compiler/rustc_middle/src/mir/visit.rs

   1 //! # The MIR Visitor
   2 //!
   3 //! ## Overview
   4 //!
   5 //! There are two visitors, one for immutable and one for mutable references,
   6 //! but both are generated by the following macro. The code is written according
   7 //! to the following conventions:
   8 //!
   9 //! - introduce a `visit_foo` and a `super_foo` method for every MIR type
  10 //! - `visit_foo`, by default, calls `super_foo`
  11 //! - `super_foo`, by default, destructures the `foo` and calls `visit_foo`
  12 //!
  13 //! This allows you as a user to override `visit_foo` for types are
  14 //! interested in, and invoke (within that method) call
  15 //! `self.super_foo` to get the default behavior. Just as in an OO
  16 //! language, you should never call `super` methods ordinarily except
  17 //! in that circumstance.
  18 //!
  19 //! For the most part, we do not destructure things external to the
  20 //! MIR, e.g., types, spans, etc, but simply visit them and stop. This
  21 //! avoids duplication with other visitors like `TypeFoldable`.
  22 //!
  23 //! ## Updating
  24 //!
  25 //! The code is written in a very deliberate style intended to minimize
  26 //! the chance of things being overlooked. You'll notice that we always
  27 //! use pattern matching to reference fields and we ensure that all
  28 //! matches are exhaustive.
  29 //!
  30 //! For example, the `super_basic_block_data` method begins like this:
  31 //!
  32 //! ```rust
  33 //! fn super_basic_block_data(&mut self,
  34 //!                           block: BasicBlock,
  35 //!                           data: & $($mutability)? BasicBlockData<'tcx>) {
  36 //!     let BasicBlockData {
  37 //!         statements,
  38 //!         terminator,
  39 //!         is_cleanup: _
  40 //!     } = *data;
  41 //!
  42 //!     for statement in statements {
  43 //!         self.visit_statement(block, statement);
  44 //!     }
  45 //!
  46 //!     ...
  47 //! }
  48 //! ```
  49 //!
  50 //! Here we used `let BasicBlockData { <fields> } = *data` deliberately,
  51 //! rather than writing `data.statements` in the body. This is because if one
  52 //! adds a new field to `BasicBlockData`, one will be forced to revise this code,
  53 //! and hence one will (hopefully) invoke the correct visit methods (if any).
  54 //!
  55 //! For this to work, ALL MATCHES MUST BE EXHAUSTIVE IN FIELDS AND VARIANTS.
  56 //! That means you never write `..` to skip over fields, nor do you write `_`
  57 //! to skip over variants in a `match`.
  58 //!
  59 //! The only place that `_` is acceptable is to match a field (or
  60 //! variant argument) that does not require visiting, as in
  61 //! `is_cleanup` above.
  62
  63 use crate::mir::*;
  64 use crate::ty::subst::SubstsRef;
  65 use crate::ty::{CanonicalUserTypeAnnotation, Ty};
  66 use rustc_span::Span;
  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<'tcx>) {
  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(gen) = &$($mutability)? body.generator {
 245                     if let Some(yield_ty) = &$($mutability)? gen.yield_ty {
 246                         self.visit_ty(
 247                             yield_ty,
 248                             TyContext::YieldTy(SourceInfo::outermost(span))
 249                         );
 250                     }
 251                 }
 252
 253                 // for best performance, we want to use an iterator rather
 254                 // than a for-loop, to avoid calling `body::Body::invalidate` for
 255                 // each basic block.
