1 use crate::dataflow::move_paths::{HasMoveData, MoveData, MovePathIndex, LookupResult};
2 use crate::dataflow::{MaybeInitializedPlaces, MaybeUninitializedPlaces};
3 use crate::dataflow::{DataflowResults};
4 use crate::dataflow::{on_all_children_bits, on_all_drop_children_bits};
5 use crate::dataflow::{drop_flag_effects_for_location, on_lookup_result_bits};
6 use crate::dataflow::MoveDataParamEnv;
7 use crate::dataflow::{self, do_dataflow, DebugFormatted};
8 use crate::transform::{MirPass, MirSource};
9 use crate::util::patch::MirPatch;
10 use crate::util::elaborate_drops::{DropFlagState, Unwind, elaborate_drop};
11 use crate::util::elaborate_drops::{DropElaborator, DropStyle, DropFlagMode};
12 use rustc::ty::{self, TyCtxt};
13 use rustc::ty::layout::VariantIdx;
16 use rustc::util::nodemap::FxHashMap;
17 use rustc_data_structures::bit_set::BitSet;
21 pub struct ElaborateDrops;
23 impl<'tcx> MirPass<'tcx> for ElaborateDrops {
24 fn run_pass(&self, tcx: TyCtxt<'tcx>, src: MirSource<'tcx>, body: &mut Body<'tcx>) {
25 debug!("elaborate_drops({:?} @ {:?})", src, body.span);
27 let def_id = src.def_id();
28 let param_env = tcx.param_env(src.def_id()).with_reveal_all();
29 let move_data = match MoveData::gather_moves(body, tcx) {
30 Ok(move_data) => move_data,
31 Err((move_data, _move_errors)) => {
32 // The only way we should be allowing any move_errors
33 // in here is if we are in the migration path for the
34 // NLL-based MIR-borrowck.
36 // If we are in the migration path, we have already
37 // reported these errors as warnings to the user. So
38 // we will just ignore them here.
39 assert!(tcx.migrate_borrowck());
43 let elaborate_patch = {
45 let env = MoveDataParamEnv {
49 let dead_unwinds = find_dead_unwinds(tcx, body, def_id, &env);
51 do_dataflow(tcx, body, def_id, &[], &dead_unwinds,
52 MaybeInitializedPlaces::new(tcx, body, &env),
53 |bd, p| DebugFormatted::new(&bd.move_data().move_paths[p]));
55 do_dataflow(tcx, body, def_id, &[], &dead_unwinds,
56 MaybeUninitializedPlaces::new(tcx, body, &env),
57 |bd, p| DebugFormatted::new(&bd.move_data().move_paths[p]));
65 drop_flags: Default::default(),
66 patch: MirPatch::new(body),
69 elaborate_patch.apply(body);
73 /// Returns the set of basic blocks whose unwind edges are known
74 /// to not be reachable, because they are `drop` terminators
75 /// that can't drop anything.
76 fn find_dead_unwinds<'tcx>(
79 def_id: hir::def_id::DefId,
80 env: &MoveDataParamEnv<'tcx>,
81 ) -> BitSet<BasicBlock> {
82 debug!("find_dead_unwinds({:?})", body.span);
83 // We only need to do this pass once, because unwind edges can only
84 // reach cleanup blocks, which can't have unwind edges themselves.
