location);
 411             }
 412
 413             fn super_terminator(&mut self,
 414                                 terminator: &$($mutability)? Terminator<'tcx>,
 415                                 location: Location) {
 416                 let Terminator { source_info, kind } = terminator;
 417
 418                 self.visit_source_info(source_info);
 419                 self.visit_terminator_kind(kind, location);
 420             }
 421
 422             fn super_terminator_kind(&mut self,
 423                                      kind: & $($mutability)? TerminatorKind<'tcx>,
 424                                      source_location: Location) {
 425                 match kind {
 426                     TerminatorKind::Goto { .. } |
 427                     TerminatorKind::Resume |
 428                     TerminatorKind::Abort |
 429                     TerminatorKind::Return |
 430                     TerminatorKind::GeneratorDrop |
 431                     TerminatorKind::Unreachable |
 432                     TerminatorKind::FalseEdges { .. } |
 433                     TerminatorKind::FalseUnwind { .. } => {
 434                     }
 435
 436                     TerminatorKind::SwitchInt {
 437                         discr,
 438                         switch_ty,
 439                         values: _,
 440                         targets: _
 441                     } => {
 442                         self.visit_operand(discr, source_location);
 443                         self.visit_ty(switch_ty, TyContext::Location(source_location));
 444                     }
 445
 446                     TerminatorKind::Drop {
 447                         location,
 448                         target: _,
 449                         unwind: _,
 450                     } => {
 451                         self.visit_place(
 452                             location,
 453                             PlaceContext::MutatingUse(MutatingUseContext::Drop),
 454                             source_location
 455                         );
 456                     }
 457
 458                     TerminatorKind::DropAndReplace {
 459                         location,
 460                         value,
 461                         target: _,
 462                         unwind: _,
 463                     } => {
 464                         self.visit_place(
 465                             location,
 466                             PlaceContext::MutatingUse(MutatingUseContext::Drop),
 467                             source_location
 468                         );
 469                         self.visit_operand(value, source_location);
 470                     }
 471
 472                     TerminatorKind::Call {
 473                         func,
 474                         args,
 475                         destination,
 476                         cleanup: _,
 477                         from_hir_call: _,
 478                     } => {
 479                         self.visit_operand(func, source_location);
 480                         for arg in args {
 481                             self.visit_operand(arg, source_location);
 482                         }
 483                         if let Some((destination, _)) = destination {
 484                             self.visit_place(
 485                                 destination,
 486                                 PlaceContext::MutatingUse(MutatingUseContext::Call),
 487                                 source_location
 488                             );
 489                         }
 490                     }
 491
 492                     TerminatorKind::Assert {
 493                         cond,
 494                         expected: _,
 495                         msg,
 496                         target: _,
 497                         cleanup: _,
 498                     } => {
 499                         self.visit_operand(cond, source_location);
 500                         self.visit_assert_message(msg, source_location);
 501                     }
 502
 503                     TerminatorKind::Yield {
 504                         value,
 505                         resume: _,
 506                         drop: _,
 507                     } => {
 508                         self.visit_operand(value, source_location);
 509                     }
 510
 511                 }
 512             }
 513
 514             fn super_assert_message(&mut self,
 515                                     msg: & $($mutability)? AssertMessage<'tcx>,
 516                                     location: Location) {
 517                 use crate::mir::interpret::InterpError::*;
 518                 use crate::mir::interpret::PanicMessage::BoundsCheck;
 519                 if let Panic(BoundsCheck { len, index }) = msg {
 520                     self.visit_operand(len, location);
 521                     self.visit_operand(index, location);
 522                 }
 523             }
 524
 525             fn super_rvalue(&mut self,
 526                             rvalue: & $($mutability)? Rvalue<'tcx>,
 527                             location: Location) {
 528                 match rvalue {
 529                     Rvalue::Use(operand) => {
 530                         self.visit_operand(operand, location);
 531                     }
 532
 533                     Rvalue::Repeat(value, _) => {
 534                         self.visit_operand(value, location);
 535                     }
 536
 537                     Rvalue::Ref(r, bk, path) => {
 538                         self.visit_region(r, location);