 256                 macro_rules! basic_blocks {
 257                     (mut) => (body.basic_blocks_mut().iter_enumerated_mut());
 258                     () => (body.basic_blocks().iter_enumerated());
 259                 }
 260                 for (bb, data) in basic_blocks!($($mutability)?) {
 261                     self.visit_basic_block_data(bb, data);
 262                 }
 263
 264                 for scope in &$($mutability)? body.source_scopes {
 265                     self.visit_source_scope_data(scope);
 266                 }
 267
 268                 self.visit_ty(
 269                     &$($mutability)? body.return_ty(),
 270                     TyContext::ReturnTy(SourceInfo::outermost(body.span))
 271                 );
 272
 273                 for local in body.local_decls.indices() {
 274                     self.visit_local_decl(local, & $($mutability)? body.local_decls[local]);
 275                 }
 276
 277                 macro_rules! type_annotations {
 278                     (mut) => (body.user_type_annotations.iter_enumerated_mut());
 279                     () => (body.user_type_annotations.iter_enumerated());
 280                 }
 281
 282                 for (index, annotation) in type_annotations!($($mutability)?) {
 283                     self.visit_user_type_annotation(
 284                         index, annotation
 285                     );
 286                 }
 287
 288                 for var_debug_info in &$($mutability)? body.var_debug_info {
 289                     self.visit_var_debug_info(var_debug_info);
 290                 }
 291
 292                 self.visit_span(&$($mutability)? body.span);
 293
 294                 for const_ in &$($mutability)? body.required_consts {
 295                     let location = START_BLOCK.start_location();
 296                     self.visit_constant(const_, location);
 297                 }
 298             }
 299
 300             fn super_basic_block_data(&mut self,
 301                                       block: BasicBlock,
 302                                       data: & $($mutability)? BasicBlockData<'tcx>) {
 303                 let BasicBlockData {
 304                     statements,
 305                     terminator,
 306                     is_cleanup: _
 307                 } = data;
 308
 309                 let mut index = 0;
 310                 for statement in statements {
 311                     let location = Location { block, statement_index: index };
 312                     self.visit_statement(statement, location);
 313                     index += 1;
 314                 }
 315
 316                 if let Some(terminator) = terminator {
 317                     let location = Location { block, statement_index: index };
 318                     self.visit_terminator(terminator, location);
 319                 }
 320             }
 321
 322             fn super_source_scope_data(
 323                 &mut self,
 324                 scope_data: & $($mutability)? SourceScopeData<'tcx>,
 325             ) {
 326                 let SourceScopeData {
 327                     span,
 328                     parent_scope,
 329                     inlined,
 330                     inlined_parent_scope,
 331                     local_data: _,
 332                 } = scope_data;
 333
 334                 self.visit_span(span);
 335                 if let Some(parent_scope) = parent_scope {
 336                     self.visit_source_scope(parent_scope);
 337                 }
 338                 if let Some((callee, callsite_span)) = inlined {
 339                     let location = START_BLOCK.start_location();
 340
 341                     self.visit_span(callsite_span);
 342
 343                     let ty::Instance { def: callee_def, substs: callee_substs } = callee;
 344                     match callee_def {
 345                         ty::InstanceDef::Item(_def_id) => {}
 346
 347                         ty::InstanceDef::Intrinsic(_def_id) |
 348                         ty::InstanceDef::VtableShim(_def_id) |
 349                         ty::InstanceDef::ReifyShim(_def_id) |
 350                         ty::InstanceDef::Virtual(_def_id, _) |
 351                         ty::InstanceDef::ClosureOnceShim { call_once: _def_id, track_caller: _ } |
 352                         ty::InstanceDef::DropGlue(_def_id, None) => {}
 353
 354                         ty::InstanceDef::FnPtrShim(_def_id, ty) |
 355                         ty::InstanceDef::DropGlue(_def_id, Some(ty)) |
 356                         ty::InstanceDef::CloneShim(_def_id, ty) => {
 357                             // FIXME(eddyb) use a better `TyContext` here.
 358                             self.visit_ty(ty, TyContext::Location(location));
 359                         }
 360                     }
 361                     self.visit_substs(callee_substs, location);
 362                 }
 363                 if let Some(inlined_parent_scope) = inlined_parent_scope {
 364                     self.visit_source_scope(inlined_parent_scope);
 365                 }
 366             }
 367
 368             fn super_statement(&mut self,
 369                                statement: & $($mutability)? Statement<'tcx>,
 370                                location: Location) {
 371                 let Statement {
 372                     source_info,
 373                     kind,
 374                 } = statement;
 375
 376                 self.visit_source_info(source_info);
 377                 match kind {
 378                     StatementKind::Assign(
 379                         box(ref $($mutability)? place, ref $($mutability)? rvalue)
 380                     ) => {
 381                         self.visit_assign(place, rvalue, location);
 382                     }
 383                     StatementKind::FakeRead(box (_, place)) => {
 384                         self.visit_place(
 385                             place,
 386                             PlaceContext::NonMutatingUse(NonMutatingUseContext::Inspect),
 387                             location
 388                         );
 389                     }
 390                     StatementKind::SetDiscriminant { place, .. } => {
 391                         self.visit_place(
 392                             place,
 393                             PlaceContext::MutatingUse(MutatingUseContext::Store),
 394                             location
 395                         );
