src/librustc/mir/visit.rs

   1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use middle::const_val::ConstVal;
  12 use hir::def_id::DefId;
  13 use ty::subst::Substs;
  14 use ty::{ClosureSubsts, Region, Ty};
  15 use mir::*;
  16 use rustc_const_math::ConstUsize;
  17 use rustc_data_structures::indexed_vec::Idx;
  18 use syntax_pos::Span;
  19
  20 // # The MIR Visitor
  21 //
  22 // ## Overview
  23 //
  24 // There are two visitors, one for immutable and one for mutable references,
  25 // but both are generated by the following macro. The code is written according
  26 // to the following conventions:
  27 //
  28 // - introduce a `visit_foo` and a `super_foo` method for every MIR type
  29 // - `visit_foo`, by default, calls `super_foo`
  30 // - `super_foo`, by default, destructures the `foo` and calls `visit_foo`
  31 //
  32 // This allows you as a user to override `visit_foo` for types are
  33 // interested in, and invoke (within that method) call
  34 // `self.super_foo` to get the default behavior. Just as in an OO
  35 // language, you should never call `super` methods ordinarily except
  36 // in that circumstance.
  37 //
  38 // For the most part, we do not destructure things external to the
  39 // MIR, e.g. types, spans, etc, but simply visit them and stop. This
  40 // avoids duplication with other visitors like `TypeFoldable`.
  41 //
  42 // ## Updating
  43 //
  44 // The code is written in a very deliberate style intended to minimize
  45 // the chance of things being overlooked. You'll notice that we always
  46 // use pattern matching to reference fields and we ensure that all
  47 // matches are exhaustive.
  48 //
  49 // For example, the `super_basic_block_data` method begins like this:
  50 //
  51 // ```rust
  52 // fn super_basic_block_data(&mut self,
  53 //                           block: BasicBlock,
  54 //                           data: & $($mutability)* BasicBlockData<'tcx>) {
  55 //     let BasicBlockData {
  56 //         ref $($mutability)* statements,
  57 //         ref $($mutability)* terminator,
  58 //         is_cleanup: _
  59 //     } = *data;
  60 //
  61 //     for statement in statements {
  62 //         self.visit_statement(block, statement);
  63 //     }
  64 //
  65 //     ...
  66 // }
  67 // ```
  68 //
  69 // Here we used `let BasicBlockData { <fields> } = *data` deliberately,
  70 // rather than writing `data.statements` in the body. This is because if one
  71 // adds a new field to `BasicBlockData`, one will be forced to revise this code,
  72 // and hence one will (hopefully) invoke the correct visit methods (if any).
  73 //
  74 // For this to work, ALL MATCHES MUST BE EXHAUSTIVE IN FIELDS AND VARIANTS.
  75 // That means you never write `..` to skip over fields, nor do you write `_`
  76 // to skip over variants in a `match`.
  77 //
  78 // The only place that `_` is acceptable is to match a field (or
  79 // variant argument) that does not require visiting, as in
  80 // `is_cleanup` above.
  81
  82 macro_rules! make_mir_visitor {
  83     ($visitor_trait_name:ident, $($mutability:ident)*) => {
  84         pub trait $visitor_trait_name<'tcx> {
  85             // Override these, and call `self.super_xxx` to revert back to the
  86             // default behavior.
