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::const_val::{ConstInt, ConstVal};
  15 use rustc::middle::lang_items;
  16 use rustc::ty::{self, Ty, TyCtxt};
  17 use rustc::ty::subst::{Kind, Substs};
  18 use rustc::ty::util::IntTypeExt;
  19 use rustc_data_structures::indexed_vec::Idx;
  20 use util::patch::MirPatch;
  21
  22 use std::{iter, 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(#6393)
 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             let field_ty =
 209                 self.tcx().normalize_associated_type_in_env(
 210                     &f.ty(self.tcx(), substs),
 211                     self.elaborator.param_env()
 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(#6393)
 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, ty: Ty<'tcx>) -> BasicBlock
 341     {
 342         debug!("open_drop_for_box({:?}, {:?})", self, ty);
 343
 344         let interior = self.place.clone().deref();
 345         let interior_path = self.elaborator.deref_subpath(self.path);
 346
 347         let succ = self.succ; // FIXME(#6393)
 348         let unwind = self.unwind;
 349         let succ = self.box_free_block(ty, succ, unwind);
 350         let unwind_succ = self.unwind.map(|unwind| {
 351             self.box_free_block(ty, unwind, Unwind::InCleanup)
 352         });
 353
 354         self.drop_subpath(&interior, interior_path, succ, unwind_succ)
 355     }
 356
 357     fn open_drop_for_adt<'a>(&mut self, adt: &'tcx ty::AdtDef, substs: &'tcx Substs<'tcx>)
 358                              -> BasicBlock {
 359         debug!("open_drop_for_adt({:?}, {:?}, {:?})", self, adt, substs);
 360         if adt.variants.len() == 0 {
 361             return self.elaborator.patch().new_block(BasicBlockData {
 362                 statements: vec![],
 363                 terminator: Some(Terminator {
 364                     source_info: self.source_info,
 365                     kind: TerminatorKind::Unreachable
 366                 }),
 367                 is_cleanup: self.unwind.is_cleanup()
 368             });
 369         }
 370
 371         let contents_drop = if adt.is_union() {
 372             (self.succ, self.unwind)
 373         } else {
 374             self.open_drop_for_adt_contents(adt, substs)
 375         };
 376
 377         if adt.has_dtor(self.tcx()) {
 378             self.destructor_call_block(contents_drop)
 379         } else {
 380             contents_drop.0
 381         }
 382     }
 383
 384     fn open_drop_for_adt_contents(&mut self, adt: &'tcx ty::AdtDef,
 385                                   substs: &'tcx Substs<'tcx>)
 386                                   -> (BasicBlock, Unwind) {
 387         let (succ, unwind) = self.drop_ladder_bottom();
 388         if !adt.is_enum() {
 389             let fields = self.move_paths_for_fields(
 390                 self.place,
 391                 self.path,
 392                 &adt.variants[0],
 393                 substs
 394             );
 395             self.drop_ladder(fields, succ, unwind)
 396         } else {
 397             self.open_drop_for_multivariant(adt, substs, succ, unwind)
 398         }
 399     }
 400
 401     fn open_drop_for_multivariant(&mut self, adt: &'tcx ty::AdtDef,
 402                                   substs: &'tcx Substs<'tcx>,
 403                                   succ: BasicBlock,
 404                                   unwind: Unwind)
 405                                   -> (BasicBlock, Unwind) {
 406         let mut values = Vec::with_capacity(adt.variants.len());
 407         let mut normal_blocks = Vec::with_capacity(adt.variants.len());
 408         let mut unwind_blocks = if unwind.is_cleanup() {
 409             None
 410         } else {
 411             Some(Vec::with_capacity(adt.variants.len()))
 412         };
 413
 414         let mut have_otherwise = false;
