Replace BorrowckResults with Borrowck.

The results of most analyses end up in a `Results<'tcx, A>`, where `A`
is the analysis. It's then possible to traverse the results via a
`ResultsVisitor`, which relies on the `ResultsVisitable` trait. (That
trait ends up using the same `apply_*` methods that were used when
computing the analysis, albeit indirectly.)

This pattern of "compute analysis results, then visit them" is common.
But there is one exception. For borrow checking we compute three
separate analyses (`Borrows`, `MaybeUninitializedPlaces`, and
`EverInitializedPlaces`), combine them into a single `BorrowckResults`,
and then do a single visit of that `BorrowckResults` with
`MirBorrowckResults`. `BorrowckResults` is just different enough from
`Results` that it requires the existence of `ResultsVisitable`, which
abstracts over the traversal differences between `Results` and
`BorrowckResults`.

This commit changes things by introducing `Borrowck` and bundling the
three borrowck analysis results into a standard `Results<Borrowck>`
instead of the exceptional `BorrowckResults`. Once that's done, the
results can be visited like any other analysis results.
`BorrowckResults` is removed, as is `impl ResultsVisitable for
BorrowckResults`. (It's instructive to see how similar the added `impl
Analysis for Borrowck` is to the removed `impl ResultsVisitable for
BorrowckResults`. They're both doing exactly the same things.)

Overall this increases the number of lines of code and might not seem
like a win. But it enables the removal of `ResultsVisitable` in the next
commit, which results in many simplifications.

compiler/rustc_borrowck/src/lib.rs

@@ -36,13 +36,13 @@ use rustc_middle::mir::*;
 use rustc_middle::query::Providers;
 use rustc_middle::ty::{self, ParamEnv, RegionVid, TyCtxt, TypingMode};
 use rustc_middle::{bug, span_bug};
-use rustc_mir_dataflow::Analysis;
 use rustc_mir_dataflow::impls::{
     EverInitializedPlaces, MaybeInitializedPlaces, MaybeUninitializedPlaces,
 };
 use rustc_mir_dataflow::move_paths::{
     InitIndex, InitLocation, LookupResult, MoveData, MoveOutIndex, MovePathIndex,
 };
+use rustc_mir_dataflow::{Analysis, EntrySets, Results};
 use rustc_session::lint::builtin::UNUSED_MUT;
 use rustc_span::{Span, Symbol};
 use smallvec::SmallVec;
@@ -50,7 +50,7 @@ use tracing::{debug, instrument};
 
 use crate::borrow_set::{BorrowData, BorrowSet};
 use crate::consumers::{BodyWithBorrowckFacts, ConsumerOptions};
-use crate::dataflow::{BorrowIndex, BorrowckDomain, BorrowckResults, Borrows};
+use crate::dataflow::{BorrowIndex, Borrowck, BorrowckDomain, Borrows};
 use crate::diagnostics::{AccessKind, IllegalMoveOriginKind, MoveError, RegionName};
 use crate::location::LocationTable;
 use crate::nll::PoloniusOutput;
@@ -221,6 +221,10 @@ fn do_mir_borrowck<'tcx>(
         consumer_options,
     );
 
+    // `flow_inits` is large, so we drop it as soon as possible. This reduces
+    // peak memory usage significantly on some benchmarks.
+    drop(flow_inits);
+
     // Dump MIR results into a file, if that is enabled. This let us
     // write unit-tests, as well as helping with debugging.
     nll::dump_nll_mir(&infcx, body, &regioncx, &opt_closure_req, &borrow_set);
@@ -229,27 +233,6 @@ fn do_mir_borrowck<'tcx>(
     // information.
     nll::dump_annotation(&infcx, body, &regioncx, &opt_closure_req, &opaque_type_values, diags);
 
-    // The various `flow_*` structures can be large. We drop `flow_inits` here
-    // so it doesn't overlap with the others below. This reduces peak memory
-    // usage significantly on some benchmarks.
-    drop(flow_inits);
-
-    let flow_borrows = Borrows::new(tcx, body, &regioncx, &borrow_set).iterate_to_fixpoint(
-        tcx,
-        body,
-        Some("borrowck"),
-    );
-    let flow_uninits = MaybeUninitializedPlaces::new(tcx, body, &move_data).iterate_to_fixpoint(
-        tcx,
-        body,
-        Some("borrowck"),
-    );
-    let flow_ever_inits = EverInitializedPlaces::new(body, &move_data).iterate_to_fixpoint(
-        tcx,
-        body,
-        Some("borrowck"),
-    );
-
     let movable_coroutine =
         // The first argument is the coroutine type passed by value
         if let Some(local) = body.local_decls.raw.get(1)
@@ -334,16 +317,11 @@ fn do_mir_borrowck<'tcx>(
     // Compute and report region errors, if any.
     mbcx.report_region_errors(nll_errors);
 
-    let mut results = BorrowckResults {
-        ever_inits: flow_ever_inits,
-        uninits: flow_uninits,
-        borrows: flow_borrows,
-    };
-
+    let mut flow_results = get_flow_results(tcx, body, &move_data, &borrow_set, &regioncx);
     rustc_mir_dataflow::visit_results(
         body,
         traversal::reverse_postorder(body).map(|(bb, _)| bb),
-        &mut results,
+        &mut flow_results,
         &mut mbcx,
     );
 
@@ -426,6 +404,47 @@ fn do_mir_borrowck<'tcx>(
     (result, body_with_facts)
 }
 
+fn get_flow_results<'a, 'tcx>(
+    tcx: TyCtxt<'tcx>,
+    body: &'a Body<'tcx>,
+    move_data: &'a MoveData<'tcx>,
+    borrow_set: &'a BorrowSet<'tcx>,
+    regioncx: &RegionInferenceContext<'tcx>,
+) -> Results<'tcx, Borrowck<'a, 'tcx>> {
+    // We compute these three analyses individually, but them combine them into
+    // a single results so that `mbcx` can visit them all together.
+    let borrows = Borrows::new(tcx, body, regioncx, borrow_set).iterate_to_fixpoint(
+        tcx,
+        body,
+        Some("borrowck"),
+    );
+    let uninits = MaybeUninitializedPlaces::new(tcx, body, move_data).iterate_to_fixpoint(
+        tcx,
+        body,
+        Some("borrowck"),
+    );
+    let ever_inits = EverInitializedPlaces::new(body, move_data).iterate_to_fixpoint(
+        tcx,
+        body,
+        Some("borrowck"),
+    );
+
+    let analysis = Borrowck {
+        borrows: borrows.analysis,
+        uninits: uninits.analysis,
+        ever_inits: ever_inits.analysis,
+    };
+
+    assert_eq!(borrows.entry_sets.len(), uninits.entry_sets.len());
+    assert_eq!(borrows.entry_sets.len(), ever_inits.entry_sets.len());
+    let entry_sets: EntrySets<'_, Borrowck<'_, '_>> =
+        itertools::izip!(borrows.entry_sets, uninits.entry_sets, ever_inits.entry_sets)
+            .map(|(borrows, uninits, ever_inits)| BorrowckDomain { borrows, uninits, ever_inits })
+            .collect();
+
+    Results { analysis, entry_sets }
+}
+
 pub(crate) struct BorrowckInferCtxt<'tcx> {
     pub(crate) infcx: InferCtxt<'tcx>,
     pub(crate) reg_var_to_origin: RefCell<FxIndexMap<ty::RegionVid, RegionCtxt>>,