src/librustc_mir/util/elaborate_drops.rs

   1 use crate::util::patch::MirPatch;
   2 use rustc_hir as hir;
   3 use rustc_hir::lang_items;
   4 use rustc_index::vec::Idx;
   5 use rustc_middle::mir::*;
   6 use rustc_middle::traits::Reveal;
   7 use rustc_middle::ty::subst::SubstsRef;
   8 use rustc_middle::ty::util::IntTypeExt;
   9 use rustc_middle::ty::{self, Ty, TyCtxt};
  10 use rustc_target::abi::VariantIdx;
  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: 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(|(&(place, path), &unwind_succ)| {
 271                 succ = self.drop_subpath(place, path, succ, unwind_succ);
 272                 succ
 273             }))
 274             .collect()
 275     }
 276
 277     fn drop_ladder_bottom(&mut self) -> (BasicBlock, Unwind) {
 278         // Clear the "master" drop flag at the end. This is needed
 279         // because the "master" drop protects the ADT's discriminant,
 280         // which is invalidated after the ADT is dropped.
 281         let (succ, unwind) = (self.succ, self.unwind); // FIXME(#43234)
 282         (
 283             self.drop_flag_reset_block(DropFlagMode::Shallow, succ, unwind),
 284             unwind.map(|unwind| {
 285                 self.drop_flag_reset_block(DropFlagMode::Shallow, unwind, Unwind::InCleanup)
 286             }),
 287         )
 288     }
 289
 290     /// Creates a full drop ladder, consisting of 2 connected half-drop-ladders
 291     ///
 292     /// For example, with 3 fields, the drop ladder is
 293     ///
 294     /// .d0:
 295     ///     ELAB(drop location.0 [target=.d1, unwind=.c1])
 296     /// .d1:
 297     ///     ELAB(drop location.1 [target=.d2, unwind=.c2])
 298     /// .d2:
 299     ///     ELAB(drop location.2 [target=`self.succ`, unwind=`self.unwind`])
 300     /// .c1:
 301     ///     ELAB(drop location.1 [target=.c2])
 302     /// .c2:
 303     ///     ELAB(drop location.2 [target=`self.unwind`])
 304     ///
 305     /// NOTE: this does not clear the master drop flag, so you need
 306     /// to point succ/unwind on a `drop_ladder_bottom`.
 307     fn drop_ladder(
 308         &mut self,
 309         fields: Vec<(Place<'tcx>, Option<D::Path>)>,
 310         succ: BasicBlock,
 311         unwind: Unwind,
 312     ) -> (BasicBlock, Unwind) {
 313         debug!("drop_ladder({:?}, {:?})", self, fields);
 314
 315         let mut fields = fields;
 316         fields.retain(|&(place, _)| {
 317             self.place_ty(place).needs_drop(self.tcx(), self.elaborator.param_env())
 318         });
 319
 320         debug!("drop_ladder - fields needing drop: {:?}", fields);
 321
 322         let unwind_ladder = vec![Unwind::InCleanup; fields.len() + 1];
 323         let unwind_ladder: Vec<_> = if let Unwind::To(target) = unwind {
 324             let halfladder = self.drop_halfladder(&unwind_ladder, target, &fields);
 325             halfladder.into_iter().map(Unwind::To).collect()
 326         } else {
 327             unwind_ladder
 328         };
 329
 330         let normal_ladder = self.drop_halfladder(&unwind_ladder, succ, &fields);
 331
 332         (*normal_ladder.last().unwrap(), *unwind_ladder.last().unwrap())
 333     }
 334
 335     fn open_drop_for_tuple(&mut self, tys: &[Ty<'tcx>]) -> BasicBlock {
 336         debug!("open_drop_for_tuple({:?}, {:?})", self, tys);
 337
 338         let fields = tys
 339             .iter()
 340             .enumerate()
 341             .map(|(i, &ty)| {
 342                 (
 343                     self.tcx().mk_place_field(self.place.clone(), Field::new(i), ty),
 344                     self.elaborator.field_subpath(self.path, Field::new(i)),
 345                 )
 346             })
 347             .collect();
 348
 349         let (succ, unwind) = self.drop_ladder_bottom();
 350         self.drop_ladder(fields, succ, unwind).0
 351     }
 352
 353     fn open_drop_for_box(&mut self, adt: &'tcx ty::AdtDef, substs: SubstsRef<'tcx>) -> BasicBlock {
 354         debug!("open_drop_for_box({:?}, {:?}, {:?})", self, adt, substs);
 355
 356         let interior = self.tcx().mk_place_deref(self.place.clone());
 357         let interior_path = self.elaborator.deref_subpath(self.path);
 358
 359         let succ = self.succ; // FIXME(#43234)
 360         let unwind = self.unwind;
 361         let succ = self.box_free_block(adt, substs, succ, unwind);
 362         let unwind_succ =
