src/librustc_mir/util/elaborate_drops.rs

   1 use crate::util::patch::MirPatch;
   2 use rustc::middle::lang_items;
   3 use rustc::mir::*;
   4 use rustc::traits::Reveal;
   5 use rustc::ty::layout::VariantIdx;
   6 use rustc::ty::subst::SubstsRef;
   7 use rustc::ty::util::IntTypeExt;
   8 use rustc::ty::{self, Ty, TyCtxt};
   9 use rustc_hir as hir;
  10 use rustc_index::vec::Idx;
  11 use std::fmt;
  12
  13 use std::convert::TryInto;
  14
  15 #[derive(Debug, PartialEq, Eq, Copy, Clone)]
  16 pub enum DropFlagState {
  17     Present, // i.e., initialized
  18     Absent,  // i.e., deinitialized or "moved"
  19 }
  20
  21 impl DropFlagState {
  22     pub fn value(self) -> bool {
  23         match self {
  24             DropFlagState::Present => true,
  25             DropFlagState::Absent => false,
  26         }
  27     }
  28 }
  29
  30 #[derive(Debug)]
  31 pub enum DropStyle {
  32     Dead,
  33     Static,
  34     Conditional,
  35     Open,
  36 }
  37
  38 #[derive(Debug)]
  39 pub enum DropFlagMode {
  40     Shallow,
  41     Deep,
  42 }
  43
  44 #[derive(Copy, Clone, Debug)]
  45 pub enum Unwind {
  46     To(BasicBlock),
  47     InCleanup,
  48 }
  49
  50 impl Unwind {
  51     fn is_cleanup(self) -> bool {
  52         match self {
  53             Unwind::To(..) => false,
  54             Unwind::InCleanup => true,
  55         }
  56     }
  57
  58     fn into_option(self) -> Option<BasicBlock> {
  59         match self {
  60             Unwind::To(bb) => Some(bb),
  61             Unwind::InCleanup => None,
  62         }
  63     }
  64
  65     fn map<F>(self, f: F) -> Self
  66     where
  67         F: FnOnce(BasicBlock) -> BasicBlock,
  68     {
  69         match self {
  70             Unwind::To(bb) => Unwind::To(f(bb)),
  71             Unwind::InCleanup => Unwind::InCleanup,
  72         }
  73     }
  74 }
  75
  76 pub trait DropElaborator<'a, 'tcx>: fmt::Debug {
  77     type Path: Copy + fmt::Debug;
  78
  79     fn patch(&mut self) -> &mut MirPatch<'tcx>;
  80     fn body(&self) -> &'a Body<'tcx>;
  81     fn tcx(&self) -> TyCtxt<'tcx>;
  82     fn param_env(&self) -> ty::ParamEnv<'tcx>;
  83
  84     fn drop_style(&self, path: Self::Path, mode: DropFlagMode) -> DropStyle;
  85     fn get_drop_flag(&mut self, path: Self::Path) -> Option<Operand<'tcx>>;
  86     fn clear_drop_flag(&mut self, location: Location, path: Self::Path, mode: DropFlagMode);
  87
  88     fn field_subpath(&self, path: Self::Path, field: Field) -> Option<Self::Path>;
  89     fn deref_subpath(&self, path: Self::Path) -> Option<Self::Path>;
  90     fn downcast_subpath(&self, path: Self::Path, variant: VariantIdx) -> Option<Self::Path>;
  91     fn array_subpath(&self, path: Self::Path, index: u32, size: u32) -> Option<Self::Path>;
  92 }
  93
  94 #[derive(Debug)]
  95 struct DropCtxt<'l, 'b, 'tcx, D>
  96 where
  97     D: DropElaborator<'b, 'tcx>,
  98 {
  99     elaborator: &'l mut D,
 100
 101     source_info: SourceInfo,
 102
 103     place: &'l Place<'tcx>,
 104     path: D::Path,
 105     succ: BasicBlock,
 106     unwind: Unwind,
 107 }
 108
 109 pub fn elaborate_drop<'b, 'tcx, D>(
 110     elaborator: &mut D,
 111     source_info: SourceInfo,
 112     place: &Place<'tcx>,
 113     path: D::Path,
 114     succ: BasicBlock,
 115     unwind: Unwind,
 116     bb: BasicBlock,
 117 ) where
 118     D: DropElaborator<'b, 'tcx>,
 119     'tcx: 'b,
 120 {
 121     DropCtxt { elaborator, source_info, place, path, succ, unwind }.elaborate_drop(bb)
 122 }
 123
 124 impl<'l, 'b, 'tcx, D> DropCtxt<'l, 'b, 'tcx, D>
 125 where
 126     D: DropElaborator<'b, 'tcx>,
 127     'tcx: 'b,
 128 {
 129     fn place_ty(&self, place: &Place<'tcx>) -> Ty<'tcx> {
 130         place.ty(self.elaborator.body(), self.tcx()).ty
 131     }
 132
 133     fn tcx(&self) -> TyCtxt<'tcx> {
 134         self.elaborator.tcx()
 135     }
 136
 137     /// This elaborates a single drop instruction, located at `bb`, and
 138     /// patches over it.
 139     ///
 140     /// The elaborated drop checks the drop flags to only drop what
 141     /// is initialized.
