rustc_mir_dataflow/move_paths/
mod.rs

1//! [`MovePath`]s track the initialization state of places and their sub-paths.
2
3use std::fmt;
4use std::ops::{Index, IndexMut};
5
6use rustc_abi::{FieldIdx, VariantIdx};
7use rustc_data_structures::fx::FxHashMap;
8use rustc_index::{IndexSlice, IndexVec};
9use rustc_middle::mir::*;
10use rustc_middle::ty::{Ty, TyCtxt};
11use rustc_span::Span;
12use smallvec::SmallVec;
13
14use crate::un_derefer::UnDerefer;
15
16rustc_index::newtype_index! {
17    #[orderable]
18    #[debug_format = "mp{}"]
19    pub struct MovePathIndex {}
20}
21
22impl polonius_engine::Atom for MovePathIndex {
23    fn index(self) -> usize {
24        rustc_index::Idx::index(self)
25    }
26}
27
28rustc_index::newtype_index! {
29    #[orderable]
30    #[debug_format = "mo{}"]
31    pub struct MoveOutIndex {}
32}
33
34rustc_index::newtype_index! {
35    #[debug_format = "in{}"]
36    pub struct InitIndex {}
37}
38
39impl MoveOutIndex {
40    pub fn move_path_index(self, move_data: &MoveData<'_>) -> MovePathIndex {
41        move_data.moves[self].path
42    }
43}
44
45/// `MovePath` is a canonicalized representation of a path that is
46/// moved or assigned to.
47///
48/// It follows a tree structure.
49///
50/// Given `struct X { m: M, n: N }` and `x: X`, moves like `drop x.m;`
51/// move *out* of the place `x.m`.
52///
53/// The MovePaths representing `x.m` and `x.n` are siblings (that is,
54/// one of them will link to the other via the `next_sibling` field,
55/// and the other will have no entry in its `next_sibling` field), and
56/// they both have the MovePath representing `x` as their parent.
57#[derive(Clone)]
58pub struct MovePath<'tcx> {
59    pub next_sibling: Option<MovePathIndex>,
60    pub first_child: Option<MovePathIndex>,
61    pub parent: Option<MovePathIndex>,
62    pub place: Place<'tcx>,
63}
64
65impl<'tcx> MovePath<'tcx> {
66    /// Returns an iterator over the parents of `self`.
67    pub fn parents<'a>(
68        &self,
69        move_paths: &'a IndexSlice<MovePathIndex, MovePath<'tcx>>,
70    ) -> impl 'a + Iterator<Item = (MovePathIndex, &'a MovePath<'tcx>)> {
71        let first = self.parent.map(|mpi| (mpi, &move_paths[mpi]));
72        MovePathLinearIter {
73            next: first,
74            fetch_next: move |_, parent: &MovePath<'_>| {
75                parent.parent.map(|mpi| (mpi, &move_paths[mpi]))
76            },
77        }
78    }
79
80    /// Returns an iterator over the immediate children of `self`.
81    pub fn children<'a>(
82        &self,
83        move_paths: &'a IndexSlice<MovePathIndex, MovePath<'tcx>>,
84    ) -> impl 'a + Iterator<Item = (MovePathIndex, &'a MovePath<'tcx>)> {
85        let first = self.first_child.map(|mpi| (mpi, &move_paths[mpi]));
86        MovePathLinearIter {
87            next: first,
88            fetch_next: move |_, child: &MovePath<'_>| {
89                child.next_sibling.map(|mpi| (mpi, &move_paths[mpi]))
90            },
91        }
92    }
93
94    /// Finds the closest descendant of `self` for which `f` returns `true` using a breadth-first
95    /// search.
96    ///
97    /// `f` will **not** be called on `self`.
98    pub fn find_descendant(
99        &self,
100        move_paths: &IndexSlice<MovePathIndex, MovePath<'_>>,
101        f: impl Fn(MovePathIndex) -> bool,
102    ) -> Option<MovePathIndex> {
103        let mut todo = if let Some(child) = self.first_child {
104            vec![child]
105        } else {
106            return None;
107        };
108
109        while let Some(mpi) = todo.pop() {
110            if f(mpi) {
111                return Some(mpi);
112            }
113
114            let move_path = &move_paths[mpi];
115            if let Some(child) = move_path.first_child {
116                todo.push(child);
117            }
118
119            // After we've processed the original `mpi`, we should always
120            // traverse the siblings of any of its children.
