compiler/rustc_mir_dataflow/src/move_paths/mod.rs - toolchain/rustc - Git at Google

 use crate::move_paths::builder::MoveDat;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_index::{IndexSlice, IndexVec};
 use rustc_middle::mir::*;
 use rustc_middle::ty::{ParamEnv, Ty, TyCtxt};
 use rustc_span::Span;
 use smallvec::SmallVec;

 use std::fmt;
 use std::ops::{Index, IndexMut};

 use self::abs_domain::{AbstractElem, Lift};

 mod abs_domain;

 rustc_index::newtype_index! {
     #[debug_format = "mp{}"]
     pub struct MovePathIndex {}
 }

 impl polonius_engine::Atom for MovePathIndex {
     fn index(self) -> usize {
         rustc_index::Idx::index(self)
     }
 }

 rustc_index::newtype_index! {
     #[debug_format = "mo{}"]
     pub struct MoveOutIndex {}
 }

 rustc_index::newtype_index! {
     #[debug_format = "in{}"]
     pub struct InitIndex {}
 }

 impl MoveOutIndex {
     pub fn move_path_index(self, move_data: &MoveData<'_>) -> MovePathIndex {
         move_data.moves[self].path
     }
 }

 /// `MovePath` is a canonicalized representation of a path that is
 /// moved or assigned to.
 ///
 /// It follows a tree structure.
 ///
 /// Given `struct X { m: M, n: N }` and `x: X`, moves like `drop x.m;`
 /// move *out* of the place `x.m`.
 ///
 /// The MovePaths representing `x.m` and `x.n` are siblings (that is,
 /// one of them will link to the other via the `next_sibling` field,
 /// and the other will have no entry in its `next_sibling` field), and
 /// they both have the MovePath representing `x` as their parent.
 #[derive(Clone)]
 pub struct MovePath<'tcx> {
     pub next_sibling: Option<MovePathIndex>,
     pub first_child: Option<MovePathIndex>,
     pub parent: Option<MovePathIndex>,
     pub place: Place<'tcx>,
 }

 impl<'tcx> MovePath<'tcx> {
     /// Returns an iterator over the parents of `self`.
     pub fn parents<'a>(
         &self,
         move_paths: &'a IndexSlice<MovePathIndex, MovePath<'tcx>>,
     ) -> impl 'a + Iterator<Item = (MovePathIndex, &'a MovePath<'tcx>)> {
         let first = self.parent.map(|mpi| (mpi, &move_paths[mpi]));
         MovePathLinearIter {
             next: first,
             fetch_next: move |_, parent: &MovePath<'_>| {
                 parent.parent.map(|mpi| (mpi, &move_paths[mpi]))
             },
         }
     }

     /// Returns an iterator over the immediate children of `self`.
     pub fn children<'a>(
         &self,
         move_paths: &'a IndexSlice<MovePathIndex, MovePath<'tcx>>,
     ) -> impl 'a + Iterator<Item = (MovePathIndex, &'a MovePath<'tcx>)> {
         let first = self.first_child.map(|mpi| (mpi, &move_paths[mpi]));
         MovePathLinearIter {
             next: first,
             fetch_next: move |_, child: &MovePath<'_>| {
                 child.next_sibling.map(|mpi| (mpi, &move_paths[mpi]))
             },
         }
     }

     /// Finds the closest descendant of `self` for which `f` returns `true` using a breadth-first
     /// search.
     ///
     /// `f` will **not** be called on `self`.
     pub fn find_descendant(
         &self,
         move_paths: &IndexSlice<MovePathIndex, MovePath<'_>>,
         f: impl Fn(MovePathIndex) -> bool,
     ) -> Option<MovePathIndex> {
         let mut todo = if let Some(child) = self.first_child {
             vec![child]
         } else {
             return None;
         };

         while let Some(mpi) = todo.pop() {
             if f(mpi) {
                 return Some(mpi);
             }

             let move_path = &move_paths[mpi];
             if let Some(child) = move_path.first_child {
                 todo.push(child);
             }