 142     ///
 143     /// In addition, the relevant drop flags also need to be cleared
 144     /// to avoid double-drops. However, in the middle of a complex
 145     /// drop, one must avoid clearing some of the flags before they
 146     /// are read, as that would cause a memory leak.
 147     ///
 148     /// In particular, when dropping an ADT, multiple fields may be
 149     /// joined together under the `rest` subpath. They are all controlled
 150     /// by the primary drop flag, but only the last rest-field dropped
 151     /// should clear it (and it must also not clear anything else).
 152     //
 153     // FIXME: I think we should just control the flags externally,
 154     // and then we do not need this machinery.
 155     pub fn elaborate_drop(&mut self, bb: BasicBlock) {
 156         debug!("elaborate_drop({:?}, {:?})", bb, self);
 157         let style = self.elaborator.drop_style(self.path, DropFlagMode::Deep);
 158         debug!("elaborate_drop({:?}, {:?}): live - {:?}", bb, self, style);
 159         match style {
 160             DropStyle::Dead => {
 161                 self.elaborator
 162                     .patch()
 163                     .patch_terminator(bb, TerminatorKind::Goto { target: self.succ });
 164             }
 165             DropStyle::Static => {
 166                 let loc = self.terminator_loc(bb);
 167                 self.elaborator.clear_drop_flag(loc, self.path, DropFlagMode::Deep);
 168                 self.elaborator.patch().patch_terminator(
 169                     bb,
 170                     TerminatorKind::Drop {
 171                         location: *self.place,
 172                         target: self.succ,
 173                         unwind: self.unwind.into_option(),
 174                     },
 175                 );
 176             }
 177             DropStyle::Conditional => {
 178                 let unwind = self.unwind; // FIXME(#43234)
 179                 let succ = self.succ;
 180                 let drop_bb = self.complete_drop(Some(DropFlagMode::Deep), succ, unwind);
 181                 self.elaborator
 182                     .patch()
 183                     .patch_terminator(bb, TerminatorKind::Goto { target: drop_bb });
 184             }
 185             DropStyle::Open => {
 186                 let drop_bb = self.open_drop();
 187                 self.elaborator
 188                     .patch()
 189                     .patch_terminator(bb, TerminatorKind::Goto { target: drop_bb });
 190             }
 191         }
 192     }
 193
 194     /// Returns the place and move path for each field of `variant`,
 195     /// (the move path is `None` if the field is a rest field).
 196     fn move_paths_for_fields(
 197         &self,
 198         base_place: &Place<'tcx>,
 199         variant_path: D::Path,
 200         variant: &'tcx ty::VariantDef,
 201         substs: SubstsRef<'tcx>,
 202     ) -> Vec<(Place<'tcx>, Option<D::Path>)> {
 203         variant
 204             .fields
 205             .iter()
 206             .enumerate()
 207             .map(|(i, f)| {
 208                 let field = Field::new(i);
 209                 let subpath = self.elaborator.field_subpath(variant_path, field);
 210                 let tcx = self.tcx();
 211
 212                 assert_eq!(self.elaborator.param_env().reveal, Reveal::All);
 213                 let field_ty =
 214                     tcx.normalize_erasing_regions(self.elaborator.param_env(), f.ty(tcx, substs));
 215                 (tcx.mk_place_field(base_place.clone(), field, field_ty), subpath)
 216             })
 217             .collect()
 218     }
 219
 220     fn drop_subpath(
 221         &mut self,
 222         place: &Place<'tcx>,
 223         path: Option<D::Path>,
 224         succ: BasicBlock,
 225         unwind: Unwind,
 226     ) -> BasicBlock {
 227         if let Some(path) = path {
 228             debug!("drop_subpath: for std field {:?}", place);
 229
 230             DropCtxt {
 231                 elaborator: self.elaborator,
 232                 source_info: self.source_info,
 233                 path,
 234                 place,
 235                 succ,
 236                 unwind,
 237             }
 238             .elaborated_drop_block()
 239         } else {
 240             debug!("drop_subpath: for rest field {:?}", place);
 241
 242             DropCtxt {
 243                 elaborator: self.elaborator,
 244                 source_info: self.source_info,
 245                 place,
 246                 succ,
 247                 unwind,
 248                 // Using `self.path` here to condition the drop on
 249                 // our own drop flag.
 250                 path: self.path,
 251             }
 252             .complete_drop(None, succ, unwind)
 253         }
 254     }
 255
 256     /// Creates one-half of the drop ladder for a list of fields, and return
 257     /// the list of steps in it in reverse order, with the first step
 258     /// dropping 0 fields and so on.
 259     ///
 260     /// `unwind_ladder` is such a list of steps in reverse order,
 261     /// which is called if the matching step of the drop glue panics.
 262     fn drop_halfladder(
 263         &mut self,
 264         unwind_ladder: &[Unwind],
 265         mut succ: BasicBlock,
 266         fields: &[(Place<'tcx>, Option<D::Path>)],
 267     ) -> Vec<BasicBlock> {
 268         Some(succ)
 269             .into_iter()
 270             .chain(fields.iter().rev().zip(unwind_ladder).map(
 271                 |(&(ref place, path), &unwind_succ)| {
 272                     succ = self.drop_subpath(place, path, succ, unwind_succ);
 273                     succ
 274                 },
 275             ))
 276             .collect()
 277     }
 278
 279     fn drop_ladder_bottom(&mut self) -> (BasicBlock, Unwind) {
 280         // Clear the "master" drop flag at the end. This is needed
 281         // because the "master" drop protects the ADT's discriminant,
 282         // which is invalidated after the ADT is dropped.