121            if let Some(sibling) = move_path.next_sibling {
122                todo.push(sibling);
123            }
124        }
125
126        None
127    }
128}
129
130impl<'tcx> fmt::Debug for MovePath<'tcx> {
131    fn fmt(&self, w: &mut fmt::Formatter<'_>) -> fmt::Result {
132        write!(w, "MovePath {{")?;
133        if let Some(parent) = self.parent {
134            write!(w, " parent: {parent:?},")?;
135        }
136        if let Some(first_child) = self.first_child {
137            write!(w, " first_child: {first_child:?},")?;
138        }
139        if let Some(next_sibling) = self.next_sibling {
140            write!(w, " next_sibling: {next_sibling:?}")?;
141        }
142        write!(w, " place: {:?} }}", self.place)
143    }
144}
145
146impl<'tcx> fmt::Display for MovePath<'tcx> {
147    fn fmt(&self, w: &mut fmt::Formatter<'_>) -> fmt::Result {
148        write!(w, "{:?}", self.place)
149    }
150}
151
152struct MovePathLinearIter<'a, 'tcx, F> {
153    next: Option<(MovePathIndex, &'a MovePath<'tcx>)>,
154    fetch_next: F,
155}
156
157impl<'a, 'tcx, F> Iterator for MovePathLinearIter<'a, 'tcx, F>
158where
159    F: FnMut(MovePathIndex, &'a MovePath<'tcx>) -> Option<(MovePathIndex, &'a MovePath<'tcx>)>,
160{
161    type Item = (MovePathIndex, &'a MovePath<'tcx>);
162
163    fn next(&mut self) -> Option<Self::Item> {
164        let ret = self.next.take()?;
165        self.next = (self.fetch_next)(ret.0, ret.1);
166        Some(ret)
167    }
168}
169
170#[derive(Debug)]
171pub struct MoveData<'tcx> {
172    pub move_paths: IndexVec<MovePathIndex, MovePath<'tcx>>,
173    pub moves: IndexVec<MoveOutIndex, MoveOut>,
174    /// Each Location `l` is mapped to the MoveOut's that are effects
175    /// of executing the code at `l`. (There can be multiple MoveOut's
176    /// for a given `l` because each MoveOut is associated with one
177    /// particular path being moved.)
178    pub loc_map: LocationMap<SmallVec<[MoveOutIndex; 4]>>,
179    pub path_map: IndexVec<MovePathIndex, SmallVec<[MoveOutIndex; 4]>>,
180    pub rev_lookup: MovePathLookup<'tcx>,
181    pub inits: IndexVec<InitIndex, Init>,
182    /// Each Location `l` is mapped to the Inits that are effects
183    /// of executing the code at `l`.
184    pub init_loc_map: LocationMap<SmallVec<[InitIndex; 4]>>,
185    pub init_path_map: IndexVec<MovePathIndex, SmallVec<[InitIndex; 4]>>,
186}
187
188pub trait HasMoveData<'tcx> {
189    fn move_data(&self) -> &MoveData<'tcx>;
190}
191
192#[derive(Debug)]
193pub struct LocationMap<T> {
194    /// Location-indexed (BasicBlock for outer index, index within BB
195    /// for inner index) map.
196    pub(crate) map: IndexVec<BasicBlock, Vec<T>>,
197}
198
199impl<T> Index<Location> for LocationMap<T> {
200    type Output = T;
201    fn index(&self, index: Location) -> &Self::Output {
202        &self.map[index.block][index.statement_index]
203    }
204}
205
206impl<T> IndexMut<Location> for LocationMap<T> {
207    fn index_mut(&mut self, index: Location) -> &mut Self::Output {
208        &mut self.map[index.block][index.statement_index]
209    }
210}
211
212impl<T> LocationMap<T>
213where
214    T: Default + Clone,
215{
216    fn new(body: &Body<'_>) -> Self {
217        LocationMap {
218            map: body
219                .basic_blocks
220                .iter()
221                .map(|block| vec![T::default(); block.statements.len() + 1])
222                .collect(),
223        }
224    }
225}
226
227/// `MoveOut` represents a point in a program that moves out of some
228/// L-value; i.e., "creates" uninitialized memory.
