compiler/rustc_middle/src/mir/visit.rs

   1 use crate::mir::*;
   2 use crate::ty::subst::SubstsRef;
   3 use crate::ty::{CanonicalUserTypeAnnotation, Ty};
   4 use rustc_span::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 $visitor_trait_name<'tcx> {
  71             // Override these, and call `self.super_xxx` to revert back to the
  72             // default behavior.
  73
  74             fn visit_body(
  75                 &mut self,
  76                 body: &$($mutability)? Body<'tcx>,
  77             ) {
  78                 self.super_body(body);
  79             }
  80
  81             fn visit_basic_block_data(&mut self,
  82                                       block: BasicBlock,
  83                                       data: & $($mutability)? BasicBlockData<'tcx>) {
  84                 self.super_basic_block_data(block, data);
  85             }
  86
  87             fn visit_source_scope_data(&mut self,
  88                                            scope_data: & $($mutability)? SourceScopeData) {
  89                 self.super_source_scope_data(scope_data);
  90             }
  91
  92             fn visit_statement(&mut self,
  93                                statement: & $($mutability)? Statement<'tcx>,
  94                                location: Location) {
  95                 self.super_statement(statement, location);
  96             }
  97
  98             fn visit_assign(&mut self,
  99                             place: & $($mutability)? Place<'tcx>,
 100                             rvalue: & $($mutability)? Rvalue<'tcx>,
 101                             location: Location) {
 102                 self.super_assign(place, rvalue, location);
 103             }
 104
 105             fn visit_terminator(&mut self,
 106                                 terminator: & $($mutability)? Terminator<'tcx>,
 107                                 location: Location) {
 108                 self.super_terminator(terminator, location);
 109             }
 110
 111             fn visit_assert_message(&mut self,
 112                                     msg: & $($mutability)? AssertMessage<'tcx>,
 113                                     location: Location) {
 114                 self.super_assert_message(msg, location);
 115             }
 116
 117             fn visit_rvalue(&mut self,
 118                             rvalue: & $($mutability)? Rvalue<'tcx>,
 119                             location: Location) {
 120                 self.super_rvalue(rvalue, location);
 121             }
 122
 123             fn visit_operand(&mut self,
 124                              operand: & $($mutability)? Operand<'tcx>,
 125                              location: Location) {
 126                 self.super_operand(operand, location);
 127             }
 128
 129             fn visit_ascribe_user_ty(&mut self,
 130                                      place: & $($mutability)? Place<'tcx>,
 131                                      variance: & $($mutability)? ty::Variance,
 132                                      user_ty: & $($mutability)? UserTypeProjection,
 133                                      location: Location) {
 134                 self.super_ascribe_user_ty(place, variance, user_ty, location);
 135             }
 136
 137             fn visit_coverage(&mut self,
 138                               coverage: & $($mutability)? Coverage,
 139                               location: Location) {
 140                 self.super_coverage(coverage, location);
 141             }
 142
 143             fn visit_retag(&mut self,
 144                            kind: & $($mutability)? RetagKind,
 145                            place: & $($mutability)? Place<'tcx>,
 146                            location: Location) {
 147                 self.super_retag(kind, place, location);
 148             }
 149
 150             fn visit_place(&mut self,
 151                             place: & $($mutability)? Place<'tcx>,
 152                             context: PlaceContext,
 153                             location: Location) {
 154                 self.super_place(place, context, location);
 155             }
 156
 157             visit_place_fns!($($mutability)?);
 158
 159             fn visit_constant(&mut self,
 160                               constant: & $($mutability)? Constant<'tcx>,
 161                               location: Location) {
 162                 self.super_constant(constant, location);
 163             }
 164
 165             fn visit_span(&mut self,
 166                           span: & $($mutability)? Span) {
 167                 self.super_span(span);
 168             }
 169
 170             fn visit_source_info(&mut self,
 171                                  source_info: & $($mutability)? SourceInfo) {
 172                 self.super_source_info(source_info);
 173             }
 174
 175             fn visit_ty(&mut self,
 176                         ty: $(& $mutability)? Ty<'tcx>,
 177                         _: TyContext) {
 178                 self.super_ty(ty);
 179             }
 180
 181             fn visit_user_type_projection(
 182                 &mut self,
 183                 ty: & $($mutability)? UserTypeProjection,
 184             ) {
 185                 self.super_user_type_projection(ty);
 186             }
 187
 188             fn visit_user_type_annotation(
 189                 &mut self,
 190                 index: UserTypeAnnotationIndex,
 191                 ty: & $($mutability)? CanonicalUserTypeAnnotation<'tcx>,
 192             ) {
 193                 self.super_user_type_annotation(index, ty);
 194             }
 195
 196             fn visit_region(&mut self,
 197                             region: & $($mutability)? ty::Region<'tcx>,
 198                             _: Location) {
 199                 self.super_region(region);
 200             }
 201
 202             fn visit_const(&mut self,
 203                            constant: & $($mutability)? &'tcx ty::Const<'tcx>,
 204                            _: Location) {
 205                 self.super_const(constant);
 206             }
 207
 208             fn visit_substs(&mut self,
 209                             substs: & $($mutability)? SubstsRef<'tcx>,
 210                             _: Location) {
 211                 self.super_substs(substs);
 212             }
 213
 214             fn visit_local_decl(&mut self,
 215                                 local: Local,
 216                                 local_decl: & $($mutability)? LocalDecl<'tcx>) {
 217                 self.super_local_decl(local, local_decl);
 218             }
 219
 220             fn visit_var_debug_info(&mut self,
 221                                     var_debug_info: & $($mutability)* VarDebugInfo<'tcx>) {
 222                 self.super_var_debug_info(var_debug_info);
 223             }
 224
 225             fn visit_local(&mut self,
 226                             _local: & $($mutability)? Local,
 227                             _context: PlaceContext,
 228                             _location: Location) {
 229             }
 230
 231             fn visit_source_scope(&mut self,
 232                                       scope: & $($mutability)? SourceScope) {
 233                 self.super_source_scope(scope);
 234             }
 235
 236             // The `super_xxx` methods comprise the default behavior and are
 237             // not meant to be overridden.
