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Diffstat (limited to 'compiler/rustc_mir_dataflow/src/elaborate_drops.rs')
| -rw-r--r-- | compiler/rustc_mir_dataflow/src/elaborate_drops.rs | 1056 |
1 files changed, 1056 insertions, 0 deletions
diff --git a/compiler/rustc_mir_dataflow/src/elaborate_drops.rs b/compiler/rustc_mir_dataflow/src/elaborate_drops.rs new file mode 100644 index 000000000..c0b0cc3c5 --- /dev/null +++ b/compiler/rustc_mir_dataflow/src/elaborate_drops.rs @@ -0,0 +1,1056 @@ +use rustc_hir as hir; +use rustc_hir::lang_items::LangItem; +use rustc_index::vec::Idx; +use rustc_middle::mir::patch::MirPatch; +use rustc_middle::mir::*; +use rustc_middle::traits::Reveal; +use rustc_middle::ty::subst::SubstsRef; +use rustc_middle::ty::util::IntTypeExt; +use rustc_middle::ty::{self, Ty, TyCtxt}; +use rustc_target::abi::VariantIdx; +use std::{fmt, iter}; + +/// The value of an inserted drop flag. +#[derive(Debug, PartialEq, Eq, Copy, Clone)] +pub enum DropFlagState { + /// The tracked value is initialized and needs to be dropped when leaving its scope. + Present, + + /// The tracked value is uninitialized or was moved out of and does not need to be dropped when + /// leaving its scope. + Absent, +} + +impl DropFlagState { + pub fn value(self) -> bool { + match self { + DropFlagState::Present => true, + DropFlagState::Absent => false, + } + } +} + +/// Describes how/if a value should be dropped. +#[derive(Debug)] +pub enum DropStyle { + /// The value is already dead at the drop location, no drop will be executed. + Dead, + + /// The value is known to always be initialized at the drop location, drop will always be + /// executed. + Static, + + /// Whether the value needs to be dropped depends on its drop flag. + Conditional, + + /// An "open" drop is one where only the fields of a value are dropped. + /// + /// For example, this happens when moving out of a struct field: The rest of the struct will be + /// dropped in such an "open" drop. It is also used to generate drop glue for the individual + /// components of a value, for example for dropping array elements. + Open, +} + +/// Which drop flags to affect/check with an operation. +#[derive(Debug)] +pub enum DropFlagMode { + /// Only affect the top-level drop flag, not that of any contained fields. + Shallow, + /// Affect all nested drop flags in addition to the top-level one. + Deep, +} + +/// Describes if unwinding is necessary and where to unwind to if a panic occurs. +#[derive(Copy, Clone, Debug)] +pub enum Unwind { + /// Unwind to this block. + To(BasicBlock), + /// Already in an unwind path, any panic will cause an abort. + InCleanup, +} + +impl Unwind { + fn is_cleanup(self) -> bool { + match self { + Unwind::To(..) => false, + Unwind::InCleanup => true, + } + } + + fn into_option(self) -> Option<BasicBlock> { + match self { + Unwind::To(bb) => Some(bb), + Unwind::InCleanup => None, + } + } + + fn map<F>(self, f: F) -> Self + where + F: FnOnce(BasicBlock) -> BasicBlock, + { + match self { + Unwind::To(bb) => Unwind::To(f(bb)), + Unwind::InCleanup => Unwind::InCleanup, + } + } +} + +pub trait DropElaborator<'a, 'tcx>: fmt::Debug { + /// The type representing paths that can be moved out of. + /// + /// Users can move out of individual fields of a struct, such as `a.b.c`. This type is used to + /// represent such move paths. Sometimes tracking individual move paths is not necessary, in + /// which case this may be set to (for example) `()`. + type Path: Copy + fmt::Debug; + + // Accessors + + fn patch(&mut self) -> &mut MirPatch<'tcx>; + fn body(&self) -> &'a Body<'tcx>; + fn tcx(&self) -> TyCtxt<'tcx>; + fn param_env(&self) -> ty::ParamEnv<'tcx>; + + // Drop logic + + /// Returns how `path` should be dropped, given `mode`. + fn drop_style(&self, path: Self::Path, mode: DropFlagMode) -> DropStyle; + + /// Returns the drop flag of `path` as a MIR `Operand` (or `None` if `path` has no drop flag). + fn get_drop_flag(&mut self, path: Self::Path) -> Option<Operand<'tcx>>; + + /// Modifies the MIR patch so that the drop flag of `path` (if any) is cleared at `location`. + /// + /// If `mode` is deep, drop flags of all child paths should also be cleared by inserting + /// additional statements. + fn clear_drop_flag(&mut self, location: Location, path: Self::Path, mode: DropFlagMode); + + // Subpaths + + /// Returns the subpath of a field of `path` (or `None` if there is no dedicated subpath). + /// + /// If this returns `None`, `field` will not get a dedicated drop flag. + fn field_subpath(&self, path: Self::Path, field: Field) -> Option<Self::Path>; + + /// Returns the subpath of a dereference of `path` (or `None` if there is no dedicated subpath). + /// + /// If this returns `None`, `*path` will not get a dedicated drop flag. + /// + /// This is only relevant for `Box<T>`, where the contained `T` can be moved out of the box. + fn deref_subpath(&self, path: Self::Path) -> Option<Self::Path>; + + /// Returns the subpath of downcasting `path` to one of its variants. + /// + /// If this returns `None`, the downcast of `path` will not get a dedicated drop flag. + fn downcast_subpath(&self, path: Self::Path, variant: VariantIdx) -> Option<Self::Path>; + + /// Returns the subpath of indexing a fixed-size array `path`. + /// + /// If this returns `None`, elements of `path` will not get a dedicated drop flag. + /// + /// This is only relevant for array patterns, which can move out of individual array elements. + fn array_subpath(&self, path: Self::Path, index: u64, size: u64) -> Option<Self::Path>; +} + +#[derive(Debug)] +struct DropCtxt<'l, 'b, 'tcx, D> +where + D: DropElaborator<'b, 'tcx>, +{ + elaborator: &'l mut D, + + source_info: SourceInfo, + + place: Place<'tcx>, + path: D::Path, + succ: BasicBlock, + unwind: Unwind, +} + +/// "Elaborates" a drop of `place`/`path` and patches `bb`'s terminator to execute it. +/// +/// The passed `elaborator` is used to determine what should happen at the drop terminator. It +/// decides whether the drop can be statically determined or whether it needs a dynamic drop flag, +/// and whether the drop is "open", ie. should be expanded to drop all subfields of the dropped +/// value. +/// +/// When this returns, the MIR patch in the `elaborator` contains the necessary changes. +pub fn elaborate_drop<'b, 'tcx, D>( + elaborator: &mut D, + source_info: SourceInfo, + place: Place<'tcx>, + path: D::Path, + succ: BasicBlock, + unwind: Unwind, + bb: BasicBlock, +) where + D: DropElaborator<'b, 'tcx>, + 'tcx: 'b, +{ + DropCtxt { elaborator, source_info, place, path, succ, unwind }.elaborate_drop(bb) +} + +impl<'l, 'b, 'tcx, D> DropCtxt<'l, 'b, 'tcx, D> +where + D: DropElaborator<'b, 'tcx>, + 'tcx: 'b, +{ + fn place_ty(&self, place: Place<'tcx>) -> Ty<'tcx> { + place.ty(self.elaborator.body(), self.tcx()).ty + } + + fn tcx(&self) -> TyCtxt<'tcx> { + self.elaborator.tcx() + } + + /// This elaborates a single drop instruction, located at `bb`, and + /// patches over it. + /// + /// The elaborated drop checks the drop flags to only drop what + /// is initialized. + /// + /// In addition, the relevant drop flags also need to be cleared + /// to avoid double-drops. However, in the middle of a complex + /// drop, one must avoid clearing some of the flags before they + /// are read, as that would cause a memory leak. + /// + /// In particular, when dropping an ADT, multiple fields may be + /// joined together under the `rest` subpath. They are all controlled + /// by the primary drop flag, but only the last rest-field dropped + /// should clear it (and it must also not clear anything else). + // + // FIXME: I think we should just control the flags externally, + // and then we do not need this machinery. + pub fn elaborate_drop(&mut self, bb: BasicBlock) { + debug!("elaborate_drop({:?}, {:?})", bb, self); + let style = self.elaborator.drop_style(self.path, DropFlagMode::Deep); + debug!("elaborate_drop({:?}, {:?}): live - {:?