85 let mut dead_unwinds = BitSet::new_empty(body.basic_blocks().len());
87 do_dataflow(tcx, body, def_id, &[], &dead_unwinds,
88 MaybeInitializedPlaces::new(tcx, body, &env),
89 |bd, p| DebugFormatted::new(&bd.move_data().move_paths[p]));
90 for (bb, bb_data) in body.basic_blocks().iter_enumerated() {
91 let location = match bb_data.terminator().kind {
92 TerminatorKind::Drop { ref location, unwind: Some(_), .. } |
93 TerminatorKind::DropAndReplace { ref location, unwind: Some(_), .. } => location,
97 let mut init_data = InitializationData {
98 live: flow_inits.sets().entry_set_for(bb.index()).to_owned(),
99 dead: BitSet::new_empty(env.move_data.move_paths.len()),
101 debug!("find_dead_unwinds @ {:?}: {:?}; init_data={:?}",
102 bb, bb_data, init_data.live);
103 for stmt in 0..bb_data.statements.len() {
104 let loc = Location { block: bb, statement_index: stmt };
105 init_data.apply_location(tcx, body, env, loc);
108 let path = match env.move_data.rev_lookup.find(location.as_ref()) {
109 LookupResult::Exact(e) => e,
110 LookupResult::Parent(..) => {
111 debug!("find_dead_unwinds: has parent; skipping");
116 debug!("find_dead_unwinds @ {:?}: path({:?})={:?}", bb, location, path);
118 let mut maybe_live = false;
119 on_all_drop_children_bits(tcx, body, &env, path, |child| {
120 let (child_maybe_live, _) = init_data.state(child);
121 maybe_live |= child_maybe_live;
124 debug!("find_dead_unwinds @ {:?}: maybe_live={}", bb, maybe_live);
126 dead_unwinds.insert(bb);
133 struct InitializationData {
134 live: BitSet<MovePathIndex>,
135 dead: BitSet<MovePathIndex>
138 impl InitializationData {
139 fn apply_location<'tcx>(
143 env: &MoveDataParamEnv<'tcx>,
146 drop_flag_effects_for_location(tcx, body, env, loc, |path, df| {
147 debug!("at location {:?}: setting {:?} to {:?}",
150 DropFlagState::Present => {
151 self.live.insert(path);
152 self.dead.remove(path);
154 DropFlagState::Absent => {
155 self.dead.insert(path);
156 self.live.remove(path);
162 fn state(&self, path: MovePathIndex) -> (bool, bool) {
163 (self.live.contains(path), self.dead.contains(path))
167 struct Elaborator<'a, 'b, 'tcx> {
168 init_data: &'a InitializationData,
169 ctxt: &'a mut ElaborateDropsCtxt<'b, 'tcx>,
172 impl<'a, 'b, 'tcx> fmt::Debug for Elaborator<'a, 'b, 'tcx> {
173 fn fmt(&self, _f: &mut fmt::Formatter<'_>) -> fmt::Result {
178 impl<'a, 'b, 'tcx> DropElaborator<'a, 'tcx> for Elaborator<'a, 'b, 'tcx> {
179 type Path = MovePathIndex;
181 fn patch(&mut self) -> &mut MirPatch<'tcx> {
185 fn body(&self) -> &'a Body<'tcx> {
189 fn tcx(&self) -> TyCtxt<'tcx> {
193 fn param_env(&self) -> ty::ParamEnv<'tcx> {
194 self.ctxt.param_env()
197 fn drop_style(&self, path: Self::Path, mode: DropFlagMode) -> DropStyle {
198 let ((maybe_live, maybe_dead), multipart) = match mode {
199 DropFlagMode::Shallow => (self.init_data.state(path), false),
200 DropFlagMode::Deep => {
201 let mut some_live = false;
202 let mut some_dead = false;
203 let mut children_count = 0;
204 on_all_drop_children_bits(
205 self.tcx(), self.body(), self.ctxt.env, path, |child| {
206 let (live, dead) = self.init_data.state(child);
207 debug!("elaborate_drop: state({:?}) = {:?}",
208 child, (live, dead));
213 ((some_live, some_dead), children_count != 1)
216 match (maybe_live, maybe_dead, multipart) {
217 (false, _, _) => DropStyle::Dead,
218 (true, false, _) => DropStyle::Static,
219 (true, true, false) => DropStyle::Conditional,
220 (true, true, true) => DropStyle::Open,
224 fn clear_drop_flag(&mut self, loc: Location, path: Self::Path, mode: DropFlagMode) {
226 DropFlagMode::Shallow => {
227 self.ctxt.set_drop_flag(loc, path, DropFlagState::Absent);
229 DropFlagMode::Deep => {
230 on_all_children_bits(
231 self.tcx(), self.body(), self.ctxt.move_data(), path,
232 |child| self.ctxt.set_drop_flag(loc, child, DropFlagState::Absent)
238 fn field_subpath(&self, path: Self::Path, field: Field) -> Option<Self::Path> {
239 dataflow::move_path_children_matching(self.ctxt.move_data(), path, |p| {
242 elem: ProjectionElem::Field(idx, _), ..
