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.

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,