Rollup merge of #55151 - ljedrz:cleanup_nll, r=estebank

Cleanup nll

- improve allocations
- improve `format!` calls
- improve common patterns

6 files changed, 51 insertions, 54 deletions

diff --git a/src/librustc_mir/borrow_check/nll/constraint_generation.rs b/src/librustc_mir/borrow_check/nll/constraint_generation.rs
index 30b263a923a..495e84528a3 100644
--- a/src/librustc_mir/borrow_check/nll/constraint_generation.rs
+++ b/src/librustc_mir/borrow_check/nll/constraint_generation.rs
@@ -141,6 +141,7 @@ impl<'cg, 'cx, 'gcx, 'tcx> Visitor<'tcx> for ConstraintGeneration<'cg, 'cx, 'gcx
         if let Some(all_facts) = self.all_facts {
             if let Place::Local(temp) = place {
                 if let Some(borrow_indices) = self.borrow_set.local_map.get(temp) {
+                    all_facts.killed.reserve(borrow_indices.len());
                     for &borrow_index in borrow_indices {
                         let location_index = self.location_table.mid_index(location);
                         all_facts.killed.push((borrow_index, location_index));
@@ -164,7 +165,9 @@ impl<'cg, 'cx, 'gcx, 'tcx> Visitor<'tcx> for ConstraintGeneration<'cg, 'cx, 'gcx
                 self.location_table.mid_index(location),
             ));
 
-            for successor_block in terminator.successors() {
+            let successor_blocks = terminator.successors();
+            all_facts.cfg_edge.reserve(successor_blocks.size_hint().0);
+            for successor_block in successor_blocks {
                 all_facts.cfg_edge.push((
                     self.location_table.mid_index(location),
                     self.location_table
diff --git a/src/librustc_mir/borrow_check/nll/explain_borrow/mod.rs b/src/librustc_mir/borrow_check/nll/explain_borrow/mod.rs
index 307112f8ba1..a0f832c5449 100644
--- a/src/librustc_mir/borrow_check/nll/explain_borrow/mod.rs
+++ b/src/librustc_mir/borrow_check/nll/explain_borrow/mod.rs
@@ -87,9 +87,9 @@ impl<'tcx> BorrowExplanation<'tcx> {
                     // Otherwise, just report the whole type (and use
                     // the intentionally fuzzy phrase "destructor")
                     ty::Closure(..) =>
-                        ("destructor", format!("closure")),
+                        ("destructor", "closure".to_owned()),
                     ty::Generator(..) =>
-                        ("destructor", format!("generator")),
+                        ("destructor", "generator".to_owned()),
 
                     _ => ("destructor", format!("type `{}`", local_decl.ty)),
                 };
@@ -279,9 +279,8 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
                         pending_locations.push(target.start_location());
                     },
                     TerminatorKind::SwitchInt { ref targets, .. } => {
-                        for target in targets {
-                            pending_locations.push(target.start_location());
-                        }
+                        pending_locations.extend(
+                            targets.into_iter().map(|target| target.start_location()));
                     },
                     TerminatorKind::Drop { target, unwind, .. } |
                     TerminatorKind::DropAndReplace { target, unwind, .. } |
@@ -303,9 +302,8 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
                     },
                     TerminatorKind::FalseEdges { real_target, ref imaginary_targets, .. } => {
                         pending_locations.push(real_target.start_location());
-                        for target in imaginary_targets {
-                            pending_locations.push(target.start_location());
-                        }
+                        pending_locations.extend(
+                            imaginary_targets.into_iter().map(|target| target.start_location()));
                     },
                     _ => {},
                 }
@@ -441,17 +439,17 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
                             Operand::Move(Place::Local(from)) if *from == target => {
                                 debug!("was_captured_by_trait_object: ty={:?}", ty);
                                 // Check the type for a trait object.
-                                match ty.sty {
+                                return match ty.sty {
                                     // `&dyn Trait`
-                                    ty::TyKind::Ref(_, ty, _) if ty.is_trait() => return true,
+                                    ty::TyKind::Ref(_, ty, _) if ty.is_trait() => true,
                                     // `Box<dyn Trait>`
                                     _ if ty.is_box() && ty.boxed_ty().is_trait() =>
-                                        return true,
+                                        true,
                                     // `dyn Trait`
-                                    _ if ty.is_trait() => return true,
+                                    _ if ty.is_trait() => true,
                                     // Anything else.
-                                    _ => return false,
-                                }
+                                    _ => false,
+                                };
                             },
                             _ => return false,
                         },
@@ -466,32 +464,29 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
                 let terminator = block.terminator();
                 debug!("was_captured_by_trait_object: terminator={:?}", terminator);
 
