src/librustc_passes/rvalue_promotion.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 // Verifies that the types and values of const and static items
  12 // are safe. The rules enforced by this module are:
  13 //
  14 // - For each *mutable* static item, it checks that its **type**:
  15 //     - doesn't have a destructor
  16 //     - doesn't own a box
  17 //
  18 // - For each *immutable* static item, it checks that its **value**:
  19 //       - doesn't own a box
  20 //       - doesn't contain a struct literal or a call to an enum variant / struct constructor where
  21 //           - the type of the struct/enum has a dtor
  22 //
  23 // Rules Enforced Elsewhere:
  24 // - It's not possible to take the address of a static item with unsafe interior. This is enforced
  25 // by borrowck::gather_loans
  26
  27 use rustc::ty::cast::CastKind;
  28 use rustc::hir::def::{Def, CtorKind};
  29 use rustc::hir::def_id::DefId;
  30 use rustc::middle::expr_use_visitor as euv;
  31 use rustc::middle::mem_categorization as mc;
  32 use rustc::middle::mem_categorization::Categorization;
  33 use rustc::ty::{self, Ty, TyCtxt};
  34 use rustc::ty::query::Providers;
  35 use rustc::ty::subst::Substs;
  36 use rustc::util::nodemap::{ItemLocalSet, NodeSet};
  37 use rustc::hir;
  38 use rustc_data_structures::sync::Lrc;
  39 use syntax::ast;
  40 use syntax_pos::{Span, DUMMY_SP};
  41 use self::Promotability::*;
  42 use std::ops::{BitAnd, BitAndAssign, BitOr};
  43
  44 pub fn provide(providers: &mut Providers) {
  45     *providers = Providers {
  46         rvalue_promotable_map,
  47         const_is_rvalue_promotable_to_static,
  48         ..*providers
  49     };
  50 }
  51
  52 pub fn check_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
  53     for &body_id in &tcx.hir.krate().body_ids {
  54         let def_id = tcx.hir.body_owner_def_id(body_id);
  55         tcx.const_is_rvalue_promotable_to_static(def_id);
  56     }
  57     tcx.sess.abort_if_errors();
  58 }
  59
  60 fn const_is_rvalue_promotable_to_static<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
  61                                                   def_id: DefId)
  62                                                   -> bool
  63 {
  64     assert!(def_id.is_local());
  65
  66     let node_id = tcx.hir.as_local_node_id(def_id)
  67         .expect("rvalue_promotable_map invoked with non-local def-id");
  68     let body_id = tcx.hir.body_owned_by(node_id);
  69     let body_hir_id = tcx.hir.node_to_hir_id(body_id.node_id);
  70     tcx.rvalue_promotable_map(def_id).contains(&body_hir_id.local_id)
  71 }
  72
  73 fn rvalue_promotable_map<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
  74                                    def_id: DefId)
  75                                    -> Lrc<ItemLocalSet>
  76 {
  77     let outer_def_id = tcx.closure_base_def_id(def_id);
  78     if outer_def_id != def_id {
  79         return tcx.rvalue_promotable_map(outer_def_id);
  80     }
  81
  82     let mut visitor = CheckCrateVisitor {
  83         tcx,
  84         tables: &ty::TypeckTables::empty(None),
  85         in_fn: false,
  86         in_static: false,
  87         mut_rvalue_borrows: NodeSet(),
  88         param_env: ty::ParamEnv::empty(),
  89         identity_substs: Substs::empty(),
  90         result: ItemLocalSet(),
  91     };
  92
  93     // `def_id` should be a `Body` owner
  94     let node_id = tcx.hir.as_local_node_id(def_id)
  95         .expect("rvalue_promotable_map invoked with non-local def-id");
  96     let body_id = tcx.hir.body_owned_by(node_id);