  87
  88             fn visit_mir(&mut self, mir: & $($mutability)* Mir<'tcx>) {
  89                 self.super_mir(mir);
  90             }
  91
  92             fn visit_basic_block_data(&mut self,
  93                                       block: BasicBlock,
  94                                       data: & $($mutability)* BasicBlockData<'tcx>) {
  95                 self.super_basic_block_data(block, data);
  96             }
  97
  98             fn visit_visibility_scope_data(&mut self,
  99                                            scope_data: & $($mutability)* VisibilityScopeData) {
 100                 self.super_visibility_scope_data(scope_data);
 101             }
 102
 103             fn visit_statement(&mut self,
 104                                block: BasicBlock,
 105                                statement: & $($mutability)* Statement<'tcx>,
 106                                location: Location) {
 107                 self.super_statement(block, statement, location);
 108             }
 109
 110             fn visit_assign(&mut self,
 111                             block: BasicBlock,
 112                             lvalue: & $($mutability)* Lvalue<'tcx>,
 113                             rvalue: & $($mutability)* Rvalue<'tcx>,
 114                             location: Location) {
 115                 self.super_assign(block, lvalue, rvalue, location);
 116             }
 117
 118             fn visit_terminator(&mut self,
 119                                 block: BasicBlock,
 120                                 terminator: & $($mutability)* Terminator<'tcx>,
 121                                 location: Location) {
 122                 self.super_terminator(block, terminator, location);
 123             }
 124
 125             fn visit_terminator_kind(&mut self,
 126                                      block: BasicBlock,
 127                                      kind: & $($mutability)* TerminatorKind<'tcx>,
 128                                      location: Location) {
 129                 self.super_terminator_kind(block, kind, location);
 130             }
 131
 132             fn visit_assert_message(&mut self,
 133                                     msg: & $($mutability)* AssertMessage<'tcx>,
 134                                     location: Location) {
 135                 self.super_assert_message(msg, location);
 136             }
 137
 138             fn visit_rvalue(&mut self,
 139                             rvalue: & $($mutability)* Rvalue<'tcx>,
 140                             location: Location) {
 141                 self.super_rvalue(rvalue, location);
 142             }
 143
 144             fn visit_operand(&mut self,
 145                              operand: & $($mutability)* Operand<'tcx>,
 146                              location: Location) {
 147                 self.super_operand(operand, location);
 148             }
 149
 150             fn visit_lvalue(&mut self,
 151                             lvalue: & $($mutability)* Lvalue<'tcx>,
 152                             context: LvalueContext<'tcx>,
 153                             location: Location) {
 154                 self.super_lvalue(lvalue, context, location);
 155             }
 156
 157             fn visit_static(&mut self,
 158                             static_: & $($mutability)* Static<'tcx>,
 159                             context: LvalueContext<'tcx>,
 160                             location: Location) {
 161                 self.super_static(static_, context, location);
 162             }
 163
 164             fn visit_projection(&mut self,
 165                                 lvalue: & $($mutability)* LvalueProjection<'tcx>,
 166                                 context: LvalueContext<'tcx>,
 167                                 location: Location) {
 168                 self.super_projection(lvalue, context, location);
 169             }
 170
 171             fn visit_projection_elem(&mut self,
 172                                      lvalue: & $($mutability)* LvalueElem<'tcx>,
 173                                      context: LvalueContext<'tcx>,
 174                                      location: Location) {
 175                 self.super_projection_elem(lvalue, context, location);
 176             }
 177
 178             fn visit_branch(&mut self,
 179                             source: BasicBlock,
 180                             target: BasicBlock) {
 181                 self.super_branch(source, target);
 182             }
 183
 184             fn visit_constant(&mut self,
 185                               constant: & $($mutability)* Constant<'tcx>,
 186                               location: Location) {
 187                 self.super_constant(constant, location);
 188             }
 189
 190             fn visit_literal(&mut self,
 191                              literal: & $($mutability)* Literal<'tcx>,
 192                              location: Location) {
 193                 self.super_literal(literal, location);
 194             }
 195
 196             fn visit_def_id(&mut self,
 197                             def_id: & $($mutability)* DefId,
 198                             _: Location) {
