src/librustc_mir/util/elaborate_drops.rs

   1 // Copyright 2017 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 std::fmt;
  12 use rustc::hir;
  13 use rustc::mir::*;
  14 use rustc::middle::lang_items;
  15 use rustc::traits::Reveal;
  16 use rustc::ty::{self, Ty, TyCtxt};
  17 use rustc::ty::subst::Substs;
  18 use rustc::ty::util::IntTypeExt;
  19 use rustc_data_structures::indexed_vec::Idx;
  20 use util::patch::MirPatch;
  21
  22 use std::u32;
  23
  24 #[derive(Debug, PartialEq, Eq, Copy, Clone)]
  25 pub enum DropFlagState {
  26     Present, // i.e. initialized
  27     Absent, // i.e. deinitialized or "moved"
  28 }
  29
  30 impl DropFlagState {
  31     pub fn value(self) -> bool {
  32         match self {
  33             DropFlagState::Present => true,
  34             DropFlagState::Absent => false
  35         }
  36     }
  37 }
  38
  39 #[derive(Debug)]
  40 pub enum DropStyle {
  41     Dead,
  42     Static,
  43     Conditional,
  44     Open,
  45 }
  46
  47 #[derive(Debug)]
  48 pub enum DropFlagMode {
  49     Shallow,
  50     Deep
  51 }
  52
  53 #[derive(Copy, Clone, Debug)]
  54 pub enum Unwind {
  55     To(BasicBlock),
  56     InCleanup
  57 }
  58
  59 impl Unwind {
  60     fn is_cleanup(self) -> bool {
  61         match self {
  62             Unwind::To(..) => false,
  63             Unwind::InCleanup => true
  64         }
  65     }
  66
  67     fn into_option(self) -> Option<BasicBlock> {
  68         match self {
  69             Unwind::To(bb) => Some(bb),
  70             Unwind::InCleanup => None,
  71         }
  72     }
  73
  74     fn map<F>(self, f: F) -> Self where F: FnOnce(BasicBlock) -> BasicBlock {
  75         match self {
  76             Unwind::To(bb) => Unwind::To(f(bb)),
  77             Unwind::InCleanup => Unwind::InCleanup
  78         }
  79     }
  80 }
  81
  82 pub trait DropElaborator<'a, 'tcx: 'a> : fmt::Debug {
  83     type Path : Copy + fmt::Debug;
  84
  85     fn patch(&mut self) -> &mut MirPatch<'tcx>;
  86     fn mir(&self) -> &'a Mir<'tcx>;
  87     fn tcx(&self) -> TyCtxt<'a, 'tcx, 'tcx>;
  88     fn param_env(&self) -> ty::ParamEnv<'tcx>;
  89
  90     fn drop_style(&self, path: Self::Path, mode: DropFlagMode) -> DropStyle;
  91     fn get_drop_flag(&mut self, path: Self::Path) -> Option<Operand<'tcx>>;
  92     fn clear_drop_flag(&mut self, location: Location, path: Self::Path, mode: DropFlagMode);
  93
  94
  95     fn field_subpath(&self, path: Self::Path, field: Field) -> Option<Self::Path>;
  96     fn deref_subpath(&self, path: Self::Path) -> Option<Self::Path>;
  97     fn downcast_subpath(&self, path: Self::Path, variant: usize) -> Option<Self::Path>;
  98     fn array_subpath(&self, path: Self::Path, index: u32, size: u32) -> Option<Self::Path>;
  99 }
 100
 101 #[derive(Debug)]
 102 struct DropCtxt<'l, 'b: 'l, 'tcx: 'b, D>
 103     where D : DropElaborator<'b, 'tcx> + 'l
 104 {
 105     elaborator: &'l mut D,
 106
 107     source_info: SourceInfo,
 108
 109     place: &'l Place<'tcx>,
 110     path: D::Path,
 111     succ: BasicBlock,
 112     unwind: Unwind,
 113 }
 114
 115 pub fn elaborate_drop<'b, 'tcx, D>(
 116     elaborator: &mut D,
 117     source_info: SourceInfo,
 118     place: &Place<'tcx>,
 119     path: D::Path,
 120     succ: BasicBlock,
 121     unwind: Unwind,
 122     bb: BasicBlock)
 123     where D: DropElaborator<'b, 'tcx>
 124 {
 125     DropCtxt {
 126         elaborator, source_info, place, path, succ, unwind
 127     }.elaborate_drop(bb)
 128 }
 129
 130 impl<'l, 'b, 'tcx, D> DropCtxt<'l, 'b, 'tcx, D>
 131     where D: DropElaborator<'b, 'tcx>
 132 {
 133     fn place_ty(&self, place: &Place<'tcx>) -> Ty<'tcx> {
 134         place.ty(self.elaborator.mir(), self.tcx()).to_ty(self.tcx())
 135     }
 136
 137     fn tcx(&self) -> TyCtxt<'b, 'tcx, 'tcx> {
 138         self.elaborator.tcx()
 139     }
 140
 141     /// This elaborates a single drop instruction, located at `bb`, and
 142     /// patches over it.
