rustc_mir_dataflow/move_paths/
builder.rs

1use std::mem;
2
3use rustc_index::IndexVec;
4use rustc_middle::mir::*;
5use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitableExt};
6use rustc_middle::{bug, span_bug};
7use smallvec::{SmallVec, smallvec};
8use tracing::debug;
9
10use super::{
11    Init, InitIndex, InitKind, InitLocation, LocationMap, LookupResult, MoveData, MoveOut,
12    MoveOutIndex, MovePath, MovePathIndex, MovePathLookup, MoveSubPath, MoveSubPathResult,
13};
14
15struct MoveDataBuilder<'a, 'tcx, F> {
16    body: &'a Body<'tcx>,
17    loc: Location,
18    tcx: TyCtxt<'tcx>,
19    data: MoveData<'tcx>,
20    filter: F,
21}
22
23impl<'a, 'tcx, F: Fn(Ty<'tcx>) -> bool> MoveDataBuilder<'a, 'tcx, F> {
24    fn new(body: &'a Body<'tcx>, tcx: TyCtxt<'tcx>, filter: F) -> Self {
25        let mut move_paths = IndexVec::new();
26        let mut path_map = IndexVec::new();
27        let mut init_path_map = IndexVec::new();
28
29        let locals = body
30            .local_decls
31            .iter_enumerated()
32            .map(|(i, l)| {
33                if l.is_deref_temp() {
34                    return None;
35                }
36                if filter(l.ty) {
37                    Some(new_move_path(
38                        &mut move_paths,
39                        &mut path_map,
40                        &mut init_path_map,
41                        None,
42                        Place::from(i),
43                    ))
44                } else {
45                    None
46                }
47            })
48            .collect();
49
50        MoveDataBuilder {
51            body,
52            loc: Location::START,
53            tcx,
54            data: MoveData {
55                moves: IndexVec::new(),
56                loc_map: LocationMap::new(body),
57                rev_lookup: MovePathLookup {
58                    locals,
59                    projections: Default::default(),
60                    un_derefer: Default::default(),
61                },
62                move_paths,
63                path_map,
64                inits: IndexVec::new(),
65                init_loc_map: LocationMap::new(body),
66                init_path_map,
67            },
68            filter,
69        }
70    }
71}
72
73fn new_move_path<'tcx>(
74    move_paths: &mut IndexVec<MovePathIndex, MovePath<'tcx>>,
75    path_map: &mut IndexVec<MovePathIndex, SmallVec<[MoveOutIndex; 4]>>,
76    init_path_map: &mut IndexVec<MovePathIndex, SmallVec<[InitIndex; 4]>>,
77    parent: Option<MovePathIndex>,
78    place: Place<'tcx>,
79) -> MovePathIndex {
80    let move_path =
81        move_paths.push(MovePath { next_sibling: None, first_child: None, parent, place });
82
83    if let Some(parent) = parent {
84        let next_sibling = mem::replace(&mut move_paths[parent].first_child, Some(move_path));
85        move_paths[move_path].next_sibling = next_sibling;
86    }
87
88    let path_map_ent = path_map.push(smallvec![]);
89    assert_eq!(path_map_ent, move_path);
90
91    let init_path_map_ent = init_path_map.push(smallvec![]);
92    assert_eq!(init_path_map_ent, move_path);
93
94    move_path
95}
96
97impl<'a, 'tcx, F: Fn(Ty<'tcx>) -> bool> MoveDataBuilder<'a, 'tcx, F> {
98    /// This creates a MovePath for a given place, calling `on_move`
99    /// if it can be moved from. If theres a union in the path, its
100    /// move place will be given to `on_move`. If there's a subslice
101    /// projection, `on_move` will be called for each element.
102    ///
103    /// NOTE: places behind references *do not* get a move path, which is
104    /// problematic for borrowck.
105    ///
106    /// Maybe we should have separate "borrowck" and "moveck" modes.
107    fn move_path_for<G>(&mut self, place: Place<'tcx>, mut on_move: G)
108    where
109        G: FnMut(&mut Self, MovePathIndex),
110    {
111        let data = &mut self.data;
112
113        debug!("lookup({:?})", place);
114        let Some(mut base) = data.rev_lookup.find_local(place.local) else {
115            return;
116        };
117
118        // The move path index of the first union that we find. Once this is
119        // some we stop creating child move paths, since moves from unions
120        // move the whole thing.
121        // We continue looking for other move errors though so that moving
122        // from `*(u.f: &_)` isn't allowed.