 415
 416         for (variant_index, discr) in adt.discriminants(self.tcx()).enumerate() {
 417             let subpath = self.elaborator.downcast_subpath(
 418                 self.path, variant_index);
 419             if let Some(variant_path) = subpath {
 420                 let base_place = self.place.clone().elem(
 421                     ProjectionElem::Downcast(adt, variant_index)
 422                         );
 423                 let fields = self.move_paths_for_fields(
 424                     &base_place,
 425                     variant_path,
 426                     &adt.variants[variant_index],
 427                     substs);
 428                 values.push(discr);
 429                 if let Unwind::To(unwind) = unwind {
 430                     // We can't use the half-ladder from the original
 431                     // drop ladder, because this breaks the
 432                     // "funclet can't have 2 successor funclets"
 433                     // requirement from MSVC:
 434                     //
 435                     //           switch       unwind-switch
 436                     //          /      \         /        \
 437                     //         v1.0    v2.0  v2.0-unwind  v1.0-unwind
 438                     //         |        |      /             |
 439                     //    v1.1-unwind  v2.1-unwind           |
 440                     //      ^                                |
 441                     //       \-------------------------------/
 442                     //
 443                     // Create a duplicate half-ladder to avoid that. We
 444                     // could technically only do this on MSVC, but I
 445                     // I want to minimize the divergence between MSVC
 446                     // and non-MSVC.
 447
 448                     let unwind_blocks = unwind_blocks.as_mut().unwrap();
 449                     let unwind_ladder = vec![Unwind::InCleanup; fields.len() + 1];
 450                     let halfladder =
 451                         self.drop_halfladder(&unwind_ladder, unwind, &fields);
 452                     unwind_blocks.push(halfladder.last().cloned().unwrap());
 453                 }
 454                 let (normal, _) = self.drop_ladder(fields, succ, unwind);
 455                 normal_blocks.push(normal);
 456             } else {
 457                 have_otherwise = true;
 458             }
 459         }
 460
 461         if have_otherwise {
 462             normal_blocks.push(self.drop_block(succ, unwind));
 463             if let Unwind::To(unwind) = unwind {
 464                 unwind_blocks.as_mut().unwrap().push(
 465                     self.drop_block(unwind, Unwind::InCleanup)
 466                         );
 467             }
 468         } else {
 469             values.pop();
 470         }
 471
 472         (self.adt_switch_block(adt, normal_blocks, &values, succ, unwind),
 473          unwind.map(|unwind| {
 474              self.adt_switch_block(
 475                  adt, unwind_blocks.unwrap(), &values, unwind, Unwind::InCleanup
 476              )
 477          }))
 478     }
 479
 480     fn adt_switch_block(&mut self,
 481                         adt: &'tcx ty::AdtDef,
 482                         blocks: Vec<BasicBlock>,
 483                         values: &[ConstInt],
 484                         succ: BasicBlock,
 485                         unwind: Unwind)
 486                         -> BasicBlock {
 487         // If there are multiple variants, then if something
 488         // is present within the enum the discriminant, tracked
 489         // by the rest path, must be initialized.
 490         //
 491         // Additionally, we do not want to switch on the
 492         // discriminant after it is free-ed, because that
 493         // way lies only trouble.