  97     let _ = visitor.check_nested_body(body_id);
  98
  99     Lrc::new(visitor.result)
 100 }
 101
 102 struct CheckCrateVisitor<'a, 'tcx: 'a> {
 103     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 104     in_fn: bool,
 105     in_static: bool,
 106     mut_rvalue_borrows: NodeSet,
 107     param_env: ty::ParamEnv<'tcx>,
 108     identity_substs: &'tcx Substs<'tcx>,
 109     tables: &'a ty::TypeckTables<'tcx>,
 110     result: ItemLocalSet,
 111 }
 112
 113 #[must_use]
 114 #[derive(Debug, Clone, Copy, PartialEq)]
 115 enum Promotability {
 116     Promotable,
 117     NotPromotable
 118 }
 119
 120 impl BitAnd for Promotability {
 121     type Output = Self;
 122
 123     fn bitand(self, rhs: Self) -> Self {
 124         match (self, rhs) {
 125             (Promotable, Promotable) => Promotable,
 126             _ => NotPromotable,
 127         }
 128     }
 129 }
 130
 131 impl BitAndAssign for Promotability {
 132     fn bitand_assign(&mut self, rhs: Self) {
 133         *self = *self & rhs
 134     }
 135 }
 136
 137 impl BitOr for Promotability {
 138     type Output = Self;
 139
 140     fn bitor(self, rhs: Self) -> Self {
 141         match (self, rhs) {
 142             (NotPromotable, NotPromotable) => NotPromotable,
 143             _ => Promotable,
 144         }
 145     }
 146 }
 147
 148 impl<'a, 'gcx> CheckCrateVisitor<'a, 'gcx> {
 149     // Returns true iff all the values of the type are promotable.
 150     fn type_promotability(&mut self, ty: Ty<'gcx>) -> Promotability {
 151         debug!("type_promotability({})", ty);
 152
 153         if ty.is_freeze(self.tcx, self.param_env, DUMMY_SP) &&
 154             !ty.needs_drop(self.tcx, self.param_env) {
 155             Promotable
 156         } else {
 157             NotPromotable
 158         }
 159     }
 160
 161     fn handle_const_fn_call(
 162         &mut self,
 163         def_id: DefId,
 164     ) -> Promotability {
 165         if self.tcx.is_promotable_const_fn(def_id) {
 166             Promotable
 167         } else {
 168             NotPromotable
 169         }
 170     }
 171
 172     /// While the `ExprUseVisitor` walks, we will identify which
 173     /// expressions are borrowed, and insert their ids into this
 174     /// table. Actually, we insert the "borrow-id", which is normally
 175     /// the id of the expession being borrowed: but in the case of
 176     /// `ref mut` borrows, the `id` of the pattern is
 177     /// inserted. Therefore later we remove that entry from the table
 178     /// and transfer it over to the value being matched. This will
 179     /// then prevent said value from being promoted.
 180     fn remove_mut_rvalue_borrow(&mut self, pat: &hir::Pat) -> bool {
 181         let mut any_removed = false;
 182         pat.walk(|p| {
 183             any_removed |= self.mut_rvalue_borrows.remove(&p.id);
 184             true
 185         });
 186         any_removed
 187     }
 188 }
 189
 190 impl<'a, 'tcx> CheckCrateVisitor<'a, 'tcx> {
 191     fn check_nested_body(&mut self, body_id: hir::BodyId) -> Promotability {
 192         let item_id = self.tcx.hir.body_owner(body_id);
 193         let item_def_id = self.tcx.hir.local_def_id(item_id);
 194
 195         let outer_in_fn = self.in_fn;
 196         let outer_tables = self.tables;
 197         let outer_param_env = self.param_env;
 198         let outer_identity_substs = self.identity_substs;
 199
 200         self.in_fn = false;
 201         self.in_static = false;
 202
 203         match self.tcx.hir.body_owner_kind(item_id) {
 204             hir::BodyOwnerKind::Fn => self.in_fn = true,