 238
 239             fn super_body(
 240                 &mut self,
 241                 body: &$($mutability)? Body<'tcx>,
 242             ) {
 243                 let span = body.span;
 244                 if let Some(yield_ty) = &$($mutability)? body.yield_ty {
 245                     self.visit_ty(
 246                         yield_ty,
 247                         TyContext::YieldTy(SourceInfo::outermost(span))
 248                     );
 249                 }
 250
 251                 // for best performance, we want to use an iterator rather
 252                 // than a for-loop, to avoid calling `body::Body::invalidate` for
 253                 // each basic block.
 254                 macro_rules! basic_blocks {
 255                     (mut) => (body.basic_blocks_mut().iter_enumerated_mut());
 256                     () => (body.basic_blocks().iter_enumerated());
 257                 };
 258                 for (bb, data) in basic_blocks!($($mutability)?) {
 259                     self.visit_basic_block_data(bb, data);
 260                 }
 261
 262                 for scope in &$($mutability)? body.source_scopes {
 263                     self.visit_source_scope_data(scope);
 264                 }
 265
 266                 self.visit_ty(
 267                     &$($mutability)? body.return_ty(),
 268                     TyContext::ReturnTy(SourceInfo::outermost(body.span))
 269                 );
 270
 271                 for local in body.local_decls.indices() {
 272                     self.visit_local_decl(local, & $($mutability)? body.local_decls[local]);
 273                 }
 274
 275                 macro_rules! type_annotations {
 276                     (mut) => (body.user_type_annotations.iter_enumerated_mut());
 277                     () => (body.user_type_annotations.iter_enumerated());
 278                 };
 279
 280                 for (index, annotation) in type_annotations!($($mutability)?) {
 281                     self.visit_user_type_annotation(
 282                         index, annotation
 283                     );
 284                 }
 285
 286                 for var_debug_info in &$($mutability)? body.var_debug_info {
 287                     self.visit_var_debug_info(var_debug_info);
 288                 }
 289
 290                 self.visit_span(&$($mutability)? body.span);
 291
 292                 for const_ in &$($mutability)? body.required_consts {
 293                     let location = START_BLOCK.start_location();
 294                     self.visit_constant(const_, location);
 295                 }
 296             }
 297
 298             fn super_basic_block_data(&mut self,
 299                                       block: BasicBlock,
 300                                       data: & $($mutability)? BasicBlockData<'tcx>) {
 301                 let BasicBlockData {
 302                     statements,
 303                     terminator,
 304                     is_cleanup: _
 305                 } = data;
 306
 307                 let mut index = 0;
 308                 for statement in statements {
 309                     let location = Location { block: block, statement_index: index };
 310                     self.visit_statement(statement, location);
 311                     index += 1;
 312                 }
 313
 314                 if let Some(terminator) = terminator {
 315                     let location = Location { block: block, statement_index: index };
 316                     self.visit_terminator(terminator, location);
 317                 }
 318             }
 319
 320             fn super_source_scope_data(&mut self, scope_data: & $($mutability)? SourceScopeData) {
 321                 let SourceScopeData {
 322                     span,
 323                     parent_scope,
 324                     local_data: _,
 325                 } = scope_data;
 326
 327                 self.visit_span(span);
 328                 if let Some(parent_scope) = parent_scope {
 329                     self.visit_source_scope(parent_scope);
 330                 }
 331             }
 332
 333             fn super_statement(&mut self,
 334                                statement: & $($mutability)? Statement<'tcx>,
 335                                location: Location) {
 336                 let Statement {
 337                     source_info,
 338                     kind,
 339                 } = statement;
 340
 341                 self.visit_source_info(source_info);
 342                 match kind {
 343                     StatementKind::Assign(
 344                         box(ref $($mutability)? place, ref $($mutability)? rvalue)
 345                     ) => {
 346                         self.visit_assign(place, rvalue, location);
 347                     }
 348                     StatementKind::FakeRead(_, place) => {
 349                         self.visit_place(
 350                             place,
 351                             PlaceContext::NonMutatingUse(NonMutatingUseContext::Inspect),
 352                             location
 353                         );
 354                     }
 355                     StatementKind::SetDiscriminant { place, .. } => {
 356                         self.visit_place(
 357                             place,
 358                             PlaceContext::MutatingUse(MutatingUseContext::Store),
 359                             location
 360                         );
 361                     }
 362                     StatementKind::StorageLive(local) => {
 363                         self.visit_local(
 364                             local,
 365                             PlaceContext::NonUse(NonUseContext::StorageLive),
 366                             location
 367                         );
 368                     }
 369                     StatementKind::StorageDead(local) => {
 370                         self.visit_local(
 371                             local,
 372                             PlaceContext::NonUse(NonUseContext::StorageDead),
 373                             location
 374                         );
 375                     }
 376                     StatementKind::LlvmInlineAsm(asm) => {
 377                         for output in & $($mutability)? asm.outputs[..] {
 378                             self.visit_place(
 379                                 output,
