Remove ResultsVisitable.

Now that `Results` is the only impl of `ResultsVisitable`, the trait can
be removed. This simplifies things by removining unnecessary layers of
indirection and abstraction.

- `ResultsVisitor` is simpler.
  - Its type parameter changes from `R` (an analysis result) to the
    simpler `A` (an analysis).
  - It no longer needs the `Domain` associated type, because it can use
    `A::Domain`.
  - Occurrences of `R` become `Results<'tcx, A>`, because there is now
    only one kind of analysis results.

- `save_as_intervals` also changes type parameter from `R` to `A`.

- The `results.reconstruct_*` method calls are replaced with
  `results.analysis.apply_*` method calls, which are equivalent.

- `Direction::visit_results_in_block` is simpler, with a single generic
  param (`A`) instead of two (`D` and `R`/`F`, with a bound connecting
  them). Likewise for `visit_results`.

- The `ResultsVisitor` impls for `MirBorrowCtxt` and
  `StorageConflictVisitor` are now specific about the type of the
  analysis results they work with. They both used to have a type param
  `R` but they weren't genuinely generic. In both cases there was only a
  single results type that made sense to instantiate them with.

Author: nnethercote

compiler/rustc_borrowck/src/lib.rs

@@ -42,7 +42,7 @@ use rustc_mir_dataflow::impls::{
 use rustc_mir_dataflow::move_paths::{
     InitIndex, InitLocation, LookupResult, MoveData, MoveOutIndex, MovePathIndex,
 };
-use rustc_mir_dataflow::{Analysis, EntrySets, Results};
+use rustc_mir_dataflow::{Analysis, EntrySets, Results, ResultsVisitor, visit_results};
 use rustc_session::lint::builtin::UNUSED_MUT;
 use rustc_span::{Span, Symbol};
 use smallvec::SmallVec;
@@ -318,7 +318,7 @@ fn do_mir_borrowck<'tcx>(
     mbcx.report_region_errors(nll_errors);
 
     let mut flow_results = get_flow_results(tcx, body, &move_data, &borrow_set, &regioncx);
-    rustc_mir_dataflow::visit_results(
+    visit_results(
         body,
         traversal::reverse_postorder(body).map(|(bb, _)| bb),
         &mut flow_results,
@@ -607,14 +607,10 @@ struct MirBorrowckCtxt<'a, 'infcx, 'tcx> {
 // 2. loans made in overlapping scopes do not conflict
 // 3. assignments do not affect things loaned out as immutable
 // 4. moves do not affect things loaned out in any way
-impl<'a, 'tcx, R> rustc_mir_dataflow::ResultsVisitor<'a, 'tcx, R>
-    for MirBorrowckCtxt<'a, '_, 'tcx>
-{
-    type Domain = BorrowckDomain<'a, 'tcx>;
-
+impl<'a, 'tcx> ResultsVisitor<'a, 'tcx, Borrowck<'a, 'tcx>> for MirBorrowckCtxt<'a, '_, 'tcx> {
     fn visit_statement_before_primary_effect(
         &mut self,
-        _results: &mut R,
+        _results: &mut Results<'tcx, Borrowck<'a, 'tcx>>,
         state: &BorrowckDomain<'a, 'tcx>,
         stmt: &'a Statement<'tcx>,
         location: Location,
@@ -686,7 +682,7 @@ impl<'a, 'tcx, R> rustc_mir_dataflow::ResultsVisitor<'a, 'tcx, R>
 
     fn visit_terminator_before_primary_effect(
         &mut self,
-        _results: &mut R,
+        _results: &mut Results<'tcx, Borrowck<'a, 'tcx>>,
         state: &BorrowckDomain<'a, 'tcx>,
         term: &'a Terminator<'tcx>,
         loc: Location,
@@ -799,7 +795,7 @@ impl<'a, 'tcx, R> rustc_mir_dataflow::ResultsVisitor<'a, 'tcx, R>
 
     fn visit_terminator_after_primary_effect(
         &mut self,
-        _results: &mut R,
+        _results: &mut Results<'tcx, Borrowck<'a, 'tcx>>,
         state: &BorrowckDomain<'a, 'tcx>,
         term: &'a Terminator<'tcx>,
         loc: Location,

compiler/rustc_mir_dataflow/src/framework/direction.rs

@@ -4,8 +4,8 @@ use rustc_middle::mir::{
     self, BasicBlock, CallReturnPlaces, Location, SwitchTargets, TerminatorEdges,
 };
 