 143     ///
 144     /// The elaborated drop checks the drop flags to only drop what
 145     /// is initialized.
 146     ///
 147     /// In addition, the relevant drop flags also need to be cleared
 148     /// to avoid double-drops. However, in the middle of a complex
 149     /// drop, one must avoid clearing some of the flags before they
 150     /// are read, as that would cause a memory leak.
 151     ///
 152     /// In particular, when dropping an ADT, multiple fields may be
 153     /// joined together under the `rest` subpath. They are all controlled
 154     /// by the primary drop flag, but only the last rest-field dropped
 155     /// should clear it (and it must also not clear anything else).
 156     ///
 157     /// FIXME: I think we should just control the flags externally
 158     /// and then we do not need this machinery.
 159     pub fn elaborate_drop<'a>(&mut self, bb: BasicBlock) {
 160         debug!("elaborate_drop({:?})", self);
 161         let style = self.elaborator.drop_style(self.path, DropFlagMode::Deep);
 162         debug!("elaborate_drop({:?}): live - {:?}", self, style);
 163         match style {
 164             DropStyle::Dead => {
 165                 self.elaborator.patch().patch_terminator(bb, TerminatorKind::Goto {
 166                     target: self.succ
 167                 });
 168             }
 169             DropStyle::Static => {
 170                 let loc = self.terminator_loc(bb);
 171                 self.elaborator.clear_drop_flag(loc, self.path, DropFlagMode::Deep);
 172                 self.elaborator.patch().patch_terminator(bb, TerminatorKind::Drop {
 173                     location: self.place.clone(),
 174                     target: self.succ,
 175                     unwind: self.unwind.into_option(),
 176                 });
 177             }
 178             DropStyle::Conditional => {
 179                 let unwind = self.unwind; // FIXME(#43234)
 180                 let succ = self.succ;
 181                 let drop_bb = self.complete_drop(Some(DropFlagMode::Deep), succ, unwind);
 182                 self.elaborator.patch().patch_terminator(bb, TerminatorKind::Goto {
 183                     target: drop_bb
 184                 });
 185             }
 186             DropStyle::Open => {
 187                 let drop_bb = self.open_drop();
 188                 self.elaborator.patch().patch_terminator(bb, TerminatorKind::Goto {
 189                     target: drop_bb
 190                 });
 191             }
 192         }
 193     }
 194
 195     /// Return the place and move path for each field of `variant`,
 196     /// (the move path is `None` if the field is a rest field).
 197     fn move_paths_for_fields(&self,
 198                              base_place: &Place<'tcx>,
 199                              variant_path: D::Path,
 200                              variant: &'tcx ty::VariantDef,
 201                              substs: &'tcx Substs<'tcx>)
 202                              -> Vec<(Place<'tcx>, Option<D::Path>)>
 203     {
 204         variant.fields.iter().enumerate().map(|(i, f)| {
 205             let field = Field::new(i);
 206             let subpath = self.elaborator.field_subpath(variant_path, field);
 207
 208             assert_eq!(self.elaborator.param_env().reveal, Reveal::All);
 209             let field_ty = self.tcx().normalize_erasing_regions(
 210                 self.elaborator.param_env(),
 211                 f.ty(self.tcx(), substs),
 212             );
 213             (base_place.clone().field(field, field_ty), subpath)
 214         }).collect()
 215     }
 216
 217     fn drop_subpath(&mut self,
 218                     place: &Place<'tcx>,
 219                     path: Option<D::Path>,
 220                     succ: BasicBlock,
 221                     unwind: Unwind)
 222                     -> BasicBlock
 223     {
 224         if let Some(path) = path {
 225             debug!("drop_subpath: for std field {:?}", place);
 226
 227             DropCtxt {
 228                 elaborator: self.elaborator,
 229                 source_info: self.source_info,
 230                 path, place, succ, unwind,
 231             }.elaborated_drop_block()
 232         } else {
 233             debug!("drop_subpath: for rest field {:?}", place);
 234
 235             DropCtxt {
 236                 elaborator: self.elaborator,
 237                 source_info: self.source_info,
 238                 place, succ, unwind,
 239                 // Using `self.path` here to condition the drop on
 240                 // our own drop flag.
 241                 path: self.path
 242             }.complete_drop(None, succ, unwind)
 243         }
 244     }
 245
 246     /// Create one-half of the drop ladder for a list of fields, and return
 247     /// the list of steps in it in reverse order, with the first step
 248     /// dropping 0 fields and so on.
 249     ///
 250     /// `unwind_ladder` is such a list of steps in reverse order,
 251     /// which is called if the matching step of the drop glue panics.
 252     fn drop_halfladder(&mut self,
 253                        unwind_ladder: &[Unwind],
 254                        mut succ: BasicBlock,
 255                        fields: &[(Place<'tcx>, Option<D::Path>)])
 256                        -> Vec<BasicBlock>
 257     {
 258         Some(succ).into_iter().chain(
 259             fields.iter().rev().zip(unwind_ladder)
 260                 .map(|(&(ref place, path), &unwind_succ)| {
 261                     succ = self.drop_subpath(place, path, succ, unwind_succ);
 262                     succ
 263                 })
 264         ).collect()
 265     }
 266
 267     fn drop_ladder_bottom(&mut self) -> (BasicBlock, Unwind) {
 268         // Clear the "master" drop flag at the end. This is needed
 269         // because the "master" drop protects the ADT's discriminant,
 270         // which is invalidated after the ADT is dropped.