 199                 self.super_def_id(def_id);
 200             }
 201
 202             fn visit_span(&mut self,
 203                           span: & $($mutability)* Span) {
 204                 self.super_span(span);
 205             }
 206
 207             fn visit_source_info(&mut self,
 208                                  source_info: & $($mutability)* SourceInfo) {
 209                 self.super_source_info(source_info);
 210             }
 211
 212             fn visit_ty(&mut self,
 213                         ty: & $($mutability)* Ty<'tcx>) {
 214                 self.super_ty(ty);
 215             }
 216
 217             fn visit_substs(&mut self,
 218                             substs: & $($mutability)* &'tcx Substs<'tcx>) {
 219                 self.super_substs(substs);
 220             }
 221
 222             fn visit_closure_substs(&mut self,
 223                                     substs: & $($mutability)* ClosureSubsts<'tcx>) {
 224                 self.super_closure_substs(substs);
 225             }
 226
 227             fn visit_const_val(&mut self,
 228                                const_val: & $($mutability)* ConstVal,
 229                                _: Location) {
 230                 self.super_const_val(const_val);
 231             }
 232
 233             fn visit_const_int(&mut self,
 234                                const_int: &ConstInt,
 235                                _: Location) {
 236                 self.super_const_int(const_int);
 237             }
 238
 239             fn visit_const_usize(&mut self,
 240                                  const_usize: & $($mutability)* ConstUsize,
 241                                  _: Location) {
 242                 self.super_const_usize(const_usize);
 243             }
 244
 245             fn visit_local_decl(&mut self,
 246                                 local_decl: & $($mutability)* LocalDecl<'tcx>) {
 247                 self.super_local_decl(local_decl);
 248             }
 249
 250             fn visit_visibility_scope(&mut self,
 251                                       scope: & $($mutability)* VisibilityScope) {
 252                 self.super_visibility_scope(scope);
 253             }
 254
 255             // The `super_xxx` methods comprise the default behavior and are
 256             // not meant to be overridden.
 257
 258             fn super_mir(&mut self,
 259                          mir: & $($mutability)* Mir<'tcx>) {
 260                 for index in 0..mir.basic_blocks().len() {
 261                     let block = BasicBlock::new(index);
 262                     self.visit_basic_block_data(block, &$($mutability)* mir[block]);
 263                 }
 264
 265                 for scope in &$($mutability)* mir.visibility_scopes {
 266                     self.visit_visibility_scope_data(scope);
 267                 }
 268
 269                 self.visit_ty(&$($mutability)* mir.return_ty);
 270
 271                 for local_decl in &$($mutability)* mir.local_decls {
 272                     self.visit_local_decl(local_decl);
 273                 }
 274
 275                 self.visit_span(&$($mutability)* mir.span);
 276             }
 277
 278             fn super_basic_block_data(&mut self,
 279                                       block: BasicBlock,
 280                                       data: & $($mutability)* BasicBlockData<'tcx>) {
 281                 let BasicBlockData {
 282                     ref $($mutability)* statements,
 283                     ref $($mutability)* terminator,
 284                     is_cleanup: _
 285                 } = *data;
 286
 287                 let mut index = 0;
 288                 for statement in statements {
 289                     let location = Location { block: block, statement_index: index };
 290                     self.visit_statement(block, statement, location);
 291                     index += 1;
 292                 }
 293
 294                 if let Some(ref $($mutability)* terminator) = *terminator {
 295                     let location = Location { block: block, statement_index: index };
 296                     self.visit_terminator(block, terminator, location);
 297                 }
 298             }
 299
 300             fn super_visibility_scope_data(&mut self,
 301                                            scope_data: & $($mutability)* VisibilityScopeData) {
 302                 let VisibilityScopeData {
 303                     ref $($mutability)* span,
 304                     ref $($mutability)* parent_scope,
 305                 } = *scope_data;
 306
 307                 self.visit_span(span);
 308                 if let Some(ref $($mutability)* parent_scope) = *parent_scope {
 309                     self.visit_visibility_scope(parent_scope);
 310                 }
 311             }
 312
 313             fn super_statement(&mut self,
 314                                block: BasicBlock,
 315                                statement: & $($mutability)* Statement<'tcx>,
 316                                location: Location) {
 317                 let Statement {
 318                     ref $($mutability)* source_info,