 283         let (succ, unwind) = (self.succ, self.unwind); // FIXME(#43234)
 284         (
 285             self.drop_flag_reset_block(DropFlagMode::Shallow, succ, unwind),
 286             unwind.map(|unwind| {
 287                 self.drop_flag_reset_block(DropFlagMode::Shallow, unwind, Unwind::InCleanup)
 288             }),
 289         )
 290     }
 291
 292     /// Creates a full drop ladder, consisting of 2 connected half-drop-ladders
 293     ///
 294     /// For example, with 3 fields, the drop ladder is
 295     ///
 296     /// .d0:
 297     ///     ELAB(drop location.0 [target=.d1, unwind=.c1])
 298     /// .d1:
 299     ///     ELAB(drop location.1 [target=.d2, unwind=.c2])
 300     /// .d2:
 301     ///     ELAB(drop location.2 [target=`self.succ`, unwind=`self.unwind`])
 302     /// .c1:
 303     ///     ELAB(drop location.1 [target=.c2])
 304     /// .c2:
 305     ///     ELAB(drop location.2 [target=`self.unwind`])
 306     ///
 307     /// NOTE: this does not clear the master drop flag, so you need
 308     /// to point succ/unwind on a `drop_ladder_bottom`.
 309     fn drop_ladder(
 310         &mut self,
 311         fields: Vec<(Place<'tcx>, Option<D::Path>)>,
 312         succ: BasicBlock,
 313         unwind: Unwind,
 314     ) -> (BasicBlock, Unwind) {
 315         debug!("drop_ladder({:?}, {:?})", self, fields);
 316
 317         let mut fields = fields;
 318         fields.retain(|&(ref place, _)| {
 319             self.place_ty(place).needs_drop(self.tcx(), self.elaborator.param_env())
 320         });
 321
 322         debug!("drop_ladder - fields needing drop: {:?}", fields);
 323
 324         let unwind_ladder = vec![Unwind::InCleanup; fields.len() + 1];
 325         let unwind_ladder: Vec<_> = if let Unwind::To(target) = unwind {
 326             let halfladder = self.drop_halfladder(&unwind_ladder, target, &fields);
 327             halfladder.into_iter().map(Unwind::To).collect()
 328         } else {
 329             unwind_ladder
 330         };
 331
 332         let normal_ladder = self.drop_halfladder(&unwind_ladder, succ, &fields);
 333
 334         (*normal_ladder.last().unwrap(), *unwind_ladder.last().unwrap())
 335     }
 336
 337     fn open_drop_for_tuple(&mut self, tys: &[Ty<'tcx>]) -> BasicBlock {
 338         debug!("open_drop_for_tuple({:?}, {:?})", self, tys);
 339
 340         let fields = tys
 341             .iter()
 342             .enumerate()
 343             .map(|(i, &ty)| {
 344                 (
 345                     self.tcx().mk_place_field(self.place.clone(), Field::new(i), ty),
 346                     self.elaborator.field_subpath(self.path, Field::new(i)),
 347                 )
 348             })
 349             .collect();
 350
 351         let (succ, unwind) = self.drop_ladder_bottom();
 352         self.drop_ladder(fields, succ, unwind).0
 353     }
 354
 355     fn open_drop_for_box(&mut self, adt: &'tcx ty::AdtDef, substs: SubstsRef<'tcx>) -> BasicBlock {
 356         debug!("open_drop_for_box({:?}, {:?}, {:?})", self, adt, substs);
 357
 358         let interior = self.tcx().mk_place_deref(self.place.clone());
 359         let interior_path = self.elaborator.deref_subpath(self.path);
 360
 361         let succ = self.succ; // FIXME(#43234)
 362         let unwind = self.unwind;
 363         let succ = self.box_free_block(adt, substs, succ, unwind);
 364         let unwind_succ =
 365             self.unwind.map(|unwind| self.box_free_block(adt, substs, unwind, Unwind::InCleanup));
 366
 367         self.drop_subpath(&interior, interior_path, succ, unwind_succ)
 368     }
 369
 370     fn open_drop_for_adt(&mut self, adt: &'tcx ty::AdtDef, substs: SubstsRef<'tcx>) -> BasicBlock {
 371         debug!("open_drop_for_adt({:?}, {:?}, {:?})", self, adt, substs);
 372         if adt.variants.is_empty() {
 373             return self.elaborator.patch().new_block(BasicBlockData {
 374                 statements: vec![],
 375                 terminator: Some(Terminator {
 376                     source_info: self.source_info,
 377                     kind: TerminatorKind::Unreachable,
 378                 }),
 379                 is_cleanup: self.unwind.is_cleanup(),
 380             });
 381         }
 382
 383         let skip_contents =
 384             adt.is_union() || Some(adt.did) == self.tcx().lang_items().manually_drop();
 385         let contents_drop = if skip_contents {
 386             (self.succ, self.unwind)
 387         } else {
 388             self.open_drop_for_adt_contents(adt, substs)
 389         };
 390
 391         if adt.has_dtor(self.tcx()) {
 392             self.destructor_call_block(contents_drop)
 393         } else {
 394             contents_drop.0
 395         }
 396     }
 397
 398     fn open_drop_for_adt_contents(
 399         &mut self,
 400         adt: &'tcx ty::AdtDef,
 401         substs: SubstsRef<'tcx>,
 402     ) -> (BasicBlock, Unwind) {
 403         let (succ, unwind) = self.drop_ladder_bottom();
 404         if !adt.is_enum() {
 405             let fields = self.move_paths_for_fields(
 406                 self.place,
 407                 self.path,
 408                 &adt.variants[VariantIdx::new(0)],
 409                 substs,
