--- /dev/null
+//! Lazily compute the inverse of each `SwitchInt`'s switch targets. Modeled after
+//! `Predecessors`/`PredecessorCache`.
+
+use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
+use rustc_data_structures::sync::OnceCell;
+use rustc_index::vec::IndexVec;
+use rustc_serialize as serialize;
+use smallvec::SmallVec;
+
+use crate::mir::{BasicBlock, BasicBlockData, Terminator, TerminatorKind};
+
+pub type SwitchSources = IndexVec<BasicBlock, IndexVec<BasicBlock, SmallVec<[Option<u128>; 1]>>>;
+
+#[derive(Clone, Debug)]
+pub(super) struct SwitchSourceCache {
+ cache: OnceCell<SwitchSources>,
+}
+
+impl SwitchSourceCache {
+ #[inline]
+ pub(super) fn new() -> Self {
+ SwitchSourceCache { cache: OnceCell::new() }
+ }
+
+ /// Invalidates the switch source cache.
+ #[inline]
+ pub(super) fn invalidate(&mut self) {
+ self.cache = OnceCell::new();
+ }
+
+ /// Returns the switch sources for this MIR.
+ #[inline]
+ pub(super) fn compute(
+ &self,
+ basic_blocks: &IndexVec<BasicBlock, BasicBlockData<'_>>,
+ ) -> &SwitchSources {
+ self.cache.get_or_init(|| {
+ let mut switch_sources = IndexVec::from_elem(
+ IndexVec::from_elem(SmallVec::new(), basic_blocks),
+ basic_blocks,
+ );
+ for (bb, data) in basic_blocks.iter_enumerated() {
+ if let Some(Terminator {
+ kind: TerminatorKind::SwitchInt { targets, .. }, ..
+ }) = &data.terminator
+ {
+ for (value, target) in targets.iter() {
+ switch_sources[target][bb].push(Some(value));
+ }
+ switch_sources[targets.otherwise()][bb].push(None);
+ }
+ }
+
+ switch_sources
+ })
+ }
+}
+
+impl<S: serialize::Encoder> serialize::Encodable<S> for SwitchSourceCache {
+ #[inline]
+ fn encode(&self, s: &mut S) -> Result<(), S::Error> {
+ s.emit_unit()
+ }
+}
+
+impl<D: serialize::Decoder> serialize::Decodable<D> for SwitchSourceCache {
+ #[inline]
+ fn decode(_: &mut D) -> Self {
+ Self::new()
+ }
+}
+
+impl<CTX> HashStable<CTX> for SwitchSourceCache {
+ #[inline]
+ fn hash_stable(&self, _: &mut CTX, _: &mut StableHasher) {
+ // do nothing
+ }
+}
+
+TrivialTypeFoldableAndLiftImpls! {
+ SwitchSourceCache,
+}