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             // The macro results in a false positive of sorts, where &mut Span
 166             // is fine, but &Span is not; just allow the lint.
 167             #[allow(rustc::pass_by_value)]
 168             fn visit_span(&mut self,
 169                           span: & $($mutability)? Span) {
 170                 self.super_span(span);
 171             }
 172
 173             fn visit_source_info(&mut self,
 174                                  source_info: & $($mutability)? SourceInfo) {
 175                 self.super_source_info(source_info);
 176             }
 177
 178             fn visit_ty(&mut self,
 179                         ty: $(& $mutability)? Ty<'tcx>,
 180                         _: TyContext) {
 181                 self.super_ty(ty);
 182             }
 183
 184             fn visit_user_type_projection(
 185                 &mut self,
 186                 ty: & $($mutability)? UserTypeProjection,
 187             ) {
 188                 self.super_user_type_projection(ty);
 189             }
 190
 191             fn visit_user_type_annotation(
 192                 &mut self,
 193                 index: UserTypeAnnotationIndex,
 194                 ty: & $($mutability)? CanonicalUserTypeAnnotation<'tcx>,
 195             ) {
 196                 self.super_user_type_annotation(index, ty);
 197             }
 198
 199             fn visit_region(&mut self,
 200                             region: $(& $mutability)? ty::Region<'tcx>,
 201                             _: Location) {
 202                 self.super_region(region);
 203             }
 204
 205             fn visit_const(&mut self,
 206                            constant: $(& $mutability)? ty::Const<'tcx>,
 207                            _: Location) {
 208                 self.super_const(constant);
 209             }
 210
 211             fn visit_substs(&mut self,
 212                             substs: & $($mutability)? SubstsRef<'tcx>,
 213                             _: Location) {
 214                 self.super_substs(substs);
 215             }
 216
 217             fn visit_local_decl(&mut self,
 218                                 local: Local,
 219                                 local_decl: & $($mutability)? LocalDecl<'tcx>) {
 220                 self.super_local_decl(local, local_decl);
 221             }
 222
 223             fn visit_var_debug_info(&mut self,
 224                                     var_debug_info: & $($mutability)* VarDebugInfo<'tcx>) {
 225                 self.super_var_debug_info(var_debug_info);
 226             }
 227
 228             #[allow(rustc::pass_by_value)]
 229             fn visit_local(&mut self,
 230                             _local: & $($mutability)? Local,
 231                             _context: PlaceContext,
 232                             _location: Location) {
 233             }
 234
 235             #[allow(rustc::pass_by_value)]
 236             fn visit_source_scope(&mut self,
 237                                       scope: & $($mutability)? SourceScope) {
 238                 self.super_source_scope(scope);
 239             }
 240
 241             // The `super_xxx` methods comprise the default behavior and are
 242             // not meant to be overridden.
 243
 244             fn super_body(
 245                 &mut self,
 246                 body: &$($mutability)? Body<'tcx>,
 247             ) {
 248                 let span = body.span;
 249                 if let Some(gen) = &$($mutability)? body.generator {
 250                     if let Some(yield_ty) = $(& $mutability)? gen.yield_ty {
 251                         self.visit_ty(
 252                             yield_ty,
 253                             TyContext::YieldTy(SourceInfo::outermost(span))
 254                         );
 255                     }
 256                 }
 257
 258                 // for best performance, we want to use an iterator rather
 259                 // than a for-loop, to avoid calling `body::Body::invalidate` for
 260                 // each basic block.