 205             hir::BodyOwnerKind::Static(_) => self.in_static = true,
 206             _ => {}
 207         };
 208
 209
 210         self.tables = self.tcx.typeck_tables_of(item_def_id);
 211         self.param_env = self.tcx.param_env(item_def_id);
 212         self.identity_substs = Substs::identity_for_item(self.tcx, item_def_id);
 213
 214         let body = self.tcx.hir.body(body_id);
 215
 216         let tcx = self.tcx;
 217         let param_env = self.param_env;
 218         let region_scope_tree = self.tcx.region_scope_tree(item_def_id);
 219         let tables = self.tables;
 220         euv::ExprUseVisitor::new(self, tcx, param_env, &region_scope_tree, tables, None)
 221             .consume_body(body);
 222
 223         let body_promotable = self.check_expr(&body.value);
 224         self.in_fn = outer_in_fn;
 225         self.tables = outer_tables;
 226         self.param_env = outer_param_env;
 227         self.identity_substs = outer_identity_substs;
 228         body_promotable
 229     }
 230
 231     fn check_stmt(&mut self, stmt: &'tcx hir::Stmt) -> Promotability {
 232         match stmt.node {
 233             hir::StmtKind::Decl(ref decl, _node_id) => {
 234                 match &decl.node {
 235                     hir::DeclKind::Local(local) => {
 236                         if self.remove_mut_rvalue_borrow(&local.pat) {
 237                             if let Some(init) = &local.init {
 238                                 self.mut_rvalue_borrows.insert(init.id);
 239                             }
 240                         }
 241
 242                         if let Some(ref expr) = local.init {
 243                             let _ = self.check_expr(&expr);
 244                         }
 245                         NotPromotable
 246                     }
 247                     // Item statements are allowed
 248                     hir::DeclKind::Item(_) => Promotable
 249                 }
 250             }
 251             hir::StmtKind::Expr(ref box_expr, _node_id) |
 252             hir::StmtKind::Semi(ref box_expr, _node_id) => {
 253                 let _ = self.check_expr(box_expr);
 254                 NotPromotable
 255             }
 256         }
 257     }
 258
 259     fn check_expr(&mut self, ex: &'tcx hir::Expr) -> Promotability {
 260         let node_ty = self.tables.node_id_to_type(ex.hir_id);
 261         let mut outer = check_expr_kind(self, ex, node_ty);
 262         outer &= check_adjustments(self, ex);
 263
 264         // Handle borrows on (or inside the autorefs of) this expression.
 265         if self.mut_rvalue_borrows.remove(&ex.id) {
 266             outer = NotPromotable
 267         }
 268
 269         if outer == Promotable {
 270             self.result.insert(ex.hir_id.local_id);
 271         }
 272         outer
 273     }
 274
 275     fn check_block(&mut self, block: &'tcx hir::Block) -> Promotability {
 276         let mut iter_result = Promotable;
 277         for index in block.stmts.iter() {
 278             iter_result &= self.check_stmt(index);
 279         }
 280         match block.expr {
 281             Some(ref box_expr) => iter_result & self.check_expr(&*box_expr),
 282             None => iter_result,
 283         }
 284     }
 285 }
 286
 287 /// This function is used to enforce the constraints on
 288 /// const/static items. It walks through the *value*
 289 /// of the item walking down the expression and evaluating
 290 /// every nested expression. If the expression is not part
 291 /// of a const/static item, it is qualified for promotion
 292 /// instead of producing errors.