 363             self.unwind.map(|unwind| self.box_free_block(adt, substs, unwind, Unwind::InCleanup));
 364
 365         self.drop_subpath(interior, interior_path, succ, unwind_succ)
 366     }
 367
 368     fn open_drop_for_adt(&mut self, adt: &'tcx ty::AdtDef, substs: SubstsRef<'tcx>) -> BasicBlock {
 369         debug!("open_drop_for_adt({:?}, {:?}, {:?})", self, adt, substs);
 370         if adt.variants.is_empty() {
 371             return self.elaborator.patch().new_block(BasicBlockData {
 372                 statements: vec![],
 373                 terminator: Some(Terminator {
 374                     source_info: self.source_info,
 375                     kind: TerminatorKind::Unreachable,
 376                 }),
 377                 is_cleanup: self.unwind.is_cleanup(),
 378             });
 379         }
 380
 381         let skip_contents =
 382             adt.is_union() || Some(adt.did) == self.tcx().lang_items().manually_drop();
 383         let contents_drop = if skip_contents {
 384             (self.succ, self.unwind)
 385         } else {
 386             self.open_drop_for_adt_contents(adt, substs)
 387         };
 388
 389         if adt.has_dtor(self.tcx()) {
 390             self.destructor_call_block(contents_drop)
 391         } else {
 392             contents_drop.0
 393         }
 394     }
 395
 396     fn open_drop_for_adt_contents(
 397         &mut self,
 398         adt: &'tcx ty::AdtDef,
 399         substs: SubstsRef<'tcx>,
 400     ) -> (BasicBlock, Unwind) {
 401         let (succ, unwind) = self.drop_ladder_bottom();
 402         if !adt.is_enum() {
 403             let fields = self.move_paths_for_fields(
 404                 self.place,
 405                 self.path,
 406                 &adt.variants[VariantIdx::new(0)],
 407                 substs,
 408             );
 409             self.drop_ladder(fields, succ, unwind)
 410         } else {
 411             self.open_drop_for_multivariant(adt, substs, succ, unwind)
 412         }
 413     }
 414
 415     fn open_drop_for_multivariant(
 416         &mut self,
 417         adt: &'tcx ty::AdtDef,
 418         substs: SubstsRef<'tcx>,
 419         succ: BasicBlock,
 420         unwind: Unwind,
 421     ) -> (BasicBlock, Unwind) {
 422         let mut values = Vec::with_capacity(adt.variants.len());
 423         let mut normal_blocks = Vec::with_capacity(adt.variants.len());
 424         let mut unwind_blocks =
 425             if unwind.is_cleanup() { None } else { Some(Vec::with_capacity(adt.variants.len())) };
 426
 427         let mut have_otherwise_with_drop_glue = false;
 428         let mut have_otherwise = false;
 429         let tcx = self.tcx();
 430
 431         for (variant_index, discr) in adt.discriminants(tcx) {
 432             let variant = &adt.variants[variant_index];
 433             let subpath = self.elaborator.downcast_subpath(self.path, variant_index);
 434
 435             if let Some(variant_path) = subpath {
 436                 let base_place = tcx.mk_place_elem(
 437                     self.place.clone(),
 438                     ProjectionElem::Downcast(Some(variant.ident.name), variant_index),
 439                 );
 440                 let fields = self.move_paths_for_fields(base_place, variant_path, &variant, substs);
 441                 values.push(discr.val);
 442                 if let Unwind::To(unwind) = unwind {
 443                     // We can't use the half-ladder from the original
 444                     // drop ladder, because this breaks the
 445                     // "funclet can't have 2 successor funclets"
 446                     // requirement from MSVC:
 447                     //
 448                     //           switch       unwind-switch
 449                     //          /      \         /        \
 450                     //         v1.0    v2.0  v2.0-unwind  v1.0-unwind
 451                     //         |        |      /             |
 452                     //    v1.1-unwind  v2.1-unwind           |
 453                     //      ^                                |
 454                     //       \-------------------------------/
 455                     //
 456                     // Create a duplicate half-ladder to avoid that. We
 457                     // could technically only do this on MSVC, but I
 458                     // I want to minimize the divergence between MSVC
 459                     // and non-MSVC.