 271         let (succ, unwind) = (self.succ, self.unwind); // FIXME(#43234)
 272         (
 273             self.drop_flag_reset_block(DropFlagMode::Shallow, succ, unwind),
 274             unwind.map(|unwind| {
 275                 self.drop_flag_reset_block(DropFlagMode::Shallow, unwind, Unwind::InCleanup)
 276             })
 277         )
 278     }
 279
 280     /// Create a full drop ladder, consisting of 2 connected half-drop-ladders
 281     ///
 282     /// For example, with 3 fields, the drop ladder is
 283     ///
 284     /// .d0:
 285     ///     ELAB(drop location.0 [target=.d1, unwind=.c1])
 286     /// .d1:
 287     ///     ELAB(drop location.1 [target=.d2, unwind=.c2])
 288     /// .d2:
 289     ///     ELAB(drop location.2 [target=`self.succ`, unwind=`self.unwind`])
 290     /// .c1:
 291     ///     ELAB(drop location.1 [target=.c2])
 292     /// .c2:
 293     ///     ELAB(drop location.2 [target=`self.unwind`])
 294     ///
 295     /// NOTE: this does not clear the master drop flag, so you need
 296     /// to point succ/unwind on a `drop_ladder_bottom`.
 297     fn drop_ladder<'a>(&mut self,
 298                        fields: Vec<(Place<'tcx>, Option<D::Path>)>,
 299                        succ: BasicBlock,
 300                        unwind: Unwind)
 301                        -> (BasicBlock, Unwind)
 302     {
 303         debug!("drop_ladder({:?}, {:?})", self, fields);
 304
 305         let mut fields = fields;
 306         fields.retain(|&(ref place, _)| {
 307             self.place_ty(place).needs_drop(self.tcx(), self.elaborator.param_env())
 308         });
 309
 310         debug!("drop_ladder - fields needing drop: {:?}", fields);
 311
 312         let unwind_ladder = vec![Unwind::InCleanup; fields.len() + 1];
 313         let unwind_ladder: Vec<_> = if let Unwind::To(target) = unwind {
 314             let halfladder = self.drop_halfladder(&unwind_ladder, target, &fields);
 315             halfladder.into_iter().map(Unwind::To).collect()
 316         } else {
 317             unwind_ladder
 318         };
 319
 320         let normal_ladder =
 321             self.drop_halfladder(&unwind_ladder, succ, &fields);
 322
 323         (*normal_ladder.last().unwrap(), *unwind_ladder.last().unwrap())
 324     }
 325
 326     fn open_drop_for_tuple<'a>(&mut self, tys: &[Ty<'tcx>])
 327                                -> BasicBlock
 328     {
 329         debug!("open_drop_for_tuple({:?}, {:?})", self, tys);
 330
 331         let fields = tys.iter().enumerate().map(|(i, &ty)| {
 332             (self.place.clone().field(Field::new(i), ty),
 333              self.elaborator.field_subpath(self.path, Field::new(i)))
 334         }).collect();
 335
 336         let (succ, unwind) = self.drop_ladder_bottom();
 337         self.drop_ladder(fields, succ, unwind).0
 338     }
 339
 340     fn open_drop_for_box<'a>(&mut self, adt: &'tcx ty::AdtDef, substs: &'tcx Substs<'tcx>)
 341                              -> BasicBlock
 342     {
 343         debug!("open_drop_for_box({:?}, {:?}, {:?})", self, adt, substs);
 344
 345         let interior = self.place.clone().deref();
 346         let interior_path = self.elaborator.deref_subpath(self.path);
 347
 348         let succ = self.succ; // FIXME(#43234)
 349         let unwind = self.unwind;
 350         let succ = self.box_free_block(adt, substs, succ, unwind);
 351         let unwind_succ = self.unwind.map(|unwind| {
 352             self.box_free_block(adt, substs, unwind, Unwind::InCleanup)
 353         });
 354
 355         self.drop_subpath(&interior, interior_path, succ, unwind_succ)
 356     }
 357
 358     fn open_drop_for_adt<'a>(&mut self, adt: &'tcx ty::AdtDef, substs: &'tcx Substs<'tcx>)
 359                              -> BasicBlock {
 360         debug!("open_drop_for_adt({:?}, {:?}, {:?})", self, adt, substs);
 361         if adt.variants.len() == 0 {
 362             return self.elaborator.patch().new_block(BasicBlockData {
 363                 statements: vec![],
 364                 terminator: Some(Terminator {
 365                     source_info: self.source_info,
 366                     kind: TerminatorKind::Unreachable
 367                 }),
 368                 is_cleanup: self.unwind.is_cleanup()
 369             });
 370         }
 371
 372         let skip_contents =
 373             adt.is_union() || Some(adt.did) == self.tcx().lang_items().manually_drop();
 374         let contents_drop = if skip_contents {
 375             (self.succ, self.unwind)
 376         } else {
 377             self.open_drop_for_adt_contents(adt, substs)
 378         };
 379
 380         if adt.has_dtor(self.tcx()) {
 381             self.destructor_call_block(contents_drop)
 382         } else {
 383             contents_drop.0
 384         }
 385     }
 386
 387     fn open_drop_for_adt_contents(&mut self, adt: &'tcx ty::AdtDef,
 388                                   substs: &'tcx Substs<'tcx>)
 389                                   -> (BasicBlock, Unwind) {