 396                     }
 397                     StatementKind::StorageLive(local) => {
 398                         self.visit_local(
 399                             local,
 400                             PlaceContext::NonUse(NonUseContext::StorageLive),
 401                             location
 402                         );
 403                     }
 404                     StatementKind::StorageDead(local) => {
 405                         self.visit_local(
 406                             local,
 407                             PlaceContext::NonUse(NonUseContext::StorageDead),
 408                             location
 409                         );
 410                     }
 411                     StatementKind::Retag(kind, place) => {
 412                         self.visit_retag(kind, place, location);
 413                     }
 414                     StatementKind::AscribeUserType(
 415                         box(ref $($mutability)? place, ref $($mutability)? user_ty),
 416                         variance
 417                     ) => {
 418                         self.visit_ascribe_user_ty(place, variance, user_ty, location);
 419                     }
 420                     StatementKind::Coverage(coverage) => {
 421                         self.visit_coverage(
 422                             coverage,
 423                             location
 424                         )
 425                     }
 426                     StatementKind::CopyNonOverlapping(box crate::mir::CopyNonOverlapping{
 427                       ref $($mutability)? src,
 428                       ref $($mutability)? dst,
 429                       ref $($mutability)? count,
 430                     }) => {
 431                       self.visit_operand(src, location);
 432                       self.visit_operand(dst, location);
 433                       self.visit_operand(count, location)
 434                     }
 435                     StatementKind::Nop => {}
 436                 }
 437             }
 438
 439             fn super_assign(&mut self,
 440                             place: &$($mutability)? Place<'tcx>,
 441                             rvalue: &$($mutability)? Rvalue<'tcx>,
 442                             location: Location) {
 443                 self.visit_place(
 444                     place,
 445                     PlaceContext::MutatingUse(MutatingUseContext::Store),
 446                     location
 447                 );
 448                 self.visit_rvalue(rvalue, location);
 449             }
 450
 451             fn super_terminator(&mut self,
 452                                 terminator: &$($mutability)? Terminator<'tcx>,
 453                                 location: Location) {
 454                 let Terminator { source_info, kind } = terminator;
 455
 456                 self.visit_source_info(source_info);
 457                 match kind {
 458                     TerminatorKind::Goto { .. } |
 459                     TerminatorKind::Resume |
 460                     TerminatorKind::Abort |
 461                     TerminatorKind::GeneratorDrop |
 462                     TerminatorKind::Unreachable |
 463                     TerminatorKind::FalseEdge { .. } |
 464                     TerminatorKind::FalseUnwind { .. } => {
 465                     }
 466
 467                     TerminatorKind::Return => {
 468                         // `return` logically moves from the return place `_0`. Note that the place
 469                         // cannot be changed by any visitor, though.
 470                         let $($mutability)? local = RETURN_PLACE;
 471                         self.visit_local(
 472                             & $($mutability)? local,
 473                             PlaceContext::NonMutatingUse(NonMutatingUseContext::Move),
 474                             location,
 475                         );
 476
 477                         assert_eq!(
 478                             local,
 479                             RETURN_PLACE,
 480                             "`MutVisitor` tried to mutate return place of `return` terminator"
 481                         );
 482                     }
 483
 484                     TerminatorKind::SwitchInt {
 485                         discr,
 486                         switch_ty,
 487                         targets: _
 488                     } => {
 489                         self.visit_operand(discr, location);
 490                         self.visit_ty(switch_ty, TyContext::Location(location));
 491                     }
 492
 493                     TerminatorKind::Drop {
 494                         place,
 495                         target: _,
 496                         unwind: _,
 497                     } => {
 498                         self.visit_place(
 499                             place,
 500                             PlaceContext::MutatingUse(MutatingUseContext::Drop),
 501                             location
 502                         );
 503                     }
 504
 505                     TerminatorKind::DropAndReplace {
 506                         place,
 507                         value,
 508                         target: _,
 509                         unwind: _,
 510                     } => {
 511                         self.visit_place(
 512                             place,
 513                             PlaceContext::MutatingUse(MutatingUseContext::Drop),
 514                             location
 515                         );
 516                         self.visit_operand(value, location);
 517                     }
 518
 519                     TerminatorKind::Call {
 520                         func,
 521                         args,
 522                         destination,
 523                         cleanup: _,
 524                         from_hir_call: _,
 525                         fn_span: _
 526                     } => {
 527                         self.visit_operand(func, location);
 528                         for arg in args {
 529                             self.visit_operand(arg, location);
 530                         }
 531                         if let Some((destination, _)) = destination {
 532                             self.visit_place(
 533                                 destination,
 534                                 PlaceContext::MutatingUse(MutatingUseContext::Call),
 535                                 location