229///
230/// With respect to dataflow analysis:
231/// - Generated by moves and declaration of uninitialized variables.
232/// - Killed by assignments to the memory.
233#[derive(Copy, Clone)]
234pub struct MoveOut {
235    /// path being moved
236    pub path: MovePathIndex,
237    /// location of move
238    pub source: Location,
239}
240
241impl fmt::Debug for MoveOut {
242    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
243        write!(fmt, "{:?}@{:?}", self.path, self.source)
244    }
245}
246
247/// `Init` represents a point in a program that initializes some L-value;
248#[derive(Copy, Clone)]
249pub struct Init {
250    /// path being initialized
251    pub path: MovePathIndex,
252    /// location of initialization
253    pub location: InitLocation,
254    /// Extra information about this initialization
255    pub kind: InitKind,
256}
257
258/// Initializations can be from an argument or from a statement. Arguments
259/// do not have locations, in those cases the `Local` is kept..
260#[derive(Copy, Clone, Debug, PartialEq, Eq)]
261pub enum InitLocation {
262    Argument(Local),
263    Statement(Location),
264}
265
266/// Additional information about the initialization.
267#[derive(Copy, Clone, Debug, PartialEq, Eq)]
268pub enum InitKind {
269    /// Deep init, even on panic
270    Deep,
271    /// Only does a shallow init
272    Shallow,
273    /// This doesn't initialize the variable on panic (and a panic is possible).
274    NonPanicPathOnly,
275}
276
277impl fmt::Debug for Init {
278    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
279        write!(fmt, "{:?}@{:?} ({:?})", self.path, self.location, self.kind)
280    }
281}
282
283impl Init {
284    pub fn span<'tcx>(&self, body: &Body<'tcx>) -> Span {
285        match self.location {
286            InitLocation::Argument(local) => body.local_decls[local].source_info.span,
287            InitLocation::Statement(location) => body.source_info(location).span,
288        }
289    }
290}
291
292/// Tables mapping from a place to its MovePathIndex.
293#[derive(Debug)]
294pub struct MovePathLookup<'tcx> {
295    locals: IndexVec<Local, Option<MovePathIndex>>,
296
297    /// projections are made from a base-place and a projection
298    /// elem. The base-place will have a unique MovePathIndex; we use
299    /// the latter as the index into the outer vector (narrowing
300    /// subsequent search so that it is solely relative to that
301    /// base-place). For the remaining lookup, we map the projection
302    /// elem to the associated MovePathIndex.
303    projections: FxHashMap<(MovePathIndex, MoveSubPath), MovePathIndex>,
304
305    un_derefer: UnDerefer<'tcx>,
306}
307
308mod builder;
309
310#[derive(Copy, Clone, Debug)]
311pub enum LookupResult {
312    Exact(MovePathIndex),
313    Parent(Option<MovePathIndex>),
314}
315
316impl<'tcx> MovePathLookup<'tcx> {
317    // Unlike the builder `fn move_path_for` below, this lookup
318    // alternative will *not* create a MovePath on the fly for an
319    // unknown place, but will rather return the nearest available
320    // parent.
321    pub fn find(&self, place: PlaceRef<'tcx>) -> LookupResult {
322        let Some(mut result) = self.find_local(place.local) else {
323            return LookupResult::Parent(None);
324        };
325
326        for (_, elem) in self.un_derefer.iter_projections(place) {
327            let subpath = match MoveSubPath::of(elem.kind()) {
328                MoveSubPathResult::One(kind) => self.projections.get(&(result, kind)),
329                MoveSubPathResult::Subslice { .. } => None, // just use the parent MovePath
330                MoveSubPathResult::Skip => continue,
331                MoveSubPathResult::Stop => None,
332            };
333
334            if let Some(&subpath) = subpath {
335                result = subpath;
336            } else {
337                return LookupResult::Parent(Some(result));
338            }
339        }
340
341        LookupResult::Exact(result)
342    }
343
344    #[inline]
345    pub fn find_local(&self, local: Local) -> Option<MovePathIndex> {
346        self.locals[local]
347    }
348
349    /// An enumerated iterator of `local`s and their associated
350    /// `MovePathIndex`es.
