1 use crate::util::patch::MirPatch;
3 use rustc_hir::lang_items::LangItem;
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;
13 /// The value of an inserted drop flag.
14 #[derive(Debug, PartialEq, Eq, Copy, Clone)]
15 pub enum DropFlagState {
16 /// The tracked value is initialized and needs to be dropped when leaving its scope.
19 /// The tracked value is uninitialized or was moved out of and does not need to be dropped when
20 /// leaving its scope.
25 pub fn value(self) -> bool {
27 DropFlagState::Present => true,
28 DropFlagState::Absent => false,
33 /// Describes how/if a value should be dropped.
36 /// The value is already dead at the drop location, no drop will be executed.
39 /// The value is known to always be initialized at the drop location, drop will always be
43 /// Whether the value needs to be dropped depends on its drop flag.
46 /// An "open" drop is one where only the fields of a value are dropped.
48 /// For example, this happens when moving out of a struct field: The rest of the struct will be
49 /// dropped in such an "open" drop. It is also used to generate drop glue for the individual
50 /// components of a value, for example for dropping array elements.
54 /// Which drop flags to affect/check with an operation.
56 pub enum DropFlagMode {
57 /// Only affect the top-level drop flag, not that of any contained fields.
59 /// Affect all nested drop flags in addition to the top-level one.
63 /// Describes if unwinding is necessary and where to unwind to if a panic occurs.
64 #[derive(Copy, Clone, Debug)]
66 /// Unwind to this block.
68 /// Already in an unwind path, any panic will cause an abort.
73 fn is_cleanup(self) -> bool {
75 Unwind::To(..) => false,
76 Unwind::InCleanup => true,
80 fn into_option(self) -> Option<BasicBlock> {
82 Unwind::To(bb) => Some(bb),
83 Unwind::InCleanup => None,
87 fn map<F>(self, f: F) -> Self
89 F: FnOnce(BasicBlock) -> BasicBlock,
92 Unwind::To(bb) => Unwind::To(f(bb)),
93 Unwind::InCleanup => Unwind::InCleanup,
98 pub trait DropElaborator<'a, 'tcx>: fmt::Debug {
99 /// The type representing paths that can be moved out of.
101 /// Users can move out of individual fields of a struct, such as `a.b.c`. This type is used to
102 /// represent such move paths. Sometimes tracking individual move paths is not necessary, in
103 /// which case this may be set to (for example) `()`.
104 type Path: Copy + fmt::Debug;
108 fn patch(&mut self) -> &mut MirPatch<'tcx>;
109 fn body(&self) -> &'a Body<'tcx>;
110 fn tcx(&self) -> TyCtxt<'tcx>;
111 fn param_env(&self) -> ty::ParamEnv<'tcx>;
115 /// Returns how `path` should be dropped, given `mode`.
116 fn drop_style(&self, path: Self::Path, mode: DropFlagMode) -> DropStyle;
118 /// Returns the drop flag of `path` as a MIR `Operand` (or `None` if `path` has no drop flag).
119 fn get_drop_flag(&mut self, path: Self::Path) -> Option<Operand<'tcx>>;
121 /// Modifies the MIR patch so that the drop flag of `path` (if any) is cleared at `location`.
123 /// If `mode` is deep, drop flags of all child paths should also be cleared by inserting
124 /// additional statements.
125 fn clear_drop_flag(&mut self, location: Location, path: Self::Path, mode: DropFlagMode);
129 /// Returns the subpath of a field of `path` (or `None` if there is no dedicated subpath).
131 /// If this returns `None`, `field` will not get a dedicated drop flag.
132 fn field_subpath(&self, path: Self::Path, field: Field) -> Option<Self::Path>;
134 /// Returns the subpath of a dereference of `path` (or `None` if there is no dedicated subpath).
136 /// If this returns `None`, `*path` will not get a dedicated drop flag.
138 /// This is only relevant for `Box<T>`, where the contained `T` can be moved out of the box.
139 fn deref_subpath(&self, path: Self::Path) -> Option<Self::Path>;
141 /// Returns the subpath of downcasting `path` to one of its variants.
