Tree in miri - Rust
Description: Tree structure with both parents and children since we want to be able to traverse the tree efficiently in both directions.

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## Tree

# Struct Tree

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    pub struct Tree {
        pub(super) tag_mapping: UniKeyMap<BorTag>,
        pub(super) nodes: UniValMap<Node>,
        pub(super) locations: DedupRangeMap<LocationTree>,
        pub(super) roots: SmallVec<[UniIndex; 2]>,
    }

Expand description

Tree structure with both parents and children since we want to be able to traverse the tree efficiently in both directions.

## Fields§

§`tag_mapping: UniKeyMap<BorTag>`

Mapping from tags to keys. The key obtained can then be used in any of the `UniValMap` relative to this allocation, i.e. `nodes`, `LocationTree::perms` and `LocationTree::exposed_cache` of the same `Tree`. The parent-child relationship in `Node` is encoded in terms of these same keys, so traversing the entire tree needs exactly one access to `tag_mapping`.

§`nodes: UniValMap<Node>`

All nodes of this tree.

§`locations: DedupRangeMap<LocationTree>`

Associates with each location its state and wildcard access tracking.

§`roots: SmallVec<[UniIndex; 2]>`

Contains both the root of the main tree as well as the roots of the wildcard subtrees.

If we reborrow a reference which has wildcard provenance, then we do not know where in the tree to attach them. Instead we create a new additional tree for this allocation with this new reference as a root. We call this additional tree a wildcard subtree.

The actual structure should be a single tree but with wildcard provenance we approximate this with this ordered set of trees. Each wildcard subtree is the direct child of some exposed tag (that is smaller than the root), but we do not know which. This also means that it can only be the child of a tree that comes before it in the vec ensuring we don’t have any cycles in our approximated tree.

Sorted according to `BorTag` from low to high. This also means the main root is `root[0]`.

Has array size 2 because that still ensures the minimum size for SmallVec.

## Implementations§

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### impl<'tcx> Tree

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#### fn nth_parent(&self, tag: BorTag, nth_parent: u8) -> Option<BorTag>

Climb the tree to get the tag of a distant ancestor. Allows operations on tags that are unreachable by the program but still exist in the tree. Not guaranteed to perform consistently if `provenance-gc=1`.

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#### pub fn give_pointer_debug_name( &mut self, tag: BorTag, nth_parent: u8, name: &str, ) -> InterpResult<'tcx>

Debug helper: assign name to tag.

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#### pub fn is_allocation_of(&self, tag: BorTag) -> bool

Debug helper: determines if the tree contains a tag.

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### impl<'tcx> Tree

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#### pub fn print_tree( &self, protected_tags: &FxHashMap<BorTag, ProtectorKind>, show_unnamed: bool, ) -> InterpResult<'tcx>

Display the contents of the tree.

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### impl Tree

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#### pub fn new(root_tag: BorTag, size: Size, span: Span) -> Self

Create a new tree, with only a root pointer.

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### impl<'tcx> Tree

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#### pub(super) fn new_child( &mut self, base_offset: Size, parent_prov: ProvenanceExtra, new_tag: BorTag, inside_perms: DedupRangeMap<LocationState>, outside_perm: Permission, protected: bool, span: Span, ) -> InterpResult<'tcx>

Insert a new tag in the tree.

`inside_perm` defines the initial permissions for a block of memory starting at `base_offset`. These may nor may not be already marked as “accessed”. `outside_perm` defines the initial permission for the rest of the allocation. These are definitely not “accessed”.

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#### fn update_idempotent_foreign_access_after_retag( &mut self, current: UniIndex, strongest_allowed: IdempotentForeignAccess, )

Restores the SIFA “children are stronger”/“parents are weaker” invariant after a retag: reduce the SIFA of `current` and its parents to be no stronger than `strongest_allowed`. See `foreign_access_skipping.rs` and `Tree::new_child`.

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#### pub fn dealloc( &mut self, prov: ProvenanceExtra, access_range: AllocRange, global: &RefCell<GlobalStateInner>, alloc_id: AllocId, span: Span, ) -> InterpResult<'tcx>

Deallocation requires

- a pointer that permits write accesses
- the absence of Strong Protectors anywhere in the allocation

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#### pub fn perform_access( &mut self, prov: ProvenanceExtra, access_range: AllocRange, access_kind: AccessKind, access_cause: AccessCause, global: &RefCell<GlobalStateInner>, alloc_id: AllocId, span: Span, ) -> InterpResult<'tcx>

Map the per-node and per-location `LocationState::perform_access` to each location of the first component of `access_range_and_kind`, on every tag of the allocation.

`LocationState::perform_access` will take care of raising transition errors and updating the `accessed` status of each location, this traversal adds to that:

- inserting into the map locations that do not exist yet,
- trimming the traversal,
- recording the history.

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#### pub fn perform_protector_end_access( &mut self, tag: BorTag, global: &RefCell<GlobalStateInner>, alloc_id: AllocId, span: Span, ) -> InterpResult<'tcx>

This is the special access that is applied on protector release:

- the access will be applied only to accessed locations of the allocation,
- it will not be visible to children,
- it will be recorded as a `FnExit` diagnostic access
- and it will be a read except if the location is `Unique`, i.e. has been written to, in which case it will be a write.
- otherwise identical to `Tree::perform_access`

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### impl Tree

Integration with the BorTag garbage collector

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#### pub fn remove_unreachable_tags(&mut self, live_tags: &FxHashSet<BorTag>)

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#### fn is_useless(&self, idx: UniIndex, live: &FxHashSet<BorTag>) -> bool

Checks if a node is useless and should be GC’ed. A node is useless if it has no children and also the tag is no longer live.

