Delay creating a ResultsCursor for MaybeInitializedPlaces.

This lets us pass an immutable `Results<...>` rather than a `&mut
ResultsCursor<...>` through several functions. Passing it by value
instead of by reference also removes the need for the explicit `drop`.

Author: nnethercote

compiler/rustc_borrowck/src/lib.rs

@@ -192,11 +192,10 @@ fn do_mir_borrowck<'tcx>(
         .iter_enumerated()
         .map(|(idx, body)| (idx, MoveData::gather_moves(body, tcx, |_| true)));
 
-    let mut flow_inits = MaybeInitializedPlaces::new(tcx, body, &move_data)
+    let flow_inits = MaybeInitializedPlaces::new(tcx, body, &move_data)
         .into_engine(tcx, body)
         .pass_name("borrowck")
-        .iterate_to_fixpoint()
-        .into_results_cursor(body);
+        .iterate_to_fixpoint();
 
     let locals_are_invalidated_at_exit = tcx.hir().body_owner_kind(def).is_fn_or_closure();
     let borrow_set = BorrowSet::build(tcx, body, locals_are_invalidated_at_exit, &move_data);
@@ -216,7 +215,7 @@ fn do_mir_borrowck<'tcx>(
         &promoted,
         &location_table,
         param_env,
-        &mut flow_inits,
+        flow_inits,
         &move_data,
         &borrow_set,
         tcx.closure_captures(def),
@@ -238,11 +237,6 @@ fn do_mir_borrowck<'tcx>(
         &mut 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)
         .into_engine(tcx, body)
         .pass_name("borrowck")

compiler/rustc_borrowck/src/nll.rs

@@ -16,7 +16,7 @@ use rustc_middle::mir::{
 };
 use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_middle::ty::{self, OpaqueHiddenType, TyCtxt};
-use rustc_mir_dataflow::ResultsCursor;
+use rustc_mir_dataflow::Results;
 use rustc_mir_dataflow::impls::MaybeInitializedPlaces;
 use rustc_mir_dataflow::move_paths::MoveData;
 use rustc_mir_dataflow::points::DenseLocationMap;
@@ -78,11 +78,11 @@ pub(crate) fn replace_regions_in_mir<'tcx>(
 pub(crate) fn compute_regions<'a, 'tcx>(
     infcx: &BorrowckInferCtxt<'tcx>,
     universal_regions: UniversalRegions<'tcx>,
-    body: &Body<'tcx>,
+    body: &'a Body<'tcx>,
     promoted: &IndexSlice<Promoted, Body<'tcx>>,
     location_table: &LocationTable,
     param_env: ty::ParamEnv<'tcx>,
-    flow_inits: &mut ResultsCursor<'a, 'tcx, MaybeInitializedPlaces<'a, 'tcx>>,
+    flow_inits: Results<'tcx, MaybeInitializedPlaces<'a, 'tcx>>,
     move_data: &MoveData<'tcx>,
     borrow_set: &BorrowSet<'tcx>,
     upvars: &[&ty::CapturedPlace<'tcx>],

compiler/rustc_borrowck/src/type_check/liveness/mod.rs

@@ -5,7 +5,7 @@ use rustc_middle::mir::{Body, Local, Location, SourceInfo};
 use rustc_middle::span_bug;
 use rustc_middle::ty::visit::TypeVisitable;
 use rustc_middle::ty::{GenericArgsRef, Region, RegionVid, Ty, TyCtxt};
-use rustc_mir_dataflow::ResultsCursor;
+use rustc_mir_dataflow::Results;
 use rustc_mir_dataflow::impls::MaybeInitializedPlaces;
 use rustc_mir_dataflow::move_paths::MoveData;
 use rustc_mir_dataflow::points::DenseLocationMap;
@@ -30,9 +30,9 @@ mod trace;
 /// performed before
 pub(super) fn generate<'a, 'tcx>(
     typeck: &mut TypeChecker<'_, 'tcx>,
-    body: &Body<'tcx>,
+    body: &'a Body<'tcx>,
     elements: &DenseLocationMap,
-    flow_inits: &mut ResultsCursor<'a, 'tcx, MaybeInitializedPlaces<'a, 'tcx>>,
+    flow_inits: Results<'tcx, MaybeInitializedPlaces<'a, 'tcx>>,
     move_data: &MoveData<'tcx>,
 ) {
     debug!("liveness::generate");