143 /// If this returns `None`, the downcast of `path` will not get a dedicated drop flag.
144 fn downcast_subpath(&self, path: Self::Path, variant: VariantIdx) -> Option<Self::Path>;
146 /// Returns the subpath of indexing a fixed-size array `path`.
148 /// If this returns `None`, elements of `path` will not get a dedicated drop flag.
150 /// This is only relevant for array patterns, which can move out of individual array elements.
151 fn array_subpath(&self, path: Self::Path, index: u64, size: u64) -> Option<Self::Path>;
155 struct DropCtxt<'l, 'b, 'tcx, D>
157 D: DropElaborator<'b, 'tcx>,
159 elaborator: &'l mut D,
161 source_info: SourceInfo,
169 /// "Elaborates" a drop of `place`/`path` and patches `bb`'s terminator to execute it.
171 /// The passed `elaborator` is used to determine what should happen at the drop terminator. It
172 /// decides whether the drop can be statically determined or whether it needs a dynamic drop flag,
173 /// and whether the drop is "open", ie. should be expanded to drop all subfields of the dropped
176 /// When this returns, the MIR patch in the `elaborator` contains the necessary changes.
177 pub fn elaborate_drop<'b, 'tcx, D>(
179 source_info: SourceInfo,
186 D: DropElaborator<'b, 'tcx>,
189 DropCtxt { elaborator, source_info, place, path, succ, unwind }.elaborate_drop(bb)
192 impl<'l, 'b, 'tcx, D> DropCtxt<'l, 'b, 'tcx, D>
194 D: DropElaborator<'b, 'tcx>,
197 fn place_ty(&self, place: Place<'tcx>) -> Ty<'tcx> {
198 place.ty(self.elaborator.body(), self.tcx()).ty
201 fn tcx(&self) -> TyCtxt<'tcx> {
202 self.elaborator.tcx()
205 /// This elaborates a single drop instruction, located at `bb`, and
208 /// The elaborated drop checks the drop flags to only drop what
211 /// In addition, the relevant drop flags also need to be cleared
212 /// to avoid double-drops. However, in the middle of a complex
213 /// drop, one must avoid clearing some of the flags before they
214 /// are read, as that would cause a memory leak.
216 /// In particular, when dropping an ADT, multiple fields may be
217 /// joined together under the `rest` subpath. They are all controlled
218 /// by the primary drop flag, but only the last rest-field dropped
219 /// should clear it (and it must also not clear anything else).
221 // FIXME: I think we should just control the flags externally,
222 // and then we do not need this machinery.
223 pub fn elaborate_drop(&mut self, bb: BasicBlock) {
224 debug!("elaborate_drop({:?}, {:?})", bb, self);
225 let style = self.elaborator.drop_style(self.path, DropFlagMode::Deep);
226 debug!("elaborate_drop({:?}, {:?}): live - {:?}", bb, self, style);
231 .patch_terminator(bb, TerminatorKind::Goto { target: self.succ });
233 DropStyle::Static => {
234 self.elaborator.patch().patch_terminator(
236 TerminatorKind::Drop {
239 unwind: self.unwind.into_option(),
243 DropStyle::Conditional => {
244 let drop_bb = self.complete_drop(self.succ, self.unwind);
247 .patch_terminator(bb, TerminatorKind::Goto { target: drop_bb });
250 let drop_bb = self.open_drop();
253 .patch_terminator(bb, TerminatorKind::Goto { target: drop_bb });
258 /// Returns the place and move path for each field of `variant`,
259 /// (the move path is `None` if the field is a rest field).