 536                             );
 537                         }
 538                     }
 539
 540                     TerminatorKind::Assert {
 541                         cond,
 542                         expected: _,
 543                         msg,
 544                         target: _,
 545                         cleanup: _,
 546                     } => {
 547                         self.visit_operand(cond, location);
 548                         self.visit_assert_message(msg, location);
 549                     }
 550
 551                     TerminatorKind::Yield {
 552                         value,
 553                         resume: _,
 554                         resume_arg,
 555                         drop: _,
 556                     } => {
 557                         self.visit_operand(value, location);
 558                         self.visit_place(
 559                             resume_arg,
 560                             PlaceContext::MutatingUse(MutatingUseContext::Yield),
 561                             location,
 562                         );
 563                     }
 564
 565                     TerminatorKind::InlineAsm {
 566                         template: _,
 567                         operands,
 568                         options: _,
 569                         line_spans: _,
 570                         destination: _,
 571                         cleanup: _,
 572                     } => {
 573                         for op in operands {
 574                             match op {
 575                                 InlineAsmOperand::In { value, .. } => {
 576                                     self.visit_operand(value, location);
 577                                 }
 578                                 InlineAsmOperand::Out { place: Some(place), .. } => {
 579                                     self.visit_place(
 580                                         place,
 581                                         PlaceContext::MutatingUse(MutatingUseContext::AsmOutput),
 582                                         location,
 583                                     );
 584                                 }
 585                                 InlineAsmOperand::InOut { in_value, out_place, .. } => {
 586                                     self.visit_operand(in_value, location);
 587                                     if let Some(out_place) = out_place {
 588                                         self.visit_place(
 589                                             out_place,
 590                                             PlaceContext::MutatingUse(MutatingUseContext::AsmOutput),
 591                                             location,
 592                                         );
 593                                     }
 594                                 }
 595                                 InlineAsmOperand::Const { value }
 596                                 | InlineAsmOperand::SymFn { value } => {
 597                                     self.visit_constant(value, location);
 598                                 }
 599                                 InlineAsmOperand::Out { place: None, .. }
 600                                 | InlineAsmOperand::SymStatic { def_id: _ } => {}
 601                             }
 602                         }
 603                     }
 604                 }
 605             }
 606
 607             fn super_assert_message(&mut self,
 608                                     msg: & $($mutability)? AssertMessage<'tcx>,
 609                                     location: Location) {
 610                 use crate::mir::AssertKind::*;
 611                 match msg {
 612                     BoundsCheck { len, index } => {
 613                         self.visit_operand(len, location);
 614                         self.visit_operand(index, location);
 615                     }
 616                     Overflow(_, l, r) => {
 617                         self.visit_operand(l, location);
 618                         self.visit_operand(r, location);
 619                     }
 620                     OverflowNeg(op) | DivisionByZero(op) | RemainderByZero(op) => {
 621                         self.visit_operand(op, location);
 622                     }
 623                     ResumedAfterReturn(_) | ResumedAfterPanic(_) => {
 624                         // Nothing to visit
 625                     }
 626                 }
 627             }
 628
 629             fn super_rvalue(&mut self,
 630                             rvalue: & $($mutability)? Rvalue<'tcx>,
 631                             location: Location) {
 632                 match rvalue {
 633                     Rvalue::Use(operand) => {
 634                         self.visit_operand(operand, location);
 635                     }
 636
 637                     Rvalue::Repeat(value, _) => {
 638                         self.visit_operand(value, location);
 639                     }
 640
 641                     Rvalue::ThreadLocalRef(_) => {}
 642
 643                     Rvalue::Ref(r, bk, path) => {
 644                         self.visit_region(r, location);
 645                         let ctx = match bk {
 646                             BorrowKind::Shared => PlaceContext::NonMutatingUse(
 647                                 NonMutatingUseContext::SharedBorrow
 648                             ),
 649                             BorrowKind::Shallow => PlaceContext::NonMutatingUse(
 650                                 NonMutatingUseContext::ShallowBorrow
 651                             ),
 652                             BorrowKind::Unique => PlaceContext::NonMutatingUse(
 653                                 NonMutatingUseContext::UniqueBorrow
 654                             ),
 655                             BorrowKind::Mut { .. } =>
 656                                 PlaceContext::MutatingUse(MutatingUseContext::Borrow),
 657                         };
 658                         self.visit_place(path, ctx, location);
 659                     }
 660
 661                     Rvalue::AddressOf(m, path) => {
 662                         let ctx = match m {
 663                             Mutability::Mut => PlaceContext::MutatingUse(
 664                                 MutatingUseContext::AddressOf
 665                             ),
 666                             Mutability::Not => PlaceContext::NonMutatingUse(