 390         let (succ, unwind) = self.drop_ladder_bottom();
 391         if !adt.is_enum() {
 392             let fields = self.move_paths_for_fields(
 393                 self.place,
 394                 self.path,
 395                 &adt.variants[0],
 396                 substs
 397             );
 398             self.drop_ladder(fields, succ, unwind)
 399         } else {
 400             self.open_drop_for_multivariant(adt, substs, succ, unwind)
 401         }
 402     }
 403
 404     fn open_drop_for_multivariant(&mut self, adt: &'tcx ty::AdtDef,
 405                                   substs: &'tcx Substs<'tcx>,
 406                                   succ: BasicBlock,
 407                                   unwind: Unwind)
 408                                   -> (BasicBlock, Unwind) {
 409         let mut values = Vec::with_capacity(adt.variants.len());
 410         let mut normal_blocks = Vec::with_capacity(adt.variants.len());
 411         let mut unwind_blocks = if unwind.is_cleanup() {
 412             None
 413         } else {
 414             Some(Vec::with_capacity(adt.variants.len()))
 415         };
 416
 417         let mut have_otherwise = false;
 418
 419         for (variant_index, discr) in adt.discriminants(self.tcx()).enumerate() {
 420             let subpath = self.elaborator.downcast_subpath(
 421                 self.path, variant_index);
 422             if let Some(variant_path) = subpath {
 423                 let base_place = self.place.clone().elem(
 424                     ProjectionElem::Downcast(adt, variant_index)
 425                         );
 426                 let fields = self.move_paths_for_fields(
 427                     &base_place,
 428                     variant_path,
 429                     &adt.variants[variant_index],
 430                     substs);
 431                 values.push(discr.val);
 432                 if let Unwind::To(unwind) = unwind {
 433                     // We can't use the half-ladder from the original
 434                     // drop ladder, because this breaks the
 435                     // "funclet can't have 2 successor funclets"
 436                     // requirement from MSVC:
 437                     //
 438                     //           switch       unwind-switch
 439                     //          /      \         /        \
 440                     //         v1.0    v2.0  v2.0-unwind  v1.0-unwind
 441                     //         |        |      /             |
 442                     //    v1.1-unwind  v2.1-unwind           |
 443                     //      ^                                |
 444                     //       \-------------------------------/
 445                     //
 446                     // Create a duplicate half-ladder to avoid that. We
 447                     // could technically only do this on MSVC, but I
 448                     // I want to minimize the divergence between MSVC
 449                     // and non-MSVC.
 450
 451                     let unwind_blocks = unwind_blocks.as_mut().unwrap();
 452                     let unwind_ladder = vec![Unwind::InCleanup; fields.len() + 1];
 453                     let halfladder =
 454                         self.drop_halfladder(&unwind_ladder, unwind, &fields);
 455                     unwind_blocks.push(halfladder.last().cloned().unwrap());
 456                 }
 457                 let (normal, _) = self.drop_ladder(fields, succ, unwind);
 458                 normal_blocks.push(normal);
 459             } else {
 460                 have_otherwise = true;
 461             }
 462         }
 463
 464         if have_otherwise {
 465             normal_blocks.push(self.drop_block(succ, unwind));
 466             if let Unwind::To(unwind) = unwind {
 467                 unwind_blocks.as_mut().unwrap().push(
 468                     self.drop_block(unwind, Unwind::InCleanup)
 469                         );
 470             }
 471         } else {
 472             values.pop();
 473         }
 474
 475         (self.adt_switch_block(adt, normal_blocks, &values, succ, unwind),
 476          unwind.map(|unwind| {
 477              self.adt_switch_block(
 478                  adt, unwind_blocks.unwrap(), &values, unwind, Unwind::InCleanup
 479              )
 480          }))
 481     }
 482
 483     fn adt_switch_block(&mut self,
 484                         adt: &'tcx ty::AdtDef,
 485                         blocks: Vec<BasicBlock>,
 486                         values: &[u128],
 487                         succ: BasicBlock,
 488                         unwind: Unwind)
 489                         -> BasicBlock {
 490         // If there are multiple variants, then if something
 491         // is present within the enum the discriminant, tracked
 492         // by the rest path, must be initialized.
 493         //
 494         // Additionally, we do not want to switch on the
 495         // discriminant after it is free-ed, because that
 496         // way lies only trouble.