260 fn move_paths_for_fields(
262 base_place: Place<'tcx>,
263 variant_path: D::Path,
264 variant: &'tcx ty::VariantDef,
265 substs: SubstsRef<'tcx>,
266 ) -> Vec<(Place<'tcx>, Option<D::Path>)> {
272 let field = Field::new(i);
273 let subpath = self.elaborator.field_subpath(variant_path, field);
274 let tcx = self.tcx();
276 assert_eq!(self.elaborator.param_env().reveal(), Reveal::All);
278 tcx.normalize_erasing_regions(self.elaborator.param_env(), f.ty(tcx, substs));
279 (tcx.mk_place_field(base_place, field, field_ty), subpath)
287 path: Option<D::Path>,
291 if let Some(path) = path {
292 debug!("drop_subpath: for std field {:?}", place);
295 elaborator: self.elaborator,
296 source_info: self.source_info,
302 .elaborated_drop_block()
304 debug!("drop_subpath: for rest field {:?}", place);
307 elaborator: self.elaborator,
308 source_info: self.source_info,
312 // Using `self.path` here to condition the drop on
313 // our own drop flag.
316 .complete_drop(succ, unwind)
320 /// Creates one-half of the drop ladder for a list of fields, and return
321 /// the list of steps in it in reverse order, with the first step
322 /// dropping 0 fields and so on.
324 /// `unwind_ladder` is such a list of steps in reverse order,
325 /// which is called if the matching step of the drop glue panics.
328 unwind_ladder: &[Unwind],
329 mut succ: BasicBlock,
330 fields: &[(Place<'tcx>, Option<D::Path>)],
331 ) -> Vec<BasicBlock> {
334 .chain(fields.iter().rev().zip(unwind_ladder).map(|(&(place, path), &unwind_succ)| {
335 succ = self.drop_subpath(place, path, succ, unwind_succ);
341 fn drop_ladder_bottom(&mut self) -> (BasicBlock, Unwind) {
342 // Clear the "master" drop flag at the end. This is needed
343 // because the "master" drop protects the ADT's discriminant,
344 // which is invalidated after the ADT is dropped.
345 (self.drop_flag_reset_block(DropFlagMode::Shallow, self.succ, self.unwind), self.unwind)
348 /// Creates a full drop ladder, consisting of 2 connected half-drop-ladders
350 /// For example, with 3 fields, the drop ladder is
353 /// ELAB(drop location.0 [target=.d1, unwind=.c1])
355 /// ELAB(drop location.1 [target=.d2, unwind=.c2])
357 /// ELAB(drop location.2 [target=`self.succ`, unwind=`self.unwind`])
359 /// ELAB(drop location.1 [target=.c2])
361 /// ELAB(drop location.2 [target=`self.unwind`])
363 /// NOTE: this does not clear the master drop flag, so you need
364 /// to point succ/unwind on a `drop_ladder_bottom`.
367 fields: Vec<(Place<'tcx>, Option<D::Path>)>,
370 ) -> (BasicBlock, Unwind) {
371 debug!("drop_ladder({:?}, {:?})", self, fields);
373 let mut fields = fields;
374 fields.retain(|&(place, _)| {
375 self.place_ty(place).needs_drop(self.tcx(), self.elaborator.param_env())
378 debug!("drop_ladder - fields needing drop: {:?}", fields);
380 let unwind_ladder = vec![Unwind::InCleanup; fields.len() + 1];
381 let unwind_ladder: Vec<_> = if let Unwind::To(target) = unwind {
382 let halfladder = self.drop_halfladder(&unwind_ladder, target, &fields);
383 halfladder.into_iter().map(Unwind::To).collect()
388 let normal_ladder = self.drop_halfladder(&unwind_ladder, succ, &fields);
390 (*normal_ladder.last().unwrap(), *unwind_ladder.last().unwrap())
393 fn open_drop_for_tuple(&mut self, tys: &[Ty<'tcx>]) -> BasicBlock {
394 debug!("open_drop_for_tuple({:?}, {:?})", self, tys);
401 self.tcx().mk_place_field(self.place, Field::new(i), ty),
402 self.elaborator.field_subpath(self.path, Field::new(i)),
407 let (succ, unwind) = self.drop_ladder_bottom();
408 self.drop_ladder(fields, succ, unwind).0
411 fn open_drop_for_box(&mut self, adt: &'tcx ty::AdtDef, substs: SubstsRef<'tcx>) -> BasicBlock {
412 debug!("open_drop_for_box({:?}, {:?}, {:?})", self, adt, substs);
414 let interior = self.tcx().mk_place_deref(self.place);
415 let interior_path = self.elaborator.deref_subpath(self.path);
417 let succ = self.box_free_block(adt, substs, self.succ, self.unwind);
419 self.unwind.map(|unwind| self.box_free_block(adt, substs, unwind, Unwind::InCleanup));