 667                                 NonMutatingUseContext::AddressOf
 668                             ),
 669                         };
 670                         self.visit_place(path, ctx, location);
 671                     }
 672
 673                     Rvalue::Len(path) => {
 674                         self.visit_place(
 675                             path,
 676                             PlaceContext::NonMutatingUse(NonMutatingUseContext::Inspect),
 677                             location
 678                         );
 679                     }
 680
 681                     Rvalue::Cast(_cast_kind, operand, ty) => {
 682                         self.visit_operand(operand, location);
 683                         self.visit_ty(ty, TyContext::Location(location));
 684                     }
 685
 686                     Rvalue::BinaryOp(_bin_op, box(lhs, rhs))
 687                     | Rvalue::CheckedBinaryOp(_bin_op, box(lhs, rhs)) => {
 688                         self.visit_operand(lhs, location);
 689                         self.visit_operand(rhs, location);
 690                     }
 691
 692                     Rvalue::UnaryOp(_un_op, op) => {
 693                         self.visit_operand(op, location);
 694                     }
 695
 696                     Rvalue::Discriminant(place) => {
 697                         self.visit_place(
 698                             place,
 699                             PlaceContext::NonMutatingUse(NonMutatingUseContext::Inspect),
 700                             location
 701                         );
 702                     }
 703
 704                     Rvalue::NullaryOp(_op, ty) => {
 705                         self.visit_ty(ty, TyContext::Location(location));
 706                     }
 707
 708                     Rvalue::Aggregate(kind, operands) => {
 709                         let kind = &$($mutability)? **kind;
 710                         match kind {
 711                             AggregateKind::Array(ty) => {
 712                                 self.visit_ty(ty, TyContext::Location(location));
 713                             }
 714                             AggregateKind::Tuple => {
 715                             }
 716                             AggregateKind::Adt(
 717                                 _adt_def,
 718                                 _variant_index,
 719                                 substs,
 720                                 _user_substs,
 721                                 _active_field_index
 722                             ) => {
 723                                 self.visit_substs(substs, location);
 724                             }
 725                             AggregateKind::Closure(
 726                                 _,
 727                                 closure_substs
 728                             ) => {
 729                                 self.visit_substs(closure_substs, location);
 730                             }
 731                             AggregateKind::Generator(
 732                                 _,
 733                                 generator_substs,
 734                                 _movability,
 735                             ) => {
 736                                 self.visit_substs(generator_substs, location);
 737                             }
 738                         }
 739
 740                         for operand in operands {
 741                             self.visit_operand(operand, location);
 742                         }
 743                     }
 744
 745                     Rvalue::ShallowInitBox(operand, ty) => {
 746                         self.visit_operand(operand, location);
 747                         self.visit_ty(ty, TyContext::Location(location));
 748                     }
 749                 }
 750             }
 751
 752             fn super_operand(&mut self,
 753                              operand: & $($mutability)? Operand<'tcx>,
 754                              location: Location) {
 755                 match operand {
 756                     Operand::Copy(place) => {
 757                         self.visit_place(
 758                             place,
 759                             PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy),
 760                             location
 761                         );
 762                     }
 763                     Operand::Move(place) => {
 764                         self.visit_place(
 765                             place,
 766                             PlaceContext::NonMutatingUse(NonMutatingUseContext::Move),
 767                             location
 768                         );
 769                     }
 770                     Operand::Constant(constant) => {
 771                         self.visit_constant(constant, location);
 772                     }
 773                 }
 774             }
 775
 776             fn super_ascribe_user_ty(&mut self,
 777                                      place: & $($mutability)? Place<'tcx>,
 778                                      _variance: & $($mutability)? ty::Variance,
 779                                      user_ty: & $($mutability)? UserTypeProjection,
 780                                      location: Location) {
 781                 self.visit_place(
 782                     place,
 783                     PlaceContext::NonUse(NonUseContext::AscribeUserTy),
 784                     location
 785                 );
 786                 self.visit_user_type_projection(user_ty);
 787             }
 788
 789             fn super_coverage(&mut self,
 790                               _coverage: & $($mutability)? Coverage,
 791                               _location: Location) {
 792             }
 793
 794             fn super_retag(&mut self,
 795                            _kind: & $($mutability)? RetagKind,
 796                            place: & $($mutability)? Place<'tcx>,
 797                            location: Location) {
 798                 self.visit_place(
 799                     place,
 800                     PlaceContext::MutatingUse(MutatingUseContext::Retag),
 801                     location,
 802                 );
 803             }
 804
 805             fn super_local_decl(&mut self,
 806                                 local: Local,
 807                                 local_decl: & $($mutability)? LocalDecl<'tcx>) {
 808                 let LocalDecl {
 809                     mutability: _,