 319                     ref $($mutability)* kind,
 320                 } = *statement;
 321
 322                 self.visit_source_info(source_info);
 323                 match *kind {
 324                     StatementKind::Assign(ref $($mutability)* lvalue,
 325                                           ref $($mutability)* rvalue) => {
 326                         self.visit_assign(block, lvalue, rvalue, location);
 327                     }
 328                     StatementKind::SetDiscriminant{ ref $($mutability)* lvalue, .. } => {
 329                         self.visit_lvalue(lvalue, LvalueContext::Store, location);
 330                     }
 331                     StatementKind::StorageLive(ref $($mutability)* lvalue) => {
 332                         self.visit_lvalue(lvalue, LvalueContext::StorageLive, location);
 333                     }
 334                     StatementKind::StorageDead(ref $($mutability)* lvalue) => {
 335                         self.visit_lvalue(lvalue, LvalueContext::StorageDead, location);
 336                     }
 337                     StatementKind::InlineAsm { ref $($mutability)* outputs,
 338                                                ref $($mutability)* inputs,
 339                                                asm: _ } => {
 340                         for output in & $($mutability)* outputs[..] {
 341                             self.visit_lvalue(output, LvalueContext::Store, location);
 342                         }
 343                         for input in & $($mutability)* inputs[..] {
 344                             self.visit_operand(input, location);
 345                         }
 346                     }
 347                     StatementKind::Nop => {}
 348                 }
 349             }
 350
 351             fn super_assign(&mut self,
 352                             _block: BasicBlock,
 353                             lvalue: &$($mutability)* Lvalue<'tcx>,
 354                             rvalue: &$($mutability)* Rvalue<'tcx>,
 355                             location: Location) {
 356                 self.visit_lvalue(lvalue, LvalueContext::Store, location);
 357                 self.visit_rvalue(rvalue, location);
 358             }
 359
 360             fn super_terminator(&mut self,
 361                                 block: BasicBlock,
 362                                 terminator: &$($mutability)* Terminator<'tcx>,
 363                                 location: Location) {
 364                 let Terminator {
 365                     ref $($mutability)* source_info,
 366                     ref $($mutability)* kind,
 367                 } = *terminator;
 368
 369                 self.visit_source_info(source_info);
 370                 self.visit_terminator_kind(block, kind, location);
 371             }
 372
 373             fn super_terminator_kind(&mut self,
 374                                      block: BasicBlock,
 375                                      kind: & $($mutability)* TerminatorKind<'tcx>,
 376                                      source_location: Location) {
 377                 match *kind {
 378                     TerminatorKind::Goto { target } => {
 379                         self.visit_branch(block, target);
 380                     }
 381
 382                     TerminatorKind::SwitchInt { ref $($mutability)* discr,
 383                                                 ref $($mutability)* switch_ty,
 384                                                 ref values,
 385                                                 ref targets } => {
 386                         self.visit_operand(discr, source_location);
 387                         self.visit_ty(switch_ty);
 388                         for value in &values[..] {
 389                             self.visit_const_int(value, source_location);
 390                         }
 391                         for &target in targets {
 392                             self.visit_branch(block, target);
 393                         }
 394                     }
 395
 396                     TerminatorKind::Resume |
 397                     TerminatorKind::Return |
 398                     TerminatorKind::Unreachable => {
 399                     }
 400
 401                     TerminatorKind::Drop { ref $($mutability)* location,
 402                                            target,
 403                                            unwind } => {
 404                         self.visit_lvalue(location, LvalueContext::Drop, source_location);
 405                         self.visit_branch(block, target);
 406                         unwind.map(|t| self.visit_branch(block, t));
 407                     }
 408
 409                     TerminatorKind::DropAndReplace { ref $($mutability)* location,
 410                                                      ref $($mutability)* value,
 411                                                      target,
 412                                                      unwind } => {
 413                         self.visit_lvalue(location, LvalueContext::Drop, source_location);
 414                         self.visit_operand(value, source_location);
