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rust/compiler/rustc_mir_transform/src/elaborate_drop.rs
Andrew Zhogin cce706ec3c Fix for async drop ice with partly dropped tuple
2025-04-29 21:41:15 +07:00

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use std::{fmt, iter, mem};
use rustc_abi::{FIRST_VARIANT, FieldIdx, VariantIdx};
use rustc_hir::lang_items::LangItem;
use rustc_index::Idx;
use rustc_middle::mir::*;
use rustc_middle::ty::adjustment::PointerCoercion;
use rustc_middle::ty::util::IntTypeExt;
use rustc_middle::ty::{self, GenericArg, GenericArgsRef, Ty, TyCtxt};
use rustc_middle::{bug, span_bug, traits};
use rustc_span::DUMMY_SP;
use rustc_span::source_map::{Spanned, dummy_spanned};
use tracing::{debug, instrument};
use crate::patch::MirPatch;
/// Describes how/if a value should be dropped.
#[derive(Debug)]
pub(crate) 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(crate) 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(crate) 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_action(self) -> UnwindAction {
match self {
Unwind::To(bb) => UnwindAction::Cleanup(bb),
Unwind::InCleanup => UnwindAction::Terminate(UnwindTerminateReason::InCleanup),
}
}
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(crate) 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_ref(&self) -> &MirPatch<'tcx>;
fn patch(&mut self) -> &mut MirPatch<'tcx>;
fn body(&self) -> &'a Body<'tcx>;
fn tcx(&self) -> TyCtxt<'tcx>;
fn typing_env(&self) -> ty::TypingEnv<'tcx>;
fn allow_async_drops(&self) -> bool;
fn terminator_loc(&self, bb: BasicBlock) -> Location;
// 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: FieldIdx) -> 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<'a, 'b, 'tcx, D>
where
D: DropElaborator<'b, 'tcx>,
{
elaborator: &'a mut D,
source_info: SourceInfo,
place: Place<'tcx>,
path: D::Path,
succ: BasicBlock,
unwind: Unwind,
dropline: Option<BasicBlock>,
}
/// "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(crate) fn elaborate_drop<'b, 'tcx, D>(
elaborator: &mut D,
source_info: SourceInfo,
place: Place<'tcx>,
path: D::Path,
succ: BasicBlock,
unwind: Unwind,
bb: BasicBlock,
dropline: Option<BasicBlock>,
) where
D: DropElaborator<'b, 'tcx>,
'tcx: 'b,
{
DropCtxt { elaborator, source_info, place, path, succ, unwind, dropline }.elaborate_drop(bb)
}
impl<'a, 'b, 'tcx, D> DropCtxt<'a, 'b, 'tcx, D>
where
D: DropElaborator<'b, 'tcx>,
'tcx: 'b,
{
#[instrument(level = "trace", skip(self), ret)]
fn place_ty(&self, place: Place<'tcx>) -> Ty<'tcx> {
if place.local < self.elaborator.body().local_decls.next_index() {
place.ty(self.elaborator.body(), self.tcx()).ty
} else {
// We don't have a slice with all the locals, since some are in the patch.
PlaceTy::from_ty(self.elaborator.patch_ref().local_ty(place.local))
.multi_projection_ty(self.elaborator.tcx(), place.projection)
.ty
}
}
fn tcx(&self) -> TyCtxt<'tcx> {
self.elaborator.tcx()
}
// Generates three blocks:
// * #1:pin_obj_bb: call Pin<ObjTy>::new_unchecked(&mut obj)
// * #2:call_drop_bb: fut = call obj.<AsyncDrop::drop>() OR call async_drop_in_place<T>(obj)
// * #3:drop_term_bb: drop (obj, fut, ...)
// We keep async drop unexpanded to poll-loop here, to expand it later, at StateTransform -
// into states expand.