421 self.drop_subpath(interior, interior_path, succ, unwind_succ)
424 fn open_drop_for_adt(&mut self, adt: &'tcx ty::AdtDef, substs: SubstsRef<'tcx>) -> BasicBlock {
425 debug!("open_drop_for_adt({:?}, {:?}, {:?})", self, adt, substs);
426 if adt.variants.is_empty() {
427 return self.elaborator.patch().new_block(BasicBlockData {
429 terminator: Some(Terminator {
430 source_info: self.source_info,
431 kind: TerminatorKind::Unreachable,
433 is_cleanup: self.unwind.is_cleanup(),
438 adt.is_union() || Some(adt.did) == self.tcx().lang_items().manually_drop();
439 let contents_drop = if skip_contents {
440 (self.succ, self.unwind)
442 self.open_drop_for_adt_contents(adt, substs)
445 if adt.has_dtor(self.tcx()) {
446 self.destructor_call_block(contents_drop)
452 fn open_drop_for_adt_contents(
454 adt: &'tcx ty::AdtDef,
455 substs: SubstsRef<'tcx>,
456 ) -> (BasicBlock, Unwind) {
457 let (succ, unwind) = self.drop_ladder_bottom();
459 let fields = self.move_paths_for_fields(
462 &adt.variants[VariantIdx::new(0)],
465 self.drop_ladder(fields, succ, unwind)
467 self.open_drop_for_multivariant(adt, substs, succ, unwind)
471 fn open_drop_for_multivariant(
473 adt: &'tcx ty::AdtDef,
474 substs: SubstsRef<'tcx>,
477 ) -> (BasicBlock, Unwind) {
478 let mut values = Vec::with_capacity(adt.variants.len());
479 let mut normal_blocks = Vec::with_capacity(adt.variants.len());
480 let mut unwind_blocks =
481 if unwind.is_cleanup() { None } else { Some(Vec::with_capacity(adt.variants.len())) };
483 let mut have_otherwise_with_drop_glue = false;
484 let mut have_otherwise = false;
485 let tcx = self.tcx();
487 for (variant_index, discr) in adt.discriminants(tcx) {
488 let variant = &adt.variants[variant_index];
489 let subpath = self.elaborator.downcast_subpath(self.path, variant_index);
491 if let Some(variant_path) = subpath {
492 let base_place = tcx.mk_place_elem(
494 ProjectionElem::Downcast(Some(variant.ident.name), variant_index),
496 let fields = self.move_paths_for_fields(base_place, variant_path, &variant, substs);
497 values.push(discr.val);
498 if let Unwind::To(unwind) = unwind {
499 // We can't use the half-ladder from the original
500 // drop ladder, because this breaks the
501 // "funclet can't have 2 successor funclets"
502 // requirement from MSVC:
504 // switch unwind-switch
506 // v1.0 v2.0 v2.0-unwind v1.0-unwind
508 // v1.1-unwind v2.1-unwind |
510 // \-------------------------------/
512 // Create a duplicate half-ladder to avoid that. We
513 // could technically only do this on MSVC, but I
514 // I want to minimize the divergence between MSVC
517 let unwind_blocks = unwind_blocks.as_mut().unwrap();
518 let unwind_ladder = vec![Unwind::InCleanup; fields.len() + 1];
519 let halfladder = self.drop_halfladder(&unwind_ladder, unwind, &fields);
520 unwind_blocks.push(halfladder.last().cloned().unwrap());
522 let (normal, _) = self.drop_ladder(fields, succ, unwind);
523 normal_blocks.push(normal);
525 have_otherwise = true;
527 let param_env = self.elaborator.param_env();
528 let have_field_with_drop_glue = variant
531 .any(|field| field.ty(tcx, substs).needs_drop(tcx, param_env));
532 if have_field_with_drop_glue {
533 have_otherwise_with_drop_glue = true;
540 } else if !have_otherwise_with_drop_glue {
541 normal_blocks.push(self.goto_block(succ, unwind));
542 if let Unwind::To(unwind) = unwind {
543 unwind_blocks.as_mut().unwrap().push(self.goto_block(unwind, Unwind::InCleanup));
546 normal_blocks.push(self.drop_block(succ, unwind));
547 if let Unwind::To(unwind) = unwind {
548 unwind_blocks.as_mut().unwrap().push(self.drop_block(unwind, Unwind::InCleanup));
553 self.adt_switch_block(adt, normal_blocks, &values, succ, unwind),
554 unwind.map(|unwind| {
555 self.adt_switch_block(
557 unwind_blocks.unwrap(),
568 adt: &'tcx ty::AdtDef,
569 blocks: Vec<BasicBlock>,
574 // If there are multiple variants, then if something
575 // is present within the enum the discriminant, tracked
576 // by the rest path, must be initialized.
