compiler/rustc_mir_dataflow/src/move_paths/mod.rs

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