Remove interior mutability in mir predecessors cache

src/librustc/arena.rs

@@ -23,17 +23,17 @@ macro_rules! arena_types {
             [] generics: rustc::ty::Generics,
             [] trait_def: rustc::ty::TraitDef,
             [] adt_def: rustc::ty::AdtDef,
-            [] steal_mir: rustc::ty::steal::Steal<rustc::mir::Body<$tcx>>,
-            [] mir: rustc::mir::Body<$tcx>,
+            [] steal_mir: rustc::ty::steal::Steal<rustc::mir::BodyCache<$tcx>>,
+            [] mir: rustc::mir::BodyCache<$tcx>,
             [] steal_promoted: rustc::ty::steal::Steal<
                 rustc_index::vec::IndexVec<
                     rustc::mir::Promoted,
-                    rustc::mir::Body<$tcx>
+                    rustc::mir::BodyCache<$tcx>
                 >
             >,
             [] promoted: rustc_index::vec::IndexVec<
                 rustc::mir::Promoted,
-                rustc::mir::Body<$tcx>
+                rustc::mir::BodyCache<$tcx>
             >,
             [] tables: rustc::ty::TypeckTables<$tcx>,
             [] const_allocs: rustc::mir::interpret::Allocation,

src/librustc/mir/cache.rs

@@ -1,16 +1,19 @@
 use rustc_index::vec::IndexVec;
-use rustc_data_structures::sync::{RwLock, MappedReadGuard, ReadGuard};
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_serialize::{Encodable, Encoder, Decodable, Decoder};
 use crate::ich::StableHashingContext;
-use crate::mir::{Body, BasicBlock};
+use crate::mir::{BasicBlock, BasicBlockData, Body, LocalDecls, Location, Successors};
+use rustc_data_structures::graph::{self, GraphPredecessors, GraphSuccessors};
+use rustc_data_structures::graph::dominators::{dominators, Dominators};
+use std::iter;
+use std::ops::{Deref, DerefMut, Index, IndexMut};
+use std::vec::IntoIter;
 
 #[derive(Clone, Debug)]
 pub struct Cache {
-    predecessors: RwLock<Option<IndexVec<BasicBlock, Vec<BasicBlock>>>>
+    predecessors: Option<IndexVec<BasicBlock, Vec<BasicBlock>>>,
 }
 
-
 impl rustc_serialize::Encodable for Cache {
     fn encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
         Encodable::encode(&(), s)
@@ -31,39 +34,264 @@ impl<'a> HashStable<StableHashingContext<'a>> for Cache {
 
 impl Cache {
     pub fn new() -> Self {
-        Cache {
-            predecessors: RwLock::new(None)
+        Self {
+            predecessors: None,
         }
     }
 
-    pub fn invalidate(&self) {
+    pub fn invalidate_predecessors(&mut self) {
         // FIXME: consider being more fine-grained
-        *self.predecessors.borrow_mut() = None;
+        self.predecessors = None;
     }
 
-    pub fn predecessors(
-        &self,
-        body: &Body<'_>
-    ) -> MappedReadGuard<'_, IndexVec<BasicBlock, Vec<BasicBlock>>> {
-        if self.predecessors.borrow().is_none() {
-            *self.predecessors.borrow_mut() = Some(calculate_predecessors(body));
+    pub fn ensure_predecessors(&mut self, body: &Body<'_>) {
+        if self.predecessors.is_none() {
+            let mut result = IndexVec::from_elem(vec![], body.basic_blocks());
+            for (bb, data) in body.basic_blocks().iter_enumerated() {
+                if let Some(ref term) = data.terminator {
+                    for &tgt in term.successors() {
+                        result[tgt].push(bb);
+                    }
+                }
+            }
+
+            self.predecessors = Some(result)
         }
+    }
+
+    /// This will recompute the predecessors cache if it is not available
+    fn predecessors(&mut self, body: &Body<'_>) -> &IndexVec<BasicBlock, Vec<BasicBlock>> {
+        self.ensure_predecessors(body);
+        self.predecessors.as_ref().unwrap()
+    }
+
+    fn unwrap_predecessors_for(&self, bb: BasicBlock) -> &[BasicBlock] {
+        &self.predecessors.as_ref().unwrap()[bb]
+    }
 