// call_destructor_only - to call only AsyncDrop::drop, not full async_drop_in_place glue
fn build_async_drop(
&mut self,
place: Place<'tcx>,
drop_ty: Ty<'tcx>,
bb: Option<BasicBlock>,
succ: BasicBlock,
unwind: Unwind,
dropline: Option<BasicBlock>,
call_destructor_only: bool,
) -> BasicBlock {
let tcx = self.tcx();
let span = self.source_info.span;
let pin_obj_bb = bb.unwrap_or_else(|| {
self.elaborator.patch().new_block(BasicBlockData {
statements: vec![],
terminator: Some(Terminator {
// Temporary terminator, will be replaced by patch
source_info: self.source_info,
kind: TerminatorKind::Return,
}),
is_cleanup: false,
})
});
let (fut_ty, drop_fn_def_id, trait_args) = if call_destructor_only {
// Resolving obj.<AsyncDrop::drop>()
let trait_ref = ty::TraitRef::new(
tcx,
tcx.require_lang_item(LangItem::AsyncDrop, Some(span)),
[drop_ty],
);
let (drop_trait, trait_args) = match tcx.codegen_select_candidate(
ty::TypingEnv::fully_monomorphized().as_query_input(trait_ref),
) {
Ok(traits::ImplSource::UserDefined(traits::ImplSourceUserDefinedData {
impl_def_id,
args,
..
})) => (*impl_def_id, *args),
impl_source => {
span_bug!(span, "invalid `AsyncDrop` impl_source: {:?}", impl_source);
}
};
let drop_fn_def_id = tcx.associated_item_def_ids(drop_trait)[0];
let drop_fn = Ty::new_fn_def(tcx, drop_fn_def_id, trait_args);
let sig = drop_fn.fn_sig(tcx);
let sig = tcx.instantiate_bound_regions_with_erased(sig);
(sig.output(), drop_fn_def_id, trait_args)
} else {
// Resolving async_drop_in_place<T> function for drop_ty
let drop_fn_def_id = tcx.require_lang_item(LangItem::AsyncDropInPlace, Some(span));
let trait_args = tcx.mk_args(&[drop_ty.into()]);
let sig = tcx.fn_sig(drop_fn_def_id).instantiate(tcx, trait_args);
let sig = tcx.instantiate_bound_regions_with_erased(sig);
(sig.output(), drop_fn_def_id, trait_args)
};
let fut = Place::from(self.new_temp(fut_ty));
// #1:pin_obj_bb >>> obj_ref = &mut obj
let obj_ref_ty = Ty::new_mut_ref(tcx, tcx.lifetimes.re_erased, drop_ty);
let obj_ref_place = Place::from(self.new_temp(obj_ref_ty));
let term_loc = self.elaborator.terminator_loc(pin_obj_bb);
self.elaborator.patch().add_assign(
term_loc,
obj_ref_place,
Rvalue::Ref(
tcx.lifetimes.re_erased,
BorrowKind::Mut { kind: MutBorrowKind::Default },
place,
),
);
// pin_obj_place preparation
let pin_obj_new_unchecked_fn = Ty::new_fn_def(
tcx,
tcx.require_lang_item(LangItem::PinNewUnchecked, Some(span)),
[GenericArg::from(obj_ref_ty)],
);
let pin_obj_ty = pin_obj_new_unchecked_fn.fn_sig(tcx).output().no_bound_vars().unwrap();
let pin_obj_place = Place::from(self.new_temp(pin_obj_ty));
let pin_obj_new_unchecked_fn = Operand::Constant(Box::new(ConstOperand {
span,
user_ty: None,
const_: Const::zero_sized(pin_obj_new_unchecked_fn),
}));
// #3:drop_term_bb
let drop_term_bb = self.new_block(
unwind,
TerminatorKind::Drop {
place,
target: succ,
unwind: unwind.into_action(),
replace: false,
drop: dropline,
async_fut: Some(fut.local),
},
);
// #2:call_drop_bb
let mut call_statements = Vec::new();
let drop_arg = if call_destructor_only {
pin_obj_place
} else {
let ty::Adt(adt_def, adt_args) = pin_obj_ty.kind() else {
bug!();
};
let obj_ptr_ty = Ty::new_mut_ptr(tcx, drop_ty);
let obj_ptr_place = Place::from(self.new_temp(obj_ptr_ty));
let unwrap_ty = adt_def.non_enum_variant().fields[FieldIdx::ZERO].ty(tcx, adt_args);
let addr = Rvalue::RawPtr(
RawPtrKind::Mut,
pin_obj_place.project_deeper(