 410             );
 411             self.drop_ladder(fields, succ, unwind)
 412         } else {
 413             self.open_drop_for_multivariant(adt, substs, succ, unwind)
 414         }
 415     }
 416
 417     fn open_drop_for_multivariant(
 418         &mut self,
 419         adt: &'tcx ty::AdtDef,
 420         substs: SubstsRef<'tcx>,
 421         succ: BasicBlock,
 422         unwind: Unwind,
 423     ) -> (BasicBlock, Unwind) {
 424         let mut values = Vec::with_capacity(adt.variants.len());
 425         let mut normal_blocks = Vec::with_capacity(adt.variants.len());
 426         let mut unwind_blocks =
 427             if unwind.is_cleanup() { None } else { Some(Vec::with_capacity(adt.variants.len())) };
 428
 429         let mut have_otherwise_with_drop_glue = false;
 430         let mut have_otherwise = false;
 431         let tcx = self.tcx();
 432
 433         for (variant_index, discr) in adt.discriminants(tcx) {
 434             let variant = &adt.variants[variant_index];
 435             let subpath = self.elaborator.downcast_subpath(self.path, variant_index);
 436
 437             if let Some(variant_path) = subpath {
 438                 let base_place = tcx.mk_place_elem(
 439                     self.place.clone(),
 440                     ProjectionElem::Downcast(Some(variant.ident.name), variant_index),
 441                 );
 442                 let fields =
 443                     self.move_paths_for_fields(&base_place, variant_path, &variant, substs);
 444                 values.push(discr.val);
 445                 if let Unwind::To(unwind) = unwind {
 446                     // We can't use the half-ladder from the original
 447                     // drop ladder, because this breaks the
 448                     // "funclet can't have 2 successor funclets"
 449                     // requirement from MSVC:
 450                     //
 451                     //           switch       unwind-switch
 452                     //          /      \         /        \
 453                     //         v1.0    v2.0  v2.0-unwind  v1.0-unwind
 454                     //         |        |      /             |
 455                     //    v1.1-unwind  v2.1-unwind           |
 456                     //      ^                                |
 457                     //       \-------------------------------/
 458                     //
 459                     // Create a duplicate half-ladder to avoid that. We
 460                     // could technically only do this on MSVC, but I
 461                     // I want to minimize the divergence between MSVC
 462                     // and non-MSVC.
 463
 464                     let unwind_blocks = unwind_blocks.as_mut().unwrap();
 465                     let unwind_ladder = vec![Unwind::InCleanup; fields.len() + 1];
 466                     let halfladder = self.drop_halfladder(&unwind_ladder, unwind, &fields);
 467                     unwind_blocks.push(halfladder.last().cloned().unwrap());
 468                 }
 469                 let (normal, _) = self.drop_ladder(fields, succ, unwind);
 470                 normal_blocks.push(normal);
 471             } else {
 472                 have_otherwise = true;
 473
 474                 let param_env = self.elaborator.param_env();
 475                 let have_field_with_drop_glue = variant
 476                     .fields
 477                     .iter()
 478                     .any(|field| field.ty(tcx, substs).needs_drop(tcx, param_env));
 479                 if have_field_with_drop_glue {
 480                     have_otherwise_with_drop_glue = true;
 481                 }
 482             }
 483         }
 484
 485         if !have_otherwise {
 486             values.pop();
 487         } else if !have_otherwise_with_drop_glue {
 488             normal_blocks.push(self.goto_block(succ, unwind));
 489             if let Unwind::To(unwind) = unwind {
 490                 unwind_blocks.as_mut().unwrap().push(self.goto_block(unwind, Unwind::InCleanup));
 491             }
 492         } else {
 493             normal_blocks.push(self.drop_block(succ, unwind));
 494             if let Unwind::To(unwind) = unwind {
 495                 unwind_blocks.as_mut().unwrap().push(self.drop_block(unwind, Unwind::InCleanup));
 496             }
 497         }
 498
 499         (
 500             self.adt_switch_block(adt, normal_blocks, &values, succ, unwind),
 501             unwind.map(|unwind| {
 502                 self.adt_switch_block(
 503                     adt,
 504                     unwind_blocks.unwrap(),
 505                     &values,
 506                     unwind,
 507                     Unwind::InCleanup,
 508                 )
 509             }),
 510         )
 511     }
 512
 513     fn adt_switch_block(
 514         &mut self,
 515         adt: &'tcx ty::AdtDef,
 516         blocks: Vec<BasicBlock>,
 517         values: &[u128],
 518         succ: BasicBlock,
 519         unwind: Unwind,
 520     ) -> BasicBlock {
 521         // If there are multiple variants, then if something
 522         // is present within the enum the discriminant, tracked
 523         // by the rest path, must be initialized.