 293 fn check_expr_kind<'a, 'tcx>(
 294     v: &mut CheckCrateVisitor<'a, 'tcx>,
 295     e: &'tcx hir::Expr, node_ty: Ty<'tcx>) -> Promotability {
 296
 297     let ty_result = match node_ty.sty {
 298         ty::Adt(def, _) if def.has_dtor(v.tcx) => {
 299             NotPromotable
 300         }
 301         _ => Promotable
 302     };
 303
 304     let node_result = match e.node {
 305         hir::ExprKind::Box(ref expr) => {
 306             let _ = v.check_expr(&expr);
 307             NotPromotable
 308         }
 309         hir::ExprKind::Unary(op, ref expr) => {
 310             let expr_promotability = v.check_expr(expr);
 311             if v.tables.is_method_call(e) || op == hir::UnDeref {
 312                 return NotPromotable;
 313             }
 314             expr_promotability
 315         }
 316         hir::ExprKind::Binary(op, ref lhs, ref rhs) => {
 317             let lefty = v.check_expr(lhs);
 318             let righty = v.check_expr(rhs);
 319             if v.tables.is_method_call(e) {
 320                 return NotPromotable;
 321             }
 322             match v.tables.node_id_to_type(lhs.hir_id).sty {
 323                 ty::RawPtr(_) | ty::FnPtr(..) => {
 324                     assert!(op.node == hir::BinOpKind::Eq || op.node == hir::BinOpKind::Ne ||
 325                             op.node == hir::BinOpKind::Le || op.node == hir::BinOpKind::Lt ||
 326                             op.node == hir::BinOpKind::Ge || op.node == hir::BinOpKind::Gt);
 327
 328                     NotPromotable
 329                 }
 330                 _ => lefty & righty
 331             }
 332         }
 333         hir::ExprKind::Cast(ref from, _) => {
 334             let expr_promotability = v.check_expr(from);
 335             debug!("Checking const cast(id={})", from.id);
 336             match v.tables.cast_kinds().get(from.hir_id) {
 337                 None => {
 338                     v.tcx.sess.delay_span_bug(e.span, "no kind for cast");
 339                     NotPromotable
 340                 },
 341                 Some(&CastKind::PtrAddrCast) | Some(&CastKind::FnPtrAddrCast) => {
 342                     NotPromotable
 343                 }
 344                 _ => expr_promotability
 345             }
 346         }
 347         hir::ExprKind::Path(ref qpath) => {
 348             let def = v.tables.qpath_def(qpath, e.hir_id);
 349             match def {
 350                 Def::VariantCtor(..) | Def::StructCtor(..) |
 351                 Def::Fn(..) | Def::Method(..) | Def::SelfCtor(..) => Promotable,
 352
 353                 // References to a static that are themselves within a static
 354                 // are inherently promotable with the exception
 355                 //  of "#[thread_local]" statics, which may not
 356                 // outlive the current function
 357                 Def::Static(did, _) => {
 358
 359                     if v.in_static {
 360                         for attr in &v.tcx.get_attrs(did)[..] {
 361                             if attr.check_name("thread_local") {
 362                                 debug!("Reference to Static(id={:?}) is unpromotable \
 363                                        due to a #[thread_local] attribute", did);
 364                                 return NotPromotable;
 365                             }
 366                         }
 367                         Promotable
 368                     } else {
 369                         debug!("Reference to Static(id={:?}) is unpromotable as it is not \
 370                                referenced from a static", did);
 371                         NotPromotable
 372                     }
 373                 }
 374
 375                 Def::Const(did) |
 376                 Def::AssociatedConst(did) => {
 377                     let promotable = if v.tcx.trait_of_item(did).is_some() {
 378                         // Don't peek inside trait associated constants.
 379                         NotPromotable
 380                     } else if v.tcx.at(e.span).const_is_rvalue_promotable_to_static(did) {
 381                         Promotable
 382                     } else {
 383                         NotPromotable
 384                     };
 385                     // Just in case the type is more specific than the definition,
 386                     // e.g. impl associated const with type parameters, check it.
 387                     // Also, trait associated consts are relaxed by this.
 388                     promotable | v.type_promotability(node_ty)
 389                 }
 390                 _ => NotPromotable
 391             }
 392         }
 393         hir::ExprKind::Call(ref callee, ref hirvec) => {
 394             let mut call_result = v.check_expr(callee);
 395             for index in hirvec.iter() {
 396                 call_result &= v.check_expr(index);
 397             }
 398             let mut callee = &**callee;
 399             loop {
 400                 callee = match callee.node {
 401                     hir::ExprKind::Block(ref block, _) => match block.expr {
 402                         Some(ref tail) => &tail,
 403                         None => break
 404                     },
 405                     _ => break
 406                 };
 407             }
 408             // The callee is an arbitrary expression, it doesn't necessarily have a definition.