 380                                 PlaceContext::MutatingUse(MutatingUseContext::AsmOutput),
 381                                 location
 382                             );
 383                         }
 384                         for (span, input) in & $($mutability)? asm.inputs[..] {
 385                             self.visit_span(span);
 386                             self.visit_operand(input, location);
 387                         }
 388                     }
 389                     StatementKind::Retag(kind, place) => {
 390                         self.visit_retag(kind, place, location);
 391                     }
 392                     StatementKind::AscribeUserType(
 393                         box(ref $($mutability)? place, ref $($mutability)? user_ty),
 394                         variance
 395                     ) => {
 396                         self.visit_ascribe_user_ty(place, variance, user_ty, location);
 397                     }
 398                     StatementKind::Coverage(coverage) => {
 399                         self.visit_coverage(
 400                             coverage,
 401                             location
 402                         )
 403                     }
 404                     StatementKind::Nop => {}
 405                 }
 406             }
 407
 408             fn super_assign(&mut self,
 409                             place: &$($mutability)? Place<'tcx>,
 410                             rvalue: &$($mutability)? Rvalue<'tcx>,
 411                             location: Location) {
 412                 self.visit_place(
 413                     place,
 414                     PlaceContext::MutatingUse(MutatingUseContext::Store),
 415                     location
 416                 );
 417                 self.visit_rvalue(rvalue, location);
 418             }
 419
 420             fn super_terminator(&mut self,
 421                                 terminator: &$($mutability)? Terminator<'tcx>,
 422                                 location: Location) {
 423                 let Terminator { source_info, kind } = terminator;
 424
 425                 self.visit_source_info(source_info);
 426                 match kind {
 427                     TerminatorKind::Goto { .. } |
 428                     TerminatorKind::Resume |
 429                     TerminatorKind::Abort |
 430                     TerminatorKind::GeneratorDrop |
 431                     TerminatorKind::Unreachable |
 432                     TerminatorKind::FalseEdge { .. } |
 433                     TerminatorKind::FalseUnwind { .. } => {
 434                     }
 435
 436                     TerminatorKind::Return => {
 437                         // `return` logically moves from the return place `_0`. Note that the place
 438                         // cannot be changed by any visitor, though.
 439                         let $($mutability)? local = RETURN_PLACE;
 440                         self.visit_local(
 441                             & $($mutability)? local,
 442                             PlaceContext::NonMutatingUse(NonMutatingUseContext::Move),
 443                             location,
 444                         );
 445
 446                         assert_eq!(
 447                             local,
 448                             RETURN_PLACE,
 449                             "`MutVisitor` tried to mutate return place of `return` terminator"
 450                         );
 451                     }
 452
 453                     TerminatorKind::SwitchInt {
 454                         discr,
 455                         switch_ty,
 456                         values: _,
 457                         targets: _
 458                     } => {
 459                         self.visit_operand(discr, location);
 460                         self.visit_ty(switch_ty, TyContext::Location(location));
 461                     }
 462
 463                     TerminatorKind::Drop {
 464                         place,
 465                         target: _,
 466                         unwind: _,
 467                     } => {
 468                         self.visit_place(
 469                             place,
 470                             PlaceContext::MutatingUse(MutatingUseContext::Drop),
 471                             location
 472                         );
 473                     }
 474
 475                     TerminatorKind::DropAndReplace {
 476                         place,
 477                         value,
 478                         target: _,
 479                         unwind: _,
 480                     } => {
 481                         self.visit_place(
 482                             place,
 483                             PlaceContext::MutatingUse(MutatingUseContext::Drop),
 484                             location
 485                         );
 486                         self.visit_operand(value, location);
 487                     }
 488
 489                     TerminatorKind::Call {
 490                         func,
 491                         args,
 492                         destination,
 493                         cleanup: _,
 494                         from_hir_call: _,
 495                         fn_span: _
 496                     } => {
 497                         self.visit_operand(func, location);
 498                         for arg in args {
 499                             self.visit_operand(arg, location);
 500                         }
 501                         if let Some((destination, _)) = destination {
 502                             self.visit_place(
 503                                 destination,
 504                                 PlaceContext::MutatingUse(MutatingUseContext::Call),
 505                                 location
 506                             );
 507                         }
 508                     }
 509
 510                     TerminatorKind::Assert {
 511                         cond,
 512                         expected: _,
 513                         msg,
 514                         target: _,
 515                         cleanup: _,
 516                     } => {
 517                         self.visit_operand(cond, location);
 518                         self.visit_assert_message(msg, location);
 519                     }
 520
 521                     TerminatorKind::Yield {
 522                         value,
