From 75108b60679ea622f57f06f636b3c02b3879eb53 Mon Sep 17 00:00:00 2001
From: Nicholas Nethercote <n.nethercote@gmail.com>
Date: Tue, 5 Nov 2024 11:52:38 +1100
Subject: [PATCH] Pass `flow_inits` by value.

It's simpler that way, and we don't need the explicit `drop`.
---
 compiler/rustc_borrowck/src/lib.rs                       | 8 ++------
 compiler/rustc_borrowck/src/nll.rs                       | 2 +-
 compiler/rustc_borrowck/src/type_check/liveness/mod.rs   | 2 +-
 compiler/rustc_borrowck/src/type_check/liveness/trace.rs | 4 ++--
 compiler/rustc_borrowck/src/type_check/mod.rs            | 2 +-
 5 files changed, 7 insertions(+), 11 deletions(-)

diff --git a/compiler/rustc_borrowck/src/lib.rs b/compiler/rustc_borrowck/src/lib.rs
index a6a554a54c0f4..03f7b05d1e3be 100644
--- a/compiler/rustc_borrowck/src/lib.rs
+++ b/compiler/rustc_borrowck/src/lib.rs
@@ -190,7 +190,7 @@ 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)
         .iterate_to_fixpoint(tcx, body, Some("borrowck"))
         .into_results_cursor(body);
 
@@ -211,16 +211,12 @@ fn do_mir_borrowck<'tcx>(
         body,
         &promoted,
         &location_table,
-        &mut flow_inits,
+        flow_inits,
         &move_data,
         &borrow_set,
         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);
diff --git a/compiler/rustc_borrowck/src/nll.rs b/compiler/rustc_borrowck/src/nll.rs
index f435f21e2aaca..be02e2f48dfd8 100644
--- a/compiler/rustc_borrowck/src/nll.rs
+++ b/compiler/rustc_borrowck/src/nll.rs
@@ -80,7 +80,7 @@ pub(crate) fn compute_regions<'a, 'tcx>(
     body: &Body<'tcx>,
     promoted: &IndexSlice<Promoted, Body<'tcx>>,
     location_table: &LocationTable,
-    flow_inits: &mut ResultsCursor<'a, 'tcx, MaybeInitializedPlaces<'a, 'tcx>>,
+    flow_inits: ResultsCursor<'a, 'tcx, MaybeInitializedPlaces<'a, 'tcx>>,
     move_data: &MoveData<'tcx>,
     borrow_set: &BorrowSet<'tcx>,
     consumer_options: Option<ConsumerOptions>,
diff --git a/compiler/rustc_borrowck/src/type_check/liveness/mod.rs b/compiler/rustc_borrowck/src/type_check/liveness/mod.rs
index fd51cc9454837..20d19a5375241 100644
--- a/compiler/rustc_borrowck/src/type_check/liveness/mod.rs
+++ b/compiler/rustc_borrowck/src/type_check/liveness/mod.rs
@@ -32,7 +32,7 @@ pub(super) fn generate<'a, 'tcx>(
     typeck: &mut TypeChecker<'_, 'tcx>,
     body: &Body<'tcx>,
     elements: &DenseLocationMap,
-    flow_inits: &mut ResultsCursor<'a, 'tcx, MaybeInitializedPlaces<'a, 'tcx>>,
+    flow_inits: ResultsCursor<'a, 'tcx, MaybeInitializedPlaces<'a, 'tcx>>,
     move_data: &MoveData<'tcx>,
 ) {
     debug!("liveness::generate");
diff --git a/compiler/rustc_borrowck/src/type_check/liveness/trace.rs b/compiler/rustc_borrowck/src/type_check/liveness/trace.rs
index 7bdd1564aff3f..3ec36c16cbfc5 100644
--- a/compiler/rustc_borrowck/src/type_check/liveness/trace.rs
+++ b/compiler/rustc_borrowck/src/type_check/liveness/trace.rs
@@ -38,7 +38,7 @@ pub(super) fn trace<'a, 'tcx>(
     typeck: &mut TypeChecker<'_, 'tcx>,
     body: &Body<'tcx>,
     elements: &DenseLocationMap,
-    flow_inits: &mut ResultsCursor<'a, 'tcx, MaybeInitializedPlaces<'a, 'tcx>>,
+    flow_inits: ResultsCursor<'a, 'tcx, MaybeInitializedPlaces<'a, 'tcx>>,
     move_data: &MoveData<'tcx>,
     relevant_live_locals: Vec<Local>,
     boring_locals: Vec<Local>,
@@ -113,7 +113,7 @@ struct LivenessContext<'a, 'typeck, 'b, 'tcx> {
 
     /// Results of dataflow tracking which variables (and paths) have been
     /// initialized.
-    flow_inits: &'a mut ResultsCursor<'b, 'tcx, MaybeInitializedPlaces<'b, 'tcx>>,
+    flow_inits: ResultsCursor<'b, 'tcx, MaybeInitializedPlaces<'b, 'tcx>>,
 
     /// Index indicating where each variable is assigned, used, or
     /// dropped.
diff --git a/compiler/rustc_borrowck/src/type_check/mod.rs b/compiler/rustc_borrowck/src/type_check/mod.rs
index d4d7ab216038c..58a23b9e55857 100644
--- a/compiler/rustc_borrowck/src/type_check/mod.rs
+++ b/compiler/rustc_borrowck/src/type_check/mod.rs
@@ -124,7 +124,7 @@ pub(crate) fn type_check<'a, 'tcx>(
     location_table: &LocationTable,
     borrow_set: &BorrowSet<'tcx>,
     all_facts: &mut Option<AllFacts>,
-    flow_inits: &mut ResultsCursor<'a, 'tcx, MaybeInitializedPlaces<'a, 'tcx>>,
+    flow_inits: ResultsCursor<'a, 'tcx, MaybeInitializedPlaces<'a, 'tcx>>,
     move_data: &MoveData<'tcx>,
     elements: Rc<DenseLocationMap>,
 ) -> MirTypeckResults<'tcx> {