 261                 macro_rules! basic_blocks {
 262                     (mut) => (body.basic_blocks_mut().iter_enumerated_mut());
 263                     () => (body.basic_blocks().iter_enumerated());
 264                 }
 265                 for (bb, data) in basic_blocks!($($mutability)?) {
 266                     self.visit_basic_block_data(bb, data);
 267                 }
 268
 269                 for scope in &$($mutability)? body.source_scopes {
 270                     self.visit_source_scope_data(scope);
 271                 }
 272
 273                 self.visit_ty(
 274                     $(& $mutability)? body.return_ty(),
 275                     TyContext::ReturnTy(SourceInfo::outermost(body.span))
 276                 );
 277
 278                 for local in body.local_decls.indices() {
 279                     self.visit_local_decl(local, & $($mutability)? body.local_decls[local]);
 280                 }
 281
 282                 macro_rules! type_annotations {
 283                     (mut) => (body.user_type_annotations.iter_enumerated_mut());
 284                     () => (body.user_type_annotations.iter_enumerated());
 285                 }
 286
 287                 for (index, annotation) in type_annotations!($($mutability)?) {
 288                     self.visit_user_type_annotation(
 289                         index, annotation
 290                     );
 291                 }
 292
 293                 for var_debug_info in &$($mutability)? body.var_debug_info {
 294                     self.visit_var_debug_info(var_debug_info);
 295                 }
 296
 297                 self.visit_span(&$($mutability)? body.span);
 298
 299                 for const_ in &$($mutability)? body.required_consts {
 300                     let location = START_BLOCK.start_location();
 301                     self.visit_constant(const_, location);
 302                 }
 303             }
 304
 305             fn super_basic_block_data(&mut self,
 306                                       block: BasicBlock,
 307                                       data: & $($mutability)? BasicBlockData<'tcx>) {
 308                 let BasicBlockData {
 309                     statements,
 310                     terminator,
 311                     is_cleanup: _
 312                 } = data;
 313
 314                 let mut index = 0;
 315                 for statement in statements {
 316                     let location = Location { block, statement_index: index };
 317                     self.visit_statement(statement, location);
 318                     index += 1;
 319                 }
 320
 321                 if let Some(terminator) = terminator {
 322                     let location = Location { block, statement_index: index };
 323                     self.visit_terminator(terminator, location);
 324                 }
 325             }
 326
 327             fn super_source_scope_data(
 328                 &mut self,
 329                 scope_data: & $($mutability)? SourceScopeData<'tcx>,
 330             ) {
 331                 let SourceScopeData {
 332                     span,
 333                     parent_scope,
 334                     inlined,
 335                     inlined_parent_scope,
 336                     local_data: _,
 337                 } = scope_data;
 338
 339                 self.visit_span(span);
 340                 if let Some(parent_scope) = parent_scope {
 341                     self.visit_source_scope(parent_scope);
 342                 }
 343                 if let Some((callee, callsite_span)) = inlined {
 344                     let location = START_BLOCK.start_location();
 345
 346                     self.visit_span(callsite_span);
 347
 348                     let ty::Instance { def: callee_def, substs: callee_substs } = callee;
 349                     match callee_def {
 350                         ty::InstanceDef::Item(_def_id) => {}
 351
 352                         ty::InstanceDef::Intrinsic(_def_id) |
 353                         ty::InstanceDef::VtableShim(_def_id) |
 354                         ty::InstanceDef::ReifyShim(_def_id) |
 355                         ty::InstanceDef::Virtual(_def_id, _) |
 356                         ty::InstanceDef::ClosureOnceShim { call_once: _def_id, track_caller: _ } |
 357                         ty::InstanceDef::DropGlue(_def_id, None) => {}
 358
 359                         ty::InstanceDef::FnPtrShim(_def_id, ty) |
 360                         ty::InstanceDef::DropGlue(_def_id, Some(ty)) |
 361                         ty::InstanceDef::CloneShim(_def_id, ty) => {
 362                             // FIXME(eddyb) use a better `TyContext` here.
 363                             self.visit_ty($(& $mutability)? *ty, TyContext::Location(location));
 364                         }
 365                     }
 366                     self.visit_substs(callee_substs, location);
 367                 }
 368                 if let Some(inlined_parent_scope) = inlined_parent_scope {
 369                     self.visit_source_scope(inlined_parent_scope);
 370                 }
 371             }
 372
 373             fn super_statement(&mut self,
 374                                statement: & $($mutability)? Statement<'tcx>,
 375                                location: Location) {
 376                 let Statement {
 377                     source_info,
 378                     kind,
 379                 } = statement;
 380
 381                 self.visit_source_info(source_info);
 382                 match kind {
 383                     StatementKind::Assign(
 384                         box(ref $($mutability)? place, ref $($mutability)? rvalue)
 385                     ) => {
 386                         self.visit_assign(place, rvalue, location);
 387                     }
 388                     StatementKind::FakeRead(box (_, place)) => {
 389                         self.visit_place(
 390                             place,
 391                             PlaceContext::NonMutatingUse(NonMutatingUseContext::Inspect),
 392                             location
 393                         );
 394                     }
 395                     StatementKind::SetDiscriminant { place, .. } => {
 396                         self.visit_place(
 397                             place,
 398                             PlaceContext::MutatingUse(MutatingUseContext::Store),
 399                             location
 400                         );
 401                     }
 402                     StatementKind::StorageLive(local) => {
 403                         self.visit_local(
 404                             local,
 405                             PlaceContext::NonUse(NonUseContext::StorageLive),
 406                             location
 407                         );
 408                     }
 409                     StatementKind::StorageDead(local) => {
 410                         self.visit_local(
 411                             local,
 412                             PlaceContext::NonUse(NonUseContext::StorageDead),
 413                             location
 414                         );
 415                     }