 523                         resume: _,
 524                         resume_arg,
 525                         drop: _,
 526                     } => {
 527                         self.visit_operand(value, location);
 528                         self.visit_place(
 529                             resume_arg,
 530                             PlaceContext::MutatingUse(MutatingUseContext::Yield),
 531                             location,
 532                         );
 533                     }
 534
 535                     TerminatorKind::InlineAsm {
 536                         template: _,
 537                         operands,
 538                         options: _,
 539                         line_spans: _,
 540                         destination: _,
 541                     } => {
 542                         for op in operands {
 543                             match op {
 544                                 InlineAsmOperand::In { value, .. }
 545                                 | InlineAsmOperand::Const { value } => {
 546                                     self.visit_operand(value, location);
 547                                 }
 548                                 InlineAsmOperand::Out { place, .. } => {
 549                                     if let Some(place) = place {
 550                                         self.visit_place(
 551                                             place,
 552                                             PlaceContext::MutatingUse(MutatingUseContext::Store),
 553                                             location,
 554                                         );
 555                                     }
 556                                 }
 557                                 InlineAsmOperand::InOut { in_value, out_place, .. } => {
 558                                     self.visit_operand(in_value, location);
 559                                     if let Some(out_place) = out_place {
 560                                         self.visit_place(
 561                                             out_place,
 562                                             PlaceContext::MutatingUse(MutatingUseContext::Store),
 563                                             location,
 564                                         );
 565                                     }
 566                                 }
 567                                 InlineAsmOperand::SymFn { value } => {
 568                                     self.visit_constant(value, location);
 569                                 }
 570                                 InlineAsmOperand::SymStatic { def_id: _ } => {}
 571                             }
 572                         }
 573                     }
 574                 }
 575             }
 576
 577             fn super_assert_message(&mut self,
 578                                     msg: & $($mutability)? AssertMessage<'tcx>,
 579                                     location: Location) {
 580                 use crate::mir::AssertKind::*;
 581                 match msg {
 582                     BoundsCheck { len, index } => {
 583                         self.visit_operand(len, location);
 584                         self.visit_operand(index, location);
 585                     }
 586                     Overflow(_, l, r) => {
 587                         self.visit_operand(l, location);
 588                         self.visit_operand(r, location);
 589                     }
 590                     OverflowNeg(op) | DivisionByZero(op) | RemainderByZero(op) => {
 591                         self.visit_operand(op, location);
 592                     }
 593                     ResumedAfterReturn(_) | ResumedAfterPanic(_) => {
 594                         // Nothing to visit
 595                     }
 596                 }
 597             }
 598
 599             fn super_rvalue(&mut self,
 600                             rvalue: & $($mutability)? Rvalue<'tcx>,
 601                             location: Location) {
 602                 match rvalue {
 603                     Rvalue::Use(operand) => {
 604                         self.visit_operand(operand, location);
 605                     }
 606
 607                     Rvalue::Repeat(value, _) => {
 608                         self.visit_operand(value, location);
 609                     }
 610
 611                     Rvalue::ThreadLocalRef(_) => {}
 612
 613                     Rvalue::Ref(r, bk, path) => {
 614                         self.visit_region(r, location);
 615                         let ctx = match bk {
 616                             BorrowKind::Shared => PlaceContext::NonMutatingUse(
 617                                 NonMutatingUseContext::SharedBorrow
 618                             ),
 619                             BorrowKind::Shallow => PlaceContext::NonMutatingUse(
 620                                 NonMutatingUseContext::ShallowBorrow
 621                             ),
 622                             BorrowKind::Unique => PlaceContext::NonMutatingUse(
 623                                 NonMutatingUseContext::UniqueBorrow
 624                             ),
 625                             BorrowKind::Mut { .. } =>
 626                                 PlaceContext::MutatingUse(MutatingUseContext::Borrow),
 627                         };
 628                         self.visit_place(path, ctx, location);
 629                     }
 630
 631                     Rvalue::AddressOf(m, path) => {
 632                         let ctx = match m {
 633                             Mutability::Mut => PlaceContext::MutatingUse(
 634                                 MutatingUseContext::AddressOf
 635                             ),
 636                             Mutability::Not => PlaceContext::NonMutatingUse(
 637                                 NonMutatingUseContext::AddressOf
 638                             ),
 639                         };
 640                         self.visit_place(path, ctx, location);
 641                     }
 642
 643                     Rvalue::Len(path) => {
 644                         self.visit_place(
 645                             path,
 646                             PlaceContext::NonMutatingUse(NonMutatingUseContext::Inspect),
 647                             location
 648                         );
 649                     }
 650