 810                     ty,
 811                     user_ty,
 812                     source_info,
 813                     internal: _,
 814                     local_info: _,
 815                     is_block_tail: _,
 816                 } = local_decl;
 817
 818                 self.visit_ty(ty, TyContext::LocalDecl {
 819                     local,
 820                     source_info: *source_info,
 821                 });
 822                 if let Some(user_ty) = user_ty {
 823                     for (user_ty, _) in & $($mutability)? user_ty.contents {
 824                         self.visit_user_type_projection(user_ty);
 825                     }
 826                 }
 827                 self.visit_source_info(source_info);
 828             }
 829
 830             fn super_var_debug_info(&mut self,
 831                                     var_debug_info: & $($mutability)? VarDebugInfo<'tcx>) {
 832                 let VarDebugInfo {
 833                     name: _,
 834                     source_info,
 835                     value,
 836                 } = var_debug_info;
 837
 838                 self.visit_source_info(source_info);
 839                 let location = START_BLOCK.start_location();
 840                 match value {
 841                     VarDebugInfoContents::Const(c) => self.visit_constant(c, location),
 842                     VarDebugInfoContents::Place(place) =>
 843                         self.visit_place(
 844                             place,
 845                             PlaceContext::NonUse(NonUseContext::VarDebugInfo),
 846                             location
 847                         ),
 848                 }
 849             }
 850
 851             fn super_source_scope(&mut self,
 852                                       _scope: & $($mutability)? SourceScope) {
 853             }
 854
 855             fn super_constant(&mut self,
 856                               constant: & $($mutability)? Constant<'tcx>,
 857                               location: Location) {
 858                 let Constant {
 859                     span,
 860                     user_ty,
 861                     literal,
 862                 } = constant;
 863
 864                 self.visit_span(span);
 865                 drop(user_ty); // no visit method for this
 866                 match literal {
 867                     ConstantKind::Ty(ct) => self.visit_const(ct, location),
 868                     ConstantKind::Val(_, t) => self.visit_ty(t, TyContext::Location(location)),
 869                 }
 870             }
 871
 872             fn super_span(&mut self, _span: & $($mutability)? Span) {
 873             }
 874
 875             fn super_source_info(&mut self, source_info: & $($mutability)? SourceInfo) {
 876                 let SourceInfo {
 877                     span,
 878                     scope,
 879                 } = source_info;
 880
 881                 self.visit_span(span);
 882                 self.visit_source_scope(scope);
 883             }
 884
 885             fn super_user_type_projection(
 886                 &mut self,
 887                 _ty: & $($mutability)? UserTypeProjection,
 888             ) {
 889             }
 890
 891             fn super_user_type_annotation(
 892                 &mut self,
 893                 _index: UserTypeAnnotationIndex,
 894                 ty: & $($mutability)? CanonicalUserTypeAnnotation<'tcx>,
 895             ) {
 896                 self.visit_span(& $($mutability)? ty.span);
 897                 self.visit_ty(& $($mutability)? ty.inferred_ty, TyContext::UserTy(ty.span));
 898             }
 899
 900             fn super_ty(&mut self, _ty: $(& $mutability)? Ty<'tcx>) {
 901             }
 902
 903             fn super_region(&mut self, _region: & $($mutability)? ty::Region<'tcx>) {
 904             }
 905
 906             fn super_const(&mut self, _const: & $($mutability)? &'tcx ty::Const<'tcx>) {
 907             }
 908
 909             fn super_substs(&mut self, _substs: & $($mutability)? SubstsRef<'tcx>) {
 910             }
 911
 912             // Convenience methods
 913
 914             fn visit_location(
 915                 &mut self,
 916                 body: &$($mutability)? Body<'tcx>,
 917                 location: Location
 918             ) {
 919                 macro_rules! basic_blocks {
 920                     (mut) => (body.basic_blocks_mut());
 921                     () => (body.basic_blocks());
 922                 }
 923                 let basic_block = & $($mutability)? basic_blocks!($($mutability)?)[location.block];
 924                 if basic_block.statements.len() == location.statement_index {
 925                     if let Some(ref $($mutability)? terminator) = basic_block.terminator {
 926                         self.visit_terminator(terminator, location)
 927                     }
 928                 } else {
 929                     let statement = & $($mutability)?
 930                         basic_block.statements[location.statement_index];
 931                     self.visit_statement(statement, location)
 932                 }
 933             }
 934         }
 935     }
 936 }
 937
 938 macro_rules! visit_place_fns {
 939     (mut) => {
 940         fn tcx<'a>(&'a self) -> TyCtxt<'tcx>;
 941
 942         fn super_place(
 943             &mut self,
 944             place: &mut Place<'tcx>,
 945             context: PlaceContext,
 946             location: Location,
 947         ) {
 948             self.visit_local(&mut place.local, context, location);
 949
 950             if let Some(new_projection) = self.process_projection(&place.projection, location) {
 951                 place.projection = self.tcx().intern_place_elems(&new_projection);
 952             }
 953         }
 954
 955         fn process_projection<'a>(
 956             &mut self,
 957             projection: &'a [PlaceElem<'tcx>],
 958             location: Location,
 959         ) -> Option<Vec<PlaceElem<'tcx>>> {
 960             let mut projection = Cow::Borrowed(projection);
 961
 962             for i in 0..projection.len() {
 963                 if let Some(&elem) = projection.get(i) {
 964                     if let Some(elem) = self.process_projection_elem(elem, location) {
 965                         // This converts the borrowed projection into `Cow::Owned(_)` and returns a
 966                         // clone of the projection so we can mutate and reintern later.
