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({:?})", self);
 157         let style = self.elaborator.drop_style(self.path, DropFlagMode::Deep);
 158         debug!("elaborate_drop({:?}): live - {:?}", 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.clone(),
 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.len() == 0 {
 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 = false;
 430         let tcx = self.tcx();
 431
 432         for (variant_index, discr) in adt.discriminants(tcx) {
 433             let subpath = self.elaborator.downcast_subpath(self.path, variant_index);
 434             if let Some(variant_path) = subpath {
 435                 let base_place = tcx.mk_place_elem(
 436                     self.place.clone(),
 437                     ProjectionElem::Downcast(
 438                         Some(adt.variants[variant_index].ident.name),
 439                         variant_index,
 440                     ),
 441                 );
 442                 let fields = self.move_paths_for_fields(
 443                     &base_place,
 444                     variant_path,
 445                     &adt.variants[variant_index],
 446                     substs,
 447                 );
 448                 values.push(discr.val);
 449                 if let Unwind::To(unwind) = unwind {
 450                     // We can't use the half-ladder from the original
 451                     // drop ladder, because this breaks the
 452                     // "funclet can't have 2 successor funclets"
 453                     // requirement from MSVC:
 454                     //
 455                     //           switch       unwind-switch
 456                     //          /      \         /        \
 457                     //         v1.0    v2.0  v2.0-unwind  v1.0-unwind
 458                     //         |        |      /             |
 459                     //    v1.1-unwind  v2.1-unwind           |
 460                     //      ^                                |
 461                     //       \-------------------------------/
 462                     //
 463                     // Create a duplicate half-ladder to avoid that. We
 464                     // could technically only do this on MSVC, but I
 465                     // I want to minimize the divergence between MSVC
 466                     // and non-MSVC.
 467
 468                     let unwind_blocks = unwind_blocks.as_mut().unwrap();
 469                     let unwind_ladder = vec![Unwind::InCleanup; fields.len() + 1];
 470                     let halfladder = self.drop_halfladder(&unwind_ladder, unwind, &fields);
 471                     unwind_blocks.push(halfladder.last().cloned().unwrap());
 472                 }
 473                 let (normal, _) = self.drop_ladder(fields, succ, unwind);
 474                 normal_blocks.push(normal);
 475             } else {
 476                 have_otherwise = true;
 477             }
 478         }
 479
 480         if have_otherwise {
 481             normal_blocks.push(self.drop_block(succ, unwind));
 482             if let Unwind::To(unwind) = unwind {
 483                 unwind_blocks.as_mut().unwrap().push(self.drop_block(unwind, Unwind::InCleanup));
 484             }
 485         } else {
 486             values.pop();
 487         }
 488
 489         (
 490             self.adt_switch_block(adt, normal_blocks, &values, succ, unwind),
 491             unwind.map(|unwind| {
 492                 self.adt_switch_block(
 493                     adt,
 494                     unwind_blocks.unwrap(),
 495                     &values,
 496                     unwind,
 497                     Unwind::InCleanup,
 498                 )
 499             }),
 500         )
 501     }
 502
 503     fn adt_switch_block(
 504         &mut self,
 505         adt: &'tcx ty::AdtDef,
 506         blocks: Vec<BasicBlock>,
 507         values: &[u128],
 508         succ: BasicBlock,
 509         unwind: Unwind,
 510     ) -> BasicBlock {
 511         // If there are multiple variants, then if something
 512         // is present within the enum the discriminant, tracked
 513         // by the rest path, must be initialized.
 514         //
 515         // Additionally, we do not want to switch on the
 516         // discriminant after it is free-ed, because that
 517         // way lies only trouble.