 651                     Rvalue::Cast(_cast_kind, operand, ty) => {
 652                         self.visit_operand(operand, location);
 653                         self.visit_ty(ty, TyContext::Location(location));
 654                     }
 655
 656                     Rvalue::BinaryOp(_bin_op, lhs, rhs)
 657                     | Rvalue::CheckedBinaryOp(_bin_op, lhs, rhs) => {
 658                         self.visit_operand(lhs, location);
 659                         self.visit_operand(rhs, location);
 660                     }
 661
 662                     Rvalue::UnaryOp(_un_op, op) => {
 663                         self.visit_operand(op, location);
 664                     }
 665
 666                     Rvalue::Discriminant(place) => {
 667                         self.visit_place(
 668                             place,
 669                             PlaceContext::NonMutatingUse(NonMutatingUseContext::Inspect),
 670                             location
 671                         );
 672                     }
 673
 674                     Rvalue::NullaryOp(_op, ty) => {
 675                         self.visit_ty(ty, TyContext::Location(location));
 676                     }
 677
 678                     Rvalue::Aggregate(kind, operands) => {
 679                         let kind = &$($mutability)? **kind;
 680                         match kind {
 681                             AggregateKind::Array(ty) => {
 682                                 self.visit_ty(ty, TyContext::Location(location));
 683                             }
 684                             AggregateKind::Tuple => {
 685                             }
 686                             AggregateKind::Adt(
 687                                 _adt_def,
 688                                 _variant_index,
 689                                 substs,
 690                                 _user_substs,
 691                                 _active_field_index
 692                             ) => {
 693                                 self.visit_substs(substs, location);
 694                             }
 695                             AggregateKind::Closure(
 696                                 _,
 697                                 closure_substs
 698                             ) => {
 699                                 self.visit_substs(closure_substs, location);
 700                             }
 701                             AggregateKind::Generator(
 702                                 _,
 703                                 generator_substs,
 704                                 _movability,
 705                             ) => {
 706                                 self.visit_substs(generator_substs, location);
 707                             }
 708                         }
 709
 710                         for operand in operands {
 711                             self.visit_operand(operand, location);
 712                         }
 713                     }
 714                 }
 715             }
 716
 717             fn super_operand(&mut self,
 718                              operand: & $($mutability)? Operand<'tcx>,
 719                              location: Location) {
 720                 match operand {
 721                     Operand::Copy(place) => {
 722                         self.visit_place(
 723                             place,
 724                             PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy),
 725                             location
 726                         );
 727                     }
 728                     Operand::Move(place) => {
 729                         self.visit_place(
 730                             place,
 731                             PlaceContext::NonMutatingUse(NonMutatingUseContext::Move),
 732                             location
 733                         );
 734                     }
 735                     Operand::Constant(constant) => {
 736                         self.visit_constant(constant, location);
 737                     }
 738                 }
 739             }
 740
 741             fn super_ascribe_user_ty(&mut self,
 742                                      place: & $($mutability)? Place<'tcx>,
 743                                      _variance: & $($mutability)? ty::Variance,
 744                                      user_ty: & $($mutability)? UserTypeProjection,
 745                                      location: Location) {
 746                 self.visit_place(
 747                     place,
 748                     PlaceContext::NonUse(NonUseContext::AscribeUserTy),
 749                     location
 750                 );
 751                 self.visit_user_type_projection(user_ty);
 752             }
 753
 754             fn super_coverage(&mut self,
 755                               _kind: & $($mutability)? Coverage,
 756                               _location: Location) {
 757             }
 758
 759             fn super_retag(&mut self,
 760                            _kind: & $($mutability)? RetagKind,
 761                            place: & $($mutability)? Place<'tcx>,
 762                            location: Location) {
 763                 self.visit_place(
 764                     place,
 765                     PlaceContext::MutatingUse(MutatingUseContext::Retag),
 766                     location,
 767                 );
 768             }
 769
 770             fn super_local_decl(&mut self,
 771                                 local: Local,
 772                                 local_decl: & $($mutability)? LocalDecl<'tcx>) {
 773                 let LocalDecl {
 774                     mutability: _,
 775                     ty,
 776                     user_ty,
 777                     source_info,
 778                     internal: _,
 779                     local_info: _,
 780                     is_block_tail: _,
 781                 } = local_decl;
 782
 783                 self.visit_ty(ty, TyContext::LocalDecl {
 784                     local,
 785                     source_info: *source_info,
 786                 });
 787                 if let Some(user_ty) = user_ty {
 788                     for (user_ty, _) in & $($mutability)? user_ty.contents {
 789                         self.visit_user_type_projection(user_ty);
 790                     }
 791                 }
 792                 self.visit_source_info(source_info);