 409             let def = if let hir::ExprKind::Path(ref qpath) = callee.node {
 410                 v.tables.qpath_def(qpath, callee.hir_id)
 411             } else {
 412                 Def::Err
 413             };
 414             let def_result = match def {
 415                 Def::StructCtor(_, CtorKind::Fn) |
 416                 Def::VariantCtor(_, CtorKind::Fn) |
 417                 Def::SelfCtor(..) => Promotable,
 418                 Def::Fn(did) => v.handle_const_fn_call(did),
 419                 Def::Method(did) => {
 420                     match v.tcx.associated_item(did).container {
 421                         ty::ImplContainer(_) => v.handle_const_fn_call(did),
 422                         ty::TraitContainer(_) => NotPromotable,
 423                     }
 424                 }
 425                 _ => NotPromotable,
 426             };
 427             def_result & call_result
 428         }
 429         hir::ExprKind::MethodCall(ref _pathsegment, ref _span, ref hirvec) => {
 430             let mut method_call_result = Promotable;
 431             for index in hirvec.iter() {
 432                 method_call_result &= v.check_expr(index);
 433             }
 434             if let Some(def) = v.tables.type_dependent_defs().get(e.hir_id) {
 435                 let def_id = def.def_id();
 436                 match v.tcx.associated_item(def_id).container {
 437                     ty::ImplContainer(_) => method_call_result & v.handle_const_fn_call(def_id),
 438                     ty::TraitContainer(_) => NotPromotable,
 439                 }
 440             } else {
 441                 v.tcx.sess.delay_span_bug(e.span, "no type-dependent def for method call");
 442                 NotPromotable
 443             }
 444         }
 445         hir::ExprKind::Struct(ref _qpath, ref hirvec, ref option_expr) => {
 446             let mut struct_result = Promotable;
 447             for index in hirvec.iter() {
 448                 struct_result &= v.check_expr(&index.expr);
 449             }
 450             if let Some(ref expr) = *option_expr {
 451                 struct_result &= v.check_expr(&expr);
 452             }
 453             if let ty::Adt(adt, ..) = v.tables.expr_ty(e).sty {
 454                 // unsafe_cell_type doesn't necessarily exist with no_core
 455                 if Some(adt.did) == v.tcx.lang_items().unsafe_cell_type() {
 456                     return NotPromotable;
 457                 }
 458             }
 459             struct_result
 460         }
 461
 462         hir::ExprKind::Lit(_) => Promotable,
 463
 464         hir::ExprKind::AddrOf(_, ref expr) |
 465         hir::ExprKind::Repeat(ref expr, _) => {
 466             v.check_expr(&expr)
 467         }
 468
 469         hir::ExprKind::Closure(_capture_clause, ref _box_fn_decl,
 470                                body_id, _span, _option_generator_movability) => {
 471             let nested_body_promotable = v.check_nested_body(body_id);
 472             // Paths in constant contexts cannot refer to local variables,
 473             // as there are none, and thus closures can't have upvars there.