 518         let discr_ty = adt.repr.discr_type().to_ty(self.tcx());
 519         let discr = Place::from(self.new_temp(discr_ty));
 520         let discr_rv = Rvalue::Discriminant(self.place.clone());
 521         let switch_block = BasicBlockData {
 522             statements: vec![self.assign(&discr, discr_rv)],
 523             terminator: Some(Terminator {
 524                 source_info: self.source_info,
 525                 kind: TerminatorKind::SwitchInt {
 526                     discr: Operand::Move(discr),
 527                     switch_ty: discr_ty,
 528                     values: From::from(values.to_owned()),
 529                     targets: blocks,
 530                 },
 531             }),
 532             is_cleanup: unwind.is_cleanup(),
 533         };
 534         let switch_block = self.elaborator.patch().new_block(switch_block);
 535         self.drop_flag_test_block(switch_block, succ, unwind)
 536     }
 537
 538     fn destructor_call_block(&mut self, (succ, unwind): (BasicBlock, Unwind)) -> BasicBlock {
 539         debug!("destructor_call_block({:?}, {:?})", self, succ);
 540         let tcx = self.tcx();
 541         let drop_trait = tcx.lang_items().drop_trait().unwrap();
 542         let drop_fn = tcx.associated_items(drop_trait).next().unwrap();
 543         let ty = self.place_ty(self.place);
 544         let substs = tcx.mk_substs_trait(ty, &[]);
 545
 546         let ref_ty =
 547             tcx.mk_ref(tcx.lifetimes.re_erased, ty::TypeAndMut { ty, mutbl: hir::Mutability::Mut });
 548         let ref_place = self.new_temp(ref_ty);
 549         let unit_temp = Place::from(self.new_temp(tcx.mk_unit()));
 550
 551         let result = BasicBlockData {
 552             statements: vec![self.assign(
 553                 &Place::from(ref_place),
 554                 Rvalue::Ref(
 555                     tcx.lifetimes.re_erased,
 556                     BorrowKind::Mut { allow_two_phase_borrow: false },
 557                     self.place.clone(),
 558                 ),
 559             )],
 560             terminator: Some(Terminator {
 561                 kind: TerminatorKind::Call {
 562                     func: Operand::function_handle(
 563                         tcx,
 564                         drop_fn.def_id,
 565                         substs,
 566                         self.source_info.span,
 567                     ),
 568                     args: vec![Operand::Move(Place::from(ref_place))],
 569                     destination: Some((unit_temp, succ)),
 570                     cleanup: unwind.into_option(),
 571                     from_hir_call: true,
 572                 },
 573                 source_info: self.source_info,
 574             }),
 575             is_cleanup: unwind.is_cleanup(),
 576         };
 577         self.elaborator.patch().new_block(result)
 578     }
 579
 580     /// Create a loop that drops an array:
 581     ///
 582     /// ```text
 583     /// loop-block:
 584     ///    can_go = cur == length_or_end
 585     ///    if can_go then succ else drop-block
 586     /// drop-block:
 587     ///    if ptr_based {
 588     ///        ptr = cur
 589     ///        cur = cur.offset(1)
 590     ///    } else {
 591     ///        ptr = &raw mut P[cur]
 592     ///        cur = cur + 1
 593     ///    }
 594     ///    drop(ptr)
 595     /// ```
 596     fn drop_loop(
 597         &mut self,
 598         succ: BasicBlock,
 599         cur: Local,
 600         length_or_end: &Place<'tcx>,
 601         ety: Ty<'tcx>,
 602         unwind: Unwind,
 603         ptr_based: bool,
 604     ) -> BasicBlock {
 605         let copy = |place: Place<'tcx>| Operand::Copy(place);
 606         let move_ = |place: Place<'tcx>| Operand::Move(place);
 607         let tcx = self.tcx();
 608
 609         let ptr_ty = tcx.mk_ptr(ty::TypeAndMut { ty: ety, mutbl: hir::Mutability::Mut });
 610         let ptr = &Place::from(self.new_temp(ptr_ty));
 611         let can_go = Place::from(self.new_temp(tcx.types.bool));
 612
 613         let one = self.constant_usize(1);
 614         let (ptr_next, cur_next) = if ptr_based {
 615             (Rvalue::Use(copy(cur.into())), Rvalue::BinaryOp(BinOp::Offset, move_(cur.into()), one))
 616         } else {
 617             (
 618                 Rvalue::AddressOf(Mutability::Mut, tcx.mk_place_index(self.place.clone(), cur)),
 619                 Rvalue::BinaryOp(BinOp::Add, move_(cur.into()), one),
 620             )
 621         };
 622
 623         let drop_block = BasicBlockData {
 624             statements: vec![self.assign(ptr, ptr_next), self.assign(&Place::from(cur), cur_next)],
 625             is_cleanup: unwind.is_cleanup(),
 626             terminator: Some(Terminator {
 627                 source_info: self.source_info,
 628                 // this gets overwritten by drop elaboration.