&[ProjectionElem::Field(FieldIdx::ZERO, unwrap_ty), ProjectionElem::Deref],
tcx,
),
);
call_statements.push(self.assign(obj_ptr_place, addr));
obj_ptr_place
};
call_statements.push(Statement {
source_info: self.source_info,
kind: StatementKind::StorageLive(fut.local),
});
let call_drop_bb = self.new_block_with_statements(
unwind,
call_statements,
TerminatorKind::Call {
func: Operand::function_handle(tcx, drop_fn_def_id, trait_args, span),
args: [Spanned { node: Operand::Move(drop_arg), span: DUMMY_SP }].into(),
destination: fut,
target: Some(drop_term_bb),
unwind: unwind.into_action(),
call_source: CallSource::Misc,
fn_span: self.source_info.span,
},
);
// StorageDead(fut) in self.succ block (at the begin)
self.elaborator.patch().add_statement(
Location { block: self.succ, statement_index: 0 },
StatementKind::StorageDead(fut.local),
);
// #1:pin_obj_bb >>> call Pin<ObjTy>::new_unchecked(&mut obj)
self.elaborator.patch().patch_terminator(
pin_obj_bb,
TerminatorKind::Call {
func: pin_obj_new_unchecked_fn,
args: [dummy_spanned(Operand::Move(obj_ref_place))].into(),
destination: pin_obj_place,
target: Some(call_drop_bb),
unwind: unwind.into_action(),
call_source: CallSource::Misc,
fn_span: span,
},
);
pin_obj_bb
}
fn build_drop(&mut self, bb: BasicBlock) {
let drop_ty = self.place_ty(self.place);
if self.tcx().features().async_drop()
&& self.elaborator.body().coroutine.is_some()
&& self.elaborator.allow_async_drops()
&& !self.elaborator.patch_ref().block(self.elaborator.body(), bb).is_cleanup
&& drop_ty.needs_async_drop(self.tcx(), self.elaborator.typing_env())
{
self.build_async_drop(
self.place,
drop_ty,
Some(bb),
self.succ,
self.unwind,
self.dropline,
false,
);
} else {
self.elaborator.patch().patch_terminator(
bb,
TerminatorKind::Drop {
place: self.place,
target: self.succ,
unwind: self.unwind.into_action(),
replace: false,
drop: None,
async_fut: None,
},
);
}
}
/// 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.
#[instrument(level = "debug")]
fn elaborate_drop(&mut self, bb: BasicBlock) {
match self.elaborator.drop_style(self.path, DropFlagMode::Deep) {
DropStyle::Dead => {
self.elaborator
.patch()
.patch_terminator(bb, TerminatorKind::Goto { target: self.succ });
}
DropStyle::Static => {
self.build_drop(bb);
}
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,
args: GenericArgsRef<'tcx>,
) -> Vec<(Place<'tcx>, Option<D::Path>)> {
variant
.fields
.iter_enumerated()
.map(|(field_idx, field)| {
let subpath = self.elaborator.field_subpath(variant_path, field_idx);
let tcx = self.tcx();
assert_eq!(self.elaborator.typing_env().typing_mode, ty::TypingMode::PostAnalysis);
let field_ty = match tcx.try_normalize_erasing_regions(
self.elaborator.typing_env(),
field.ty(tcx, args),
) {
Ok(t) => t,
Err(_) => Ty::new_error(
self.tcx(),
self.tcx().dcx().span_delayed_bug(
self.elaborator.body().span,
"Error normalizing in drop elaboration.",
),
),
};
(tcx.mk_place_field(base_place, field_idx, field_ty), subpath)
})
.collect()
}
fn drop_subpath(
&mut self,
place: Place<'tcx>,
path: Option<D::Path>,
succ: BasicBlock,
unwind: Unwind,
dropline: Option<BasicBlock>,
) -> 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,
dropline,
}
.elaborated_drop_block()
} else {
debug!("drop_subpath: for rest field {:?}", place);
DropCtxt {
elaborator: self.elaborator,
source_info: self.source_info,
place,
succ,
unwind,
dropline,
// 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.