 474             if v.tcx.with_freevars(e.id, |fv| !fv.is_empty()) {
 475                 NotPromotable
 476             } else {
 477                 nested_body_promotable
 478             }
 479         }
 480
 481         hir::ExprKind::Field(ref expr, _ident) => {
 482             let expr_promotability = v.check_expr(&expr);
 483             if let Some(def) = v.tables.expr_ty(expr).ty_adt_def() {
 484                 if def.is_union() {
 485                     return NotPromotable;
 486                 }
 487             }
 488             expr_promotability
 489         }
 490
 491         hir::ExprKind::Block(ref box_block, ref _option_label) => {
 492             v.check_block(box_block)
 493         }
 494
 495         hir::ExprKind::Index(ref lhs, ref rhs) => {
 496             let lefty = v.check_expr(lhs);
 497             let righty = v.check_expr(rhs);
 498             if v.tables.is_method_call(e) {
 499                 return NotPromotable;
 500             }
 501             lefty & righty
 502         }
 503
 504         hir::ExprKind::Array(ref hirvec) => {
 505             let mut array_result = Promotable;
 506             for index in hirvec.iter() {
 507                 array_result &= v.check_expr(index);
 508             }
 509             array_result
 510         }
 511
 512         hir::ExprKind::Type(ref expr, ref _ty) => {
 513             v.check_expr(&expr)
 514         }
 515
 516         hir::ExprKind::Tup(ref hirvec) => {
 517             let mut tup_result = Promotable;
 518             for index in hirvec.iter() {
 519                 tup_result &= v.check_expr(index);
 520             }
 521             tup_result
 522         }
 523
 524
 525         // Conditional control flow (possible to implement).
 526         hir::ExprKind::Match(ref expr, ref hirvec_arm, ref _match_source) => {
 527             // Compute the most demanding borrow from all the arms'
 528             // patterns and set that on the discriminator.
 529             let mut mut_borrow = false;
 530             for pat in hirvec_arm.iter().flat_map(|arm| &arm.pats) {
 531                 mut_borrow = v.remove_mut_rvalue_borrow(pat);
 532             }
 533             if mut_borrow {
 534                 v.mut_rvalue_borrows.insert(expr.id);
 535             }
 536
 537             let _ = v.check_expr(expr);
 538             for index in hirvec_arm.iter() {
 539                 let _ = v.check_expr(&*index.body);
 540                 if let Some(hir::Guard::If(ref expr)) = index.guard {
 541                     let _ = v.check_expr(&expr);
 542                 }
 543             }
 544             NotPromotable
 545         }
 546
 547         hir::ExprKind::If(ref lhs, ref rhs, ref option_expr) => {
 548             let _ = v.check_expr(lhs);
 549             let _ = v.check_expr(rhs);
 550             if let Some(ref expr) = option_expr {
 551                 let _ = v.check_expr(&expr);
 552             }
 553             NotPromotable
 554         }
 555
 556         // Loops (not very meaningful in constants).
 557         hir::ExprKind::While(ref expr, ref box_block, ref _option_label) => {
 558             let _ = v.check_expr(expr);
 559             let _ = v.check_block(box_block);
 560             NotPromotable
 561         }
 562
 563         hir::ExprKind::Loop(ref box_block, ref _option_label, ref _loop_source) => {
 564             let _ = v.check_block(box_block);
 565             NotPromotable
 566         }
 567
 568         // More control flow (also not very meaningful).
 569         hir::ExprKind::Break(_, ref option_expr) | hir::ExprKind::Ret(ref option_expr) => {
 570             if let Some(ref expr) = *option_expr {
 571                  let _ = v.check_expr(&expr);
 572             }
 573             NotPromotable
 574         }
 575
 576         hir::ExprKind::Continue(_) => {
 577             NotPromotable
 578         }
 579
 580         // Generator expressions
 581         hir::ExprKind::Yield(ref expr) => {
 582             let _ = v.check_expr(&expr);
 583             NotPromotable
 584         }
 585
 586         // Expressions with side-effects.