}", bb, self, style); + match style { + DropStyle::Dead => { + self.elaborator + .patch() + .patch_terminator(bb, TerminatorKind::Goto { target: self.succ }); + } + DropStyle::Static => { + self.elaborator.patch().patch_terminator( + bb, + TerminatorKind::Drop { + place: self.place, + target: self.succ, + unwind: self.unwind.into_option(), + }, + ); + } + DropStyle::Conditional => { + let drop_bb = self.complete_drop(self.succ, self.unwind); + self.elaborator + .patch() + .patch_terminator(bb, TerminatorKind::Goto { target: drop_bb }); + } + DropStyle::Open => { + let drop_bb = self.open_drop(); + self.elaborator + .patch() + .patch_terminator(bb, TerminatorKind::Goto { target: drop_bb }); + } + } + } + + /// Returns the place and move path for each field of `variant`, + /// (the move path is `None` if the field is a rest field). + fn move_paths_for_fields( + &self, + base_place: Place<'tcx>, + variant_path: D::Path, + variant: &'tcx ty::VariantDef, + substs: SubstsRef<'tcx>, + ) -> Vec<(Place<'tcx>, Option<D::Path>)> { + variant + .fields + .iter() + .enumerate() + .map(|(i, f)| { + let field = Field::new(i); + let subpath = self.elaborator.field_subpath(variant_path, field); + let tcx = self.tcx(); + + assert_eq!(self.elaborator.param_env().reveal(), Reveal::All); + let field_ty = + tcx.normalize_erasing_regions(self.elaborator.param_env(), f.ty(tcx, substs)); + (tcx.mk_place_field(base_place, field, field_ty), subpath) + }) + .collect() + } + + fn drop_subpath( + &mut self, + place: Place<'tcx>, + path: Option<D::Path>, + succ: BasicBlock, + unwind: Unwind, + ) -> BasicBlock { + if let Some(path) = path { + debug!("drop_subpath: for std field {:?}", place); + + DropCtxt { + elaborator: self.elaborator, + source_info: self.source_info, + path, + place, + succ, + unwind, + } + .elaborated_drop_block() + } else { + debug!("drop_subpath: for rest field {:?}", place); + + DropCtxt { + elaborator: self.elaborator, + source_info: self.source_info, + place, + succ, + unwind, + // Using `self.path` here to condition the drop on + // our own drop flag. + path: self.path, + } + .complete_drop(succ, unwind) + } + } + + /// Creates one-half of the drop ladder for a list of fields, and return + /// the list of steps in it in reverse order, with the first step + /// dropping 0 fields and so on. + /// + /// `unwind_ladder` is such a list of steps in reverse order, + /// which is called if the matching step of the drop glue panics. + fn drop_halfladder( + &mut self, + unwind_ladder: &[Unwind], + mut succ: BasicBlock, + fields: &[(Place<'tcx>, Option<D::Path>)], + ) -> Vec<BasicBlock> { + iter::once(succ) + .chain(fields.iter().rev().zip(unwind_ladder).map(|(&(place, path), &unwind_succ)| { + succ = self.drop_subpath(place, path, succ, unwind_succ); + succ + })) + .collect() + } + + fn drop_ladder_bottom(&mut self) -> (BasicBlock, Unwind) { + // Clear the "master" drop flag at the end. This is needed + // because the "master" drop protects the ADT's discriminant, + // which is invalidated after the ADT is dropped. + (self.drop_flag_reset_block(DropFlagMode::Shallow, self.succ, self.unwind), self.unwind) + } + + /// Creates a full drop ladder, consisting of 2 connected half-drop-ladders + /// + /// For example, with 3 fields, the drop ladder is + /// + /// .d0: + /// ELAB(drop location.0 [target=.d1, unwind=.c1]) + /// .d1: + /// ELAB(drop location.1 [target=.d2, unwind=.c2]) + /// .d2: + /// ELAB(drop location.2 [target=`self.succ`, unwind=`self.unwind`]) + /// .c1: + /// ELAB(drop location.1 [target=.c2]) + /// .c2: + /// ELAB(drop location.2 [target=`self.unwind`]) + /// + /// NOTE: this does not clear the master drop flag, so you need + /// to point succ/unwind on a `drop_ladder_bottom`. + fn drop_ladder( + &mut self, + fields: Vec<(Place<'tcx>, Option<D::Path>)>, + succ: BasicBlock, + unwind: Unwind, + ) -> (BasicBlock, Unwind) { + debug!("drop_ladder({:?}, {:?})", self, fields); + + let mut fields = fields; + fields.retain(|&(place, _)| { + self.place_ty(place).needs_drop(self.tcx(), self.elaborator.param_env()) + }); + + debug!("drop_ladder - fields needing drop: {:?}", fields); + + let unwind_ladder = vec![Unwind::InCleanup; fields.len() + 1]; + let unwind_ladder: Vec<_> = if let Unwind::To(target) = unwind { + let halfladder = self.drop_halfladder(&unwind_ladder, target, &fields); + halfladder.into_iter().map(Unwind::To).collect() + } else { + unwind_ladder + }; + + let normal_ladder = self.drop_halfladder(&unwind_ladder, succ, &fields); + + (*normal_ladder.last().unwrap(), *unwind_ladder.last().unwrap()) + } + + fn open_drop_for_tuple(&mut self, tys: &[Ty<'tcx>]) -> BasicBlock { + debug!