 416                     StatementKind::Retag(kind, place) => {
 417                         self.visit_retag(kind, place, location);
 418                     }
 419                     StatementKind::AscribeUserType(
 420                         box(ref $($mutability)? place, ref $($mutability)? user_ty),
 421                         variance
 422                     ) => {
 423                         self.visit_ascribe_user_ty(place, variance, user_ty, location);
 424                     }
 425                     StatementKind::Coverage(coverage) => {
 426                         self.visit_coverage(
 427                             coverage,
 428                             location
 429                         )
 430                     }
 431                     StatementKind::CopyNonOverlapping(box crate::mir::CopyNonOverlapping{
 432                       ref $($mutability)? src,
 433                       ref $($mutability)? dst,
 434                       ref $($mutability)? count,
 435                     }) => {
 436                       self.visit_operand(src, location);
 437                       self.visit_operand(dst, location);
 438                       self.visit_operand(count, location)
 439                     }
 440                     StatementKind::Nop => {}
 441                 }
 442             }
 443
 444             fn super_assign(&mut self,
 445                             place: &$($mutability)? Place<'tcx>,
 446                             rvalue: &$($mutability)? Rvalue<'tcx>,
 447                             location: Location) {
 448                 self.visit_place(
 449                     place,
 450                     PlaceContext::MutatingUse(MutatingUseContext::Store),
 451                     location
 452                 );
 453                 self.visit_rvalue(rvalue, location);
 454             }
 455
 456             fn super_terminator(&mut self,
 457                                 terminator: &$($mutability)? Terminator<'tcx>,
 458                                 location: Location) {
 459                 let Terminator { source_info, kind } = terminator;
 460
 461                 self.visit_source_info(source_info);
 462                 match kind {
 463                     TerminatorKind::Goto { .. } |
 464                     TerminatorKind::Resume |
 465                     TerminatorKind::Abort |
 466                     TerminatorKind::GeneratorDrop |
 467                     TerminatorKind::Unreachable |
 468                     TerminatorKind::FalseEdge { .. } |
 469                     TerminatorKind::FalseUnwind { .. } => {
 470                     }
 471
 472                     TerminatorKind::Return => {
 473                         // `return` logically moves from the return place `_0`. Note that the place
 474                         // cannot be changed by any visitor, though.
 475                         let $($mutability)? local = RETURN_PLACE;
 476                         self.visit_local(
 477                             & $($mutability)? local,
 478                             PlaceContext::NonMutatingUse(NonMutatingUseContext::Move),
 479                             location,
 480                         );
 481
 482                         assert_eq!(
 483                             local,
 484                             RETURN_PLACE,
 485                             "`MutVisitor` tried to mutate return place of `return` terminator"
 486                         );
 487                     }
 488
 489                     TerminatorKind::SwitchInt {
 490                         discr,
 491                         switch_ty,
 492                         targets: _
 493                     } => {
 494                         self.visit_operand(discr, location);
 495                         self.visit_ty($(& $mutability)? *switch_ty, TyContext::Location(location));
 496                     }
 497
 498                     TerminatorKind::Drop {
 499                         place,
 500                         target: _,
 501                         unwind: _,
 502                     } => {
 503                         self.visit_place(
 504                             place,
 505                             PlaceContext::MutatingUse(MutatingUseContext::Drop),
 506                             location
 507                         );
 508                     }
 509
 510                     TerminatorKind::DropAndReplace {
 511                         place,
 512                         value,
 513                         target: _,
 514                         unwind: _,
 515                     } => {
 516                         self.visit_place(
 517                             place,
 518                             PlaceContext::MutatingUse(MutatingUseContext::Drop),
 519                             location
 520                         );
 521                         self.visit_operand(value, location);
 522                     }
 523
 524                     TerminatorKind::Call {
 525                         func,
 526                         args,
 527                         destination,
 528                         cleanup: _,
 529                         from_hir_call: _,
 530                         fn_span: _
 531                     } => {
 532                         self.visit_operand(func, location);
 533                         for arg in args {
 534                             self.visit_operand(arg, location);
 535                         }
 536                         if let Some((destination, _)) = destination {
 537                             self.visit_place(
 538                                 destination,
 539                                 PlaceContext::MutatingUse(MutatingUseContext::Call),
 540                                 location
 541                             );
 542                         }
 543                     }
 544
 545                     TerminatorKind::Assert {
 546                         cond,
 547                         expected: _,
 548                         msg,
 549                         target: _,
 550                         cleanup: _,
 551                     } => {
 552                         self.visit_operand(cond, location);
 553                         self.visit_assert_message(msg, location);
 554                     }
 555
 556                     TerminatorKind::Yield {
 557                         value,
 558                         resume: _,
 559                         resume_arg,
 560                         drop: _,
 561                     } => {
 562                         self.visit_operand(value, location);
 563                         self.visit_place(
 564                             resume_arg,
 565                             PlaceContext::MutatingUse(MutatingUseContext::Yield),
 566                             location,
 567                         );
 568                     }
 569
 570                     TerminatorKind::InlineAsm {
 571                         template: _,
 572                         operands,
 573                         options: _,
 574                         line_spans: _,
 575                         destination: _,
 576                         cleanup: _,
 577                     } => {