 967                         let vec = projection.to_mut();
 968                         vec[i] = elem;
 969                     }
 970                 }
 971             }
 972
 973             match projection {
 974                 Cow::Borrowed(_) => None,
 975                 Cow::Owned(vec) => Some(vec),
 976             }
 977         }
 978
 979         fn process_projection_elem(
 980             &mut self,
 981             elem: PlaceElem<'tcx>,
 982             location: Location,
 983         ) -> Option<PlaceElem<'tcx>> {
 984             match elem {
 985                 PlaceElem::Index(local) => {
 986                     let mut new_local = local;
 987                     self.visit_local(
 988                         &mut new_local,
 989                         PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy),
 990                         location,
 991                     );
 992
 993                     if new_local == local { None } else { Some(PlaceElem::Index(new_local)) }
 994                 }
 995                 PlaceElem::Field(field, ty) => {
 996                     let mut new_ty = ty;
 997                     self.visit_ty(&mut new_ty, TyContext::Location(location));
 998                     if ty != new_ty { Some(PlaceElem::Field(field, new_ty)) } else { None }
 999                 }
1000                 PlaceElem::Deref
1001                 | PlaceElem::ConstantIndex { .. }
1002                 | PlaceElem::Subslice { .. }
1003                 | PlaceElem::Downcast(..) => None,
1004             }
1005         }
1006     };
1007
1008     () => {
1009         fn visit_projection(
1010             &mut self,
1011             place_ref: PlaceRef<'tcx>,
1012             context: PlaceContext,
1013             location: Location,
1014         ) {
1015             self.super_projection(place_ref, context, location);
1016         }
1017
1018         fn visit_projection_elem(
1019             &mut self,
1020             local: Local,
1021             proj_base: &[PlaceElem<'tcx>],
1022             elem: PlaceElem<'tcx>,
1023             context: PlaceContext,
1024             location: Location,
1025         ) {
1026             self.super_projection_elem(local, proj_base, elem, context, location);
1027         }
1028
1029         fn super_place(&mut self, place: &Place<'tcx>, context: PlaceContext, location: Location) {
1030             let mut context = context;
1031
1032             if !place.projection.is_empty() {
1033                 if context.is_use() {
1034                     // ^ Only change the context if it is a real use, not a "use" in debuginfo.
1035                     context = if context.is_mutating_use() {
1036                         PlaceContext::MutatingUse(MutatingUseContext::Projection)
1037                     } else {
1038                         PlaceContext::NonMutatingUse(NonMutatingUseContext::Projection)
1039                     };
1040                 }
1041             }
1042
1043             self.visit_local(&place.local, context, location);
1044
1045             self.visit_projection(place.as_ref(), context, location);
1046         }
1047
1048         fn super_projection(
1049             &mut self,
1050             place_ref: PlaceRef<'tcx>,
1051             context: PlaceContext,
1052             location: Location,
1053         ) {
1054             // FIXME: Use PlaceRef::iter_projections, once that exists.
1055             let mut cursor = place_ref.projection;
1056             while let &[ref proj_base @ .., elem] = cursor {
1057                 cursor = proj_base;
1058                 self.visit_projection_elem(place_ref.local, cursor, elem, context, location);
1059             }
1060         }
1061
1062         fn super_projection_elem(
1063             &mut self,
1064             _local: Local,
1065             _proj_base: &[PlaceElem<'tcx>],
1066             elem: PlaceElem<'tcx>,
1067             _context: PlaceContext,
1068             location: Location,
1069         ) {
1070             match elem {
1071                 ProjectionElem::Field(_field, ty) => {
1072                     self.visit_ty(ty, TyContext::Location(location));
1073                 }
1074                 ProjectionElem::Index(local) => {
1075                     self.visit_local(
1076                         &local,
1077                         PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy),
1078                         location,
1079                     );
1080                 }
1081                 ProjectionElem::Deref
1082                 | ProjectionElem::Subslice { from: _, to: _, from_end: _ }
1083                 | ProjectionElem::ConstantIndex { offset: _, min_length: _, from_end: _ }
1084                 | ProjectionElem::Downcast(_, _) => {}
1085             }
1086         }
1087     };
1088 }
1089
1090 make_mir_visitor!(Visitor,);
1091 make_mir_visitor!(MutVisitor, mut);
1092
1093 pub trait MirVisitable<'tcx> {
1094     fn apply(&self, location: Location, visitor: &mut dyn Visitor<'tcx>);
1095 }
1096
1097 impl<'tcx> MirVisitable<'tcx> for Statement<'tcx> {
1098     fn apply(&self, location: Location, visitor: &mut dyn Visitor<'tcx>) {
1099         visitor.visit_statement(self, location)
1100     }
1101 }
1102
1103 impl<'tcx> MirVisitable<'tcx> for Terminator<'tcx> {
1104     fn apply(&self, location: Location, visitor: &mut dyn Visitor<'tcx>) {
1105         visitor.visit_terminator(self, location)
1106     }
1107 }
1108
1109 impl<'tcx> MirVisitable<'tcx> for Option<Terminator<'tcx>> {
1110     fn apply(&self, location: Location, visitor: &mut dyn Visitor<'tcx>) {
1111         visitor.visit_terminator(self.as_ref().unwrap(), location)
1112     }
1113 }
1114
1115 /// Extra information passed to `visit_ty` and friends to give context
1116 /// about where the type etc appears.