 460
 461                     let unwind_blocks = unwind_blocks.as_mut().unwrap();
 462                     let unwind_ladder = vec![Unwind::InCleanup; fields.len() + 1];
 463                     let halfladder = self.drop_halfladder(&unwind_ladder, unwind, &fields);
 464                     unwind_blocks.push(halfladder.last().cloned().unwrap());
 465                 }
 466                 let (normal, _) = self.drop_ladder(fields, succ, unwind);
 467                 normal_blocks.push(normal);
 468             } else {
 469                 have_otherwise = true;
 470
 471                 let param_env = self.elaborator.param_env();
 472                 let have_field_with_drop_glue = variant
 473                     .fields
 474                     .iter()
 475                     .any(|field| field.ty(tcx, substs).needs_drop(tcx, param_env));
 476                 if have_field_with_drop_glue {
 477                     have_otherwise_with_drop_glue = true;
 478                 }
 479             }
 480         }
 481
 482         if !have_otherwise {
 483             values.pop();
 484         } else if !have_otherwise_with_drop_glue {
 485             normal_blocks.push(self.goto_block(succ, unwind));
 486             if let Unwind::To(unwind) = unwind {
 487                 unwind_blocks.as_mut().unwrap().push(self.goto_block(unwind, Unwind::InCleanup));
 488             }
 489         } else {
 490             normal_blocks.push(self.drop_block(succ, unwind));
 491             if let Unwind::To(unwind) = unwind {
 492                 unwind_blocks.as_mut().unwrap().push(self.drop_block(unwind, Unwind::InCleanup));
 493             }
 494         }
 495
 496         (
 497             self.adt_switch_block(adt, normal_blocks, &values, succ, unwind),
 498             unwind.map(|unwind| {
 499                 self.adt_switch_block(
 500                     adt,
 501                     unwind_blocks.unwrap(),
 502                     &values,
 503                     unwind,
 504                     Unwind::InCleanup,
 505                 )
 506             }),
 507         )
 508     }
 509
 510     fn adt_switch_block(
 511         &mut self,
 512         adt: &'tcx ty::AdtDef,
 513         blocks: Vec<BasicBlock>,
 514         values: &[u128],
 515         succ: BasicBlock,
 516         unwind: Unwind,
 517     ) -> BasicBlock {
 518         // If there are multiple variants, then if something
 519         // is present within the enum the discriminant, tracked
 520         // by the rest path, must be initialized.
 521         //
 522         // Additionally, we do not want to switch on the
 523         // discriminant after it is free-ed, because that
 524         // way lies only trouble.