 587         hir::ExprKind::AssignOp(_, ref lhs, ref rhs) | hir::ExprKind::Assign(ref lhs, ref rhs) => {
 588             let _ = v.check_expr(lhs);
 589             let _ = v.check_expr(rhs);
 590             NotPromotable
 591         }
 592
 593         hir::ExprKind::InlineAsm(ref _inline_asm, ref hirvec_lhs, ref hirvec_rhs) => {
 594             for index in hirvec_lhs.iter().chain(hirvec_rhs.iter()) {
 595                 let _ = v.check_expr(index);
 596             }
 597             NotPromotable
 598         }
 599     };
 600     ty_result & node_result
 601 }
 602
 603 /// Check the adjustments of an expression
 604 fn check_adjustments<'a, 'tcx>(
 605     v: &mut CheckCrateVisitor<'a, 'tcx>,
 606     e: &hir::Expr) -> Promotability {
 607     use rustc::ty::adjustment::*;
 608
 609     let mut adjustments = v.tables.expr_adjustments(e).iter().peekable();
 610     while let Some(adjustment) = adjustments.next() {
 611         match adjustment.kind {
 612             Adjust::NeverToAny |
 613             Adjust::ReifyFnPointer |
 614             Adjust::UnsafeFnPointer |
 615             Adjust::ClosureFnPointer |
 616             Adjust::MutToConstPointer |
 617             Adjust::Borrow(_) |
 618             Adjust::Unsize => {}
 619
 620             Adjust::Deref(_) => {
 621                 if let Some(next_adjustment) = adjustments.peek() {
 622                     if let Adjust::Borrow(_) = next_adjustment.kind {
 623                         continue;
 624                     }
 625                 }
 626                 return NotPromotable;
 627             }
 628         }
 629     }
 630     Promotable
 631 }
 632
 633 impl<'a, 'gcx, 'tcx> euv::Delegate<'tcx> for CheckCrateVisitor<'a, 'gcx> {
 634     fn consume(&mut self,
 635                _consume_id: ast::NodeId,
 636                _consume_span: Span,
 637                _cmt: &mc::cmt_,
 638                _mode: euv::ConsumeMode) {}
 639
 640     fn borrow(&mut self,
 641               borrow_id: ast::NodeId,
 642               _borrow_span: Span,
 643               cmt: &mc::cmt_<'tcx>,
 644               _loan_region: ty::Region<'tcx>,
 645               bk: ty::BorrowKind,
 646               loan_cause: euv::LoanCause) {
 647         debug!(
 648             "borrow(borrow_id={:?}, cmt={:?}, bk={:?}, loan_cause={:?})",
 649             borrow_id,
 650             cmt,
 651             bk,
 652             loan_cause,
 653         );
 654
 655         // Kind of hacky, but we allow Unsafe coercions in constants.
 656         // These occur when we convert a &T or *T to a *U, as well as
 657         // when making a thin pointer (e.g., `*T`) into a fat pointer
 658         // (e.g., `*Trait`).
 659         if let euv::LoanCause::AutoUnsafe = loan_cause {
 660             return;
 661         }
 662
 663         let mut cur = cmt;
 664         loop {
 665             match cur.cat {
 666                 Categorization::Rvalue(..) => {
 667                     if loan_cause == euv::MatchDiscriminant {
 668                         // Ignore the dummy immutable borrow created by EUV.
 669                         break;
 670                     }
 671                     if bk.to_mutbl_lossy() == hir::MutMutable {
 672                         self.mut_rvalue_borrows.insert(borrow_id);
 673                     }
 674                     break;
 675                 }
 676                 Categorization::StaticItem => {
 677                     break;
 678                 }
 679                 Categorization::Deref(ref cmt, _) |
 680                 Categorization::Downcast(ref cmt, _) |
 681                 Categorization::Interior(ref cmt, _) => {
 682                     cur = cmt;
 683                 }
 684
 685                 Categorization::Upvar(..) |
 686                 Categorization::Local(..) => break,
 687             }
 688         }
 689     }
 690
 691     fn decl_without_init(&mut self, _id: ast::NodeId, _span: Span) {}
 692     fn mutate(&mut self,
 693               _assignment_id: ast::NodeId,
 694               _assignment_span: Span,
 695               _assignee_cmt: &mc::cmt_,
 696               _mode: euv::MutateMode) {
 697     }
 698
 699     fn matched_pat(&mut self, _: &hir::Pat, _: &mc::cmt_, _: euv::MatchMode) {}
 700
 701     fn consume_pat(&mut self, _consume_pat: &hir::Pat, _cmt: &mc::cmt_, _mode: euv::ConsumeMode) {}
 702 }