             // After we've processed the original `mpi`, we should always
             // traverse the siblings of any of its children.
             if let Some(sibling) = move_path.next_sibling {
                 todo.push(sibling);
             }
         }

         None
     }
 }

 impl<'tcx> fmt::Debug for MovePath<'tcx> {
     fn fmt(&self, w: &mut fmt::Formatter<'_>) -> fmt::Result {
         write!(w, "MovePath {{")?;
         if let Some(parent) = self.parent {
             write!(w, " parent: {parent:?},")?;
         }
         if let Some(first_child) = self.first_child {
             write!(w, " first_child: {first_child:?},")?;
         }
         if let Some(next_sibling) = self.next_sibling {
             write!(w, " next_sibling: {next_sibling:?}")?;
         }
         write!(w, " place: {:?} }}", self.place)
     }
 }

 impl<'tcx> fmt::Display for MovePath<'tcx> {
     fn fmt(&self, w: &mut fmt::Formatter<'_>) -> fmt::Result {
         write!(w, "{:?}", self.place)
     }
 }

 struct MovePathLinearIter<'a, 'tcx, F> {
     next: Option<(MovePathIndex, &'a MovePath<'tcx>)>,
     fetch_next: F,
 }

 impl<'a, 'tcx, F> Iterator for MovePathLinearIter<'a, 'tcx, F>
 where
     F: FnMut(MovePathIndex, &'a MovePath<'tcx>) -> Option<(MovePathIndex, &'a MovePath<'tcx>)>,
 {
     type Item = (MovePathIndex, &'a MovePath<'tcx>);

     fn next(&mut self) -> Option<Self::Item> {
         let ret = self.next.take()?;
         self.next = (self.fetch_next)(ret.0, ret.1);
         Some(ret)
     }
 }

 #[derive(Debug)]
 pub struct MoveData<'tcx> {
     pub move_paths: IndexVec<MovePathIndex, MovePath<'tcx>>,
     pub moves: IndexVec<MoveOutIndex, MoveOut>,
     /// Each Location `l` is mapped to the MoveOut's that are effects
     /// of executing the code at `l`. (There can be multiple MoveOut's
     /// for a given `l` because each MoveOut is associated with one
     /// particular path being moved.)
     pub loc_map: LocationMap<SmallVec<[MoveOutIndex; 4]>>,
     pub path_map: IndexVec<MovePathIndex, SmallVec<[MoveOutIndex; 4]>>,
     pub rev_lookup: MovePathLookup,
     pub inits: IndexVec<InitIndex, Init>,
     /// Each Location `l` is mapped to the Inits that are effects
     /// of executing the code at `l`.
     pub init_loc_map: LocationMap<SmallVec<[InitIndex; 4]>>,
     pub init_path_map: IndexVec<MovePathIndex, SmallVec<[InitIndex; 4]>>,
 }

 pub trait HasMoveData<'tcx> {
     fn move_data(&self) -> &MoveData<'tcx>;
 }

 #[derive(Debug)]
 pub struct LocationMap<T> {
     /// Location-indexed (BasicBlock for outer index, index within BB
     /// for inner index) map.
     pub(crate) map: IndexVec<BasicBlock, Vec<T>>,
 }

 impl<T> Index<Location> for LocationMap<T> {
     type Output = T;
     fn index(&self, index: Location) -> &Self::Output {
         &self.map[index.block][index.statement_index]
     }
 }

 impl<T> IndexMut<Location> for LocationMap<T> {
     fn index_mut(&mut self, index: Location) -> &mut Self::Output {
         &mut self.map[index.block][index.statement_index]
     }
 }

 impl<T> LocationMap<T>
 where
     T: Default + Clone,
 {
     fn new(body: &Body<'_>) -> Self {
         LocationMap {
             map: body
                 .basic_blocks
                 .iter()
                 .map(|block| vec![T::default(); block.statements.len() + 1])
                 .collect(),
         }
     }
 }