249 fn array_subpath(&self, path: Self::Path, index: u32, size: u32) -> Option<Self::Path> {
250 dataflow::move_path_children_matching(self.ctxt.move_data(), path, |p| {
253 elem: ProjectionElem::ConstantIndex{offset, min_length: _, from_end: false}, ..
254 } => offset == index,
256 elem: ProjectionElem::ConstantIndex{offset, min_length: _, from_end: true}, ..
257 } => size - offset == index,
263 fn deref_subpath(&self, path: Self::Path) -> Option<Self::Path> {
264 dataflow::move_path_children_matching(self.ctxt.move_data(), path, |p| {
266 &Projection { elem: ProjectionElem::Deref, .. } => true,
272 fn downcast_subpath(&self, path: Self::Path, variant: VariantIdx) -> Option<Self::Path> {
273 dataflow::move_path_children_matching(self.ctxt.move_data(), path, |p| {
276 elem: ProjectionElem::Downcast(_, idx), ..
283 fn get_drop_flag(&mut self, path: Self::Path) -> Option<Operand<'tcx>> {
284 self.ctxt.drop_flag(path).map(Operand::Copy)
288 struct ElaborateDropsCtxt<'a, 'tcx> {
290 body: &'a Body<'tcx>,
291 env: &'a MoveDataParamEnv<'tcx>,
292 flow_inits: DataflowResults<'tcx, MaybeInitializedPlaces<'a, 'tcx>>,
293 flow_uninits: DataflowResults<'tcx, MaybeUninitializedPlaces<'a, 'tcx>>,
294 drop_flags: FxHashMap<MovePathIndex, Local>,
295 patch: MirPatch<'tcx>,
298 impl<'b, 'tcx> ElaborateDropsCtxt<'b, 'tcx> {
299 fn move_data(&self) -> &'b MoveData<'tcx> { &self.env.move_data }
301 fn param_env(&self) -> ty::ParamEnv<'tcx> {
305 fn initialization_data_at(&self, loc: Location) -> InitializationData {
306 let mut data = InitializationData {
307 live: self.flow_inits.sets().entry_set_for(loc.block.index())
309 dead: self.flow_uninits.sets().entry_set_for(loc.block.index())
312 for stmt in 0..loc.statement_index {
313 data.apply_location(self.tcx, self.body, self.env,
314 Location { block: loc.block, statement_index: stmt });
319 fn create_drop_flag(&mut self, index: MovePathIndex, span: Span) {
321 let patch = &mut self.patch;
322 debug!("create_drop_flag({:?})", self.body.span);
323 self.drop_flags.entry(index).or_insert_with(|| {
324 patch.new_internal(tcx.types.bool, span)
328 fn drop_flag(&mut self, index: MovePathIndex) -> Option<Place<'tcx>> {
329 self.drop_flags.get(&index).map(|t| Place::from(*t))
332 /// create a patch that elaborates all drops in the input
334 fn elaborate(mut self) -> MirPatch<'tcx>
336 self.collect_drop_flags();
338 self.elaborate_drops();
340 self.drop_flags_on_init();
341 self.drop_flags_for_fn_rets();
342 self.drop_flags_for_args();
343 self.drop_flags_for_locs();
348 fn collect_drop_flags(&mut self)
350 for (bb, data) in self.body.basic_blocks().iter_enumerated() {
351 let terminator = data.terminator();
352 let location = match terminator.kind {
353 TerminatorKind::Drop { ref location, .. } |
354 TerminatorKind::DropAndReplace { ref location, .. } => location,
358 let init_data = self.initialization_data_at(Location {
360 statement_index: data.statements.len()
363 let path = self.move_data().rev_lookup.find(location.as_ref());
364 debug!("collect_drop_flags: {:?}, place {:?} ({:?})",
367 let path = match path {
368 LookupResult::Exact(e) => e,
369 LookupResult::Parent(None) => continue,
370 LookupResult::Parent(Some(parent)) => {
371 let (_maybe_live, maybe_dead) = init_data.state(parent);
373 span_bug!(terminator.source_info.span,
374 "drop of untracked, uninitialized value {:?}, place {:?} ({:?})",