 578                         for op in operands {
 579                             match op {
 580                                 InlineAsmOperand::In { value, .. } => {
 581                                     self.visit_operand(value, location);
 582                                 }
 583                                 InlineAsmOperand::Out { place: Some(place), .. } => {
 584                                     self.visit_place(
 585                                         place,
 586                                         PlaceContext::MutatingUse(MutatingUseContext::AsmOutput),
 587                                         location,
 588                                     );
 589                                 }
 590                                 InlineAsmOperand::InOut { in_value, out_place, .. } => {
 591                                     self.visit_operand(in_value, location);
 592                                     if let Some(out_place) = out_place {
 593                                         self.visit_place(
 594                                             out_place,
 595                                             PlaceContext::MutatingUse(MutatingUseContext::AsmOutput),
 596                                             location,
 597                                         );
 598                                     }
 599                                 }
 600                                 InlineAsmOperand::Const { value }
 601                                 | InlineAsmOperand::SymFn { value } => {
 602                                     self.visit_constant(value, location);
 603                                 }
 604                                 InlineAsmOperand::Out { place: None, .. }
 605                                 | InlineAsmOperand::SymStatic { def_id: _ } => {}
 606                             }
 607                         }
 608                     }
 609                 }
 610             }
 611
 612             fn super_assert_message(&mut self,
 613                                     msg: & $($mutability)? AssertMessage<'tcx>,
 614                                     location: Location) {
 615                 use crate::mir::AssertKind::*;
 616                 match msg {
 617                     BoundsCheck { len, index } => {
 618                         self.visit_operand(len, location);
 619                         self.visit_operand(index, location);
 620                     }
 621                     Overflow(_, l, r) => {
 622                         self.visit_operand(l, location);
 623                         self.visit_operand(r, location);
 624                     }
 625                     OverflowNeg(op) | DivisionByZero(op) | RemainderByZero(op) => {
 626                         self.visit_operand(op, location);
 627                     }
 628                     ResumedAfterReturn(_) | ResumedAfterPanic(_) => {
 629                         // Nothing to visit
 630                     }
 631                 }
 632             }
 633
 634             fn super_rvalue(&mut self,
 635                             rvalue: & $($mutability)? Rvalue<'tcx>,
 636                             location: Location) {
 637                 match rvalue {
 638                     Rvalue::Use(operand) => {
 639                         self.visit_operand(operand, location);
 640                     }
 641
 642                     Rvalue::Repeat(value, _) => {
 643                         self.visit_operand(value, location);
 644                     }
 645
 646                     Rvalue::ThreadLocalRef(_) => {}
 647
 648                     Rvalue::Ref(r, bk, path) => {
 649                         self.visit_region($(& $mutability)? *r, location);
 650                         let ctx = match bk {
 651                             BorrowKind::Shared => PlaceContext::NonMutatingUse(
 652                                 NonMutatingUseContext::SharedBorrow
 653                             ),
 654                             BorrowKind::Shallow => PlaceContext::NonMutatingUse(
 655                                 NonMutatingUseContext::ShallowBorrow
 656                             ),
 657                             BorrowKind::Unique => PlaceContext::NonMutatingUse(
 658                                 NonMutatingUseContext::UniqueBorrow
 659                             ),
 660                             BorrowKind::Mut { .. } =>
 661                                 PlaceContext::MutatingUse(MutatingUseContext::Borrow),
 662                         };
 663                         self.visit_place(path, ctx, location);
 664                     }
 665
 666                     Rvalue::AddressOf(m, path) => {
 667                         let ctx = match m {
 668                             Mutability::Mut => PlaceContext::MutatingUse(
 669                                 MutatingUseContext::AddressOf
 670                             ),
 671                             Mutability::Not => PlaceContext::NonMutatingUse(
 672                                 NonMutatingUseContext::AddressOf
 673                             ),
 674                         };
 675                         self.visit_place(path, ctx, location);
 676                     }
 677
 678                     Rvalue::Len(path) => {
 679                         self.visit_place(
 680                             path,
 681                             PlaceContext::NonMutatingUse(NonMutatingUseContext::Inspect),
 682                             location
 683                         );
 684                     }
 685
 686                     Rvalue::Cast(_cast_kind, operand, ty) => {
 687                         self.visit_operand(operand, location);
 688                         self.visit_ty($(& $mutability)? *ty, TyContext::Location(location));
 689                     }
 690
 691                     Rvalue::BinaryOp(_bin_op, box(lhs, rhs))
 692                     | Rvalue::CheckedBinaryOp(_bin_op, box(lhs, rhs)) => {
 693                         self.visit_operand(lhs, location);
 694                         self.visit_operand(rhs, location);
 695                     }
 696
 697                     Rvalue::UnaryOp(_un_op, op) => {
 698                         self.visit_operand(op, location);
 699                     }
 700
 701                     Rvalue::Discriminant(place) => {
 702                         self.visit_place(
 703                             place,
 704                             PlaceContext::NonMutatingUse(NonMutatingUseContext::Inspect),
 705                             location
 706                         );
 707                     }
 708
 709                     Rvalue::NullaryOp(_op, ty) => {
 710                         self.visit_ty($(& $mutability)? *ty, TyContext::Location(location));
 711                     }
 712
 713                     Rvalue::Aggregate(kind, operands) => {
 714                         let kind = &$($mutability)? **kind;
 715                         match kind {
 716                             AggregateKind::Array(ty) => {
 717                                 self.visit_ty($(& $mutability)? *ty, TyContext::Location(location));
 718                             }