 /// `MoveOut` represents a point in a program that moves out of some
 /// L-value; i.e., "creates" uninitialized memory.
 ///
 /// With respect to dataflow analysis:
 /// - Generated by moves and declaration of uninitialized variables.
 /// - Killed by assignments to the memory.
 #[derive(Copy, Clone)]
 pub struct MoveOut {
     /// path being moved
     pub path: MovePathIndex,
     /// location of move
     pub source: Location,
 }

 impl fmt::Debug for MoveOut {
     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
         write!(fmt, "{:?}@{:?}", self.path, self.source)
     }
 }

 /// `Init` represents a point in a program that initializes some L-value;
 #[derive(Copy, Clone)]
 pub struct Init {
     /// path being initialized
     pub path: MovePathIndex,
     /// location of initialization
     pub location: InitLocation,
     /// Extra information about this initialization
     pub kind: InitKind,
 }

 /// Initializations can be from an argument or from a statement. Arguments
 /// do not have locations, in those cases the `Local` is kept..
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
 pub enum InitLocation {
     Argument(Local),
     Statement(Location),
 }

 /// Additional information about the initialization.
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
 pub enum InitKind {
     /// Deep init, even on panic
     Deep,
     /// Only does a shallow init
     Shallow,
     /// This doesn't initialize the variable on panic (and a panic is possible).
     NonPanicPathOnly,
 }

 impl fmt::Debug for Init {
     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
         write!(fmt, "{:?}@{:?} ({:?})", self.path, self.location, self.kind)
     }
 }

 impl Init {
     pub fn span<'tcx>(&self, body: &Body<'tcx>) -> Span {
         match self.location {
             InitLocation::Argument(local) => body.local_decls[local].source_info.span,
             InitLocation::Statement(location) => body.source_info(location).span,
         }
     }
 }

 /// Tables mapping from a place to its MovePathIndex.
 #[derive(Debug)]
 pub struct MovePathLookup {
     locals: IndexVec<Local, MovePathIndex>,

     /// projections are made from a base-place and a projection
     /// elem. The base-place will have a unique MovePathIndex; we use
     /// the latter as the index into the outer vector (narrowing
     /// subsequent search so that it is solely relative to that
     /// base-place). For the remaining lookup, we map the projection
     /// elem to the associated MovePathIndex.
     projections: FxHashMap<(MovePathIndex, AbstractElem), MovePathIndex>,
 }

 mod builder;

 #[derive(Copy, Clone, Debug)]
 pub enum LookupResult {
     Exact(MovePathIndex),
     Parent(Option<MovePathIndex>),
 }

 impl MovePathLookup {
     // Unlike the builder `fn move_path_for` below, this lookup
     // alternative will *not* create a MovePath on the fly for an
     // unknown place, but will rather return the nearest available
     // parent.
     pub fn find(&self, place: PlaceRef<'_>) -> LookupResult {
         let mut result = self.locals[place.local];

         for elem in place.projection.iter() {
             if let Some(&subpath) = self.projections.get(&(result, elem.lift())) {
                 result = subpath;
             } else {
                 return LookupResult::Parent(Some(result));
             }
         }

         LookupResult::Exact(result)
     }

     pub fn find_local(&self, local: Local) -> MovePathIndex {
         self.locals[local]
     }

     /// An enumerated iterator of `local`s and their associated
     /// `MovePathIndex`es.
     pub fn iter_locals_enumerated(
         &self,
     ) -> impl DoubleEndedIterator<Item = (Local, MovePathIndex)> + ExactSizeIterator + '_ {
         self.locals.iter_enumerated().map(|(l, &idx)| (l, idx))
     }
 }

 #[derive(Debug)]
 pub struct IllegalMoveOrigin<'tcx> {
     pub location: Location,
     pub kind: IllegalMoveOriginKind<'tcx>,
 }

 #[derive(Debug)]
 pub enum IllegalMoveOriginKind<'tcx> {
     /// Illegal move due to attempt to move from behind a reference.
     BorrowedContent {
         /// The place the reference refers to: if erroneous code was trying to
         /// move from `(*x).f` this will be `*x`.
         target_place: Place<'tcx>,
     },

     /// Illegal move due to attempt to move from field of an ADT that
     /// implements `Drop`. Rust maintains invariant that all `Drop`
     /// ADT's remain fully-initialized so that user-defined destructor
     /// can safely read from all of the ADT's fields.
     InteriorOfTypeWithDestructor { container_ty: Ty<'tcx> },