 494         let discr_ty = adt.repr.discr_type().to_ty(self.tcx());
 495         let discr = Place::Local(self.new_temp(discr_ty));
 496         let discr_rv = Rvalue::Discriminant(self.place.clone());
 497         let switch_block = BasicBlockData {
 498             statements: vec![self.assign(&discr, discr_rv)],
 499             terminator: Some(Terminator {
 500                 source_info: self.source_info,
 501                 kind: TerminatorKind::SwitchInt {
 502                     discr: Operand::Move(discr),
 503                     switch_ty: discr_ty,
 504                     values: From::from(values.to_owned()),
 505                     targets: blocks,
 506                 }
 507             }),
 508             is_cleanup: unwind.is_cleanup(),
 509         };
 510         let switch_block = self.elaborator.patch().new_block(switch_block);
 511         self.drop_flag_test_block(switch_block, succ, unwind)
 512     }
 513
 514     fn destructor_call_block<'a>(&mut self, (succ, unwind): (BasicBlock, Unwind))
 515                                  -> BasicBlock
 516     {
 517         debug!("destructor_call_block({:?}, {:?})", self, succ);
 518         let tcx = self.tcx();
 519         let drop_trait = tcx.lang_items().drop_trait().unwrap();
 520         let drop_fn = tcx.associated_items(drop_trait).next().unwrap();
 521         let ty = self.place_ty(self.place);
 522         let substs = tcx.mk_substs(iter::once(Kind::from(ty)));
 523
 524         let ref_ty = tcx.mk_ref(tcx.types.re_erased, ty::TypeAndMut {
 525             ty,
 526             mutbl: hir::Mutability::MutMutable
 527         });
 528         let ref_place = self.new_temp(ref_ty);
 529         let unit_temp = Place::Local(self.new_temp(tcx.mk_nil()));
 530
 531         let result = BasicBlockData {
 532             statements: vec![self.assign(
 533                 &Place::Local(ref_place),
 534                 Rvalue::Ref(tcx.types.re_erased, BorrowKind::Mut, self.place.clone())
 535             )],
 536             terminator: Some(Terminator {
 537                 kind: TerminatorKind::Call {
 538                     func: Operand::function_handle(tcx, drop_fn.def_id, substs,
 539                                                    self.source_info.span),
 540                     args: vec![Operand::Move(Place::Local(ref_place))],
 541                     destination: Some((unit_temp, succ)),
 542                     cleanup: unwind.into_option(),
 543                 },
 544                 source_info: self.source_info
 545             }),
 546             is_cleanup: unwind.is_cleanup(),
 547         };
 548         self.elaborator.patch().new_block(result)
 549     }
 550
 551     /// create a loop that drops an array:
 552     ///
 553
 554     ///
 555     /// loop-block:
 556     ///    can_go = cur == length_or_end
 557     ///    if can_go then succ else drop-block
 558     /// drop-block:
 559     ///    if ptr_based {
 560     ///        ptr = cur
 561     ///        cur = cur.offset(1)
 562     ///    } else {
 563     ///        ptr = &mut LV[cur]
 564     ///        cur = cur + 1
 565     ///    }
 566     ///    drop(ptr)
 567     fn drop_loop(&mut self,
 568                  succ: BasicBlock,
 569                  cur: Local,
 570                  length_or_end: &Place<'tcx>,
 571                  ety: Ty<'tcx>,
 572                  unwind: Unwind,
 573                  ptr_based: bool)
 574                  -> BasicBlock
 575     {
 576         let copy = |place: &Place<'tcx>| Operand::Copy(place.clone());
 577         let move_ = |place: &Place<'tcx>| Operand::Move(place.clone());
 578         let tcx = self.tcx();
 579
 580         let ref_ty = tcx.mk_ref(tcx.types.re_erased, ty::TypeAndMut {
 581             ty: ety,
 582             mutbl: hir::Mutability::MutMutable
 583         });
 584         let ptr = &Place::Local(self.new_temp(ref_ty));
 585         let can_go = &Place::Local(self.new_temp(tcx.types.bool));
 586
 587         let one = self.constant_usize(1);
 588         let (ptr_next, cur_next) = if ptr_based {
 589             (Rvalue::Use(copy(&Place::Local(cur))),
 590              Rvalue::BinaryOp(BinOp::Offset, copy(&Place::Local(cur)), one))
 591         } else {
 592             (Rvalue::Ref(
 593                  tcx.types.re_erased,
 594                  BorrowKind::Mut,
 595                  self.place.clone().index(cur)),
 596              Rvalue::BinaryOp(BinOp::Add, copy(&Place::Local(cur)), one))
 597         };
 598
 599         let drop_block = BasicBlockData {
 600             statements: vec![
 601                 self.assign(ptr, ptr_next),
 602                 self.assign(&Place::Local(cur), cur_next)
 603             ],
 604             is_cleanup: unwind.is_cleanup(),
 605             terminator: Some(Terminator {
 606                 source_info: self.source_info,
 607                 // this gets overwritten by drop elaboration.