-                match &terminator.kind {
-                    TerminatorKind::Call {
-                        destination: Some((Place::Local(dest), block)),
-                        args,
-                        ..
-                    } => {
-                        debug!(
-                            "was_captured_by_trait_object: target={:?} dest={:?} args={:?}",
-                            target, dest, args
-                        );
-                        // Check if one of the arguments to this function is the target place.
-                        let found_target = args.iter().any(|arg| {
-                            if let Operand::Move(Place::Local(potential)) = arg {
-                                *potential == target
-                            } else {
-                                false
-                            }
-                        });
-
-                        // If it is, follow this to the next block and update the target.
-                        if found_target {
-                            target = *dest;
-                            queue.push(block.start_location());
+                if let TerminatorKind::Call {
+                    destination: Some((Place::Local(dest), block)),
+                    args,
+                    ..
+                } = &terminator.kind {
+                    debug!(
+                        "was_captured_by_trait_object: target={:?} dest={:?} args={:?}",
+                        target, dest, args
+                    );
+                    // Check if one of the arguments to this function is the target place.
+                    let found_target = args.iter().any(|arg| {
+                        if let Operand::Move(Place::Local(potential)) = arg {
+                            *potential == target
+                        } else {
+                            false
                         }
-                    },
-                    _ => {},
+                    });
+
+                    // If it is, follow this to the next block and update the target.
+                    if found_target {
+                        target = *dest;
+                        queue.push(block.start_location());
+                    }
                 }
             }
 
diff --git a/src/librustc_mir/borrow_check/nll/invalidation.rs b/src/librustc_mir/borrow_check/nll/invalidation.rs
index a9b5531bae5..002f35880ae 100644
--- a/src/librustc_mir/borrow_check/nll/invalidation.rs
+++ b/src/librustc_mir/borrow_check/nll/invalidation.rs
@@ -35,7 +35,7 @@ pub(super) fn generate_invalidates<'cx, 'gcx, 'tcx>(
     mir: &Mir<'tcx>,
     borrow_set: &BorrowSet<'tcx>,
 ) {
-    if !all_facts.is_some() {
+    if all_facts.is_none() {
         // Nothing to do if we don't have any facts
         return;
     }
diff --git a/src/librustc_mir/borrow_check/nll/region_infer/dump_mir.rs b/src/librustc_mir/borrow_check/nll/region_infer/dump_mir.rs
index ee900afc44d..268a37c7086 100644
--- a/src/librustc_mir/borrow_check/nll/region_infer/dump_mir.rs
+++ b/src/librustc_mir/borrow_check/nll/region_infer/dump_mir.rs
@@ -36,12 +36,12 @@ impl<'tcx> RegionInferenceContext<'tcx> {
                 let outlived_by = self.universal_region_relations.regions_outlived_by(region);
                 writeln!(
                     out,
-                    "| {r:rw$} | {c:cw$} | {ob}",
-                    r = format!("{:?}", region),
+                    "| {r:rw$?} | {c:cw$?} | {ob:?}",
+                    r = region,
                     rw = REGION_WIDTH,
-                    c = format!("{:?}", classification),
+                    c = classification,
                     cw = 8, // "External" at most
-                    ob = format!("{:?}", outlived_by)
+                    ob = outlived_by
                 )?;
             }
         }
@@ -51,8 +51,8 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         for region in self.regions() {
             writeln!(
                 out,
-                "| {r:rw$} | {ui:4?} | {v}",
-                r = format!("{:?}", region),
+                "| {r:rw$?} | {ui:4?} | {v}",
+                r = region,
                 rw = REGION_WIDTH,
                 ui = self.region_universe(region),
                 v = self.region_value_str(region),
diff --git a/src/librustc_mir/borrow_check/nll/region_infer/error_reporting/mod.rs b/src/librustc_mir/borrow_check/nll/region_infer/error_reporting/mod.rs
index 8191dd720e7..5ff50c606d6 100644
--- a/src/librustc_mir/borrow_check/nll/region_infer/error_reporting/mod.rs
+++ b/src/librustc_mir/borrow_check/nll/region_infer/error_reporting/mod.rs
@@ -550,7 +550,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
                     let span = infcx.tcx.def_span(*did);
                     if let Ok(snippet) = infcx.tcx.sess.source_map().span_to_snippet(span) {
                         let suggestable_fr_name = if fr_name.was_named() {
-                            format!("{}", fr_name)
+                            fr_name.to_string()
                         } else {
                             "'_".to_string()
                         };
diff --git a/src/librustc_mir/borrow_check/nll/region_infer/error_reporting/region_name.rs b/src/librustc_mir/borrow_check/nll/region_infer/error_reporting/region_name.rs
index 65ba2f537bf..e07dfda406b 100644
--- a/src/librustc_mir/borrow_check/nll/region_infer/error_reporting/region_name.rs
+++ b/src/librustc_mir/borrow_check/nll/region_infer/error_reporting/region_name.rs
@@ -462,9 +462,8 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         argument_hir_ty: &hir::Ty,
         counter: &mut usize,
     ) -> Option<RegionName> {
-        let search_stack: &mut Vec<(Ty<'tcx>, &hir::Ty)> = &mut Vec::new();
-
-        search_stack.push((argument_ty, argument_hir_ty));
+        let search_stack: &mut Vec<(Ty<'tcx>, &hir::Ty)> =
+            &mut vec![(argument_ty, argument_hir_ty)];
 
         while let Some((ty, hir_ty)) = search_stack.pop() {
             match (&ty.sty, &hir_ty.node) {
@@ -567,10 +566,10 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             | hir::LifetimeName::Underscore => {
                 let region_name = self.synthesize_region_name(counter);
                 let ampersand_span = lifetime.span;
-                return Some(RegionName {
+                Some(RegionName {
                     name: region_name,
                     source: RegionNameSource::MatchedAdtAndSegment(ampersand_span),
-                });
+                })
             }
 
             hir::LifetimeName::Implicit => {
@@ -585,7 +584,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
                 // T>`. We don't consider this a match; instead we let
                 // the "fully elaborated" type fallback above handle
                 // it.
-                return None;
+                None
             }
         }
     }