     /// Illegal move due to attempt to move out of a slice or array.
     InteriorOfSliceOrArray { ty: Ty<'tcx>, is_index: bool },
 }

 #[derive(Debug)]
 pub enum MoveError<'tcx> {
     IllegalMove { cannot_move_out_of: IllegalMoveOrigin<'tcx> },
     UnionMove { path: MovePathIndex },
 }

 impl<'tcx> MoveError<'tcx> {
     fn cannot_move_out_of(location: Location, kind: IllegalMoveOriginKind<'tcx>) -> Self {
         let origin = IllegalMoveOrigin { location, kind };
         MoveError::IllegalMove { cannot_move_out_of: origin }
     }
 }

 impl<'tcx> MoveData<'tcx> {
     pub fn gather_moves(
         body: &Body<'tcx>,
         tcx: TyCtxt<'tcx>,
         param_env: ParamEnv<'tcx>,
     ) -> MoveDat<'tcx> {
         builder::gather_moves(body, tcx, param_env)
     }

     /// For the move path `mpi`, returns the root local variable (if any) that starts the path.
     /// (e.g., for a path like `a.b.c` returns `Some(a)`)
     pub fn base_local(&self, mut mpi: MovePathIndex) -> Option<Local> {
         loop {
             let path = &self.move_paths[mpi];
             if let Some(l) = path.place.as_local() {
                 return Some(l);
             }
             if let Some(parent) = path.parent {
                 mpi = parent;
                 continue;
             } else {
                 return None;
             }
         }
     }

     pub fn find_in_move_path_or_its_descendants(
         &self,
         root: MovePathIndex,
         pred: impl Fn(MovePathIndex) -> bool,
     ) -> Option<MovePathIndex> {
         if pred(root) {
             return Some(root);
         }

         self.move_paths[root].find_descendant(&self.move_paths, pred)
     }
 }
	use crate::move_paths::builder::MoveDat;
	use rustc_data_structures::fx::FxHashMap;
	use rustc_index::{IndexSlice, IndexVec};
	use rustc_middle::mir::*;
	use rustc_middle::ty::{ParamEnv, Ty, TyCtxt};
	use rustc_span::Span;
	use smallvec::SmallVec;

	use std::fmt;
	use std::ops::{Index, IndexMut};

	use self::abs_domain::{AbstractElem, Lift};

	mod abs_domain;

	rustc_index::newtype_index! {
	#[debug_format = "mp{}"]
	pub struct MovePathIndex {}
	}

	impl polonius_engine::Atom for MovePathIndex {
	fn index(self) -> usize {
	rustc_index::Idx::index(self)
	}
	}

	rustc_index::newtype_index! {
	#[debug_format = "mo{}"]
	pub struct MoveOutIndex {}
	}

	rustc_index::newtype_index! {
	#[debug_format = "in{}"]
	pub struct InitIndex {}
	}

	impl MoveOutIndex {
	pub fn move_path_index(self, move_data: &MoveData<'_>) -> MovePathIndex {
	move_data.moves[self].path
	}
	}

	/// `MovePath` is a canonicalized representation of a path that is
	/// moved or assigned to.
	///
	/// It follows a tree structure.
	///
	/// Given `struct X { m: M, n: N }` and `x: X`, moves like `drop x.m;`
	/// move out of the place `x.m`.
	///
	/// The MovePaths representing `x.m` and `x.n` are siblings (that is,
	/// one of them will link to the other via the `next_sibling` field,
	/// and the other will have no entry in its `next_sibling` field), and
	/// they both have the MovePath representing `x` as their parent.
	#[derive(Clone)]
	pub struct MovePath<'tcx> {
	pub next_sibling: Option<MovePathIndex>,
	pub first_child: Option<MovePathIndex>,
	pub parent: Option<MovePathIndex>,
	pub place: Place<'tcx>,
	}

	impl<'tcx> MovePath<'tcx> {
	/// Returns an iterator over the parents of `self`.
	pub fn parents<'a>(
	&self,
	move_paths: &'a IndexSlice<MovePathIndex, MovePath<'tcx>>,
	) -> impl 'a + Iterator<Item = (MovePathIndex, &'a MovePath<'tcx>)> {
	let first = self.parent.map(\|mpi\| (mpi, &move_paths[mpi]));
	MovePathLinearIter {
	next: first,
	fetch_next: move \|_, parent: &MovePath<'_>\| {
	parent.parent.map(\|mpi\| (mpi, &move_paths[mpi]))
	},
	}
	}