123        let mut union_path = None;
124
125        let mut iter = data.rev_lookup.un_derefer.iter_projections(place.as_ref());
126        while let Some((place_ref, elem)) = iter.next() {
127            let body = self.body;
128            let tcx = self.tcx;
129            let place_ty = place_ref.ty(body, tcx).ty;
130            if place_ty.references_error() {
131                return;
132            }
133
134            let res = MoveSubPath::of(elem.kind());
135
136            let move_elem = match res {
137                MoveSubPathResult::One(move_elem) => {
138                    match move_elem {
139                        MoveSubPath::Deref => match place_ty.kind() {
140                            ty::Ref(..) | ty::RawPtr(..) => {
141                                return;
142                            }
143                            ty::Adt(adt, _) => {
144                                if !adt.is_box() {
145                                    bug!("Adt should be a box type when Place is deref");
146                                }
147                            }
148                            ty::Bool
149                            | ty::Char
150                            | ty::Int(_)
151                            | ty::Uint(_)
152                            | ty::Float(_)
153                            | ty::Foreign(_)
154                            | ty::Str
155                            | ty::Array(_, _)
156                            | ty::Pat(_, _)
157                            | ty::Slice(_)
158                            | ty::FnDef(_, _)
159                            | ty::FnPtr(..)
160                            | ty::Dynamic(_, _)
161                            | ty::Closure(..)
162                            | ty::CoroutineClosure(..)
163                            | ty::Coroutine(_, _)
164                            | ty::CoroutineWitness(..)
165                            | ty::Never
166                            | ty::Tuple(_)
167                            | ty::UnsafeBinder(_)
168                            | ty::Alias(_, _)
169                            | ty::Param(_)
170                            | ty::Bound(_, _)
171                            | ty::Infer(_)
172                            | ty::Error(_)
173                            | ty::Placeholder(_) => {
174                                bug!("When Place is Deref it's type shouldn't be {place_ty:#?}")
175                            }
176                        },
177                        MoveSubPath::Field(_) => match place_ty.kind() {
178                            ty::Adt(adt, _) => {
179                                if adt.has_dtor(tcx) {
180                                    return;
181                                }
182                                if adt.is_union() {
183                                    union_path.get_or_insert(base);
184                                }
185                            }
186                            ty::Closure(..)
187                            | ty::CoroutineClosure(..)
188                            | ty::Coroutine(_, _)
189                            | ty::Tuple(_) => (),
190                            ty::Bool
191                            | ty::Char
192                            | ty::Int(_)
193                            | ty::Uint(_)
194                            | ty::Float(_)
195                            | ty::Foreign(_)
196                            | ty::Str
197                            | ty::Array(_, _)
198                            | ty::Pat(_, _)
199                            | ty::Slice(_)
200                            | ty::RawPtr(_, _)
201                            | ty::Ref(_, _, _)
202                            | ty::FnDef(_, _)
203                            | ty::FnPtr(..)
204                            | ty::Dynamic(_, _)
205                            | ty::CoroutineWitness(..)
206                            | ty::Never
207                            | ty::UnsafeBinder(_)
208                            | ty::Alias(_, _)
209                            | ty::Param(_)
210                            | ty::Bound(_, _)
211                            | ty::Infer(_)
212                            | ty::Error(_)
213                            | ty::Placeholder(_) => bug!(
214                                "When Place contains ProjectionElem::Field its type shouldn't be {place_ty:#?}"
215                            ),
216                        },
217                        MoveSubPath::ConstantIndex(_) => match place_ty.kind() {
218                            ty::Slice(_) => {
219                                return;
220                            }
221                            ty::Array(_, _) => (),
222                            _ => bug!("Unexpected type {:#?}", place_ty.is_array()),
223                        },
224                        MoveSubPath::Downcast(_) => (),
225                        MoveSubPath::UnwrapUnsafeBinder => (),
226                    };
227
228                    move_elem
229                }
230
231                // Split `Subslice` patterns into the corresponding list of
232                // `ConstIndex` patterns. This is done to ensure that all move paths
233                // are disjoint, which is expected by drop elaboration.
