use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
-use rustc_data_structures::sync::{Lock, LockGuard, MappedLockGuard};
+use rustc_data_structures::sync::{Lock, Lrc};
use rustc_index::vec::IndexVec;
use rustc_serialize as serialize;
use smallvec::SmallVec;
#[derive(Clone, Debug)]
pub struct PredecessorCache {
- cache: Lock<Option<Predecessors>>,
+ cache: Lock<Option<Lrc<Predecessors>>>,
}
impl PredecessorCache {
PredecessorCache { cache: Lock::new(None) }
}
+ /// Invalidates the predecessor cache.
+ ///
+ /// Invalidating the predecessor cache requires mutating the MIR, which in turn requires a
+ /// unique reference (`&mut`) to the `mir::Body`. Because of this, we can assume that all
+ /// callers of `invalidate` have a unique reference to the MIR and thus to the predecessor
+ /// cache. This means we don't actually need to take a lock when `invalidate` is called.
#[inline]
pub fn invalidate(&mut self) {
*self.cache.get_mut() = None;
}
+ /// Returns a ref-counted smart pointer containing the predecessor graph for this MIR.
+ ///
+ /// We use ref-counting instead of a mapped `LockGuard` here to ensure that the lock for
+ /// `cache` is only held inside this function. As long as no other locks are taken while
+ /// computing the predecessor graph, deadlock is impossible.
#[inline]
pub fn compute(
&self,
basic_blocks: &IndexVec<BasicBlock, BasicBlockData<'_>>,
- ) -> MappedLockGuard<'_, Predecessors> {
- LockGuard::map(self.cache.lock(), |cache| {
- cache.get_or_insert_with(|| {
- let mut preds = IndexVec::from_elem(SmallVec::new(), basic_blocks);
- for (bb, data) in basic_blocks.iter_enumerated() {
- if let Some(term) = &data.terminator {
- for &succ in term.successors() {
- preds[succ].push(bb);
- }
+ ) -> Lrc<Predecessors> {
+ Lrc::clone(self.cache.lock().get_or_insert_with(|| {
+ let mut preds = IndexVec::from_elem(SmallVec::new(), basic_blocks);
+ for (bb, data) in basic_blocks.iter_enumerated() {
+ if let Some(term) = &data.terminator {
+ for &succ in term.successors() {
+ preds[succ].push(bb);
}
}
+ }
- preds
- })
- })
+ Lrc::new(preds)
+ }))
}
}