 539                         let ctx = match bk {
 540                             BorrowKind::Shared => PlaceContext::NonMutatingUse(
 541                                 NonMutatingUseContext::SharedBorrow
 542                             ),
 543                             BorrowKind::Shallow => PlaceContext::NonMutatingUse(
 544                                 NonMutatingUseContext::ShallowBorrow
 545                             ),
 546                             BorrowKind::Unique => PlaceContext::NonMutatingUse(
 547                                 NonMutatingUseContext::UniqueBorrow
 548                             ),
 549                             BorrowKind::Mut { .. } =>
 550                                 PlaceContext::MutatingUse(MutatingUseContext::Borrow),
 551                         };
 552                         self.visit_place(path, ctx, location);
 553                     }
 554
 555                     Rvalue::Len(path) => {
 556                         self.visit_place(
 557                             path,
 558                             PlaceContext::NonMutatingUse(NonMutatingUseContext::Inspect),
 559                             location
 560                         );
 561                     }
 562
 563                     Rvalue::Cast(_cast_kind, operand, ty) => {
 564                         self.visit_operand(operand, location);
 565                         self.visit_ty(ty, TyContext::Location(location));
 566                     }
 567
 568                     Rvalue::BinaryOp(_bin_op, lhs, rhs)
 569                     | Rvalue::CheckedBinaryOp(_bin_op, lhs, rhs) => {
 570                         self.visit_operand(lhs, location);
 571                         self.visit_operand(rhs, location);
 572                     }
 573
 574                     Rvalue::UnaryOp(_un_op, op) => {
 575                         self.visit_operand(op, location);
 576                     }
 577
 578                     Rvalue::Discriminant(place) => {
 579                         self.visit_place(
 580                             place,
 581                             PlaceContext::NonMutatingUse(NonMutatingUseContext::Inspect),
 582                             location
 583                         );
 584                     }
 585
 586                     Rvalue::NullaryOp(_op, ty) => {
 587                         self.visit_ty(ty, TyContext::Location(location));
 588                     }
 589
 590                     Rvalue::Aggregate(kind, operands) => {
 591                         let kind = &$($mutability)? **kind;
 592                         match kind {
 593                             AggregateKind::Array(ty) => {
 594                                 self.visit_ty(ty, TyContext::Location(location));
 595                             }
 596                             AggregateKind::Tuple => {
 597                             }
 598                             AggregateKind::Adt(
 599                                 _adt_def,
 600                                 _variant_index,
 601                                 substs,
 602                                 _user_substs,
 603                                 _active_field_index
 604                             ) => {
 605                                 self.visit_substs(substs, location);
 606                             }
 607                             AggregateKind::Closure(
 608                                 _,
 609                                 closure_substs
 610                             ) => {
 611                                 self.visit_closure_substs(closure_substs, location);
 612                             }
 613                             AggregateKind::Generator(
 614                                 _,
 615                                 generator_substs,
 616                                 _movability,
 617                             ) => {
 618                                 self.visit_generator_substs(generator_substs, location);
 619                             }
 620                         }
 621
 622                         for operand in operands {
 623                             self.visit_operand(operand, location);
 624                         }
 625                     }
 626                 }
 627             }
 628
 629             fn super_operand(&mut self,
 630                              operand: & $($mutability)? Operand<'tcx>,
 631                              location: Location) {
 632                 match operand {
 633                     Operand::Copy(place) => {
 634                         self.visit_place(
 635                             place,
 636                             PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy),
 637                             location
 638                         );
 639                     }
 640                     Operand::Move(place) => {
 641                         self.visit_place(
 642                             place,
 643                             PlaceContext::NonMutatingUse(NonMutatingUseContext::Move),
 644                             location
 645                         );
 646                     }
 647                     Operand::Constant(constant) => {
 648                         self.visit_constant(constant, location);
 649                     }
 650                 }
 651             }
 652
 653             fn super_ascribe_user_ty(&mut self,
 654                                      place: & $($mutability)? Place<'tcx>,
 655                                      _variance: & $($mutability)? ty::Variance,
 656                                      user_ty: & $($mutability)? UserTypeProjection,