234                MoveSubPathResult::Subslice { from, to } => {
235                    assert!(
236                        iter.all(
237                            |(_, elem)| MoveSubPath::of(elem.kind()) == MoveSubPathResult::Skip
238                        )
239                    );
240                    drop(iter); // drop for borrowck
241
242                    let (&elem_ty, len) = match place_ty.kind() {
243                        ty::Array(ty, size) => (
244                            ty,
245                            size.try_to_target_usize(self.tcx)
246                                .expect("expected subslice projection on fixed-size array"),
247                        ),
248                        _ => bug!("from_end: false slice pattern of non-array type"),
249                    };
250
251                    if !(self.filter)(elem_ty) {
252                        return;
253                    }
254
255                    for offset in from..to {
256                        let place_elem =
257                            PlaceElem::ConstantIndex { offset, min_length: len, from_end: false };
258                        let subpath_elem = MoveSubPath::ConstantIndex(offset);
259
260                        let mpi = self.add_move_path(base, subpath_elem, |tcx| {
261                            place_ref.project_deeper(&[place_elem], tcx)
262                        });
263                        on_move(self, mpi);
264                    }
265
266                    return;
267                }
268
269                MoveSubPathResult::Skip => continue,
270                MoveSubPathResult::Stop => return,
271            };
272
273            let elem_ty = PlaceTy::from_ty(place_ty).projection_ty(tcx, elem).ty;
274            if !(self.filter)(elem_ty) {
275                return;
276            }
277            if union_path.is_none() {
278                // inlined from add_move_path because of a borrowck conflict with the iterator
279                base = *data.rev_lookup.projections.entry((base, move_elem)).or_insert_with(|| {
280                    new_move_path(
281                        &mut data.move_paths,
282                        &mut data.path_map,
283                        &mut data.init_path_map,
284                        Some(base),
285                        place_ref.project_deeper(&[elem], tcx),
286                    )
287                })
288            }
289        }
290
291        drop(iter); // drop for borrowck
292
293        if let Some(base) = union_path {
294            // Move out of union - always move the entire union.
295            on_move(self, base);
296        } else {
297            on_move(self, base);
298        }
299    }
300
301    fn add_move_path(
302        &mut self,
303        base: MovePathIndex,
304        elem: MoveSubPath,
305        mk_place: impl FnOnce(TyCtxt<'tcx>) -> Place<'tcx>,
306    ) -> MovePathIndex {
307        let MoveDataBuilder {
308            data: MoveData { rev_lookup, move_paths, path_map, init_path_map, .. },
309            tcx,
310            ..
311        } = self;
312        *rev_lookup.projections.entry((base, elem)).or_insert_with(move || {
313            new_move_path(move_paths, path_map, init_path_map, Some(base), mk_place(*tcx))
314        })
315    }
316
317    fn create_move_path(&mut self, place: Place<'tcx>) {
318        // This is an non-moving access (such as an overwrite or
319        // drop), so this not being a valid move path is OK.
320        self.move_path_for(place, |_, _| ());
321    }
322
323    fn finalize(self) -> MoveData<'tcx> {
324        debug!("{}", {
325            debug!("moves for {:?}:", self.body.span);
326            for (j, mo) in self.data.moves.iter_enumerated() {
327                debug!("    {:?} = {:?}", j, mo);
328            }
329            debug!("move paths for {:?}:", self.body.span);
330            for (j, path) in self.data.move_paths.iter_enumerated() {
331                debug!("    {:?} = {:?}", j, path);
332            }
333            "done dumping moves"
334        });
335
336        self.data
337    }
338}
339
340pub(super) fn gather_moves<'tcx>(
341    body: &Body<'tcx>,
342    tcx: TyCtxt<'tcx>,
343    filter: impl Fn(Ty<'tcx>) -> bool,
344) -> MoveData<'tcx> {
345    let mut builder = MoveDataBuilder::new(body, tcx, filter);
346
347    builder.gather_args();
348
349    for (bb, block) in body.basic_blocks.iter_enumerated() {
350        for (i, stmt) in block.statements.iter().enumerate() {
351            builder.loc = Location { block: bb, statement_index: i };
352            builder.gather_statement(stmt);
353        }
354
355        builder.loc = Location { block: bb, statement_index: block.statements.len() };
356        builder.gather_terminator(block.terminator());
357    }
358
359    builder.finalize()
360}
361
362impl<'a, 'tcx, F: Fn(Ty<'tcx>) -> bool> MoveDataBuilder<'a, 'tcx, F> {
363    fn gather_args(&mut self) {
364        for arg in self.body.args_iter() {
365            if let Some(path) = self.data.rev_lookup.find_local(arg) {
366                let init = self.data.inits.push(Init {
367                    path,
368                    kind: InitKind::Deep,
369                    location: InitLocation::Argument(arg),
370                });
371
372                debug!("gather_args: adding init {:?} of {:?} for argument {:?}", init, path, arg);
373
374                self.data.init_path_map[path].push(init);
375            }
376        }
377    }
378
379    fn gather_statement(&mut self, stmt: &Statement<'tcx>) {
380        debug!("gather_statement({:?}, {:?})", self.loc, stmt);
381        match &stmt.kind {
382            StatementKind::Assign(box (place, Rvalue::CopyForDeref(reffed))) => {
383                let local = place.as_local().unwrap();
384                assert!(self.body.local_decls[local].is_deref_temp());
385
386                let rev_lookup = &mut self.data.rev_lookup;
387
388                rev_lookup.un_derefer.insert(local, reffed.as_ref());
389                let base_local = rev_lookup.un_derefer.deref_chain(local).first().unwrap().local;
390                rev_lookup.locals[local] = rev_lookup.locals[base_local];
391            }
392            StatementKind::Assign(box (place, rval)) => {
393                self.create_move_path(*place);
394                if let RvalueInitializationState::Shallow = rval.initialization_state() {
395                    // Box starts out uninitialized - need to create a separate
396                    // move-path for the interior so it will be separate from
397                    // the exterior.