381 on_all_drop_children_bits(self.tcx, self.body, self.env, path, |child| {
382 let (maybe_live, maybe_dead) = init_data.state(child);
383 debug!("collect_drop_flags: collecting {:?} from {:?}@{:?} - {:?}",
384 child, location, path, (maybe_live, maybe_dead));
385 if maybe_live && maybe_dead {
386 self.create_drop_flag(child, terminator.source_info.span)
392 fn elaborate_drops(&mut self)
394 for (bb, data) in self.body.basic_blocks().iter_enumerated() {
395 let loc = Location { block: bb, statement_index: data.statements.len() };
396 let terminator = data.terminator();
398 let resume_block = self.patch.resume_block();
399 match terminator.kind {
400 TerminatorKind::Drop { ref location, target, unwind } => {
401 let init_data = self.initialization_data_at(loc);
402 match self.move_data().rev_lookup.find(location.as_ref()) {
403 LookupResult::Exact(path) => {
406 init_data: &init_data,
409 terminator.source_info,
416 Unwind::To(Option::unwrap_or(unwind, resume_block))
420 LookupResult::Parent(..) => {
421 span_bug!(terminator.source_info.span,
422 "drop of untracked value {:?}", bb);
426 TerminatorKind::DropAndReplace { ref location, ref value,
429 assert!(!data.is_cleanup);
431 self.elaborate_replace(
442 /// Elaborate a MIR `replace` terminator. This instruction
443 /// is not directly handled by codegen, and therefore
444 /// must be desugared.
446 /// The desugaring drops the location if needed, and then writes
447 /// the value (including setting the drop flag) over it in *both* arms.
449 /// The `replace` terminator can also be called on places that
450 /// are not tracked by elaboration (for example,
451 /// `replace x[i] <- tmp0`). The borrow checker requires that
452 /// these locations are initialized before the assignment,
453 /// so we just generate an unconditional drop.
454 fn elaborate_replace(
457 location: &Place<'tcx>,
458 value: &Operand<'tcx>,
460 unwind: Option<BasicBlock>)
463 let data = &self.body[bb];
464 let terminator = data.terminator();
465 assert!(!data.is_cleanup, "DropAndReplace in unwind path not supported");
467 let assign = Statement {
468 kind: StatementKind::Assign(location.clone(), box Rvalue::Use(value.clone())),
469 source_info: terminator.source_info
472 let unwind = unwind.unwrap_or_else(|| self.patch.resume_block());
473 let unwind = self.patch.new_block(BasicBlockData {
474 statements: vec![assign.clone()],
475 terminator: Some(Terminator {
476 kind: TerminatorKind::Goto { target: unwind },
482 let target = self.patch.new_block(BasicBlockData {
483 statements: vec![assign],
484 terminator: Some(Terminator {
485 kind: TerminatorKind::Goto { target },
491 match self.move_data().rev_lookup.find(location.as_ref()) {
492 LookupResult::Exact(path) => {
493 debug!("elaborate_drop_and_replace({:?}) - tracked {:?}", terminator, path);
494 let init_data = self.initialization_data_at(loc);
498 init_data: &init_data,
501 terminator.source_info,
507 on_all_children_bits(self.tcx, self.body, self.move_data(), path, |child| {
508 self.set_drop_flag(Location { block: target, statement_index: 0 },
509 child, DropFlagState::Present);
510 self.set_drop_flag(Location { block: unwind, statement_index: 0 },
511 child, DropFlagState::Present);
514 LookupResult::Parent(parent) => {
515 // drop and replace behind a pointer/array/whatever. The location
516 // must be initialized.