 525         let discr_ty = adt.repr.discr_type().to_ty(self.tcx());
 526         let discr = Place::from(self.new_temp(discr_ty));
 527         let discr_rv = Rvalue::Discriminant(self.place);
 528         let switch_block = BasicBlockData {
 529             statements: vec![self.assign(discr, discr_rv)],
 530             terminator: Some(Terminator {
 531                 source_info: self.source_info,
 532                 kind: TerminatorKind::SwitchInt {
 533                     discr: Operand::Move(discr),
 534                     switch_ty: discr_ty,
 535                     values: From::from(values.to_owned()),
 536                     targets: blocks,
 537                 },
 538             }),
 539             is_cleanup: unwind.is_cleanup(),
 540         };
 541         let switch_block = self.elaborator.patch().new_block(switch_block);
 542         self.drop_flag_test_block(switch_block, succ, unwind)
 543     }
 544
 545     fn destructor_call_block(&mut self, (succ, unwind): (BasicBlock, Unwind)) -> BasicBlock {
 546         debug!("destructor_call_block({:?}, {:?})", self, succ);
 547         let tcx = self.tcx();
 548         let drop_trait = tcx.lang_items().drop_trait().unwrap();
 549         let drop_fn = tcx.associated_items(drop_trait).in_definition_order().next().unwrap();
 550         let ty = self.place_ty(self.place);
 551         let substs = tcx.mk_substs_trait(ty, &[]);
 552
 553         let ref_ty =
 554             tcx.mk_ref(tcx.lifetimes.re_erased, ty::TypeAndMut { ty, mutbl: hir::Mutability::Mut });
 555         let ref_place = self.new_temp(ref_ty);
 556         let unit_temp = Place::from(self.new_temp(tcx.mk_unit()));
 557
 558         let result = BasicBlockData {
 559             statements: vec![self.assign(
 560                 Place::from(ref_place),
 561                 Rvalue::Ref(
 562                     tcx.lifetimes.re_erased,
 563                     BorrowKind::Mut { allow_two_phase_borrow: false },
 564                     self.place,
 565                 ),
 566             )],
 567             terminator: Some(Terminator {
 568                 kind: TerminatorKind::Call {
 569                     func: Operand::function_handle(
 570                         tcx,
 571                         drop_fn.def_id,
 572                         substs,
 573                         self.source_info.span,
 574                     ),
 575                     args: vec![Operand::Move(Place::from(ref_place))],
 576                     destination: Some((unit_temp, succ)),
 577                     cleanup: unwind.into_option(),
 578                     from_hir_call: true,
 579                 },
 580                 source_info: self.source_info,
 581             }),
 582             is_cleanup: unwind.is_cleanup(),
 583         };
 584         self.elaborator.patch().new_block(result)
 585     }
 586
 587     /// Create a loop that drops an array:
 588     ///
 589     /// ```text
 590     /// loop-block:
 591     ///    can_go = cur == length_or_end
 592     ///    if can_go then succ else drop-block
 593     /// drop-block:
 594     ///    if ptr_based {
 595     ///        ptr = cur
 596     ///        cur = cur.offset(1)
 597     ///    } else {
 598     ///        ptr = &raw mut P[cur]
 599     ///        cur = cur + 1
 600     ///    }
 601     ///    drop(ptr)
 602     /// ```
 603     fn drop_loop(
 604         &mut self,
 605         succ: BasicBlock,
 606         cur: Local,
 607         length_or_end: Place<'tcx>,
 608         ety: Ty<'tcx>,
 609         unwind: Unwind,
 610         ptr_based: bool,
 611     ) -> BasicBlock {
 612         let copy = |place: Place<'tcx>| Operand::Copy(place);
 613         let move_ = |place: Place<'tcx>| Operand::Move(place);
 614         let tcx = self.tcx();
 615
 616         let ptr_ty = tcx.mk_ptr(ty::TypeAndMut { ty: ety, mutbl: hir::Mutability::Mut });
 617         let ptr = Place::from(self.new_temp(ptr_ty));
 618         let can_go = Place::from(self.new_temp(tcx.types.bool));
 619
 620         let one = self.constant_usize(1);
 621         let (ptr_next, cur_next) = if ptr_based {
 622             (Rvalue::Use(copy(cur.into())), Rvalue::BinaryOp(BinOp::Offset, move_(cur.into()), one))
 623         } else {
 624             (
 625                 Rvalue::AddressOf(Mutability::Mut, tcx.mk_place_index(self.place.clone(), cur)),
 626                 Rvalue::BinaryOp(BinOp::Add, move_(cur.into()), one),
 627             )
 628         };
 629
 630         let drop_block = BasicBlockData {
 631             statements: vec![self.assign(ptr, ptr_next), self.assign(Place::from(cur), cur_next)],
 632             is_cleanup: unwind.is_cleanup(),
 633             terminator: Some(Terminator {
 634                 source_info: self.source_info,
 635                 // this gets overwritten by drop elaboration.