	/// Returns an iterator over the immediate children of `self`.
	pub fn children<'a>(
	&self,
	move_paths: &'a IndexSlice<MovePathIndex, MovePath<'tcx>>,
	) -> impl 'a + Iterator<Item = (MovePathIndex, &'a MovePath<'tcx>)> {
	let first = self.first_child.map(\|mpi\| (mpi, &move_paths[mpi]));
	MovePathLinearIter {
	next: first,
	fetch_next: move \|_, child: &MovePath<'_>\| {
	child.next_sibling.map(\|mpi\| (mpi, &move_paths[mpi]))
	},
	}
	}

	/// Finds the closest descendant of `self` for which `f` returns `true` using a breadth-first
	/// search.
	///
	/// `f` will not be called on `self`.
	pub fn find_descendant(
	&self,
	move_paths: &IndexSlice<MovePathIndex, MovePath<'_>>,
	f: impl Fn(MovePathIndex) -> bool,
	) -> Option<MovePathIndex> {
	let mut todo = if let Some(child) = self.first_child {
	vec![child]
	} else {
	return None;
	};

	while let Some(mpi) = todo.pop() {
	if f(mpi) {
	return Some(mpi);
	}

	let move_path = &move_paths[mpi];
	if let Some(child) = move_path.first_child {
	todo.push(child);
	}

	// After we've processed the original `mpi`, we should always
	// traverse the siblings of any of its children.
	if let Some(sibling) = move_path.next_sibling {
	todo.push(sibling);
	}
	}

	None
	}
	}

	impl<'tcx> fmt::Debug for MovePath<'tcx> {
	fn fmt(&self, w: &mut fmt::Formatter<'_>) -> fmt::Result {
	write!(w, "MovePath {{")?;
	if let Some(parent) = self.parent {
	write!(w, " parent: {parent:?},")?;
	}
	if let Some(first_child) = self.first_child {
	write!(w, " first_child: {first_child:?},")?;
	}
	if let Some(next_sibling) = self.next_sibling {
	write!(w, " next_sibling: {next_sibling:?}")?;
	}
	write!(w, " place: {:?} }}", self.place)
	}
	}

	impl<'tcx> fmt::Display for MovePath<'tcx> {
	fn fmt(&self, w: &mut fmt::Formatter<'_>) -> fmt::Result {
	write!(w, "{:?}", self.place)
	}
	}

	struct MovePathLinearIter<'a, 'tcx, F> {
	next: Option<(MovePathIndex, &'a MovePath<'tcx>)>,
	fetch_next: F,
	}

	impl<'a, 'tcx, F> Iterator for MovePathLinearIter<'a, 'tcx, F>
	where
	F: FnMut(MovePathIndex, &'a MovePath<'tcx>) -> Option<(MovePathIndex, &'a MovePath<'tcx>)>,
	{
	type Item = (MovePathIndex, &'a MovePath<'tcx>);

	fn next(&mut self) -> Option<Self::Item> {
	let ret = self.next.take()?;
	self.next = (self.fetch_next)(ret.0, ret.1);
	Some(ret)
	}
	}