 719                             AggregateKind::Tuple => {
 720                             }
 721                             AggregateKind::Adt(
 722                                 _adt_def,
 723                                 _variant_index,
 724                                 substs,
 725                                 _user_substs,
 726                                 _active_field_index
 727                             ) => {
 728                                 self.visit_substs(substs, location);
 729                             }
 730                             AggregateKind::Closure(
 731                                 _,
 732                                 closure_substs
 733                             ) => {
 734                                 self.visit_substs(closure_substs, location);
 735                             }
 736                             AggregateKind::Generator(
 737                                 _,
 738                                 generator_substs,
 739                                 _movability,
 740                             ) => {
 741                                 self.visit_substs(generator_substs, location);
 742                             }
 743                         }
 744
 745                         for operand in operands {
 746                             self.visit_operand(operand, location);
 747                         }
 748                     }
 749
 750                     Rvalue::ShallowInitBox(operand, ty) => {
 751                         self.visit_operand(operand, location);
 752                         self.visit_ty($(& $mutability)? *ty, TyContext::Location(location));
 753                     }
 754                 }
 755             }
 756
 757             fn super_operand(&mut self,
 758                              operand: & $($mutability)? Operand<'tcx>,
 759                              location: Location) {
 760                 match operand {
 761                     Operand::Copy(place) => {
 762                         self.visit_place(
 763                             place,
 764                             PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy),
 765                             location
 766                         );
 767                     }
 768                     Operand::Move(place) => {
 769                         self.visit_place(
 770                             place,
 771                             PlaceContext::NonMutatingUse(NonMutatingUseContext::Move),
 772                             location
 773                         );
 774                     }
 775                     Operand::Constant(constant) => {
 776                         self.visit_constant(constant, location);
 777                     }
 778                 }
 779             }
 780
 781             fn super_ascribe_user_ty(&mut self,
 782                                      place: & $($mutability)? Place<'tcx>,
 783                                      _variance: & $($mutability)? ty::Variance,
 784                                      user_ty: & $($mutability)? UserTypeProjection,
 785                                      location: Location) {
 786                 self.visit_place(
 787                     place,
 788                     PlaceContext::NonUse(NonUseContext::AscribeUserTy),
 789                     location
 790                 );
 791                 self.visit_user_type_projection(user_ty);
 792             }
 793
 794             fn super_coverage(&mut self,
 795                               _coverage: & $($mutability)? Coverage,
 796                               _location: Location) {
 797             }
 798
 799             fn super_retag(&mut self,
 800                            _kind: & $($mutability)? RetagKind,
 801                            place: & $($mutability)? Place<'tcx>,
 802                            location: Location) {
 803                 self.visit_place(
 804                     place,
 805                     PlaceContext::MutatingUse(MutatingUseContext::Retag),
 806                     location,
 807                 );
 808             }
 809
 810             fn super_local_decl(&mut self,
 811                                 local: Local,
 812                                 local_decl: & $($mutability)? LocalDecl<'tcx>) {
 813                 let LocalDecl {
 814                     mutability: _,
 815                     ty,
 816                     user_ty,
 817                     source_info,
 818                     internal: _,
 819                     local_info: _,
 820                     is_block_tail: _,
 821                 } = local_decl;
 822
 823                 self.visit_ty($(& $mutability)? *ty, TyContext::LocalDecl {
 824                     local,
 825                     source_info: *source_info,
 826                 });
 827                 if let Some(user_ty) = user_ty {
 828                     for (user_ty, _) in & $($mutability)? user_ty.contents {
 829                         self.visit_user_type_projection(user_ty);
 830                     }
 831                 }
 832                 self.visit_source_info(source_info);
 833             }
 834
 835             fn super_var_debug_info(&mut self,
 836                                     var_debug_info: & $($mutability)? VarDebugInfo<'tcx>) {
 837                 let VarDebugInfo {
 838                     name: _,
 839                     source_info,
 840                     value,
 841                 } = var_debug_info;
 842
 843                 self.visit_source_info(source_info);
 844                 let location = START_BLOCK.start_location();
 845                 match value {
 846                     VarDebugInfoContents::Const(c) => self.visit_constant(c, location),
 847                     VarDebugInfoContents::Place(place) =>
 848                         self.visit_place(
 849                             place,
 850                             PlaceContext::NonUse(NonUseContext::VarDebugInfo),
 851                             location
 852                         ),
 853                 }
 854             }
 855
 856             #[allow(rustc::pass_by_value)]
 857             fn super_source_scope(&mut self,
 858                                       _scope: & $($mutability)? SourceScope) {
 859             }
 860
 861             fn super_constant(&mut self,
 862                               constant: & $($mutability)? Constant<'tcx>,
 863                               location: Location) {
 864                 let Constant {
 865                     span,
 866                     user_ty,
 867                     literal,
 868                 } = constant;
 869
 870                 self.visit_span(span);
 871                 drop(user_ty); // no visit method for this
 872                 match literal {
 873                     ConstantKind::Ty(ct) => self.visit_const($(& $mutability)? *ct, location),
 874                     ConstantKind::Val(_, ty) => self.visit_ty($(& $mutability)? *ty, TyContext::Location(location)),
 875                 }
 876             }
 877
 878             // The macro results in a false positive of sorts, where &mut Span
 879             // is fine, but &Span is not; just allow the lint.