 524         //
 525         // Additionally, we do not want to switch on the
 526         // discriminant after it is free-ed, because that
 527         // way lies only trouble.
 528         let discr_ty = adt.repr.discr_type().to_ty(self.tcx());
 529         let discr = Place::from(self.new_temp(discr_ty));
 530         let discr_rv = Rvalue::Discriminant(*self.place);
 531         let switch_block = BasicBlockData {
 532             statements: vec![self.assign(&discr, discr_rv)],
 533             terminator: Some(Terminator {
 534                 source_info: self.source_info,
 535                 kind: TerminatorKind::SwitchInt {
 536                     discr: Operand::Move(discr),
 537                     switch_ty: discr_ty,
 538                     values: From::from(values.to_owned()),
 539                     targets: blocks,
 540                 },
 541             }),
 542             is_cleanup: unwind.is_cleanup(),
 543         };
 544         let switch_block = self.elaborator.patch().new_block(switch_block);
 545         self.drop_flag_test_block(switch_block, succ, unwind)
 546     }
 547
 548     fn destructor_call_block(&mut self, (succ, unwind): (BasicBlock, Unwind)) -> BasicBlock {
 549         debug!("destructor_call_block({:?}, {:?})", self, succ);
 550         let tcx = self.tcx();
 551         let drop_trait = tcx.lang_items().drop_trait().unwrap();
 552         let drop_fn = tcx.associated_items(drop_trait).in_definition_order().next().unwrap();
 553         let ty = self.place_ty(self.place);
 554         let substs = tcx.mk_substs_trait(ty, &[]);
 555
 556         let ref_ty =
 557             tcx.mk_ref(tcx.lifetimes.re_erased, ty::TypeAndMut { ty, mutbl: hir::Mutability::Mut });
 558         let ref_place = self.new_temp(ref_ty);
 559         let unit_temp = Place::from(self.new_temp(tcx.mk_unit()));
 560
 561         let result = BasicBlockData {
 562             statements: vec![self.assign(
 563                 &Place::from(ref_place),
 564                 Rvalue::Ref(
 565                     tcx.lifetimes.re_erased,
 566                     BorrowKind::Mut { allow_two_phase_borrow: false },
 567                     *self.place,
 568                 ),
 569             )],
 570             terminator: Some(Terminator {
 571                 kind: TerminatorKind::Call {
 572                     func: Operand::function_handle(
 573                         tcx,
 574                         drop_fn.def_id,
 575                         substs,
 576                         self.source_info.span,
 577                     ),
 578                     args: vec![Operand::Move(Place::from(ref_place))],
 579                     destination: Some((unit_temp, succ)),
 580                     cleanup: unwind.into_option(),
 581                     from_hir_call: true,
 582                 },
 583                 source_info: self.source_info,
 584             }),
 585             is_cleanup: unwind.is_cleanup(),
 586         };
 587         self.elaborator.patch().new_block(result)
 588     }
 589
 590     /// Create a loop that drops an array:
 591     ///
 592     /// ```text
 593     /// loop-block:
 594     ///    can_go = cur == length_or_end
 595     ///    if can_go then succ else drop-block
 596     /// drop-block:
 597     ///    if ptr_based {
 598     ///        ptr = cur
 599     ///        cur = cur.offset(1)
 600     ///    } else {
 601     ///        ptr = &raw mut P[cur]
 602     ///        cur = cur + 1
 603     ///    }
 604     ///    drop(ptr)
 605     /// ```
 606     fn drop_loop(
 607         &mut self,
 608         succ: BasicBlock,
 609         cur: Local,
 610         length_or_end: &Place<'tcx>,
 611         ety: Ty<'tcx>,
 612         unwind: Unwind,
 613         ptr_based: bool,
 614     ) -> BasicBlock {
 615         let copy = |place: Place<'tcx>| Operand::Copy(place);
 616         let move_ = |place: Place<'tcx>| Operand::Move(place);
 617         let tcx = self.tcx();
 618
 619         let ptr_ty = tcx.mk_ptr(ty::TypeAndMut { ty: ety, mutbl: hir::Mutability::Mut });
 620         let ptr = &Place::from(self.new_temp(ptr_ty));
 621         let can_go = Place::from(self.new_temp(tcx.types.bool));
 622
 623         let one = self.constant_usize(1);
 624         let (ptr_next, cur_next) = if ptr_based {
 625             (Rvalue::Use(copy(cur.into())), Rvalue::BinaryOp(BinOp::Offset, move_(cur.into()), one))
 626         } else {
 627             (
 628                 Rvalue::AddressOf(Mutability::Mut, tcx.mk_place_index(self.place.clone(), cur)),
 629                 Rvalue::BinaryOp(BinOp::Add, move_(cur.into()), one),
 630             )
 631         };
 632
 633         let drop_block = BasicBlockData {
 634             statements: vec![self.assign(ptr, ptr_next), self.assign(&Place::from(cur), cur_next)],
 635             is_cleanup: unwind.is_cleanup(),
 636             terminator: Some(Terminator {
 637                 source_info: self.source_info,
 638                 // this gets overwritten by drop elaboration.