	#[derive(Debug)]
	pub struct MoveData<'tcx> {
	pub move_paths: IndexVec<MovePathIndex, MovePath<'tcx>>,
	pub moves: IndexVec<MoveOutIndex, MoveOut>,
	/// Each Location `l` is mapped to the MoveOut's that are effects
	/// of executing the code at `l`. (There can be multiple MoveOut's
	/// for a given `l` because each MoveOut is associated with one
	/// particular path being moved.)
	pub loc_map: LocationMap<SmallVec<[MoveOutIndex; 4]>>,
	pub path_map: IndexVec<MovePathIndex, SmallVec<[MoveOutIndex; 4]>>,
	pub rev_lookup: MovePathLookup,
	pub inits: IndexVec<InitIndex, Init>,
	/// Each Location `l` is mapped to the Inits that are effects
	/// of executing the code at `l`.
	pub init_loc_map: LocationMap<SmallVec<[InitIndex; 4]>>,
	pub init_path_map: IndexVec<MovePathIndex, SmallVec<[InitIndex; 4]>>,
	}

	pub trait HasMoveData<'tcx> {
	fn move_data(&self) -> &MoveData<'tcx>;
	}

	#[derive(Debug)]
	pub struct LocationMap<T> {
	/// Location-indexed (BasicBlock for outer index, index within BB
	/// for inner index) map.
	pub(crate) map: IndexVec<BasicBlock, Vec<T>>,
	}

	impl<T> Index<Location> for LocationMap<T> {
	type Output = T;
	fn index(&self, index: Location) -> &Self::Output {
	&self.map[index.block][index.statement_index]
	}
	}

	impl<T> IndexMut<Location> for LocationMap<T> {
	fn index_mut(&mut self, index: Location) -> &mut Self::Output {
	&mut self.map[index.block][index.statement_index]
	}
	}

	impl<T> LocationMap<T>
	where
	T: Default + Clone,
	{
	fn new(body: &Body<'_>) -> Self {
	LocationMap {
	map: body
	.basic_blocks
	.iter()
	.map(\|block\| vec![T::default(); block.statements.len() + 1])
	.collect(),
	}
	}
	}

	/// `MoveOut` represents a point in a program that moves out of some
	/// L-value; i.e., "creates" uninitialized memory.
	///
	/// With respect to dataflow analysis:
	/// - Generated by moves and declaration of uninitialized variables.
	/// - Killed by assignments to the memory.
	#[derive(Copy, Clone)]
	pub struct MoveOut {
	/// path being moved
	pub path: MovePathIndex,
	/// location of move
	pub source: Location,
	}

	impl fmt::Debug for MoveOut {
	fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
	write!(fmt, "{:?}@{:?}", self.path, self.source)
	}
	}

	/// `Init` represents a point in a program that initializes some L-value;
	#[derive(Copy, Clone)]
	pub struct Init {
	/// path being initialized
	pub path: MovePathIndex,
	/// location of initialization
	pub location: InitLocation,
	/// Extra information about this initialization
	pub kind: InitKind,
	}

	/// Initializations can be from an argument or from a statement. Arguments
	/// do not have locations, in those cases the `Local` is kept..
	#[derive(Copy, Clone, Debug, PartialEq, Eq)]
	pub enum InitLocation {
	Argument(Local),
	Statement(Location),
	}

	/// Additional information about the initialization.
	#[derive(Copy, Clone, Debug, PartialEq, Eq)]
	pub enum InitKind {
	/// Deep init, even on panic
	Deep,
	/// Only does a shallow init
	Shallow,
	/// This doesn't initialize the variable on panic (and a panic is possible).
	NonPanicPathOnly,
	}

	impl fmt::Debug for Init {
	fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
	write!(fmt, "{:?}@{:?} ({:?})", self.path, self.location, self.kind)
	}
	}

	impl Init {
	pub fn span<'tcx>(&self, body: &Body<'tcx>) -> Span {
	match self.location {
	InitLocation::Argument(local) => body.local_decls[local].source_info.span,
	InitLocation::Statement(location) => body.source_info(location).span,
	}
	}
	}

	/// Tables mapping from a place to its MovePathIndex.
	#[derive(Debug)]
	pub struct MovePathLookup {
	locals: IndexVec<Local, MovePathIndex>,

	/// projections are made from a base-place and a projection
	/// elem. The base-place will have a unique MovePathIndex; we use
	/// the latter as the index into the outer vector (narrowing
	/// subsequent search so that it is solely relative to that
	/// base-place). For the remaining lookup, we map the projection
	/// elem to the associated MovePathIndex.
	projections: FxHashMap<(MovePathIndex, AbstractElem), MovePathIndex>,
	}

	mod builder;