("open_drop_for_tuple({:?}, {:?})", self, tys); + + let fields = tys + .iter() + .enumerate() + .map(|(i, &ty)| { + ( + self.tcx().mk_place_field(self.place, Field::new(i), ty), + self.elaborator.field_subpath(self.path, Field::new(i)), + ) + }) + .collect(); + + let (succ, unwind) = self.drop_ladder_bottom(); + self.drop_ladder(fields, succ, unwind).0 + } + + fn open_drop_for_box(&mut self, adt: ty::AdtDef<'tcx>, substs: SubstsRef<'tcx>) -> BasicBlock { + debug!("open_drop_for_box({:?}, {:?}, {:?})", self, adt, substs); + + // drop glue is sent straight to codegen + // box cannot be directly dereferenced + let unique_ty = adt.non_enum_variant().fields[0].ty(self.tcx(), substs); + let nonnull_ty = + unique_ty.ty_adt_def().unwrap().non_enum_variant().fields[0].ty(self.tcx(), substs); + let ptr_ty = self.tcx().mk_imm_ptr(substs[0].expect_ty()); + + let unique_place = self.tcx().mk_place_field(self.place, Field::new(0), unique_ty); + let nonnull_place = self.tcx().mk_place_field(unique_place, Field::new(0), nonnull_ty); + let ptr_place = self.tcx().mk_place_field(nonnull_place, Field::new(0), ptr_ty); + let interior = self.tcx().mk_place_deref(ptr_place); + + let interior_path = self.elaborator.deref_subpath(self.path); + + let succ = self.box_free_block(adt, substs, self.succ, self.unwind); + let unwind_succ = + self.unwind.map(|unwind| self.box_free_block(adt, substs, unwind, Unwind::InCleanup)); + + self.drop_subpath(interior, interior_path, succ, unwind_succ) + } + + fn open_drop_for_adt(&mut self, adt: ty::AdtDef<'tcx>, substs: SubstsRef<'tcx>) -> BasicBlock { + debug!("open_drop_for_adt({:?}, {:?}, {:?})", self, adt, substs); + if adt.variants().is_empty() { + return self.elaborator.patch().new_block(BasicBlockData { + statements: vec![], + terminator: Some(Terminator { + source_info: self.source_info, + kind: TerminatorKind::Unreachable, + }), + is_cleanup: self.unwind.is_cleanup(), + }); + } + + let skip_contents = + adt.is_union() || Some(adt.did()) == self.tcx().lang_items().manually_drop(); + let contents_drop = if skip_contents { + (self.succ, self.unwind) + } else { + self.open_drop_for_adt_contents(adt, substs) + }; + + if adt.has_dtor(self.tcx()) { + self.destructor_call_block(contents_drop) + } else { + contents_drop.0 + } + } + + fn open_drop_for_adt_contents( + &mut self, + adt: ty::AdtDef<'tcx>, + substs: SubstsRef<'tcx>, + ) -> (BasicBlock, Unwind) { + let (succ, unwind) = self.drop_ladder_bottom(); + if !adt.is_enum() { + let fields = self.move_paths_for_fields( + self.place, + self.path, + &adt.variant(VariantIdx::new(0)), + substs, + ); + self.drop_ladder(fields, succ, unwind) + } else { + self.open_drop_for_multivariant(adt, substs, succ, unwind) + } + } + + fn open_drop_for_multivariant( + &mut self, + adt: ty::AdtDef<'tcx>, + substs: SubstsRef<'tcx>, + succ: BasicBlock, + unwind: Unwind, + ) -> (BasicBlock, Unwind) { + let mut values = Vec::with_capacity(adt.variants().len()); + let mut normal_blocks = Vec::with_capacity(adt.variants().len()); + let mut unwind_blocks = + if unwind.is_cleanup() { None } else { Some(Vec::with_capacity(adt.variants().len())) }; + + let mut have_otherwise_with_drop_glue = false; + let mut have_otherwise = false; + let tcx = self.tcx(); + + for (variant_index, discr) in adt.discriminants(tcx) { + let variant = &adt.variant(variant_index); + let subpath = self.elaborator.downcast_subpath(self.path, variant_index); + + if let Some(variant_path) = subpath { + let base_place = tcx.mk_place_elem( + self.place, + ProjectionElem::Downcast(Some(variant.name), variant_index), + ); + let fields = self.move_paths_for_fields(base_place, variant_path, &variant, substs); + values.push(discr.val); + if let Unwind::To(unwind) = unwind { + // We can't use the half-ladder from the original + // drop ladder, because this breaks the + // "funclet can't have 2 successor