 608                 kind: TerminatorKind::Unreachable,
 609             })
 610         };
 611         let drop_block = self.elaborator.patch().new_block(drop_block);
 612
 613         let loop_block = BasicBlockData {
 614             statements: vec![
 615                 self.assign(can_go, Rvalue::BinaryOp(BinOp::Eq,
 616                                                      copy(&Place::Local(cur)),
 617                                                      copy(length_or_end)))
 618             ],
 619             is_cleanup: unwind.is_cleanup(),
 620             terminator: Some(Terminator {
 621                 source_info: self.source_info,
 622                 kind: TerminatorKind::if_(tcx, move_(can_go), succ, drop_block)
 623             })
 624         };
 625         let loop_block = self.elaborator.patch().new_block(loop_block);
 626
 627         self.elaborator.patch().patch_terminator(drop_block, TerminatorKind::Drop {
 628             location: ptr.clone().deref(),
 629             target: loop_block,
 630             unwind: unwind.into_option()
 631         });
 632
 633         loop_block
 634     }
 635
 636     fn open_drop_for_array(&mut self, ety: Ty<'tcx>, opt_size: Option<u64>) -> BasicBlock {
 637         debug!("open_drop_for_array({:?}, {:?})", ety, opt_size);
 638
 639         // if size_of::<ety>() == 0 {
 640         //     index_based_loop
 641         // } else {
 642         //     ptr_based_loop
 643         // }
 644
 645         if let Some(size) = opt_size {
 646             assert!(size <= (u32::MAX as u64),
 647                     "move out check doesn't implemented for array bigger then u32");
 648             let size = size as u32;
 649             let fields: Vec<(Place<'tcx>, Option<D::Path>)> = (0..size).map(|i| {
 650                 (self.place.clone().elem(ProjectionElem::ConstantIndex{
 651                     offset: i,
 652                     min_length: size,
 653                     from_end: false
 654                 }),
 655                  self.elaborator.array_subpath(self.path, i, size))
 656             }).collect();
 657
 658             if fields.iter().any(|(_,path)| path.is_some()) {
 659                 let (succ, unwind) = self.drop_ladder_bottom();
 660                 return self.drop_ladder(fields, succ, unwind).0
 661             }
 662         }
 663
 664         let move_ = |place: &Place<'tcx>| Operand::Move(place.clone());
 665         let tcx = self.tcx();
 666         let size = &Place::Local(self.new_temp(tcx.types.usize));
 667         let size_is_zero = &Place::Local(self.new_temp(tcx.types.bool));
 668         let base_block = BasicBlockData {
 669             statements: vec![
 670                 self.assign(size, Rvalue::NullaryOp(NullOp::SizeOf, ety)),
 671                 self.assign(size_is_zero, Rvalue::BinaryOp(BinOp::Eq,
 672                                                            move_(size),
 673                                                            self.constant_usize(0)))
 674             ],
 675             is_cleanup: self.unwind.is_cleanup(),
 676             terminator: Some(Terminator {
 677                 source_info: self.source_info,
 678                 kind: TerminatorKind::if_(
 679                     tcx,
 680                     move_(size_is_zero),
 681                     self.drop_loop_pair(ety, false),
 682                     self.drop_loop_pair(ety, true)
 683                 )
 684             })
 685         };
 686         self.elaborator.patch().new_block(base_block)
 687     }
 688
 689     // create a pair of drop-loops of `place`, which drops its contents
 690     // even in the case of 1 panic. If `ptr_based`, create a pointer loop,
 691     // otherwise create an index loop.