1117 #[derive(Debug)]
1118 pub enum TyContext {
1119     LocalDecl {
1120         /// The index of the local variable we are visiting.
1121         local: Local,
1122
1123         /// The source location where this local variable was declared.
1124         source_info: SourceInfo,
1125     },
1126
1127     /// The inferred type of a user type annotation.
1128     UserTy(Span),
1129
1130     /// The return type of the function.
1131     ReturnTy(SourceInfo),
1132
1133     YieldTy(SourceInfo),
1134
1135     /// A type found at some location.
1136     Location(Location),
1137 }
1138
1139 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
1140 pub enum NonMutatingUseContext {
1141     /// Being inspected in some way, like loading a len.
1142     Inspect,
1143     /// Consumed as part of an operand.
1144     Copy,
1145     /// Consumed as part of an operand.
1146     Move,
1147     /// Shared borrow.
1148     SharedBorrow,
1149     /// Shallow borrow.
1150     ShallowBorrow,
1151     /// Unique borrow.
1152     UniqueBorrow,
1153     /// AddressOf for *const pointer.
1154     AddressOf,
1155     /// Used as base for another place, e.g., `x` in `x.y`. Will not mutate the place.
1156     /// For example, the projection `x.y` is not marked as a mutation in these cases:
1157     ///
1158     ///     z = x.y;
1159     ///     f(&x.y);
1160     ///
1161     Projection,
1162 }
1163
1164 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
1165 pub enum MutatingUseContext {
1166     /// Appears as LHS of an assignment.
1167     Store,
1168     /// Output operand of an inline assembly block.
1169     AsmOutput,
1170     /// Destination of a call.
1171     Call,
1172     /// Destination of a yield.
1173     Yield,
1174     /// Being dropped.
1175     Drop,
1176     /// Mutable borrow.
1177     Borrow,
1178     /// AddressOf for *mut pointer.
1179     AddressOf,
1180     /// Used as base for another place, e.g., `x` in `x.y`. Could potentially mutate the place.
1181     /// For example, the projection `x.y` is marked as a mutation in these cases:
1182     ///
1183     ///     x.y = ...;
1184     ///     f(&mut x.y);
1185     ///
1186     Projection,
1187     /// Retagging, a "Stacked Borrows" shadow state operation
1188     Retag,
1189 }
1190
1191 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
1192 pub enum NonUseContext {
1193     /// Starting a storage live range.
1194     StorageLive,
1195     /// Ending a storage live range.
1196     StorageDead,
1197     /// User type annotation assertions for NLL.
1198     AscribeUserTy,
1199     /// The data of a user variable, for debug info.
1200     VarDebugInfo,
1201 }
1202
1203 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
1204 pub enum PlaceContext {
1205     NonMutatingUse(NonMutatingUseContext),
1206     MutatingUse(MutatingUseContext),
1207     NonUse(NonUseContext),
1208 }
1209
1210 impl PlaceContext {
1211     /// Returns `true` if this place context represents a drop.
1212     #[inline]
1213     pub fn is_drop(&self) -> bool {
1214         matches!(self, PlaceContext::MutatingUse(MutatingUseContext::Drop))
1215     }
1216
1217     /// Returns `true` if this place context represents a borrow.
1218     pub fn is_borrow(&self) -> bool {
1219         matches!(
1220             self,
1221             PlaceContext::NonMutatingUse(
1222                 NonMutatingUseContext::SharedBorrow
1223                     | NonMutatingUseContext::ShallowBorrow
1224                     | NonMutatingUseContext::UniqueBorrow
1225             ) | PlaceContext::MutatingUse(MutatingUseContext::Borrow)
1226         )
1227     }
1228
1229     /// Returns `true` if this place context represents a storage live or storage dead marker.
1230     #[inline]
1231     pub fn is_storage_marker(&self) -> bool {
1232         matches!(
1233             self,
1234             PlaceContext::NonUse(NonUseContext::StorageLive | NonUseContext::StorageDead)
1235         )
1236     }
1237
1238     /// Returns `true` if this place context represents a use that potentially changes the value.
1239     #[inline]
1240     pub fn is_mutating_use(&self) -> bool {
1241         matches!(self, PlaceContext::MutatingUse(..))
1242     }
1243
1244     /// Returns `true` if this place context represents a use.
1245     #[inline]
1246     pub fn is_use(&self) -> bool {
1247         !matches!(self, PlaceContext::NonUse(..))
1248     }
1249
1250     /// Returns `true` if this place context represents an assignment statement.
1251     pub fn is_place_assignment(&self) -> bool {
1252         matches!(
1253             self,
1254             PlaceContext::MutatingUse(
1255                 MutatingUseContext::Store
1256                     | MutatingUseContext::Call
1257                     | MutatingUseContext::AsmOutput,
1258             )
1259         )
1260     }
1261 }