funclets" + // requirement from MSVC: + // + // switch unwind-switch + // / \ / \ + // v1.0 v2.0 v2.0-unwind v1.0-unwind + // | | / | + // v1.1-unwind v2.1-unwind | + // ^ | + // \-------------------------------/ + // + // Create a duplicate half-ladder to avoid that. We + // could technically only do this on MSVC, but I + // I want to minimize the divergence between MSVC + // and non-MSVC. + + let unwind_blocks = unwind_blocks.as_mut().unwrap(); + let unwind_ladder = vec![Unwind::InCleanup; fields.len() + 1]; + let halfladder = self.drop_halfladder(&unwind_ladder, unwind, &fields); + unwind_blocks.push(halfladder.last().cloned().unwrap()); + } + let (normal, _) = self.drop_ladder(fields, succ, unwind); + normal_blocks.push(normal); + } else { + have_otherwise = true; + + let param_env = self.elaborator.param_env(); + let have_field_with_drop_glue = variant + .fields + .iter() + .any(|field| field.ty(tcx, substs).needs_drop(tcx, param_env)); + if have_field_with_drop_glue { + have_otherwise_with_drop_glue = true; + } + } + } + + if !have_otherwise { + values.pop(); + } else if !have_otherwise_with_drop_glue { + normal_blocks.push(self.goto_block(succ, unwind)); + if let Unwind::To(unwind) = unwind { + unwind_blocks.as_mut().unwrap().push(self.goto_block(unwind, Unwind::InCleanup)); + } + } else { + normal_blocks.push(self.drop_block(succ, unwind)); + if let Unwind::To(unwind) = unwind { + unwind_blocks.as_mut().unwrap().push(self.drop_block(unwind, Unwind::InCleanup)); + } + } + + ( + self.adt_switch_block(adt, normal_blocks, &values, succ, unwind), + unwind.map(|unwind| { + self.adt_switch_block( + adt, + unwind_blocks.unwrap(), + &values, + unwind, + Unwind::InCleanup, + ) + }), + ) + } + + fn adt_switch_block( + &mut self, + adt: ty::AdtDef<'tcx>, + blocks: Vec<BasicBlock>, + values: &[u128], + succ: BasicBlock, + unwind: Unwind, + ) -> BasicBlock { + // If there are multiple variants, then if something + // is present within the enum the discriminant, tracked + // by the rest path, must be initialized. + // + // Additionally, we do not want to switch on the + // discriminant after it is free-ed, because that + // way lies only trouble. + let discr_ty = adt.repr().discr_type().to_ty(self.tcx()); + let discr = Place::from(self.new_temp(discr_ty)); + let discr_rv = Rvalue::Discriminant(self.place); + let switch_block = BasicBlockData { + statements: vec![self.assign(discr, discr_rv)], + terminator: Some(Terminator { + source_info: self.source_info, + kind: TerminatorKind::SwitchInt { + discr: Operand::Move(discr), + switch_ty: discr_ty, + targets: SwitchTargets::new( + values.iter().copied().zip(blocks.iter().copied()), + *blocks.last().unwrap(), + ), + }, + }), + is_cleanup: unwind.is_cleanup(), + }; + let switch_block = self.elaborator.patch().new_block(switch_block); + self.drop_flag_test_block(switch_block, succ, unwind) + } + + fn destructor_call_block(&mut self, (succ, unwind): (BasicBlock, Unwind)) -> BasicBlock { + debug!("destructor_call_block({:?}, {:?})", self, succ); + let tcx = self.tcx(); + let drop_trait = tcx.require_lang_item(LangItem::Drop, None); + let drop_fn = tcx.associated_item_def_ids(drop_trait)[0]; + let ty = self.place_ty(self.place); + let substs = tcx.mk_substs_trait(ty, &[]); + + let ref_ty = + tcx.mk_ref(tcx.lifetimes.re_erased, ty::TypeAndMut { ty, mutbl: hir::Mutability::Mut }); + let ref_place = self.new_temp(ref_ty); + let unit_temp = Place::from(self.new_temp(tcx.mk_unit())); + + let result = BasicBlockData { + statements: vec![self.assign( + Place::from(ref_place), + Rvalue::Ref( + tcx.lifetimes.re_erased, + BorrowKind::Mut { allow_two_phase_borrow: false }, + self.place, + ), + )], + terminator: Some(Terminator { + kind: TerminatorKind::Call { + func: Operand::function_handle(tcx, drop_fn, substs, self.source_info.span), + args: vec![Operand::Move(Place::from(ref_place))], + destination: unit_temp, + target: Some(succ), + cleanup: unwind.into_option(), + from_hir_call: true, + fn_span: self.source_info.span, + }, + source_info: self.source_info, + }), + is_cleanup: unwind.is_cleanup(), + }; + self.elaborator.patch().new_block(result) + } + + /// Create a loop that drops an array: + /// + /// ```text + /// loop-block: + /// can_go = cur == length_or_end + /// if can_go then succ else drop-block + /// drop-block: + /// if ptr_based { + /// ptr = cur + /// cur = cur.offset(1) + /// } else { + /// ptr = &raw mut P[cur] + /// cur = cur + 1 + /// } + /// drop(ptr) + /// ``` + fn drop_loop( + &mut self, + succ: BasicBlock, + cur: Local, + length_or_end: Place<'tcx>, + ety: Ty<'tcx>, + unwind: Unwind, + ptr_based: bool, + ) -> BasicBlock { + let copy = |place: Place<'tcx>| Operand::Copy(place); + let move_ = |place: Place<'tcx>| Operand::Move(place); + let tcx = self.tcx(); + + let ptr_ty = tcx.mk_ptr(ty::TypeAndMut { ty: ety, mutbl: hir::Mutability::Mut }); + let ptr = Place::from(self.new_temp(ptr_ty)); + let can_go = Place::from(self.new_temp(tcx.types.bool)); + + let one = self.constant_usize(1); + let (ptr_next, cur_next) = if ptr_based { + ( + Rvalue::Use(copy(cur.into())), + Rvalue::BinaryOp(BinOp::Offset, Box::new((move_(cur.into()), one))), + ) + } else { + ( + Rvalue::AddressOf(Mutability::Mut, tcx.mk_place_index(self.place, cur)), + Rvalue::BinaryOp(BinOp::Add, Box::new((move_(cur.into()), one))), + ) + }; + + let drop_block = BasicBlockData { + statements: vec![self.assign(ptr, ptr_next), self.assign(Place::from(cur), cur_next)], + is_cleanup: unwind.is_cleanup(), + terminator: Some(Terminator { + source_info: self.source_info, + // this gets overwritten by drop elaboration. + kind: TerminatorKind::Unreachable, + }), + }; + let drop_block = self.elaborator.patch().new_block(drop_block); + + let loop_block = BasicBlockData { + statements: vec![self.assign( + can_go, + Rvalue::BinaryOp( + BinOp::Eq, + Box::new((copy(Place::from(cur)), copy(length_or_end))), + ), + )], + is_cleanup: unwind.is_cleanup(), + terminator: Some(Terminator { + source_info: self.source_info, + kind: TerminatorKind::if_(tcx, move_(can_go), succ, drop_block), + }), + }; + let loop_block = self.elaborator.patch().new_block(loop_block); + + self.elaborator.patch().patch_terminator( + drop_block, + TerminatorKind::Drop { + place: tcx.mk_place_deref(ptr), + target: loop_block, + unwind: unwind.into_option(), + }, + ); + + loop_block + } + + fn open_drop_for_array(&mut self, ety: Ty<'tcx>, opt_size: Option<u64>) -> BasicBlock { + debug!("open_drop_for_array({:?}, {:?})", ety, opt_size); + + // if size_of::<ety>() == 0 { + // index_based_loop + // } else { + // ptr_based_loop + // } + + let tcx = self.tcx(); + + if let Some(size) = opt_size { + let fields: Vec<(Place<'tcx>, Option<D::Path>)> = (0..size) + .map(|i| { + ( + tcx.mk_place_elem( + self.place, + ProjectionElem::ConstantIndex { + offset: i, + min_length: size, + from_end: false, + }, + ), + self.elaborator.array_subpath(self.path, i, size), + ) + }) + .collect(); + + if fields.iter().any(|(_, path)| path.is_some()) { + let (succ, unwind) = self.drop_ladder_bottom(); + return self.drop_ladder(fields, succ, unwind).0; + } + } + + let move_ = |place: Place<'tcx>| Operand::Move(place); + let elem_size = Place::from(self.new_temp(tcx.types.usize)); + let len = Place::from(self.new_temp(tcx.types.usize)); + + let base_block = BasicBlockData { + statements: vec![ + self.assign(elem_size, Rvalue::NullaryOp(NullOp::SizeOf, ety)), + self.assign(len, Rvalue::Len(self.place)), + ], + is_cleanup: self.unwind.is_cleanup(), + terminator: Some(Terminator { + source_info: self.source_info, + kind: TerminatorKind::SwitchInt { + discr: move_(elem_size), + switch_ty: tcx.types.usize, + targets: SwitchTargets::static_if( + 0, + self.drop_loop_pair(ety, false, len), + self.drop_loop_pair(ety, true, len), + ), + }, + }), + }; + self.elaborator.patch().new_block(base_block) + } + + /// Creates a pair of drop-loops of `place`, which drops its contents, even + /// in the case of 1 panic. If `ptr_based`, creates a pointer loop, + /// otherwise create an index loop. + fn drop_loop_pair( + &mut self, + ety: Ty<'tcx>, + ptr_based: bool, + length: Place<'tcx>, + ) -> BasicBlock { + debug!("drop_loop_pair({:?}, {:?