578 // Additionally, we do not want to switch on the
579 // discriminant after it is free-ed, because that
580 // way lies only trouble.
581 let discr_ty = adt.repr.discr_type().to_ty(self.tcx());
582 let discr = Place::from(self.new_temp(discr_ty));
583 let discr_rv = Rvalue::Discriminant(self.place);
584 let switch_block = BasicBlockData {
585 statements: vec![self.assign(discr, discr_rv)],
586 terminator: Some(Terminator {
587 source_info: self.source_info,
588 kind: TerminatorKind::SwitchInt {
589 discr: Operand::Move(discr),
591 values: From::from(values.to_owned()),
595 is_cleanup: unwind.is_cleanup(),
597 let switch_block = self.elaborator.patch().new_block(switch_block);
598 self.drop_flag_test_block(switch_block, succ, unwind)
601 fn destructor_call_block(&mut self, (succ, unwind): (BasicBlock, Unwind)) -> BasicBlock {
602 debug!("destructor_call_block({:?}, {:?})", self, succ);
603 let tcx = self.tcx();
604 let drop_trait = tcx.require_lang_item(LangItem::Drop, None);
605 let drop_fn = tcx.associated_items(drop_trait).in_definition_order().next().unwrap();
606 let ty = self.place_ty(self.place);
607 let substs = tcx.mk_substs_trait(ty, &[]);
610 tcx.mk_ref(tcx.lifetimes.re_erased, ty::TypeAndMut { ty, mutbl: hir::Mutability::Mut });
611 let ref_place = self.new_temp(ref_ty);
612 let unit_temp = Place::from(self.new_temp(tcx.mk_unit()));
614 let result = BasicBlockData {
615 statements: vec![self.assign(
616 Place::from(ref_place),
618 tcx.lifetimes.re_erased,
619 BorrowKind::Mut { allow_two_phase_borrow: false },
623 terminator: Some(Terminator {
624 kind: TerminatorKind::Call {
625 func: Operand::function_handle(
629 self.source_info.span,
631 args: vec![Operand::Move(Place::from(ref_place))],
632 destination: Some((unit_temp, succ)),
633 cleanup: unwind.into_option(),
635 fn_span: self.source_info.span,
637 source_info: self.source_info,
639 is_cleanup: unwind.is_cleanup(),
641 self.elaborator.patch().new_block(result)
644 /// Create a loop that drops an array:
648 /// can_go = cur == length_or_end
649 /// if can_go then succ else drop-block
653 /// cur = cur.offset(1)
655 /// ptr = &raw mut P[cur]
664 length_or_end: Place<'tcx>,
669 let copy = |place: Place<'tcx>| Operand::Copy(place);
670 let move_ = |place: Place<'tcx>| Operand::Move(place);
671 let tcx = self.tcx();
673 let ptr_ty = tcx.mk_ptr(ty::TypeAndMut { ty: ety, mutbl: hir::Mutability::Mut });
674 let ptr = Place::from(self.new_temp(ptr_ty));
675 let can_go = Place::from(self.new_temp(tcx.types.bool));
677 let one = self.constant_usize(1);
678 let (ptr_next, cur_next) = if ptr_based {
679 (Rvalue::Use(copy(cur.into())), Rvalue::BinaryOp(BinOp::Offset, move_(cur.into()), one))
682 Rvalue::AddressOf(Mutability::Mut, tcx.mk_place_index(self.place, cur)),
683 Rvalue::BinaryOp(BinOp::Add, move_(cur.into()), one),
687 let drop_block = BasicBlockData {
688 statements: vec![self.assign(ptr, ptr_next), self.assign(Place::from(cur), cur_next)],
689 is_cleanup: unwind.is_cleanup(),
690 terminator: Some(Terminator {
691 source_info: self.source_info,
692 // this gets overwritten by drop elaboration.