 880             #[allow(rustc::pass_by_value)]
 881             fn super_span(&mut self, _span: & $($mutability)? Span) {
 882             }
 883
 884             fn super_source_info(&mut self, source_info: & $($mutability)? SourceInfo) {
 885                 let SourceInfo {
 886                     span,
 887                     scope,
 888                 } = source_info;
 889
 890                 self.visit_span(span);
 891                 self.visit_source_scope(scope);
 892             }
 893
 894             fn super_user_type_projection(
 895                 &mut self,
 896                 _ty: & $($mutability)? UserTypeProjection,
 897             ) {
 898             }
 899
 900             fn super_user_type_annotation(
 901                 &mut self,
 902                 _index: UserTypeAnnotationIndex,
 903                 ty: & $($mutability)? CanonicalUserTypeAnnotation<'tcx>,
 904             ) {
 905                 self.visit_span(& $($mutability)? ty.span);
 906                 self.visit_ty($(& $mutability)? ty.inferred_ty, TyContext::UserTy(ty.span));
 907             }
 908
 909             fn super_ty(&mut self, _ty: $(& $mutability)? Ty<'tcx>) {
 910             }
 911
 912             fn super_region(&mut self, _region: $(& $mutability)? ty::Region<'tcx>) {
 913             }
 914
 915             fn super_const(&mut self, _const: $(& $mutability)? ty::Const<'tcx>) {
 916             }
 917
 918             fn super_substs(&mut self, _substs: & $($mutability)? SubstsRef<'tcx>) {
 919             }
 920
 921             // Convenience methods
 922
 923             fn visit_location(
 924                 &mut self,
 925                 body: &$($mutability)? Body<'tcx>,
 926                 location: Location
 927             ) {
 928                 macro_rules! basic_blocks {
 929                     (mut) => (body.basic_blocks_mut());
 930                     () => (body.basic_blocks());
 931                 }
 932                 let basic_block = & $($mutability)? basic_blocks!($($mutability)?)[location.block];
 933                 if basic_block.statements.len() == location.statement_index {
 934                     if let Some(ref $($mutability)? terminator) = basic_block.terminator {
 935                         self.visit_terminator(terminator, location)
 936                     }
 937                 } else {
 938                     let statement = & $($mutability)?
 939                         basic_block.statements[location.statement_index];
 940                     self.visit_statement(statement, location)
 941                 }
 942             }
 943         }
 944     }
 945 }
 946
 947 macro_rules! visit_place_fns {
 948     (mut) => {
 949         fn tcx<'a>(&'a self) -> TyCtxt<'tcx>;
 950
 951         fn super_place(
 952             &mut self,
 953             place: &mut Place<'tcx>,
 954             context: PlaceContext,
 955             location: Location,
 956         ) {
 957             self.visit_local(&mut place.local, context, location);
 958
 959             if let Some(new_projection) = self.process_projection(&place.projection, location) {
 960                 place.projection = self.tcx().intern_place_elems(&new_projection);
 961             }
 962         }
 963
 964         fn process_projection<'a>(
 965             &mut self,
 966             projection: &'a [PlaceElem<'tcx>],
 967             location: Location,
 968         ) -> Option<Vec<PlaceElem<'tcx>>> {
 969             let mut projection = Cow::Borrowed(projection);
 970
 971             for i in 0..projection.len() {
 972                 if let Some(&elem) = projection.get(i) {
 973                     if let Some(elem) = self.process_projection_elem(elem, location) {
 974                         // This converts the borrowed projection into `Cow::Owned(_)` and returns a
 975                         // clone of the projection so we can mutate and reintern later.