})", ety, ptr_based); + let tcx = self.tcx(); + let iter_ty = if ptr_based { tcx.mk_mut_ptr(ety) } else { tcx.types.usize }; + + let cur = self.new_temp(iter_ty); + let length_or_end = if ptr_based { Place::from(self.new_temp(iter_ty)) } else { length }; + + let unwind = self.unwind.map(|unwind| { + self.drop_loop(unwind, cur, length_or_end, ety, Unwind::InCleanup, ptr_based) + }); + + let loop_block = self.drop_loop(self.succ, cur, length_or_end, ety, unwind, ptr_based); + + let cur = Place::from(cur); + let drop_block_stmts = if ptr_based { + let tmp_ty = tcx.mk_mut_ptr(self.place_ty(self.place)); + let tmp = Place::from(self.new_temp(tmp_ty)); + // tmp = &raw mut P; + // cur = tmp as *mut T; + // end = Offset(cur, len); + vec![ + self.assign(tmp, Rvalue::AddressOf(Mutability::Mut, self.place)), + self.assign(cur, Rvalue::Cast(CastKind::Misc, Operand::Move(tmp), iter_ty)), + self.assign( + length_or_end, + Rvalue::BinaryOp( + BinOp::Offset, + Box::new((Operand::Copy(cur), Operand::Move(length))), + ), + ), + ] + } else { + // cur = 0 (length already pushed) + let zero = self.constant_usize(0); + vec![self.assign(cur, Rvalue::Use(zero))] + }; + let drop_block = self.elaborator.patch().new_block(BasicBlockData { + statements: drop_block_stmts, + is_cleanup: unwind.is_cleanup(), + terminator: Some(Terminator { + source_info: self.source_info, + kind: TerminatorKind::Goto { target: loop_block }, + }), + }); + + // FIXME(#34708): handle partially-dropped array/slice elements. + let reset_block = self.drop_flag_reset_block(DropFlagMode::Deep, drop_block, unwind); + self.drop_flag_test_block(reset_block, self.succ, unwind) + } + + /// The slow-path - create an "open", elaborated drop for a type + /// which is moved-out-of only partially, and patch `bb` to a jump + /// to it. This must not be called on ADTs with a destructor, + /// as these can't be moved-out-of, except for `Box<T>`, which is + /// special-cased. + /// + /// This creates a "drop ladder" that drops the needed fields of the + /// ADT, both in the success case or if one of the destructors fail. + fn open_drop(&mut self) -> BasicBlock { + let ty = self.place_ty(self.place); + match ty.kind() { + ty::Closure(_, substs) => { + let tys: Vec<_> = substs.as_closure().upvar_tys().collect(); + self.open_drop_for_tuple(&tys) + } + // Note that `elaborate_drops` only drops the upvars of a generator, + // and this is ok because `open_drop` here can only be reached + // within that own generator's resume function. + // This should only happen for the self argument on the resume function. + // It effectively only contains upvars until the generator transformation runs. + // See librustc_body/transform/generator.rs for more details. + ty::Generator(_, substs, _) => { + let tys: Vec<_> = substs.as_generator().upvar_tys().collect(); + self.open_drop_for_tuple(&tys) + } + ty::Tuple(fields) => self.open_drop_for_tuple(fields), + ty::Adt(def, substs) => { + if def.is_box() { + self.open_drop_for_box(*def, substs) + } else { + self.open_drop_for_adt(*def, substs) + } + } + ty::Dynamic(..) => self.complete_drop(self.succ, self.unwind), + ty::Array(ety, size) => { + let size = size.try_eval_usize(self.tcx(), self.elaborator.param_env()); + self.open_drop_for_array(*ety, size) + } + ty::Slice(ety) => self.open_drop_for_array(*ety, None), + + _ => bug!("open drop from non-ADT `{:?}`", ty), + } + } + + fn complete_drop(&mut self, succ: BasicBlock, unwind: Unwind) -> BasicBlock { + debug!("complete_drop(succ={:?}, unwind={:?})", succ, unwind); + + let drop_block = self.drop_block(succ, unwind); + + self.drop_flag_test_block(drop_block, succ, unwind) + } + + /// Creates a block that resets the drop flag. If `mode` is deep, all children drop flags will + /// also be cleared. + fn drop_flag_reset_block( + &mut self, + mode: DropFlagMode, + succ: BasicBlock, + unwind: Unwind, + ) -> BasicBlock { + debug!("drop_flag_reset_block({:?},{:?})", self, mode); + + if unwind.is_cleanup() { + // The drop flag isn't read again on the unwind path, so don't + // bother setting it. + return succ; + } + let block = self.new_block(unwind, TerminatorKind::Goto { target: succ }); + let block_start = Location { block, statement_index: 0 }; + self.elaborator.clear_drop_flag(block_start, self.path, mode); + block + } + + fn elaborated_drop_block(&mut self) -> BasicBlock { + debug!