Cache dominators.

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -2382,7 +2382,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         let mut back_edge_stack = Vec::new();
 
         predecessor_locations(self.body, location).for_each(|predecessor| {
-            if location.dominates(predecessor, self.dominators()) {
+            if location.dominates(predecessor, self.dominators) {
                 back_edge_stack.push(predecessor)
             } else {
                 stack.push(predecessor);
@@ -2494,7 +2494,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 
             let mut has_predecessor = false;
             predecessor_locations(self.body, location).for_each(|predecessor| {
-                if location.dominates(predecessor, self.dominators()) {
+                if location.dominates(predecessor, self.dominators) {
                     back_edge_stack.push(predecessor)
                 } else {
                     stack.push(predecessor);

compiler/rustc_borrowck/src/invalidation.rs

@@ -46,7 +46,7 @@ struct InvalidationGenerator<'cx, 'tcx> {
     all_facts: &'cx mut AllFacts,
     location_table: &'cx LocationTable,
     body: &'cx Body<'tcx>,
-    dominators: Dominators<BasicBlock>,
+    dominators: &'cx Dominators<BasicBlock>,
     borrow_set: &'cx BorrowSet<'tcx>,
 }
 

compiler/rustc_borrowck/src/lib.rs

@@ -43,7 +43,6 @@ use rustc_target::abi::FieldIdx;
 
 use either::Either;
 use smallvec::SmallVec;
-use std::cell::OnceCell;
 use std::cell::RefCell;
 use std::collections::BTreeMap;
 use std::ops::Deref;
@@ -331,7 +330,7 @@ fn do_mir_borrowck<'tcx>(
                 used_mut: Default::default(),
                 used_mut_upvars: SmallVec::new(),
                 borrow_set: Rc::clone(&borrow_set),
-                dominators: Default::default(),
+                dominators: promoted_body.basic_blocks.dominators(),
                 upvars: Vec::new(),
                 local_names: IndexVec::from_elem(None, &promoted_body.local_decls),
                 region_names: RefCell::default(),
@@ -360,7 +359,7 @@ fn do_mir_borrowck<'tcx>(
         used_mut: Default::default(),
         used_mut_upvars: SmallVec::new(),
         borrow_set: Rc::clone(&borrow_set),
-        dominators: Default::default(),
+        dominators: body.basic_blocks.dominators(),
         upvars,
         local_names,
         region_names: RefCell::default(),
@@ -592,7 +591,7 @@ struct MirBorrowckCtxt<'cx, 'tcx> {
     borrow_set: Rc<BorrowSet<'tcx>>,
 
     /// Dominators for MIR
-    dominators: OnceCell<Dominators<BasicBlock>>,
+    dominators: &'cx Dominators<BasicBlock>,
 
     /// Information about upvars not necessarily preserved in types or MIR
     upvars: Vec<Upvar<'tcx>>,
@@ -1103,7 +1102,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 
                 (Read(kind), BorrowKind::Unique | BorrowKind::Mut { .. }) => {
                     // Reading from mere reservations of mutable-borrows is OK.
-                    if !is_active(this.dominators(), borrow, location) {
+                    if !is_active(this.dominators, borrow, location) {
                         assert!(allow_two_phase_borrow(borrow.kind));
                         return Control::Continue;
                     }
@@ -2267,10 +2266,6 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
     fn is_upvar_field_projection(&self, place_ref: PlaceRef<'tcx>) -> Option<FieldIdx> {
         path_utils::is_upvar_field_projection(self.infcx.tcx, &self.upvars, place_ref, self.body())
     }
-
-    fn dominators(&self) -> &Dominators<BasicBlock> {
-        self.dominators.get_or_init(|| self.body.basic_blocks.dominators())
-    }
 }
 
 mod error {

compiler/rustc_codegen_ssa/src/mir/analyze.rs

@@ -84,7 +84,7 @@ impl DefLocation {
 
 struct LocalAnalyzer<'mir, 'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> {
     fx: &'mir FunctionCx<'a, 'tcx, Bx>,
-    dominators: Dominators<mir::BasicBlock>,
+    dominators: &'mir Dominators<mir::BasicBlock>,
     locals: IndexVec<mir::Local, LocalKind>,
 }
 

compiler/rustc_middle/src/mir/basic_blocks.rs

@@ -28,6 +28,8 @@ struct Cache {
     switch_sources: OnceCell<SwitchSources>,
     is_cyclic: OnceCell<bool>,
     postorder: OnceCell<Vec<BasicBlock>>,
+    dominator_tree: OnceCell<DominatorTree<BasicBlock>>,
+    dominators: OnceCell<Dominators<BasicBlock>>,
 }
 
 impl<'tcx> BasicBlocks<'tcx> {
@@ -42,12 +44,12 @@ impl<'tcx> BasicBlocks<'tcx> {
         *self.cache.is_cyclic.get_or_init(|| graph::is_cyclic(self))
     }
 
-    pub fn dominator_tree(&self) -> DominatorTree<BasicBlock> {
+    pub fn dominator_tree(&self) -> &DominatorTree<BasicBlock> {
-        dominator_tree(&self)
+        self.cache.dominator_tree.get_or_init(|| dominator_tree(&self))
     }
 
-    pub fn dominators(&self) -> Dominators<BasicBlock> {
+    pub fn dominators(&self) -> &Dominators<BasicBlock> {
-        dominators(&self.dominator_tree())
+        self.cache.dominators.get_or_init(|| dominators(self.dominator_tree()))
     }
 
     /// Returns predecessors for each basic block.

compiler/rustc_mir_transform/src/ssa.rs

@@ -68,8 +68,11 @@ impl SsaLocals {
         let assignment_order = Vec::with_capacity(body.local_decls.len());
 
         let assignments = IndexVec::from_elem(Set1::Empty, &body.local_decls);
-        let dominators =
+        let dominators = if body.basic_blocks.len() > 2 {
-            if body.basic_blocks.len() > 2 { Some(body.basic_blocks.dominators()) } else { None };
+            Some(body.basic_blocks.dominators().clone())
+        } else {
+            None
+        };
         let dominators = SmallDominators { inner: dominators };
 
         let direct_uses = IndexVec::from_elem(0, &body.local_decls);