 415                         self.visit_branch(block, target);
 416                         unwind.map(|t| self.visit_branch(block, t));
 417                     }
 418
 419                     TerminatorKind::Call { ref $($mutability)* func,
 420                                            ref $($mutability)* args,
 421                                            ref $($mutability)* destination,
 422                                            cleanup } => {
 423                         self.visit_operand(func, source_location);
 424                         for arg in args {
 425                             self.visit_operand(arg, source_location);
 426                         }
 427                         if let Some((ref $($mutability)* destination, target)) = *destination {
 428                             self.visit_lvalue(destination, LvalueContext::Call, source_location);
 429                             self.visit_branch(block, target);
 430                         }
 431                         cleanup.map(|t| self.visit_branch(block, t));
 432                     }
 433
 434                     TerminatorKind::Assert { ref $($mutability)* cond,
 435                                              expected: _,
 436                                              ref $($mutability)* msg,
 437                                              target,
 438                                              cleanup } => {
 439                         self.visit_operand(cond, source_location);
 440                         self.visit_assert_message(msg, source_location);
 441                         self.visit_branch(block, target);
 442                         cleanup.map(|t| self.visit_branch(block, t));
 443                     }
 444                 }
 445             }
 446
 447             fn super_assert_message(&mut self,
 448                                     msg: & $($mutability)* AssertMessage<'tcx>,
 449                                     location: Location) {
 450                 match *msg {
 451                     AssertMessage::BoundsCheck {
 452                         ref $($mutability)* len,
 453                         ref $($mutability)* index
 454                     } => {
 455                         self.visit_operand(len, location);
 456                         self.visit_operand(index, location);
 457                     }
 458                     AssertMessage::Math(_) => {}
 459                 }
 460             }
 461
 462             fn super_rvalue(&mut self,
 463                             rvalue: & $($mutability)* Rvalue<'tcx>,
 464                             location: Location) {
 465                 match *rvalue {
 466                     Rvalue::Use(ref $($mutability)* operand) => {
 467                         self.visit_operand(operand, location);
 468                     }
 469
 470                     Rvalue::Repeat(ref $($mutability)* value,
 471                                    ref $($mutability)* length) => {
 472                         self.visit_operand(value, location);
 473                         self.visit_const_usize(length, location);
 474                     }
 475
 476                     Rvalue::Ref(r, bk, ref $($mutability)* path) => {
 477                         self.visit_lvalue(path, LvalueContext::Borrow {
 478                             region: r,
 479                             kind: bk
 480                         }, location);
 481                     }
 482
 483                     Rvalue::Len(ref $($mutability)* path) => {
 484                         self.visit_lvalue(path, LvalueContext::Inspect, location);
 485                     }
 486
 487                     Rvalue::Cast(_cast_kind,
 488                                  ref $($mutability)* operand,
 489                                  ref $($mutability)* ty) => {
 490                         self.visit_operand(operand, location);
 491                         self.visit_ty(ty);
 492                     }
 493
 494                     Rvalue::BinaryOp(_bin_op,
 495                                      ref $($mutability)* lhs,
 496                                      ref $($mutability)* rhs) |
 497                     Rvalue::CheckedBinaryOp(_bin_op,
 498                                      ref $($mutability)* lhs,
 499                                      ref $($mutability)* rhs) => {
 500                         self.visit_operand(lhs, location);
 501                         self.visit_operand(rhs, location);
 502                     }
 503
 504                     Rvalue::UnaryOp(_un_op, ref $($mutability)* op) => {
 505                         self.visit_operand(op, location);
 506                     }
 507
 508                     Rvalue::Discriminant(ref $($mutability)* lvalue) => {
 509                         self.visit_lvalue(lvalue, LvalueContext::Inspect, location);
 510                     }
 511
 512                     Rvalue::NullaryOp(_op, ref $($mutability)* ty) => {
 513                         self.visit_ty(ty);
 514                     }
 515
 516                     Rvalue::Aggregate(ref $($mutability)* kind,
 517                                       ref $($mutability)* operands) => {