-use super::visitor::{ResultsVisitable, ResultsVisitor};
-use super::{Analysis, Effect, EffectIndex, SwitchIntTarget};
+use super::visitor::ResultsVisitor;
+use super::{Analysis, Effect, EffectIndex, Results, SwitchIntTarget};
 
 pub trait Direction {
     const IS_FORWARD: bool;
@@ -33,14 +33,14 @@ pub trait Direction {
     where
         A: Analysis<'tcx>;
 
-    fn visit_results_in_block<'mir, 'tcx, D, R>(
-        state: &mut D,
+    fn visit_results_in_block<'mir, 'tcx, A>(
+        state: &mut A::Domain,
         block: BasicBlock,
         block_data: &'mir mir::BasicBlockData<'tcx>,
-        results: &mut R,
-        vis: &mut impl ResultsVisitor<'mir, 'tcx, R, Domain = D>,
+        results: &mut Results<'tcx, A>,
+        vis: &mut impl ResultsVisitor<'mir, 'tcx, A>,
     ) where
-        R: ResultsVisitable<'tcx, Domain = D>;
+        A: Analysis<'tcx>;
 
     fn join_state_into_successors_of<'tcx, A>(
         analysis: &mut A,
@@ -53,7 +53,7 @@ pub trait Direction {
         A: Analysis<'tcx>;
 }
 
-/// Dataflow that runs from the exit of a block (the terminator), to its entry (the first statement).
+/// Dataflow that runs from the exit of a block (terminator), to its entry (the first statement).
 pub struct Backward;
 
 impl Direction for Backward {
@@ -157,32 +157,32 @@ impl Direction for Backward {
         analysis.apply_statement_effect(state, statement, location);
     }
 
-    fn visit_results_in_block<'mir, 'tcx, D, R>(
-        state: &mut D,
+    fn visit_results_in_block<'mir, 'tcx, A>(
+        state: &mut A::Domain,
         block: BasicBlock,
         block_data: &'mir mir::BasicBlockData<'tcx>,
-        results: &mut R,
-        vis: &mut impl ResultsVisitor<'mir, 'tcx, R, Domain = D>,
+        results: &mut Results<'tcx, A>,
+        vis: &mut impl ResultsVisitor<'mir, 'tcx, A>,
     ) where
-        R: ResultsVisitable<'tcx, Domain = D>,
+        A: Analysis<'tcx>,
     {
-        results.reset_to_block_entry(state, block);
+        state.clone_from(results.entry_set_for_block(block));
 
         vis.visit_block_end(state);
 
         // Terminator
         let loc = Location { block, statement_index: block_data.statements.len() };
         let term = block_data.terminator();
-        results.reconstruct_before_terminator_effect(state, term, loc);
+        results.analysis.apply_before_terminator_effect(state, term, loc);
         vis.visit_terminator_before_primary_effect(results, state, term, loc);
-        results.reconstruct_terminator_effect(state, term, loc);
+        results.analysis.apply_terminator_effect(state, term, loc);
         vis.visit_terminator_after_primary_effect(results, state, term, loc);
 
         for (statement_index, stmt) in block_data.statements.iter().enumerate().rev() {
             let loc = Location { block, statement_index };
-            results.reconstruct_before_statement_effect(state, stmt, loc);
+            results.analysis.apply_before_statement_effect(state, stmt, loc);
             vis.visit_statement_before_primary_effect(results, state, stmt, loc);
-            results.reconstruct_statement_effect(state, stmt, loc);
+            results.analysis.apply_statement_effect(state, stmt, loc);
             vis.visit_statement_after_primary_effect(results, state, stmt, loc);
         }
 
@@ -389,32 +389,32 @@ impl Direction for Forward {
         }
     }
 
-    fn visit_results_in_block<'mir, 'tcx, F, R>(
-        state: &mut F,
+    fn visit_results_in_block<'mir, 'tcx, A>(
+        state: &mut A::Domain,
         block: BasicBlock,
         block_data: &'mir mir::BasicBlockData<'tcx>,
-        results: &mut R,
-        vis: &mut impl ResultsVisitor<'mir, 'tcx, R, Domain = F>,
+        results: &mut Results<'tcx, A>,
+        vis: &mut impl ResultsVisitor<'mir, 'tcx, A>,
     ) where
-        R: ResultsVisitable<'tcx, Domain = F>,
+        A: Analysis<'tcx>,
     {
-        results.reset_to_block_entry(state, block);
+        state.clone_from(results.entry_set_for_block(block));
 
         vis.visit_block_start(state);
 