 629                 kind: TerminatorKind::Unreachable,
 630             }),
 631         };
 632         let drop_block = self.elaborator.patch().new_block(drop_block);
 633
 634         let loop_block = BasicBlockData {
 635             statements: vec![self.assign(
 636                 &can_go,
 637                 Rvalue::BinaryOp(BinOp::Eq, copy(Place::from(cur)), copy(length_or_end.clone())),
 638             )],
 639             is_cleanup: unwind.is_cleanup(),
 640             terminator: Some(Terminator {
 641                 source_info: self.source_info,
 642                 kind: TerminatorKind::if_(tcx, move_(can_go), succ, drop_block),
 643             }),
 644         };
 645         let loop_block = self.elaborator.patch().new_block(loop_block);
 646
 647         self.elaborator.patch().patch_terminator(
 648             drop_block,
 649             TerminatorKind::Drop {
 650                 location: tcx.mk_place_deref(ptr.clone()),
 651                 target: loop_block,
 652                 unwind: unwind.into_option(),
 653             },
 654         );
 655
 656         loop_block
 657     }
 658
 659     fn open_drop_for_array(&mut self, ety: Ty<'tcx>, opt_size: Option<u64>) -> BasicBlock {
 660         debug!("open_drop_for_array({:?}, {:?})", ety, opt_size);
 661
 662         // if size_of::<ety>() == 0 {
 663         //     index_based_loop
 664         // } else {
 665         //     ptr_based_loop
 666         // }
 667
 668         let tcx = self.tcx();
 669
 670         if let Some(size) = opt_size {
 671             let size: u32 = size.try_into().unwrap_or_else(|_| {
 672                 bug!("move out check isn't implemented for array sizes bigger than u32::MAX");
 673             });
 674             let fields: Vec<(Place<'tcx>, Option<D::Path>)> = (0..size)
 675                 .map(|i| {
 676                     (
 677                         tcx.mk_place_elem(
 678                             self.place.clone(),
 679                             ProjectionElem::ConstantIndex {
 680                                 offset: i,
 681                                 min_length: size,
 682                                 from_end: false,
 683                             },
 684                         ),
 685                         self.elaborator.array_subpath(self.path, i, size),
 686                     )
 687                 })
 688                 .collect();
 689
 690             if fields.iter().any(|(_, path)| path.is_some()) {
 691                 let (succ, unwind) = self.drop_ladder_bottom();
 692                 return self.drop_ladder(fields, succ, unwind).0;
 693             }
 694         }
 695
 696         let move_ = |place: &Place<'tcx>| Operand::Move(place.clone());
 697         let elem_size = &Place::from(self.new_temp(tcx.types.usize));
 698         let len = &Place::from(self.new_temp(tcx.types.usize));
 699
 700         static USIZE_SWITCH_ZERO: &[u128] = &[0];
 701
 702         let base_block = BasicBlockData {
 703             statements: vec![
 704                 self.assign(elem_size, Rvalue::NullaryOp(NullOp::SizeOf, ety)),
 705                 self.assign(len, Rvalue::Len(self.place.clone())),
 706             ],
 707             is_cleanup: self.unwind.is_cleanup(),
 708             terminator: Some(Terminator {
 709                 source_info: self.source_info,
 710                 kind: TerminatorKind::SwitchInt {
 711                     discr: move_(elem_size),
 712                     switch_ty: tcx.types.usize,
 713                     values: From::from(USIZE_SWITCH_ZERO),
 714                     targets: vec![
 715                         self.drop_loop_pair(ety, false, len.clone()),
 716                         self.drop_loop_pair(ety, true, len.clone()),
 717                     ],
 718                 },
 719             }),
 720         };
 721         self.elaborator.patch().new_block(base_block)
 722     }
 723
 724     /// Ceates a pair of drop-loops of `place`, which drops its contents, even
 725     /// in the case of 1 panic. If `ptr_based`, creates a pointer loop,
 726     /// otherwise create an index loop.
