diff options
| -rw-r--r-- | src/librustc_middle/mir/predecessors.rs | 37 |
1 files changed, 23 insertions, 14 deletions
diff --git a/src/librustc_middle/mir/predecessors.rs b/src/librustc_middle/mir/predecessors.rs index 629b5c2efb7..8f1f9278521 100644 --- a/src/librustc_middle/mir/predecessors.rs +++ b/src/librustc_middle/mir/predecessors.rs @@ -1,5 +1,5 @@ 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; @@ -11,7 +11,7 @@ pub type Predecessors = IndexVec<BasicBlock, SmallVec<[BasicBlock; 4]>>; #[derive(Clone, Debug)] pub struct PredecessorCache { - cache: Lock<Option<Predecessors>>, + cache: Lock<Option<Lrc<Predecessors>>>, } impl PredecessorCache { @@ -20,30 +20,39 @@ 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) + })) } } |