 657                                      location: Location) {
 658                 self.visit_place(
 659                     place,
 660                     PlaceContext::NonUse(NonUseContext::AscribeUserTy),
 661                     location
 662                 );
 663                 self.visit_user_type_projection(user_ty);
 664             }
 665
 666             fn super_retag(&mut self,
 667                            _kind: & $($mutability)? RetagKind,
 668                            place: & $($mutability)? Place<'tcx>,
 669                            location: Location) {
 670                 self.visit_place(
 671                     place,
 672                     PlaceContext::MutatingUse(MutatingUseContext::Retag),
 673                     location,
 674                 );
 675             }
 676
 677             fn super_place(&mut self,
 678                             place: & $($mutability)? Place<'tcx>,
 679                             context: PlaceContext,
 680                             location: Location) {
 681                 let mut context = context;
 682
 683                 if place.projection.is_some() {
 684                     context = if context.is_mutating_use() {
 685                         PlaceContext::MutatingUse(MutatingUseContext::Projection)
 686                     } else {
 687                         PlaceContext::NonMutatingUse(NonMutatingUseContext::Projection)
 688                     };
 689                 }
 690
 691                 self.visit_place_base(& $($mutability)? place.base, context, location);
 692
 693                 if let Some(box proj) = & $($mutability)? place.projection {
 694                     self.visit_projection(& $($mutability)? place.base, proj, context, location);
 695                 }
 696             }
 697
 698             fn super_place_base(&mut self,
 699                                 place_base: & $($mutability)? PlaceBase<'tcx>,
 700                                 context: PlaceContext,
 701                                 location: Location) {
 702                 match place_base {
 703                     PlaceBase::Local(local) => {
 704                         self.visit_local(local, context, location);
 705                     }
 706                     PlaceBase::Static(box Static { kind: _, ty }) => {
 707                         self.visit_ty(& $($mutability)? *ty, TyContext::Location(location));
 708                     }
 709                 }
 710             }
 711
 712             fn super_projection(&mut self,
 713                                 place_base: & $($mutability)? PlaceBase<'tcx>,
 714                                 proj: & $($mutability)? Projection<'tcx>,
 715                                 context: PlaceContext,
 716                                 location: Location) {
 717                 if let Some(box proj_base) = & $($mutability)? proj.base {
 718                     self.visit_projection(place_base, proj_base, context, location);
 719                 }
 720
 721                 match & $($mutability)? proj.elem {
 722                     ProjectionElem::Deref => {
 723                     }
 724                     ProjectionElem::Subslice { from: _, to: _ } => {
 725                     }
 726                     ProjectionElem::Field(_field, ty) => {
 727                         self.visit_ty(ty, TyContext::Location(location));
 728                     }
 729                     ProjectionElem::Index(local) => {
 730                         self.visit_local(
 731                             local,
 732                             PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy),
 733                             location
 734                         );
 735                     }
 736                     ProjectionElem::ConstantIndex { offset: _,
 737                                                     min_length: _,
 738                                                     from_end: _ } => {
 739                     }
 740                     ProjectionElem::Downcast(_name, _variant_index) => {
 741                     }
 742                 }
 743             }
 744
 745             fn super_local_decl(&mut self,
 746                                 local: Local,
 747                                 local_decl: & $($mutability)? LocalDecl<'tcx>) {
 748                 let LocalDecl {
 749                     mutability: _,
 750                     ty,
 751                     user_ty,
 752                     name: _,
 753                     source_info,
 754                     visibility_scope,
 755                     internal: _,
 756                     is_user_variable: _,
 757                     is_block_tail: _,
 758                 } = local_decl;
 759
 760                 self.visit_ty(ty, TyContext::LocalDecl {
 761                     local,
 762                     source_info: *source_info,
 763                 });
 764                 for (user_ty, _) in & $($mutability)? user_ty.contents {
 765                     self.visit_user_type_projection(user_ty);
 766                 }
 767                 self.visit_source_info(source_info);
 768                 self.visit_source_scope(visibility_scope);
 769             }
 770
 771             fn super_source_scope(&mut self,
 772                                       _scope: & $($mutability)? SourceScope) {
 773             }
 774
 775             fn super_constant(&mut self,
 776                               constant: & $($mutability)? Constant<'tcx>,
 777                               location: Location) {