 636                 kind: TerminatorKind::Unreachable,
 637             }),
 638         };
 639         let drop_block = self.elaborator.patch().new_block(drop_block);
 640
 641         let loop_block = BasicBlockData {
 642             statements: vec![self.assign(
 643                 can_go,
 644                 Rvalue::BinaryOp(BinOp::Eq, copy(Place::from(cur)), copy(length_or_end)),
 645             )],
 646             is_cleanup: unwind.is_cleanup(),
 647             terminator: Some(Terminator {
 648                 source_info: self.source_info,
 649                 kind: TerminatorKind::if_(tcx, move_(can_go), succ, drop_block),
 650             }),
 651         };
 652         let loop_block = self.elaborator.patch().new_block(loop_block);
 653
 654         self.elaborator.patch().patch_terminator(
 655             drop_block,
 656             TerminatorKind::Drop {
 657                 location: tcx.mk_place_deref(ptr.clone()),
 658                 target: loop_block,
 659                 unwind: unwind.into_option(),
 660             },
 661         );
 662
 663         loop_block
 664     }
 665
 666     fn open_drop_for_array(&mut self, ety: Ty<'tcx>, opt_size: Option<u64>) -> BasicBlock {
 667         debug!("open_drop_for_array({:?}, {:?})", ety, opt_size);
 668
 669         // if size_of::<ety>() == 0 {
 670         //     index_based_loop
 671         // } else {
 672         //     ptr_based_loop
 673         // }
 674
 675         let tcx = self.tcx();
 676
 677         if let Some(size) = opt_size {
 678             let size: u32 = size.try_into().unwrap_or_else(|_| {
 679                 bug!("move out check isn't implemented for array sizes bigger than u32::MAX");
 680             });
 681             let fields: Vec<(Place<'tcx>, Option<D::Path>)> = (0..size)
 682                 .map(|i| {
 683                     (
 684                         tcx.mk_place_elem(
 685                             self.place.clone(),
 686                             ProjectionElem::ConstantIndex {
 687                                 offset: i,
 688                                 min_length: size,
 689                                 from_end: false,
 690                             },
 691                         ),
 692                         self.elaborator.array_subpath(self.path, i, size),
 693                     )
 694                 })
 695                 .collect();
 696
 697             if fields.iter().any(|(_, path)| path.is_some()) {
 698                 let (succ, unwind) = self.drop_ladder_bottom();
 699                 return self.drop_ladder(fields, succ, unwind).0;
 700             }
 701         }
 702
 703         let move_ = |place: Place<'tcx>| Operand::Move(place);
 704         let elem_size = Place::from(self.new_temp(tcx.types.usize));
 705         let len = Place::from(self.new_temp(tcx.types.usize));
 706
 707         static USIZE_SWITCH_ZERO: &[u128] = &[0];
 708
 709         let base_block = BasicBlockData {
 710             statements: vec![
 711                 self.assign(elem_size, Rvalue::NullaryOp(NullOp::SizeOf, ety)),
 712                 self.assign(len, Rvalue::Len(self.place)),
 713             ],
 714             is_cleanup: self.unwind.is_cleanup(),
 715             terminator: Some(Terminator {
 716                 source_info: self.source_info,
 717                 kind: TerminatorKind::SwitchInt {
 718                     discr: move_(elem_size),
 719                     switch_ty: tcx.types.usize,
 720                     values: From::from(USIZE_SWITCH_ZERO),
 721                     targets: vec![
 722                         self.drop_loop_pair(ety, false, len.clone()),
 723                         self.drop_loop_pair(ety, true, len.clone()),
 724                     ],
 725                 },
 726             }),
 727         };
 728         self.elaborator.patch().new_block(base_block)
 729     }
 730
 731     /// Creates a pair of drop-loops of `place`, which drops its contents, even
 732     /// in the case of 1 panic. If `ptr_based`, creates a pointer loop,
 733     /// otherwise create an index loop.