 639                 kind: TerminatorKind::Unreachable,
 640             }),
 641         };
 642         let drop_block = self.elaborator.patch().new_block(drop_block);
 643
 644         let loop_block = BasicBlockData {
 645             statements: vec![self.assign(
 646                 &can_go,
 647                 Rvalue::BinaryOp(BinOp::Eq, copy(Place::from(cur)), copy(*length_or_end)),
 648             )],
 649             is_cleanup: unwind.is_cleanup(),
 650             terminator: Some(Terminator {
 651                 source_info: self.source_info,
 652                 kind: TerminatorKind::if_(tcx, move_(can_go), succ, drop_block),
 653             }),
 654         };
 655         let loop_block = self.elaborator.patch().new_block(loop_block);
 656
 657         self.elaborator.patch().patch_terminator(
 658             drop_block,
 659             TerminatorKind::Drop {
 660                 location: tcx.mk_place_deref(ptr.clone()),
 661                 target: loop_block,
 662                 unwind: unwind.into_option(),
 663             },
 664         );
 665
 666         loop_block
 667     }
 668
 669     fn open_drop_for_array(&mut self, ety: Ty<'tcx>, opt_size: Option<u64>) -> BasicBlock {
 670         debug!("open_drop_for_array({:?}, {:?})", ety, opt_size);
 671
 672         // if size_of::<ety>() == 0 {
 673         //     index_based_loop
 674         // } else {
 675         //     ptr_based_loop
 676         // }
 677
 678         let tcx = self.tcx();
 679
 680         if let Some(size) = opt_size {
 681             let size: u32 = size.try_into().unwrap_or_else(|_| {
 682                 bug!("move out check isn't implemented for array sizes bigger than u32::MAX");
 683             });
 684             let fields: Vec<(Place<'tcx>, Option<D::Path>)> = (0..size)
 685                 .map(|i| {
 686                     (
 687                         tcx.mk_place_elem(
 688                             self.place.clone(),
 689                             ProjectionElem::ConstantIndex {
 690                                 offset: i,
 691                                 min_length: size,
 692                                 from_end: false,
 693                             },
 694                         ),
 695                         self.elaborator.array_subpath(self.path, i, size),
 696                     )
 697                 })
 698                 .collect();
 699
 700             if fields.iter().any(|(_, path)| path.is_some()) {
 701                 let (succ, unwind) = self.drop_ladder_bottom();
 702                 return self.drop_ladder(fields, succ, unwind).0;
 703             }
 704         }
 705
 706         let move_ = |place: &Place<'tcx>| Operand::Move(*place);
 707         let elem_size = &Place::from(self.new_temp(tcx.types.usize));
 708         let len = &Place::from(self.new_temp(tcx.types.usize));
 709
 710         static USIZE_SWITCH_ZERO: &[u128] = &[0];
 711
 712         let base_block = BasicBlockData {
 713             statements: vec![
 714                 self.assign(elem_size, Rvalue::NullaryOp(NullOp::SizeOf, ety)),
 715                 self.assign(len, Rvalue::Len(*self.place)),
 716             ],
 717             is_cleanup: self.unwind.is_cleanup(),
 718             terminator: Some(Terminator {
 719                 source_info: self.source_info,
 720                 kind: TerminatorKind::SwitchInt {
 721                     discr: move_(elem_size),
 722                     switch_ty: tcx.types.usize,
 723                     values: From::from(USIZE_SWITCH_ZERO),
 724                     targets: vec![
 725                         self.drop_loop_pair(ety, false, len.clone()),
 726                         self.drop_loop_pair(ety, true, len.clone()),
 727                     ],
 728                 },
 729             }),
 730         };
 731         self.elaborator.patch().new_block(base_block)
 732     }
 733
 734     /// Creates a pair of drop-loops of `place`, which drops its contents, even
 735     /// in the case of 1 panic. If `ptr_based`, creates a pointer loop,
 736     /// otherwise create an index loop.
