compiler/rustc_mir_dataflow/src/move_paths/mod.rs

   1 use crate::un_derefer::UnDerefer;
   2 use rustc_data_structures::fx::FxHashMap;
   3 use rustc_index::{IndexSlice, 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     #[orderable]
  18     #[debug_format = "mp{}"]
  19     pub struct MovePathIndex {}
  20 }
  21
  22 impl polonius_engine::Atom for MovePathIndex {
  23     fn index(self) -> usize {
  24         rustc_index::Idx::index(self)
  25     }
  26 }
  27
  28 rustc_index::newtype_index! {
  29     #[orderable]
  30     #[debug_format = "mo{}"]
  31     pub struct MoveOutIndex {}
  32 }
  33
  34 rustc_index::newtype_index! {
  35     #[debug_format = "in{}"]
  36     pub struct InitIndex {}
  37 }
  38
  39 impl 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)]
  58 pub 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
  65 impl<'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
 130 impl<'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
 146 impl<'tcx> fmt::Display for MovePath<'tcx> {
 147     fn fmt(&self, w: &mut fmt::Formatter<'_>) -> fmt::Result {
 148         write!(w, "{:?}", self.place)
 149     }
 150 }
 151
 152 struct MovePathLinearIter<'a, 'tcx, F> {
 153     next: Option<(MovePathIndex, &'a MovePath<'tcx>)>,
 154     fetch_next: F,
 155 }
 156
 157 impl<'a, 'tcx, F> Iterator for MovePathLinearIter<'a, 'tcx, F>
 158 where
 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)]
 171 pub 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
 188 pub trait HasMoveData<'tcx> {
 189     fn move_data(&self) -> &MoveData<'tcx>;
 190 }
 191
 192 #[derive(Debug)]
 193 pub 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
 199 impl<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
 206 impl<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
 212 impl<T> LocationMap<T>
 213 where
 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)]
 234 pub struct MoveOut {
 235     /// path being moved
 236     pub path: MovePathIndex,
 237     /// location of move
 238     pub source: Location,
 239 }
 240
 241 impl 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)]
 249 pub 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)]
 261 pub enum InitLocation {
 262     Argument(Local),
 263     Statement(Location),
 264 }
 265
 266 /// Additional information about the initialization.
 267 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
 268 pub 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
 277 impl 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
 283 impl 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)]
 294 pub 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, AbstractElem), MovePathIndex>,
 304
 305     un_derefer: UnDerefer<'tcx>,
 306 }
 307
 308 mod builder;
 309
 310 #[derive(Copy, Clone, Debug)]
 311 pub enum LookupResult {
 312     Exact(MovePathIndex),
 313     Parent(Option<MovePathIndex>),
 314 }
 315
 316 impl<'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             if let Some(&subpath) = self.projections.get(&(result, elem.lift())) {
 328                 result = subpath;
 329             } else {
 330                 return LookupResult::Parent(Some(result));
 331             }
 332         }
 333
 334         LookupResult::Exact(result)
 335     }
 336
 337     #[inline]
 338     pub fn find_local(&self, local: Local) -> Option<MovePathIndex> {
 339         self.locals[local]
 340     }
 341
 342     /// An enumerated iterator of `local`s and their associated
 343     /// `MovePathIndex`es.
 344     pub fn iter_locals_enumerated(
 345         &self,
 346     ) -> impl DoubleEndedIterator<Item = (Local, MovePathIndex)> + '_ {
 347         self.locals.iter_enumerated().filter_map(|(l, &idx)| Some((l, idx?)))
 348     }
 349 }
 350
 351 impl<'tcx> MoveData<'tcx> {
 352     pub fn gather_moves(
 353         body: &Body<'tcx>,
 354         tcx: TyCtxt<'tcx>,
 355         param_env: ParamEnv<'tcx>,
 356         filter: impl Fn(Ty<'tcx>) -> bool,
 357     ) -> MoveData<'tcx> {
 358         builder::gather_moves(body, tcx, param_env, filter)
 359     }
 360
 361     /// For the move path `mpi`, returns the root local variable (if any) that starts the path.
 362     /// (e.g., for a path like `a.b.c` returns `Some(a)`)
 363     pub fn base_local(&self, mut mpi: MovePathIndex) -> Option<Local> {
 364         loop {
 365             let path = &self.move_paths[mpi];
 366             if let Some(l) = path.place.as_local() {
 367                 return Some(l);
 368             }
 369             if let Some(parent) = path.parent {
 370                 mpi = parent;
 371                 continue;
 372             } else {
 373                 return None;
 374             }
 375         }
 376     }
 377
 378     pub fn find_in_move_path_or_its_descendants(
 379         &self,
 380         root: MovePathIndex,
 381         pred: impl Fn(MovePathIndex) -> bool,
 382     ) -> Option<MovePathIndex> {
 383         if pred(root) {
 384             return Some(root);
 385         }
 386
 387         self.move_paths[root].find_descendant(&self.move_paths, pred)
 388     }
 389 }