 497         let discr_ty = adt.repr.discr_type().to_ty(self.tcx());
 498         let discr = Place::Local(self.new_temp(discr_ty));
 499         let discr_rv = Rvalue::Discriminant(self.place.clone());
 500         let switch_block = BasicBlockData {
 501             statements: vec![self.assign(&discr, discr_rv)],
 502             terminator: Some(Terminator {
 503                 source_info: self.source_info,
 504                 kind: TerminatorKind::SwitchInt {
 505                     discr: Operand::Move(discr),
 506                     switch_ty: discr_ty,
 507                     values: From::from(values.to_owned()),
 508                     targets: blocks,
 509                 }
 510             }),
 511             is_cleanup: unwind.is_cleanup(),
 512         };
 513         let switch_block = self.elaborator.patch().new_block(switch_block);
 514         self.drop_flag_test_block(switch_block, succ, unwind)
 515     }
 516
 517     fn destructor_call_block<'a>(&mut self, (succ, unwind): (BasicBlock, Unwind))
 518                                  -> BasicBlock
 519     {
 520         debug!("destructor_call_block({:?}, {:?})", self, succ);
 521         let tcx = self.tcx();
 522         let drop_trait = tcx.lang_items().drop_trait().unwrap();
 523         let drop_fn = tcx.associated_items(drop_trait).next().unwrap();
 524         let ty = self.place_ty(self.place);
 525         let substs = tcx.mk_substs_trait(ty, &[]);
 526
 527         let ref_ty = tcx.mk_ref(tcx.types.re_erased, ty::TypeAndMut {
 528             ty,
 529             mutbl: hir::Mutability::MutMutable
 530         });
 531         let ref_place = self.new_temp(ref_ty);
 532         let unit_temp = Place::Local(self.new_temp(tcx.mk_unit()));
 533
 534         let result = BasicBlockData {
 535             statements: vec![self.assign(
 536                 &Place::Local(ref_place),
 537                 Rvalue::Ref(tcx.types.re_erased,
 538                             BorrowKind::Mut { allow_two_phase_borrow: false },
 539                             self.place.clone())
 540             )],
 541             terminator: Some(Terminator {
 542                 kind: TerminatorKind::Call {
 543                     func: Operand::function_handle(tcx, drop_fn.def_id, substs,
 544                                                    self.source_info.span),
 545                     args: vec![Operand::Move(Place::Local(ref_place))],
 546                     destination: Some((unit_temp, succ)),
 547                     cleanup: unwind.into_option(),
 548                     from_hir_call: true,
 549                 },
 550                 source_info: self.source_info,
 551             }),
 552             is_cleanup: unwind.is_cleanup(),
 553         };
 554         self.elaborator.patch().new_block(result)
 555     }
 556
 557     /// create a loop that drops an array:
 558     ///
 559
 560     ///
 561     /// loop-block:
 562     ///    can_go = cur == length_or_end
 563     ///    if can_go then succ else drop-block
 564     /// drop-block:
 565     ///    if ptr_based {
 566     ///        ptr = &mut *cur
 567     ///        cur = cur.offset(1)
 568     ///    } else {
 569     ///        ptr = &mut P[cur]
 570     ///        cur = cur + 1
 571     ///    }
 572     ///    drop(ptr)
 573     fn drop_loop(&mut self,
 574                  succ: BasicBlock,
 575                  cur: Local,
 576                  length_or_end: &Place<'tcx>,
 577                  ety: Ty<'tcx>,
 578                  unwind: Unwind,
 579                  ptr_based: bool)
 580                  -> BasicBlock
 581     {
 582         let copy = |place: &Place<'tcx>| Operand::Copy(place.clone());
 583         let move_ = |place: &Place<'tcx>| Operand::Move(place.clone());
 584         let tcx = self.tcx();
 585
 586         let ref_ty = tcx.mk_ref(tcx.types.re_erased, ty::TypeAndMut {
 587             ty: ety,
 588             mutbl: hir::Mutability::MutMutable
 589         });
 590         let ptr = &Place::Local(self.new_temp(ref_ty));
 591         let can_go = &Place::Local(self.new_temp(tcx.types.bool));
 592
 593         let one = self.constant_usize(1);
 594         let (ptr_next, cur_next) = if ptr_based {
 595             (Rvalue::Ref(
 596                 tcx.types.re_erased,
 597                 BorrowKind::Mut { allow_two_phase_borrow: false },
 598                 Place::Projection(Box::new(Projection {
 599                     base: Place::Local(cur),
 600                     elem: ProjectionElem::Deref,
 601                 }))
 602              ),
 603              Rvalue::BinaryOp(BinOp::Offset, copy(&Place::Local(cur)), one))
 604         } else {
 605             (Rvalue::Ref(
 606                  tcx.types.re_erased,
 607                  BorrowKind::Mut { allow_two_phase_borrow: false },
 608                  self.place.clone().index(cur)),
 609              Rvalue::BinaryOp(BinOp::Add, copy(&Place::Local(cur)), one))
 610         };
 611
 612         let drop_block = BasicBlockData {
 613             statements: vec![
 614                 self.assign(ptr, ptr_next),
 615                 self.assign(&Place::Local(cur), cur_next)
 616             ],
 617             is_cleanup: unwind.is_cleanup(),
 618             terminator: Some(Terminator {
 619                 source_info: self.source_info,
 620                 // this gets overwritten by drop elaboration.