693 kind: TerminatorKind::Unreachable,
696 let drop_block = self.elaborator.patch().new_block(drop_block);
698 let loop_block = BasicBlockData {
699 statements: vec![self.assign(
701 Rvalue::BinaryOp(BinOp::Eq, copy(Place::from(cur)), copy(length_or_end)),
703 is_cleanup: unwind.is_cleanup(),
704 terminator: Some(Terminator {
705 source_info: self.source_info,
706 kind: TerminatorKind::if_(tcx, move_(can_go), succ, drop_block),
709 let loop_block = self.elaborator.patch().new_block(loop_block);
711 self.elaborator.patch().patch_terminator(
713 TerminatorKind::Drop {
714 place: tcx.mk_place_deref(ptr),
716 unwind: unwind.into_option(),
723 fn open_drop_for_array(&mut self, ety: Ty<'tcx>, opt_size: Option<u64>) -> BasicBlock {
724 debug!("open_drop_for_array({:?}, {:?})", ety, opt_size);
726 // if size_of::<ety>() == 0 {
732 let tcx = self.tcx();
734 if let Some(size) = opt_size {
735 let fields: Vec<(Place<'tcx>, Option<D::Path>)> = (0..size)
740 ProjectionElem::ConstantIndex {
746 self.elaborator.array_subpath(self.path, i, size),
751 if fields.iter().any(|(_, path)| path.is_some()) {
752 let (succ, unwind) = self.drop_ladder_bottom();
753 return self.drop_ladder(fields, succ, unwind).0;
757 let move_ = |place: Place<'tcx>| Operand::Move(place);
758 let elem_size = Place::from(self.new_temp(tcx.types.usize));
759 let len = Place::from(self.new_temp(tcx.types.usize));
761 static USIZE_SWITCH_ZERO: &[u128] = &[0];
763 let base_block = BasicBlockData {
765 self.assign(elem_size, Rvalue::NullaryOp(NullOp::SizeOf, ety)),
766 self.assign(len, Rvalue::Len(self.place)),
768 is_cleanup: self.unwind.is_cleanup(),
769 terminator: Some(Terminator {
770 source_info: self.source_info,
771 kind: TerminatorKind::SwitchInt {
772 discr: move_(elem_size),
773 switch_ty: tcx.types.usize,
774 values: From::from(USIZE_SWITCH_ZERO),
776 self.drop_loop_pair(ety, false, len),
777 self.drop_loop_pair(ety, true, len),
782 self.elaborator.patch().new_block(base_block)
785 /// Creates a pair of drop-loops of `place`, which drops its contents, even
786 /// in the case of 1 panic. If `ptr_based`, creates a pointer loop,
787 /// otherwise create an index loop.
