src/librustc_mir/dataflow/move_paths/mod.rs - toolchain/rustc - Git at Google

 use rustc::ty::{self, TyCtxt};
 use rustc::mir::*;
 use rustc::util::nodemap::FxHashMap;
 use rustc_data_structures::indexed_vec::{IndexVec};
 use smallvec::SmallVec;
 use syntax_pos::{Span};

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

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

 mod abs_domain;

 // This submodule holds some newtype'd Index wrappers that are using
 // NonZero to ensure that Option<Index> occupies only a single word.
 // They are in a submodule to impose privacy restrictions; namely, to
 // ensure that other code does not accidentally access `index.0`
 // (which is likely to yield a subtle off-by-one error).
 pub(crate) mod indexes {
     use std::fmt;
     use std::num::NonZeroUsize;
     use rustc_data_structures::indexed_vec::Idx;

     macro_rules! new_index {
         ($(#[$attrs:meta])* $Index:ident, $debug_name:expr) => {
             #[derive(Copy, Clone, PartialEq, Eq, Hash, PartialOrd, Ord)]
             pub struct $Index(NonZeroUsize);

             impl Idx for $Index {
                 fn new(idx: usize) -> Self {
                     $Index(NonZeroUsize::new(idx + 1).unwrap())
                 }
                 fn index(self) -> usize {
                     self.0.get() - 1
                 }
             }

             impl fmt::Debug for $Index {
                 fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
                     write!(fmt, "{}{}", $debug_name, self.index())
                 }
             }
         }
     }

     new_index!(
         /// Index into MovePathData.move_paths
         MovePathIndex,
         "mp"
     );

     new_index!(
         /// Index into MoveData.moves.
         MoveOutIndex,
         "mo"
     );

     new_index!(
         /// Index into MoveData.inits.
         InitIndex,
         "in"
     );

     new_index!(
         /// Index into Borrows.locations
         BorrowIndex,
         "bw"
     );
 }

 pub use self::indexes::MovePathIndex;
 pub use self::indexes::MoveOutIndex;
 pub use self::indexes::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> {
     pub fn parents(
         &self,
         move_paths: &IndexVec<MovePathIndex, MovePath<'_>>,
     ) -> Vec<MovePathIndex> {
         let mut parents = Vec::new();

         let mut curr_parent = self.parent;
         while let Some(parent_mpi) = curr_parent {
             parents.push(parent_mpi);
             curr_parent = move_paths[parent_mpi].parent;
         }

         parents
     }
 }

 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)
     }
 }

 #[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(mir: &Mir<'_>) -> Self {
         LocationMap {
             map: mir.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 {
     crate fn span<'gcx>(&self, mir: &Mir<'gcx>) -> Span {
         match self.location {
             InitLocation::Argument(local) => mir.local_decls[local].source_info.span,
             InitLocation::Statement(location) => mir.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: &Place<'tcx>) -> LookupResult {
         match *place {
             Place::Base(PlaceBase::Local(local)) => LookupResult::Exact(self.locals[local]),
             Place::Base(PlaceBase::Static(..)) => LookupResult::Parent(None),
             Place::Projection(ref proj) => {
                 match self.find(&proj.base) {
                     LookupResult::Exact(base_path) => {
                         match self.projections.get(&(base_path, proj.elem.lift())) {
                             Some(&subpath) => LookupResult::Exact(subpath),
                             None => LookupResult::Parent(Some(base_path))
                         }
                     }
                     inexact => inexact
                 }
             }
         }
     }

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

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

 #[derive(Debug)]
 pub(crate) enum IllegalMoveOriginKind<'tcx> {
     /// Illegal move due to attempt to move from `static` variable.
     Static,

     /// 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::Ty<'tcx> },

     /// Illegal move due to attempt to move out of a slice or array.
     InteriorOfSliceOrArray { ty: 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<'a, 'gcx, 'tcx> MoveData<'tcx> {
     pub fn gather_moves(mir: &Mir<'tcx>, tcx: TyCtxt<'a, 'gcx, 'tcx>)
                         -> Result<Self, (Self, Vec<(Place<'tcx>, MoveError<'tcx>)>)> {
         builder::gather_moves(mir, tcx)
     }