 793             }
 794
 795             fn super_var_debug_info(&mut self,
 796                                     var_debug_info: & $($mutability)? VarDebugInfo<'tcx>) {
 797                 let VarDebugInfo {
 798                     name: _,
 799                     source_info,
 800                     place,
 801                 } = var_debug_info;
 802
 803                 self.visit_source_info(source_info);
 804                 let location = START_BLOCK.start_location();
 805                 self.visit_place(
 806                     place,
 807                     PlaceContext::NonUse(NonUseContext::VarDebugInfo),
 808                     location,
 809                 );
 810             }
 811
 812             fn super_source_scope(&mut self,
 813                                       _scope: & $($mutability)? SourceScope) {
 814             }
 815
 816             fn super_constant(&mut self,
 817                               constant: & $($mutability)? Constant<'tcx>,
 818                               location: Location) {
 819                 let Constant {
 820                     span,
 821                     user_ty,
 822                     literal,
 823                 } = constant;
 824
 825                 self.visit_span(span);
 826                 drop(user_ty); // no visit method for this
 827                 self.visit_const(literal, location);
 828             }
 829
 830             fn super_span(&mut self, _span: & $($mutability)? Span) {
 831             }
 832
 833             fn super_source_info(&mut self, source_info: & $($mutability)? SourceInfo) {
 834                 let SourceInfo {
 835                     span,
 836                     scope,
 837                 } = source_info;
 838
 839                 self.visit_span(span);
 840                 self.visit_source_scope(scope);
 841             }
 842
 843             fn super_user_type_projection(
 844                 &mut self,
 845                 _ty: & $($mutability)? UserTypeProjection,
 846             ) {
 847             }
 848
 849             fn super_user_type_annotation(
 850                 &mut self,
 851                 _index: UserTypeAnnotationIndex,
 852                 ty: & $($mutability)? CanonicalUserTypeAnnotation<'tcx>,
 853             ) {
 854                 self.visit_span(& $($mutability)? ty.span);
 855                 self.visit_ty(& $($mutability)? ty.inferred_ty, TyContext::UserTy(ty.span));
 856             }
 857
 858             fn super_ty(&mut self, _ty: $(& $mutability)? Ty<'tcx>) {
 859             }
 860
 861             fn super_region(&mut self, _region: & $($mutability)? ty::Region<'tcx>) {
 862             }
 863
 864             fn super_const(&mut self, _const: & $($mutability)? &'tcx ty::Const<'tcx>) {
 865             }
 866
 867             fn super_substs(&mut self, _substs: & $($mutability)? SubstsRef<'tcx>) {
 868             }
 869
 870             // Convenience methods
 871
 872             fn visit_location(
 873                 &mut self,
 874                 body: &$($mutability)? Body<'tcx>,
 875                 location: Location
 876             ) {
 877                 macro_rules! basic_blocks {
 878                     (mut) => (body.basic_blocks_mut());
 879                     () => (body.basic_blocks());
 880                 };
 881                 let basic_block = & $($mutability)? basic_blocks!($($mutability)?)[location.block];
 882                 if basic_block.statements.len() == location.statement_index {
 883                     if let Some(ref $($mutability)? terminator) = basic_block.terminator {
 884                         self.visit_terminator(terminator, location)
 885                     }
 886                 } else {
 887                     let statement = & $($mutability)?
 888                         basic_block.statements[location.statement_index];
 889                     self.visit_statement(statement, location)
 890                 }
 891             }
 892         }
 893     }
 894 }
 895
 896 macro_rules! visit_place_fns {
 897     (mut) => {
 898         fn tcx<'a>(&'a self) -> TyCtxt<'tcx>;
 899
 900         fn super_place(
 901             &mut self,
 902             place: &mut Place<'tcx>,
 903             context: PlaceContext,
 904             location: Location,
 905         ) {
 906             self.visit_local(&mut place.local, context, location);
 907
 908             if let Some(new_projection) = self.process_projection(&place.projection, location) {
 909                 place.projection = self.tcx().intern_place_elems(&new_projection);
 910             }
 911         }
 912
 913         fn process_projection(
 914             &mut self,
 915             projection: &'a [PlaceElem<'tcx>],
 916             location: Location,
 917         ) -> Option<Vec<PlaceElem<'tcx>>> {
 918             let mut projection = Cow::Borrowed(projection);
 919
 920             for i in 0..projection.len() {
 921                 if let Some(&elem) = projection.get(i) {
 922                     if let Some(elem) = self.process_projection_elem(elem, location) {
 923                         // This converts the borrowed projection into `Cow::Owned(_)` and returns a
 924                         // clone of the projection so we can mutate and reintern later.
 925                         let vec = projection.to_mut();
 926                         vec[i] = elem;
 927                     }
 928                 }
 929             }
 930
 931             match projection {
 932                 Cow::Borrowed(_) => None,
 933                 Cow::Owned(vec) => Some(vec),
 934             }
 935         }
 936
 937         fn process_projection_elem(
 938             &mut self,
 939             elem: PlaceElem<'tcx>,
 940             location: Location,
 941         ) -> Option<PlaceElem<'tcx>> {
 942             match elem {
 943                 PlaceElem::Index(local) => {
 944                     let mut new_local = local;
 945                     self.visit_local(
 946                         &mut new_local,
 947                         PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy),
 948                         location,
 949                     );
 950
 951                     if new_local == local { None } else { Some(PlaceElem::Index(new_local)) }
 952                 }
 953                 PlaceElem::Deref
 954                 | PlaceElem::Field(..)