794 debug!("drop_loop_pair({:?}, {:?})", ety, ptr_based);
795 let tcx = self.tcx();
796 let iter_ty = if ptr_based { tcx.mk_mut_ptr(ety) } else { tcx.types.usize };
798 let cur = self.new_temp(iter_ty);
799 let length_or_end = if ptr_based { Place::from(self.new_temp(iter_ty)) } else { length };
801 let unwind = self.unwind.map(|unwind| {
802 self.drop_loop(unwind, cur, length_or_end, ety, Unwind::InCleanup, ptr_based)
805 let loop_block = self.drop_loop(self.succ, cur, length_or_end, ety, unwind, ptr_based);
807 let cur = Place::from(cur);
808 let drop_block_stmts = if ptr_based {
809 let tmp_ty = tcx.mk_mut_ptr(self.place_ty(self.place));
810 let tmp = Place::from(self.new_temp(tmp_ty));
812 // cur = tmp as *mut T;
813 // end = Offset(cur, len);
815 self.assign(tmp, Rvalue::AddressOf(Mutability::Mut, self.place)),
816 self.assign(cur, Rvalue::Cast(CastKind::Misc, Operand::Move(tmp), iter_ty)),
819 Rvalue::BinaryOp(BinOp::Offset, Operand::Copy(cur), Operand::Move(length)),
823 // cur = 0 (length already pushed)
824 let zero = self.constant_usize(0);
825 vec![self.assign(cur, Rvalue::Use(zero))]
827 let drop_block = self.elaborator.patch().new_block(BasicBlockData {
828 statements: drop_block_stmts,
829 is_cleanup: unwind.is_cleanup(),
830 terminator: Some(Terminator {
831 source_info: self.source_info,
832 kind: TerminatorKind::Goto { target: loop_block },
836 // FIXME(#34708): handle partially-dropped array/slice elements.
837 let reset_block = self.drop_flag_reset_block(DropFlagMode::Deep, drop_block, unwind);
838 self.drop_flag_test_block(reset_block, self.succ, unwind)
841 /// The slow-path - create an "open", elaborated drop for a type
842 /// which is moved-out-of only partially, and patch `bb` to a jump
843 /// to it. This must not be called on ADTs with a destructor,
844 /// as these can't be moved-out-of, except for `Box<T>`, which is
847 /// This creates a "drop ladder" that drops the needed fields of the
848 /// ADT, both in the success case or if one of the destructors fail.
849 fn open_drop(&mut self) -> BasicBlock {
850 let ty = self.place_ty(self.place);
852 ty::Closure(_, substs) => {
853 let tys: Vec<_> = substs.as_closure().upvar_tys().collect();
854 self.open_drop_for_tuple(&tys)
856 // Note that `elaborate_drops` only drops the upvars of a generator,
857 // and this is ok because `open_drop` here can only be reached
858 // within that own generator's resume function.
859 // This should only happen for the self argument on the resume function.
860 // It effetively only contains upvars until the generator transformation runs.
861 // See librustc_body/transform/generator.rs for more details.
862 ty::Generator(_, substs, _) => {
863 let tys: Vec<_> = substs.as_generator().upvar_tys().collect();
864 self.open_drop_for_tuple(&tys)
867 let tys: Vec<_> = ty.tuple_fields().collect();
868 self.open_drop_for_tuple(&tys)
870 ty::Adt(def, substs) => {
872 self.open_drop_for_box(def, substs)
874 self.open_drop_for_adt(def, substs)
877 ty::Dynamic(..) => self.complete_drop(self.succ, self.unwind),
878 ty::Array(ety, size) => {
879 let size = size.try_eval_usize(self.tcx(), self.elaborator.param_env());
880 self.open_drop_for_array(ety, size)
882 ty::Slice(ety) => self.open_drop_for_array(ety, None),
884 _ => bug!("open drop from non-ADT `{:?}`", ty),
888 fn complete_drop(&mut self, succ: BasicBlock, unwind: Unwind) -> BasicBlock {
889 debug!("complete_drop(succ={:?}, unwind={:?})", succ, unwind);
891 let drop_block = self.drop_block(succ, unwind);
893 self.drop_flag_test_block(drop_block, succ, unwind)
896 /// Creates a block that resets the drop flag. If `mode` is deep, all children drop flags will
898 fn drop_flag_reset_block(
904 debug!("drop_flag_reset_block({:?},{:?})", self, mode);
906 if unwind.is_cleanup() {
907 // The drop flag isn't read again on the unwind path, so don't
908 // bother setting it.