398                    self.create_move_path(self.tcx.mk_place_deref(*place));
399                    self.gather_init(place.as_ref(), InitKind::Shallow);
400                } else {
401                    self.gather_init(place.as_ref(), InitKind::Deep);
402                }
403                self.gather_rvalue(rval);
404            }
405            StatementKind::FakeRead(box (_, place)) => {
406                self.create_move_path(*place);
407            }
408            StatementKind::StorageLive(_) => {}
409            StatementKind::StorageDead(local) => {
410                // DerefTemp locals (results of CopyForDeref) don't actually move anything.
411                if !self.body.local_decls[*local].is_deref_temp() {
412                    self.gather_move(Place::from(*local));
413                }
414            }
415            StatementKind::SetDiscriminant { .. } => {
416                span_bug!(
417                    stmt.source_info.span,
418                    "SetDiscriminant/Deinit should not exist during borrowck"
419                );
420            }
421            StatementKind::Retag { .. }
422            | StatementKind::AscribeUserType(..)
423            | StatementKind::PlaceMention(..)
424            | StatementKind::Coverage(..)
425            | StatementKind::Intrinsic(..)
426            | StatementKind::ConstEvalCounter
427            | StatementKind::BackwardIncompatibleDropHint { .. }
428            | StatementKind::Nop => {}
429        }
430    }
431
432    fn gather_rvalue(&mut self, rvalue: &Rvalue<'tcx>) {
433        match *rvalue {
434            Rvalue::ThreadLocalRef(_) => {} // not-a-move
435            Rvalue::Use(ref operand)
436            | Rvalue::Repeat(ref operand, _)
437            | Rvalue::Cast(_, ref operand, _)
438            | Rvalue::ShallowInitBox(ref operand, _)
439            | Rvalue::UnaryOp(_, ref operand)
440            | Rvalue::WrapUnsafeBinder(ref operand, _) => self.gather_operand(operand),
441            Rvalue::BinaryOp(ref _binop, box (ref lhs, ref rhs)) => {
442                self.gather_operand(lhs);
443                self.gather_operand(rhs);
444            }
445            Rvalue::Aggregate(ref _kind, ref operands) => {
446                for operand in operands {
447                    self.gather_operand(operand);
448                }
449            }
450            Rvalue::CopyForDeref(..) => unreachable!(),
451            Rvalue::Ref(..)
452            | Rvalue::RawPtr(..)
453            | Rvalue::Discriminant(..)
454            | Rvalue::NullaryOp(
455                NullOp::OffsetOf(..) | NullOp::UbChecks | NullOp::ContractChecks,
456                _,
457            ) => {}
458        }
459    }
460
461    fn gather_terminator(&mut self, term: &Terminator<'tcx>) {
462        debug!("gather_terminator({:?}, {:?})", self.loc, term);
463        match term.kind {
464            TerminatorKind::Goto { target: _ }
465            | TerminatorKind::FalseEdge { .. }
466            | TerminatorKind::FalseUnwind { .. }
467            // In some sense returning moves the return place into the current
468            // call's destination, however, since there are no statements after
469            // this that could possibly access the return place, this doesn't
470            // need recording.