         for (statement_index, stmt) in block_data.statements.iter().enumerate() {
             let loc = Location { block, statement_index };
-            results.reconstruct_before_statement_effect(state, stmt, loc);
+            results.analysis.apply_before_statement_effect(state, stmt, loc);
             vis.visit_statement_before_primary_effect(results, state, stmt, loc);
-            results.reconstruct_statement_effect(state, stmt, loc);
+            results.analysis.apply_statement_effect(state, stmt, loc);
             vis.visit_statement_after_primary_effect(results, state, stmt, loc);
         }
 
         let loc = Location { block, statement_index: block_data.statements.len() };
         let term = block_data.terminator();
-        results.reconstruct_before_terminator_effect(state, term, loc);
+        results.analysis.apply_before_terminator_effect(state, term, loc);
         vis.visit_terminator_before_primary_effect(results, state, term, loc);
-        results.reconstruct_terminator_effect(state, term, loc);
+        results.analysis.apply_terminator_effect(state, term, loc);
         vis.visit_terminator_after_primary_effect(results, state, term, loc);
 
         vis.visit_block_end(state);

compiler/rustc_mir_dataflow/src/framework/graphviz.rs

@@ -544,20 +544,18 @@ impl<D> StateDiffCollector<D> {
     }
 }
 
-impl<'tcx, A> ResultsVisitor<'_, 'tcx, Results<'tcx, A>> for StateDiffCollector<A::Domain>
+impl<'tcx, A> ResultsVisitor<'_, 'tcx, A> for StateDiffCollector<A::Domain>
 where
     A: Analysis<'tcx>,
     A::Domain: DebugWithContext<A>,
 {
-    type Domain = A::Domain;
-
-    fn visit_block_start(&mut self, state: &Self::Domain) {
+    fn visit_block_start(&mut self, state: &A::Domain) {
         if A::Direction::IS_FORWARD {
             self.prev_state.clone_from(state);
         }
     }
 
-    fn visit_block_end(&mut self, state: &Self::Domain) {
+    fn visit_block_end(&mut self, state: &A::Domain) {
         if A::Direction::IS_BACKWARD {
             self.prev_state.clone_from(state);
         }
@@ -566,7 +564,7 @@ where
     fn visit_statement_before_primary_effect(
         &mut self,
         results: &mut Results<'tcx, A>,
-        state: &Self::Domain,
+        state: &A::Domain,
         _statement: &mir::Statement<'tcx>,
         _location: Location,
     ) {
@@ -579,7 +577,7 @@ where
     fn visit_statement_after_primary_effect(
         &mut self,
         results: &mut Results<'tcx, A>,
-        state: &Self::Domain,
+        state: &A::Domain,
         _statement: &mir::Statement<'tcx>,
         _location: Location,
     ) {
@@ -590,7 +588,7 @@ where
     fn visit_terminator_before_primary_effect(
         &mut self,
         results: &mut Results<'tcx, A>,
-        state: &Self::Domain,
+        state: &A::Domain,
         _terminator: &mir::Terminator<'tcx>,
         _location: Location,
     ) {
@@ -603,7 +601,7 @@ where
     fn visit_terminator_after_primary_effect(
         &mut self,
         results: &mut Results<'tcx, A>,
-        state: &Self::Domain,
+        state: &A::Domain,
         _terminator: &mir::Terminator<'tcx>,
         _location: Location,
     ) {

compiler/rustc_mir_dataflow/src/framework/mod.rs

@@ -56,7 +56,7 @@ pub use self::cursor::ResultsCursor;
 pub use self::direction::{Backward, Direction, Forward};
 pub use self::lattice::{JoinSemiLattice, MaybeReachable};
 pub use self::results::{EntrySets, Results};
-pub use self::visitor::{ResultsVisitable, ResultsVisitor, visit_results};
+pub use self::visitor::{ResultsVisitor, visit_results};
 
 /// Analysis domains are all bitsets of various kinds. This trait holds
 /// operations needed by all of them.

compiler/rustc_mir_dataflow/src/framework/results.rs

@@ -51,15 +51,15 @@ where
         &mut self,
         body: &'mir mir::Body<'tcx>,
         blocks: impl IntoIterator<Item = BasicBlock>,
-        vis: &mut impl ResultsVisitor<'mir, 'tcx, Self, Domain = A::Domain>,
+        vis: &mut impl ResultsVisitor<'mir, 'tcx, A>,
     ) {
         visit_results(body, blocks, self, vis)
     }
 
     pub fn visit_reachable_with<'mir>(
         &mut self,
         body: &'mir mir::Body<'tcx>,
-        vis: &mut impl ResultsVisitor<'mir, 'tcx, Self, Domain = A::Domain>,
+        vis: &mut impl ResultsVisitor<'mir, 'tcx, A>,
     ) {
         let blocks = traversal::reachable(body);
         visit_results(body, blocks.map(|(bb, _)| bb), self, vis)