rustc_mir_dataflow/
un_derefer.rs

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1use rustc_data_structures::fx::FxHashMap;
2use rustc_middle::mir::*;
3
4/// Used for reverting changes made by `DerefSeparator`
5#[derive(Default, Debug)]
6pub(crate) struct UnDerefer<'tcx> {
7    deref_chains: FxHashMap<Local, Vec<PlaceRef<'tcx>>>,
8}
9
10impl<'tcx> UnDerefer<'tcx> {
11    #[inline]
12    pub(crate) fn insert(&mut self, local: Local, reffed: PlaceRef<'tcx>) {
13        let mut chain = self.deref_chains.remove(&reffed.local).unwrap_or_default();
14        chain.push(reffed);
15        self.deref_chains.insert(local, chain);
16    }
17
18    /// Returns the chain of places behind `DerefTemp` locals
19    #[inline]
20    pub(crate) fn deref_chain(&self, local: Local) -> &[PlaceRef<'tcx>] {
21        self.deref_chains.get(&local).map(Vec::as_slice).unwrap_or_default()
22    }
23
24    /// Iterates over the projections of a place and its deref chain.
25    ///
26    /// See [`PlaceRef::iter_projections`]
27    #[inline]
28    pub(crate) fn iter_projections(
29        &self,
30        place: PlaceRef<'tcx>,
31    ) -> impl Iterator<Item = (PlaceRef<'tcx>, PlaceElem<'tcx>)> + '_ {
32        ProjectionIter::new(self.deref_chain(place.local), place)
33    }
34}
35
36/// The iterator returned by [`UnDerefer::iter_projections`].
37struct ProjectionIter<'a, 'tcx> {
38    places: SlicePlusOne<'a, PlaceRef<'tcx>>,
39    proj_idx: usize,
40}
41
42impl<'a, 'tcx> ProjectionIter<'a, 'tcx> {
43    #[inline]
44    fn new(deref_chain: &'a [PlaceRef<'tcx>], place: PlaceRef<'tcx>) -> Self {
45        // just return an empty iterator for a bare local
46        let last = if place.as_local().is_none() {
47            Some(place)
48        } else {
49            debug_assert!(deref_chain.is_empty());
50            None
51        };
52
53        ProjectionIter { places: SlicePlusOne { slice: deref_chain, last }, proj_idx: 0 }
54    }
55}
56
57impl<'tcx> Iterator for ProjectionIter<'_, 'tcx> {
58    type Item = (PlaceRef<'tcx>, PlaceElem<'tcx>);
59
60    #[inline]
61    fn next(&mut self) -> Option<(PlaceRef<'tcx>, PlaceElem<'tcx>)> {
62        let place = self.places.read()?;
63
64        // the projection should never be empty except for a bare local which is handled in new
65        let partial_place =
66            PlaceRef { local: place.local, projection: &place.projection[..self.proj_idx] };
67        let elem = place.projection[self.proj_idx];
68
69        if self.proj_idx == place.projection.len() - 1 {
70            self.proj_idx = 0;
71            self.places.advance();
72        } else {
73            self.proj_idx += 1;
74        }
75
76        Some((partial_place, elem))
77    }
78}
79
80struct SlicePlusOne<'a, T> {
81    slice: &'a [T],
82    last: Option<T>,
83}
84
85impl<T: Copy> SlicePlusOne<'_, T> {
86    #[inline]
87    fn read(&self) -> Option<T> {
88        self.slice.first().copied().or(self.last)
89    }
90
91    #[inline]
92    fn advance(&mut self) {
93        match self.slice {
94            [_, ref remainder @ ..] => {
95                self.slice = remainder;
96            }
97            [] => self.last = None,
98        }
99    }
100}
rustc_mir_dataflow/un_derefer.rs

rustc_mir_dataflow/
un_derefer.rs