 727     fn drop_loop_pair(
 728         &mut self,
 729         ety: Ty<'tcx>,
 730         ptr_based: bool,
 731         length: Place<'tcx>,
 732     ) -> BasicBlock {
 733         debug!("drop_loop_pair({:?}, {:?})", ety, ptr_based);
 734         let tcx = self.tcx();
 735         let iter_ty = if ptr_based { tcx.mk_mut_ptr(ety) } else { tcx.types.usize };
 736
 737         let cur = self.new_temp(iter_ty);
 738         let length_or_end =
 739             if ptr_based { Place::from(self.new_temp(iter_ty)) } else { length.clone() };
 740
 741         let unwind = self.unwind.map(|unwind| {
 742             self.drop_loop(unwind, cur, &length_or_end, ety, Unwind::InCleanup, ptr_based)
 743         });
 744
 745         let loop_block = self.drop_loop(self.succ, cur, &length_or_end, ety, unwind, ptr_based);
 746
 747         let cur = Place::from(cur);
 748         let drop_block_stmts = if ptr_based {
 749             let tmp_ty = tcx.mk_mut_ptr(self.place_ty(self.place));
 750             let tmp = Place::from(self.new_temp(tmp_ty));
 751             // tmp = &raw mut P;
 752             // cur = tmp as *mut T;
 753             // end = Offset(cur, len);
 754             vec![
 755                 self.assign(&tmp, Rvalue::AddressOf(Mutability::Mut, self.place.clone())),
 756                 self.assign(&cur, Rvalue::Cast(CastKind::Misc, Operand::Move(tmp), iter_ty)),
 757                 self.assign(
 758                     &length_or_end,
 759                     Rvalue::BinaryOp(BinOp::Offset, Operand::Copy(cur), Operand::Move(length)),
 760                 ),
 761             ]
 762         } else {
 763             // cur = 0 (length already pushed)
 764             let zero = self.constant_usize(0);
 765             vec![self.assign(&cur, Rvalue::Use(zero))]
 766         };
 767         let drop_block = self.elaborator.patch().new_block(BasicBlockData {
 768             statements: drop_block_stmts,
 769             is_cleanup: unwind.is_cleanup(),
 770             terminator: Some(Terminator {
 771                 source_info: self.source_info,
 772                 kind: TerminatorKind::Goto { target: loop_block },
 773             }),
 774         });
 775
 776         // FIXME(#34708): handle partially-dropped array/slice elements.
 777         let reset_block = self.drop_flag_reset_block(DropFlagMode::Deep, drop_block, unwind);
 778         self.drop_flag_test_block(reset_block, self.succ, unwind)
 779     }
 780
 781     /// The slow-path - create an "open", elaborated drop for a type
 782     /// which is moved-out-of only partially, and patch `bb` to a jump
 783     /// to it. This must not be called on ADTs with a destructor,
 784     /// as these can't be moved-out-of, except for `Box<T>`, which is
 785     /// special-cased.
 786     ///
 787     /// This creates a "drop ladder" that drops the needed fields of the
 788     /// ADT, both in the success case or if one of the destructors fail.
 789     fn open_drop(&mut self) -> BasicBlock {
 790         let ty = self.place_ty(self.place);
 791         match ty.kind {
 792             ty::Closure(def_id, substs) => {
 793                 let tys: Vec<_> = substs.as_closure().upvar_tys(def_id, self.tcx()).collect();
 794                 self.open_drop_for_tuple(&tys)
 795             }
 796             // Note that `elaborate_drops` only drops the upvars of a generator,
 797             // and this is ok because `open_drop` here can only be reached
 798             // within that own generator's resume function.