///
/// `dropline_ladder` is a similar list of steps in reverse order,
/// which is called if the matching step of the drop glue will contain async drop
/// (expanded later to Yield) and the containing coroutine will be dropped at this point.
fn drop_halfladder(
&mut self,
unwind_ladder: &[Unwind],
dropline_ladder: &[Option<BasicBlock>],
mut succ: BasicBlock,
fields: &[(Place<'tcx>, Option<D::Path>)],
) -> Vec<BasicBlock> {
iter::once(succ)
.chain(itertools::izip!(fields.iter().rev(), unwind_ladder, dropline_ladder).map(
|(&(place, path), &unwind_succ, &dropline_to)| {
succ = self.drop_subpath(place, path, succ, unwind_succ, dropline_to);
succ
},
))
.collect()
}
fn drop_ladder_bottom(&mut self) -> (BasicBlock, Unwind, Option<BasicBlock>) {
// 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,
self.dropline,
)
}
/// 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`])
///
/// For possible-async drops in coroutines we also need dropline ladder
/// .d0 (mainline):
/// ELAB(drop location.0 [target=.d1, unwind=.c1, drop=.e1])
/// .d1 (mainline):
/// ELAB(drop location.1 [target=.d2, unwind=.c2, drop=.e2])
/// .d2 (mainline):
/// ELAB(drop location.2 [target=`self.succ`, unwind=`self.unwind`, drop=`self.drop`])
/// .c1 (unwind):
/// ELAB(drop location.1 [target=.c2])
/// .c2 (unwind):
/// ELAB(drop location.2 [target=`self.unwind`])
/// .e1 (dropline):
/// ELAB(drop location.1 [target=.e2, unwind=.c2])
/// .e2 (dropline):
/// ELAB(drop location.2 [target=`self.drop`, unwind=`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,
dropline: Option<BasicBlock>,
) -> (BasicBlock, Unwind, Option<BasicBlock>) {
debug!("drop_ladder({:?}, {:?})", self, fields);
assert!(
if unwind.is_cleanup() { dropline.is_none() } else { true },
"Dropline is set for cleanup drop ladder"
);
let mut fields = fields;
fields.retain(|&(place, _)| {
self.place_ty(place).needs_drop(self.tcx(), self.elaborator.typing_env())
});
debug!("drop_ladder - fields needing drop: {:?}", fields);
let dropline_ladder: Vec<Option<BasicBlock>> = vec![None; fields.len() + 1];
let unwind_ladder = vec![Unwind::InCleanup; fields.len() + 1];
let unwind_ladder: Vec<_> = if let Unwind::To(succ) = unwind {
let halfladder = self.drop_halfladder(&unwind_ladder, &dropline_ladder, succ, &fields);
halfladder.into_iter().map(Unwind::To).collect()
} else {
unwind_ladder
};
let dropline_ladder: Vec<_> = if let Some(succ) = dropline {
let halfladder = self.drop_halfladder(&unwind_ladder, &dropline_ladder, succ, &fields);
halfladder.into_iter().map(Some).collect()
} else {
dropline_ladder
};
let normal_ladder = self.drop_halfladder(&unwind_ladder, &dropline_ladder, succ, &fields);
(
*normal_ladder.last().unwrap(),
*unwind_ladder.last().unwrap(),
*dropline_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, FieldIdx::new(i), ty),
self.elaborator.field_subpath(self.path, FieldIdx::new(i)),
)
})
.collect();
let (succ, unwind, dropline) = self.drop_ladder_bottom();
self.drop_ladder(fields, succ, unwind, dropline).0
}
/// Drops the T contained in a `Box<T>` if it has not been moved out of
#[instrument(level = "debug", ret)]
fn open_drop_for_box_contents(
&mut self,
adt: ty::AdtDef<'tcx>,
args: GenericArgsRef<'tcx>,
succ: BasicBlock,
unwind: Unwind,
dropline: Option<BasicBlock>,
) -> BasicBlock {
// drop glue is sent straight to codegen
// box cannot be directly dereferenced
let unique_ty = adt.non_enum_variant().fields[FieldIdx::ZERO].ty(self.tcx(), args);