 955                 | PlaceElem::ConstantIndex { .. }
 956                 | PlaceElem::Subslice { .. }
 957                 | PlaceElem::Downcast(..) => None,
 958             }
 959         }
 960     };
 961
 962     () => {
 963         fn visit_projection(
 964             &mut self,
 965             local: Local,
 966             projection: &[PlaceElem<'tcx>],
 967             context: PlaceContext,
 968             location: Location,
 969         ) {
 970             self.super_projection(local, projection, context, location);
 971         }
 972
 973         fn visit_projection_elem(
 974             &mut self,
 975             local: Local,
 976             proj_base: &[PlaceElem<'tcx>],
 977             elem: PlaceElem<'tcx>,
 978             context: PlaceContext,
 979             location: Location,
 980         ) {
 981             self.super_projection_elem(local, proj_base, elem, context, location);
 982         }
 983
 984         fn super_place(&mut self, place: &Place<'tcx>, context: PlaceContext, location: Location) {
 985             let mut context = context;
 986
 987             if !place.projection.is_empty() {
 988                 context = if context.is_mutating_use() {
 989                     PlaceContext::MutatingUse(MutatingUseContext::Projection)
 990                 } else {
 991                     PlaceContext::NonMutatingUse(NonMutatingUseContext::Projection)
 992                 };
 993             }
 994
 995             self.visit_local(&place.local, context, location);
 996
 997             self.visit_projection(place.local, &place.projection, context, location);
 998         }
 999
1000         fn super_projection(
1001             &mut self,
1002             local: Local,
1003             projection: &[PlaceElem<'tcx>],
1004             context: PlaceContext,
1005             location: Location,
1006         ) {
1007             let mut cursor = projection;
1008             while let &[ref proj_base @ .., elem] = cursor {
1009                 cursor = proj_base;
1010                 self.visit_projection_elem(local, cursor, elem, context, location);
1011             }
1012         }
1013
1014         fn super_projection_elem(
1015             &mut self,
1016             _local: Local,
1017             _proj_base: &[PlaceElem<'tcx>],
1018             elem: PlaceElem<'tcx>,
1019             _context: PlaceContext,
1020             location: Location,
1021         ) {
1022             match elem {
1023                 ProjectionElem::Field(_field, ty) => {
1024                     self.visit_ty(ty, TyContext::Location(location));
1025                 }
1026                 ProjectionElem::Index(local) => {
1027                     self.visit_local(
1028                         &local,
1029                         PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy),
1030                         location,
1031                     );
1032                 }
1033                 ProjectionElem::Deref
1034                 | ProjectionElem::Subslice { from: _, to: _, from_end: _ }
1035                 | ProjectionElem::ConstantIndex { offset: _, min_length: _, from_end: _ }
1036                 | ProjectionElem::Downcast(_, _) => {}
1037             }
1038         }
1039     };
1040 }
1041
1042 make_mir_visitor!(Visitor,);
1043 make_mir_visitor!(MutVisitor, mut);
1044
1045 pub trait MirVisitable<'tcx> {
1046     fn apply(&self, location: Location, visitor: &mut dyn Visitor<'tcx>);
1047 }
1048
1049 impl<'tcx> MirVisitable<'tcx> for Statement<'tcx> {
1050     fn apply(&self, location: Location, visitor: &mut dyn Visitor<'tcx>) {
1051         visitor.visit_statement(self, location)
1052     }
1053 }
1054
1055 impl<'tcx> MirVisitable<'tcx> for Terminator<'tcx> {
1056     fn apply(&self, location: Location, visitor: &mut dyn Visitor<'tcx>) {
1057         visitor.visit_terminator(self, location)
1058     }
1059 }
1060
1061 impl<'tcx> MirVisitable<'tcx> for Option<Terminator<'tcx>> {
1062     fn apply(&self, location: Location, visitor: &mut dyn Visitor<'tcx>) {
1063         visitor.visit_terminator(self.as_ref().unwrap(), location)
1064     }
1065 }
1066
1067 /// Extra information passed to `visit_ty` and friends to give context
1068 /// about where the type etc appears.
1069 #[derive(Debug)]
1070 pub enum TyContext {
1071     LocalDecl {
1072         /// The index of the local variable we are visiting.
1073         local: Local,
1074
1075         /// The source location where this local variable was declared.
1076         source_info: SourceInfo,
1077     },
1078
1079     /// The inferred type of a user type annotation.
1080     UserTy(Span),
1081
1082     /// The return type of the function.
1083     ReturnTy(SourceInfo),
1084
1085     YieldTy(SourceInfo),
1086
1087     /// A type found at some location.
1088     Location(Location),
1089 }
1090
1091 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
1092 pub enum NonMutatingUseContext {
1093     /// Being inspected in some way, like loading a len.
1094     Inspect,
1095     /// Consumed as part of an operand.
1096     Copy,
1097     /// Consumed as part of an operand.
1098     Move,
1099     /// Shared borrow.