     /// 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 Place::Base(PlaceBase::Local(l)) = path.place { return Some(l); }
             if let Some(parent) = path.parent { mpi = parent; continue } else { return None }
         }
     }
 }
	use rustc::ty::{self, TyCtxt};
	use rustc::mir::*;
	use rustc::util::nodemap::FxHashMap;
	use rustc_data_structures::indexed_vec::{IndexVec};
	use smallvec::SmallVec;
	use syntax_pos::{Span};

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

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

	mod abs_domain;

	// This submodule holds some newtype'd Index wrappers that are using
	// NonZero to ensure that Option<Index> occupies only a single word.
	// They are in a submodule to impose privacy restrictions; namely, to
	// ensure that other code does not accidentally access `index.0`
	// (which is likely to yield a subtle off-by-one error).
	pub(crate) mod indexes {
	use std::fmt;
	use std::num::NonZeroUsize;
	use rustc_data_structures::indexed_vec::Idx;

	macro_rules! new_index {
	($(#[$attrs:meta])* $Index:ident, $debug_name:expr) => {
	#[derive(Copy, Clone, PartialEq, Eq, Hash, PartialOrd, Ord)]
	pub struct $Index(NonZeroUsize);

	impl Idx for $Index {
	fn new(idx: usize) -> Self {
	$Index(NonZeroUsize::new(idx + 1).unwrap())
	}
	fn index(self) -> usize {
	self.0.get() - 1
	}
	}

	impl fmt::Debug for $Index {
	fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
	write!(fmt, "{}{}", $debug_name, self.index())
	}
	}
	}
	}

	new_index!(
	/// Index into MovePathData.move_paths
	MovePathIndex,
	"mp"
	);

	new_index!(
	/// Index into MoveData.moves.
	MoveOutIndex,
	"mo"
	);

	new_index!(
	/// Index into MoveData.inits.
	InitIndex,
	"in"
	);

	new_index!(
	/// Index into Borrows.locations
	BorrowIndex,
	"bw"
	);
	}

	pub use self::indexes::MovePathIndex;
	pub use self::indexes::MoveOutIndex;
	pub use self::indexes::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> {
	pub fn parents(
	&self,
	move_paths: &IndexVec<MovePathIndex, MovePath<'_>>,
	) -> Vec<MovePathIndex> {
	let mut parents = Vec::new();

	let mut curr_parent = self.parent;
	while let Some(parent_mpi) = curr_parent {
	parents.push(parent_mpi);
	curr_parent = move_paths[parent_mpi].parent;
	}

	parents
	}
	}

	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)
	}
	}

	#[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(mir: &Mir<'_>) -> Self {
	LocationMap {
	map: mir.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 {
	crate fn span<'gcx>(&self, mir: &Mir<'gcx>) -> Span {
	match self.location {
	InitLocation::Argument(local) => mir.local_decls[local].source_info.span,
	InitLocation::Statement(location) => mir.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: &Place<'tcx>) -> LookupResult {
	match *place {
	Place::Base(PlaceBase::Local(local)) => LookupResult::Exact(self.locals[local]),
	Place::Base(PlaceBase::Static(..)) => LookupResult::Parent(None),
	Place::Projection(ref proj) => {
	match self.find(&proj.base) {
	LookupResult::Exact(base_path) => {
	match self.projections.get(&(base_path, proj.elem.lift())) {
	Some(&subpath) => LookupResult::Exact(subpath),
	None => LookupResult::Parent(Some(base_path))
	}
	}
	inexact => inexact
	}
	}
	}
	}

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

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

	#[derive(Debug)]
	pub(crate) enum IllegalMoveOriginKind<'tcx> {
	/// Illegal move due to attempt to move from `static` variable.
	Static,

	/// 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::Ty<'tcx> },

	/// Illegal move due to attempt to move out of a slice or array.
	InteriorOfSliceOrArray { ty: 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<'a, 'gcx, 'tcx> MoveData<'tcx> {
	pub fn gather_moves(mir: &Mir<'tcx>, tcx: TyCtxt<'a, 'gcx, 'tcx>)
	-> Result<Self, (Self, Vec<(Place<'tcx>, MoveError<'tcx>)>)> {
	builder::gather_moves(mir, tcx)
	}

	/// 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 Place::Base(PlaceBase::Local(l)) = path.place { return Some(l); }
	if let Some(parent) = path.parent { mpi = parent; continue } else { return None }
	}
	}
	}