let unique_variant = unique_ty.ty_adt_def().unwrap().non_enum_variant();
let nonnull_ty = unique_variant.fields[FieldIdx::ZERO].ty(self.tcx(), args);
let ptr_ty = Ty::new_imm_ptr(self.tcx(), args[0].expect_ty());
let unique_place = self.tcx().mk_place_field(self.place, FieldIdx::ZERO, unique_ty);
let nonnull_place = self.tcx().mk_place_field(unique_place, FieldIdx::ZERO, nonnull_ty);
let ptr_local = self.new_temp(ptr_ty);
let interior = self.tcx().mk_place_deref(Place::from(ptr_local));
let interior_path = self.elaborator.deref_subpath(self.path);
let do_drop_bb = self.drop_subpath(interior, interior_path, succ, unwind, dropline);
let setup_bbd = BasicBlockData {
statements: vec![self.assign(
Place::from(ptr_local),
Rvalue::Cast(CastKind::Transmute, Operand::Copy(nonnull_place), ptr_ty),
)],
terminator: Some(Terminator {
kind: TerminatorKind::Goto { target: do_drop_bb },
source_info: self.source_info,
}),
is_cleanup: unwind.is_cleanup(),
};
self.elaborator.patch().new_block(setup_bbd)
}
#[instrument(level = "debug", ret)]
fn open_drop_for_adt(
&mut self,
adt: ty::AdtDef<'tcx>,
args: GenericArgsRef<'tcx>,
) -> BasicBlock {
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() || adt.is_manually_drop();
let contents_drop = if skip_contents {
(self.succ, self.unwind, self.dropline)
} else {
self.open_drop_for_adt_contents(adt, args)
};
if adt.is_box() {
// we need to drop the inside of the box before running the destructor
let succ = self.destructor_call_block_sync((contents_drop.0, contents_drop.1));
let unwind = contents_drop
.1
.map(|unwind| self.destructor_call_block_sync((unwind, Unwind::InCleanup)));
let dropline = contents_drop
.2
.map(|dropline| self.destructor_call_block_sync((dropline, contents_drop.1)));
self.open_drop_for_box_contents(adt, args, succ, unwind, dropline)
} else 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>,
args: GenericArgsRef<'tcx>,
) -> (BasicBlock, Unwind, Option<BasicBlock>) {
let (succ, unwind, dropline) = self.drop_ladder_bottom();
if !adt.is_enum() {
let fields =
self.move_paths_for_fields(self.place, self.path, adt.variant(FIRST_VARIANT), args);
self.drop_ladder(fields, succ, unwind, dropline)
} else {
self.open_drop_for_multivariant(adt, args, succ, unwind, dropline)
}
}
fn open_drop_for_multivariant(
&mut self,
adt: ty::AdtDef<'tcx>,
args: GenericArgsRef<'tcx>,
succ: BasicBlock,
unwind: Unwind,
dropline: Option<BasicBlock>,
) -> (BasicBlock, Unwind, Option<BasicBlock>) {
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 dropline_blocks =
if dropline.is_none() { 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, args);
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 dropline_ladder: Vec<Option<BasicBlock>> = vec![None; fields.len() + 1];
let halfladder =
self.drop_halfladder(&unwind_ladder, &dropline_ladder, unwind, &fields);
unwind_blocks.push(halfladder.last().cloned().unwrap());
}
let (normal, _, drop_bb) = self.drop_ladder(fields, succ, unwind, dropline);
normal_blocks.push(normal);
if dropline.is_some() {
dropline_blocks.as_mut().unwrap().push(drop_bb.unwrap());
}
} else {
have_otherwise = true;
let typing_env = self.elaborator.typing_env();
let have_field_with_drop_glue = variant
.fields
.iter()
.any(|field| field.ty(tcx, args).needs_drop(tcx, typing_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,
)
}),
dropline.map(|dropline| {
self.adt_switch_block(adt, dropline_blocks.unwrap(), &values, dropline, unwind)
}),
)
}