 778                 let Constant {
 779                     span,
 780                     ty,
 781                     user_ty,
 782                     literal,
 783                 } = constant;
 784
 785                 self.visit_span(span);
 786                 self.visit_ty(ty, TyContext::Location(location));
 787                 drop(user_ty); // no visit method for this
 788                 self.visit_const(literal, location);
 789             }
 790
 791             fn super_span(&mut self, _span: & $($mutability)? Span) {
 792             }
 793
 794             fn super_source_info(&mut self, source_info: & $($mutability)? SourceInfo) {
 795                 let SourceInfo {
 796                     span,
 797                     scope,
 798                 } = source_info;
 799
 800                 self.visit_span(span);
 801                 self.visit_source_scope(scope);
 802             }
 803
 804             fn super_user_type_projection(
 805                 &mut self,
 806                 _ty: & $($mutability)? UserTypeProjection,
 807             ) {
 808             }
 809
 810             fn super_user_type_annotation(
 811                 &mut self,
 812                 _index: UserTypeAnnotationIndex,
 813                 ty: & $($mutability)? CanonicalUserTypeAnnotation<'tcx>,
 814             ) {
 815                 self.visit_span(& $($mutability)? ty.span);
 816                 self.visit_ty(& $($mutability)? ty.inferred_ty, TyContext::UserTy(ty.span));
 817             }
 818
 819             fn super_ty(&mut self, _ty: $(& $mutability)? Ty<'tcx>) {
 820             }
 821
 822             fn super_region(&mut self, _region: & $($mutability)? ty::Region<'tcx>) {
 823             }
 824
 825             fn super_const(&mut self, _const: & $($mutability)? &'tcx ty::Const<'tcx>) {
 826             }
 827
 828             fn super_substs(&mut self, _substs: & $($mutability)? SubstsRef<'tcx>) {
 829             }
 830
 831             fn super_generator_substs(&mut self,
 832                                       _substs: & $($mutability)? GeneratorSubsts<'tcx>) {
 833             }
 834
 835             fn super_closure_substs(&mut self,
 836                                     _substs: & $($mutability)? ClosureSubsts<'tcx>) {
 837             }
 838
 839             // Convenience methods
 840
 841             fn visit_location(&mut self, body: & $($mutability)? Body<'tcx>, location: Location) {
 842                 let basic_block = & $($mutability)? body[location.block];
 843                 if basic_block.statements.len() == location.statement_index {
 844                     if let Some(ref $($mutability)? terminator) = basic_block.terminator {
 845                         self.visit_terminator(terminator, location)
 846                     }
 847                 } else {
 848                     let statement = & $($mutability)?
 849                         basic_block.statements[location.statement_index];
 850                     self.visit_statement(statement, location)
 851                 }
 852             }
 853         }
 854     }
 855 }
 856
 857 make_mir_visitor!(Visitor,);
 858 make_mir_visitor!(MutVisitor,mut);
 859
 860 pub trait MirVisitable<'tcx> {
 861     fn apply(&self, location: Location, visitor: &mut dyn Visitor<'tcx>);
 862 }
 863
 864 impl<'tcx> MirVisitable<'tcx> for Statement<'tcx> {
 865     fn apply(&self, location: Location, visitor: &mut dyn Visitor<'tcx>)
 866     {
 867         visitor.visit_statement(self, location)
 868     }
 869 }
 870
 871 impl<'tcx> MirVisitable<'tcx> for Terminator<'tcx> {
 872     fn apply(&self, location: Location, visitor: &mut dyn Visitor<'tcx>)
 873     {
 874         visitor.visit_terminator(self, location)
 875     }
 876 }
 877
 878 impl<'tcx> MirVisitable<'tcx> for Option<Terminator<'tcx>> {
 879     fn apply(&self, location: Location, visitor: &mut dyn Visitor<'tcx>)
 880     {
 881         visitor.visit_terminator(self.as_ref().unwrap(), location)
 882     }
 883 }
 884
 885 /// Extra information passed to `visit_ty` and friends to give context
 886 /// about where the type etc appears.
 887 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
 888 pub enum TyContext {
 889     LocalDecl {
 890         /// The index of the local variable we are visiting.
 891         local: Local,
 892
 893         /// The source location where this local variable was declared.
 894         source_info: SourceInfo,
 895     },
 896
 897     /// The inferred type of a user type annotation.
 898     UserTy(Span),
 899
 900     /// The return type of the function.
 901     ReturnTy(SourceInfo),
 902
 903     YieldTy(SourceInfo),
 904
 905     /// A type found at some location.
 906     Location(Location),
 907 }
 908
 909 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
 910 pub enum NonMutatingUseContext {
 911     /// Being inspected in some way, like loading a len.
 912     Inspect,
 913     /// Consumed as part of an operand.
 914     Copy,
 915     /// Consumed as part of an operand.
 916     Move,
 917     /// Shared borrow.
 918     SharedBorrow,
 919     /// Shallow borrow.
 920     ShallowBorrow,
 921     /// Unique borrow.
 922     UniqueBorrow,
 923     /// Used as base for another place, e.g., `x` in `x.y`. Will not mutate the place.
 924     /// For example, the projection `x.y` is not marked as a mutation in these cases:
 925     ///
 926     ///     z = x.y;
 927     ///     f(&x.y);
 928     ///
 929     Projection,
 930 }
 931
 932 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
 933 pub enum MutatingUseContext {
 934     /// Appears as LHS of an assignment.