 799             // This should only happen for the self argument on the resume function.
 800             // It effetively only contains upvars until the generator transformation runs.
 801             // See librustc_body/transform/generator.rs for more details.
 802             ty::Generator(def_id, substs, _) => {
 803                 let tys: Vec<_> = substs.as_generator().upvar_tys(def_id, self.tcx()).collect();
 804                 self.open_drop_for_tuple(&tys)
 805             }
 806             ty::Tuple(..) => {
 807                 let tys: Vec<_> = ty.tuple_fields().collect();
 808                 self.open_drop_for_tuple(&tys)
 809             }
 810             ty::Adt(def, substs) => {
 811                 if def.is_box() {
 812                     self.open_drop_for_box(def, substs)
 813                 } else {
 814                     self.open_drop_for_adt(def, substs)
 815                 }
 816             }
 817             ty::Dynamic(..) => {
 818                 let unwind = self.unwind; // FIXME(#43234)
 819                 let succ = self.succ;
 820                 self.complete_drop(Some(DropFlagMode::Deep), succ, unwind)
 821             }
 822             ty::Array(ety, size) => {
 823                 let size = size.try_eval_usize(self.tcx(), self.elaborator.param_env());
 824                 self.open_drop_for_array(ety, size)
 825             }
 826             ty::Slice(ety) => self.open_drop_for_array(ety, None),
 827
 828             _ => bug!("open drop from non-ADT `{:?}`", ty),
 829         }
 830     }
 831
 832     /// Returns a basic block that drop a place using the context
 833     /// and path in `c`. If `mode` is something, also clear `c`
 834     /// according to it.
 835     ///
 836     /// if FLAG(self.path)
 837     ///     if let Some(mode) = mode: FLAG(self.path)[mode] = false
 838     ///     drop(self.place)
 839     fn complete_drop(
 840         &mut self,
 841         drop_mode: Option<DropFlagMode>,
 842         succ: BasicBlock,
 843         unwind: Unwind,
 844     ) -> BasicBlock {
 845         debug!("complete_drop({:?},{:?})", self, drop_mode);
 846
 847         let drop_block = self.drop_block(succ, unwind);
 848         let drop_block = if let Some(mode) = drop_mode {
 849             self.drop_flag_reset_block(mode, drop_block, unwind)
 850         } else {
 851             drop_block
 852         };
 853
 854         self.drop_flag_test_block(drop_block, succ, unwind)
 855     }
 856
 857     fn drop_flag_reset_block(
 858         &mut self,
 859         mode: DropFlagMode,
 860         succ: BasicBlock,
 861         unwind: Unwind,
 862     ) -> BasicBlock {
 863         debug!("drop_flag_reset_block({:?},{:?})", self, mode);
 864
 865         let block = self.new_block(unwind, TerminatorKind::Goto { target: succ });
 866         let block_start = Location { block: block, statement_index: 0 };
 867         self.elaborator.clear_drop_flag(block_start, self.path, mode);
 868         block
 869     }
 870
 871     fn elaborated_drop_block(&mut self) -> BasicBlock {
 872         debug!("elaborated_drop_block({:?})", self);
 873         let unwind = self.unwind; // FIXME(#43234)
 874         let succ = self.succ;
 875         let blk = self.drop_block(succ, unwind);
 876         self.elaborate_drop(blk);
 877         blk
 878     }
 879
 880     fn box_free_block(
 881         &mut self,
 882         adt: &'tcx ty::AdtDef,
 883         substs: SubstsRef<'tcx>,
 884         target: BasicBlock,
 885         unwind: Unwind,
 886     ) -> BasicBlock {
 887         let block = self.unelaborated_free_block(adt, substs, target, unwind);
 888         self.drop_flag_test_block(block, target, unwind)
 889     }
 890
 891     fn unelaborated_free_block(
 892         &mut self,
 893         adt: &'tcx ty::AdtDef,