 692     fn drop_loop_pair(&mut self, ety: Ty<'tcx>, ptr_based: bool) -> BasicBlock {
 693         debug!("drop_loop_pair({:?}, {:?})", ety, ptr_based);
 694         let tcx = self.tcx();
 695         let iter_ty = if ptr_based {
 696             tcx.mk_mut_ptr(ety)
 697         } else {
 698             tcx.types.usize
 699         };
 700
 701         let cur = self.new_temp(iter_ty);
 702         let length = Place::Local(self.new_temp(tcx.types.usize));
 703         let length_or_end = if ptr_based {
 704             Place::Local(self.new_temp(iter_ty))
 705         } else {
 706             length.clone()
 707         };
 708
 709         let unwind = self.unwind.map(|unwind| {
 710             self.drop_loop(unwind,
 711                            cur,
 712                            &length_or_end,
 713                            ety,
 714                            Unwind::InCleanup,
 715                            ptr_based)
 716         });
 717
 718         let succ = self.succ; // FIXME(#6393)
 719         let loop_block = self.drop_loop(
 720             succ,
 721             cur,
 722             &length_or_end,
 723             ety,
 724             unwind,
 725             ptr_based);
 726
 727         let cur = Place::Local(cur);
 728         let zero = self.constant_usize(0);
 729         let mut drop_block_stmts = vec![];
 730         drop_block_stmts.push(self.assign(&length, Rvalue::Len(self.place.clone())));
 731         if ptr_based {
 732             let tmp_ty = tcx.mk_mut_ptr(self.place_ty(self.place));
 733             let tmp = Place::Local(self.new_temp(tmp_ty));
 734             // tmp = &LV;
 735             // cur = tmp as *mut T;
 736             // end = Offset(cur, len);
 737             drop_block_stmts.push(self.assign(&tmp, Rvalue::Ref(
 738                 tcx.types.re_erased, BorrowKind::Mut, self.place.clone()
 739             )));
 740             drop_block_stmts.push(self.assign(&cur, Rvalue::Cast(
 741                 CastKind::Misc, Operand::Move(tmp.clone()), iter_ty
 742             )));
 743             drop_block_stmts.push(self.assign(&length_or_end,
 744                 Rvalue::BinaryOp(BinOp::Offset,
 745                      Operand::Copy(cur.clone()), Operand::Move(length.clone())
 746             )));
 747         } else {
 748             // index = 0 (length already pushed)
 749             drop_block_stmts.push(self.assign(&cur, Rvalue::Use(zero)));
 750         }
 751         let drop_block = self.elaborator.patch().new_block(BasicBlockData {
 752             statements: drop_block_stmts,
 753             is_cleanup: unwind.is_cleanup(),
 754             terminator: Some(Terminator {
 755                 source_info: self.source_info,
 756                 kind: TerminatorKind::Goto { target: loop_block }
 757             })
 758         });
 759
 760         // FIXME(#34708): handle partially-dropped array/slice elements.
 761         let reset_block = self.drop_flag_reset_block(DropFlagMode::Deep, drop_block, unwind);
 762         self.drop_flag_test_block(reset_block, succ, unwind)
 763     }
 764
 765     /// The slow-path - create an "open", elaborated drop for a type
 766     /// which is moved-out-of only partially, and patch `bb` to a jump
 767     /// to it. This must not be called on ADTs with a destructor,
 768     /// as these can't be moved-out-of, except for `Box<T>`, which is
 769     /// special-cased.
 770     ///
 771     /// This creates a "drop ladder" that drops the needed fields of the
 772     /// ADT, both in the success case or if one of the destructors fail.
 773     fn open_drop<'a>(&mut self) -> BasicBlock {
 774         let ty = self.place_ty(self.place);
 775         match ty.sty {
 776             ty::TyClosure(def_id, substs) |
 777             // Note that `elaborate_drops` only drops the upvars of a generator,
 778             // and this is ok because `open_drop` here can only be reached
 779             // within that own generator's resume function.