-        ReadGuard::map(self.predecessors.borrow(), |p| p.as_ref().unwrap())
+    fn unwrap_predecessor_locations<'a>(
+        &'a self,
+        loc: Location,
+        body: &'a Body<'a>
+    ) -> impl Iterator<Item = Location> + 'a {
+        let if_zero_locations = if loc.statement_index == 0 {
+            let predecessor_blocks = self.unwrap_predecessors_for(loc.block);
+            let num_predecessor_blocks = predecessor_blocks.len();
+            Some(
+                (0..num_predecessor_blocks)
+                    .map(move |i| predecessor_blocks[i])
+                    .map(move |bb| body.terminator_loc(bb)),
+            )
+        } else {
+            None
+        };
+
+        let if_not_zero_locations = if loc.statement_index == 0 {
+            None
+        } else {
+            Some(Location { block: loc.block, statement_index: loc.statement_index - 1 })
+        };
+
+        if_zero_locations.into_iter().flatten().chain(if_not_zero_locations)
+    }
+
+    pub fn basic_blocks_mut<'a, 'tcx>(
+        &mut self,
+        body: &'a mut Body<'tcx>
+    ) -> &'a mut IndexVec<BasicBlock, BasicBlockData<'tcx>> {
+        debug!("bbm: Clearing predecessors cache for body at: {:?}", body.span.data());
+        self.invalidate_predecessors();
+        &mut body.basic_blocks
+    }
+
+    pub fn basic_blocks_and_local_decls_mut<'a, 'tcx>(
+        &mut self,
+        body: &'a mut Body<'tcx>
+    ) -> (&'a mut IndexVec<BasicBlock, BasicBlockData<'tcx>>, &'a mut LocalDecls<'tcx>) {
+        debug!("bbaldm: Clearing predecessors cache for body at: {:?}", body.span.data());
+        self.invalidate_predecessors();
+        (&mut body.basic_blocks, &mut body.local_decls)
     }
 }
 
-fn calculate_predecessors(body: &Body<'_>) -> IndexVec<BasicBlock, Vec<BasicBlock>> {
-    let mut result = IndexVec::from_elem(vec![], body.basic_blocks());
-    for (bb, data) in body.basic_blocks().iter_enumerated() {
-        if let Some(ref term) = data.terminator {
-            for &tgt in term.successors() {
-                result[tgt].push(bb);
-            }
+#[derive(Clone, Debug, HashStable, RustcEncodable, RustcDecodable, TypeFoldable)]
+pub struct BodyCache<'tcx> {
+    cache: Cache,
+    body: Body<'tcx>,
+}
+
+impl BodyCache<'tcx> {
+    pub fn new(body: Body<'tcx>) -> Self {
+        Self {
+            cache: Cache::new(),
+            body,
+        }
+    }
+}
+
+#[macro_export]
+macro_rules! read_only {
+    ($body:expr) => {
+        {
+            $body.ensure_predecessors();
+            $body.unwrap_read_only()
+        }
+    };
+}
+
+impl BodyCache<'tcx> {
+    pub fn ensure_predecessors(&mut self) {
+        self.cache.ensure_predecessors(&self.body);
+    }
+
+    pub fn predecessors(&mut self) -> &IndexVec<BasicBlock, Vec<BasicBlock>> {
+        self.cache.predecessors(&self.body)
+    }
+
+    pub fn unwrap_read_only(&self) -> ReadOnlyBodyCache<'_, 'tcx> {
+        ReadOnlyBodyCache::new(&self.cache, &self.body)
+    }
+
+    pub fn basic_blocks_mut(&mut self) -> &mut IndexVec<BasicBlock, BasicBlockData<'tcx>> {
+        self.cache.basic_blocks_mut(&mut self.body)
+    }
+
+    pub fn basic_blocks_and_local_decls_mut(
+        &mut self
+    ) -> (&mut IndexVec<BasicBlock, BasicBlockData<'tcx>>, &mut LocalDecls<'tcx>) {
+        self.cache.basic_blocks_and_local_decls_mut(&mut self.body)
+    }
+}
+
+impl<'tcx> Index<BasicBlock> for BodyCache<'tcx> {
+    type Output = BasicBlockData<'tcx>;
+
+    fn index(&self, index: BasicBlock) -> &BasicBlockData<'tcx> {
+        &self.body[index]
+    }
+}
+
+impl<'tcx> IndexMut<BasicBlock> for BodyCache<'tcx> {
+    fn index_mut(&mut self, index: BasicBlock) -> &mut Self::Output {
+        &mut self.basic_blocks_mut()[index]
+    }
+}
+
+impl<'tcx> Deref for BodyCache<'tcx> {
+    type Target = Body<'tcx>;
+
+    fn deref(&self) -> &Self::Target {
+        &self.body
+    }
+}
+
+impl<'tcx> DerefMut for BodyCache<'tcx> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.body
+    }
+}
+
+#[derive(Copy, Clone, Debug)]
+pub struct ReadOnlyBodyCache<'a, 'tcx> {
+    cache: &'a Cache,
+    body: &'a Body<'tcx>,
+}
+
+impl ReadOnlyBodyCache<'a, 'tcx> {
+    fn new(cache: &'a Cache, body: &'a Body<'tcx>) -> Self {
+        assert!(
+            cache.predecessors.is_some(),
+            "Cannot construct ReadOnlyBodyCache without computed predecessors");
+        Self {
+            cache,
+            body,
         }
     }
 