 894         substs: SubstsRef<'tcx>,
 895         target: BasicBlock,
 896         unwind: Unwind,
 897     ) -> BasicBlock {
 898         let tcx = self.tcx();
 899         let unit_temp = Place::from(self.new_temp(tcx.mk_unit()));
 900         let free_func =
 901             tcx.require_lang_item(lang_items::BoxFreeFnLangItem, Some(self.source_info.span));
 902         let args = adt.variants[VariantIdx::new(0)]
 903             .fields
 904             .iter()
 905             .enumerate()
 906             .map(|(i, f)| {
 907                 let field = Field::new(i);
 908                 let field_ty = f.ty(tcx, substs);
 909                 Operand::Move(tcx.mk_place_field(self.place.clone(), field, field_ty))
 910             })
 911             .collect();
 912
 913         let call = TerminatorKind::Call {
 914             func: Operand::function_handle(tcx, free_func, substs, self.source_info.span),
 915             args: args,
 916             destination: Some((unit_temp, target)),
 917             cleanup: None,
 918             from_hir_call: false,
 919         }; // FIXME(#43234)
 920         let free_block = self.new_block(unwind, call);
 921
 922         let block_start = Location { block: free_block, statement_index: 0 };
 923         self.elaborator.clear_drop_flag(block_start, self.path, DropFlagMode::Shallow);
 924         free_block
 925     }
 926
 927     fn drop_block(&mut self, target: BasicBlock, unwind: Unwind) -> BasicBlock {
 928         let block = TerminatorKind::Drop {
 929             location: self.place.clone(),
 930             target,
 931             unwind: unwind.into_option(),
 932         };
 933         self.new_block(unwind, block)
 934     }
 935
 936     fn drop_flag_test_block(
 937         &mut self,
 938         on_set: BasicBlock,
 939         on_unset: BasicBlock,
 940         unwind: Unwind,
 941     ) -> BasicBlock {
 942         let style = self.elaborator.drop_style(self.path, DropFlagMode::Shallow);
 943         debug!(
 944             "drop_flag_test_block({:?},{:?},{:?},{:?}) - {:?}",
 945             self, on_set, on_unset, unwind, style
 946         );
 947
 948         match style {
 949             DropStyle::Dead => on_unset,
 950             DropStyle::Static => on_set,
 951             DropStyle::Conditional | DropStyle::Open => {
 952                 let flag = self.elaborator.get_drop_flag(self.path).unwrap();
 953                 let term = TerminatorKind::if_(self.tcx(), flag, on_set, on_unset);
 954                 self.new_block(unwind, term)
 955             }
 956         }
 957     }
 958
 959     fn new_block(&mut self, unwind: Unwind, k: TerminatorKind<'tcx>) -> BasicBlock {
 960         self.elaborator.patch().new_block(BasicBlockData {
 961             statements: vec![],
 962             terminator: Some(Terminator { source_info: self.source_info, kind: k }),
 963             is_cleanup: unwind.is_cleanup(),
 964         })
 965     }
 966
 967     fn new_temp(&mut self, ty: Ty<'tcx>) -> Local {
 968         self.elaborator.patch().new_temp(ty, self.source_info.span)
 969     }
 970
 971     fn terminator_loc(&mut self, bb: BasicBlock) -> Location {
 972         let body = self.elaborator.body();
 973         self.elaborator.patch().terminator_loc(body, bb)
 974     }
 975
 976     fn constant_usize(&self, val: u16) -> Operand<'tcx> {
 977         Operand::Constant(box Constant {
 978             span: self.source_info.span,
 979             user_ty: None,
 980             literal: ty::Const::from_usize(self.tcx(), val.into()),
 981         })
 982     }
 983
 984     fn assign(&self, lhs: &Place<'tcx>, rhs: Rvalue<'tcx>) -> Statement<'tcx> {
 985         Statement {
 986             source_info: self.source_info,
 987             kind: StatementKind::Assign(box (lhs.clone(), rhs)),
 988         }
 989     }
 990 }