 737     fn drop_loop_pair(
 738         &mut self,
 739         ety: Ty<'tcx>,
 740         ptr_based: bool,
 741         length: Place<'tcx>,
 742     ) -> BasicBlock {
 743         debug!("drop_loop_pair({:?}, {:?})", ety, ptr_based);
 744         let tcx = self.tcx();
 745         let iter_ty = if ptr_based { tcx.mk_mut_ptr(ety) } else { tcx.types.usize };
 746
 747         let cur = self.new_temp(iter_ty);
 748         let length_or_end = if ptr_based { Place::from(self.new_temp(iter_ty)) } else { length };
 749
 750         let unwind = self.unwind.map(|unwind| {
 751             self.drop_loop(unwind, cur, &length_or_end, ety, Unwind::InCleanup, ptr_based)
 752         });
 753
 754         let loop_block = self.drop_loop(self.succ, cur, &length_or_end, ety, unwind, ptr_based);
 755
 756         let cur = Place::from(cur);
 757         let drop_block_stmts = if ptr_based {
 758             let tmp_ty = tcx.mk_mut_ptr(self.place_ty(self.place));
 759             let tmp = Place::from(self.new_temp(tmp_ty));
 760             // tmp = &raw mut P;
 761             // cur = tmp as *mut T;
 762             // end = Offset(cur, len);
 763             vec![
 764                 self.assign(&tmp, Rvalue::AddressOf(Mutability::Mut, *self.place)),
 765                 self.assign(&cur, Rvalue::Cast(CastKind::Misc, Operand::Move(tmp), iter_ty)),
 766                 self.assign(
 767                     &length_or_end,
 768                     Rvalue::BinaryOp(BinOp::Offset, Operand::Copy(cur), Operand::Move(length)),
 769                 ),
 770             ]
 771         } else {
 772             // cur = 0 (length already pushed)
 773             let zero = self.constant_usize(0);
 774             vec![self.assign(&cur, Rvalue::Use(zero))]
 775         };
 776         let drop_block = self.elaborator.patch().new_block(BasicBlockData {
 777             statements: drop_block_stmts,
 778             is_cleanup: unwind.is_cleanup(),
 779             terminator: Some(Terminator {
 780                 source_info: self.source_info,
 781                 kind: TerminatorKind::Goto { target: loop_block },
 782             }),
 783         });
 784
 785         // FIXME(#34708): handle partially-dropped array/slice elements.
 786         let reset_block = self.drop_flag_reset_block(DropFlagMode::Deep, drop_block, unwind);
 787         self.drop_flag_test_block(reset_block, self.succ, unwind)
 788     }
 789
 790     /// The slow-path - create an "open", elaborated drop for a type
 791     /// which is moved-out-of only partially, and patch `bb` to a jump
 792     /// to it. This must not be called on ADTs with a destructor,
 793     /// as these can't be moved-out-of, except for `Box<T>`, which is
 794     /// special-cased.
 795     ///
 796     /// This creates a "drop ladder" that drops the needed fields of the
 797     /// ADT, both in the success case or if one of the destructors fail.
 798     fn open_drop(&mut self) -> BasicBlock {
 799         let ty = self.place_ty(self.place);
 800         match ty.kind {
 801             ty::Closure(def_id, substs) => {
 802                 let tys: Vec<_> = substs.as_closure().upvar_tys(def_id, self.tcx()).collect();
 803                 self.open_drop_for_tuple(&tys)
 804             }
 805             // Note that `elaborate_drops` only drops the upvars of a generator,
 806             // and this is ok because `open_drop` here can only be reached
 807             // within that own generator's resume function.
 808             // This should only happen for the self argument on the resume function.
 809             // It effetively only contains upvars until the generator transformation runs.
 810             // See librustc_body/transform/generator.rs for more details.
 811             ty::Generator(def_id, substs, _) => {
 812                 let tys: Vec<_> = substs.as_generator().upvar_tys(def_id, self.tcx()).collect();
 813                 self.open_drop_for_tuple(&tys)
 814             }
 815             ty::Tuple(..) => {
 816                 let tys: Vec<_> = ty.tuple_fields().collect();
 817                 self.open_drop_for_tuple(&tys)
 818             }
 819             ty::Adt(def, substs) => {
 820                 if def.is_box() {
 821                     self.open_drop_for_box(def, substs)
 822                 } else {
 823                     self.open_drop_for_adt(def, substs)
 824                 }
 825             }
 826             ty::Dynamic(..) => {
 827                 let unwind = self.unwind; // FIXME(#43234)
 828                 let succ = self.succ;
 829                 self.complete_drop(Some(DropFlagMode::Deep), succ, unwind)
 830             }
 831             ty::Array(ety, size) => {
 832                 let size = size.try_eval_usize(self.tcx(), self.elaborator.param_env());
 833                 self.open_drop_for_array(ety, size)
 834             }
 835             ty::Slice(ety) => self.open_drop_for_array(ety, None),
 836
 837             _ => bug!("open drop from non-ADT `{:?}`", ty),
 838         }
 839     }
 840
 841     /// Returns a basic block that drop a place using the context
 842     /// and path in `c`. If `mode` is something, also clear `c`
 843     /// according to it.