-    result
+    pub fn predecessors(&self) -> &IndexVec<BasicBlock, Vec<BasicBlock>> {
+        self.cache.predecessors.as_ref().unwrap()
+    }
+
+    pub fn predecessors_for(&self, bb: BasicBlock) -> &[BasicBlock] {
+        self.cache.unwrap_predecessors_for(bb)
+    }
+
+    pub fn predecessor_locations(&self, loc: Location) -> impl Iterator<Item = Location> + '_ {
+        self.cache.unwrap_predecessor_locations(loc, self.body)
+    }
+
+    pub fn body(&self) -> &'a Body<'tcx> {
+        self.body
+    }
+
+    pub fn basic_blocks(&self) -> &IndexVec<BasicBlock, BasicBlockData<'tcx>> {
+        &self.body.basic_blocks
+    }
+
+    pub fn dominators(&self) -> Dominators<BasicBlock> {
+        dominators(self)
+    }
+}
+
+impl graph::DirectedGraph for ReadOnlyBodyCache<'a, 'tcx> {
+    type Node = BasicBlock;
+}
+
+impl graph::GraphPredecessors<'graph> for ReadOnlyBodyCache<'a, 'tcx> {
+    type Item = BasicBlock;
+    type Iter = IntoIter<BasicBlock>;
+}
+
+impl graph::WithPredecessors for ReadOnlyBodyCache<'a, 'tcx> {
+    fn predecessors(
+        &self,
+        node: Self::Node,
+    ) -> <Self as GraphPredecessors<'_>>::Iter {
+        self.cache.unwrap_predecessors_for(node).to_vec().into_iter()
+    }
+}
+
+impl graph::WithNumNodes for ReadOnlyBodyCache<'a, 'tcx> {
+    fn num_nodes(&self) -> usize {
+        self.body.num_nodes()
+    }
+}
+
+impl graph::WithStartNode for ReadOnlyBodyCache<'a, 'tcx> {
+    fn start_node(&self) -> Self::Node {
+        self.body.start_node()
+    }
+}
+
+impl graph::WithSuccessors for ReadOnlyBodyCache<'a, 'tcx> {
+    fn successors(
+        &self,
+        node: Self::Node,
+    ) -> <Self as GraphSuccessors<'_>>::Iter {
+        self.body.successors(node)
+    }
+}
+
+impl<'a, 'b, 'tcx> graph::GraphSuccessors<'b> for ReadOnlyBodyCache<'a, 'tcx> {
+    type Item = BasicBlock;
+    type Iter = iter::Cloned<Successors<'b>>;
+}
+
+
+impl Deref for ReadOnlyBodyCache<'a, 'tcx> {
+    type Target = Body<'tcx>;
+
+    fn deref(&self) -> &Self::Target {
+        self.body
+    }
+}
+
+impl Index<BasicBlock> for ReadOnlyBodyCache<'a, 'tcx> {
+    type Output = BasicBlockData<'tcx>;
+
+    fn index(&self, index: BasicBlock) -> &BasicBlockData<'tcx> {
+        &self.body[index]
+    }
 }
 
 CloneTypeFoldableAndLiftImpls! {