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#### fn can_be_replaced_by_single_child( &self, idx: UniIndex, live: &FxHashSet<BorTag>, ) -> Option<UniIndex>

Checks whether a node can be replaced by its only child. If so, returns the index of said only child. If not, returns none.

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#### fn remove_useless_node(&mut self, this: UniIndex)

Properly removes a node. The node to be removed should not otherwise be usable. It also should have no children, but this is not checked, so that nodes whose children were rotated somewhere else can be deleted without having to first modify them to clear that array.

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#### fn remove_useless_children(&mut self, root: UniIndex, live: &FxHashSet<BorTag>)

Traverses the entire tree looking for useless tags. Removes from the tree all useless child nodes of root. It will not delete the root itself.

NOTE: This leaves in the middle of the tree tags that are unreachable but have reachable children. There is a potential for compacting the tree by reassigning children of dead tags to the nearest live parent, but it must be done with care not to remove UB.

Example: Consider the tree `root - parent - child`, with `parent: Frozen` and `child: Reserved`. This tree can exist. If we blindly delete `parent` and reassign `child` to be a direct child of `root` then Writes to `child` are now permitted whereas they were not when `parent` was still there.

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### impl Tree

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#### pub fn expose_tag(&mut self, tag: BorTag, protected: bool)

Marks the tag as exposed & updates the wildcard tracking data structure to represent its access level. Also takes as an argument whether the tag is protected or not.

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#### pub(super) fn update_exposure_for_protector_release(&mut self, tag: BorTag)

This updates the wildcard tracking data structure to reflect the release of the protector on `tag`.

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### impl<'tcx> Tree

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#### pub fn new_allocation( id: AllocId, size: Size, state: &mut GlobalStateInner, _kind: MemoryKind, machine: &MiriMachine<'tcx>, ) -> Self

Create a new allocation, i.e. a new tree

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#### pub fn before_memory_access( &mut self, access_kind: AccessKind, alloc_id: AllocId, prov: ProvenanceExtra, range: AllocRange, machine: &MiriMachine<'tcx>, ) -> InterpResult<'tcx>

Check that an access on the entire range is permitted, and update the tree.

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#### pub fn before_memory_deallocation( &mut self, alloc_id: AllocId, prov: ProvenanceExtra, size: Size, machine: &MiriMachine<'tcx>, ) -> InterpResult<'tcx>

Check that this pointer has permission to deallocate this range.

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#### pub fn release_protector( &mut self, machine: &MiriMachine<'tcx>, global: &RefCell<GlobalStateInner>, tag: BorTag, alloc_id: AllocId, ) -> InterpResult<'tcx>

A tag just lost its protector.

This emits a special kind of access that is only applied to accessed locations, as a protection against other tags not having been made aware of the existence of this protector.

## Trait Implementations§

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### impl Clone for Tree

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#### fn clone(&self) -> Tree

Returns a duplicate of the value. Read more
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#### fn clone_from(&mut self, source: &Self)

Performs copy-assignment from `source`. Read more
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### impl Debug for Tree

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#### fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more
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### impl VisitProvenance for Tree

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#### fn visit_provenance(&self, visit: &mut VisitWith<'_>)

## Auto Trait Implementations§

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### impl Freeze for Tree

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### impl RefUnwindSafe for Tree

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### impl Send for Tree

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### impl Sync for Tree

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### impl Unpin for Tree

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### impl UnsafeUnpin for Tree

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### impl UnwindSafe for Tree

## Blanket Implementations§

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### impl<T> Any for T
where T: 'static + ?Sized,

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#### fn type_id(&self) -> TypeId

Gets the `TypeId` of `self`. Read more
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### impl<T> Borrow<T> for T
where T: ?Sized,

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#### fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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### impl<T> BorrowMut<T> for T
where T: ?Sized,

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#### fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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### impl<T> CloneToUninit for T
where T: Clone,

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#### unsafe fn clone_to_uninit(&self, dest: *mut u8)

🔬This is a nightly-only experimental API. (`clone_to_uninit`)
Performs copy-assignment from `self` to `dest`. Read more
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### impl<T> From<T> for T

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#### fn from(t: T) -> T

Returns the argument unchanged.

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### impl<T, U> Into<U> for T
where U: From<T>,

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#### fn into(self) -> U

Calls `U::from(self)`.

That is, this conversion is whatever the implementation of `From<T> for U` chooses to do.

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### impl<T> Same for T

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#### type Output = T

Should always be `Self`
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### impl<T> ToOwned for T
where T: Clone,

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#### type Owned = T

The resulting type after obtaining ownership.
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#### fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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#### fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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### impl<T, U> TryFrom<U> for T
where U: Into<T>,

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#### type Error = Infallible

The type returned in the event of a conversion error.
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#### fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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### impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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#### type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.
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### impl<V, T> VZip<V> for T
where V: MultiLane<T>,

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#### fn vzip(self) -> V

## Layout§

Note: Most layout information is completely unstable and may even differ between compilations. The only exception is types with certain `repr(...)` attributes. Please see the Rust Reference's “Type Layout” chapter for details on type layout guarantees.

Size: 128 bytes