 621                 kind: TerminatorKind::Unreachable,
 622             })
 623         };
 624         let drop_block = self.elaborator.patch().new_block(drop_block);
 625
 626         let loop_block = BasicBlockData {
 627             statements: vec![
 628                 self.assign(can_go, Rvalue::BinaryOp(BinOp::Eq,
 629                                                      copy(&Place::Local(cur)),
 630                                                      copy(length_or_end)))
 631             ],
 632             is_cleanup: unwind.is_cleanup(),
 633             terminator: Some(Terminator {
 634                 source_info: self.source_info,
 635                 kind: TerminatorKind::if_(tcx, move_(can_go), succ, drop_block)
 636             })
 637         };
 638         let loop_block = self.elaborator.patch().new_block(loop_block);
 639
 640         self.elaborator.patch().patch_terminator(drop_block, TerminatorKind::Drop {
 641             location: ptr.clone().deref(),
 642             target: loop_block,
 643             unwind: unwind.into_option()
 644         });
 645
 646         loop_block
 647     }
 648
 649     fn open_drop_for_array(&mut self, ety: Ty<'tcx>, opt_size: Option<u64>) -> BasicBlock {
 650         debug!("open_drop_for_array({:?}, {:?})", ety, opt_size);
 651
 652         // if size_of::<ety>() == 0 {
 653         //     index_based_loop
 654         // } else {
 655         //     ptr_based_loop
 656         // }
 657
 658         if let Some(size) = opt_size {
 659             assert!(size <= (u32::MAX as u64),
 660                     "move out check doesn't implemented for array bigger then u32");
 661             let size = size as u32;
 662             let fields: Vec<(Place<'tcx>, Option<D::Path>)> = (0..size).map(|i| {
 663                 (self.place.clone().elem(ProjectionElem::ConstantIndex{
 664                     offset: i,
 665                     min_length: size,
 666                     from_end: false
 667                 }),
 668                  self.elaborator.array_subpath(self.path, i, size))
 669             }).collect();
 670
 671             if fields.iter().any(|(_,path)| path.is_some()) {
 672                 let (succ, unwind) = self.drop_ladder_bottom();
 673                 return self.drop_ladder(fields, succ, unwind).0
 674             }
 675         }
 676
 677         let move_ = |place: &Place<'tcx>| Operand::Move(place.clone());
 678         let tcx = self.tcx();
 679         let size = &Place::Local(self.new_temp(tcx.types.usize));
 680         let size_is_zero = &Place::Local(self.new_temp(tcx.types.bool));
 681         let base_block = BasicBlockData {
 682             statements: vec![
 683                 self.assign(size, Rvalue::NullaryOp(NullOp::SizeOf, ety)),
 684                 self.assign(size_is_zero, Rvalue::BinaryOp(BinOp::Eq,
 685                                                            move_(size),
 686                                                            self.constant_usize(0)))
 687             ],
 688             is_cleanup: self.unwind.is_cleanup(),
 689             terminator: Some(Terminator {
 690                 source_info: self.source_info,
 691                 kind: TerminatorKind::if_(
 692                     tcx,
 693                     move_(size_is_zero),
 694                     self.drop_loop_pair(ety, false),
 695                     self.drop_loop_pair(ety, true)
 696                 )
 697             })
 698         };
 699         self.elaborator.patch().new_block(base_block)
 700     }
 701
 702     // create a pair of drop-loops of `place`, which drops its contents
 703     // even in the case of 1 panic. If `ptr_based`, create a pointer loop,
 704     // otherwise create an index loop.
 705     fn drop_loop_pair(&mut self, ety: Ty<'tcx>, ptr_based: bool) -> BasicBlock {
 706         debug!("drop_loop_pair({:?}, {:?})", ety, ptr_based);
 707         let tcx = self.tcx();
 708         let iter_ty = if ptr_based {
 709             tcx.mk_mut_ptr(ety)
 710         } else {
 711             tcx.types.usize
 712         };
 713
 714         let cur = self.new_temp(iter_ty);
 715         let length = Place::Local(self.new_temp(tcx.types.usize));
 716         let length_or_end = if ptr_based {
 717             Place::Local(self.new_temp(iter_ty))
 718         } else {
 719             length.clone()
 720         };
 721
 722         let unwind = self.unwind.map(|unwind| {
 723             self.drop_loop(unwind,
 724                            cur,
 725                            &length_or_end,
 726                            ety,
 727                            Unwind::InCleanup,
 728                            ptr_based)
 729         });
 730
 731         let succ = self.succ; // FIXME(#43234)
 732         let loop_block = self.drop_loop(
 733             succ,
 734             cur,
 735             &length_or_end,
 736             ety,
 737             unwind,
 738             ptr_based);
 739
 740         let cur = Place::Local(cur);
 741         let zero = self.constant_usize(0);
 742         let mut drop_block_stmts = vec![];
 743         drop_block_stmts.push(self.assign(&length, Rvalue::Len(self.place.clone())));
 744         if ptr_based {
 745             let tmp_ty = tcx.mk_mut_ptr(self.place_ty(self.place));
 746             let tmp = Place::Local(self.new_temp(tmp_ty));
 747             // tmp = &mut P;
 748             // cur = tmp as *mut T;
 749             // end = Offset(cur, len);
 750             drop_block_stmts.push(self.assign(&tmp, Rvalue::Ref(
 751                 tcx.types.re_erased,
 752                 BorrowKind::Mut { allow_two_phase_borrow: false },
 753                 self.place.clone()
 754             )));
 755             drop_block_stmts.push(self.assign(&cur, Rvalue::Cast(
 756                 CastKind::Misc, Operand::Move(tmp.clone()), iter_ty
 757             )));
 758             drop_block_stmts.push(self.assign(&length_or_end,
 759                 Rvalue::BinaryOp(BinOp::Offset,
 760                      Operand::Copy(cur.clone()), Operand::Move(length.clone())
 761             )));
 762         } else {
 763             // index = 0 (length already pushed)
 764             drop_block_stmts.push(self.assign(&cur, Rvalue::Use(zero)));
 765         }
 766         let drop_block = self.elaborator.patch().new_block(BasicBlockData {
 767             statements: drop_block_stmts,
 768             is_cleanup: unwind.is_cleanup(),
 769             terminator: Some(Terminator {
 770                 source_info: self.source_info,
 771                 kind: TerminatorKind::Goto { target: loop_block }
 772             })
 773         });
 774
 775         // FIXME(#34708): handle partially-dropped array/slice elements.