("elaborated_drop_block({:?})", self); + let blk = self.drop_block(self.succ, self.unwind); + self.elaborate_drop(blk); + blk + } + + /// Creates a block that frees the backing memory of a `Box` if its drop is required (either + /// statically or by checking its drop flag). + /// + /// The contained value will not be dropped. + fn box_free_block( + &mut self, + adt: ty::AdtDef<'tcx>, + substs: SubstsRef<'tcx>, + target: BasicBlock, + unwind: Unwind, + ) -> BasicBlock { + let block = self.unelaborated_free_block(adt, substs, target, unwind); + self.drop_flag_test_block(block, target, unwind) + } + + /// Creates a block that frees the backing memory of a `Box` (without dropping the contained + /// value). + fn unelaborated_free_block( + &mut self, + adt: ty::AdtDef<'tcx>, + substs: SubstsRef<'tcx>, + target: BasicBlock, + unwind: Unwind, + ) -> BasicBlock { + let tcx = self.tcx(); + let unit_temp = Place::from(self.new_temp(tcx.mk_unit())); + let free_func = tcx.require_lang_item(LangItem::BoxFree, Some(self.source_info.span)); + let args = adt + .variant(VariantIdx::new(0)) + .fields + .iter() + .enumerate() + .map(|(i, f)| { + let field = Field::new(i); + let field_ty = f.ty(tcx, substs); + Operand::Move(tcx.mk_place_field(self.place, field, field_ty)) + }) + .collect(); + + let call = TerminatorKind::Call { + func: Operand::function_handle(tcx, free_func, substs, self.source_info.span), + args, + destination: unit_temp, + target: Some(target), + cleanup: None, + from_hir_call: false, + fn_span: self.source_info.span, + }; // FIXME(#43234) + let free_block = self.new_block(unwind, call); + + let block_start = Location { block: free_block, statement_index: 0 }; + self.elaborator.clear_drop_flag(block_start, self.path, DropFlagMode::Shallow); + free_block + } + + fn drop_block(&mut self, target: BasicBlock, unwind: Unwind) -> BasicBlock { + let block = + TerminatorKind::Drop { place: self.place, target, unwind: unwind.into_option() }; + self.new_block(unwind, block) + } + + fn goto_block(&mut self, target: BasicBlock, unwind: Unwind) -> BasicBlock { + let block = TerminatorKind::Goto { target }; + self.new_block(unwind, block) + } + + /// Returns the block to jump to in order to test the drop flag and execute the drop. + /// + /// Depending on the required `DropStyle`, this might be a generated block with an `if` + /// terminator (for dynamic/open drops), or it might be `on_set` or `on_unset` itself, in case + /// the drop can be statically determined. + fn drop_flag_test_block( + &mut self, + on_set: BasicBlock, + on_unset: BasicBlock, + unwind: Unwind, + ) -> BasicBlock { + let style = self.elaborator.drop_style(self.path, DropFlagMode::Shallow); + debug!( + "drop_flag_test_block({:?},{:?},{:?},{:?}) - {:?}", + self, on_set, on_unset, unwind, style + ); + + match style { + DropStyle::Dead => on_unset, + DropStyle::Static => on_set, + DropStyle::Conditional | DropStyle::Open => { + let flag = self.elaborator.get_drop_flag(self.path).unwrap(); + let term = TerminatorKind::if_(self.tcx(), flag, on_set, on_unset); + self.new_block(unwind, term) + } + } + } + + fn new_block(&mut self, unwind: Unwind, k: TerminatorKind<'tcx>) -> BasicBlock { + self.elaborator.patch().new_block(BasicBlockData { + statements: vec![], + terminator: Some(Terminator { source_info: self.source_info, kind: k }), + is_cleanup: unwind.is_cleanup(), + }) + } + + fn new_temp(&mut self, ty: Ty<'tcx>) -> Local { + self.elaborator.patch().new_temp(ty, self.source_info.span) + } + + fn constant_usize(&self, val: u16) -> Operand<'tcx> { + Operand::Constant(Box::new(Constant { + span: self.source_info.span, + user_ty: None, + literal: ConstantKind::from_usize(self.tcx(), val.into()), + })) + } + + fn assign(&self, lhs: Place<'tcx>, rhs: Rvalue<'tcx>) -> Statement<'tcx> { + Statement { + source_info: self.source_info, + kind: StatementKind::Assign(Box::new((lhs, rhs))), + } + } +} |