 518                         let kind = &$($mutability)* **kind;
 519                         match *kind {
 520                             AggregateKind::Array(ref $($mutability)* ty) => {
 521                                 self.visit_ty(ty);
 522                             }
 523                             AggregateKind::Tuple => {
 524                             }
 525                             AggregateKind::Adt(_adt_def,
 526                                                _variant_index,
 527                                                ref $($mutability)* substs,
 528                                                _active_field_index) => {
 529                                 self.visit_substs(substs);
 530                             }
 531                             AggregateKind::Closure(ref $($mutability)* def_id,
 532                                                    ref $($mutability)* closure_substs) => {
 533                                 self.visit_def_id(def_id, location);
 534                                 self.visit_closure_substs(closure_substs);
 535                             }
 536                         }
 537
 538                         for operand in operands {
 539                             self.visit_operand(operand, location);
 540                         }
 541                     }
 542                 }
 543             }
 544
 545             fn super_operand(&mut self,
 546                              operand: & $($mutability)* Operand<'tcx>,
 547                              location: Location) {
 548                 match *operand {
 549                     Operand::Consume(ref $($mutability)* lvalue) => {
 550                         self.visit_lvalue(lvalue, LvalueContext::Consume, location);
 551                     }
 552                     Operand::Constant(ref $($mutability)* constant) => {
 553                         self.visit_constant(constant, location);
 554                     }
 555                 }
 556             }
 557
 558             fn super_lvalue(&mut self,
 559                             lvalue: & $($mutability)* Lvalue<'tcx>,
 560                             context: LvalueContext<'tcx>,
 561                             location: Location) {
 562                 match *lvalue {
 563                     Lvalue::Local(_) => {
 564                     }
 565                     Lvalue::Static(ref $($mutability)* static_) => {
 566                         self.visit_static(static_, context, location);
 567                     }
 568                     Lvalue::Projection(ref $($mutability)* proj) => {
 569                         self.visit_projection(proj, context, location);
 570                     }
 571                 }
 572             }
 573
 574             fn super_static(&mut self,
 575                             static_: & $($mutability)* Static<'tcx>,
 576                             _context: LvalueContext<'tcx>,
 577                             location: Location) {
 578                 let Static {
 579                     ref $($mutability)* def_id,
 580                     ref $($mutability)* ty,
 581                 } = *static_;
 582                 self.visit_def_id(def_id, location);
 583                 self.visit_ty(ty);
 584             }
 585
 586             fn super_projection(&mut self,
 587                                 proj: & $($mutability)* LvalueProjection<'tcx>,
 588                                 context: LvalueContext<'tcx>,
 589                                 location: Location) {
 590                 let Projection {
 591                     ref $($mutability)* base,
 592                     ref $($mutability)* elem,
 593                 } = *proj;
 594                 let context = if context.is_mutating_use() {
 595                     LvalueContext::Projection(Mutability::Mut)
 596                 } else {
 597                     LvalueContext::Projection(Mutability::Not)
 598                 };
 599                 self.visit_lvalue(base, context, location);
 600                 self.visit_projection_elem(elem, context, location);
 601             }
 602
 603             fn super_projection_elem(&mut self,
 604                                      proj: & $($mutability)* LvalueElem<'tcx>,
 605                                      _context: LvalueContext<'tcx>,
 606                                      location: Location) {
 607                 match *proj {
 608                     ProjectionElem::Deref => {
 609                     }
 610                     ProjectionElem::Subslice { from: _, to: _ } => {
 611                     }
 612                     ProjectionElem::Field(_field, ref $($mutability)* ty) => {
 613                         self.visit_ty(ty);
 614                     }
 615                     ProjectionElem::Index(ref $($mutability)* operand) => {
 616                         self.visit_operand(operand, location);
 617                     }
 618                     ProjectionElem::ConstantIndex { offset: _,
 619                                                     min_length: _,
 620                                                     from_end: _ } => {