 776         let reset_block = self.drop_flag_reset_block(DropFlagMode::Deep, drop_block, unwind);
 777         self.drop_flag_test_block(reset_block, succ, unwind)
 778     }
 779
 780     /// The slow-path - create an "open", elaborated drop for a type
 781     /// which is moved-out-of only partially, and patch `bb` to a jump
 782     /// to it. This must not be called on ADTs with a destructor,
 783     /// as these can't be moved-out-of, except for `Box<T>`, which is
 784     /// special-cased.
 785     ///
 786     /// This creates a "drop ladder" that drops the needed fields of the
 787     /// ADT, both in the success case or if one of the destructors fail.
 788     fn open_drop<'a>(&mut self) -> BasicBlock {
 789         let ty = self.place_ty(self.place);
 790         match ty.sty {
 791             ty::Closure(def_id, substs) => {
 792                 let tys : Vec<_> = substs.upvar_tys(def_id, self.tcx()).collect();
 793                 self.open_drop_for_tuple(&tys)
 794             }
 795             // Note that `elaborate_drops` only drops the upvars of a generator,
 796             // and this is ok because `open_drop` here can only be reached
 797             // within that own generator's resume function.
 798             // This should only happen for the self argument on the resume function.
 799             // It effetively only contains upvars until the generator transformation runs.
 800             // See librustc_mir/transform/generator.rs for more details.
 801             ty::Generator(def_id, substs, _) => {
 802                 let tys : Vec<_> = substs.upvar_tys(def_id, self.tcx()).collect();
 803                 self.open_drop_for_tuple(&tys)
 804             }
 805             ty::Tuple(tys) => {
 806                 self.open_drop_for_tuple(tys)
 807             }
 808             ty::Adt(def, substs) => {
 809                 if def.is_box() {
 810                     self.open_drop_for_box(def, substs)
 811                 } else {
 812                     self.open_drop_for_adt(def, substs)
 813                 }
 814             }
 815             ty::Dynamic(..) => {
 816                 let unwind = self.unwind; // FIXME(#43234)
 817                 let succ = self.succ;
 818                 self.complete_drop(Some(DropFlagMode::Deep), succ, unwind)
 819             }
 820             ty::Array(ety, size) => {
 821                 let size = size.assert_usize(self.tcx());
 822                 self.open_drop_for_array(ety, size)
 823             },
 824             ty::Slice(ety) => self.open_drop_for_array(ety, None),
 825
 826             _ => bug!("open drop from non-ADT `{:?}`", ty)
 827         }
 828     }
 829
 830     /// Return a basic block that drop a place using the context
 831     /// and path in `c`. If `mode` is something, also clear `c`
 832     /// according to it.