 844     ///
 845     /// if FLAG(self.path)
 846     ///     if let Some(mode) = mode: FLAG(self.path)[mode] = false
 847     ///     drop(self.place)
 848     fn complete_drop(
 849         &mut self,
 850         drop_mode: Option<DropFlagMode>,
 851         succ: BasicBlock,
 852         unwind: Unwind,
 853     ) -> BasicBlock {
 854         debug!("complete_drop({:?},{:?})", self, drop_mode);
 855
 856         let drop_block = self.drop_block(succ, unwind);
 857         let drop_block = if let Some(mode) = drop_mode {
 858             self.drop_flag_reset_block(mode, drop_block, unwind)
 859         } else {
 860             drop_block
 861         };
 862
 863         self.drop_flag_test_block(drop_block, succ, unwind)
 864     }
 865
 866     fn drop_flag_reset_block(
 867         &mut self,
 868         mode: DropFlagMode,
 869         succ: BasicBlock,
 870         unwind: Unwind,
 871     ) -> BasicBlock {
 872         debug!("drop_flag_reset_block({:?},{:?})", self, mode);
 873
 874         let block = self.new_block(unwind, TerminatorKind::Goto { target: succ });
 875         let block_start = Location { block, statement_index: 0 };
 876         self.elaborator.clear_drop_flag(block_start, self.path, mode);
 877         block
 878     }
 879
 880     fn elaborated_drop_block(&mut self) -> BasicBlock {
 881         debug!("elaborated_drop_block({:?})", self);
 882         let unwind = self.unwind; // FIXME(#43234)
 883         let succ = self.succ;
 884         let blk = self.drop_block(succ, unwind);
 885         self.elaborate_drop(blk);
 886         blk
 887     }
 888
 889     fn box_free_block(
 890         &mut self,
 891         adt: &'tcx ty::AdtDef,
 892         substs: SubstsRef<'tcx>,
 893         target: BasicBlock,
 894         unwind: Unwind,
 895     ) -> BasicBlock {
 896         let block = self.unelaborated_free_block(adt, substs, target, unwind);
 897         self.drop_flag_test_block(block, target, unwind)
 898     }
 899
 900     fn unelaborated_free_block(
 901         &mut self,
 902         adt: &'tcx ty::AdtDef,
 903         substs: SubstsRef<'tcx>,
 904         target: BasicBlock,
 905         unwind: Unwind,
 906     ) -> BasicBlock {
 907         let tcx = self.tcx();
 908         let unit_temp = Place::from(self.new_temp(tcx.mk_unit()));
 909         let free_func =
 910             tcx.require_lang_item(lang_items::BoxFreeFnLangItem, Some(self.source_info.span));
 911         let args = adt.variants[VariantIdx::new(0)]
 912             .fields
 913             .iter()
 914             .enumerate()
 915             .map(|(i, f)| {
 916                 let field = Field::new(i);
 917                 let field_ty = f.ty(tcx, substs);
 918                 Operand::Move(tcx.mk_place_field(self.place.clone(), field, field_ty))
 919             })
 920             .collect();
 921
 922         let call = TerminatorKind::Call {
 923             func: Operand::function_handle(tcx, free_func, substs, self.source_info.span),
 924             args,
 925             destination: Some((unit_temp, target)),
 926             cleanup: None,
 927             from_hir_call: false,
 928         }; // FIXME(#43234)
 929         let free_block = self.new_block(unwind, call);
 930
 931         let block_start = Location { block: free_block, statement_index: 0 };
 932         self.elaborator.clear_drop_flag(block_start, self.path, DropFlagMode::Shallow);
 933         free_block
 934     }
 935
 936     fn drop_block(&mut self, target: BasicBlock, unwind: Unwind) -> BasicBlock {
 937         let block =
 938             TerminatorKind::Drop { location: *self.place, target, unwind: unwind.into_option() };
 939         self.new_block(unwind, block)
 940     }
 941
 942     fn goto_block(&mut self, target: BasicBlock, unwind: Unwind) -> BasicBlock {
 943         let block = TerminatorKind::Goto { target };
 944         self.new_block(unwind, block)
 945     }
 946
 947     fn drop_flag_test_block(
 948         &mut self,
 949         on_set: BasicBlock,
 950         on_unset: BasicBlock,
 951         unwind: Unwind,
 952     ) -> BasicBlock {
 953         let style = self.elaborator.drop_style(self.path, DropFlagMode::Shallow);
 954         debug!(
 955             "drop_flag_test_block({:?},{:?},{:?},{:?}) - {:?}",
 956             self, on_set, on_unset, unwind, style
 957         );
 958
 959         match style {
 960             DropStyle::Dead => on_unset,
 961             DropStyle::Static => on_set,
 962             DropStyle::Conditional | DropStyle::Open => {
 963                 let flag = self.elaborator.get_drop_flag(self.path).unwrap();
 964                 let term = TerminatorKind::if_(self.tcx(), flag, on_set, on_unset);
 965                 self.new_block(unwind, term)
 966             }
 967         }
 968     }
 969
 970     fn new_block(&mut self, unwind: Unwind, k: TerminatorKind<'tcx>) -> BasicBlock {
 971         self.elaborator.patch().new_block(BasicBlockData {
 972             statements: vec![],
 973             terminator: Some(Terminator { source_info: self.source_info, kind: k }),
 974             is_cleanup: unwind.is_cleanup(),
 975         })
 976     }
 977
 978     fn new_temp(&mut self, ty: Ty<'tcx>) -> Local {
 979         self.elaborator.patch().new_temp(ty, self.source_info.span)
 980     }
 981
 982     fn terminator_loc(&mut self, bb: BasicBlock) -> Location {
 983         let body = self.elaborator.body();
 984         self.elaborator.patch().terminator_loc(body, bb)
 985     }
 986
 987     fn constant_usize(&self, val: u16) -> Operand<'tcx> {
 988         Operand::Constant(box Constant {
 989             span: self.source_info.span,
 990             user_ty: None,
 991             literal: ty::Const::from_usize(self.tcx(), val.into()),
 992         })
 993     }
 994
 995     fn assign(&self, lhs: &Place<'tcx>, rhs: Rvalue<'tcx>) -> Statement<'tcx> {
 996         Statement { source_info: self.source_info, kind: StatementKind::Assign(box (*lhs, rhs)) }
 997     }
 998 }