In MaybeRequiresStorage, store Results instead of ResultsCursor.

This requires a `clone` call in `check_for_move`, but makes
`MaybeRequiresStorage` an immutable analysis, which enables the next
commit.

Author: nnethercote

compiler/rustc_mir_dataflow/src/impls/storage_liveness.rs

@@ -5,7 +5,7 @@ use rustc_middle::mir::visit::{NonMutatingUseContext, PlaceContext, Visitor};
 use rustc_middle::mir::*;
 
 use super::MaybeBorrowedLocals;
-use crate::{Analysis, GenKill, ResultsCursor};
+use crate::{Analysis, GenKill, Results, ResultsCursor};
 
 pub struct MaybeStorageLive<'a> {
     always_live_locals: Cow<'a, BitSet<Local>>,
@@ -96,17 +96,19 @@ impl<'a, 'tcx> Analysis<'tcx> for MaybeStorageDead<'a> {
     }
 }
 
-type BorrowedLocalsResults<'mir, 'tcx> = ResultsCursor<'mir, 'tcx, MaybeBorrowedLocals>;
-
 /// Dataflow analysis that determines whether each local requires storage at a
 /// given location; i.e. whether its storage can go away without being observed.
 pub struct MaybeRequiresStorage<'mir, 'tcx> {
-    borrowed_locals: BorrowedLocalsResults<'mir, 'tcx>,
+    body: &'mir Body<'tcx>,
+    borrowed_locals: Results<'tcx, MaybeBorrowedLocals>,
 }
 
 impl<'mir, 'tcx> MaybeRequiresStorage<'mir, 'tcx> {
-    pub fn new(borrowed_locals: BorrowedLocalsResults<'mir, 'tcx>) -> Self {
-        MaybeRequiresStorage { borrowed_locals }
+    pub fn new(
+        body: &'mir Body<'tcx>,
+        borrowed_locals: Results<'tcx, MaybeBorrowedLocals>,
+    ) -> Self {
+        MaybeRequiresStorage { body, borrowed_locals }
     }
 }
 
@@ -135,7 +137,7 @@ impl<'tcx> Analysis<'tcx> for MaybeRequiresStorage<'_, 'tcx> {
         loc: Location,
     ) {
         // If a place is borrowed in a statement, it needs storage for that statement.
-        self.borrowed_locals.mut_analysis().apply_statement_effect(trans, stmt, loc);
+        self.borrowed_locals.analysis.apply_statement_effect(trans, stmt, loc);
 
         match &stmt.kind {
             StatementKind::StorageDead(l) => trans.kill(*l),
@@ -179,10 +181,7 @@ impl<'tcx> Analysis<'tcx> for MaybeRequiresStorage<'_, 'tcx> {
         loc: Location,
     ) {
         // If a place is borrowed in a terminator, it needs storage for that terminator.
-        self.borrowed_locals
-            .mut_analysis()
-            .transfer_function(trans)
-            .visit_terminator(terminator, loc);
+        self.borrowed_locals.analysis.transfer_function(trans).visit_terminator(terminator, loc);
 
         match &terminator.kind {
             TerminatorKind::Call { destination, .. } => {
@@ -283,15 +282,15 @@ impl<'tcx> Analysis<'tcx> for MaybeRequiresStorage<'_, 'tcx> {
 
 impl<'tcx> MaybeRequiresStorage<'_, 'tcx> {
     /// Kill locals that are fully moved and have not been borrowed.
-    fn check_for_move(&mut self, trans: &mut <Self as Analysis<'tcx>>::Domain, loc: Location) {
-        let body = self.borrowed_locals.body();
-        let mut visitor = MoveVisitor { trans, borrowed_locals: &mut self.borrowed_locals };
-        visitor.visit_location(body, loc);
+    fn check_for_move(&self, trans: &mut <Self as Analysis<'tcx>>::Domain, loc: Location) {
+        let borrowed_locals = self.borrowed_locals.clone().into_results_cursor(self.body);
+        let mut visitor = MoveVisitor { trans, borrowed_locals };
+        visitor.visit_location(self.body, loc);
     }
 }
 
 struct MoveVisitor<'a, 'mir, 'tcx> {
-    borrowed_locals: &'a mut BorrowedLocalsResults<'mir, 'tcx>,
+    borrowed_locals: ResultsCursor<'mir, 'tcx, MaybeBorrowedLocals>,
     trans: &'a mut BitSet<Local>,
 }
 

compiler/rustc_mir_transform/src/coroutine.rs

@@ -679,11 +679,10 @@ fn locals_live_across_suspend_points<'tcx>(
 
     // Calculate the MIR locals that we actually need to keep storage around
     // for.
-    let mut requires_storage_cursor =
-        MaybeRequiresStorage::new(borrowed_locals_results.into_results_cursor(body))
-            .into_engine(tcx, body)
-            .iterate_to_fixpoint()
-            .into_results_cursor(body);
+    let mut requires_storage_cursor = MaybeRequiresStorage::new(body, borrowed_locals_results)
+        .into_engine(tcx, body)
+        .iterate_to_fixpoint()
+        .into_results_cursor(body);
 
     // Calculate the liveness of MIR locals ignoring borrows.
     let mut liveness = MaybeLiveLocals