 833     ///
 834     /// if FLAG(self.path)
 835     ///     if let Some(mode) = mode: FLAG(self.path)[mode] = false
 836     ///     drop(self.place)
 837     fn complete_drop<'a>(&mut self,
 838                          drop_mode: Option<DropFlagMode>,
 839                          succ: BasicBlock,
 840                          unwind: Unwind) -> BasicBlock
 841     {
 842         debug!("complete_drop({:?},{:?})", self, drop_mode);
 843
 844         let drop_block = self.drop_block(succ, unwind);
 845         let drop_block = if let Some(mode) = drop_mode {
 846             self.drop_flag_reset_block(mode, drop_block, unwind)
 847         } else {
 848             drop_block
 849         };
 850
 851         self.drop_flag_test_block(drop_block, succ, unwind)
 852     }
 853
 854     fn drop_flag_reset_block(&mut self,
 855                              mode: DropFlagMode,
 856                              succ: BasicBlock,
 857                              unwind: Unwind) -> BasicBlock
 858     {
 859         debug!("drop_flag_reset_block({:?},{:?})", self, mode);
 860
 861         let block = self.new_block(unwind, TerminatorKind::Goto { target: succ });
 862         let block_start = Location { block: block, statement_index: 0 };
 863         self.elaborator.clear_drop_flag(block_start, self.path, mode);
 864         block
 865     }
 866
 867     fn elaborated_drop_block<'a>(&mut self) -> BasicBlock {
 868         debug!("elaborated_drop_block({:?})", self);
 869         let unwind = self.unwind; // FIXME(#43234)
 870         let succ = self.succ;
 871         let blk = self.drop_block(succ, unwind);
 872         self.elaborate_drop(blk);
 873         blk
 874     }
 875
 876     fn box_free_block<'a>(
 877         &mut self,
 878         adt: &'tcx ty::AdtDef,
 879         substs: &'tcx Substs<'tcx>,
 880         target: BasicBlock,
 881         unwind: Unwind,
 882     ) -> BasicBlock {
 883         let block = self.unelaborated_free_block(adt, substs, target, unwind);
 884         self.drop_flag_test_block(block, target, unwind)
 885     }
 886
 887     fn unelaborated_free_block<'a>(
 888         &mut self,
 889         adt: &'tcx ty::AdtDef,
 890         substs: &'tcx Substs<'tcx>,
 891         target: BasicBlock,
 892         unwind: Unwind
 893     ) -> BasicBlock {
 894         let tcx = self.tcx();
 895         let unit_temp = Place::Local(self.new_temp(tcx.mk_unit()));
 896         let free_func = tcx.require_lang_item(lang_items::BoxFreeFnLangItem);
 897         let args = adt.variants[0].fields.iter().enumerate().map(|(i, f)| {
 898             let field = Field::new(i);
 899             let field_ty = f.ty(self.tcx(), substs);
 900             Operand::Move(self.place.clone().field(field, field_ty))
 901         }).collect();
 902
 903         let call = TerminatorKind::Call {
 904             func: Operand::function_handle(tcx, free_func, substs, self.source_info.span),
 905             args: args,
 906             destination: Some((unit_temp, target)),
 907             cleanup: None,
 908             from_hir_call: false,
 909         }; // FIXME(#43234)
 910         let free_block = self.new_block(unwind, call);
 911
 912         let block_start = Location { block: free_block, statement_index: 0 };
 913         self.elaborator.clear_drop_flag(block_start, self.path, DropFlagMode::Shallow);
 914         free_block
 915     }
 916
 917     fn drop_block<'a>(&mut self, target: BasicBlock, unwind: Unwind) -> BasicBlock {
 918         let block = TerminatorKind::Drop {
 919             location: self.place.clone(),
 920             target,
 921             unwind: unwind.into_option()
 922         };
 923         self.new_block(unwind, block)
 924     }
 925
 926     fn drop_flag_test_block(&mut self,
 927                             on_set: BasicBlock,
 928                             on_unset: BasicBlock,
 929                             unwind: Unwind)
 930                             -> BasicBlock
 931     {
 932         let style = self.elaborator.drop_style(self.path, DropFlagMode::Shallow);
 933         debug!("drop_flag_test_block({:?},{:?},{:?},{:?}) - {:?}",
 934                self, on_set, on_unset, unwind, style);
 935
 936         match style {
 937             DropStyle::Dead => on_unset,
 938             DropStyle::Static => on_set,
 939             DropStyle::Conditional | DropStyle::Open => {
 940                 let flag = self.elaborator.get_drop_flag(self.path).unwrap();
 941                 let term = TerminatorKind::if_(self.tcx(), flag, on_set, on_unset);
 942                 self.new_block(unwind, term)
 943             }
 944         }
 945     }
 946
 947     fn new_block<'a>(&mut self,
 948                      unwind: Unwind,
 949                      k: TerminatorKind<'tcx>)
 950                      -> BasicBlock
 951     {
 952         self.elaborator.patch().new_block(BasicBlockData {
 953             statements: vec![],
 954             terminator: Some(Terminator {
 955                 source_info: self.source_info, kind: k
 956             }),
 957             is_cleanup: unwind.is_cleanup()
 958         })
 959     }
 960
 961     fn new_temp(&mut self, ty: Ty<'tcx>) -> Local {
 962         self.elaborator.patch().new_temp(ty, self.source_info.span)
 963     }
 964
 965     fn terminator_loc(&mut self, bb: BasicBlock) -> Location {
 966         let mir = self.elaborator.mir();
 967         self.elaborator.patch().terminator_loc(mir, bb)
 968     }
 969
 970     fn constant_usize(&self, val: u16) -> Operand<'tcx> {
 971         Operand::Constant(box Constant {
 972             span: self.source_info.span,
 973             ty: self.tcx().types.usize,
 974             user_ty: None,
 975             literal: ty::Const::from_usize(self.tcx(), val.into()),
 976         })
 977     }
 978
 979     fn assign(&self, lhs: &Place<'tcx>, rhs: Rvalue<'tcx>) -> Statement<'tcx> {
 980         Statement {
 981             source_info: self.source_info,
 982             kind: StatementKind::Assign(lhs.clone(), box rhs)
 983         }
 984     }
 985 }