 621                     }
 622                     ProjectionElem::Downcast(_adt_def, _variant_index) => {
 623                     }
 624                 }
 625             }
 626
 627             fn super_local_decl(&mut self,
 628                                 local_decl: & $($mutability)* LocalDecl<'tcx>) {
 629                 let LocalDecl {
 630                     mutability: _,
 631                     ref $($mutability)* ty,
 632                     name: _,
 633                     ref $($mutability)* source_info,
 634                     is_user_variable: _,
 635                 } = *local_decl;
 636
 637                 self.visit_ty(ty);
 638                 self.visit_source_info(source_info);
 639             }
 640
 641             fn super_visibility_scope(&mut self,
 642                                       _scope: & $($mutability)* VisibilityScope) {
 643             }
 644
 645             fn super_branch(&mut self,
 646                             _source: BasicBlock,
 647                             _target: BasicBlock) {
 648             }
 649
 650             fn super_constant(&mut self,
 651                               constant: & $($mutability)* Constant<'tcx>,
 652                               location: Location) {
 653                 let Constant {
 654                     ref $($mutability)* span,
 655                     ref $($mutability)* ty,
 656                     ref $($mutability)* literal,
 657                 } = *constant;
 658
 659                 self.visit_span(span);
 660                 self.visit_ty(ty);
 661                 self.visit_literal(literal, location);
 662             }
 663
 664             fn super_literal(&mut self,
 665                              literal: & $($mutability)* Literal<'tcx>,
 666                              location: Location) {
 667                 match *literal {
 668                     Literal::Item { ref $($mutability)* def_id,
 669                                     ref $($mutability)* substs } => {
 670                         self.visit_def_id(def_id, location);
 671                         self.visit_substs(substs);
 672                     }
 673                     Literal::Value { ref $($mutability)* value } => {
 674                         self.visit_const_val(value, location);
 675                     }
 676                     Literal::Promoted { index: _ } => {}
 677                 }
 678             }
 679
 680             fn super_def_id(&mut self, _def_id: & $($mutability)* DefId) {
 681             }
 682
 683             fn super_span(&mut self, _span: & $($mutability)* Span) {
 684             }
 685
 686             fn super_source_info(&mut self, source_info: & $($mutability)* SourceInfo) {
 687                 let SourceInfo {
 688                     ref $($mutability)* span,
 689                     ref $($mutability)* scope,
 690                 } = *source_info;
 691
 692                 self.visit_span(span);
 693                 self.visit_visibility_scope(scope);
 694             }
 695
 696             fn super_ty(&mut self, _ty: & $($mutability)* Ty<'tcx>) {
 697             }
 698
 699             fn super_substs(&mut self, _substs: & $($mutability)* &'tcx Substs<'tcx>) {
 700             }
 701
 702             fn super_closure_substs(&mut self,
 703                                     _substs: & $($mutability)* ClosureSubsts<'tcx>) {
 704             }
 705
 706             fn super_const_val(&mut self, _const_val: & $($mutability)* ConstVal) {
 707             }
 708
 709             fn super_const_int(&mut self, _const_int: &ConstInt) {
 710             }
 711
 712             fn super_const_usize(&mut self, _const_usize: & $($mutability)* ConstUsize) {
 713             }
 714
 715             // Convenience methods
 716
 717             fn visit_location(&mut self, mir: & $($mutability)* Mir<'tcx>, location: Location) {
 718                 let basic_block = & $($mutability)* mir[location.block];
 719                 if basic_block.statements.len() == location.statement_index {
 720                     if let Some(ref $($mutability)* terminator) = basic_block.terminator {
 721                         self.visit_terminator(location.block, terminator, location)
 722                     }
 723                 } else {
 724                     let statement = & $($mutability)*
 725                         basic_block.statements[location.statement_index];
 726                     self.visit_statement(location.block, statement, location)
 727                 }
 728             }
 729         }
 730     }
 731 }
 732
 733 make_mir_visitor!(Visitor,);
 734 make_mir_visitor!(MutVisitor,mut);
 735
 736 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
 737 pub enum LvalueContext<'tcx> {
 738     // Appears as LHS of an assignment
 739     Store,
 740
 741     // Dest of a call
 742     Call,
 743
 744     // Being dropped
 745     Drop,
 746
 747     // Being inspected in some way, like loading a len
 748     Inspect,
 749
 750     // Being borrowed
 751     Borrow { region: Region<'tcx>, kind: BorrowKind },
 752
 753     // Used as base for another lvalue, e.g. `x` in `x.y`.