 780             // This should only happen for the self argument on the resume function.
 781             // It effetively only contains upvars until the generator transformation runs.
 782             // See librustc_mir/transform/generator.rs for more details.
 783             ty::TyGenerator(def_id, substs, _) => {
 784                 let tys : Vec<_> = substs.upvar_tys(def_id, self.tcx()).collect();
 785                 self.open_drop_for_tuple(&tys)
 786             }
 787             ty::TyTuple(tys, _) => {
 788                 self.open_drop_for_tuple(tys)
 789             }
 790             ty::TyAdt(def, _) if def.is_box() => {
 791                 self.open_drop_for_box(ty.boxed_ty())
 792             }
 793             ty::TyAdt(def, substs) => {
 794                 self.open_drop_for_adt(def, substs)
 795             }
 796             ty::TyDynamic(..) => {
 797                 let unwind = self.unwind; // FIXME(#6393)
 798                 let succ = self.succ;
 799                 self.complete_drop(Some(DropFlagMode::Deep), succ, unwind)
 800             }
 801             ty::TyArray(ety, size) => self.open_drop_for_array(
 802                 ety, size.val.to_const_int().and_then(|v| v.to_u64())),
 803             ty::TySlice(ety) => self.open_drop_for_array(ety, None),
 804
 805             _ => bug!("open drop from non-ADT `{:?}`", ty)
 806         }
 807     }
 808
 809     /// Return a basic block that drop a place using the context
 810     /// and path in `c`. If `mode` is something, also clear `c`
 811     /// according to it.
 812     ///
 813     /// if FLAG(self.path)
 814     ///     if let Some(mode) = mode: FLAG(self.path)[mode] = false
 815     ///     drop(self.place)
 816     fn complete_drop<'a>(&mut self,
 817                          drop_mode: Option<DropFlagMode>,
 818                          succ: BasicBlock,
 819                          unwind: Unwind) -> BasicBlock
 820     {
 821         debug!("complete_drop({:?},{:?})", self, drop_mode);
 822
 823         let drop_block = self.drop_block(succ, unwind);
 824         let drop_block = if let Some(mode) = drop_mode {
 825             self.drop_flag_reset_block(mode, drop_block, unwind)
 826         } else {
 827             drop_block
 828         };
 829
 830         self.drop_flag_test_block(drop_block, succ, unwind)
 831     }
 832
 833     fn drop_flag_reset_block(&mut self,
 834                              mode: DropFlagMode,
 835                              succ: BasicBlock,
 836                              unwind: Unwind) -> BasicBlock
 837     {
 838         debug!("drop_flag_reset_block({:?},{:?})", self, mode);
 839
 840         let block = self.new_block(unwind, TerminatorKind::Goto { target: succ });
 841         let block_start = Location { block: block, statement_index: 0 };
 842         self.elaborator.clear_drop_flag(block_start, self.path, mode);
 843         block
 844     }
 845
 846     fn elaborated_drop_block<'a>(&mut self) -> BasicBlock {
 847         debug!("elaborated_drop_block({:?})", self);
 848         let unwind = self.unwind; // FIXME(#6393)
 849         let succ = self.succ;
 850         let blk = self.drop_block(succ, unwind);
 851         self.elaborate_drop(blk);
 852         blk
 853     }
 854
 855     fn box_free_block<'a>(
 856         &mut self,
 857         ty: Ty<'tcx>,
 858         target: BasicBlock,
 859         unwind: Unwind,
 860     ) -> BasicBlock {
 861         let block = self.unelaborated_free_block(ty, target, unwind);
 862         self.drop_flag_test_block(block, target, unwind)
 863     }
 864
 865     fn unelaborated_free_block<'a>(
 866         &mut self,
 867         ty: Ty<'tcx>,
 868         target: BasicBlock,
 869         unwind: Unwind