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),
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_sync(&mut self, (succ, unwind): (BasicBlock, Unwind)) -> BasicBlock {
debug!("destructor_call_block_sync({:?}, {:?})", 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 ref_ty = Ty::new_mut_ref(tcx, tcx.lifetimes.re_erased, ty);
let ref_place = self.new_temp(ref_ty);
let unit_temp = Place::from(self.new_temp(tcx.types.unit));
let result = BasicBlockData {
statements: vec![self.assign(
Place::from(ref_place),
Rvalue::Ref(
tcx.lifetimes.re_erased,
BorrowKind::Mut { kind: MutBorrowKind::Default },
self.place,
),
)],
terminator: Some(Terminator {
kind: TerminatorKind::Call {
func: Operand::function_handle(
tcx,
drop_fn,
[ty.into()],
self.source_info.span,
),
args: [Spanned { node: Operand::Move(Place::from(ref_place)), span: DUMMY_SP }]
.into(),
destination: unit_temp,
target: Some(succ),
unwind: unwind.into_action(),
call_source: CallSource::Misc,
fn_span: self.source_info.span,
},
source_info: self.source_info,
}),
is_cleanup: unwind.is_cleanup(),
};
let destructor_block = self.elaborator.patch().new_block(result);
let block_start = Location { block: destructor_block, statement_index: 0 };
self.elaborator.clear_drop_flag(block_start, self.path, DropFlagMode::Shallow);
self.drop_flag_test_block(destructor_block, succ, unwind)
}
fn destructor_call_block(
&mut self,
(succ, unwind, dropline): (BasicBlock, Unwind, Option<BasicBlock>),
) -> BasicBlock {
debug!("destructor_call_block({:?}, {:?})", self, succ);
let ty = self.place_ty(self.place);
if self.tcx().features().async_drop()
&& self.elaborator.body().coroutine.is_some()
&& self.elaborator.allow_async_drops()
&& !unwind.is_cleanup()
&& ty.is_async_drop(self.tcx(), self.elaborator.typing_env())
{
let destructor_block =
self.build_async_drop(self.place, ty, None, succ, unwind, dropline, true);
let block_start = Location { block: destructor_block, statement_index: 0 };
self.elaborator.clear_drop_flag(block_start, self.path, DropFlagMode::Shallow);
self.drop_flag_test_block(destructor_block, succ, unwind)
} else {
self.destructor_call_block_sync((succ, unwind))
}
}
/// Create a loop that drops an array:
///
/// ```text
/// loop-block:
/// can_go = cur == len
/// if can_go then succ else drop-block
/// drop-block:
/// ptr = &raw mut P[cur]
/// cur = cur + 1
/// drop(ptr)
/// ```
fn drop_loop(
&mut self,
succ: BasicBlock,
cur: Local,
len: Local,
ety: Ty<'tcx>,
unwind: Unwind,
dropline: Option<BasicBlock>,
) -> BasicBlock {
let copy = |place: Place<'tcx>| Operand::Copy(place);
let move_ = |place: Place<'tcx>| Operand::Move(place);
let tcx = self.tcx();
let ptr_ty = Ty::new_mut_ptr(tcx, ety);
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 drop_block = BasicBlockData {
statements: vec![
self.assign(
ptr,
Rvalue::RawPtr(RawPtrKind::Mut, tcx.mk_place_index(self.place, cur)),
),
self.assign(
cur.into(),
Rvalue::BinaryOp(BinOp::Add, Box::new((move_(cur.into()), one))),
),
],
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(len.into())))),
)],
is_cleanup: unwind.is_cleanup(),
terminator: Some(Terminator {
source_info: self.source_info,
kind: TerminatorKind::if_(move_(can_go), succ, drop_block),
}),
};
let loop_block = self.elaborator.patch().new_block(loop_block);
let place = tcx.mk_place_deref(ptr);
if self.tcx().features().async_drop()
&& self.elaborator.body().coroutine.is_some()
&& self.elaborator.allow_async_drops()
&& !unwind.is_cleanup()