	#[derive(Copy, Clone, Debug)]
	pub enum LookupResult {
	Exact(MovePathIndex),
	Parent(Option<MovePathIndex>),
	}

	impl MovePathLookup {
	// Unlike the builder `fn move_path_for` below, this lookup
	// alternative will not create a MovePath on the fly for an
	// unknown place, but will rather return the nearest available
	// parent.
	pub fn find(&self, place: PlaceRef<'_>) -> LookupResult {
	let mut result = self.locals[place.local];

	for elem in place.projection.iter() {
	if let Some(&subpath) = self.projections.get(&(result, elem.lift())) {
	result = subpath;
	} else {
	return LookupResult::Parent(Some(result));
	}
	}

	LookupResult::Exact(result)
	}

	pub fn find_local(&self, local: Local) -> MovePathIndex {
	self.locals[local]
	}

	/// An enumerated iterator of `local`s and their associated
	/// `MovePathIndex`es.
	pub fn iter_locals_enumerated(
	&self,
	) -> impl DoubleEndedIterator<Item = (Local, MovePathIndex)> + ExactSizeIterator + '_ {
	self.locals.iter_enumerated().map(\|(l, &idx)\| (l, idx))
	}
	}

	#[derive(Debug)]
	pub struct IllegalMoveOrigin<'tcx> {
	pub location: Location,
	pub kind: IllegalMoveOriginKind<'tcx>,
	}

	#[derive(Debug)]
	pub enum IllegalMoveOriginKind<'tcx> {
	/// Illegal move due to attempt to move from behind a reference.
	BorrowedContent {
	/// The place the reference refers to: if erroneous code was trying to
	/// move from `(x).f` this will be `x`.
	target_place: Place<'tcx>,
	},

	/// Illegal move due to attempt to move from field of an ADT that
	/// implements `Drop`. Rust maintains invariant that all `Drop`
	/// ADT's remain fully-initialized so that user-defined destructor
	/// can safely read from all of the ADT's fields.
	InteriorOfTypeWithDestructor { container_ty: Ty<'tcx> },

	/// Illegal move due to attempt to move out of a slice or array.
	InteriorOfSliceOrArray { ty: Ty<'tcx>, is_index: bool },
	}

	#[derive(Debug)]
	pub enum MoveError<'tcx> {
	IllegalMove { cannot_move_out_of: IllegalMoveOrigin<'tcx> },
	UnionMove { path: MovePathIndex },
	}

	impl<'tcx> MoveError<'tcx> {
	fn cannot_move_out_of(location: Location, kind: IllegalMoveOriginKind<'tcx>) -> Self {
	let origin = IllegalMoveOrigin { location, kind };
	MoveError::IllegalMove { cannot_move_out_of: origin }
	}
	}

	impl<'tcx> MoveData<'tcx> {
	pub fn gather_moves(
	body: &Body<'tcx>,
	tcx: TyCtxt<'tcx>,
	param_env: ParamEnv<'tcx>,
	) -> MoveDat<'tcx> {
	builder::gather_moves(body, tcx, param_env)
	}

	/// For the move path `mpi`, returns the root local variable (if any) that starts the path.
	/// (e.g., for a path like `a.b.c` returns `Some(a)`)
	pub fn base_local(&self, mut mpi: MovePathIndex) -> Option<Local> {
	loop {
	let path = &self.move_paths[mpi];
	if let Some(l) = path.place.as_local() {
	return Some(l);
	}
	if let Some(parent) = path.parent {
	mpi = parent;
	continue;
	} else {
	return None;
	}
	}
	}

	pub fn find_in_move_path_or_its_descendants(
	&self,
	root: MovePathIndex,
	pred: impl Fn(MovePathIndex) -> bool,
	) -> Option<MovePathIndex> {
	if pred(root) {
	return Some(root);
	}

	self.move_paths[root].find_descendant(&self.move_paths, pred)
	}
	}