compiler/rustc_borrowck/src/type_check/liveness/trace.rs

@@ -6,10 +6,10 @@ use rustc_infer::infer::outlives::for_liveness;
 use rustc_middle::mir::{BasicBlock, Body, ConstraintCategory, Local, Location};
 use rustc_middle::traits::query::DropckOutlivesResult;
 use rustc_middle::ty::{Ty, TyCtxt, TypeVisitable, TypeVisitableExt};
-use rustc_mir_dataflow::ResultsCursor;
 use rustc_mir_dataflow::impls::MaybeInitializedPlaces;
 use rustc_mir_dataflow::move_paths::{HasMoveData, MoveData, MovePathIndex};
 use rustc_mir_dataflow::points::{DenseLocationMap, PointIndex};
+use rustc_mir_dataflow::{Results, ResultsCursor};
 use rustc_span::DUMMY_SP;
 use rustc_trait_selection::traits::query::type_op::{DropckOutlives, TypeOp, TypeOpOutput};
 use tracing::debug;
@@ -36,9 +36,9 @@ use crate::type_check::{NormalizeLocation, TypeChecker};
 /// this respects `#[may_dangle]` annotations).
 pub(super) fn trace<'a, 'tcx>(
     typeck: &mut TypeChecker<'_, 'tcx>,
-    body: &Body<'tcx>,
+    body: &'a Body<'tcx>,
     elements: &DenseLocationMap,
-    flow_inits: &mut ResultsCursor<'a, 'tcx, MaybeInitializedPlaces<'a, 'tcx>>,
+    flow_inits: Results<'tcx, MaybeInitializedPlaces<'a, 'tcx>>,
     move_data: &MoveData<'tcx>,
     relevant_live_locals: Vec<Local>,
     boring_locals: Vec<Local>,
@@ -79,7 +79,7 @@ pub(super) fn trace<'a, 'tcx>(
     let cx = LivenessContext {
         typeck,
         body,
-        flow_inits,
+        flow_inits: &mut flow_inits.into_results_cursor(body),
         elements,
         local_use_map,
         move_data,

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -32,7 +32,7 @@ use rustc_middle::ty::{
     UserType, UserTypeAnnotationIndex,
 };
 use rustc_middle::{bug, span_bug};
-use rustc_mir_dataflow::ResultsCursor;
+use rustc_mir_dataflow::Results;
 use rustc_mir_dataflow::impls::MaybeInitializedPlaces;
 use rustc_mir_dataflow::move_paths::MoveData;
 use rustc_mir_dataflow::points::DenseLocationMap;
@@ -119,13 +119,13 @@ mod relate_tys;
 pub(crate) fn type_check<'a, 'tcx>(
     infcx: &BorrowckInferCtxt<'tcx>,
     param_env: ty::ParamEnv<'tcx>,
-    body: &Body<'tcx>,
+    body: &'a Body<'tcx>,
     promoted: &IndexSlice<Promoted, Body<'tcx>>,
     universal_regions: Rc<UniversalRegions<'tcx>>,
     location_table: &LocationTable,
     borrow_set: &BorrowSet<'tcx>,
     all_facts: &mut Option<AllFacts>,
-    flow_inits: &mut ResultsCursor<'a, 'tcx, MaybeInitializedPlaces<'a, 'tcx>>,
+    flow_inits: Results<'tcx, MaybeInitializedPlaces<'a, 'tcx>>,
     move_data: &MoveData<'tcx>,
     elements: Rc<DenseLocationMap>,
     upvars: &[&ty::CapturedPlace<'tcx>],