 870     ) -> BasicBlock {
 871         let tcx = self.tcx();
 872         let unit_temp = Place::Local(self.new_temp(tcx.mk_nil()));
 873         let free_func = tcx.require_lang_item(lang_items::BoxFreeFnLangItem);
 874         let substs = tcx.mk_substs(iter::once(Kind::from(ty)));
 875
 876         let call = TerminatorKind::Call {
 877             func: Operand::function_handle(tcx, free_func, substs, self.source_info.span),
 878             args: vec![Operand::Move(self.place.clone())],
 879             destination: Some((unit_temp, target)),
 880             cleanup: None
 881         }; // FIXME(#6393)
 882         let free_block = self.new_block(unwind, call);
 883
 884         let block_start = Location { block: free_block, statement_index: 0 };
 885         self.elaborator.clear_drop_flag(block_start, self.path, DropFlagMode::Shallow);
 886         free_block
 887     }
 888
 889     fn drop_block<'a>(&mut self, target: BasicBlock, unwind: Unwind) -> BasicBlock {
 890         let block = TerminatorKind::Drop {
 891             location: self.place.clone(),
 892             target,
 893             unwind: unwind.into_option()
 894         };
 895         self.new_block(unwind, block)
 896     }
 897
 898     fn drop_flag_test_block(&mut self,
 899                             on_set: BasicBlock,
 900                             on_unset: BasicBlock,
 901                             unwind: Unwind)
 902                             -> BasicBlock
 903     {
 904         let style = self.elaborator.drop_style(self.path, DropFlagMode::Shallow);
 905         debug!("drop_flag_test_block({:?},{:?},{:?},{:?}) - {:?}",
 906                self, on_set, on_unset, unwind, style);
 907
 908         match style {
 909             DropStyle::Dead => on_unset,
 910             DropStyle::Static => on_set,
 911             DropStyle::Conditional | DropStyle::Open => {
 912                 let flag = self.elaborator.get_drop_flag(self.path).unwrap();
 913                 let term = TerminatorKind::if_(self.tcx(), flag, on_set, on_unset);
 914                 self.new_block(unwind, term)
 915             }
 916         }
 917     }
 918
 919     fn new_block<'a>(&mut self,
 920                      unwind: Unwind,
 921                      k: TerminatorKind<'tcx>)
 922                      -> BasicBlock
 923     {
 924         self.elaborator.patch().new_block(BasicBlockData {
 925             statements: vec![],
 926             terminator: Some(Terminator {
 927                 source_info: self.source_info, kind: k
 928             }),
 929             is_cleanup: unwind.is_cleanup()
 930         })
 931     }
 932
 933     fn new_temp(&mut self, ty: Ty<'tcx>) -> Local {
 934         self.elaborator.patch().new_temp(ty, self.source_info.span)
 935     }
 936
 937     fn terminator_loc(&mut self, bb: BasicBlock) -> Location {
 938         let mir = self.elaborator.mir();
 939         self.elaborator.patch().terminator_loc(mir, bb)
 940     }
 941
 942     fn constant_usize(&self, val: u16) -> Operand<'tcx> {
 943         Operand::Constant(box Constant {
 944             span: self.source_info.span,
 945             ty: self.tcx().types.usize,
 946             literal: Literal::Value {
 947                 value: self.tcx().mk_const(ty::Const {
 948                     val: ConstVal::Integral(self.tcx().const_usize(val)),
 949                     ty: self.tcx().types.usize
 950                 })
 951             }
 952         })
 953     }
 954
 955     fn assign(&self, lhs: &Place<'tcx>, rhs: Rvalue<'tcx>) -> Statement<'tcx> {
 956         Statement {
 957             source_info: self.source_info,
 958             kind: StatementKind::Assign(lhs.clone(), rhs)
 959         }
 960     }
 961 }