| use rustc::hir; |
| use rustc::mir::ProjectionElem; |
| use rustc::mir::{Body, Place, PlaceBase, Mutability, Static, StaticKind}; |
| use rustc::ty::{self, TyCtxt}; |
| use crate::borrow_check::borrow_set::LocalsStateAtExit; |
| |
| /// Extension methods for the `Place` type. |
| crate trait PlaceExt<'tcx> { |
| /// Returns `true` if we can safely ignore borrows of this place. |
| /// This is true whenever there is no action that the user can do |
| /// to the place `self` that would invalidate the borrow. This is true |
| /// for borrows of raw pointer dereferents as well as shared references. |
| fn ignore_borrow( |
| &self, |
| tcx: TyCtxt<'tcx>, |
| body: &Body<'tcx>, |
| locals_state_at_exit: &LocalsStateAtExit, |
| ) -> bool; |
| } |
| |
| impl<'tcx> PlaceExt<'tcx> for Place<'tcx> { |
| fn ignore_borrow( |
| &self, |
| tcx: TyCtxt<'tcx>, |
| body: &Body<'tcx>, |
| locals_state_at_exit: &LocalsStateAtExit, |
| ) -> bool { |
| let ignore = match self.base { |
| // If a local variable is immutable, then we only need to track borrows to guard |
| // against two kinds of errors: |
| // * The variable being dropped while still borrowed (e.g., because the fn returns |
| // a reference to a local variable) |
| // * The variable being moved while still borrowed |
| // |
| // In particular, the variable cannot be mutated -- the "access checks" will fail -- |
| // so we don't have to worry about mutation while borrowed. |
| PlaceBase::Local(index) => { |
| match locals_state_at_exit { |
| LocalsStateAtExit::AllAreInvalidated => false, |
| LocalsStateAtExit::SomeAreInvalidated { has_storage_dead_or_moved } => { |
| let ignore = !has_storage_dead_or_moved.contains(index) && |
| body.local_decls[index].mutability == Mutability::Not; |
| debug!("ignore_borrow: local {:?} => {:?}", index, ignore); |
| ignore |
| } |
| } |
| } |
| PlaceBase::Static(box Static{ kind: StaticKind::Promoted(_, _), .. }) => |
| false, |
| PlaceBase::Static(box Static{ kind: StaticKind::Static, def_id, .. }) => { |
| tcx.is_mutable_static(def_id) |
| } |
| }; |
| |
| for (i, elem) in self.projection.iter().enumerate() { |
| let proj_base = &self.projection[..i]; |
| |
| if *elem == ProjectionElem::Deref { |
| let ty = Place::ty_from(&self.base, proj_base, body, tcx).ty; |
| if let ty::RawPtr(..) | ty::Ref(_, _, hir::MutImmutable) = ty.sty { |
| // For both derefs of raw pointers and `&T` |
| // references, the original path is `Copy` and |
| // therefore not significant. In particular, |
| // there is nothing the user can do to the |
| // original path that would invalidate the |
| // newly created reference -- and if there |
| // were, then the user could have copied the |
| // original path into a new variable and |
| // borrowed *that* one, leaving the original |
| // path unborrowed. |
| return true; |
| } |
| } |
| } |
| |
| ignore |
| } |
| } |