 976                         let vec = projection.to_mut();
 977                         vec[i] = elem;
 978                     }
 979                 }
 980             }
 981
 982             match projection {
 983                 Cow::Borrowed(_) => None,
 984                 Cow::Owned(vec) => Some(vec),
 985             }
 986         }
 987
 988         fn process_projection_elem(
 989             &mut self,
 990             elem: PlaceElem<'tcx>,
 991             location: Location,
 992         ) -> Option<PlaceElem<'tcx>> {
 993             match elem {
 994                 PlaceElem::Index(local) => {
 995                     let mut new_local = local;
 996                     self.visit_local(
 997                         &mut new_local,
 998                         PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy),
 999                         location,
1000                     );
1001
1002                     if new_local == local { None } else { Some(PlaceElem::Index(new_local)) }
1003                 }
1004                 PlaceElem::Field(field, ty) => {
1005                     let mut new_ty = ty;
1006                     self.visit_ty(&mut new_ty, TyContext::Location(location));
1007                     if ty != new_ty { Some(PlaceElem::Field(field, new_ty)) } else { None }
1008                 }
1009                 PlaceElem::Deref
1010                 | PlaceElem::ConstantIndex { .. }
1011                 | PlaceElem::Subslice { .. }
1012                 | PlaceElem::Downcast(..) => None,
1013             }
1014         }
1015     };
1016
1017     () => {
1018         fn visit_projection(
1019             &mut self,
1020             place_ref: PlaceRef<'tcx>,
1021             context: PlaceContext,
1022             location: Location,
1023         ) {
1024             self.super_projection(place_ref, context, location);
1025         }
1026
1027         fn visit_projection_elem(
1028             &mut self,
1029             local: Local,
1030             proj_base: &[PlaceElem<'tcx>],
1031             elem: PlaceElem<'tcx>,
1032             context: PlaceContext,
1033             location: Location,
1034         ) {
1035             self.super_projection_elem(local, proj_base, elem, context, location);
1036         }
1037
1038         fn super_place(&mut self, place: &Place<'tcx>, context: PlaceContext, location: Location) {
1039             let mut context = context;
1040
1041             if !place.projection.is_empty() {
1042                 if context.is_use() {
1043                     // ^ Only change the context if it is a real use, not a "use" in debuginfo.
1044                     context = if context.is_mutating_use() {
1045                         PlaceContext::MutatingUse(MutatingUseContext::Projection)
1046                     } else {
1047                         PlaceContext::NonMutatingUse(NonMutatingUseContext::Projection)
1048                     };
1049                 }
1050             }
1051
1052             self.visit_local(&place.local, context, location);
1053
1054             self.visit_projection(place.as_ref(), context, location);
1055         }
1056
1057         fn super_projection(
1058             &mut self,
1059             place_ref: PlaceRef<'tcx>,
1060             context: PlaceContext,
1061             location: Location,
1062         ) {
1063             // FIXME: Use PlaceRef::iter_projections, once that exists.
1064             let mut cursor = place_ref.projection;
1065             while let &[ref proj_base @ .., elem] = cursor {
1066                 cursor = proj_base;
1067                 self.visit_projection_elem(place_ref.local, cursor, elem, context, location);
1068             }
1069         }
1070
1071         fn super_projection_elem(
1072             &mut self,
1073             _local: Local,
1074             _proj_base: &[PlaceElem<'tcx>],
1075             elem: PlaceElem<'tcx>,
1076             _context: PlaceContext,
1077             location: Location,
1078         ) {
1079             match elem {
1080                 ProjectionElem::Field(_field, ty) => {
1081                     self.visit_ty(ty, TyContext::Location(location));
1082                 }
1083                 ProjectionElem::Index(local) => {
1084                     self.visit_local(
1085                         &local,
1086                         PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy),
1087                         location,
1088                     );
1089                 }
1090                 ProjectionElem::Deref
1091                 | ProjectionElem::Subslice { from: _, to: _, from_end: _ }
1092                 | ProjectionElem::ConstantIndex { offset: _, min_length: _, from_end: _ }
1093                 | ProjectionElem::Downcast(_, _) => {}
1094             }
1095         }
1096     };
1097 }
1098
1099 make_mir_visitor!(Visitor,);
1100 make_mir_visitor!(MutVisitor, mut);
1101
1102 pub trait MirVisitable<'tcx> {
1103     fn apply(&self, location: Location, visitor: &mut dyn Visitor<'tcx>);
1104 }
1105
1106 impl<'tcx> MirVisitable<'tcx> for Statement<'tcx> {
1107     fn apply(&self, location: Location, visitor: &mut dyn Visitor<'tcx>) {
1108         visitor.visit_statement(self, location)
1109     }
1110 }
1111
1112 impl<'tcx> MirVisitable<'tcx> for Terminator<'tcx> {
1113     fn apply(&self, location: Location, visitor: &mut dyn Visitor<'tcx>) {
1114         visitor.visit_terminator(self, location)
1115     }
1116 }
1117
1118 impl<'tcx> MirVisitable<'tcx> for Option<Terminator<'tcx>> {
1119     fn apply(&self, location: Location, visitor: &mut dyn Visitor<'tcx>) {
1120         visitor.visit_terminator(self.as_ref().unwrap(), location)
1121     }
1122 }
1123
1124 /// Extra information passed to `visit_ty` and friends to give context
1125 /// about where the type etc appears.