&& ety.needs_async_drop(self.tcx(), self.elaborator.typing_env())
{
self.build_async_drop(
place,
ety,
Some(drop_block),
loop_block,
unwind,
dropline,
false,
);
} else {
self.elaborator.patch().patch_terminator(
drop_block,
TerminatorKind::Drop {
place,
target: loop_block,
unwind: unwind.into_action(),
replace: false,
drop: None,
async_fut: None,
},
);
}
loop_block
}
fn open_drop_for_array(
&mut self,
array_ty: Ty<'tcx>,
ety: Ty<'tcx>,
opt_size: Option<u64>,
) -> BasicBlock {
debug!("open_drop_for_array({:?}, {:?}, {:?})", array_ty, ety, opt_size);
let tcx = self.tcx();
if let Some(size) = opt_size {
enum ProjectionKind<Path> {
Drop(std::ops::Range<u64>),
Keep(u64, Path),
}
// Previously, we'd make a projection for every element in the array and create a drop
// ladder if any `array_subpath` was `Some`, i.e. moving out with an array pattern.
// This caused huge memory usage when generating the drops for large arrays, so we instead
// record the *subslices* which are dropped and the *indexes* which are kept
let mut drop_ranges = vec![];
let mut dropping = true;
let mut start = 0;
for i in 0..size {
let path = self.elaborator.array_subpath(self.path, i, size);
if dropping && path.is_some() {
drop_ranges.push(ProjectionKind::Drop(start..i));
dropping = false;
} else if !dropping && path.is_none() {
dropping = true;
start = i;
}
if let Some(path) = path {
drop_ranges.push(ProjectionKind::Keep(i, path));
}
}
if !drop_ranges.is_empty() {
if dropping {
drop_ranges.push(ProjectionKind::Drop(start..size));
}
let fields = drop_ranges
.iter()
.rev()
.map(|p| {
let (project, path) = match p {
ProjectionKind::Drop(r) => (
ProjectionElem::Subslice {
from: r.start,
to: r.end,
from_end: false,
},
None,
),
&ProjectionKind::Keep(offset, path) => (
ProjectionElem::ConstantIndex {
offset,
min_length: size,
from_end: false,
},
Some(path),
),
};
(tcx.mk_place_elem(self.place, project), path)
})
.collect::<Vec<_>>();
let (succ, unwind, dropline) = self.drop_ladder_bottom();
return self.drop_ladder(fields, succ, unwind, dropline).0;
}
}
let array_ptr_ty = Ty::new_mut_ptr(tcx, array_ty);
let array_ptr = self.new_temp(array_ptr_ty);
let slice_ty = Ty::new_slice(tcx, ety);
let slice_ptr_ty = Ty::new_mut_ptr(tcx, slice_ty);
let slice_ptr = self.new_temp(slice_ptr_ty);
let mut delegate_block = BasicBlockData {
statements: vec![
self.assign(Place::from(array_ptr), Rvalue::RawPtr(RawPtrKind::Mut, self.place)),
self.assign(
Place::from(slice_ptr),
Rvalue::Cast(
CastKind::PointerCoercion(
PointerCoercion::Unsize,
CoercionSource::Implicit,
),
Operand::Move(Place::from(array_ptr)),
slice_ptr_ty,
),
),
],
is_cleanup: self.unwind.is_cleanup(),
terminator: None,
};
let array_place = mem::replace(
&mut self.place,
Place::from(slice_ptr).project_deeper(&[PlaceElem::Deref], tcx),
);
let slice_block = self.drop_loop_trio_for_slice(ety);
self.place = array_place;
delegate_block.terminator = Some(Terminator {
source_info: self.source_info,
kind: TerminatorKind::Goto { target: slice_block },
});
self.elaborator.patch().new_block(delegate_block)
}
/// Creates a trio of drop-loops of `place`, which drops its contents, even
/// in the case of 1 panic or in the case of coroutine drop
fn drop_loop_trio_for_slice(&mut self, ety: Ty<'tcx>) -> BasicBlock {
debug!("drop_loop_trio_for_slice({:?})", ety);
let tcx = self.tcx();
let len = self.new_temp(tcx.types.usize);
let cur = self.new_temp(tcx.types.usize);
let unwind = self
.unwind