 734     fn drop_loop_pair(
 735         &mut self,
 736         ety: Ty<'tcx>,
 737         ptr_based: bool,
 738         length: Place<'tcx>,
 739     ) -> BasicBlock {
 740         debug!("drop_loop_pair({:?}, {:?})", ety, ptr_based);
 741         let tcx = self.tcx();
 742         let iter_ty = if ptr_based { tcx.mk_mut_ptr(ety) } else { tcx.types.usize };
 743
 744         let cur = self.new_temp(iter_ty);
 745         let length_or_end = if ptr_based { Place::from(self.new_temp(iter_ty)) } else { length };
 746
 747         let unwind = self.unwind.map(|unwind| {
 748             self.drop_loop(unwind, cur, length_or_end, ety, Unwind::InCleanup, ptr_based)
 749         });
 750
 751         let loop_block = self.drop_loop(self.succ, cur, length_or_end, ety, unwind, ptr_based);
 752
 753         let cur = Place::from(cur);
 754         let drop_block_stmts = if ptr_based {
 755             let tmp_ty = tcx.mk_mut_ptr(self.place_ty(self.place));
 756             let tmp = Place::from(self.new_temp(tmp_ty));
 757             // tmp = &raw mut P;
 758             // cur = tmp as *mut T;
 759             // end = Offset(cur, len);
 760             vec![
 761                 self.assign(tmp, Rvalue::AddressOf(Mutability::Mut, self.place)),
 762                 self.assign(cur, Rvalue::Cast(CastKind::Misc, Operand::Move(tmp), iter_ty)),
 763                 self.assign(
 764                     length_or_end,
 765                     Rvalue::BinaryOp(BinOp::Offset, Operand::Copy(cur), Operand::Move(length)),
 766                 ),
 767             ]
 768         } else {
 769             // cur = 0 (length already pushed)
 770             let zero = self.constant_usize(0);
 771             vec![self.assign(cur, Rvalue::Use(zero))]
 772         };
 773         let drop_block = self.elaborator.patch().new_block(BasicBlockData {
 774             statements: drop_block_stmts,
 775             is_cleanup: unwind.is_cleanup(),
 776             terminator: Some(Terminator {
 777                 source_info: self.source_info,
 778                 kind: TerminatorKind::Goto { target: loop_block },
 779             }),
 780         });
 781
 782         // FIXME(#34708): handle partially-dropped array/slice elements.
 783         let reset_block = self.drop_flag_reset_block(DropFlagMode::Deep, drop_block, unwind);
 784         self.drop_flag_test_block(reset_block, self.succ, unwind)
 785     }
 786
 787     /// The slow-path - create an "open", elaborated drop for a type
 788     /// which is moved-out-of only partially, and patch `bb` to a jump
 789     /// to it. This must not be called on ADTs with a destructor,
 790     /// as these can't be moved-out-of, except for `Box<T>`, which is
 791     /// special-cased.
 792     ///
 793     /// This creates a "drop ladder" that drops the needed fields of the
 794     /// ADT, both in the success case or if one of the destructors fail.
 795     fn open_drop(&mut self) -> BasicBlock {
 796         let ty = self.place_ty(self.place);
 797         match ty.kind {
 798             ty::Closure(_, substs) => {
 799                 let tys: Vec<_> = substs.as_closure().upvar_tys().collect();
 800                 self.open_drop_for_tuple(&tys)
 801             }
 802             // Note that `elaborate_drops` only drops the upvars of a generator,
 803             // and this is ok because `open_drop` here can only be reached
 804             // within that own generator's resume function.