517 debug!("elaborate_drop_and_replace({:?}) - untracked {:?}", terminator, parent);
518 self.patch.patch_terminator(bb, TerminatorKind::Drop {
519 location: location.clone(),
527 fn constant_bool(&self, span: Span, val: bool) -> Rvalue<'tcx> {
528 Rvalue::Use(Operand::Constant(Box::new(Constant {
531 literal: ty::Const::from_bool(self.tcx, val),
535 fn set_drop_flag(&mut self, loc: Location, path: MovePathIndex, val: DropFlagState) {
536 if let Some(&flag) = self.drop_flags.get(&path) {
537 let span = self.patch.source_info_for_location(self.body, loc).span;
538 let val = self.constant_bool(span, val.value());
539 self.patch.add_assign(loc, Place::from(flag), val);
543 fn drop_flags_on_init(&mut self) {
544 let loc = Location::START;
545 let span = self.patch.source_info_for_location(self.body, loc).span;
546 let false_ = self.constant_bool(span, false);
547 for flag in self.drop_flags.values() {
548 self.patch.add_assign(loc, Place::from(*flag), false_.clone());
552 fn drop_flags_for_fn_rets(&mut self) {
553 for (bb, data) in self.body.basic_blocks().iter_enumerated() {
554 if let TerminatorKind::Call {
555 destination: Some((ref place, tgt)), cleanup: Some(_), ..
556 } = data.terminator().kind {
557 assert!(!self.patch.is_patched(bb));
559 let loc = Location { block: tgt, statement_index: 0 };
560 let path = self.move_data().rev_lookup.find(place.as_ref());
561 on_lookup_result_bits(
562 self.tcx, self.body, self.move_data(), path,
563 |child| self.set_drop_flag(loc, child, DropFlagState::Present)
569 fn drop_flags_for_args(&mut self) {
570 let loc = Location::START;
571 dataflow::drop_flag_effects_for_function_entry(
572 self.tcx, self.body, self.env, |path, ds| {
573 self.set_drop_flag(loc, path, ds);
578 fn drop_flags_for_locs(&mut self) {
579 // We intentionally iterate only over the *old* basic blocks.
581 // Basic blocks created by drop elaboration update their
582 // drop flags by themselves, to avoid the drop flags being
583 // clobbered before they are read.
585 for (bb, data) in self.body.basic_blocks().iter_enumerated() {
586 debug!("drop_flags_for_locs({:?})", data);
587 for i in 0..(data.statements.len()+1) {
588 debug!("drop_flag_for_locs: stmt {}", i);
589 let mut allow_initializations = true;
590 if i == data.statements.len() {
591 match data.terminator().kind {
592 TerminatorKind::Drop { .. } => {
593 // drop elaboration should handle that by itself
596 TerminatorKind::DropAndReplace { .. } => {
597 // this contains the move of the source and
598 // the initialization of the destination. We
599 // only want the former - the latter is handled
600 // by the elaboration code and must be done
601 // *after* the destination is dropped.
602 assert!(self.patch.is_patched(bb));
603 allow_initializations = false;
605 TerminatorKind::Resume => {
606 // It is possible for `Resume` to be patched
607 // (in particular it can be patched to be replaced with
608 // a Goto; see `MirPatch::new`).
611 assert!(!self.patch.is_patched(bb));
615 let loc = Location { block: bb, statement_index: i };
616 dataflow::drop_flag_effects_for_location(
617 self.tcx, self.body, self.env, loc, |path, ds| {
618 if ds == DropFlagState::Absent || allow_initializations {
619 self.set_drop_flag(loc, path, ds)
625 // There may be a critical edge after this call,
626 // so mark the return as initialized *before* the
628 if let TerminatorKind::Call {
629 destination: Some((ref place, _)), cleanup: None, ..
630 } = data.terminator().kind {
631 assert!(!self.patch.is_patched(bb));
633 let loc = Location { block: bb, statement_index: data.statements.len() };
634 let path = self.move_data().rev_lookup.find(place.as_ref());
635 on_lookup_result_bits(
636 self.tcx, self.body, self.move_data(), path,
637 |child| self.set_drop_flag(loc, child, DropFlagState::Present)