src/librustc_mir/dataflow/move_paths/mod.rs

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