1126 #[derive(Debug)]
1127 pub enum TyContext {
1128     LocalDecl {
1129         /// The index of the local variable we are visiting.
1130         local: Local,
1131
1132         /// The source location where this local variable was declared.
1133         source_info: SourceInfo,
1134     },
1135
1136     /// The inferred type of a user type annotation.
1137     UserTy(Span),
1138
1139     /// The return type of the function.
1140     ReturnTy(SourceInfo),
1141
1142     YieldTy(SourceInfo),
1143
1144     /// A type found at some location.
1145     Location(Location),
1146 }
1147
1148 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
1149 pub enum NonMutatingUseContext {
1150     /// Being inspected in some way, like loading a len.
1151     Inspect,
1152     /// Consumed as part of an operand.
1153     Copy,
1154     /// Consumed as part of an operand.
1155     Move,
1156     /// Shared borrow.
1157     SharedBorrow,
1158     /// Shallow borrow.
1159     ShallowBorrow,
1160     /// Unique borrow.
1161     UniqueBorrow,
1162     /// AddressOf for *const pointer.
1163     AddressOf,
1164     /// Used as base for another place, e.g., `x` in `x.y`. Will not mutate the place.
1165     /// For example, the projection `x.y` is not marked as a mutation in these cases:
1166     ///
1167     ///     z = x.y;
1168     ///     f(&x.y);
1169     ///
1170     Projection,
1171 }
1172
1173 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
1174 pub enum MutatingUseContext {
1175     /// Appears as LHS of an assignment.
1176     Store,
1177     /// Output operand of an inline assembly block.
1178     AsmOutput,
1179     /// Destination of a call.
1180     Call,
1181     /// Destination of a yield.
1182     Yield,
1183     /// Being dropped.
1184     Drop,
1185     /// Mutable borrow.
1186     Borrow,
1187     /// AddressOf for *mut pointer.
1188     AddressOf,
1189     /// Used as base for another place, e.g., `x` in `x.y`. Could potentially mutate the place.
1190     /// For example, the projection `x.y` is marked as a mutation in these cases:
1191     ///
1192     ///     x.y = ...;
1193     ///     f(&mut x.y);
1194     ///
1195     Projection,
1196     /// Retagging, a "Stacked Borrows" shadow state operation
1197     Retag,
1198 }
1199
1200 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
1201 pub enum NonUseContext {
1202     /// Starting a storage live range.
1203     StorageLive,
1204     /// Ending a storage live range.
1205     StorageDead,
1206     /// User type annotation assertions for NLL.
1207     AscribeUserTy,
1208     /// The data of a user variable, for debug info.
1209     VarDebugInfo,
1210 }
1211
1212 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
1213 pub enum PlaceContext {
1214     NonMutatingUse(NonMutatingUseContext),
1215     MutatingUse(MutatingUseContext),
1216     NonUse(NonUseContext),
1217 }
1218
1219 impl PlaceContext {
1220     /// Returns `true` if this place context represents a drop.
1221     #[inline]
1222     pub fn is_drop(&self) -> bool {
1223         matches!(self, PlaceContext::MutatingUse(MutatingUseContext::Drop))
1224     }
1225
1226     /// Returns `true` if this place context represents a borrow.
1227     pub fn is_borrow(&self) -> bool {
1228         matches!(
1229             self,
1230             PlaceContext::NonMutatingUse(
1231                 NonMutatingUseContext::SharedBorrow
1232                     | NonMutatingUseContext::ShallowBorrow
1233                     | NonMutatingUseContext::UniqueBorrow
1234             ) | PlaceContext::MutatingUse(MutatingUseContext::Borrow)
1235         )
1236     }
1237
1238     /// Returns `true` if this place context represents a storage live or storage dead marker.
1239     #[inline]
1240     pub fn is_storage_marker(&self) -> bool {
1241         matches!(
1242             self,
1243             PlaceContext::NonUse(NonUseContext::StorageLive | NonUseContext::StorageDead)
1244         )
1245     }
1246
1247     /// Returns `true` if this place context represents a use that potentially changes the value.
1248     #[inline]
1249     pub fn is_mutating_use(&self) -> bool {
1250         matches!(self, PlaceContext::MutatingUse(..))
1251     }
1252
1253     /// Returns `true` if this place context represents a use.
1254     #[inline]
1255     pub fn is_use(&self) -> bool {
1256         !matches!(self, PlaceContext::NonUse(..))
1257     }
1258
1259     /// Returns `true` if this place context represents an assignment statement.
1260     pub fn is_place_assignment(&self) -> bool {
1261         matches!(
1262             self,
1263             PlaceContext::MutatingUse(
1264                 MutatingUseContext::Store
1265                     | MutatingUseContext::Call
1266                     | MutatingUseContext::AsmOutput,
1267             )
1268         )
1269     }
1270 }