471            | TerminatorKind::Return
472            | TerminatorKind::UnwindResume
473            | TerminatorKind::UnwindTerminate(_)
474            | TerminatorKind::CoroutineDrop
475            | TerminatorKind::Unreachable
476            | TerminatorKind::Drop { .. } => {}
477
478            TerminatorKind::Assert { ref cond, .. } => {
479                self.gather_operand(cond);
480            }
481
482            TerminatorKind::SwitchInt { ref discr, .. } => {
483                self.gather_operand(discr);
484            }
485
486            TerminatorKind::Yield { ref value, resume_arg: place, .. } => {
487                self.gather_operand(value);
488                self.create_move_path(place);
489                self.gather_init(place.as_ref(), InitKind::Deep);
490            }
491            TerminatorKind::Call {
492                ref func,
493                ref args,
494                destination,
495                target,
496                unwind: _,
497                call_source: _,
498                fn_span: _,
499            } => {
500                self.gather_operand(func);
501                for arg in args {
502                    self.gather_operand(&arg.node);
503                }
504                if let Some(_bb) = target {
505                    self.create_move_path(destination);
506                    self.gather_init(destination.as_ref(), InitKind::NonPanicPathOnly);
507                }
508            }
509            TerminatorKind::TailCall { ref func, ref args, .. } => {
510                self.gather_operand(func);
511                for arg in args {
512                    self.gather_operand(&arg.node);
513                }
514            }
515            TerminatorKind::InlineAsm {
516                asm_macro: _,
517                template: _,
518                ref operands,
519                options: _,
520                line_spans: _,
521                targets: _,
522                unwind: _,
523            } => {
524                for op in operands {
525                    match *op {
526                        InlineAsmOperand::In { reg: _, ref value }
527                         => {
528                            self.gather_operand(value);
529                        }
530                        InlineAsmOperand::Out { reg: _, late: _, place, .. } => {
531                            if let Some(place) = place {
532                                self.create_move_path(place);
533                                self.gather_init(place.as_ref(), InitKind::Deep);
534                            }
535                        }
536                        InlineAsmOperand::InOut { reg: _, late: _, ref in_value, out_place } => {
537                            self.gather_operand(in_value);
538                            if let Some(out_place) = out_place {
539                                self.create_move_path(out_place);
540                                self.gather_init(out_place.as_ref(), InitKind::Deep);
541                            }
542                        }
543                        InlineAsmOperand::Const { value: _ }
544                        | InlineAsmOperand::SymFn { value: _ }
545                        | InlineAsmOperand::SymStatic { def_id: _ }
546                        | InlineAsmOperand::Label { target_index: _ } => {}
547                    }
548                }
549            }
550        }
551    }
552
553    fn gather_operand(&mut self, operand: &Operand<'tcx>) {
554        match *operand {
555            Operand::Constant(..) | Operand::Copy(..) => {} // not-a-move
556            Operand::Move(place) => {
557                // a move
558                self.gather_move(place);
559            }
560        }
561    }
562
563    fn gather_move(&mut self, place: Place<'tcx>) {
564        debug!("gather_move({:?}, {:?})", self.loc, place);
565        self.move_path_for(place, |this, mpi| this.record_move(place, mpi));
566    }
567
568    fn record_move(&mut self, place: Place<'tcx>, path: MovePathIndex) {
569        let move_out = self.data.moves.push(MoveOut { path, source: self.loc });
570        debug!(
571            "gather_move({:?}, {:?}): adding move {:?} of {:?}",
572            self.loc, place, move_out, path
573        );
574        self.data.path_map[path].push(move_out);
575        self.data.loc_map[self.loc].push(move_out);
576    }
577
578    fn gather_init(&mut self, place: PlaceRef<'tcx>, kind: InitKind) {
579        debug!("gather_init({:?}, {:?})", self.loc, place);
580
581        let mut place = place;
582
583        // Check if we are assigning into a field of a union, if so, lookup the place
584        // of the union so it is marked as initialized again.
585        if let Some((place_base, ProjectionElem::Field(_, _))) = place.last_projection() {
586            if place_base.ty(self.body, self.tcx).ty.is_union() {
587                place = place_base;
588            }
589        }
590
591        if let LookupResult::Exact(path) = self.data.rev_lookup.find(place) {
592            let init = self.data.inits.push(Init {
593                location: InitLocation::Statement(self.loc),
594                path,
595                kind,
596            });
597
598            debug!(
599                "gather_init({:?}, {:?}): adding init {:?} of {:?}",
600                self.loc, place, init, path
601            );
602
603            self.data.init_path_map[path].push(init);
604            self.data.init_loc_map[self.loc].push(init);
605        }
606    }
607}
rustc_mir_dataflow/move_paths/builder.rs

rustc_mir_dataflow/move_paths/
builder.rs