351    pub fn iter_locals_enumerated(
352        &self,
353    ) -> impl DoubleEndedIterator<Item = (Local, MovePathIndex)> {
354        self.locals.iter_enumerated().filter_map(|(l, &idx)| Some((l, idx?)))
355    }
356}
357
358impl<'tcx> MoveData<'tcx> {
359    pub fn gather_moves(
360        body: &Body<'tcx>,
361        tcx: TyCtxt<'tcx>,
362        filter: impl Fn(Ty<'tcx>) -> bool,
363    ) -> MoveData<'tcx> {
364        builder::gather_moves(body, tcx, filter)
365    }
366
367    /// For the move path `mpi`, returns the root local variable that starts the path.
368    /// (e.g., for a path like `a.b.c` returns `a`)
369    pub fn base_local(&self, mut mpi: MovePathIndex) -> Local {
370        loop {
371            let path = &self.move_paths[mpi];
372            if let Some(l) = path.place.as_local() {
373                return l;
374            }
375            mpi = path.parent.expect("root move paths should be locals");
376        }
377    }
378
379    pub fn find_in_move_path_or_its_descendants(
380        &self,
381        root: MovePathIndex,
382        pred: impl Fn(MovePathIndex) -> bool,
383    ) -> Option<MovePathIndex> {
384        if pred(root) {
385            return Some(root);
386        }
387
388        self.move_paths[root].find_descendant(&self.move_paths, pred)
389    }
390}
391
392/// A projection into a move path producing a child path
393#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
394pub enum MoveSubPath {
395    Deref,
396    Field(FieldIdx),
397    ConstantIndex(u64),
398    Downcast(VariantIdx),
399    UnwrapUnsafeBinder,
400}
401
402#[derive(Copy, Clone, Debug, PartialEq, Eq)]
403pub enum MoveSubPathResult {
404    One(MoveSubPath),
405    Subslice { from: u64, to: u64 },
406    Skip,
407    Stop,
408}
409
410impl MoveSubPath {
411    pub fn of(elem: ProjectionKind) -> MoveSubPathResult {
412        let subpath = match elem {
413            // correspond to a MoveSubPath
414            ProjectionKind::Deref => MoveSubPath::Deref,
415            ProjectionKind::Field(idx, _) => MoveSubPath::Field(idx),
416            ProjectionKind::ConstantIndex { offset, min_length: _, from_end: false } => {
417                MoveSubPath::ConstantIndex(offset)
418            }
419            ProjectionKind::Downcast(_, idx) => MoveSubPath::Downcast(idx),
420            ProjectionKind::UnwrapUnsafeBinder(_) => MoveSubPath::UnwrapUnsafeBinder,
421
422            // this should be the same move path as its parent
423            // its fine to skip because it cannot have sibling move paths
424            // and it is not a user visible path
425            ProjectionKind::OpaqueCast(_) => {
426                return MoveSubPathResult::Skip;
427            }
428
429            // these cannot be moved through
430            ProjectionKind::Index(_)
431            | ProjectionKind::ConstantIndex { offset: _, min_length: _, from_end: true }
432            | ProjectionKind::Subslice { from: _, to: _, from_end: true } => {
433                return MoveSubPathResult::Stop;
434            }
435
436            // subslice is special.
437            // it needs to be split into individual move paths
438            ProjectionKind::Subslice { from, to, from_end: false } => {
439                return MoveSubPathResult::Subslice { from, to };
440            }
441        };
442
443        MoveSubPathResult::One(subpath)
444    }
445}
rustc_mir_dataflow/move_paths/mod.rs

rustc_mir_dataflow/move_paths/
mod.rs