911 let block = self.new_block(unwind, TerminatorKind::Goto { target: succ });
912 let block_start = Location { block, statement_index: 0 };
913 self.elaborator.clear_drop_flag(block_start, self.path, mode);
917 fn elaborated_drop_block(&mut self) -> BasicBlock {
918 debug!("elaborated_drop_block({:?})", self);
919 let blk = self.drop_block(self.succ, self.unwind);
920 self.elaborate_drop(blk);
924 /// Creates a block that frees the backing memory of a `Box` if its drop is required (either
925 /// statically or by checking its drop flag).
927 /// The contained value will not be dropped.
930 adt: &'tcx ty::AdtDef,
931 substs: SubstsRef<'tcx>,
935 let block = self.unelaborated_free_block(adt, substs, target, unwind);
936 self.drop_flag_test_block(block, target, unwind)
939 /// Creates a block that frees the backing memory of a `Box` (without dropping the contained
941 fn unelaborated_free_block(
943 adt: &'tcx ty::AdtDef,
944 substs: SubstsRef<'tcx>,
948 let tcx = self.tcx();
949 let unit_temp = Place::from(self.new_temp(tcx.mk_unit()));
950 let free_func = tcx.require_lang_item(LangItem::BoxFree, Some(self.source_info.span));
951 let args = adt.variants[VariantIdx::new(0)]
956 let field = Field::new(i);
957 let field_ty = f.ty(tcx, substs);
958 Operand::Move(tcx.mk_place_field(self.place, field, field_ty))
962 let call = TerminatorKind::Call {
963 func: Operand::function_handle(tcx, free_func, substs, self.source_info.span),
965 destination: Some((unit_temp, target)),
967 from_hir_call: false,
968 fn_span: self.source_info.span,
970 let free_block = self.new_block(unwind, call);
972 let block_start = Location { block: free_block, statement_index: 0 };
973 self.elaborator.clear_drop_flag(block_start, self.path, DropFlagMode::Shallow);
977 fn drop_block(&mut self, target: BasicBlock, unwind: Unwind) -> BasicBlock {
979 TerminatorKind::Drop { place: self.place, target, unwind: unwind.into_option() };
980 self.new_block(unwind, block)
983 fn goto_block(&mut self, target: BasicBlock, unwind: Unwind) -> BasicBlock {
984 let block = TerminatorKind::Goto { target };
985 self.new_block(unwind, block)
988 /// Returns the block to jump to in order to test the drop flag and execute the drop.
990 /// Depending on the required `DropStyle`, this might be a generated block with an `if`
991 /// terminator (for dynamic/open drops), or it might be `on_set` or `on_unset` itself, in case
992 /// the drop can be statically determined.
993 fn drop_flag_test_block(
996 on_unset: BasicBlock,
999 let style = self.elaborator.drop_style(self.path, DropFlagMode::Shallow);
1001 "drop_flag_test_block({:?},{:?},{:?},{:?}) - {:?}",
1002 self, on_set, on_unset, unwind, style
1006 DropStyle::Dead => on_unset,
1007 DropStyle::Static => on_set,
1008 DropStyle::Conditional | DropStyle::Open => {
1009 let flag = self.elaborator.get_drop_flag(self.path).unwrap();
1010 let term = TerminatorKind::if_(self.tcx(), flag, on_set, on_unset);
1011 self.new_block(unwind, term)
1016 fn new_block(&mut self, unwind: Unwind, k: TerminatorKind<'tcx>) -> BasicBlock {
1017 self.elaborator.patch().new_block(BasicBlockData {
1019 terminator: Some(Terminator { source_info: self.source_info, kind: k }),
1020 is_cleanup: unwind.is_cleanup(),
1024 fn new_temp(&mut self, ty: Ty<'tcx>) -> Local {
1025 self.elaborator.patch().new_temp(ty, self.source_info.span)
1028 fn constant_usize(&self, val: u16) -> Operand<'tcx> {
1029 Operand::Constant(box Constant {
1030 span: self.source_info.span,
1032 literal: ty::Const::from_usize(self.tcx(), val.into()),
1036 fn assign(&self, lhs: Place<'tcx>, rhs: Rvalue<'tcx>) -> Statement<'tcx> {
1037 Statement { source_info: self.source_info, kind: StatementKind::Assign(box (lhs, rhs)) }