1100     SharedBorrow,
1101     /// Shallow borrow.
1102     ShallowBorrow,
1103     /// Unique borrow.
1104     UniqueBorrow,
1105     /// AddressOf for *const pointer.
1106     AddressOf,
1107     /// Used as base for another place, e.g., `x` in `x.y`. Will not mutate the place.
1108     /// For example, the projection `x.y` is not marked as a mutation in these cases:
1109     ///
1110     ///     z = x.y;
1111     ///     f(&x.y);
1112     ///
1113     Projection,
1114 }
1115
1116 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
1117 pub enum MutatingUseContext {
1118     /// Appears as LHS of an assignment.
1119     Store,
1120     /// Can often be treated as a `Store`, but needs to be separate because
1121     /// ASM is allowed to read outputs as well, so a `Store`-`AsmOutput` sequence
1122     /// cannot be simplified the way a `Store`-`Store` can be.
1123     AsmOutput,
1124     /// Destination of a call.
1125     Call,
1126     /// Destination of a yield.
1127     Yield,
1128     /// Being dropped.
1129     Drop,
1130     /// Mutable borrow.
1131     Borrow,
1132     /// AddressOf for *mut pointer.
1133     AddressOf,
1134     /// Used as base for another place, e.g., `x` in `x.y`. Could potentially mutate the place.
1135     /// For example, the projection `x.y` is marked as a mutation in these cases:
1136     ///
1137     ///     x.y = ...;
1138     ///     f(&mut x.y);
1139     ///
1140     Projection,
1141     /// Retagging, a "Stacked Borrows" shadow state operation
1142     Retag,
1143 }
1144
1145 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
1146 pub enum NonUseContext {
1147     /// Starting a storage live range.
1148     StorageLive,
1149     /// Ending a storage live range.
1150     StorageDead,
1151     /// User type annotation assertions for NLL.
1152     AscribeUserTy,
1153     /// The data of an user variable, for debug info.
1154     VarDebugInfo,
1155 }
1156
1157 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
1158 pub enum PlaceContext {
1159     NonMutatingUse(NonMutatingUseContext),
1160     MutatingUse(MutatingUseContext),
1161     NonUse(NonUseContext),
1162 }
1163
1164 impl PlaceContext {
1165     /// Returns `true` if this place context represents a drop.
1166     pub fn is_drop(&self) -> bool {
1167         match *self {
1168             PlaceContext::MutatingUse(MutatingUseContext::Drop) => true,
1169             _ => false,
1170         }
1171     }
1172
1173     /// Returns `true` if this place context represents a borrow.
1174     pub fn is_borrow(&self) -> bool {
1175         match *self {
1176             PlaceContext::NonMutatingUse(
1177                 NonMutatingUseContext::SharedBorrow
1178                 | NonMutatingUseContext::ShallowBorrow
1179                 | NonMutatingUseContext::UniqueBorrow,
1180             )
1181             | PlaceContext::MutatingUse(MutatingUseContext::Borrow) => true,
1182             _ => false,
1183         }
1184     }
1185
1186     /// Returns `true` if this place context represents a storage live or storage dead marker.
1187     pub fn is_storage_marker(&self) -> bool {
1188         match *self {
1189             PlaceContext::NonUse(NonUseContext::StorageLive | NonUseContext::StorageDead) => true,
1190             _ => false,
1191         }
1192     }
1193
1194     /// Returns `true` if this place context represents a storage live marker.
1195     pub fn is_storage_live_marker(&self) -> bool {
1196         match *self {
1197             PlaceContext::NonUse(NonUseContext::StorageLive) => true,
1198             _ => false,
1199         }
1200     }
1201
1202     /// Returns `true` if this place context represents a storage dead marker.
1203     pub fn is_storage_dead_marker(&self) -> bool {
1204         match *self {
1205             PlaceContext::NonUse(NonUseContext::StorageDead) => true,
1206             _ => false,
1207         }
1208     }
1209
1210     /// Returns `true` if this place context represents a use that potentially changes the value.
1211     pub fn is_mutating_use(&self) -> bool {
1212         match *self {
1213             PlaceContext::MutatingUse(..) => true,
1214             _ => false,
1215         }
1216     }
1217
1218     /// Returns `true` if this place context represents a use that does not change the value.
1219     pub fn is_nonmutating_use(&self) -> bool {
1220         match *self {
1221             PlaceContext::NonMutatingUse(..) => true,
1222             _ => false,
1223         }
1224     }
1225
1226     /// Returns `true` if this place context represents a use.
1227     pub fn is_use(&self) -> bool {
1228         match *self {
1229             PlaceContext::NonUse(..) => false,
1230             _ => true,
1231         }
1232     }
1233
1234     /// Returns `true` if this place context represents an assignment statement.
1235     pub fn is_place_assignment(&self) -> bool {
1236         match *self {
1237             PlaceContext::MutatingUse(
1238                 MutatingUseContext::Store
1239                 | MutatingUseContext::Call
1240                 | MutatingUseContext::AsmOutput,
1241             ) => true,
1242             _ => false,
1243         }
1244     }
1245 }