 805             // This should only happen for the self argument on the resume function.
 806             // It effetively only contains upvars until the generator transformation runs.
 807             // See librustc_body/transform/generator.rs for more details.
 808             ty::Generator(_, substs, _) => {
 809                 let tys: Vec<_> = substs.as_generator().upvar_tys().collect();
 810                 self.open_drop_for_tuple(&tys)
 811             }
 812             ty::Tuple(..) => {
 813                 let tys: Vec<_> = ty.tuple_fields().collect();
 814                 self.open_drop_for_tuple(&tys)
 815             }
 816             ty::Adt(def, substs) => {
 817                 if def.is_box() {
 818                     self.open_drop_for_box(def, substs)
 819                 } else {
 820                     self.open_drop_for_adt(def, substs)
 821                 }
 822             }
 823             ty::Dynamic(..) => {
 824                 let unwind = self.unwind; // FIXME(#43234)
 825                 let succ = self.succ;
 826                 self.complete_drop(Some(DropFlagMode::Deep), succ, unwind)
 827             }
 828             ty::Array(ety, size) => {
 829                 let size = size.try_eval_usize(self.tcx(), self.elaborator.param_env());
 830                 self.open_drop_for_array(ety, size)
 831             }
 832             ty::Slice(ety) => self.open_drop_for_array(ety, None),
 833
 834             _ => bug!("open drop from non-ADT `{:?}`", ty),
 835         }
 836     }
 837
 838     /// Returns a basic block that drop a place using the context
 839     /// and path in `c`. If `mode` is something, also clear `c`
 840     /// according to it.
 841     ///
 842     /// if FLAG(self.path)
 843     ///     if let Some(mode) = mode: FLAG(self.path)[mode] = false
 844     ///     drop(self.place)
 845     fn complete_drop(
 846         &mut self,
 847         drop_mode: Option<DropFlagMode>,
 848         succ: BasicBlock,
 849         unwind: Unwind,
 850     ) -> BasicBlock {
 851         debug!("complete_drop({:?},{:?})", self, drop_mode);
 852
 853         let drop_block = self.drop_block(succ, unwind);
 854         let drop_block = if let Some(mode) = drop_mode {
 855             self.drop_flag_reset_block(mode, drop_block, unwind)
 856         } else {
 857             drop_block
 858         };
 859
 860         self.drop_flag_test_block(drop_block, succ, unwind)
 861     }
 862
 863     fn drop_flag_reset_block(
 864         &mut self,
 865         mode: DropFlagMode,
 866         succ: BasicBlock,
 867         unwind: Unwind,
 868     ) -> BasicBlock {
 869         debug!("drop_flag_reset_block({:?},{:?})", self, mode);
 870
 871         let block = self.new_block(unwind, TerminatorKind::Goto { target: succ });
 872         let block_start = Location { block, statement_index: 0 };
 873         self.elaborator.clear_drop_flag(block_start, self.path, mode);
 874         block
 875     }
 876
 877     fn elaborated_drop_block(&mut self) -> BasicBlock {
 878         debug!("elaborated_drop_block({:?})", self);
 879         let unwind = self.unwind; // FIXME(#43234)
 880         let succ = self.succ;
 881         let blk = self.drop_block(succ, unwind);
 882         self.elaborate_drop(blk);
 883         blk
 884     }
 885
 886     fn box_free_block(
 887         &mut self,
 888         adt: &'tcx ty::AdtDef,
 889         substs: SubstsRef<'tcx>,
 890         target: BasicBlock,
 891         unwind: Unwind,
 892     ) -> BasicBlock {
 893         let block = self.unelaborated_free_block(adt, substs, target, unwind);
 894         self.drop_flag_test_block(block, target, unwind)
 895     }
 896
 897     fn unelaborated_free_block(
 898         &mut self,
 899         adt: &'tcx ty::AdtDef,
 900         substs: SubstsRef<'tcx>,
 901         target: BasicBlock,