 754     //
 755     // The `Mutability` argument specifies whether the projection is being performed in order to
 756     // (potentially) mutate the lvalue. For example, the projection `x.y` is marked as a mutation
 757     // in these cases:
 758     //
 759     //     x.y = ...;
 760     //     f(&mut x.y);
 761     //
 762     // But not in these cases:
 763     //
 764     //     z = x.y;
 765     //     f(&x.y);
 766     Projection(Mutability),
 767
 768     // Consumed as part of an operand
 769     Consume,
 770
 771     // Starting and ending a storage live range
 772     StorageLive,
 773     StorageDead,
 774 }
 775
 776 impl<'tcx> LvalueContext<'tcx> {
 777     /// Returns true if this lvalue context represents a drop.
 778     pub fn is_drop(&self) -> bool {
 779         match *self {
 780             LvalueContext::Drop => true,
 781             _ => false,
 782         }
 783     }
 784
 785     /// Returns true if this lvalue context represents a storage live or storage dead marker.
 786     pub fn is_storage_marker(&self) -> bool {
 787         match *self {
 788             LvalueContext::StorageLive | LvalueContext::StorageDead => true,
 789             _ => false,
 790         }
 791     }
 792
 793     /// Returns true if this lvalue context represents a storage live marker.
 794     pub fn is_storage_live_marker(&self) -> bool {
 795         match *self {
 796             LvalueContext::StorageLive => true,
 797             _ => false,
 798         }
 799     }
 800
 801     /// Returns true if this lvalue context represents a storage dead marker.
 802     pub fn is_storage_dead_marker(&self) -> bool {
 803         match *self {
 804             LvalueContext::StorageDead => true,
 805             _ => false,
 806         }
 807     }
 808
 809     /// Returns true if this lvalue context represents a use that potentially changes the value.
 810     pub fn is_mutating_use(&self) -> bool {
 811         match *self {
 812             LvalueContext::Store | LvalueContext::Call |
 813             LvalueContext::Borrow { kind: BorrowKind::Mut, .. } |
 814             LvalueContext::Projection(Mutability::Mut) |
 815             LvalueContext::Drop => true,
 816             LvalueContext::Inspect |
 817             LvalueContext::Borrow { kind: BorrowKind::Shared, .. } |
 818             LvalueContext::Borrow { kind: BorrowKind::Unique, .. } |
 819             LvalueContext::Projection(Mutability::Not) | LvalueContext::Consume |
 820             LvalueContext::StorageLive | LvalueContext::StorageDead => false,
 821         }
 822     }
 823
 824     /// Returns true if this lvalue context represents a use that does not change the value.
 825     pub fn is_nonmutating_use(&self) -> bool {
 826         match *self {
 827             LvalueContext::Inspect | LvalueContext::Borrow { kind: BorrowKind::Shared, .. } |
 828             LvalueContext::Borrow { kind: BorrowKind::Unique, .. } |
 829             LvalueContext::Projection(Mutability::Not) | LvalueContext::Consume => true,
 830             LvalueContext::Borrow { kind: BorrowKind::Mut, .. } | LvalueContext::Store |
 831             LvalueContext::Call | LvalueContext::Projection(Mutability::Mut) |
 832             LvalueContext::Drop | LvalueContext::StorageLive | LvalueContext::StorageDead => false,
 833         }
 834     }
 835
 836     pub fn is_use(&self) -> bool {
 837         self.is_mutating_use() || self.is_nonmutating_use()
 838     }
 839 }