.map(|unwind| self.drop_loop(unwind, cur, len, ety, Unwind::InCleanup, None));
let dropline =
self.dropline.map(|dropline| self.drop_loop(dropline, cur, len, ety, unwind, None));
let loop_block = self.drop_loop(self.succ, cur, len, ety, unwind, dropline);
let [PlaceElem::Deref] = self.place.projection.as_slice() else {
span_bug!(
self.source_info.span,
"Expected place for slice drop shim to be *_n, but it's {:?}",
self.place,
);
};
let zero = self.constant_usize(0);
let block = BasicBlockData {
statements: vec![
self.assign(
len.into(),
Rvalue::UnaryOp(
UnOp::PtrMetadata,
Operand::Copy(Place::from(self.place.local)),
),
),
self.assign(cur.into(), Rvalue::Use(zero)),
],
is_cleanup: unwind.is_cleanup(),
terminator: Some(Terminator {
source_info: self.source_info,
kind: TerminatorKind::Goto { target: loop_block },
}),
};
let drop_block = self.elaborator.patch().new_block(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(_, args) => self.open_drop_for_tuple(args.as_closure().upvar_tys()),
ty::CoroutineClosure(_, args) => {
self.open_drop_for_tuple(args.as_coroutine_closure().upvar_tys())
}
// Note that `elaborate_drops` only drops the upvars of a coroutine,
// and this is ok because `open_drop` here can only be reached
// within that own coroutine's resume function.
// This should only happen for the self argument on the resume function.
// It effectively only contains upvars until the coroutine transformation runs.
// See librustc_body/transform/coroutine.rs for more details.
ty::Coroutine(_, args) => self.open_drop_for_tuple(args.as_coroutine().upvar_tys()),
ty::Tuple(fields) => self.open_drop_for_tuple(fields),
ty::Adt(def, args) => self.open_drop_for_adt(*def, args),
ty::Dynamic(..) => self.complete_drop(self.succ, self.unwind),
ty::Array(ety, size) => {
let size = size.try_to_target_usize(self.tcx());
self.open_drop_for_array(ty, *ety, size)
}
ty::Slice(ety) => self.drop_loop_trio_for_slice(*ety),
_ => span_bug!(self.source_info.span, "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_simple(self.succ, self.unwind);
self.elaborate_drop(blk);
blk
}
fn drop_block_simple(&mut self, target: BasicBlock, unwind: Unwind) -> BasicBlock {
let block = TerminatorKind::Drop {
place: self.place,
target,
unwind: unwind.into_action(),
replace: false,
drop: self.dropline,
async_fut: None,
};
self.new_block(unwind, block)
}
fn drop_block(&mut self, target: BasicBlock, unwind: Unwind) -> BasicBlock {
let drop_ty = self.place_ty(self.place);
if self.tcx().features().async_drop()
&& self.elaborator.body().coroutine.is_some()
&& self.elaborator.allow_async_drops()
&& !unwind.is_cleanup()
&& drop_ty.needs_async_drop(self.tcx(), self.elaborator.typing_env())
{
self.build_async_drop(
self.place,
drop_ty,
None,
self.succ,
unwind,
self.dropline,
false,
)
} else {
let block = TerminatorKind::Drop {
place: self.place,
target,
unwind: unwind.into_action(),
replace: false,
drop: None,
async_fut: None,
};
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_(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_block_with_statements(
&mut self,
unwind: Unwind,
statements: Vec<Statement<'tcx>>,
k: TerminatorKind<'tcx>,
) -> BasicBlock {
self.elaborator.patch().new_block(BasicBlockData {
statements,
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(ConstOperand {
span: self.source_info.span,
user_ty: None,
const_: Const::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))),
}
}
}
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