 902         unwind: Unwind,
 903     ) -> BasicBlock {
 904         let tcx = self.tcx();
 905         let unit_temp = Place::from(self.new_temp(tcx.mk_unit()));
 906         let free_func =
 907             tcx.require_lang_item(lang_items::BoxFreeFnLangItem, Some(self.source_info.span));
 908         let args = adt.variants[VariantIdx::new(0)]
 909             .fields
 910             .iter()
 911             .enumerate()
 912             .map(|(i, f)| {
 913                 let field = Field::new(i);
 914                 let field_ty = f.ty(tcx, substs);
 915                 Operand::Move(tcx.mk_place_field(self.place.clone(), field, field_ty))
 916             })
 917             .collect();
 918
 919         let call = TerminatorKind::Call {
 920             func: Operand::function_handle(tcx, free_func, substs, self.source_info.span),
 921             args,
 922             destination: Some((unit_temp, target)),
 923             cleanup: None,
 924             from_hir_call: false,
 925         }; // FIXME(#43234)
 926         let free_block = self.new_block(unwind, call);
 927
 928         let block_start = Location { block: free_block, statement_index: 0 };
 929         self.elaborator.clear_drop_flag(block_start, self.path, DropFlagMode::Shallow);
 930         free_block
 931     }
 932
 933     fn drop_block(&mut self, target: BasicBlock, unwind: Unwind) -> BasicBlock {
 934         let block =
 935             TerminatorKind::Drop { location: self.place, target, unwind: unwind.into_option() };
 936         self.new_block(unwind, block)
 937     }
 938
 939     fn goto_block(&mut self, target: BasicBlock, unwind: Unwind) -> BasicBlock {
 940         let block = TerminatorKind::Goto { target };
 941         self.new_block(unwind, block)
 942     }
 943
 944     fn drop_flag_test_block(
 945         &mut self,
 946         on_set: BasicBlock,
 947         on_unset: BasicBlock,
 948         unwind: Unwind,
 949     ) -> BasicBlock {
 950         let style = self.elaborator.drop_style(self.path, DropFlagMode::Shallow);
 951         debug!(
 952             "drop_flag_test_block({:?},{:?},{:?},{:?}) - {:?}",
 953             self, on_set, on_unset, unwind, style
 954         );
 955
 956         match style {
 957             DropStyle::Dead => on_unset,
 958             DropStyle::Static => on_set,
 959             DropStyle::Conditional | DropStyle::Open => {
 960                 let flag = self.elaborator.get_drop_flag(self.path).unwrap();
 961                 let term = TerminatorKind::if_(self.tcx(), flag, on_set, on_unset);
 962                 self.new_block(unwind, term)
 963             }
 964         }
 965     }
 966
 967     fn new_block(&mut self, unwind: Unwind, k: TerminatorKind<'tcx>) -> BasicBlock {
 968         self.elaborator.patch().new_block(BasicBlockData {
 969             statements: vec![],
 970             terminator: Some(Terminator { source_info: self.source_info, kind: k }),
 971             is_cleanup: unwind.is_cleanup(),
 972         })
 973     }
 974
 975     fn new_temp(&mut self, ty: Ty<'tcx>) -> Local {
 976         self.elaborator.patch().new_temp(ty, self.source_info.span)
 977     }
 978
 979     fn terminator_loc(&mut self, bb: BasicBlock) -> Location {
 980         let body = self.elaborator.body();
 981         self.elaborator.patch().terminator_loc(body, bb)
 982     }
 983
 984     fn constant_usize(&self, val: u16) -> Operand<'tcx> {
 985         Operand::Constant(box Constant {
 986             span: self.source_info.span,
 987             user_ty: None,
 988             literal: ty::Const::from_usize(self.tcx(), val.into()),
 989         })
 990     }
 991
 992     fn assign(&self, lhs: Place<'tcx>, rhs: Rvalue<'tcx>) -> Statement<'tcx> {
 993         Statement { source_info: self.source_info, kind: StatementKind::Assign(box (lhs, rhs)) }
 994     }
 995 }