 935     Store,
 936     /// Can often be treated as a `Store`, but needs to be separate because
 937     /// ASM is allowed to read outputs as well, so a `Store`-`AsmOutput` sequence
 938     /// cannot be simplified the way a `Store`-`Store` can be.
 939     AsmOutput,
 940     /// Destination of a call.
 941     Call,
 942     /// Being dropped.
 943     Drop,
 944     /// Mutable borrow.
 945     Borrow,
 946     /// Used as base for another place, e.g., `x` in `x.y`. Could potentially mutate the place.
 947     /// For example, the projection `x.y` is marked as a mutation in these cases:
 948     ///
 949     ///     x.y = ...;
 950     ///     f(&mut x.y);
 951     ///
 952     Projection,
 953     /// Retagging, a "Stacked Borrows" shadow state operation
 954     Retag,
 955 }
 956
 957 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
 958 pub enum NonUseContext {
 959     /// Starting a storage live range.
 960     StorageLive,
 961     /// Ending a storage live range.
 962     StorageDead,
 963     /// User type annotation assertions for NLL.
 964     AscribeUserTy,
 965 }
 966
 967 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
 968 pub enum PlaceContext {
 969     NonMutatingUse(NonMutatingUseContext),
 970     MutatingUse(MutatingUseContext),
 971     NonUse(NonUseContext),
 972 }
 973
 974 impl PlaceContext {
 975     /// Returns `true` if this place context represents a drop.
 976     pub fn is_drop(&self) -> bool {
 977         match *self {
 978             PlaceContext::MutatingUse(MutatingUseContext::Drop) => true,
 979             _ => false,
 980         }
 981     }
 982
 983     /// Returns `true` if this place context represents a borrow.
 984     pub fn is_borrow(&self) -> bool {
 985         match *self {
 986             PlaceContext::NonMutatingUse(NonMutatingUseContext::SharedBorrow) |
 987             PlaceContext::NonMutatingUse(NonMutatingUseContext::ShallowBorrow) |
 988             PlaceContext::NonMutatingUse(NonMutatingUseContext::UniqueBorrow) |
 989             PlaceContext::MutatingUse(MutatingUseContext::Borrow) => true,
 990             _ => false,
 991         }
 992     }
 993
 994     /// Returns `true` if this place context represents a storage live or storage dead marker.
 995     pub fn is_storage_marker(&self) -> bool {
 996         match *self {
 997             PlaceContext::NonUse(NonUseContext::StorageLive) |
 998             PlaceContext::NonUse(NonUseContext::StorageDead) => true,
 999             _ => false,
1000         }
1001     }
1002
1003     /// Returns `true` if this place context represents a storage live marker.
1004     pub fn is_storage_live_marker(&self) -> bool {
1005         match *self {
1006             PlaceContext::NonUse(NonUseContext::StorageLive) => true,
1007             _ => false,
1008         }
1009     }
1010
1011     /// Returns `true` if this place context represents a storage dead marker.
1012     pub fn is_storage_dead_marker(&self) -> bool {
1013         match *self {
1014             PlaceContext::NonUse(NonUseContext::StorageDead) => true,
1015             _ => false,
1016         }
1017     }
1018
1019     /// Returns `true` if this place context represents a use that potentially changes the value.
1020     pub fn is_mutating_use(&self) -> bool {
1021         match *self {
1022             PlaceContext::MutatingUse(..) => true,
1023             _ => false,
1024         }
1025     }
1026
1027     /// Returns `true` if this place context represents a use that does not change the value.
1028     pub fn is_nonmutating_use(&self) -> bool {
1029         match *self {
1030             PlaceContext::NonMutatingUse(..) => true,
1031             _ => false,
1032         }
1033     }
1034
1035     /// Returns `true` if this place context represents a use.
1036     pub fn is_use(&self) -> bool {
1037         match *self {
1038             PlaceContext::NonUse(..) => false,
1039             _ => true,
1040         }
1041     }
1042
1043     /// Returns `true` if this place context represents an assignment statement.
1044     pub fn is_place_assignment(&self) -> bool {
1045         match *self {
1046             PlaceContext::MutatingUse(MutatingUseContext::Store) |
1047             PlaceContext::MutatingUse(MutatingUseContext::Call) |
1048             PlaceContext::MutatingUse(MutatingUseContext::AsmOutput) => true,
1049             _ => false,
1050         }
1051     }
1052 }