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Make ignore_borrow iterate instead of recurse #61099

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May 25, 2019
Merged

Make ignore_borrow iterate instead of recurse #61099

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68 changes: 33 additions & 35 deletions src/librustc_mir/borrow_check/place_ext.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -25,40 +25,36 @@ impl<'tcx> PlaceExt<'tcx> for Place<'tcx> {
mir: &Mir<'tcx>,
locals_state_at_exit: &LocalsStateAtExit,
) -> bool {
match self {
// 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.
Place::Base(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) &&
mir.local_decls[*index].mutability == Mutability::Not;
debug!("ignore_borrow: local {:?} => {:?}", index, ignore);
ignore
self.iterate(|place_base, place_projection| {
let ignore = match place_base {
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// 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) &&
mir.local_decls[*index].mutability == Mutability::Not;
debug!("ignore_borrow: local {:?} => {:?}", index, ignore);
ignore
}
}
}
}
Place::Base(PlaceBase::Static(box Static{ kind: StaticKind::Promoted(_), .. })) =>
false,
Place::Base(PlaceBase::Static(box Static{ kind: StaticKind::Static(def_id), .. })) => {
tcx.is_mutable_static(*def_id)
}
Place::Projection(proj) => match proj.elem {
ProjectionElem::Field(..)
| ProjectionElem::Downcast(..)
| ProjectionElem::Subslice { .. }
| ProjectionElem::ConstantIndex { .. }
| ProjectionElem::Index(_) => proj.base.ignore_borrow(
tcx, mir, locals_state_at_exit),
PlaceBase::Static(box Static{ kind: StaticKind::Promoted(_), .. }) =>
false,
PlaceBase::Static(box Static{ kind: StaticKind::Static(def_id), .. }) => {
tcx.is_mutable_static(*def_id)
}
};

ProjectionElem::Deref => {
for proj in place_projection {
if proj.elem == ProjectionElem::Deref {
let ty = proj.base.ty(mir, tcx).ty;
match ty.sty {
// For both derefs of raw pointers and `&T`
Expand All @@ -71,11 +67,13 @@ impl<'tcx> PlaceExt<'tcx> for Place<'tcx> {
// original path into a new variable and
// borrowed *that* one, leaving the original
// path unborrowed.
ty::RawPtr(..) | ty::Ref(_, _, hir::MutImmutable) => true,
_ => proj.base.ignore_borrow(tcx, mir, locals_state_at_exit),
ty::RawPtr(..) | ty::Ref(_, _, hir::MutImmutable) => return true,
_ => {}
}
}
},
}
}

ignore
})
}
}